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SCIENCE ROUNDUP
In This Issue:

Sleep, Dreams, and Memory
Cholesterol:  Good For Your Brain
Lipids:  Cellular Heroes . . . and Villains
New Partners in the mRNA Export Business
Building Blocks for Genome Studies
Portraits of Unpredictable Epidemics
Bouncing Back (or Not) from Ecological Catastrophe
Dinosaurs for Supper
Putting Nanotech to Work
New Spins on Magnetism
Asteroid Families


Sleep, Dreams, and Memory
http://www.sciencemag.org/content/vol294/issue5544/index.shtml#specialintro

Just why *do* animals sleep?  Despite years of research, we still
don't know the precise neurological purpose of sleep and dreams.
The 2 Nov 2001 special issue of *Science* focused on the latest
research in sleep, dreams, and memory -- as well as other unsolved
neuroscience riddles.  Reviews by Maquet and Stickgold et al.
explored the connection between sleep and learning and detailed
new experimental approaches in the field.  A third review by
Siegel, in contrast, reviewed the state of the literature on REM
sleep and memory consolidation, and suggested that, for sleep, "a
major role in memory consolidation is unproven."  Also in this
neuroscience special issue:

--A six-page news focus
( http://www.sciencemag.org/cgi/content/short/294/5544/980 )
delved into the latest research into addictions and the long-term
neural changes seen in addicts' brains.

--A research article by Fukuchi-Shimogori and Grove 
( http://www.sciencemag.org/cgi/content/short/294/5544/1071 ),
accompanied by a Perspective by P. Rakic
( http://www.sciencemag.org/cgi/content/short/294/5544/1011 ),
addressed the puzzle of how the map of the cerebral cortex neurons
is laid in the developing mouse brain.

--Gershon et al.
( http://www.sciencemag.org/cgi/content/short/294/5544/957 ), in
an editorial, stressed the need for funding and concentrated
research on major mental illnesses to identify susceptibility genes,
in light of recent advances in genomics and statistical methods.

--Fascinating essays by the three winners of the 2000 Nobel Prize
in Medicine
( http://www.sciencemag.org/content/vol294/issue5544/index.shtml#review ),
given for discoveries into neurotransmission, reviewed
the work that led to each recipient's prize.

--Additional neuroscience-related material appeared on three
different *Science*-related Web sites: a perspective on melatonin
receptors and a review of circadian clocks on the Signal
Transduction Knowledge Environment ( http://www.stke.org );
reviews on Alzheimer's disease on the Science of Aging
Knowledge Environment ( http://sageke.sciencemag.org ); and a
discussion of neurological modifier genes on the *Science*
Functional Genomics site ( http://www.sciencegenomics.org ).


Cholesterol:  Good For Your Brain

Neurons communicate at junctions called synapses -- connections
that are made and broken all the time.  Researchers have known for
several years that generating and maintaining these junctions
requires some kind of chemical signal from other cells in the brain,
called glia.  Now, reporting in the 9 Nov 2001 issue, Mauch et al.
( http://www.sciencemag.org/cgi/content/short/294/5545/1354 )
have isolated the specific molecule secreted by glia to regulate
synapse development -- and that winning molecule is, of all things,
cholesterol.  The group isolated fractions of media from glial
cultures, applied them to neurons, and then characterized the
fractions that increased synaptic activity.  Pursuing several lines of
evidence, they found that glia secrete a protein, apoE, that is bound
to cholesterol.  The apoE-cholesterol complex is then ferried over
to neurons and the cholesterol is incorporated into their cell
membranes, beefing up the supply of cholesterol for use in
construction of new synaptic components -- and, perhaps,
supplying a signal to neurons that it's time to build new synapses. 
B. A. Barres and S. J. Smith
( http://www.sciencemag.org/cgi/content/short/294/5545/1296 ), in
a Perspective, noted that this development has implications for
regulation of synaptic plasticity, thought to be lost in conditions
such as Alzheimer's disease.  Unfortunately, cholesterol in the
brain comes from synthesis by glia and not from your diet -- so
eating steak won't make you smarter.


Lipids: Cellular Heroes . . . and Villains
http://www.sciencemag.org/content/vol294/issue5548/index.shtml#specialintro

Although many of us try to avoid extra fat in our diets, lipids play
many important roles in our body's functions.  A special issue on
lipid biology, published 30 Nov 2001, put the limelight on both the
good and bad roles of lipids in cellular processes.  Two reports in
the issue detailed new connections between signaling pathways
and lipid components.  Fang et al.
( http://www.sciencemag.org/cgi/content/short/294/5548/1942 )
explored the links between lipids and the signaling cascade
initiated by treatment with the immunosuppressant drug
rapamycin.  By mining sequence databases, Zheng et al.
( http://www.sciencemag.org/cgi/content/short/294/5548/1939 )
discovered a novel protein, RGS-PX1, that may connect signaling
events involving lipid additions to proteins with molecular
trafficking events in the cell's membranes.  A news article
( http://www.sciencemag.org/cgi/content/short/294/5548/1862 )
focused on caveolae and lipid "rafts" -- microdomains of the lipid-
rich cell membrane that apparently specialize in transporting
proteins to the cell's interior.  But, lipids also have their dark side,
and reviews by Chawla et al.
( http://www.sciencemag.org/cgi/content/short/294/5548/1866 )
and Hla et al.
( http://www.sciencemag.org/cgi/content/short/294/5548/1875 )
detailed some of their roles in pathogenesis, particularly in heart
disease.  Lipid enthusiasts can rejoice over three more reviews in
the special issue, as well as two lipid-focused articles on
*Science*'s Signal Transduction Knowledge Environment
( http://www.stke.org ) and a report by Baron and Maholtra on the
publish-before-print online service *Science* Express
( http://www.sciencexpress.org ).


New Partners in the mRNA Export Business

To be translated into proteins, most messenger RNAs need to get
out of the nucleus and into the cytoplasm.  Since mRNAs are too
large to get through nuclear pores alone, they are bound by adapter
proteins with nuclear export signals.  The adapters are recognized
by receptors at the nuclear pore, and the adapter-mRNA complex
is pushed out through the pore and into the cytoplasm.  Figuring
out just which adapters bound to which receptors was a tedious
task, until work reported by Gallouzi and Steitz in the 30 Nov 2001
issue
( http://www.sciencemag.org/cgi/content/short/294/5548/1895 ).
The researchers used the innovative approach of constructing small
peptides with nuclear export signals and feeding those peptides to
specially treated cells.  The peptides presumably swamp out the
cell's native adapter-receptor binding, and thus prevent export of
certain mRNAs.  By monitoring the mRNA traffic, Gallouzi and
Steitz were able to decipher which mRNAs bound to the specific
adapter protein blocked by the peptides -- and to show for the first
time that one adapter can use two different receptors, and thus two
completely different pathways, to get out of the nucleus.  Most
important, as noted in an accompanying Perspective by M. J.
Moore and M. Rosbash
( http://www.sciencemag.org/cgi/content/short/294/5548/1841 ),
their strategy works in living cells, and could thus be used to
design an entire panel of peptide inhibitors for mRNA export that
have minimal side effects -- "a dream for cell biology."


Building Blocks for Genome Studies

One of the year's big events in postgenomics has been the race to
use the human genome sequence to identify useful information,
focusing on markers called single nucleotide polymorphisms
(SNPs).  Because mutations causing SNPs are rare, SNPs can be
compared among individual genomes to build a history of humans,
and can be used to map traits controlled by nearby genes.  When
using SNPs to look for a linked gene, the ideal would be to quickly
scan the entire genome, testing the smallest number of SNPs but
getting the maximum amount of information.  An exciting paper
by Patil et al. in the 23 Nov 2001 issue
( http://www.sciencemag.org/cgi/content/short/294/5547/1719 ) has
started that process for one entire human chromosome.  The
authors set out to find all common SNPs on chromosome 21 and
determine the linkage between them.  They then grouped the SNPs
into blocks, or haplotypes, that have traveled together through
time, and that thus can be linked to the same ancestral
chromosome.  Because they are linked, testing one SNP in the
block gives information for all SNPs in the block.  By defining
blocks on chromosome 21, Patil et al. have greatly reduced the
work needed to scan the chromosome for markers linked to genes,
from testing over 32 million base pairs to only testing 1794 single
bases or SNPs.  The work also revealed a tantalizing finding for
population biology: a mere three common haplotypes can describe
variations among 80% of the human population -- a far smaller
level of genetic population diversity than had previously been
assumed.  Although there are still obstacles to overcome in setting
up large linkage studies based on these results, P.-Y. Kwok
suggested in an accompanying Perspective
( http://www.sciencemag.org/cgi/content/short/294/5547/1669 )
that the study "marks a paradigm shift in strategic thinking."


Portraits of Unpredictable Epidemics

We now know that almost 100 humans in the U.K. have contracted
variant Creutzfeldt-Jakob disease (vCJD) by eating meat from
animals infected with bovine spongiform encephalopathy (BSE),
or "mad cow disease," before 1989.  What we still don't know is
how many more cases to expect, mainly because we don't know
much about the incubation period from these disorders.  Several
studies in the 23 Nov 2001 issue of *Science* used statistical
methods to estimate the eventual epidemic size, a considerable
public health concern for the U.K.  Drawing on existing
epidemiological data, Valleron et al.
( http://www.sciencemag.org/cgi/content/short/294/5547/1726 )
assumed that "the force of infection decreases exponentially" after
the age of 15, and built a statistical model that yielded an estimated
16.7-year incubation period for the disease -- and a prediction of
only 205 total vCJD cases (twice the current known case figure). 
Huillard d'Aignaux et al.
( http://www.sciencemag.org/cgi/content/short/294/5547/1729 ),
making different assumptions from the existing data, used back-
calculation models to conclude that the upper limit of vCJD cases
is unlikely to exceed several thousand, regardless of incubation
period.  Finally, Kao et al.
( http://www.sciencemag.org/cgi/content/abstract/1067475 ), in
work posted the same date on the publish-before-print online
service *Science* Express, examined the patterns of infection by
BSE in sheep in the U.K.  In an accompanying Perspective, G. F.
Medley
( http://www.sciencemag.org/cgi/content/short/294/5547/1663 )
expressed a certain skepticism on the details of the model results --
"In each study," he observed, "the width of the confidence
intervals . . . can only be described as unhealthy."  Yet he found
encouragement in the fact that the upper bound of the disease's
expected toll seems to be ratcheting down with each new
prediction.


Bouncing Back (or Not) from Ecological Catastrophe

The Caribbean is a conservation hot spot, with some 84 native
mammal and bird species threatened by extinction in the
intermediate-term future.  It's also an area where natural
catastrophes, such as hurricanes, occur all too frequently.  How can
ecologists separate the biodiversity impacts of natural disasters
from those due to human pressures?  Two complementary studies
published 16 Nov 2001 offered notes toward an answer.  Ricklefs
and Bermingham
( http://www.sciencemag.org/cgi/content/short/294/5546/1522 ),
examining mitochondrial DNA sequences of 161 separate island
populations of 37 Lesser Antilles bird species, found that around
half of the populations showed a sharp genetic divergence from
sister populations on Trinidad and the South American continent. 
The patterns of divergence suggest a catastrophic event half a
million years ago, after which the Antillean avifauna had never
really regained long-term equilibrium.  Schoener et al.
( http://www.sciencemag.org/cgi/content/short/294/5546/1525 )
took an opposite tack, looking at the response of a single lizard
species in the Bahamas to a single event: Hurricane Floyd, which
struck the islands in autumn 1999.  In marked contrast to the
experience noted in the Lesser Antilles study, the group found that,
only two years after the catastrophe, the lizard species had
essentially fully recovered its original foothold on the stricken
islands.  As T. Brooks and M. L. Smith noted in an accompanying
Perspective
( http://www.sciencemag.org/cgi/content/short/294/5546/1469 ),
the two studies neatly encompass the two extremes of the
extinction "frequency-magnitude curve," and suggest that whereas
frequent catastrophes affecting simple communities in small areas
carry little long-term importance, huge, rare catastrophes of
regional scope can "remain imprinted in local community structure
for millennia."  The finding, they suggest, has important
implications for efforts to conserve the Caribbean's unique
biodiversity.


Dinosaurs for Supper

We think of the Cretaceous Period (146 to 65 million years ago) as
the climax of the age of dinosaurs, a time dominated by enormous
beasts such as *T. rex*, *Triceratops*, and *Maiasaura*.  Yet it
was an age of extremes for other creatures as well -- such as the
bus-sized crocodile *Sarcosuchus imperator*, which thrived in
riverine settings in the early part of the period.  Though fossils of
this enormous croc were first discovered more than 35 years ago,
its anatomy, longevity, and phylogeny have remained a mystery. 
Now Sereno et al.
( http://www.sciencemag.org/cgi/content/short/294/5546/1516 ), in
the 16 Nov 2001 issue of *Science*, have reported a spectacular
new set of *Sarchosuchus* finds from Niger that illuminate just
how big this creature really was -- and how it may have lived.  By
comparing the ancient crocodile's huge snout (approximately the
length of a good-sized man) with specimens of living crocodilians,
the group estimated the length of a full-sized adult *S. imperator*
at a whopping 11 to 12 meters (37 to 40 feet).  A careful analysis
of annual "growth rings" from midsection fossils suggested that
the creatures reached that size after 50 to 60 years of life.  And the
morphology of the immense skull -- with a broader snout than that
of many extant fish-eating crocs, and with stout, 5-cm-long teeth
that didn't interlock -- imply that this river-dweller may have fed
not only on large fish, but on the dinosaurs that also roamed the
region.


Putting Nanotech to Work

Much of the development thus far in the burgeoning field of
nanotechnology has involved exploring the remarkable material
properties of exotic, diminutive items such as carbon nanotubes
and gold nanowires.  Developing useful devices and applications at
the nanometer scale is an altogether tougher proposition -- but a
variety of findings reported in *Science* during the past month
pegged significant progress toward the goal of practical nano-
applications, in areas ranging from electronics to medicine:

--A set of tour de force papers in the 9 Nov 2001 issue together
marked out a giant step toward one of nanotech's most significant
goals: practical nanocomputers.  Huang et al.
( http://www.sciencemag.org/cgi/content/short/294/5545/1313 )
and Bachtold et al.
( http://www.sciencemag.org/cgi/content/short/294/5545/1317 )
reported techniques for assembling logic circuits -- the electronic
gates denoting logical relations such as AND and OR that are
essential to computation -- only a few micrometers in size, using
semiconductor nanowires and individual carbon nanotubes,
respectively.  In a related paper the same week appearing on
*Science*'s online publish-before-print service, *Science*
Express, Schoen et al.
( http://www.sciencemag.org/cgi/content/short/1066171 ) reported
another breakthrough: The development of a true single-molecule
field-effect transistor, only two nanometers in length.  These
seminal studies, noted G. Y. Tseng and J. C. Ellenbogen
( http://www.sciencemag.org/cgi/content/short/294/5545/1293 ) in
an accompanying Perspective, constitute "an indicator of how far
molecular electronics and nanotechnology have come."

--McDevitt et al.
( http://www.sciencemag.org/cgi/content/short/294/5546/1537 ), in
the 16 Nov 2001 issue, reported progress in the realm of practical
nano-devices in a very different arena -- that of cancer therapy. 
Putting together two traditional strands of cancer treatment,
radiation therapy and the use of monoclonal antibodies, the group
devised a sort of nanoscale nuclear "smart bomb":  They fashioned
a molecule-size nuclear generator that pumps out tumor-killing
alpha particles with a dosage and half-life suitable for therapeutic
use, and then bound the device to an antibody targeted to the tumor
cells.  In experiments with mice, treatment with the souped-up
antibodies diminished tumor size and prolonged survival without
toxicity -- a finding that holds out the prospect of anticancer
nuclear nanogenerators for human cancers as well.

--Bone is an engineering marvel -- a material whose light weight,
rigidity, and strength have made it something of a lodestar for
materials scientists.  The roots of bone's unique properties lie in its
nanostructure, basically a collection of collagen fibers bound by an
aligned microcrystalline calcium-phosphate mineral called
hydroxyapatite.  But development of a practical substitute for
bone, or of practical engineered materials with bone-like structure
and strength, requires being able to grow the tiny hydroxyapatite
crystallites not on collagen but on a completely synthetic substrate. 
Hartgerink et al. (23 Nov 2001;
http://www.sciencemag.org/cgi/content/short/294/5547/1684 )
were able to accomplish that feat, developing a completely
synthetic self-assembling material that mimics bone's structure
down to the nanoscale.  As is explained in an accompanying news
article
( http://www.sciencemag.org/cgi/content/short/294/5547/1635a ),
the group believes that the technique could ultimately find use not
only in manufacturing synthetic bone, but in applications ranging
from high-strength composite materials to circuitry for molecular
computers.


New Spins on Magnetism
http://www.sciencemag.org/cgi/content/short/294/5546/1483

Although used as practical tools for millennia, and understood
quantitatively since the early 20th century, magnetic materials
have never quite lost their air of mystery.  Yet understanding, and
harnessing, the behavior of increasingly complex magnetic systems
and materials holds much of the key to the information processing
and electronics of the future, as was richly demonstrated in
*Science*'s 16 Nov 2001 special issue on the subject.  Among the
offerings was a review by Freeman and Choi detailing recent
advances in magnetic microscopy, the blend of theory and
application that is pushing the imaging of magnetic phenomena
down to nanometer and femtosecond resolutions.  Wolf et al.,
meanwhile, examined the burgeoning field of "spintronics," the
development of devices and techniques for manipulating the
quantum-mechanical property of electron spin that forms the root
of magnetism in materials -- a research path that could ultimately
transcend the limitations of traditional semiconductor-based
electronics, leading to a new generation of fast and highly efficient
electronic devices.  And Bramwell and Gingras explored the highly
complex interactions of the "spin ice state" -- a "frustrated"
magnetic system, the understanding of which could have
implications in areas ranging from superconductivity to
ferromagnetic films.  On another front in magnetic materials, Rajca
et al.
( http://www.sciencemag.org/cgi/content/short/294/5546/1503 )
reported in the same issue on a new technique for creating
magnetic materials out of an apparently unpromising material --
organic polymers -- that could ultimately find use in lightweight
and low-cost applications.


Asteroid Families

It's perhaps the ultimate nightmare scenario:  a rogue near-Earth
asteroid (NEA) smashes into our planet, wreaking ecological
destruction not seen since the demise of the dinosaurs 65 million
years ago.  That apocalyptic vision, powerful enough to spawn
several Hollywood movies, underscores the need to comprehend
the populations, orbital characteristics, and size distributions of
NEAs, the topic three reports in the 23 Nov 2001 *Science*. 
Stuart
( http://www.sciencemag.org/cgi/content/short/294/5547/1691 )
analyzed the wealth of data from the Lincoln Near-Earth Asteroid
Research (LINEAR) project to estimate the size and distribution of
the NEA population at large.  He found that the number of NEAs
more than a kilometer in diameter amounts to more than 1200, a
higher number than recent estimates would suggest -- but that orbit
of the NEA population is more highly inclined to the ecliptic than
had previously been thought, which may slightly reduce the
probability of an impact with Earth.  Bottke et al.
( http://www.sciencemag.org/cgi/content/short/294/5547/1693 )
modeled the Yarkovsky effect, a thermal radiation force associated
with large asteroid bodies in the main asteroid belt, between Mars
and Jupiter.  Their study suggested that the effect may be a prime
mover shuttling kilometer-scale asteroids toward the gravitational
resonance regions that serve as embarkation points for ejecting
them into near-Earth orbits.  Finally, Michel et al.
( http://www.sciencemag.org/cgi/content/short/294/5547/1696 )
numerically simulated the processes of collision and gravitational
reaccumulation that explain the size distribution of asteroid
"families" in the main belt -- including the outcasts of those
families, the orbitally perturbed members that can venture off to
become NEAs.

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