Welcome to the March, 2002 issue of Science Roundup!
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In This Month's SCIENCE ROUNDUP:
A Systems Approach
Ancient DNA: North and South
Finding the Right Mismatch
A Hidden Enemy Revealed
Keeping an Eye on What Matters
The Power of Loss
Bubble Fusion?
Toward Cheaper MRI
Spinning Tales of Black Holes
Out of Asia
TV Viewing and Aggression
Public Health: So Much Done, So Much to Do
Radium Hero
A Systems Appoach
http://www.sciencemag.org/cgi/content/short/295/5560/1661
The vast human complement of thousands of genes and proteins
actually forms only the "parts catalog" of much more complex
biological systems and regulatory networks, from cell to organ to
organism. The study of such complexity -- using tools and ideas
gleaned from not only from life science but also from engineering,
physics, mathematical modeling, and computer science -- is
spawning the new discipline of "systems biology," explored in a
*Science* special issue on 1 Mar 2002. H. Kitano, in an overview
article, set the tone for the issue, noting that the maturing of
computational and molecular-biology techniques offers "a golden
opportunity" for understanding biological systems. M. E. Csete
and J. C. Doyle presented an engineer's perspective on biological
complexity, drawing analogies between biological regulatory
systems and central engineering concepts such as feedback loops,
protocols, modularity, and redundancy. Davidson et al. applied
systems thinking to developmental biology, summarizing the
genomic regulatory network for the developing sea urchin embryo.
Finally, D. Noble reviewed progress in systems-level modeling of
the function of the heart, perhaps the most advanced example thus
far of "whole-organ modeling." Rounding out the presentation
were additional articles on *Science*'s Web-based Signal
Transduction Knowledge Environment ( http://www.stke.org ).
Ancient DNA: North and South
Two reports in the 22 Mar 2002 *Science* took a new look at
some very old bones -- and harvested some surprising evolutionary
insights:
--Barnes et al.
( http://www.sciencemag.org/cgi/content/short/295/5563/2267 ),
taking advantage of the natural preservation capabilities of
permafrost, used DNA from the bones of 36 subarctic brown bears,
the radiocarbon dates of which spanned the past 60,000 years, to
reconstruct the species' migration history at the "biological
crossroads of the Beringia land bridge, which connected North
America and Asia until around 11,000 years ago. Among other
things, the group found that the last big changes in the species'
"phylogeographic structure" occurred some 10,000 years *before*
the wrenching environmental impacts of the last glacial maximum
-- which suggests that the histories of mammalian taxa from this
period are more complex than previously thought.
--Lambert et al.
( http://www.sciencemag.org/cgi/content/short/295/5563/2270 ),
on the other side of the world, sequenced mitochondrial DNA from
the bones of long-dead Adelie penguins in Antarctica. Because
these birds return to the same roosting sites year after year -- with
single colonies persisting for millennia -- the researchers were able
to use 96 radiocarbon-dated, ice-preserved bones from only 13
Antarctic locations to construct a DNA record dating back some
7,000 years. From that record, they estimated rates of evolutionary
change two to seven times faster than previous estimates based on
only a few data points.
E. Pennisi
( http://www.sciencemag.org/cgi/content/short/295/5563/2197 )
described the two studies in a news story in the same issue.
Finding the Right Mismatch
Work published in the 15 Mar 2002 *Science* has revealed that
natural killer (NK) cells -- the immune-system soldiers that target
cancerous and virus-infected cells in the body and chemically
destroy them -- may play a surprising role in another arena:
helping to prevent rejection of bone marrow transplants in
leukemia patients. Most such transplants seek as close a match as
possible between donor and host, to avoid host-versus-graft disease
(rejection of the transplanted material by the host) and graft-
versus-host disease (attack by the transplanted tissue's immune
system against the host tissues). In studies involving both human
leukemia patients and laboratory mice, however, Ruggeri et al.
( http://www.sciencemag.org/cgi/content/short/295/5562/297 )
found that a carefully tuned *mismatch* between the donor and
host tissues -- in genetic loci important for NK cell action -- may
actually promote a more successful transplant, and at the same
time prevent leukemia relapse in the recipients. As explained in a
Perspective by K. Kaerre
( http://www.sciencemag.org/cgi/content/short/295/5562/2029 ),
appropriately mismatched NK cells from the donor apparently can
attack antigen-presenting cells of the host, thereby preventing the
proliferation of host-destroying T cells in the donor tissue (and
stemming graft-versus-host disease); neutralize the host's own T
cells (minimizing host-versus-graft disease); and still assault the
leukemia cells remaining in the host after chemotherapy (helping
to prevent leukemia relapse). The result suggests that patients
could be "preconditioned" with donor NK cells before transplant,
and thereby avoid more destructive regimens, such as irradiation,
now used to set up bone marrow transplants.
A Hidden Enemy Revealed
Nearly a quarter of a million people living in Africa and South
America have lost their sight to river blindness, a disease tied to
infection and inflammation of the eyes by tiny, parasitic nematode
worm larvae. Drugs used to treat the disease by killing the larvae
have had only partial success -- possibly because the real culprit in
river blindness, according to research published in the 8 Mar 2002
*Science*, may be not the worms at all, but symbiotic bacteria,
*Wolbachia*, that live within them. Saint Andre et al.
( http://www.sciencemag.org/cgi/content/short/295/5561/1892 )
found that extracts of worm proteins without *Wolbachia*
bacterial proteins, applied to the eyes of mice, caused much less
damage -- measured by clouding in the mice's eyes -- than did
solutions of including both worm and *Wolbachia* proteins. As
noted in a news article by E. Pennisi
( http://www.sciencemag.org/cgi/content/short/295/5561/1809 ), the
case is not open ad shut: proteins from the worm larvae may also
have a role in the eye inflammation that characterizes the disease.
Still, the work points to the possibility that antibiotic therapies for
the disease could pack a double punch against river blindness: By
killing the *Wolbachia*, such therapies could both disrupt the life
cycle of the worms (which need the symbiotic bacteria to
reproduce) and eliminate the bacteria's ability to wreck its own
havoc on victims' sight.
Keeping an Eye on What Matters
Every few seconds while you're awake, your eyes perform a
"saccade" -- a rapid shift from one fixation point to another. As
your eyes shift, your brain is busily editing the visual signal,
retaining only the images of the fixation points, so that crucial
information is not overwhelmed by useless data about the shift
itself. But is this "saccadic suppression" based on information that
the retina transmits to the primary visual cortex, or could other
areas of the brain be involved? In the 29 Mar 2002 *Science*,
Thiele et al.
( http://www.sciencemag.org/cgi/content/short/295/5564/2460 )
offered the first compelling evidence for the latter hypothesis.
In experiments with monkeys, the group found that when the
subjects' eyes shifted in a saccade, the response of certain neurons
in the brain's middle temporal (MT) and middle superior temporal
(MST) areas -- which specialize in detecting and perceiving
motion -- differed from the response when the scene the monkeys
were viewing was externally shifted. The result suggests, as M.
Barinaga
( http://www.sciencemag.org/cgi/content/short/295/5564/2347 )
noted in a news article in the same issue, that the signal to turn on
the important editing function of saccadic suppression may come
from not from the retina, but from areas of the brain responsible
for the eye motion itself.
The Power of Loss
"I'm due for a win": It's a statement heard from the stockbroker's
office to the gambling table -- and it iplies that participants in
such games keep an unconscious mental tally of how well things
are going at any one moment. In the 22 Mar 2002 *Science*,
Gehring and Willoughby
( http://www.sciencemag.org/cgi/content/short/295/5563/2279 ) tied
this sort of split-second gain-or-loss assessment to a specific brain
region, the anterior cingulate cortex (ACC), a small area tucked
between the cerebral hemispheres. The researchers hooked
subjects to an electroencephalogram (EEG) and had them play a
simple, two-choice gambling game. Immediately after making
their choice, the subjects learned both the outcome and what the
result *would* have been had they made the alternate choice, a
scheme that allowed the subjects to assess not only absolute, but
relative, gain or loss. Within 200 to 300 milliseconds, the EEG
recorded a negative trace in the area corresponding to the ACC,
with the amplitude greater in losses than in gains -- tangible
evidence that losses loom largest in gamblers' minds. And the
researchers found that after a loss, subjects were apt to make a
larger bet in subsequent trials -- and that the negative EEG spike
was correspondingly larger if the subsequent bet, too, turned out to
be a loser. Thus, the ACC could turn out to be the area of the brain
responsible for the gambler's "due for a win" emotional calculus,
as noted in an accompanying news article by G. Miller
( http://www.sciencemag.org/cgi/content/short/295/5563/2193a ).
Bubble Fusion?
http://www.sciencemag.org/feature/data/hottopics/bubble/index.shtml
One of the biggest stories in *Science* in the past month came
with a hefty measure of controversy: In the 8 Mar 2002 issue,
Taleyarkhan et al. reported that they had seen evidence consistent
with nuclear fusion in a small, tabletop experiment. The group
subjected acetone in which the hydrogen atoms had been replaced
with deuterium ("heavy" hydrogen, with a nucleus consisting of
one proton and one neutron) to acoustic shock wave, which
caused the nucleation, growth, and then catastrophic collapse of
tiny bubbles in the solution. The collapse of such bubbles is
known to produce very high temperatures and pressures -- indeed,
in certain conditions, the bubbles' collapse is associated with
flashes of light, a phenomenon known as sonoluminescence.
Taleyarkhan et al., however, reported that their experiments
yielded levels of tritium (hydrogen atoms consisting of one proton
and two neutrons) above background levels, and also found
evidence of neutron emissions at a characteristic energy -- both
hallmarks of deuterium-deuterium fusion. And numerical
modeling of the system suggested that the collapsing bubbles reach
temperatures on the order of 10 million Kelvins, consistent with
the conditions required for fusion reactions.
In addition to the Taleyarkhan et al. paper itself, *Science* offered
a number of other items in the same issue to provide context on
this highly controversial result: a Perspective by F. D. Becchetti on
the theory behind the experiment; a news article by C. Seife on the
heat the paper has generated in the physics community; and an
editorial by *Science*'s Editor-in-Chief, Donald Kennedy, on why
the journal decided that "publication is the right option."
Toward Cheaper MRI
Magnetic resonance imaging (MRI), central to advanced medical
diagnostics, is based on nuclear magnetic resonance (NMR)
spectroscopy, in which the structure of individual molecules is
determined by the precession, or wobbling, of their constituent
atoms' nucleii in an externally applied magnetic field. It's also
costly, because of the enormous and expensive magnets required to
attain a decent signal in conventional MRI systems. Work by
McDermott et al.
( http://www.sciencemag.org/cgi/content/short/295/5563/2247 )
in the 22 Mar 2002 *Science*, however, could ultimately point to
much more affordable MRI. The group used a second magnetic
signature of atoms within molecules, kown as J-coupling, the
signal for which is independent of the strength of the applied
external magnetic field. Using an extremely sensitive DC
superconducting quantum interference device (SQUID), they were
able to obtain NMR spectra in external magnetic fields less than
one-tenth as strong as the Earth's ambient magnetism. Many
hurdles remain before the new technique can be applied to medical
imaging, as noted in a news article by R. Service
( http://www.sciencemag.org/cgi/content/short/295/5563/2195a ). If
those hurdles are cleared, however, it's possible that J-coupling
could ultimately lead to MRI systems "cheap enough for the
doctor's office."
Spinning Tales of Black Holes
Black holes offer paradox on a grand scale. Mass and energy sinks
with gravitational pulls so powerful that not even light can escape,
they nonetheless are associated with spectacular high-energy
phenomena in their surroundings, such as jets of plasma that
geyser away from the black hole at 99% of the speed of light. Two
articles in *Science* during the past month delved into the way
that rapidly spinning black holes, known as Kerr black holes,
might achieve these cosmic conjuring tricks -- and presented some
strategies for future investigators to observe these elusive objects:
--Koide et al.
( http://www.sciencemag.org/cgi/content/short/295/5560/1688 ;
1 Mar 2002) presented a complex and elegant numerical model
showing one way that energy sufficient to power plasma jets might
be extracted from a Kerr black hole. In the model, the rapid
spinning of the hole within a powerful magnetic field rotationally
drags the fabric of space immediately around the hole, which in
turn creates a torsional wave that siphons off the energy in the
plasma surrounding the hole along the magnetic field lines. The
process depletes the energy of the plasma near the hole to negative
values -- and the spin velocity (and thus the energy) of the black
hole is reduced to balance the books R. D. Blandford
( http://www.sciencemag.org/cgi/content/short/295/5560/1653 )
described the work in a Perspective in the same issue.
--Because of their energy emissions, Kerr black holes offer a
potential observational window into black holes, which are
otherwise by definition invisible. Van Putten and Levinson
( http://www.sciencemag.org/cgi/content/short/295/5561/1874 ;
8 Mar 2002) have painstakingly calculated the fractions of energy
that might be released from spinning black holes through different
energy "channels" such as gravitational waves, electromagnetic
waves, thermal emissions, and high-energy neutrino emissions.
The resultant understanding could ultimately allow astrophysicists
to "see" Kerr black holes by observing their gravitational radiation -
- and to better grasp the physics behind such high-energy cosmic
events as gamma ray bursts.
Out of Asia
Around 55 million years ago, Earth saw its most striking biotic
change since the extinction of the dinosaurs: the emergence of a
wave of anatomically modern new mammal groups across all
continents of the Northern Hemisphere. The faunal shift was
profound enough to mark the end of one geological epoch (the
Paleocene) and the start of another (the Eocene). Fossil evidence
has tantalizingly suggested Asia as the late Paleocene cradle of this
burst of mammalian diversity -- but the geochronology to back up
such a hypothesis has been sparse. Now, in the 15 Mar 2002 issue
of *Science*, Bowen et al.
( http://www.sciencemag.org/cgi/content/short/295/5562/2062 )
have provided solid new evidence for the Asian claim. The group
studied a dramatic spike in the carbon isotope record that serves as
a worldwide marker of rocks at the Paleocene/Eocene (P/E)
boundary, and that also likely records a period of brief but intense
global warming at that time. Applying that marker to some key
fossil-bearing strata, Bowen et al. were able to document that the
Asian appearance of a variety of impotant modern taxa, including
primates, occurred no later than the P/E boundary -- and thousands
of years *before* the Eocene appearance of similar taxa in Europe
and North America. As C. Beard noted in an accompanying
Perspective
( http://www.sciencemag.org/cgi/content/short/295/5562/2028 ),
the work not only strengthens the notion that Asia was a late
Paleocene mammalian "Garden of Eden," but also underscores the
role of global warming as "the driving force behind the most
profound biotic reorganization of the Age of Mammals."
TV Viewing and Aggression
A long-term study published in the 29 Mar 2002 *Science* has
provided additional quantitative support for something that many
parents have long known at a gut level: violent TV boosts
aggression in children who watch it. In the study, Johnson et al.
( http://www.sciencemag.org/cgi/content/short/295/5564/2468 )
tracked 707 children, randomly selected from two counties in
northern New York State, over a period of 17 years, beginning
when the children were 1 to 10 years of age. The results,
particularly among males, were sobering: Adolescent boys aged 14
with a previous history of aggression who watched 1 to 3 hours of
TV daily were five times more likely during their young adulthood
to commit aggressive acts (ranging from physical fighting to
robbery) than were similar adolescents who watched less than an
hour a day. Even among adolescents with no previous history of
aggression, those who watched 1 to 3 hours of TV a day were more
than twice as likely to engage in subsequent aggression as were
those who watched less than an hour. A Perspective by C. A.
Anderson and B. A. Bushman
( http://www.sciencemag.org/cgi/content/short/295/5564/2377 )
looked at the study's implications for the larger debate on media
violence and its societal impacts.
Public Health: So Much Done, So Much to Do
http://www.sciencemag.org/cgi/content/summary/295/5562/2035
Despite the profound advances in public healh over the past
century, far more remains to be accomplished -- both in fighting
resilient enemies like HIV, tuberculosis, and drug-resistant strains,
and in getting the fruits of public-health victories already won in
the affluent West to the poorer, and needier, populations of the
developing world. A special section in the 15 Mar 2002 *Science*
provided a glimpse at several key topics informing today's
multivalent public-health debate. Review and Viewpoint articles
explored the feasibility of a major program to improve the health
of the global poor; the resources and strategies necessary to defeat
the worldwide scourge of tuberculosis (including the insidious new
multi-drug-resistant TB strains); and the challenges implicit in
communicable-disease surveillance even in advanced societies
such as the European Union. A special News Focus in the same
issue investigated the serious supply shortage of common vaccines
now threatening the U.S., and the debate over whether the last
remaining known research stocks of smallpox should be destroyed
-- a debate that has gained a new dimension with the recent fears
regarding global bioterrorism.
Radium Hero
http://www.sciencemag.org/cgi/content/summary/295/5560/1647
The March 2002 Portraits of Science essay zeroed in on one of
history's most celebrated scientists: Marie Curie, whose early
twentieth century work on the then-novel phenomenon of
radioactivity snagged her not one, but two Nobel prizes. In the
essay, R. M. Macklis traced Curie's life from her birth in Warsaw
to her later, pioneering work in Paris with her husband, Pierre; her
continued work in both pure and applied science after Pierre's
premature death; her patriotic efforts during World War I to
organize a fleet of mobile radiology trucks -- "little Curies" -- for
use in treating the French wounded on the front lines; and her
emergence as a kind of scientific superstar in the 1920s, partly
owing to the publicity-seeking efforts of n American society-page
journalist, Marie "Missy" Meloney. Sizing up Curie's life,
Macklis wrote: "[I]n this current era of 'big science' it is clear that
major scientific and medical advances require both creative
inspiration and excellent organizational skills, both of which Marie
had in abundance."
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