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ScienceWeek
SCIENCE-WEEK
A Weekly Email Digest of the News of Science
A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy-makers.
July 20, 2001 -- Vol. 5 Number 29
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Many a scientist has patiently designed experiments
for the purpose of substantiating his belief that
animal operations are motivated by no purpose...
Scientists animated by the purpose of proving that
they are purposeless constitute an interesting subject
for study.
-- Alfred North Whitehead (1861-1947)
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Section 1
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Contents of this Issue (Full reports in Section 2):
1. IN BRIEF: Science and Africa... A helium quantum fluid...
Early oceanic crust... Active galactic nuclei... Chronic fatigue
syndrome... Dopamine receptors... Post-genomic era... Alzheimer's
disease and cholesterol.
2. SCIENCE POLICY:
LACK OF DIVERSITY IN US CHEMISTRY DEPARTMENTS
Although the number of chemistry PhDs awarded to blacks each year
in the US has more than doubled since 1990, during the same time-
frame, the number of blacks hired as assistant professors at the
top 50 chemistry departments in the US has held steady: the
number is zero.
3. ASTROPHYSICS: NEW DATA ON THE BIRTH OF STARS
The exact process by which interstellar matter condenses to form
young stars is of great interest, in part because they bear on
the formation of planets like our own from the material that
fails to become part of the star. New observations of water-vapor
maser emission from a young star show a spherical symmetry that
contradicts the current theory of new star formation.
4. NEUROBIOLOGY: ON MARIJUANA CANNABINOIDS
Experiments indicate that endogenous cannabinoids are involved in
retrograde signaling in the brain. Signaling by the
endocannabinoid system represents a mechanism by which neurons
can communicate backwards across synapses to modulate their
inputs. The new results represent the first identification of a
physiological process mediated by endogenous brain cannabinoids.
5. MOLECULAR BIOLOGY: GLYCOPROTEINS AND THE IMMUNE SYSTEM
Almost all the key molecules in the innate and adaptive immune
response are glycoproteins. In the cellular immune system,
specific glycoforms are involved in the folding, quality control,
and assembly of peptide-loaded major histocompatibility complex
(MHC) antigens and the T cell receptor complex.
6. MEDICAL BIOLOGY: NEW DATA ON RETROVIRUSES AND LUNG CANCER
Retroviruses can splice into the host-cell genome pieces of their
own genome, the result either the introduction of new genes into
the host genome or the activation or inactivation of specific
nearby genes of the host genome. In principle, either of these
scenarios can lead to corruption of the growth regulation process
of the host genome, and thus to a line of malignant cells.
7. IN FOCUS: ON MIND AND BODY AND C.S. SHERRINGTON
Charles Sherrington on mind and body and embryonic nerve cells.
After 65 years, the philosophical conundrum of mind and body as
expressed by Sherrington in his unique prose is as seductive as
ever. Many neurobiologists believe the apparent conundrum is a
mirage. Or is it merely a problem placed in a drawer because it
has no apparent method of solution?
8. FROM THE SCIENCEWEEK ARCHIVE:
ON PUBLIC HEALTH DISPARITIES
Although immense gains in public health were made during the 20th
century, the distribution of these gains has been far from
uniform both globally and in the US. Overall, disparities in life
expectancy between different parts of the US are greater than for
any other nation in the world, and the reasons for this are not
clear.
9. SOURCES
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Section 2
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1. IN BRIEF (Sources tabulated in Item #9 near end of Section 2):
... ... SCIENCE AND AFRICA: M.H.A. Hassan, president of the
African Academy of Sciences and executive director of the Third
World Academy of Sciences, points out that 30,000 PhDs of African
descent, many with science degrees, live and work outside their
home countries, and that this figure far exceeds the total number
of African-born scientists with PhDs working in Africa. Hassan
suggests that that is why it is important for all scientists, and
especially those of African origin living and working in the
North, to assist efforts to rebuild the capacities of Africa's
scientific communities. Hassan concludes: "And that is why it is
important for the governments of Africa to nurture environments
that not only provide sufficient financial resources but also
allow scientists from Africa and elsewhere to interact freely and
without constraints." (SCI 2001 292:1609)
... ... A HELIUM QUANTUM FLUID: When liquid helium is cooled to 2
kelvins it becomes a superfluid and flows without friction. The
phenomenon was first discovered in 1930, and involves all the
helium atoms in the sample joining together in a single quantum
state, the population of atoms called a "Bose-Einstein
condensate". Now two groups in France report the creation of
Bose-Einstein condensates of a gas of ionized helium atoms. It is
expected that the unique properties of a Bose-Einstein condensate
of ionized helium gas will provide a powerful tool to learn more
about Bose-Einstein condensates in general. There is also the
possibility of using excited helium atoms for atomic lithography,
which involves direct nanoscale deposition of atoms on a surface.
(NAT 2001 411:425) (SCI 2001 292:461) (PRL 2001 86:3459)
... ... THE EARLY OCEANIC CRUST: "Ophiolite complexes" are
fragments of ancient oceanic lithosphere that survived in
collisional mountain belts. They are thought to represent slices
of the basaltic ocean crust that have been tectonically emplaced
onto continental margins. Researchers now report the discovery of
an approximately 2.5 billion-year-old ophiolite complex in North
China. T.M. Kusky et al suggest their find implies that
mechanisms of oceanic crustal accretion similar to those of today
were in operation by 2.5 billion years ago at divergent tectonic
plate margins, and that the temperature of the early mantle of
Earth was not extremely elevated as compared to the present-day
temperature. The authors suggest that plate tectonic processes
similar to those of the present must have emplaced the ophiolite
in a convergent margin setting. (SCI 2001 292:1142)
... ... ACTIVE GALACTIC NUCLEI: Some galaxies are known to have
very "active" central regions from which enormous amounts of
energy are emitted each second, and it is believed that these
"active galactic nuclei" are probably powered by accretion of
matter into a supermassive black hole of 10^(6) to 10^(9)
solar-masses. Astronomers have recently discovered that many
active galactic nuclei eject clouds of ionized gas with
velocities of up to 10 percent of the speed of light over a wide
range of angles, in contrast to the previously known collimated
jets. These mass outflows are considered to be intriguing because
they provide information about the dynamical forces (such as
radiation and wind pressure) near an active supermassive black
hole. D. Michael Crenshaw points out that a greater understanding
of mass outflow from active galactic nuclei will come through
comparison between observations and dynamical models, which have
grown in sophistication over the past few years. "It also remains
to be shown how matter reaches the active nucleus in order to
fuel the central engine. The UV and x-ray observations have found
no evidence for infalling matter." (SCI 2001 292:1500)
... ... CHRONIC FATIGUE SYNDROME: The current consensus among
clinicians is that the entity called "chronic fatigue syndrome"
is not a homogeneous abnormality, and that there is no single
pathogenic mechanism: no physical finding or laboratory test can
be used to confirm the diagnosis of chronic fatigue syndrome. In
a recent review, Benjamin H. Natelson points out that chronic
fatigue syndrome comprises a number of poorly understood signs
and symptoms, and whether a patient receives the diagnosis for
one or another of these symptom clusters may depend on the
specialty of the physician making the diagnosis. Natelson points
out three difficulties in research: a) Researchers tend to test
their favorite theories and rarely perform confirmatory studies.
b) Studies often compare data from inactive patients to healthy
subjects who might be extremely active, and thus differences
between groups could reflect activity level or fitness rather
than underlying disease. c) Patients with chronic fatigue
syndrome are a heterogeneous group with frequent co-morbid
diagnoses (e.g., depression, fibromyalgia, irritable bowel
syndrome) whose presence could alter study outcomes.
(JAMA 2001 285:2557)
... ... DOPAMINE RECEPTORS: Dopamine is a neurotransmitter found
in several major areas of the brain, and the degeneration of
so-called dopamine neurons is apparently involved in Parkinson's
disease. Dopamine has also been implicated in the intricate
effects of the psychostimulating drugs associated with drug
abuse. The dietary precursors of dopamine are phenylalanine and
l-tyrosine. So-called "brain-derived neurotrophic factor" (BNDF)
is a polypeptide initially thought to be responsible for neuron
proliferation, differentiation, and survival via its uptake at
nerve terminals and retrograde transport to the cell body. But
observations also indicate that BNDF is transported in an
anterograde direction, is released on neuron depolarization, and
triggers intracellular signals and action potentials in central
nervous system neurons. A new study indicates that BDNF elicits
long-term neuronal adaptations by controlling the responsiveness
of its target neurons to dopamine. The authors suggest their
results indicate that BDNF may be an important determinant of
pathophysiological conditions such as drug addiction,
schizophrenia, or Parkinson's disease, in which dopamine receptor
expression is abnormal. (NAT 2001 411:86)
... ... POST-GENOMIC ERA: Francis S. Collins, of the National
Human Genome Research Institute suggests that his colleagues
collectively agree to cease using the phrase "the post-genome
era", at least for several decades. Collins says, "This is the
beginning of genomics, not the end. Critical understanding of
gene expression, the connection between sequence variations and
phenotype, large-scale protein-protein interactions, and a host
of other global analyses of human biology can now get seriously
underway. In fact we should probably also agree to deep-six the
use of the term 'the post-sequencing era', at lease for a while.
After all, finishing the sequence of the human genome to the same
standard already achieved for chromosomes 21 and 22 will take
major efforts by the genome centers over the next two years...
So, to borrow a phrase from Winston Churchill, this is not the
end of genomics. This is not even the beginning of the end. But
it may be the end of the beginning." (GR 2001 11:641)
... ... ALZHEIMER'S DISEASE AND CHOLESTEROL: The pathophysiology
of Alzheimer's disease is believed to involve a small peptide,
called "A-beta", which accumulates in the brain causing
neurotoxicity and neurodegeneration. There is growing evidence
pointing toward a possible link between cholesterol, A-beta, and
Alzheimer's disease, with recent epidemiological studies
indicating that the prevalence of Alzheimer's disease is reduced
among people taking a class of cholesterol lowering medications
called "statins", such as simvastatin and lovastatin. Now two new
studies, involving both cell culture and in vivo experiments,
demonstrate that inhibiting cholesterol production reduces A-beta
production. In a commentary on this research, Benjamin Wolozin
suggests that together these studies indicate that inhibiting
cholesterol production in the brain might inhibit A-beta
production and reduce the accumulation of A-beta that apparently
causes Alzheimer's disease. (PNAS 2001 98:5371)
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2. SCIENCE POLICY:
LACK OF DIVERSITY IN US CHEMISTRY DEPARTMENTS
Thirty years ago, when the lack of diversity in US
university science departments was first a subject of public
attention, many science policy-makers and university
administrators made public avowals and resolutions to do
something about the problem. Now a generation has passed, and
apparently the evidence indicates that avowals and resolutions
have not accomplished much, and in fact the numbers may be headed
in the other direction. Why? Is it that people don't care about
the problem? And if they don't care, why don't they care? Does
the science community need to call in the psychiatry community to
unravel this irony?
... ... Jeffrey Mervis (Science) reports the results of a new
survey of major US chemistry departments by D. Nelson et al
(University of Oklahoma, US), the report by Mervis making the
following points:
1) The number of chemistry PhDs awarded to blacks each year
in the US has more than doubled since 1990. But during the same
time-frame, the number of blacks hired as assistant professors at
the top 50 chemistry departments in the US has held steady: the
number is zero. (The top 50 academic departments were determined
by expenditures for chemistry research.)
2) African American blacks and Hispanics constitute barely 1
percent of the 1637 tenured or tenure-track chemistry faculty
members at the top 50 schools, and 23 of the 50 chemistry
departments have no black or Hispanics on the tenured or tenure-
track faculty. In addition, 12 of the 18 blacks are full
professors at or near retirement age, and none is an assistant
professor.
3) Concerning women, of the 1637 faculty in the 50 top
chemistry departments, there are a total of 7 women who are
tenured or tenure-track faculty.
4) The chair-persons of some top-ranked chemistry
departments insist that the real problem is the small number of
chemistry PhDs awarded to underrepresented minorities: in 1999,
there were 56 blacks and 42 Hispanics, which represent,
respectively, 4 percent and 3 percent of the 1400 chemistry PhDs
produced that year.
5) Jim Henderson, chair of the division of chemistry at
Harvard University, which has 4 Asians and no underrepresented
minorities, says that faculty-searches at his university are
color-blind: "We have found that excellence doesn't have anything
to do with ethnic categories or gender." But he states: "I didn't
realize it was so bad."
6) Philip Phillips, a West-Indian black trained as a
theoretical chemist, who is now a full professor in the physics
department at the University of Illinois Urbana-Champaign,
states: "People think that the situation will improve if there
are more minority PhDs. That's important, but there also has to
be active involvement and a commitment to the cause. And I don't
see that."
7) The following universities with "top 50" chemistry
departments have no (zero) blacks or Hispanics as tenured or
tenure-track chemistry faculty: California Institute of
Technology, Colorado State University, Columbia University,
Florida State University, Harvard University, Indiana University
Bloomington, Johns Hopkins University, Massachusetts Institute of
Technology, Northwestern University, Pennsylvania State
University, Princeton University, Stanford University, University
of Akron, University of Chicago, University of Colorado Boulder,
University of Kansas, University of North Carolina Chapel Hill,
University of Rochester, University of South Carolina, University
of Texas Austin, University of Utah, University of Wisconsin
Madison, Virginia Polytechnic Institute.
-----------
Jeffrey Mervis: New data in chemistry show "zero" diversity.
(Science 18 May 01 292:1291)
QY: Jeffrey Mervis: editors@aaas.org
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Summary by SCIENCE-WEEK http://scienceweek.com 20Jul01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
SCIENCE POLICY:
RACIAL AND ETHNIC DISPARITIES IN FACULTY PROMOTION
IN ACADEMIC MEDICINE
From a purely rational perspective, the last place one would
expect to find racial, ethnic, and gender discrimination is in
professional academia, an arena where merit is assumed (and
touted) as the basis for advancement. Unfortunately, in the US,
this assumption concerning merit is an apparent myth. Several
studies have demonstrated that female faculty in US medical
schools are less likely than men to be promoted to senior rank,
and now a new study confirms that racial and ethnic minority
faculty in US medical schools are promoted at lower rates
compared with white faculty.
... ... D. Fang et al (3 authors (Association of American Medical
Colleges, US) present a study designed to compare promotion rates
of minority and white medical school faculty in the US. The study
involved a total of 50,145 full-time US medical school faculty
who became assistant professors or associate professors between
1980 and 1989. Faculty of historically black and Puerto Rican
medical schools were excluded from the study. The authors
tabulated attainment of associate or full professorships among
assistant professors and full professorships among associate
professors by 1997, among white, Asian or Pacific Islanders,
"underrepresented minority" (including black, Mexican American,
Puerto Rican, Native American, and Native Alaskan), and other
Hispanic faculty.
1) The authors report the following results:
Assistant Professors Promoted by 1997:
--------------------------------------
White 46 percent
Asian or Pacific Islanders 37
Underrepresented Minorities 30
Other Hispanic 43
Associate Professors Promoted by 1997:
--------------------------------------
White 50 percent
Asian and Pacific Islanders 44
Underrepresented Minorities 36
Other Hispanic 43
2) The authors report that racial/ethnic disparities in
promotion were evident among tenure and nontenure faculty and
among faculty who received and did not receive National
Institutes of Health research awards. After adjusting for cohort,
sex, tenure status, degree, department, medical school type, and
receipt of NIH awards, underrepresented minority faculty remained
less likely to be promoted compared with white faculty (relative
risk 0.68 for assistant professors and 0.81 for associated
professors). Asian and Pacific Islander assistant professors also
were less likely to be promoted (relative risk 0.91), whereas
Asian and Pacific Islander associate professors and other
Hispanic assistant and associate professors were promoted at
comparable rates.
3) The authors state: "The major finding of this study is
that racial/ethnic minority faculty, at both the assistant and
associate professor rank, are lagging in rates of promotion
compared with white faculty, even though their representation in
academic medicine has steadily increased over time."
-----------
D. Fang et al: Racial and ethnic disparities in faculty promotion
in academic medicine.
(J. Amer. Med. Assoc. 6 Sep 00 284:1085)
QY: Ernest Moy emoy@aamc.org
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Summary by SCIENCE-WEEK http://scienceweek.com 29Sep00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
MINORITY FACULTY AND ACADEMIC RANK IN MEDICINE
Recent efforts to improve the representation of minority faculty
in US academic medicine have focused on increasing the number of
minority physicians who pursue academic careers. However, the
number of minority students entering US medical schools has
reached a plateau, despite efforts to achieve racial and ethnic
diversity in these schools. At the present time, only 3.9 percent
of all US medical faculty identify themselves as black, Native
American, Mexican American, or Puerto Rican, and these groups
have been classified as underrepresented in medicine compared to
their representation in the general population. Asian Americans
are currently not classified as underrepresented.
... ... A. Palepu et al now report a study to determine whether
minority faculty were as likely as majority faculty to have
attained senior rank (associate professor or full professor)
after adjusting for other factors that typically influence
promotion. The study consisted of a self-administered mailed
survey of US medical school faculty using the Association of
American Medical Colleges database, the sample stratified by
department, graduation cohort, and sex. Of 1807 respondents, 54
percent had attained senior academic rank. The authors report
that after adjusting for the medical school, department, years as
medical school faculty, number of peer-reviewed publications,
receipt of research grant funding, proportion of time in clinical
activities, sex, and tenure status, the odds ratios relative to
white faculty of holding senior rank were 0.33 for black faculty,
0.36 for Hispanic faculty, and 0.58 for Asian faculty. The
authors conclude that minority faculty are less likely than white
faculty to hold senior academic rank, and they suggest this
finding is not explained by potential confounders such as years
as a faculty member or measures of academic productivity. The
authors further suggest that "medical school deans and department
heads need to foster and provided greater support for the careers
of minority faculty to ensure their equitable representation at
all levels in academic medicine."
-----------
A. Palepu et al (6 authors at 2 installations, US): Minority
faculty and academic rank in medicine.
(J. Amer. Med. Assoc. 2 Sep 98 280:767)
QY: Anita Palepu: anita@hivnet.ubc.ca
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 25Sep98
-------------------
Related Background:
DECLINE IN MINORITY GRADUATE ADMISSIONS
In 1996, voters in California approved an anti-affirmative action
referendum, and that same year a federal district court banned
affirmative action at universities in Texas, Louisiana, and
Mississippi. Educators and federal executive branch officials
feared the consequence of the referendum and court decision would
be a drop in minority university enrollments nationwide, and the
data now coming in apparently justifies their fears. A report
released the week of September 11th by the American Association
for the Advancement of Science presents the results of analysis
of admissions data for the past 4 years from science and
engineering graduate programs at 93 major research universities.
From 1994 to 1996, there was little change in black graduate
admissions and a slight increase in Hispanic admissions
(approximately 5 percent). But in 1997, black admissions declined
20 percent and Hispanic admissions declined 18 percent from the
previous year. The declines are attributed to the uncertainty of
university administrators: "They don't know what is allowed and
what is not."
-----------
M. Barinaga (~Science~): Graduate Admissions Down for Minorities.
(Science 18 Sep 98 281:1778)
QY: Marcia Barinaga: science_editors@aaas.org>
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 9Oct98
-------------------
Related Background:
UNEVEN PROGRESS IN SHARE OF SCIENCE PHDS OF WOMEN AND MINORITIES
A new US National Science Foundation report indicates uneven
recent progress in the share of US PhDs in the sciences by women
and minorities. From 1985 to 1995, the share of PhDs awarded to
women in the physical sciences increased from 16 percent to 23
percent, in the biological sciences from 38 percent to 46
percent, and in engineering from 6 percent to 12 percent. But the
share of science PhDs by African-Americans and Hispanics
apparently hardly changed during that decade. On the other hand,
Asian share of PhDs increased significantly in all 3 areas,
particularly in the physical and biological sciences.
(Science 11 Jun 99) (ScienceWeek Bulletin 9 Oct 99)
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
3. ASTROPHYSICS: NEW DATA ON THE BIRTH OF STARS
A star is apparently born as a consequence of the
gravitational condensation of huge clouds of gas and dust, the
process accounted for, at least in its outlines, by current
theories of gravitation and atomic physics.
"Accretion" is considered an important factor in the
evolution of stars, planets, and comets. The essential idea is
the coalescence of small particles in space as a result of
collisions, and the gradual formation of larger bodies from
smaller ones as a result of gravitational attraction. An
"accretion disk" is a disk of gas or particles in orbit around an
object, the disk formed by inflowing matter. In the case of a
young star, its accretion disk is an aggregation of material in
excess of the material whose gravitational condensation was
responsible for the initial star formation.
The term "maser" derives from the phrase "microwave
amplification by stimulated emission of radiation", the process
analogous to that of a laser but at microwave frequencies. Masers
are used as atomic clocks and as low-noise amplifiers in radio
astronomy. An astronomical (cosmic) "maser source" is a radio
source in which the spectral lines of a particular atom, ion, or
molecule are greatly amplified by local maser action to produce
an intense source of radio emission. Astronomical maser emission
has been identified for many molecules, including water. Maser
sources occur in star-forming regions ("interstellar masers"), in
the circumstellar envelopes of old stars (e.g., *red giant stars)
("circumstellar masers), in comets, in some planetary
atmospheres, and in some *active galactic nuclei.
Water-vapor masers are the most widely distributed of all
cosmic masers, and have many different water-maser lines. They
were first discovered in 1969, and they are usually difficult to
observe with ground-based radio telescopes because of strong
absorption by water vapor in the Earth's atmosphere.
The term "very long baseline interferometry" (VLBI) refers
to a technique in radio interferometry where telescopes separated
by large distances (e.g., many thousands of kilometers) may be
operated as an interferometer to achieve angular resolutions
better than one-thousandth of an arc-second. The essential idea
is that each telescope works independently, recording signals
with precise timing information, and later the signal records are
combined. The advent of space-borne radio telescopes is expected
to extend VLBI baselines to hundreds of thousands of kilometers,
producing a substantial increase in angular resolution.
... ... J.M. Torrrelles et al (10 authors 7 installations, ES,
US, MX, CL) present a report of new observations of material
ejected from a young star, the authors making the following
points:
1) The authors point out that the exact process by which
interstellar matter condenses to form young stars is of great
interest, in part because they bear on the formation of planets
like our own from the material that fails to become part of the
star. Theoretical models suggest that ejection of gas during
early phases of stellar evolution is a key mechanism for removing
excess angular momentum, thereby allowing material to drift
inward toward the star through an accretion disk. Such ejections
also limit the mass that can be accumulated by the stellar core.
To date, these ejections of gas have been observed to be bipolar
and highly collimated, which is in agreement with current theory.
2) The authors report VLBI observations at very high angular
resolution of the proper motions of an arc of water-vapor masers
near a very young massive star in the Cepheus constellation. The
authors report that the arc of masers can be fitted to a circle
with an accuracy of one part in a thousand, and that the
structure is expanding. Since only a sphere will always produce a
circle in projection, the authors suggest their results strongly
indicate that the perfectly spherical ejection of material from
this star occurred approximately 33 years earlier. The authors
state: "The spherical symmetry of the ejecta and its episodic
nature are very surprising in the light of present theories."
... ... In a commentary on this work, Kevin B. Marvel (American
Astronomical Society, US) states: "Existing theories of stellar
formation cannot explain this unique source, so there is a chance
it could actually be a mature star. The current observations only
reveal details about the masers themselves, not their stellar
host, and so we cannot be entirely certain of the host star's
age. Only time will tell if the source that has formed this
symmetric shell of water masers will eject more material, perhaps
allowing a sequel to the stunning set of images presented by
Torrelles and colleagues."
-----------
J.M. Torrelles et al: Spherical episodic ejection of material
from a young star.
(Nature 17 May 01 411:277)
QY: P.T.P. Ho: ho@cfa.harvard.edu
-----------
Kevin B. Marvel: A stellar performance.
(Nature 17 May 01 411:251)
QY: Kevin B. Marvel: marvel@aas.org
-----------
Text Notes:
... ... *red giant stars: A "red giant star" is a star in a late
stage of evolution, the star having exhausted the hydrogen fuel
in its core. It has a surface temperature of less than 4700
kelvins and a diameter 10 to 100 times that of the Sun.
... ... *active galactic nuclei: (active nuclei) Central regions
of galaxies in which considerable energy is generated by
processes other than those operating in ordinary stars. The
energy may result from the accretion of material into a massive
black hole situated at the core of the galaxy.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 20Jul01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ASTROPHYSICS: ON WATER AND THE BIRTH OF STARS
One of the great achievements of 20th century science was
the detailed quantitative understanding of star formation. In
general, a star is born when a massive clump of gas contracts
under its own gravity, an idea first introduced by the
mathematician and physicist Pierre Simon de Laplace (1749-1827).
Laplace proposed that a rotating cloud of gas, as it pulled
itself together, would flatten into a disk, and the central
portion of the disk would gather itself into a ball to form a
star, while the outlying regions of the disk coalesced into
planets. Although physics and mathematics were not advanced
enough during the time of Laplace to develop the details of this
model, the general idea is still a good qualitative description
of the process that creates new stars.
Today we know that the most likely stellar nurseries are
gigantic molecular clouds, huge aggregations of cold gas, these
clouds containing a significant number of molecules, rather than
merely solitary atoms. As each would-be star collapses due to its
self-gravity, the gas retains its spin (angular momentum), and
forms a disk similar to that imagined by Laplace. The collapse
compresses the gas, causing the gas to increase in temperature.
Some of the rotational energy of the gas is carried away,
possibly by magnetic fields threading the cloud, allowing further
collapse and compression at the center. Eventually, most of the
matter accumulates at the center, while the rest remains in an
encircling disk. The central sphere of condensed gas, now a
"protostar", continues to contract and heat. As its temperature
rises, more and more of its hydrogen ionizes. Free electrons
scatter and absorb photons very effectively, so the more
electrons that are liberated, the more opaque the protostar
becomes. If photons cannot escape from the gas, their energy is
trapped within the protostar, causing the temperature to rise
even further. Finally, the temperature within the core of the
protostar rises to a sufficient level to ignite nuclear fusion,
and the energy generated from this process provides the newborn
star with the pressure required to prevent further collapse.
Thus, a star is born. The entire gravitational condensation
followed by nuclear fusion ignition may take 100 million years;
if the star is of "ordinary" mass (like our Sun), it will then
survive approximately 10 billion years before its nuclear fuel is
exhausted and it begins the phase of star death.
... ... Brunella Nisini (Rome Astronomical Observatory, IT)
presents a commentary on recent research on the role of water in
star formation, the author making the following points:
1) The author points out that the water molecule plays a
fundamental role during the first stages of star formation. Water
is an important oxygen reservoir in the warm environments of
star-forming regions and is believed to contribute substantially
to the cooling of the circumstellar gas disk, thereby helping to
remove the excess energy accumulating during protostellar
collapse.
2) Water may be present in the star-forming region of a
molecular cloud either as a gas or as ice on the surface of dust
particles. The relative abundance of gas to ice depends on the
physical and chemical characteristics of the environment and can
thus be used as a diagnostic parameter to probe different stages
of stellar evolution -- but only if the water molecules can be
detected. Such detection is difficult with ground-based
instruments because of water vapor in Earth's atmosphere. In
recent years, this problem has been overcome by two space
missions, the Infrared Space Observatory (ISO), which ended its
activity in 1998, and the Submillimeter Wave Astronomy Satellite,
which has been operating since the beginning of 1999.
3) According to current models, as gravitational collapse
proceeds in a molecular cloud, the radiation energy released by
the accretion of matter onto the newly born protostar is absorbed
by the dense and thick circumstellar envelope, which quickly
heats up as a result. At the same time, protostars also violently
eject mass in the form of bipolar jets, which transport the
excess energy and angular momentum away from the central object.
When the jets encounter the dense ambient medium, they produce
strong shock waves that can increase the gas temperature up to a
few thousand degrees kelvin.
4) Concerning water, the Infrared Space Observatory was able
to confirm, for the first time, the expectations of current
models of star formation. The observatory detected a large amount
of warm gaseous water in active star-forming regions such as the
cluster of protostars inside the Orion BN region, which shows a
very strong and complex water spectrum originating both from
shocked gas and from the hot core surrounding the cluster. The
infrared water abundance exceeds 10^(-4) relative to molecular
hydrogen, thus confirming that large amounts of gas phase water
are produced once the protostar is formed.
-----------
Brunella Nisini: Water's role in making stars.
(Science 24 Nov 00 290:1513)
QY: Brunella Nisini: bruni@coma.mporzio.astro.it
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 15Dec00
For more information: http://scienceweek.com/swfr.htm
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4. NEUROBIOLOGY: ON MARIJUANA CANNABINOIDS
The drug "marijuana" is derived from the hemp plant Cannabis
sativa. The parts of the plant vary in potency, the resinous
exudate of the flowering tops of the female plant the most
potent, providing "hashish" and "charas". Next in potency are the
dried leaves and flowering shoots of the female plant (providing
"bhang"), and the resinous mass from small leaves of
inflorescence (providing "ganja"). The drug is usually inhaled by
smoking, with marijuana "joints" containing approximately 500
milligrams of marijuana, which in turn contains approximately 5
to 15 milligrams of tetrahydrocannabinol (THC).
With moderate dosage, marijuana produces mild euphoria
followed by sleepiness. In the acute state, the user has an
altered time perception, less inhibited emotions, psychomotor
problems, and impaired immediate memory. High doses produce
transient effects resembling psychosis. The drug frequently
aggravates existing mental illness, adversely affects motor
performance, and slows the learning process in children. Studies
of long-term effects have conclusively demonstrated abnormalities
in the lungs, laryngitis, rhinitis, and chronic obstructive
pulmonary disease. Chronic usage has resulted in depression of
plasma testosterone levels and reduced sperm counts. Abnormal
menstruation and failure to ovulate have occurred in some female
users. Sudden withdrawal produces insomnia, nausea, muscle pain
(myalgia), and irritability. In general, marijuana is a potent
psychoactive drug acting on the central nervous system and
producing both acute and chronic neurophysiological effects.
The most important neuroactive chemical ingredients in
marijuana are the lipophilic cannabinoids, especially delta-9-
tetrahydrocannabinol. Cannabinoids are believed to act at several
specific cannabinoid receptors in the brain. When a human inhales
or ingests marijuana, the liver transforms it into a number of
metabolites, the most important of which is 11-hydroxy-delta-9-
tetrahydrocannabinol, which has effects identical to those of the
parent compound. 11-hydroxy-delta-9-THC is in turn converted to
more polar and inactive metabolites which are excreted in urine.
Since certain cannabinoids are already present in the
nervous system without input of any drug, cannabinoids need to be
categorized as "exogenous" (from outside) versus "endogenous"
(from inside).
In this context, the term "G-proteins" refers to a family of
signal-coupling proteins that act as intermediaries between
activated cell receptors and effectors, for example, the
transduction of hormonal signals from the cell surface to the
cell interior. The G-protein is apparently embedded in the cell
membrane with parts exposed on the outside surface and inside
surface. The outside moiety is activated by the "first messenger"
(e.g., a hormone), and the inside moiety activates a "second
messenger", the G-protein thus acting as a trans-membrane signal
transducer.
"Neurotransmitters" are chemical substances released at the
terminals of nerve axons in response to the propagation of an
impulse to the end of that axon. The neurotransmitter substance
diffuses into the synapse, the junction between the presynaptic
nerve ending and the postsynaptic neuron, and at the membrane of
the postsynaptic neuron the transmitter substance interacts with
a receptor. Depending on the type of receptor, the result may be
an excitatory or an inhibitory effect on the postsynaptic nerve
cell.
"GABA" is gamma-amino butyric acid, a neurotransmitter
substance. The term "GABA receptor" refers to any of several
membrane proteins that bind GABA and mediate its effects as an
inhibitory neurotransmitter.
In this context, the term "depolarization" refers to a
reduction in the potential difference across the cell membrane.
The neuron action potential involves not only a transient
depolarization of the membrane but also a transient reversal of
polarity of the potential difference, the potential difference
across the neuron membrane during an action potential changing
from approximately -60 millivolts (inside negative) to
approximately +40 millivolts.
The "hippocampus" is a brain cortex structure in the medial
part of the temporal lobe. In humans, among other functions, the
hippocampus is apparently involved in short-term memory. Analysis
of the neurological correlates of learning behavior in the rat
indicates that the hippocampus is also involved in memory in that
species. Nerve cells in rat brain slices remain active in vitro
in appropriate solutions for up to 24 hours, and such slices are
convenient tissues for experiments. "Hippocampal pyramidal
neurons" are a specific type of nerve cell in the hippocampus.
The term "retrograde signaling" refers to neural information
transmission in a direction opposite to the primary signal
direction. In this context, the term refers to signaling from
postsynaptic neuron to presynaptic neuron. In general, retrograde
signaling in neural systems is usually part of a negative
feedback process.
In general, an "interneuron" is any neuron that branches
locally to innervate other neurons.
In general, in this context, an "agonist" is any substance
that binds to and activates a receptor.
... ... R.I. Wilson and R.A. Nicoll (University of California San
Francisco, US) report a study of the action of endogenous
cannabinoids, the authors making the following points:
1) The authors point out that marijuana affects brain
function primarily by activating the G-protein-coupled
cannabinoid receptor-1 (CB1), which is genetically expressed
throughout the brain at high levels. Two endogenous lipids,
anandamide and 2-arachidonylglycerol (2-AG), have been identified
as cannabinoid receptor-1 ligands, and depolarized hippocampal
neurons have been shown to rapidly release both anandamide and 2-
AG in a calcium-dependent manner. In the hippocampus, cannabinoid
receptor-1 is expressed mainly by GABA-mediated inhibitory
interneurons, where cannabinoid receptor-1 apparently clusters on
axon terminals of such interneurons. A synthetic cannabinoid
receptor-1 agonist has been demonstrated to depress GABA release
from hippocampal slices, which suggests that the function of
endogenous cannabinoids released by depolarized hippocampal
neurons might be to reduce GABA release (down-regulate GABA
release).
2) The authors report that their experiments indicate that
the transient suppression of GABA-mediated transmission that
follows depolarization of hippocampal pyramidal neurons is
mediated by retrograde signaling through release of endogenous
cannabinoids. Signaling by the endocannabinoid system thus
represents a mechanism by which neurons can communicate backwards
across synapses to modulate their inputs. The authors suggest
this study represents the first identification of a physiological
process mediated by endogenous brain cannabinoids. Exogenous
cannabinoids such as marijuana may destroy the information
contained in endogenous cannabinoid feedback loops and thus
promote a more random pattern of synaptic modification.
-----------
R.I. Wilson and R.A. Nicoll: Endogenous cannabinoids mediate
retrograde signalling at hippocampal synapses.
(Nature 29 Mar 01 410:588)
QY: Roger A. Nicoll: nicoll@phys.ucsf.edu
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 20Jul01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON THE MECHANISM OF PAIN MODULATION BY CANNABINOIDS
In general, the clinical entity "hyperalgesia" (sometimes known
as "hyperalgia") is a heightened sensitivity to painful stimuli.
Cannabinoids are derivatives or preparations from the plant
Cannabis sativa (the marijuana plant), a group of a dozen
compounds chemically related to cannabinol, including delta-9-
tetrahydrocannabinol (THC), and the cannabinoid receptor is the
binding site for the psychoactive component of marijuana, as well
as for anandamide, the endogenous physiological ligand. Anand-
amide is known to modulate the pain pathway, but the mechanisms
are not clear. ... ... Richardson et al (3 authors at Univ. of
Minnesota Minneapolis, US) now report studies in animal models
that indicate that hyperalgesia may be linked to a faulty
cannabinoid system in the spinal cord. The authors suggest that
endogenous cannabinoids attenuate pain by preventing the release
of glutamate from presynaptic terminals of neurons that transmit
pain messages to the spinal cord.
-----------
QY: Jenelle D. Richardson, Harvard Univ. Medical School, Dept.
Neurobiology 617-432-1550.
(Chem. & Eng. News 19 Jan 98) (Science-Week 30 Jan 98)
For more information: http://scienceweek.com/swfr.htm
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5. MOLECULAR BIOLOGY: GLYCOPROTEINS AND THE IMMUNE SYSTEM
The term "saccharide" refers to any carbohydrate, especially
to simple sugars. Of saccharides there are 4 general classes:
monosaccharides, disaccharides, oligosaccharides, and
polysaccharides (also called "glycans"), with all cases except
monosaccharides consisting of simple sugars in a chain of
glycosidic linkages. The term "oligosaccharides" usually refers
to carbohydrates involving 2 to 20 sugars in a chain, although
some authors use "polysaccharide" for any carbohydrate chain
involving more than 10 sugars.
The term "glycosylation" refers in general to the process in
which a carbohydrate is joined to another molecule (e.g., to
proteins or lipids).
The term "glycoproteins" refers in general to proteins to
which oligosaccharides are attached. The glycoprotein
carbohydrate chains are often branched rather than linear, and
they may or may not be negatively charged. In general, depending
on type, glycoproteins contain highly variable amounts of
carbohydrate.
The term "glycoform" refers to any of several differently
glycosylated variants of a specific glycoprotein, including
variation in type, number, and/or position of the sugar residues.
Membrane-bound glycoproteins participate in a broad range of
cellular phenomena, including cell-surface recognition (by other
cells, by hormones, and by viruses), cell-surface antigenicity
(e.g., blood group *antigens), as components of the
*extracellular matrix, and as components of various biological
"lubricants" (mucins) of the gastrointestinal and urogenital
tracts. In addition, almost all the globular proteins present in
human plasma (with the notable exception of albumin), and the
secreted enzymes and proteins, are glycoproteins.
Glycoproteins are also intimately involved in the operations
of the immune system. In biology, the "immunity" of organisms to
infection by various pathogens is functionally characterized into
2 types: The term "innate immunity" refers to non-specific
antimicrobial systems of response (e.g., phagocytosis: engulfment
and digestion of microbes by "killer" cells) that are innate and
not intrinsically affected by prior contact with the infectious
agent; the term "adaptive immunity" refers to immune responses
which involve an enhanced ability to respond to specific
molecular antigens presented by the invading pathogenic entity,
the enhancement dependent on prior contact with the same
pathogen. In addition, the concept of innate immunity generally
refers to the first-line host defense that serves to limit
infection in the early hours after exposure to microorganisms.
The adaptive immune system has many mechanisms to destroy an
antigen invader, with the responses generally categorized into
two types, the "humoral response" and the "cell-mediated
response". Both types of response involve two special classes of
immune system cells, the B cells and the T cells (B and T
lymphocytes).
Lymphocytes (lymph cells, lympho-leukocytes) are a type of
leukocyte (white blood cell) responsible for the immune response.
In general, there are two classes of lymphocytes: 1) the B-cells,
when presented with a foreign chemical entity (antigen), change
into antibody producing plasma cells; 2) the T-cells, which
interact directly with foreign invaders such as bacteria and
viruses, and some types of which assist B-cells in the B-cell
response. The general terminological differentiation between
B-cells and T-cells is based on where the cells mature: B-cells
generally mature in (b)one marrow, and T-cells mature in the
(t)hymus gland.
The humoral response depends primarily on B-cells, aided by
certain "helper T-cells" which provoke proliferation of B-cells,
and involves the secretion of specific antibodies by B-cells, the
antibodies consisting of proteins of the immunoglobulin class
that bind to specific antigens. The immunoglobulins are a large
glycoprotein category that includes antibodies as a subset. In
general, an "antibody" is a protein molecule produced by the
immune system of vertebrate organisms, the molecule designed to
specifically interact with a particular antigen.
The cell-mediated immune response is executed by both helper
T-cells and a class of T-lymphocytes called cytotoxic T-cells
("killer T-cells"), which attack host cells that have been
infected by a pathogen. In the cell-mediated immune response,
T-cells may also begin a T-cell proliferation process as a result
of contact with an "antigen-presenting cell" (see below), the
proliferation involving cellular specialization (differentiation)
and the production of a large number of specific-antigen-
activated T-cells from a single progenitor cell (clonal
expansion).
The basic function of the T-cell in recognizing a target
antigen involves the use of T-cell surface receptors to recognize
an antigen when it is presented on the surface of another cell,
either an infected target cell or an immune system antigen-
presenting cell. In the former case, various antigen fragments of
the infecting intracellular pathogen are transported to the host-
cell surface; in the latter case, immune system cells specialized
to present antigens on their surfaces are involved, the antigens
derived from engulfment (phagocytosis) and fragmentation of the
pathogen. In both cases, the antigen is presented on the cell
surface by a special protein called "major histocompatibility
complex" (MHC), and in order for the antigen to be recognized by
the T-cell, the antigen must be presented by one of the MHC group
of proteins. It is apparently the combination of the antigen
peptide fragment and MHC protein which is recognized by the T-
cell receptor.
In general, then, T-cells have various roles in immune
responses: there are types of T-cells involved in the humoral
immune response and types of T-cells involved in the cell-
mediated immune response. But in both cases, T-cell receptors
interact with antigen-MHC complexes presented by an "antigen-
presenting cell": in the case of the humoral immune response, the
antigen-presenting cell is a host immune system cell which
presents to the T-cells an antigen-MHC entity derived from the
pathogen, and the T-cells (in this case, helper T-cells) are then
involved in antibody production by B-cells; in the case of the
cell-mediated immune response, the antigen-MHC-presenting cell is
an infected host cell, the responding T-cells are helper T-cells
and cytotoxic T-cells, with both helper T-cells and cytotoxic T-
cells indirectly and directly involved, respectively, in the
destruction of the infected host cell. Another generalization is
that the humoral immune response is primarily directed against
extracellular pathogens or pathogen derivatives, while the cell-
mediated immune response is primarily directed against
intracellular pathogens (or, in special cases, malignant host or
foreign tissue cells).
The "complement system" consists of a group of more than 30
normally inactive proteins in blood plasma and in cell membranes.
When activated, these proteins enhance certain immune, allergic,
and inflammatory reactions.
In general, the term "autoimmune disease" (autoimmune
response) refers to any pathology that involves a self-
immunological process against the individual's own cells or
tissues. Classified as human autoimmune diseases are rheumatoid
arthritis, systemic lupus erythematosus, rheumatic fever,
Addison's disease, multiple sclerosis, type 1 diabetes mellitus,
etc.
The "lectins" are a group of sugar-binding proteins of non-
immune system origin which agglutinate cells and/or precipitate
glycoconjugates. Lectins are widely distributed in nature, found
in seeds and other parts of certain plants, and are also found in
other organisms ranging from bacteria to mammals.
... ... P.M. Rudd et al (5 authors at 4 installations, UK US)
present a detailed review of glycosylation and the immune system,
the authors making the following points:
1) The authors point out that almost all the key molecules
in the innate and adaptive immune response are glycoproteins. In
the cellular immune system, specific glycoforms are involved in
the folding, quality control, and assembly of peptide-loaded
major histocompatibility complex (MHC) antigens and the T cell
receptor complex. Although some glycopeptide antigens are
presented by the MHC, the generation of peptide antigens from
glycoproteins may require enzymatic removal of sugars before the
protein can be cleaved.
2) Oligosaccharides attached to glycoproteins in the
junction between T cells and antigen-presenting cells help to
orient binding faces, provide *protease protection, and restrict
non-specific lateral protein-protein interactions,
3) In the humoral immune system, all of the immunoglobulins
and most of the complement components are glycosylated. Although
a major function of sugars is to contribute to the stability of
the proteins to which they are attached, specific glycoforms are
apparently involved in recognition events. For example, in
rheumatoid arthritis, an autoimmune disease, agalactosylated
glycoforms of a specific aggregated immunoglobulin
(immunoglobulin G) may induce association with mannose-binding
lectin and contribute to the pathology of the disease.
4) The authors conclude: "Glycoproteins are key components
of the immune system effectors. Their oligosaccharides are
important in synthesis, stability, recognition, and regulation of
the proteins themselves and in many of their diverse
interactions. Establishing the extent and variability of
glycosylation in the context of the 3-dimensional structure of
the proteins to which they are attached will lead to further
insights into immune processes in health and disease."
-----------
P.M. Rudd: Glycosylation and the immune system.
(Science 23 Mar 01 291:2370)
QY: Pauline M. Rudd: pmr@glycob.ox.ac.uk
-----------
Text Notes:
... ... *antigens: In general, an antigen is any entity that
provokes an immune response, and this includes, in certain
disease states, entities that are not "foreign" to the body.
... ... *extracellular matrix: In general, the extracellular
matrix is a layer consisting mainly of proteins and
glycosaminoglycans that form a sheet underlying endothelial and
epithelial cells. The molecular constituents of the matrix are
secreted by cells in the vicinity. Endothelial cells are the
cells that line blood vessels. In animals, "epithelial cells"
compose the cell layers that form the interface between a tissue
and the external environment, for example, the cells of the skin,
the lining of the intestinal tract, and the lung airway passages.
... ... *protease: In general, any enzyme that cleaves proteins,
usually by hydrolysis.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 20Jul01
For more information: http://scienceweek.com/swfr.htm
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6. MEDICAL BIOLOGY: NEW DATA ON RETROVIRUSES AND LUNG CANCER
Whether viruses are classified as "living" or "non-living"
is arbitrary, but in either case one is dealing with a remarkable
entity. As a group, viruses are in the size range 20 to 300
nanometers, compact bundles of genetic information that have
apparently existed for billions of years. They are unable to
replicate except inside a living host cell, and outside the host
cell they are inert. Viruses pass through filters that trap
bacteria, and they can be seen only be electron microscopy. Like
other biological systems, each virus contains molecular genetic
information in the form of nucleic acid, but in viruses this
information comes in the form of DNA or RNA, never both. The
viral genome is transcribed and replicated only with a host cell,
with variations in process dependent on the type of virus and the
type of host cell.
When viruses are categorized in terms of their genomes,
there are two general types: a) viruses with a DNA genome (DNA
viruses), and b) viruses with an RNA genome (RNA viruses). RNA
viruses are unique: only in these viruses do we find genomes
consisting of RNA; all other biological entities, DNA viruses,
bacteria, plant cells, animal cells, etc., contain DNA genomes.
There are more than 2500 groups of different viruses now
recognized and at least partially characterized. In each case,
for both DNA and RNA viruses, once it enters the host cell, the
general challenge for the virus is the same: directly or
indirectly, the viral genome must bring about the production of
the *messenger RNAs needed by the host *ribosomes to produce the
specific proteins necessary for replication of the complete
virus.
With DNA viruses, the DNA viral genome acts as the template
for the production of messenger RNA. With RNA viruses, however,
the process is more complicated.
In general, with some types of RNA viruses, the RNA genome
("plus-sense"; "positive-strand") can itself act as messenger RNA
for host ribosomes; while other types of RNA viruses, the RNA
genome ("minus-sense"; negative-strand) must first produce a
complementary RNA, which then acts as messenger RNA for the host
ribosomes. The replication process in minus-sense RNA viruses is
complex, since host cells do not carry enzymes that can
polymerize complementary RNA from an RNA template, and such
viruses therefore must carry their own special enzymes ("RNA-
dependent transcriptases") to achieve this synthesis.
A third and special type of RNA virus is the so-called
"retrovirus", of which there are many versions. Retroviruses are
single-stranded RNA viruses that have an enzyme called reverse
transcriptase, and with this enzyme the viral RNA is used as a
template to produce viral DNA from host-cellular material. This
DNA is then incorporated into the host cell's genome, where it
codes for the production of messenger RNA and the ultimate
synthesis of viral components. The HIV virus, for example, is a
retrovirus.
As a class, retroviruses are usually spherical, 80 to 110
nanometers in diameter, with an RNA genome of approximately 7000
to 10,000 nucleotide bases. An outstanding characteristic of such
viruses is that if they kill host cells at all it is usually only
after a long latent period (although there are certain important
exception). In addition, these viruses are apparently capable of
altering, or affecting the expression of, host cell genes
involved in cancer (oncogenes).
The three primary genes of the retrovirus genome are called
"gag", "pol", and "env". The gag gene encodes the protein of the
virus capsid, the protein coat directly encapsulating the viral
genome; the pol gene encodes a reverse transcriptase involved in
replication of the genome; the env gene encodes the protein of
the membrane envelope of the virus when it is outside a host cell
(the membrane envelope of the "virion"). (These 3 genes actually
produce more than 3 different proteins; what these genes encode
for are precursor proteins, each of which is a precursor for
several varieties of proteins with different viral functions. In
addition, different proteins can be produced by splices of
elements from the 3 primary genes.
Concerning the general structure of the retrovirus, the
internal nucleic acid genome is encapsulated by a protein coat
(the capsid), and the capsid in turn is surrounded by the
external lipoprotein envelope. Beyond this general scheme, there
is no single morphology for retroviruses.
The protein encoded by the env gene (called the Env protein)
is important in recognition of host-cell surface receptors, with
which it interacts to secure entry of the virus into the host
cell. In addition, after infection the host-cell expresses Env
protein on its own surface, and this evidently prevents
reinfection of that host cell after new viruses are released.
Perhaps the most important property of retroviruses is their
ability to splice into the host-cell genome pieces of their own
genome, the result either the introduction of new genes into the
host genome or the activation or inactivation of specific nearby
genes of the host genome. In principle, either of these scenarios
can lead to corruption of the growth regulation process of the
host genome, and thus to a line of malignant cells.
Viruses have been implicated in the etiology of several
types of human cancers, including cervical cancer and liver
cancer. The viruses that have been strongly associated with human
cancers include human papillomaviruses, Epstein-Barr virus,
hepatitis B virus, and a human retrovirus. Many viruses can cause
tumors in animals, either as a result of natural infection or
after experimental inoculation. Animal viruses are studied to
learn how a limited amount of genetic information (only one or a
few viral genes) can profoundly alter the growth behavior of host
cells, and ultimately convert a normal cell into a malignant
cell. For example, classical studies of RNA tumor viruses first
revealed the involvement of cellular *oncogenes in cancer, and
similar studies with DNA tumor viruses first implicated a role
for *tumor suppressor genes in cancer. In the 1980s, these
discoveries revolutionized thinking about the molecular
mechanisms of carcinogenesis.
Alveolar cell cancer (bronchiolo-alveolar cancer, broncho-
alveolar cancer) is a human lung cancer, a subtype of
*adenocarcinoma, and apparently a lung cancer unrelated to
cigarette smoking. The cause of this disease is unknown.
"Jaagsiekte" is a contagious lung cancer (ovine pulmonary
carcinoma) of sheep, sometimes also of goats and guinea pigs, the
disease resembling the more benign forms of human alveolar cell
cancer. Jagsiekte in sheep is apparently caused by a retrovirus
(jagsiekte sheep retrovirus), and infected sheep secrete large
amounts of lung fluids from which copious quantities of the virus
may be obtained.
The term "fibroblasts" refers to a type of connective tissue
cell that secretes the structural proteins (e.g., collagen) that
form certain tissue components. Fibroblasts are easy to maintain
in tissue culture, and they are often used as experimental cell
systems.
In this context, the term "transformation" refers to the
transformation of a normal cell into a malignant (cancer) cell.
... ... N. Maeda et al (4 authors at University of California
Irvine, US) present a report on cancerous transformation of mouse
fibroblasts by jaagsiekte sheep retrovirus DNA, the authors
making the following points:
1) The authors point out that animal retrovirus-induced
cancers have played fundamental roles in understanding the
molecular basis of cancer. Jaagsiekte sheep retrovirus is the
causative agent of ovine pulmonary carcinoma, a contagious lung
cancer of sheep (also known as sheep pulmonary adenomatosis).
This retrovirus-induced cancer consists of transformed secretory
*epithelial cells of the lungs, and a characteristic feature of
the tumors is the production of large amounts of fluid secreted
from tumor cells containing infectious virus. The disease closely
resembles human alveolar carcinoma, and is thus an important
model for understanding the latter.
2) The authors point out that oncogenic retroviruses induce
tumors by two mechanisms. a) Acutely transforming retroviruses
capture a normal host-cell gene (a "protooncogene") and convert
it into a viral oncogene. Such retroviruses typically induce
rapid neoplasms in vivo, and they frequently can transform cells
in culture. b) Retroviruses that lack oncogenes (non-acute
retroviruses) also can induce tumors, although they typically
require longer incubation periods and multiple rounds of
infection in vivo. An important molecular mechanism for these
viruses is insertion in the host-cell genome of viral genetic
material in the vicinity of a protooncogene. This results in
overexpression of the protooncogene.
3) The authors report their experiments indicate that
jaagsiekte sheep retrovirus DNA (i.e., DNA produced by
transcription of the viral genome) can induce transformation in a
line of mouse fibroblasts (NIH 3T3 cells), and that additional
experiments have localized the transforming activity to the viral
env gene. The authors suggest their results indicate that the
envelope gene carries the transforming potential in this virus,
an unusual case of a transformation potential carried by a viral
structural protein.
... ... In a contiguous independent report, S.K. Rai et al (6
authors at 3 installations, US) report that the envelope (env)
gene of jaagsiekte sheep retrovirus "has the unusual property
that it can induce transformation in rat fibroblasts, and thus is
likely to be responsible for oncogenesis in animals."
... ... In a commentary on the above work, Naomi Rosenberg (Tufts
University, US) points out that more than 50 oncogenes now known
to be involved in human cancers were first discovered and studied
in retroviral models. "Nonetheless, only one retrovirus, human T
cell lymphotrophic virus (HTLV), is oncogenic in humans, and, as
we enter the 21st century, retroviral oncogenesis models may seem
to be of largely historical interest. However, analyses of
jaagsiekte sheep retrovirus by Maeda et al and Rai et al...
reveal that oncogenic retroviruses still hold important secrets
that may be directly relevant to human cancer."
-----------
N. Maeda et al: Direct transformation of rodent fibroblasts by
jaagsiekte sheep retrovirus DNA.
(Proc. Natl. Acad. Sci. US 10 Apr 01 98:4449)
QY: Hung Fan: hyfan@uci.edu
-----------
S.K. Rai et al: Candidate tumor suppressor HYAL2 is a
glycosylphosphatidylinositol (GPI)-anchored cell-surface receptor
for jaagsiekte sheep retrovirus, the envelope protein of which
mediates oncogenic transformation.
(Proc. Natl. Acad. Sci. US 10 Apr 01 98:4443)
QY: A. Dusty Miller: dmiller@fhcrc.org
-----------
Naomi Rosenberg: New transformation tricks from a barnyard
retrovirus: Implications for human lung cancer.
(Proc. Natl. Acad. Sci. US 10 Apr 01 98:4285)
QY: Naomi Rosenberg: naomi.rosenberg@tufts.edu
-----------
Text Notes:
... ... *messenger RNAs: (mRNAs) The ribonucleic acid molecules
transcribed from DNA that carry the coded information
specifying the sequence of amino acids in proteins.
... ... *ribosomes: A ribosome (not to be confused with riboZYME)
is a small particle, a complex of various ribonucleic acid
component subunits and proteins that functions as the site of
protein synthesis. In general, ribosomes read the messenger RNA
template to produce specific polypeptide sequences by
polymerizing amino acids.
... ... *oncogenes: There are two general meanings of this term
in current use. The first meaning refers to any of a family of
cellular genes that normally code for proteins involved in cell
growth or regulation, but which may produce malignant processes
when mutated or activated by viruses. The second meaning of the
term "oncogene" refers to viral genes found in certain DNA tumor
viruses, genes that are required for viral replication, but whose
activation produces malignant transformations.
... ... *tumor suppressor genes: Tumor suppressor genes code for
proteins that apparently either prevent cell division or provoke
cell death in defective cells. Thus, deletion or inactivation of
tumor suppressor genes can result in malignant cell replication.
... ... *adenocarcinoma: In general, a tumor of epithelial cells
(see below) in which the cells are in a glandular or gland-like
pattern.
... ... *epithelial cells: In animals, "epithelial cells" compose
the cell layers that form the interface between a tissue and the
external environment, for example, the cells of the skin, the
lining of the intestinal tract, and the lung airway passages.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 20Jul01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
TUMOR VIRUSES AND ONCOGENES
Viruses, first discovered in 1892 [*Note #1], are infectious
agents that are smaller than biological cells such as bacteria,
their size ranging from about 20 nanometers to about 900
nanometers. Beginning in the 1930s, there was much controversy
about classification, with the central question whether viruses
are a "life" form. The answer, of course, depends on the
definition of "life", and since there are various definitions
possible, the question is ill-defined. In general, a virus is a
self-organizing molecular system capable of using living cells to
replicate itself, the sequence of events in many cases altering
or destroying the cells and thus causing a disease process.
In addition to disease processes caused by the destruction
of cells, viruses are now known to be etiologic factors in the
development of several types of human tumors, including two of
worldwide significance: cervical cancer and liver cancer. Viruses
have also been strongly associated epidemiologically with other
human cancers, and these viruses include *human papillomavirus,
*Epstein-Barr virus, and *hepatitis B virus.
Like other viruses, tumor viruses are classified among
different virus families according to the nucleic acid of their
genome and the biophysical characteristics of their virions
(virion = the complete virus particle as it exists outside the
host cell). All known tumor viruses either have a DNA genome or
an RNA genome. In the case of an RNA genome, the RNA genome
generates a DNA "provirus" (a preliminary virus entity) after
infection of cells. All RNA tumor viruses (i.e., tumor viruses
with an RNA genome) belong to the "retrovirus" family.
Retroviruses carry an RNA-directed polymerizing enzyme (reverse
transcriptase) that constructs a DNA copy of the RNA genome of
the virus. This DNA copy (the provirus) becomes integrated into
the DNA of the infected host cell, and it is from this integrated
DNA that all proteins of the virus are translated.
Tumor viruses are of two general types with respect to tumor
induction, distinguished by (among other things) whether or not
they carry "oncogenes" (i.e., any gene associated with the
causation of cancer). All DNA tumor viruses carry oncogenes,
these oncogenes an integral part of the viral genome and not
derived from host cells. Of RNA tumor viruses, there are two
types: a) the highly oncogenic ("direct-transforming") RNA tumor
viruses (class I RNA tumor viruses) carry an oncogene of host-
cell origin; b) the weakly oncogenic ("slowly transforming") RNA
tumor viruses (class II RNA tumor viruses) do not contain an
oncogene but induce leukemias after long incubation periods by
indirect mechanisms. In this context, the term "transforming"
refers to the transformation of a normal host-cell into a cancer
cell. ... ... George Klein (Karolinska Institute, SE) presents an
essay on the history of the idea of tumor viruses, the author
making the following points:
1) In 1911, Peyton Rous (1879-1970) demonstrated that fowl
*sarcomas could be transmitted with cell-free filtrates, and the
rapid consensus was that cancer was a viral disease. But when
similar experiments with mouse and rat tumors failed soon after,
it was concluded that tumor viruses occurred only in birds, and
the field fell into disrepute.
2) The discovery in the 1920s of the Shope papilloma virus,
which causes warts in rabbits, produced little enthusiasm among
researchers because the tumors were largely benign.
3) In the 1930s, the mouse mammary tumor virus was
discovered, and this virus was called "*milk factor" rather than
"milk virus" to avoid a negative reaction from people in the
medical science community who had relegated tumor viruses to the
cabinet of freaks.
4) The great change in the climate of opinion concerning
tumor viruses came in the 1950s when Ludvik Gross discovered the
mouse leukemia virus, and Sarah Stewart and Bernice Eddy
identified the *polyomavirus. Within a few years the pendulum had
swung to the opposite extreme. After decades of failed attempts,
viruses that could induce tumors in mammals were now isolated in
quick succession. Tumor virology rapidly became favored by grant-
giving agencies, and the oncogene concept -- that tumor viruses
carry "cancer genes" that can transform some of their target
cells into a cancerous or precancerous state -- was formulated in
the context of this enthusiasm.
5) The class I RNA tumor viruses can induce tumors because
they have accidentally incorporated from host cells genes that
regulate growth. After entering a new host cell, the viral enzyme
reverse transcriptase copies the viral RNA into provirus DNA
which integrates randomly into the host cell DNA. When the virus
starts to reproduce itself, and the proviral DNA is transcribed
back into RNA, some of the new virus particles may also carry
additional cellular sequences from regions adjacent to the random
integration site of the proviral DNA. These newly replicated
virus particles have the potential to corrupt the DNA of other
host cells when these host cells are subsequently infected.
6) Class II RNA tumor viruses do not themselves contain
oncogenes, but contribute to malignant tumor development
relatively infrequently when their proviral DNA happens to
integrate into the host DNA near host oncogenes.
7) By discovering cellular genes that regulate growth and
that can contribute to cancer development after illegitimate
viral activation, the virologists demonstrated the existence of
host oncogenes that when mutated can promote cancer formation
independent of viruses. This discovery once again relegated tumor
virology to a less prominent place and reaffirmed the sovereignty
of cell biology. Cancer is essentially a disease of cellular DNA;
when viruses are involved in cancer, they are involved as one of
many possible DNA-corrupting agents.
8) All oncogenes have turned out to be *highly conserved
housekeeping genes that participate in the regulation of the
*cell cycle. Their potentially tumorigenic forms drive the cell
towards proliferation. For overt tumor development, additional
genetic changes are required, including loss of *cell-cycle
check-point controls, inhibition of programmed cell death
(apoptosis), and *up-regulation of blood supply (*angiogenesis).
The current oncogene field, therefore, emerged from erroneous
concepts concerning the etiology of cancer, but these concepts,
when combined with several decades of diligent experimentation,
finally produced a valuable outline of the events that cause the
formation of cancerous tumors.
-----------
George Klein: The tale of the great cuckoo egg.
(Nature 5 Aug 99 400:515)
QY: George Klein, Karolinska Institute, PO Box 280, S-171, 77
Stockholm, SE.
-----------
Text Notes:
... ... *Note #1: In 1892, a Russian botanist named Dmitri
Ivanovsky (1864-1920) became interested in the cause of a disease
of the valuable tobacco plant, a disease called "mosaic disease".
The name was due to the mosaic patterns the disease produced on
the leaves of the plant. Ivanovsky devised an experiment, mashed
up infected leaves, and forced them through filters designed to
remove all bacteria. He discovered that the liquid that passed
through the filters could still infect healthy tobacco plants.
Ivanovsky concluded, in error, that the infectious agent was
still a bacterium, but that his filters were somehow defective,
and it was this conclusion that he published in a Russian
scientific journal. Six years later, a Dutch botanist named
Martinus Beijerinck (1851-1931) repeated the experiments and
concluded the infectious agent was not a bacterium but the liquid
itself, a poison, and he called it a filterable "virus", the word
"virus" being the Latin word for poison. In the 1930s, an
American biochemist named Wendell Meredith Stanley (1904-1971)
became interested in this mysterious "virus" liquid. He believed
the poison to be a protein. He repeated the filtration
experiments with diseased tobacco leaves, and he isolated a
crystalline substance in high concentration that had all the
infective properties of the so-called virus liquid. In the report
which Stanley published in 1935, he concluded: "Tobacco mosaic
virus is regarded as an autocatalytic protein which, for the
present, may be assumed to require the presence of living cells
for multiplication." For this work, Stanley received the Nobel
Prize in Chemistry in 1946. Although the tobacco mosaic virus,
like all viruses, is much more than just a simple autocatalytic
protein, the first understanding of the true nature of viruses
was now in place. The experiments that had begun in Russia in
1892 culminated 43 years later in the startling realization that
an entire class of infectious agents much smaller than bacteria
existed.
... ... *human papillomavirus: The papillomavirus causes benign
tumors called "warts". The virus in its extracellular form
(virion) is 55 nanometers in diameter, with a circular double-
stranded DNA genome of approximately 8000 nucleotide base pairs.
The virus primarily infects surface *epithelia. There are more
than 70 different types of human papillomaviruses.
... ... *epithelia: In animals, epithelial cells compose the cell
layers that form the interface between a tissue and the external
environment, for example, the cells of the skin, the lining of
the intestinal tract, and the lung airway passages.
... ... *Epstein-Barr virus: The Epstein-Barr virus is a large
ubiquitous herpesvirus that is the causative agent of acute
infectious mononucleosis and a factor in the development of
nasopharyngeal carcinoma, Burkitt's lymphoma, and other
disorders. The virion is approximately 100 nanometers in
diameters, and contains a double-stranded DNA genome consisting
of approximately 172,000 nucleotide base pairs.
... ... *carcinoma: In general, a carcinoma is any malignancy
derived from epithelial tissue.
... ... *hepatitis B virus: The hepatitis B virus is the
causative agent of *serum hepatitis. The virion is 42 nanometers
in diameter, the genome double-stranded DNA with 3200 nucleotide
base pairs.
... ... *serum hepatitis: In general, "hepatitis" is any
inflammation of the liver. "Serum hepatitis" is usually
transmitted by injection of infected blood or blood derivatives,
or by the use of contaminated needles or other instruments.
... ... *sarcomas: A sarcoma is a connective tissue neoplasm,
usually highly malignant.
... ... *milk factor: The prototype of RNA tumor viruses is the
"mouse mammary tumor virus", which occurs in high-mammary-cancer
strains of inbred mice, and is found in particularly large
amounts in lactating mammary tissues and milk. The virus is
readily transferred to suckling mice, in whom the incidence of
subsequent development of carcinoma of the breast is high. The
work of J.J. Bittner (1904-1961) on this virus is classic: In the
1930s, carefully inbred strains of mice were kept for research on
cancer. Some strains were highly resistant to cancer and rarely
developed it, while other strains were so prone to cancer that
almost every individual animal developed the disease. In 1936,
Bittner established that if young mice of a cancer-resistant
strain were transferred to the breast of a foster mother of a
cancer-prone strain, the young mice developed cancer in the
course of their lives. If, on the other hand, young mice of a
cancer-prone strain were fed at the breast of a foster mother of
a cancer-resistant strain, they did not usually develop cancer.
The Bittner "milk factor" was isolated in 1949 and was found to
consist of virus-like particles containing nucleic acid.
... ... *polyomavirus: Papillomaviruses and polyomaviruses are
the two classes of papovaviruses. Like papillomaviruses,
polyomaviruses have a double-stranded DNA genome, but with only
5000 nucleotide base pairs. The polyoma virion is 45 nanometers
in diameter, and the target tissues are internal organs. An
important research tool, the SV40 monkey virus, is a
polyomavirus.
... ... *highly conserved housekeeping genes: The term "highly
conserved" refers to a gene sequence maintained across
evolutionary time. So-called "housekeeping" genes are genes
coding for proteins involved in essential functions such as
metabolic cycles.
... ... *cell cycle: The "cell cycle" is the name given to the
ordered sequence of phases through which a cell passes from one
mitotic cell division to the next.
... ... *cell-cycle check-point controls: So-called "checkpoints"
are points in the cell division cycle where the cycle can be
halted until conditions are suitable for the cell to proceed to
the next stage.
... ... *up-regulation: In general, the term "up-regulation"
refers to an increase in the activity of some entity or process.
... ... *angiogenesis: Angiogenesis, the origin and development
of blood vessels, is an important consideration in the growth of
cancerous tumors, since the tumor provokes directed angiogenesis
into itself (up-regulation of a blood supply) with the end result
that the tumor is supplied with oxygen and nutrients. Without
angiogenesis, tumors can attain only a small size before becoming
self-inhibiting.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 10Sep99
-------------------
Related Background:
ON RECEPTOR ACTIVATED RETROVIRAL MEMBRANE ASSOCIATION
Retroviruses are single-stranded RNA viruses that have an enzyme
called reverse transcriptase, and with this enzyme the viral RNA
is used as a template to produce viral DNA from cellular
material. This DNA is then incorporated into the host cell's
genome, where it codes for the synthesis of viral components.
Envelope proteins are the proteins found in the envelopes of
viruses in their virion stage (i.e., the entire virus as it
exists before or after the replication phase). Liposomes are
laboratory created vesicles (spherules) in which the lipid
molecules are spontaneously arranged into bilayers with
hydrophilic groups exposed to water molecules both outside the
vesicle and in the core. Rous sarcoma virus is a cancer-producing
virus that infects birds, discovered by Francis Peyton Rous
(1879-1970) in 1911, and the first discovered tumor-producing
virus. In 1966, Rous shared the Nobel Prize in Medicine and
Physiology for this work. Current models of the entry of
retroviruses into host cells propose conformational changes in
the envelope protein of the virus as a precursor to fusion of the
virus with the host cell membrane. ... ... Damico et al (3
authors at University of Pennsylvania, US) report the use of a
cell-free liposome-binding assay to study the behavior of a model
virus envelope protein (from Rous sarcoma virus). In the presence
of purified viral receptor, the viral envelope protein apparently
converts from a water-soluble form to a liposome membrane-
associated form, which is consistent with the conversion of the
envelope protein to its fusogenic state (the state involving
fusion with the host cell membrane). The authors suggest their
results provide direct evidence that receptor binding triggers
conversion of the virus envelope protein to a membrane-fusing
form, and illustrates that Rous sarcoma virus is a useful model
for the study of retroviral entry.
-----------
QY: Paul Bates (pbates@mail.med.upenn.edu)
(Proc. Natl. Acad. Sci. US 3 Mar 98) (Science-Week 10 Apr 98)
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
7. IN FOCUS: ON MIND AND BODY AND C.S. SHERRINGTON
[Charles S. Sherrington (1857-1952) loomed over early 20th
century neurobiology the way Max Planck loomed over physics.
Sherrington was awarded the Nobel Prize for Physiology and
Medicine in 1932 for his experimental work in neurophysiology.]
---------------------
"Much as one special organ, the heart, maintains the flow of
nutriment throughout the body, so one organ, the brain, is
provider of mind for the whole individual. If we smile at so bald
a statement, we must yet agree that it states the practical
situation with which the physician and the surgeon deal. It shows
us too the body in the grip of integration. Much of the body has
no demonstrable mind. Of the rest, most has mind only lent to it,
in the form of sensation by proxy. Such of it merely communicates
with a certain restricted piece of the body, a particular part of
a single organ, and there, so much of the body as feels, has its
sensation done for it. There too the body's thinking seems to be
done for it, namely, in the brain. Of man we know even more
confidently than of any other concrete life that his mind is
correlated with his brain. But let us avoid the sophistication
that for the mind to be in the brain is any self-evident
proposition. 'Many men', wrote Kant, 'fancy they feel their
thought in their head, but that is a mistake. No experience tells
me that I am shut up some place in my brain.' We owe I suppose to
medicine in the main the knowledge of where in the body the 'seat
of the mind', as it is termed, is. But so far from its being a
self-evident fact, one of the greatest of biologists, Aristotle,
did not subscribe to it although it was accepted by physicians in
his time... A brain cell is not unalterably from birth a brain
cell. In the embryo-frog, the cells destined to be brain can be
replaced by cells from the skin of the back, the back even of
another embryo; these after transplantation become in their new
host brain-cells and seem to serve the brain's purpose duly. But
cells of the skin it is difficult to suppose as having a special
germ of mind. Moreover, cells, like those of the brain in
microscopic appearance, in chemical character and in provenance,
are elsewhere concerned with acts wholly devoid of mind, e.g.,
the knee jerk, the light-reflex of the pupil. A knee-jerk kick
and a mathematical problem employ similar-looking cells. With the
spine broken and the spinal cord so torn across as to disconnect
the body below from the brain above, although the former retains
the unharmed remainder of the spinal cord consisting of masses of
nervous cells, and retains a number of its nervous reactions, it
reveals no trace of recognizable mind."
-----------
(C.S. Sherrington:
_Man on His Nature: Gifford Lectures 1937-1938_)
-------------------
SCIENCE-WEEK http://scienceweek.com 20Jul01
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
8. FROM THE SCIENCEWEEK ARCHIVE:
SCIENCE POLICY: ON PUBLIC HEALTH DISPARITIES
Public health is best distinguished from clinical medicine by its
emphasis on preventing disease rather than curing it, and by the
focus of public health on populations and communities rather than
on the individual patient.
... ... Barry R. Bloom (Harvard School of Public Health, US)
presents a commentary on recent and current public health with a
focus on disparities both globally and in the US. The author
makes the following points:
1) Half of all the increases in life expectancy in recorded
history occurred within the 20th century, and most increases
occurred within the first half of the 20th century and before the
introduction of modern drugs and vaccines. The major gains in
health in the past century are attributable largely to the impact
of public health and disease prevention, rather than to medical
interventions.
2) In the past 20 years, deaths from heart attacks and
strokes in the US have dropped by 30 to 50 percent, in part as a
result of behavior changes, in part as a result of primary
prevention with medications. Smoking, estimated to be responsible
for approximately 20 percent of all deaths in the US, has
declined from 42 percent to 25 percent in adults over 30 years of
age (although it has increased to 36 percent among US teenagers
and is still rising). In addition, the use of the drug tamoxifen
has reduced the incidence of breast cancer by 45 percent in women
at high risk.
3) Perhaps the most dramatic effect of all is the impact of
immunization. Vaccines have eliminated smallpox from the world
and polio from the Northern Hemisphere, and have reduced the
incidence of measles, rubella, tetanus, diphtheria, and
meningitis in many countries to a handful of cases each year,
saving millions of lives and billions of dollars. Vaccines remain
the most cost-effective intervention known for preventing death
and disease. In 1999, for the first time, infectious diseases
were no longer the largest cause of death worldwide.
4) Unfortunately, the benefits of biomedical science and
public health are not uniformly distributed, and the disparities
are striking. Japan, with the highest life expectancy of 80
years, contrasts with Sierra Leone and its life expectancy of 37
years in 1998. What is most striking are the strong disparities
within single countries. It is generally believed that in
industrialized countries life expectancy is high for everyone and
that the major health issues center on the quality of life and
health care rather than on life expectancy. But the
contradictions to this idea are striking:
... ... a) People born in particular rural counties of Minnesota,
Colorado, Iowa, or Wisconsin on average will live 25 years longer
than those born in 4 counties of South Dakota, 23 years longer
than in 12 counties in Mississippi and Alabama, and 22 years
longer than people born in Washington, DC or Baltimore, MD.
... ... b) The variance in life expectancy in the US between
women of Japanese extraction in Bergen County, New Jersey, and
Bennett County, South Dakota is 41 years.
... ... c) Overall, disparities in life expectancy between
different parts of the US are greater than for any other nation
in the world, and the reasons for this are not clear. As in many
countries, the correlation in the US between per capita income
and life expectancy is not particularly good. For example, per
capita income is significantly higher in the county of
Washington, DC than in several counties along the Texas-Mexican
border, but life expectancy is significantly lower -- by
approximately 15 years -- in Washington, DC.
5) The author concludes: "We know that cardiovascular
disease, psychiatric disease, and physical injuries represent the
major global burdens of disease and disability in industrialized
and developing countries alike. The challenge for biomedical
science and public health in the coming century is to develop the
population-based interventions needed to reduce these burdens."
-----------
Barry R. Bloom: The future of public health.
(Nature 2 Dec 99 402supp:C63)
QY: Barry R. Bloom: bbloom@hsph.harvard.edu
-------------------
Summary by SCIENCE-WEEK Http://scienceweek.com 10Mar00
For more information: http://scienceweek.com/swfr.htm
-------------------
SCIENCE-WEEK http://scienceweek.com 20Jul01
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9. SOURCES:
APL: Applied Physics Letters
AS: American Scientist
CEN: Chemical & Engineering News
GD: Genes & Development
GR: Genome Research
JAMA: Journal of the American Medical Association
JCE: Journal of Chemical Education
NAT: Nature
NEJM: New England Journal of Medicine
NYT: New York Times
PNAS: Proceedings of the National Academy of Sciences
PRL: Physical Review Letters
PT: Physics Today
SA: Scientific American
SCI: Science
SW: ScienceWeek
TB: The Biochemist
TS: The Scientist
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