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.

October 16, 1998 -- Vol. 2 Number 42

-----------------------------------------------

And the end of all our exploring
Will be to arrive where we started
And know the place for the first time.
-- T.S. Eliot (1888-1965)

-----------------------------------------------

Contents of This Issue:

1. On the New Relevance of Evolutionary Biology
2. Scientific Journal Citation Ratings of US Universities
3. Bio-Taxonomy: Emergence of a Sharp Personal Controversy
4. Extrasolar Planets: Imaging via a Nulling-Interferometer
5. Extrasolar Planets: On Young Stars and Protoplanetary Disks
6. Theoretical Physics: On String Theory
7. Evolution: A New Coelacanth Discovery
8. Cellular Aging: Donor Age and Cellular Replication Lifespan
9. Resistance of Meningitis Pathogen to Chloramphenicol

-----------------------------------------------------------

1. ON THE NEW RELEVANCE OF EVOLUTIONARY BIOLOGY
In an editorial in the journal *Science*, J. Bull and H. Wichman
consider the recent renaissance in evolutionary biology and its
new relevance. The authors make the following points: 1)
Evolution is now widely perceived as the organizing principle at
all levels of life, the principle so pervading research that the
evolutionary underpinning of many experimental approaches is
assumed and unstated. 2) The field has now become socially and
economically relevant: heavy use of pesticides and antibiotics
has fostered the evolution of resistant pathogens and pests;
phylogenies are used to track infectious diseases; drug
development technology makes use of in vitro directed evolution,
using in vitro selection, mutation, and recombination to find
molecules for specific tasks. 3) But many mysteries remain:
complex evolutionary phenomena are difficult to explain in terms
of elemental mechanisms. A fundamental challenge is to understand
the extent to which the mechanisms that account for
microevolution can explain the elaboration of forms in
macroevolution. Can we learn the rules of adaptation at the
molecular level? 4) But despite its scientific renaissance and
new social and economic relevance, evolutionary biology continues
to face the social and legal opposition it has experienced since
before the Scopes trial (1925). The authors conclude: "At a time
when evolution is the unifying fabric of biology, it is barely
mentioned in some high school textbooks and classrooms."
-----------
J. Bull and H. Wichman (2 installations, US)
A revolution in evolution.
(Science 25 Sep 98 281:1959)
QY: J.J. Bull, University of Texas Austin 512-471-3434.
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 16Oct98


2. SCIENTIFIC JOURNAL CITATION RATINGS OF US UNIVERSITIES
Measurement of the "impact" of scientific papers is an activity
that has burgeoned during the past 30 years as a result of the
possibility of computer tabulation and analysis of journal
references. The idea is that the number of citations of a
scientific paper in other scientific papers is a measure of its
impact on the scientific community, and the number of citations
of papers published by a research installation a measure of the
research impact of that installation. But there are difficulties:
few physicists who write papers in quantum mechanics, for
example, bother to mention the foundation papers by Planck,
Schroedinger, Heisenberg, etc., and few people who write papers
about genetics, DNA, and so on, bother to mention the foundation
paper by Watson and Crick. When one publishes in a particular
field, one assumes that the fundamental papers have been read by
everyone, even though there are no consensual rules about which
papers are "fundamental". Nevertheless, the measurement of
"impact" continues, a citation race rather than a horse race. The
Institute for Scientific Information (Philadelphia, US), which is
responsible for much of the impact measuring, has now ranked the
top 100 federally funded US universities in 21 separate fields,
measuring the "average number of times that papers from
researchers at each institution were cited in another paper."
Citations were apparently tracked in hundreds of scientific
journals, and here are the results, with universities ranked
according to impact in 4 different fields in the biological
sciences (top rank first): 1) Neuroscience: California Institute
of Technology, Stanford University, Johns Hopkins University. 2)
Immunology: Washington University St. Louis, Harvard University,
Stanford University. 3) Molecular Biology and Genetics:
Massachusetts Institute of Technology, Rockefeller University,
Harvard University. 4) Biology and Biochemistry: Duke University,
University of Texas Southwestern Medical Center Dallas, Harvard
University. The conclusion is apparently that Harvard University
is the leader in scientific impact in the biological sciences.
-----------
A. Adams (*Science*)
Harvard tops in scientific impact.
(Science 25 Sep 98 281:1936)
QY: Amy Adams science_editors@aaas.org
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 16Oct98


3. BIO-TAXONOMY: EMERGENCE OF A SHARP PERSONAL CONTROVERSY
In a recent report (see Related Background material below) we
briefed a proposal by Ernst Mayr for a return to the *prokaryote-
eukaryote domain dichotomy from the present *archaea-eubacteria-
eukaryote domain trichotomy that has come to be used by many
biologists during the past decade. The details of the distinction
are provided in the report attached below, so we will not repeat
them. The controversy is of some interest in biology, as perhaps
a possible controversy concerning the present standard model
classification scheme of fundamental particles and forces in
physics would be to physicists. The domain trichotomy idea in
bio-taxonomy was first proposed in the 1980s by Carl Woese, who
like Ernst Mayr, is a member of the US National Academy of
Sciences. Writing in the same journal in which Mayr's proposal
appeared a few weeks ago, Woese now attempts to rebut Mayr's
ideas with an apparent singular vehemence, proposing that the
issue is more profound than that of merely assessing the utility
of a classification scheme. Woese writes: "If there were ever an
issue in biological classification that cannot be settled by
pedantry, it is this one." [Editor's note: This is not completely
gratuitous, since in his paper Mayr states, "Here it must be
remembered that Woese was not trained as a biologist and quite
naturally does not have an extensive familiarity with the
principles of classification."] And again from Woese: "To Mayr,
the issue is one of whether we should define two or three domains
and what the classificatory precedents or rules for deciding this
are. However, the *universal phylogenetic tree tells us that the
domains are unique among taxa and that their number and their
composition are not subject to classificatory fiat, but are
naturally defined." Woese's idea, apparently, is that the
trichotomous classification scheme is discovered rather than
constructed, which implies a significant problematic
philosophical subtext that is not amplified in his paper. In
summary, Woese makes the following points concerning his
position: 1) Mayr's article is not a taxonomic quibble but a "de
facto pronouncement on the nature of biology." A biological
classification is in effect an overarching evolutionary theory
that guides our thinking and experimentation, and it must be
structured to reflect evolutionary reality. 2) The prokaryote-
eukaryote dichotomy, which Mayr proposes to reinstitute, is a
failed taxonomic theory that was never recognized as theory and
therefore never tested in a timely fashion, with the consequence
that it has adversely affected the development of biology,
especially microbiology, in the latter half of this century. 3)
The scientifically perceived importance of a group of organisms
must reflect the natural importance of the group. 4) Microbial
diversity is far more than a listing of distinguishable microbial
species. We need to understand the quality of microbial
diversity, for it is the diversity that defines the biosphere of
this planet. 5) Evolution must be integrated into the fabric of
molecular biology... Any comprehensive understanding of a
biological entity, be it an organism or a molecule, necessarily
has an evolutionary component. Woese concludes: "The disagreement
between Dr. Mayr and myself is not actually about classification.
It concerns the nature of Biology itself. Dr. Mayr's biology
reflects the last billion years of evolution; mine, the first
three billion. His biology is centered on multicellular organisms
and their evolutions; mine on the *universal ancestor and its
immediate descendants. His is the biology of visual experience,
of direct observation. Mine cannot be directly seen or touched;
it is the biology of molecules, of genes and their inferred
histories. Evolution for Dr. Mayr is an "affair of phenotypes".
For me, evolution is primarily the evolutionary _process_, not
its outcomes. The science of biology is very different from these
two perspectives, and its future even more so." [Editor's note:
Ignoring the personalized undercurrents, the essential
controversy here is apparently between a classification system
based on utility criteria and observed similarities and
differences among entities (Mayr), and a classification scheme
based on theoretical and experimental molecular-genetic
relationships (Woese). The question of why there must be only one
classification scheme in use by working biologists is not
addressed by either Mayr or Woese.]
-----------
C.R. Woese (University of Illinois Urbana-Champaign)
Default taxonomy: Ernst Mayr's view of the microbial world.
(Proc. Natl. Acad. Sci. US 15 Sep 98 95:11043)
QY: Carl R. Woese 
-----------

Text Notes:
... ... *prokaryote-eukaryote domain dichotomy: See reports
attached below.
... ... *archaea-eubacteria-eukaryote domain trichotomy: See
reports attached below.
... ... *universal phylogenetic tree: Refers to the present
taxonomic-evolutionary classification scheme for all life on
Earth.
... ... *universal ancestor: Refers to the common ancestor from
which all life on Earth is considered to have derived. See
Related Background report attached below of SW 3 Jul 98).
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Oct98

-------------------

Related Background:

BIO-TAXONOMY: A PROPOSAL FOR ONLY TWO EMPIRES
The physicist confronting bio-taxonomy for the first time may
experience bewilderment: there are in excess of 30 million
species of life forms, the classification system is far from
simple, the system has some historically based confusions, and
the system is frequently redefined. Perhaps only the organic
chemist can feel a full empathy here, since organic chemistry is
faced with the similar problem of classifying millions of organic
chemical entities. A fundamental consideration is that in the
context of such a diversity of objects, a self-consistent
classification scheme is of extreme importance. At the present
time, in biology, there is a significant controversy concerning
primary categories, and that is the subject of this report. Two
main groups of life forms have been recognized for some time,
prokaryotes and eukaryotes. Prokaryotes are cells without a cell
nucleus and other membrane-bound organelles, and eukaryotes are
cells with a cell nucleus and other membrane-bound organelles.
(Organisms composed of eukaryote cells are also called
"eukaryotes"). For example, all bacteria are prokaryotes; all
complex animals, plants, etc., are eukaryotes. Fifteen years ago,
C.R. Woese (University of Illinois Urbana-Champaign, US) proposed
that the prokaryotes actually consist of two main groups, the
eubacteria and the archaebacteria, and that the differences
between these two groups are as great as the differences between
prokaryotes and eukaryotes, and that as a consequence a
tripartite primary scheme should be used, the primary categories
(kingdoms or empires) consisting of Eubacteria, Archaebacteria,
and Eukaryotes. Woese's differentiation of eubacteria and
archaebacteria was based on *habitats, cell wall constituents,
genome organization, and various aspects of protein synthesis
biochemical machinery, and during the past decade most biologists
have apparently accepted his categorization scheme. ... ... Now
Ernst Mayr (1904- ), a prominent biologist, proposes a rejection
of the Woese categorization and a return to a scheme involving
only 2 primary categories (empires), the Prokaryotes and
Eukaryotes. Mayr makes the following points: 1) A classification
scheme is essentially an information storage and retrieval
system, permitting the location of an entity with a minimum of
effort and loss of time, the objective optimally achieved by
arranging entities in a hierarchy of classes, ranked by degree of
similarity. 2) Evidence indicates that the archaebacteria are so
much more similar to the eubacteria than to the eukaryotes, that
their removal from the prokaryotes is not justified. The
eukaryotes differ from the prokaryotes (including the
archaebacteria) not only by the possession of a nucleus and
*mitosis but also by individual protein-rich chromosomes,
*meiotic sexuality (including viable regular cell fusions),
cellular organelles, highly complex sets of regulatory genes, and
all those genes that permit biodiversity... When a biologist
speaks of eukaryotes, he or she has in mind palms, oaks, and
orchids; mice, bats, and whales; and hummingbirds, chickens, and
ostriches. And this world of highly evolved eukaryotes is simply
an entirely different world from the world of the two kinds of
bacteria, the Prokaryotes. 3) Ranking, in any scheme of
classification of items (living or not), is by necessity based on
degree of difference. The two kinds of bacteria, in the vast
majority of their characteristics, are exceedingly similar to
each other and fundamentally so different from the eukaryotes
that they have to be ranked as a single *taxon, the prokaryotes,
different from the only other taxon of this rank, the eukaryotes.
Mayr suggests that only a two-empire classification correctly
reflects this structure of the living world.
-----------
E. Mayr (Harvard University, US)
Two empires of three?
(Proc. Natl. Acad. Sci. US 18 Aug 98 95:9720)
QY: Ernst Mayr 
-----------

Text Notes:
... ... *habitats: Many species of archaebacteria live in hot
acidic conditions, growing best at temperatures approaching 100
degrees centigrade. Because of this, it has been suggested the
lineage is more ancient than eubacteria, arising during
primordial conditions on Earth.
... ... *mitosis: In this context, division of the cell nucleus.
... ... *meiotic sexuality: A reduction division process whereby
a nucleus divides by 2 divisions into 4 nuclei, each containing
half the original number of chromosomes.
... ... *taxon: The organisms comprising a particular taxonomic
entity.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 25Sep98

-------------------

Related Background:

ORIGIN OF LIFE: A MODEL FOR THE UNIVERSAL ANCESTOR
Biologists have long subscribed to the idea that all life on
Earth arose from a common ancestor. Until recently, nothing
concrete was said about this ancestor, but it was intuitively
assumed to be simple, often likened to a *prokaryote, and
generally held to have had little or no *intermediary metabolism.
Only when biology became defined on the level of molecular
sequences did it become possible to seriously consider the nature
of this ancestor. ... ... Carl Woese (University of Illinois
Urbana-Champaign, US) presents a "genetic annealing" model for
the universal ancestor of all extant life. Physical annealing
involves a first stage heating to a high temperature followed by
a slow cooling of the system to produce new structures,
particularly special crystalline forms. The term "annealing" is
also used in molecular biology to refer to the separation of DNA
strands by heating and the recombination of complimentary strands
by cooling. In Woese's model, the term "annealing" is used in
still a third sense. In the author's model, in the evolutionary
counterpart of physical annealing, the elements of the system are
primitive cells, mobile genetic elements, and so on, and physical
temperature becomes "evolutionary temperature", the evolutionary
"tempo". The evolutionary analog of "crystallization" is
emergence of new structures, new cellular subsystems that are
refractory to major evolutionary change. The author defines the
entities in which *translation had not yet developed to the point
that proteins of the modern type could arise as "progenotes", and
the era during which these were the most advanced forms as the
"progenote era". Concerning "evolutionary temperature", the
author points out that macroscopic evolutionists recognized long
ago a relationship between the "tempo" (rate) of evolution and
its "mode" (a measure of the outcomes). When microbial evolution
finally came into the picture, a similar phenomenon was
encountered on the molecular level, suggesting that this
tempo/mode relationship was a fundamental manifestation of the
evolutionary process. Because of high mutation rates and other
factors, the progenote era is proposed as one of very high
evolutionary tempo. In the author's model, progenotes were very
unlike modern cells, their component parts with different
ancestries, and the complexion of their components changing
drastically over time. Progenotes possessed the machinery for
gene expression and genome replication and at least some
rudimentary capacity for cell division, but the ordinary cellular
functions had no genealogical continuity, since they were too
subject to the confusion of *lateral gene transfer. According to
the author, the transition from progenotes to genotes turned upon
the evolution of translation, the conversion of messenger RNA
code into the specific amino acid sequences of specific proteins.
The author proposes the genetic annealing model as "an attempt to
develop a consistent general picture of the universal ancestor...
The ancestor cannot have been a particular organism, a single
organismal lineage. It was communal, a loosely knit, diverse
conglomeration of primitive cells that evolved as a unit... The
universal ancestor is not an entity, not a thing. It is a process
characteristic of a particular evolutionary stage." The author
concludes with a conjecture that genomes resulting from episodes
of rapid evolution will contain an abnormally high proportion of
foreign genes, and a suggestion that "genome sequences will soon
be available in sufficient number to properly test whether the
tempo/mode relationship (rapid evolution) invariably links
increased mutation rate and increased levels of lateral gene
transfer or vice versa."
QY: Carl Woese (carl@ninja.life.uiuc.edu)
(Proc. Natl. Acad. Sci. US 9 Jun 98 95:6854)
(Science-Week 3 Jul 98)

Notes by ScienceWeek:

... ... *prokaryote: Prokaryotes are cells without a cell nucleus
and other membrane-bound organelles.
... ... *intermediate metabolism: The sum of all metabolic
reactions between the uptake of nutrients and the excretion of
waste products.
... ... *lateral gene transfer: This refers to the "horizontal"
transfer of genetic information between individuals of the same
generation, the mechanism involving the incorporation by the
genome of accessible new genetic elements. The process is common
among primitive life forms such as bacteria.

-------------------

Related Background:

ON PROKARYOTES IN THE BIOSPHERE
Prokaryotes (bacteria) are unicellular life forms lacking a
membrane-bound nucleus, structured chromosomes, and complex
internal organization. They are invisible to the naked eye, but
they are an essential component of the Earth's biota. They
catalyze unique and indispensable transformations in the
biogeochemical cycles of the biosphere, produce important
components of the Earth's atmosphere, and represent a large
portion of life's genetic diversity. Although the abundance of
prokaryotes has been estimated indirectly, the actual number of
prokaryotes and the total amount of their cellular carbon on
Earth has never been directly assessed. ... ... Whitman et al (3
authors at University of Georgia, US) present an array of
calculations based on analysis of various habitats, and make the
following points: 1) The number of prokaryotes and the total
amount of their cellular carbon on Earth are estimated to be 4-6
x 10^(30) cells and 350-550 x 10^(15) grams of carbon,
respectively. The total amount of prokaryotic carbon is thus 60
to 100 percent of the estimated total carbon in plants, and
inclusion of prokaryotic carbon in global models will almost
double estimates of the amount of carbon stored in living
organisms. 2) In addition, the Earth's prokaryotes contain 85-130
x 10^(15) grams of nitrogen, and 9-14 x 10^(15) grams of
phosphorus, or about 10-fold more of these nutrients than do
plants, and represent the largest pool of these nutrients in
living organisms. 3) Most of the Earth's prokaryotes occur in the
open ocean, in soil, and in oceanic and terrestrial subsurfaces,
where the numbers of cells is of the order of 10^(29) to 10^(30).
4) The numbers of heterotrophic prokaryotes (bacteria that feed
on organic material) in the upper 200 meters of open ocean, the
ocean below 200 meters, and soil are consistent with average
turnover times of 6-25 days, 0.8 years, 2.5 years, respectively.
An uncertain estimate for the average turnover time of
prokaryotes in the subsurface is of the order of 1000 to 2000
years. 5) The cellular production rate for all prokaryotes on
Earth is estimated at 1.7 x 10^(30) cells per year and is highest
in the open ocean. The authors suggest that the large population
size and rapid growth of prokaryotes provides and enormous
capacity for genetic diversity, and that given the numerical
abundance and importance of prokaryotes in biogeochemical
transformations, the absence of detailed knowledge of prokaryotic
diversity is a major omission in our knowledge of life on Earth.
QY: William B. Whitman (whitman@uga.cc.uga.edu)
(Proc. Natl. Acad. Sci. US 9 Jun 98 95:6578)
(Science-Week 3 Jul 98)

-------------------

Related Background:

HYDROGEN HYPOTHESIS FOR THE FIRST EUKARYOTE
The classification system of bacteria is presently in a state of
flux due to new relationships continually revealed by molecular
biology, but the following nomenclature is generally accepted.
Eubacteria is a subkingdom of bacteria. All Eubacteria members
are prokaryotes, which means they lack a membrane-bound nucleus,
structured chromosomes, and complex internal organization. The
eukaryotes, in contrast, contain membrane-bound organelles,
including a nucleus. The archaebacteria (also called the Archaea)
are a subkingdom of bacteria considered to be ancient compared to
other bacterial kingdoms, and possibly the most ancient life
forms and the ancestors of all eukaryotes. They typically exist
in extreme environments, and include the methane-producing
bacteria (methanogens), the "salt-loving" bacteria (halophilic
bacteria), and the sulfur-acid tolerant thermoacidophilic
bacteria. In biology, "symbiosis" is an intimate and protracted
association of individuals of different species, and if both
participants receive benefits from the association, it is usually
called "mutualism". The term "autotrophic" means self-feeding,
and is used to characterize organisms that can synthesize all
their necessary nutrients from the oxidation of inorganic
compounds. Autotrophs are the primary producers of organic
compounds for all "heterotrophic" organism (i.e., organisms that
feed on other organisms). The term "anaerobic" refers to the
absence of oxygen. ... ... Martin and Muller (2 installations, DE
US) present a new hypothesis for the origin of eukaryotic cells,
the hypothesis based on the comparative biochemistry of energy
metabolism. Eukaryotes are proposed to have arisen through
symbiotic association of an anaerobic, strictly hydrogen-
dependent, strictly autotrophic archaebacterium (the host) with a
eubacterium (the symbiont) that was able to respire, but which
generated molecular hydrogen as a waste product of anaerobic
heterotrophic metabolism. The host's dependence upon molecular
hydrogen produced by the symbiont is proposed as the selective
principle that forged the common ancestor of eukaryotic cells.
The authors suggest their hypothesis generates numerous testable
predictions, and they firmly predict that evidence for a strictly
H(sub2)-dependent ancestry, and most probably a methanogenic
ancestry, of the host should ultimately be revealed by
comparative genomics. They also predict that anaerobic
heterotrophic habitats devoid of geological hydrogen may harbor
eukaryotes more primitive than known forms, the metabolism of
which should be accountable for by their hypothesis.
QY: William Martin 
(Nature 5 Mar 98) (Science-Week 20 Mar 98)


4. EXTRASOLAR PLANETS: IMAGING VIA A NULLING-INTERFEROMETER
Currently, the identification and study of extrasolar planets
depends for the most part on indirect methods such as those
involving the measurement of perturbations of the observed
brightness or motions of their parent stars. The ideal method
would be direct imaging of extrasolar planets, and this would
considerably enhance the possibilities for understanding their
nature. A major problem in direct imaging of extrasolar planets
is that the bright light from the parent star (more particularly,
its diffracted halo in the imaging apparatus) can easily
overwhelm nearby faint light sources such as orbiting planets.
Exactly 20 years ago, R.N. Bracewell proposed a method for direct
imaging of extrasolar planets that eliminates or at least reduces
the problem of overwhelmed faint light, the method based on the
selective removal of starlight before detection by the
superposition of light from 2 telescopes so that the stellar
wavefronts destructively interfere. In principle, such a "nulling
interferometer" could be used to search for extrasolar Earth-like
planets through their thermal emission, with spectroscopic
analysis used to identify planets that possess the atmospheric
signatures of life. ... ... P.M. Hinz et al now report mid-
infrared observations using 2 co-mounted telescopes of the
*Multiple Mirror Telescope that demonstrate the feasibility of
the Bracewell technique. The authors report that interfering
light of unresolved stars is seen to disappear almost completely,
while light from a nearby source as close as 0.2 *arc seconds
remains, as shown by images of *Betelgeuse. With this star
canceled, there remains the thermal image of its surrounding
small dust nebula. The authors suggest that in the future larger
ground-based interferometers that correct for atmospheric
distortions should achieve better cancellation, and thus allow
direct detection of warm Jupiter-size planets and detection of
the faint *zodiacal dust around other nearby stars.
-----------
P.M. Hinz et al (8 authors at 2 installations, US)
Imaging circumstellar environments with a nulling interferometer.
(Nature 17 Sep 98 395:251)
QY: Phillip M. Hinz 
-----------

Text Notes: 
... ... *Multiple Mirror Telescope: Completed and operational in
1980, this telescope near Tucson, Arizona (US) originally
comprised 6 identical mirrors, each 1.8 meters in diameter,
arranged symmetrically about a central axis, with a complex
alignment and electronic guidance to bring all 6 images to a
common focus.
... ... *arc seconds: (arcsec) A unit of angular measure equal to
1/3600 of a degree. 60 arcsec = 1 arc minute. The full Moon is
approximately 30 arc minutes in diameter.
... ... *Betelgeuse: (Alpha orionis) 10th brightest star in the
sky. Distance estimated at 400 light years. This is an extremely
large semiregular variable star, hundreds of times the diameter
of the Sun, with variations in brightness as swells and contracts
in size.
... ... *zodiacal dust: This refers to particles of 1 to 300
microns in size and originating from decaying comets and
asteroids spiraling inward to a star. In our Solar System, this
is the dust cloud primarily responsible for the "zodiacal light",
a permanent faint sky glow visible from Earth. The glow is
apparently caused by dust particle-scattering of sunlight.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Oct98


5. EXTRASOLAR PLANETS: ON YOUNG STARS AND PROTOPLANETARY DISKS
During the past decade, astronomers have been accumulating
evidence interpreted to display the history of the formation of
planets around stars other than our Sun. ... ... R. Jayawardhana
reviews this field and makes the following points: 1) In 1995,
astronomers reported the first tentative evidence of planets
orbiting another solar-type star, and since then astronomers have
detected perturbations in the motions of a dozen nearby stars,
these perturbations presumably due to the gravity of planets. 2)
An important focus of extrasolar planetary research is the dust
disks from which such planets form, and within the past year
astronomers have obtained detailed images of dust disks
surrounding a host of nearby young stars, the images showing dust
disks at different stages of evolution. 3) One-million-year-old
disks contain mostly gas and show no evidence for planet
formation. Disks can form around binary stars as well as single
stars, but the evolution of dust disks in binary star systems is
not clarified. Perhaps as much as 70 to 80 percent of the young
stars in the center of the *Orion Nebula show evidence of disks.
It is estimated that the mass of young circumstellar disks such
as those in Orion range from 1 to 10 percent of the mass of the
Sun, which is 10 times the mass needed to make a planetary system
like our own. Dust accounts for approximately 1 percent of the
mass of the disk, and the remaining 99 percent is mostly hydrogen
and helium gas. 4) The generally accepted theory is that dust
disks produce planetary systems at approximately the age of 10
million years. The evolutionary sequence is that dust grains
adhere to make entities as large as pebbles, the pebbles then
collide and adhere to make planetesimals, and the gravity of the
planetesimals begins to gather in more and more material, until a
planetesimal may grow as large as the Moon in about 100,000
years. Within several million years, rocky planets the size of
Mercury, Venus, and Earth would complete their agglomeration. In
summary, as the disk ages, planets begin forming in the central
regions, clearing gaps near the star; by 10 million years, most
of the gas is gone, and either planets or planetesimals have
already formed. In the outer regions analogous to the *Kuiper
belt in our Solar System, collisions between asteroids and comets
continue to generate small amounts of dust.
-----------
R. Jayawardhana (Harvard University, US)
Planetary nurseries.
(Astronomy November 1998)
QY: Ray Jayawardhana, Harvard University 617-495-1000.
-----------

Text Notes:
... ... *Orion Nebula: A gaseous nebula visible to the naked eye
as a diffuse glow marking Orion's sword in the Orion
constellation. The nebula is approximately 1500 light years from
Earth, and contains a group of newborn stars (the Trapezium)
probably less than 1 million years old, with star formation near
this group still occurring.
... ... *Kuiper belt: In 1951 the astronomer Gerard P. Kuiper
(1905-1973) postulated the existence of a belt of objects beyond
the orbit of Pluto. Both the existence and nature of the objects
were matters of speculation for decades, and finally in 1992
Jewitt and Luu identified the first Kuiper object. The current
estimate is that as many as 10^(8) objects larger than 10
kilometers in diameter may exist in what is called the "Kuiper
belt", a disc that hugs the plane of the planetary system and
lies between 35 and 1000 *AU from the Sun. Observations to date 
have yielded some 55 trans-Neptune bodies with radii on the order
of 100 km or larger, and Pluto is considered by some astronomers
to be a member of this population.
... ... *AU: Astronomical Unit. 1 AU = the mean distance from the
Sun to the Earth = approximately 93 million miles, and exactly
149,597,870 kilometers.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Oct98


6. THEORETICAL PHYSICS: ON STRING THEORY
In particle physics, string theory is a theory of elementary
particles based on the idea that the fundamental entities are not
point-like particles but finite lines (strings), or closed loops
formed by strings, the strings one-dimensional curves with zero
thickness and lengths (or loop diameters) of the order of the
Planck length of 10^(-35) meters. ... ... B.R. Greene et al
present a short review of recent developments in string theory
and make the following points: 1) Particle physics has spent much
of this century grappling with one basic question in various
forms: What are the fundamental *degrees of freedom needed to
describe nature, and what are the laws that govern their
dynamics. 2) The current "standard model" of particle physics --
which is nearly 25 years old and which has much experimental
evidence in its favor -- involves 6 *quarks, 6 *leptons, 4
*forces, and the as yet unobserved *Higgs boson. But this model
contains internal indications that it too may be just another
step along the path of uncovering the truly fundamental degrees
of freedom. The standard model is valid to distances as small as
10^(-16) cm, and there is some evidence that the next level of
structure will be detected only at a distance scale of the order
of 10^(-32) cm, which is far beyond our abilities to measure in
the laboratory. 3) A related important issue concerns the
unification of general relativity and quantum mechanics. A
serious problem arises when general relativity is extrapolated to
small distance scales of the order of 10^(-32) cm where quantum
effects must be taken into account: the relevant theoretical
equations produce uncontrollable divergences, and the history of
particle physics suggests this is an indication of a new physics
occurring at these distance scales. 4) String theory offers hope
of addressing both of these issues. There is only one known way
to cure the divergence problem in the quantum-mechanical
expansion of general relativity, and that is to model the
particles in the theory not as points but as one-dimensional
loops of "string". Every consistent such string model necessarily
contains a special kind of particle -- the "*graviton" --  whose
long-distance interactions are described by general relativity.
So in a sense, string theory predicts gravity. 5) An exciting new
frontier was opened during the past few years with the discovery
of "string duality", which predicts equivalences among various
different physical systems. This discovery has its roots in the
properties of "supersymmetry", a novel type of symmetry that all
consistent string theories possess. Briefly, supersymmetry
relates properties of two basic types of particles -- bosons and
*fermions --  which cannot be related by ordinary symmetry. There
is a current belief that supersymmetry will play a role in the
structure of particle physics beyond the standard model. One of
the important achievements of string duality has been the
determination of the behavior of the 5 consistent string theories
when interactions become strong. All the consistent string
theories are apparently related to each other, and to an
elaboration known as "membrane theory" (M-theory). String duality
has produced hope that there may be only one possible string-
theoretic model of the universe, and that it may be possible to
eventually predict such features as particle masses and
interaction strengths directly from such a theory. The authors
conclude: "Development has been rapid on many fronts since string
duality was introduced. We may be seeing glimpses of the
underlying principle manifested in these new results. The
challenging task that lies ahead is to discover that principle
and thereby find what may well be the truly fundamental degrees
of freedom in our universe."
-----------
B.R. Greene et al (3 authors at 3 installations, US)
String theory.
(Proc. Natl. Acad. Sci. US 15 Sep 98 95:11039)
QY: David R. Morrison 
-----------

Text Notes:
... ... *degrees of freedom: In general, this refers to the
independent variables that must be specified in order to define
the state of a system.
... ... *quarks: A quark is a hypothetical fundamental particle,
having charges whose magnitudes are one-third or two-thirds of
the electron charge, and from which the elementary particles may
in theory be constructed.
... ... *leptons: A class of elementary particles. Although they
are affected by electromagnetic and gravitational forces, apart
from that they are involved only with weak interactions, acted
upon by weak forces but not by strong forces, as opposed to
quarks, which are acted upon by strong forces but not by weak
forces. One further difference between leptons and quarks is that
leptons can be isolated as single particles, whereas quarks
apparently cannot. The leptons include the electron, the muon,
the tau, and their associated neutrinos. The mass of the tau is
approximately 3484 times the mass of the electron; the mass of
the muon is intermediate.
... ... *forces: The fundamental forces comprise the
gravitational force, the electromagnetic force, the nuclear
strong force, and the nuclear weak force.
... ... *Higgs boson: Higgs fields (named after Peter W. Higgs,
University of Edinburgh, UK) constitute a set of fundamental
theoretical fields that induce spontaneous symmetry breaking. In 
general, spontaneous symmetry breaking occurs in systems whose
underlying symmetry state is unstable. A Higgs particle is
associated with a Higgs field in the same way that a photon is
associated with the electromagnetic field. Higgs bosons are
massive mesons whose existence is predicted by certain theories.
Mesons are apparently composed of quark and anti-quark pairs;
they are produced by various high-energy interactions and decay
into stable particles.
... ... *graviton: Several quantum field theories consistent with
both quantum mechanics and special relativity postulate that the
gravitational force between two quantum domain particles is
generated by the exchange of an intermediate particle called a
graviton.
... ... *fermions: Fermions (electrons, protons, neutrons) are
particles that obey the Pauli exclusion principle: i.e., no two
fermions of the same kind can occupy the same quantum state.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Oct98

-------------------

Related Background:

ON RECENT DEVELOPMENTS IN SUPERSTRING THEORY
Bose-Einstein statistics is the statistical mechanics of a system
of indistinguishable particles for which there is no restriction
on the number of particles that may simultaneously exist in the
same quantum energy state. Bosons are particles that obey Bose-
Einstein statistics, and they include photons, pi mesons, all
nuclei having an even number of particles, and all particles with
integer spin. Fermions (electrons, protons, neutrons) are
particles that obey the Pauli exclusion principle: i.e., no two
fermions of the same kind can occupy the same quantum state.
In particle physics, string theory is a theory of elementary
particles based on the idea that the fundamental entities are not
point-like particles but finite lines (strings), or closed loops
formed by strings, the strings one-dimensional curves with zero
thickness and lengths (or loop diameters) of the order of the
Planck length of 10^(-35) meters. The fundamental forces comprise
the gravitational force, the electromagnetic force, the nuclear
strong force, and the nuclear weak force, and the "grand unified
theories" are theories that aim to provide a mathematical frame-
work in which the electromagnetic forces, strong forces, and weak
forces emerge as parts of a single unified force, with the three
forces related by symmetry. Supersymmetry is an aspect of an
extension of the grand unified theories, an attempt to unify all
the four fundamental forces, i.e., linking gravitation to the
electromagnetic force, the strong force, and the weak force
through a supersymmetry scheme, and superstrings are strings in
this scheme that obey supersymmetry. ... ... John H. Schwarz
(California Institute of Technology, US) presents a brief
overview of some of the advances in understanding super-
string theory that have been achieved in the last few years.
String theories that have a symmetry relating bosons and
fermions, called "supersymmetry", are called "superstring"
theories. Major advances in understanding of the physical world
have been achieved during the past century by focusing on
apparent contradictions between well-established theoretical
structures. In each case the reconciliation required a better
theory, often involving radical new concepts and striking exper-
imental predictions. Four major advances of this type were the
discoveries of special relativity, quantum mechanics, general
relativity, and quantum field theory. This was quite an achieve-
ment for one century, but there is one fundamental contradiction
that still needs to be resolved, namely the clash between general
relativity and quantum field theory. Many theoretical physicists
are convinced that superstring theory will provide the answer.
QY: John H. Schwarz, Calif. Inst. of Technology 818-395-6811.
(Proc. Natl. Acad. Sci. US 17 Mar 98)
(Science-Week 10 Apr 98)

-------------------

Related Background:

ON THE EVOLUTION OF STRING THEORY TO MEMBRANE THEORY
... Membrane theory (M-theory) is a recent extension of string
theory in which the fundamental physical entities are considered
as surfaces in a many-dimensional space (membranes) rather than
as lines or loop elements (open or closed strings). Given all of
the above, some caution is necessary: the translation of a highly
abstract mathematical model of physical reality into non-mathem-
atical language is often an exercise of limited usefulness, and
in this case in particular, we are presenting only the ghost of
the theoretical scheme. String theory was originally invented in
the 1960s as a theory of the strong force, became overshadowed by
the strong force theory of gluons and quarks, then had a revival
in the 1980s -- but with the history more dependent on new work
than on fashion. ... ... M. Duff (Texas A & M Univ., US), who is
active in string theory and membrane theory, in a review of
various aspects of the history and essentials of string theory
and membrane theory, suggests that future historians may judge
the 20th century as "a time when theorists were like children
playing on the seashore, diverting themselves with the smoother
pebbles or prettier shells of superstrings, while the great ocean
of M-theory lay undiscovered before them."
QY: Michael J. Duff, Texas A & M Univ. 409-847-9451.
(Scientific American February 1998)
(Science-Week 23 Jan 98)


7. EVOLUTION: A NEW COELACANTH DISCOVERY
The coelacanth is a primitive *teleost fish that apparently first
appeared in the *Devonian Period, with the most recent fossil
specimens dating from the *Cretaceous Period. The group was
assumed to be extinct, but a living specimen was caught in 1938
in the mouth of the Chalumna River in South Africa and named
Latimeria chalumnae. The 1938 specimen was 2 meters in length and
weighed 40 kilograms. Several more specimens have since been
caught, all off the coast of South Africa and near the island of
Madagascar (Comoros archipelago) in the Indian Ocean.
... ... M.V. Erdmann et al now report the capture and observation
of a live coelacanth specimen near the island of Manado Tua
(north Sulawesi) in Indonesia on 30 July 1998. The Indonesian
specimen was caught in a net at a depth of 100 to 150 meters. The
specimen is 1.24 meters in length and weighs 29.2 kilograms, and
the authors report it was observed by them live for more than 3
hours before the carcass was deep frozen and tissue samples
collected for molecular analysis. The authors suggest that
interviews with the local fishermen, and the vast distance from
the Comoros archipelago to Indonesia (approximately 10,000
kilometers), strongly support the idea that the Indonesian
coelacanths (which are evidently well known in the region and
called "raja laut" or King of the Sea) are part of an established
north Sulawesi coelacanth population and not simply strays. Like
its Indian Ocean counterpart, the Indonesian coelacanth was
found
in the vicinity of oceanic volcanic caves, its presumed habitat.
... ... In a companion article concerning the M.V. Erdmann et al
paper, P. Forey makes the following points: 1) Before the 1938
discovery, the date of the youngest coelacanth fossil recovered
was approximately 80 million years ago. This raises the question
of how the lineage survived for that time without leaving any
trace in the fossil record. 2) The theory of relationships
prevalent in the late 1930s held that the coelacanth was a direct
descendant of Devonian fish-like ancestors of land-living
vertebrates (tetrapods), but from modern evolutionary analysis it
seems that coelacanths are more distantly related to land-living
vertebrates, and that lungfishes are the closest living relatives
to the tetrapods. 3) Significant in the coelacanth are paired
fins that move in a manner unlike that seen in most fishes but in
a manner identical to limb movement in vertebrates. There are
also sensory structures in the coelacanth that are apparently
precursors of structures responsible for hearing in air. The
author concludes: "The new discovery underlines how little we
really know about the coelacanth in particular and oceanic life
in general."
-----------
M.V. Erdmann et al (2 installations, US ID)
Indonesian "king of the sea" discovered.
(Nature 24 Sep 98 395:335)
QY: Mark V. Erdmann, Univ. of Calif. Berkeley 510-642-6000.
-----------
P. Forey (Natural History Museum London, UK)
A home from home for coelacanths.
(Nature 24 Sep 98 395:319)
QY: Peter Forey 
-----------

Text Notes:
... ... *teleost: In general, this refers to any of the bony
fish, the most advanced in terms of evolution and the largest
group of fish. Besides the calcified internal skeleton, the most
obvious uniform characteristic of the teleost fish is their tail,
with upper and lower halves of about equal size, whereas in
cartilaginous fish the tail has two lobes of unequal size. Almost
all sport, commercial, and ornamental fish are teleosts.
... ... *Devonian Period: From approximately 400 million to 345
million years ago. Sometimes called the Age of the Sea, since
more of the Earth was underwater than is now.
... ... *Cretaceous Period: The geological period ranging
approximately from 146 million years ago to 65 million years ago.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Oct98


8. CELLULAR AGING: DONOR AGE AND CELLULAR REPLICATION LIFESPAN
Fibroblasts are a type of connective tissue cell, secreting
structural proteins such as collagen, the proteins forming a
matrix in which the fibroblasts become embedded. These cells can
be easily obtained from skin, and they can be easily cultured
outside the body. Normal human fibroblasts have a finite
replicative lifespan in vitro (i.e., they divide a finite number
of times), and this has been postulated to be a cellular
manifestation of aging of the human organism. Several studies
have indeed shown an inverse relationship between donor age (the
age of the persons from which cultured cells are derived) and
fibroblast culture replicative lifespan. But in all cases the
correlation was weak, and with few exceptions the health status
of the donors was unknown. Thus, the relationship between the
replicative lifespan and the age of the donor from which the
cells are derived has remained equivocal (*Note #1).
... ... V.J. Cristofalo et al now report a study of the
replicative lifespan of 124 skin fibroblast cell lines
established from donors of different ages. All donors were
medically examined and were declared "healthy" (according to
Baltimore Longitudinal Study of Aging protocols) at the time the
biopsies were taken. The authors report that both long- and
short-lived cell lines were observed in all age groups, but no
significant correlation between the proliferative potential of
the cell lines and donor age was found. A comparison of multiple
cell lines established from the same donors at different ages
also failed to reveal any significant trends between
proliferative potential and donor age. The authors suggest their
results clearly indicate that if health status and biopsy
conditions are controlled, the replicative lifespan of
fibroblasts in culture does not correlate with donor age.
-----------
V.J. Cristofalo et al (5 authors at 2 installations, US)
Relationship between donor age and the replicative lifespan of
human cells in culture: A reevaluation.
(Proc. Natl. Acad. Sci. US 1 Sep 98 95:10614)
QY: Vincent J. Cristofalo, Center for Gerontological Research,
Alleghany University of the Health Sciences, Philadelphia, PA
19129 US.
-------------------

Notes by ScienceWeek:

... ... *Note #1: The possibility that the process of cell aging
and death is under genetic control was first suggested by Leonard
Hayflick in 1961. Hayflick reported that normal human
fibroblasts
apparently have an intrinsic limit to the number of times they
can proliferate, with human fibroblasts removed from an embryo
and grown in culture dividing approximately 50 times before they
deteriorate and die. In contrast, human fibroblasts removed from
adults multiply only 15 to 30 times before dying. Also,
fibroblasts removed from young children suffering from Werner's
syndrome (a rare disease that causes premature aging) divide only
2 to 10 times in culture. Further evidence for a relationship
between aging and the replicative capacity of cells was provided
by the discovery that the number of replications in culture is
apparently related to the lifespan of organism. For example,
cultured cells of the Galapagos tortoise, whose maximum life span
is approximately 175 years, divide more than 100 times in
culture, whereas cells from the mouse, whose maximum life
expectancy is only a few years, divide fewer than 30 times in
culture. The correlation roughly holds for other species as well.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Oct98

-------------------

Related Background:

BIOLOGY OF AGING: ON TELOMERES AND REPLICATIVE SENESCENCE
Telomeres are defined ends of chromosomes that contain specific
repeated DNA sequences. They are essential for normal chromosome
replication, and since their length shortens a bit with each
replication, they are believed to be involved in the aging of the
cell. Telomerase is an enzyme that repairs damage to telomeres,
and it is thought by some that cancerous cells may have mutant
telomerase, the mutant enzyme conferring immortality on the
cancer cell. ... ... In a review of cell senescence, the aging of
cell cultures, and the immortalization of mammalian cells, John
M. Sedivy (Brown University, US) makes the following points: 1)
Finite replicative lifespan (senescence) of mammalian cells in
culture is a phenomenon that has generated much curiosity since
its description. The obvious significance of senescence to
organismal aging and the development of cancer has engendered a
long-lasting and lively debate about its mechanisms. 2) Three
classical observations are usually cited to argue that in vitro
replicative senescence is a phenomenon with biological
significance: a) the correlation of in vitro lifespan with the
age of the donor; b) the correlation of in vitro lifespan with
the average life expectancy of species; and, c) the reduced in
vitro lifespan of cells from patients afflicted with premature
aging syndromes. 3) Two major theories have been used to explain
limited replicative capacity. The first hypothesis invokes the
gradual accumulation of mutations, and the second hypothesis
invokes the existence of a molecular clock (or clocks) that can
keep track of cell divisions. The second theory is now believed
to be generally true. 4) It is known that cell senescence can be
overcome, because many cell lines in common laboratory use are
quite obviously immortal. Rodent cells can overcome senescence
spontaneously. Human, chicken, bovine, and horse cells rarely, if
ever, immortalize spontaneously. 5) Certain viral or biochemical
interventions in human cell cultures can overcome cell
senescence, typically by causing 20 to 30 extra population
doublings. At the end of this extended lifespan, there is a
decline and death of the culture in 4 to 6 weeks, which has been
termed "crisis". Senescent cells, on the other hand, can be
maintained in vitro in a viable non-proliferative state for very
long periods of time (reports of from 4 to 6 months, and up to 2
years). 6) The author suggests it is amazing that in spite of
very long periods of apparent "immortality", the senescent
program in cells remains intact in cells in which senescence has
been overridden, so that on removal of the overriding agent, the
program is capable of establishing rapid growth arrest. 7) The
current prevailing hypothesis for the nature of the molecular
clock involved in cell senescence is the attrition of telomeres.
*Germ cells, and some key *stem cells, are known to express
telomerase catalytic activity, whereas the majority of somatic
cells lack it. Murine (mouse) embryonic stem cells express
telomerase and are functionally immortal, and elimination of
telomerase eventually results in loss of proliferation. 8) The
author proposes that immortalization of human cells requires a
bypass of both cell senescence and crisis, whereas in rodent
cells cell crisis does not exist and culture lifespan is limited
only by senescence. 9) Evidence indicates that, at least in human
cells, telomere length appears to be linked critically to the
triggering of senescence. The author suggests that although it
remains to be rigorously demonstrated, this strongly implies that
activation of telomerase can result in one-step immortalization.
In conclusion, the author states the two most significant
questions in this field: a) Does cell senescence limit organismal
lifespan? And, b) Is telomerase expression necessary for cancer
progression in vivo?
QY: John M. Sedivy 
(Proc. Natl. Acad. Sci. US 4 Aug 98 95:9078)
(Science-Week 4 Sep 98)

-------------------

Related Background:

... ... *Germ cells: Any cell from which gametes (sperm cells and
egg cells) are derived. All other cells are called "somatic"
cells.
... ... *stem cells: In general, a stem cell is any precursor
cell, a form prior to cell differentiation. E.g., stem cells in
bone marrow that give rise to blood cells.

-------------------

Related Background:

ROLE OF MOUSE TELOMERASE IN HIGHLY PROLIFERATIVE ORGANS
Telomeres are guanine-rich repeat sequences that form the
physical ends of the chromosomes of cells containing membrane-
bound organelles, and there is evidence these terminal structures
may be important in chromosome function. Synthesis and
maintenance of telomeric repeats are mediated by the specialized
ribonucleoprotein complex "telomerase". ... ... Lee et al (6
authors at 4 installations, US ES) report a study of the role of
the enzyme telomerase in highly proliferative organs in
successive generations of mice lacking telomerase RNA. Late
generation animals exhibited defective spermatogenesis, with
increased programmed cell death (apoptosis) and decreased
proliferation in the testis. The proliferative capacity of
hematopoietic cells in bone marrow and spleen was also
compromised. These progressively adverse effects coincided with
substantial erosion of telomeres and fusion and loss of
chromosomes. The authors suggest their findings indicate an
essential role for telomerase, and hence telomeres, in the
maintenance of genomic integrity and in the long-term viability
of high-renewal organ systems. They also suggest that the high
proliferation index of most cancer cells compared with the more
sporadic cycling of normal stem-cell populations indicates that
telomerase inhibition should be well tolerated in clinical
settings.
QY: R.A. DePinho, Albert Einstein Coll. of Medicine 718-430-2106.
(Nature 9 Apr 98 392:569) (Science-Week 1 May 98)

-------------------

Related Background:

EXTENSION OF MITOTIC LIMITS BY TELOMERASE EXPRESSION
Somatic cells are all cells other than germline cells such as egg
cells and sperm cells and their progenitors, and the term
"cellular replicative senescence" refers to the observation that
somatic cells, in contrast to germline cells, can proliferate
(divide) only a fixed number of times, the actual number
dependent on the organism from which the somatic cells derive.
Since there is a general correlation between cellular replicative
senescence in vitro and the average life-spans of various animals
(including humans), cellular replicative senescence has been
implicated in aging and age-related pathologies. Telomeres are
regions at the ends of chromosomes consisting of repeats of
particular nucleotide sequences, and with each somatic cell
division a small part of the telomere is ordinarily lost. What
has been observed is that in germline cells the lengths of
telomeres are maintained constant by repair, while in somatic
cells this repair does not occur, and this difference has led to
the idea that the finite proliferative capacity of somatic cells
is related to the ultimate depletion of telomere lengths. The
enzyme telomerase is the enzyme that causes repair of telomeres,
and this enzyme is active in germline cells, but it is not
expressed in most somatic 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,
and fibroblasts are a type of connective tissue cell that secret
structured proteins such as collagen. Transfection is the uptake
of exogenous (foreign) DNA fragments in solution directly into
animals cells in laboratory culture, and is one method of
introducing foreign genes into cells. The term "vector", in the
context of DNA cloning, is any DNA fragment used in a
transfection process. ... ... Bodnar et al (10 authors at 2
installations, US) now report that two normal human cell types
(retinal pigment epithelial cells and foreskin fibroblasts) that
do not ordinarily express telomerase, can be transfected with
vectors encoding the human telomerase catalytic subunit, the
transfected cells (as opposed to controls) then exhibiting
elongated telomeres, dividing vigorously and exceeding their
normal life-span by at least 20 doublings. The authors suggest
their results establish a causal relationship between telomere
shortening and in vitro cellular replicative senescence, and that
the ability to maintain normal human cells in a youthful state
can have important applications in research and medicine.
QY: Serge Lichtsteiner 
(Science 16 Jan 98) (Science-Week 30 Jan 98)

-------------------

Related Background:

NEW DATA AGAINST IMPORTANT TELOMERASE ROLE IN CANCER
Telomeres are defined ends of chromosomes that contain specific
repeated DNA sequences. They are essential for normal chromosome
replication, and since their length shortens a bit with each
replication, they are believed to be involved in the aging of the
cell. Telomerase is an enzyme that repairs damage to telomeres,
and it is thought by some that cancerous cells may have mutant
telomerase, the mutant enzyme conferring immortality on the
cancer cell. Now M. A. Blasco et al (Cell 91:25 1997) have
genetically engineered telomerase-deficient mice and have shown
that after 6 generations these mice are both viable and fertile.
Commenting on this research, David Wynford-Thomas and David
Kipling (University of Wales College of Medicine, Cardiff UK)
suggest that telomerase inhibitors that have been envisaged for
cancer therapy will therefore not have any acute toxicity against
cancer cells or other cells. Blasco et al have suggested that
current dogma that telomerase facilitates tumor growth may be
wrong, with telomerase nothing more than a "passive bystander" in
oncogenesis.
(Nature 9 Oct 97) (Science-Week 24 Oct 97)

-------------------

Related Background:

ANALYSIS OF PROTEIN COMPONENT OF TELOMERASE
... Toru M. Nakamura et al (University of Colorado, US;
Geron Corp., Menlo Park CA US) report that telomerase catalytic
subunits are identical in yeast and humans, indicating the
molecular biology of telomere maintenance is evidently phylo-
genetically conserved.
QY: Thomas R. Cech, Univ. Colorado Boulder (303) 492-6301
(Science 15 Aug 97) (Science-Report 29 Aug 97)


9. RESISTANCE OF MENINGITIS PATHOGEN TO CHLORAMPHENICOL
There are many different mechanisms by which microorganisms might
exhibit resistance to drugs. One mechanism is the production of a
drug-destroying enzyme by the microorganism, the drug destroyed
before it has a chance to do any damage to the microorganism. The
pathogen Neisseria meningitidis is a coccus bacterium that can
cause a spectrum of diseases ranging from transient fever to
*meningitis and *fulminant septicemia. Meningitis is spread by
airborne droplets or direct contact with discharge from the nose
or throat of an infected person, and meningococcal infections are
common in both temperate and subtropical climates. The pathogen
N. meningitidis has nearly always been susceptible to the
penicillin antibiotics, the *cephalosporin antibiotics, and
*chloramphenicol. However, between 1987 and 1996,
chloramphenicol-resistant strains of N. meningitidis were
isolated from 11 patients in Vietnam and 1 in France.... ... M.
Galimand et al now report an analysis of bacterial isolates from
the cerebrospinal fluid of the 12 mentioned cases. The authors
report high-level resistance to chloramphenicol in what appear to
be epidemiologically unrelated strains, the resistance achieved
via the production by the pathogen of a chloramphenicol-
destroying enzyme (chloramphenicol acetyltransferase). Molecular
genetic analysis was used to identify a *transposon gene
responsible for the drug-destroying enzyme, and the authors
relate this gene to a similar gene in the pathogen *Clostridium
perfringens. The authors suggest the initial acquisition of
chloramphenicol resistance by N. meningitidis could have occurred
by *transformation or *conjugation, raising the possibility of a
transfer of genetic information from a strict *anaerobe (C.
perfringens) to a strict *aerobe (N. meningitidis). The authors
discuss possible mechanisms for the transfer. The authors
conclude: "The emergence of high-level chloramphenicol resistance
in N. meningitidis isolates is of great concern, since the
intramuscular administration of chloramphenicol in oil is the
standard treatment for meningococcal meningitis in developing
countries." [*Note #1]
-----------
M. Galimand et al (5 authors at 2 installations, FR)
High-level chloramphenicol resistance in Neisseria meningitidis.
(New England J. Med. 24 Sep 98 339:868)
QY: Marc Galimand, Institut Pasteur, 28 Rue du Dr. Roux, 75724
Paris CEDEX 15, FR.
-----------

Text Notes:
... ... *meningitis: In general, this term refers to any
inflammation of the connective tissue membranes (meninges) of the
brain or spinal cord. Meningitis caused by the pathogen
Neisseria
meningitidis is called meningococcal meningitis, the suffix
"-coccal" referring to the cocci group of bacteria (shape:
spheroidal) of which N. meningitidis is a member.
... ... *fulminant septicemia: Sudden and severe systemic disease
caused by the spread of microorganisms and their toxins via the
blood. Septicemia was formerly called "blood poisoning". In this
context, fulminant = sudden and severe.
... ... *cephalosporin antibiotics: A group of beta-lactam
antibiotics originally identified in cephalosporium fungi. The
mechanism of action is similar to that of penicillins, i.e.,
inhibition of bacterial cell wall synthesis and/or activation of
degradation of the bacterial cell wall.
... ... *chloramphenicol: An antibiotic originally produced from
cultures of Streptomyces venezuelae but now manufactured
synthetically. The drug is a potent inhibitor of protein
synthesis in microorganisms.
... ... *transposon: A limited DNA sequence that under the proper
dynamic conditions can effectively translocate from one DNA
system to another, either in the same cell, or between cells, or
between cells of different organisms of the same or different
species, and remain functional.
... ... *Clostridium perfringens: Clostridium is a species of
spore-forming anaerobic bacilli, and C. perfringens produces
invasive infection if introduced into damaged tissue. C.
perfringens can be involved in food poisoning, but it is perhaps
best known as a pathogen associated with "gas gangrene".
... ... *transformation: A mechanism of gene transfer involving
the direct uptake of donor DNA by the recipient cell.
... ... *conjugation: A mechanism of gene transfer involving the
translocation of a complex of genes with often cooperative
functions. In bacteria, *plasmids are the usual vehicle for
conjugative gene transfer.
... ... *plasmids: In general, genetic fragments physically
separate from any chromosome of the host cell, the fragments
functionally stable and able to replicate. They are common in
bacteria.
... ... *anaerobe: Refers to a life form sustained in the absence
of free (gaseous or dissolved) oxygen. 
... ... *aerobe: An organism requiring the presence of free
oxygen for viability.
... ... *Note #1: A collection of reports extracted from past
issues of SCIENCE-WEEK and concerning microbial drug resistance
can be accessed at .
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Oct98