Science Roundup

This month in Science Roundup:

 

  • Breaking the Ice
  • Keeping Cool
  • Detection Technologies
  • Powering Artificial Muscles
  • Cassini at Enceladus
  • Impact of the Sunda Megaquake
  • Early Maya Writing
  • A Living Rodent Fossil
  • Grain-Shattering Insights
  • Bird Flu Clues
  • Chimps Lend a Hand
  • Protein Misfolding and Neurodegeneration
  • Type 1 Diabetes Reversal, Revisited
  • Plankton Biogeography

 

This month's Science Roundup is sponsored by
The AAAS Member-Get-a-Member Program

No one knows the value of AAAS better than our members. That's why we are asking you to refer a friend or colleague to help AAAS do even more to advance science and serve society. Bring in just one new member, and receive a AAAS/Science umbrella. Three members equal a travel bag; five members, a USB memory stick; 10 members, an iPod Shuffle; 50 members, a trip for two to the AAAS Annual Meeting; 100 members, an iMac computer. Start earning your rewards through our newest member benefit program. Go to http://promo.aaas.org/mgam. For details, visit http://promo.aaas.org/mgamtc/. Promotion ends 31 December 2008.

 

 

Breaking the Ice

http://www.sciencemag.org/sciext/ice/

 

The Greenland and Antarctic ice sheets are losing mass to the oceans at an alarming rate, and scientists fear that continued climate warming may lead to catastrophic sea-level rise during the next several centuries.  In a special collection of articles published in the 24 Mar 2006 issue, Science examined the state of the world's ice and its sobering implications (see the News Focus by R. Kerr).  Contrary to the assumption that ice sheets respond slowly to climate change, with dynamic response times measured in centuries to millennia, new research reports document dramatic changes in just the last few years.  Greenland glacier earthquakes produced beneath ice streams and outlet glaciers have doubled in frequency over the past 5 years.  And satellite measurements of Earth's gravity reveal that the mass of ice in Antarctica decreased from 2002 to 2005, mainly from losses in the West Antarctic Ice Sheet.  Are these worrisome trends likely to continue?  Faced with uncertainty about the present, paleoclimatologists look to the past (see the related Editorial by Kennedy and Hanson).  Simulations of ice dynamics and climate 130,000 years ago -- when polar temperatures were warmer and the sea level was higher -- indicate that melting of ice sheets in Greenland and the Canadian Arctic raised sea level by 2.2 to 3.4 meters during that time.  When compared with warming projected to occur over the next century, the simulations imply that widespread melting of the Greenland Ice Sheet is possible.  For more on the disappearance of the world's great ice sheets, listen to the 24 March Science Podcast, featuring commentary from news writers R. Kerr and E. Kinitsch ( http://www.sciencemag.org/about/podcast.dtl ).

 

 

Keeping Cool

 

Many traditional refrigeration technologies use environmentally damaging chemicals or require a tremendous amount of energy, so the search has been on for safer, more efficient alternatives.  According to a Report in the 3 Mar 2006 Science, hope may be found in a thin lead film.  Electrocaloric materials, which can change temperature when an applied electric field is removed from them, represent one route to improved cooling, but no materials thus far have proven effective enough for commercial applications.  Now Mischenko et al. ( http://www.sciencemag.org/cgi/content/short/311/5765/1270 ) report on a "giant electrocaloric effect" in perovskite, an insulating oxide that contains lead, zirconium, and titanium.  The researchers calculate that the material cools down by as much as 12 degrees kelvin with an applied voltage of just 25 V.  That means that it is more than 100 times better at cooling surrounding matter than other known substances.  Although practical applications are still years away, the results demonstrate the possibility of using electrocaloric thin films as cooling solutions, perhaps for electronic components like computer chips.

 

 

Detection Technologies

http://www.sciencemag.org/sciext/detection/

 

As scientists delve deeper into the complexities underlying the natural world, their tools for detection, measurement, and analysis are becoming ever more sophisticated.  In a special section of the 17 Mar 2006 issue, Science explored some of the technological advances aiding researchers in fields ranging from earth science to cell biology.  Two Review articles examined the power of ambient mass spectrometry, which enables the identification of chemical compounds in ordinary samples in their native environment, and the applications of microelectrodes in cellular chemistry.  Three Reports highlighted an approach for detecting biomolecules that involves microcantilevers, a method to observe single protein molecules as they are made in live bacteria cells, and a new spectroscopic method for detecting diffuse species like atmospheric contaminants.  Related Perspectives in the Signal Transduction Knowledge Environment explored techniques for single-molecule tracking and the challenges of using nanoparticles to manipulate cellular processes and deliver therapeutic agents.

 

 

Powering Artificial Muscles

 

Humans are capable of strenuous activity because our bodies can store the energy required to power our muscles.  But the development of effective prosthetic limbs and active, autonomous robots has been limited by the need for electrically powering artificial muscles, motors, or actuators.  In a Report in the 17 Mar 2006 Science, Ebron et al. ( http://www.sciencemag.org/cgi/content/short/311/5767/1580 ) describe the development of two different types of artificial muscles that, like natural muscles, convert chemical energy of an energetic fuel to mechanical energy.  One design involves a catalyst-containing carbon nanotube electrode that simultaneously acts as a muscle, a fuel cell, and a supercapacitor electrode to store the electrical energy and convert it into mechanical energy (dimensional changes in the nanotubes).  In the second design, chemical energy in the fuel (hydrogen, methanol, or formic acid) is converted to heat by a catalytic reaction of a mixture of fuel and oxygen in the air.  The resulting temperature increase in this "shorted fuel-cell muscle" causes contraction of a shape memory metal muscle wire that supports the catalyst.  Subsequent cooling completes the work cycle by causing expansion of the muscle wire.  This second artificial muscle achieves actuator stroke and power density comparable to that of natural skeletal muscle, but is able to do 100 times greater work per cycle.  As noted in an accompanying Perspective by J. D. Madden ( http://www.sciencemag.org/cgi/content/short/311/5767/1559 ), the new work "changes the perception of what is possible."

 

 

Cassini at Enceladus

http://www.sciencemag.org/cgi/content/short/311/5766/1388

 

The exploration of Saturn by the Cassini mission has yielded a rich collection of data about the planet and its rings and moons.  In a special section of the 10 Mar 2006 Science, two Research Articles, seven Reports, and two Perspective articles highlighted a wealth of new information provided by three recent flybys of Saturn's enigmatic moon Enceladus.  With a diameter of only about 500 kilometers, Enceladus is the sixth largest saturnian satellite -- but what it lacks in size it makes up for with geologic activity.  From an underground heat source at its south pole, Enceladus spouts a spectacular plume of water ice, gas, and dust thousands of kilometers into space.  This plume is the most likely source of particles forming Saturn's outermost E ring.  Other images reveal that tidal forces have twisted and buckled the moon's surface ice, producing long ridges and fractures and that the south polar landscape is actively being resurfaced by cryovolcanism and fresh snowfall.  That a tiny moon turns out to be one of the most geologically dynamic objects in the solar system is a big surprise that makes the prospect of future Cassini discoveries all the more tantalizing.

 

 

Impact of the Sunda Megaquake

 

On 28 March 2005, just three months after the devastating Sumatra-Andaman earthquake and tsunami, another giant quake rattled offshore northern Sumatra.  This magnitude 8.7 Sunda megathrust earthquake produced dramatic tectonic deformation along a 400-kilometer strip of islands and tiny coral atolls in the western Sumatran archipelago.  In a Research Article in the 31 Mar 2006 Science, Briggs et al. ( http://www.sciencemag.org/cgi/content/short/311/5769/1897 ) combined measurements of uplifted coral and Global Positioning System data to map the pattern of deformation in the region.  The data reveal belts of uplift nearly 3 meters high parallel to the trench, and a 1-meter-deep subsidence trough between the islands and the main Sumatran coast.  Surface measurements suggest that the fault between the Australian Plate and the Sunda plate slipped about 11 meters under the Sumatran archipelago.  Unlike the December 2004 event, however, the Sunda megaquake produced no substantial tsunami because its rupture length was shorter, the maximum uplift was substantially less, and most of the uplift occurred on land rather than deep under water.  The researchers also identified a barrier -- a wrinkle in the plate boundary -- that may help explain why the Sunda rupture stopped where it did.  A related Perspective by R. Bilham ( http://www.sciencemag.org/cgi/content/short/311/5769/1873 ) underscored the need for earthquake-resistant construction and replacement throughout the region.

 

 

Early Maya Writing

 

Archaeological discoveries at San Bartolo, Guatemala, have provided a rich trove of information about the ancient Maya culture.  In a Report in the 3 Mar 2006 Science Saturno et al. ( http://www.sciencemag.org/cgi/content/short/311/5765/1281 ) described new finds from San Bartolo that shed light on the emergence of writing in the New World.  Writing is thought to have emerged in the New World in the Olmec culture, which thrived between about 1200 and 300 B.C.  Notwithstanding a few exceptions, clear writing in Maya ruins could only be dated to a period several centuries later.  The new evidence -- a series of painted hieroglyphs -- lies on preserved walls and plaster fragments from a Maya temple built between 200 and 300 B.C.  One of the glyphs appears to represent a lord or other noble, but the meaning of this, as well as many Preclassic texts, remains a mystery.  Nevertheless, the finding suggests that writing emerged in the Maya region much earlier than previously thought, near the time when it appeared widely elsewhere in Mesoamerica.  An accompanying Perspective by S. D. Houston ( http://www.sciencemag.org/cgi/content/short/311/5765/1249 ) highlighted the Report.

 

 

A Living Rodent Fossil

 

In a recent survey of biodiversity in Laos, scientists reported the discovery of a new species of rodent, Laonastes aenigmamus, interpreted as a member of an entirely new family of living mammals.  Now a Report by Dawson et al. ( http://www.sciencemag.org/cgi/content/short/311/5766/1456 ) in the 10 Mar 2006 Science shows that Laonastes is actually a surviving member of a group believed to have been extinct for 11 million years.  The team compared skeletal remains of the squirrel-like animal with those of a poorly known family of Southeast Asian rodents called Diatomyidae, known from early Oligocene to late Miocene sites in Pakistan, India, Thailand, China, and Japan.  The tooth and jaw morphology of these ancient rodents bears a striking resemblance to that of Laonastes, and even the microstructure of their tooth enamel is remarkably similar.  Comparable body and tail size and a number of shared postcranial characters provide further support that Laonastes is a member of Diatomyidae.  As noted in a related ScienceNOW story by K. Unger ( http://sciencenow.sciencemag.org/cgi/content/full/2006/309/1 ), finding a living example of a fossilized family represents a very rare case of the "Lazarus effect --  the reappearance of a taxon after a long gap in the fossil record.

 

 

Grain-Shattering Insights

 

Cereal crops including wheat, rice, maize, and oats were domesticated from wild grass species and now constitute a primary food source for human populations worldwide.  Two studies reported in the 31 Mar 2006 Science offered new insights into when and how the domestication of two major cereals came about.  A Report by Li et al. (published online 9 Mar 2006; http://www.sciencemag.org/cgi/content/short/311/5769/1936 ) looked at the molecular basis of successful rice domestication.  Because wild grasses tend to release their mature seed fairly easily to facilitate widespread propagation (a process called shattering), a necessary step toward domestication was to select plants that could hold on to ripe grains to allow for harvesting.  Interestingly, the team found that the retention of rice grains exhibited in domesticated species of today is the result of a single nucleotide change in a transcription factor gene.  The gene is expressed late in grain development at the junction between the seed and the mother plant.  The mutation reduces shattering by hindering separation of the mature grain.

 

In a Brevium, Tanno and Willcox ( http://www.sciencemag.org/cgi/content/short/311/5769/1886 ) provided a timeline of wheat domestication based on analysis of wheat remains from archaeological sites in northern Syria and southeastern Turkey.  Because wild ears of wheat shatter at maturity into small pieces called spikelets, and ears of domesticated wheat do not shatter as readily, the researchers were able to identify the ancient fragments as wild or domestic based the shape of their spikelet scars.  The analysis indicates that wheat domestication started early, perhaps soon after humans settled in the Near East around 11,000 years ago.  However, the persistence of wild wheat in cultivated fields suggests that it was a slow process.

 

 

Bird Flu Clues

 

The spread of H5N1 avian influenza viruses from Asia to Europe and Africa have raised global concern about the potential for human-to-human transmission and the prospect of a pandemic.  In an attempt to better understand the molecular basis of avian influenza virulence, Obenauer et al. ( http://www.sciencemag.org/cgi/content/short/311/5767/1576 ) performed a large-scale sequence analysis of avian influenza viruses, including 2196 genes and 169 complete genomes culled from wild birds and poultry. Their results, reported in the 17 Mar 2006 Science (and published online 26 Jan 2006), confirm known hallmarks of flu biology, including variability in the two major surface proteins hemagglutinin and neuraminidase, and the high frequency of gene segment reassortment.  Other results suggest that, in addition to two known surface proteins, a previously unnoticed amino acid sequence in a small nonstructural viral protein called NS1 may contribute to virulence.  This protein is present only in infected cells and regulates many cell functions during infection.  Intriguingly, the recent high-mortality H5N1 outbreaks are all characterized by NS1 proteins with a particular "avian" sequence motif, whereas NS1 proteins from low-virulence human influenza viruses contain a different motif that appears to be less capable of binding to host proteins.  An accompanying Perspective by R. M. Krug ( http://www.sciencemag.org/cgi/content/short/311/5767/1562 ) highlighted the findings.

 

Related research published online Science Express on 23 Mar 2006 helped explain why the avian influenza virus can be lethal to humans but is so difficult to spread (see the News story by D. Normile in the 24 Mar issue; http://www.sciencemag.org/cgi/content/short/311/5768/1692b ).  van Riel et al. ( http://www.sciencemag.org/cgi/content/abstract/1125548 ) reported that the H5N1 virus attaches most efficiently to cells located deep within the lower respiratory tract.  Therefore, it is not easily expelled by coughing or sneezing -- the usual routes of spread.

 

 

Chimps Lend a Hand

 

Human beings routinely help others to achieve their goals, even if the recipients are strangers and there is no reward at stake.  Such behavior is extremely rare evolutionarily, leading some researchers to argue that cooperation and altruism are uniquely human behaviors.  Two studies reported in the 3 Mar 2006 Science investigated this idea by looking to our closest living relative, the chimpanzee.  Melis et al. ( http://www.sciencemag.org/cgi/content/short/311/5765/1297 ) showed that chimpanzees have the capacity to be effective collaborators.  In a series of experiments in which food was attached to an out-of-reach platform, the researchers found that individual chimps would recruit a collaborator to help retrieve the food, but only when necessary.  Like humans, the chimps also came to show a strong preference for helpers that were especially adept at the task.  In another study, Warneken and Tomasello ( http://www.sciencemag.org/cgi/content/short/311/5765/1301 ) tested human infants and young chimpanzees to see if, given the opportunity, they would commit a helpful action without reward.  They found that children as young as 18 months of age were eager to help an adult with a task, such as stacking books in a pile or placing them onto a cabinet shelf.  The chimps were also willing to help, but were much less reliable, choosing to help with only some tasks.  An accompanying Perspective by J. B. Silk ( http://www.sciencemag.org/cgi/content/short/311/5765/1248 ) highlighted the studies.

 

 

Protein Misfolding and Neurodegeneration

 

A number of neurodegenerative disorders such as Huntington's disease, Parkinson's, and Alzheimer's, have been linked to genetic mutations that result in the chronic aggregation of a single specific protein.  What is puzzling about the progression of each of these diseases is the disruption of such a wide range of cellular pathways including those involved in transcription, energy metabolism, and cell death.  In a Report in the 10 Mar 2006 Science (published online 9 Feb 2006), Gidalevitz et al. ( http://www.sciencemag.org/cgi/content/short/311/5766/1471 ) used a genetic approach to investigate whether there might be a common mechanism by which a single "aggregation-prone" protein can have such diverse effects.  The researchers used a worm model of polyglutamine (polyQ) diseases, a subset of neurodegenerative diseases including Huntingon's, in which a long stretch of glutamine residues in the causative protein spurs aggregation and toxicity.  Their experiments show that polyQ proteins actually disrupt the global balance of protein folding quality control.  As cells try to eliminate chronic protein aggregates, other misfolded proteins may go undetected, leading to dysfunction of many structurally and functionally unrelated proteins in a variety of cellular pathways.  This in turn exacerbates misfolding of the aggregation-prone protein, perhaps because the overall folding capacity of the cell is compromised.  An accompanying Perspective by G. P. Bates ( http://www.sciencemag.org/cgi/content/short/311/5766/1385 ) highlighted the study.

 

 

Type 1 Diabetes Reversal, Revisited

 

Type 1 diabetes is a chronic disease that occurs when the body attacks its own insulin-producing beta-islet cells in the pancreas.  Research on potential treatments has therefore focused both on ways to curtail the destructive immune response and on ways of regenerating beta cells.  In 2003, researchers reported that treatment involving an immune-modulating agent, along with donor spleen cells, and a temporary transplant of new islet cells could reverse type 1 diabetes in mice and that the restoration of beta cells was due to differentiation of stem cells from the spleen.  In the 24 Mar 2004 Science three teams reported that this protocol does alleviate symptoms of type 1 diabetes in the same mouse model, but not via spleen cell transdifferentiation as had been suggested.  Chong et al. ( http://www.sciencemag.org/cgi/content/short/311/5768/1774  ), Nishio et al. ( http://www.sciencemag.org/cgi/content/short/311/5768/1775 ), and Suri et al. ( http://www.sciencemag.org/cgi/content/short/311/5768/1778 ) found that injection of the immune adjuvant alone promoted recovery, presumably by providing a window of opportunity for the few remaining beta-islet cells to proliferate and produce a sufficient supply of insulin.  As noted in an accompanying News story by J. Couzin ( http://www.sciencemag.org/cgi/content/short/311/5768/1694 ), the findings "weaken the theory that the spleen cradles stem cells with curative powers against mouse diabetes." However, they do provide hope for future development of immune-based therapies for the condition.

 

 

Plankton Biogeography

 

The marine bacterium Prochlorococcus dominates the ocean environment, accounting for up to half of the photosynthetic biomass and production in some regions.  As such, its abundance and dynamics have a substantial impact on open ocean ecosystems and biogeochemical cycles.  In a Research Article in the 24 Mar 2006 Science, Johnson et al. ( http://www.sciencemag.org/cgi/content/short/311/5768/1737 ) showed that closely related strains have dramatically different distributions in the water column and throughout the Atlantic Ocean.  The researchers found that strains cluster into distinct "ecotypes" based on temperature preference, light intensity, nutrient availability, and competitor abundance.  In a related Report, Coleman et al. ( http://www.sciencemag.org/cgi/content/short/311/5768/1768 ) took a closer look at two Prochlorococcus ecotypes and found that genetic diversity was concentrated in genomic islands -- clusters of related genes that may have been acquired through lateral gene transfer, possibly via bacterial viruses called phages.  Although the islands are located in about the same place on the chromosome, the genes they contain vary from strain to strain.  Genomic islands may thus be a general mechanism for niche differentiation in microbial species.  As noted in an accompanying News story by E. Pennisi ( http://www.sciencemag.org/cgi/content/short/311/5768/1697 ), the new findings "will aid the understanding of this organism's ecology and role in the environment."

 

 

This month's Science Roundup is sponsored by
The AAAS Member-Get-a-Member Program

No one knows the value of AAAS better than our members. That's why we are asking you to refer a friend or colleague to help AAAS do even more to advance science and serve society. Bring in just one new member, and receive a AAAS/Science umbrella. Three members equal a travel bag; five members, a USB memory stick; 10 members, an iPod Shuffle; 50 members, a trip for two to the AAAS Annual Meeting; 100 members, an iMac computer. Start earning your rewards through our newest member benefit program. Go to http://promo.aaas.org/mgam. For details, visit http://promo.aaas.org/mgamtc/.  Promotion ends 31 December 2008.