Science Roundup - The monthy review of Science

This month in Science Roundup:

 

The State of Influenza
http://www.sciencemag.org/cgi/content/summary/312/5772/379

The rapid spread of H5N1 avian influenza has raised global concern about the prospect of a human influenza pandemic, and preparing for such a crisis poses a great challenge to both scientists and policy makers. In a special section of the 21 Apr 2006 issue, Science examined the current picture of influenza, including News reports on antivirals and vaccines, Review and Perspective articles on flu transmission and prevention, and an Editorial underscoring the need for faster and more robust tests to diagnose infection. Three new research papers looked at how seasonal flu epidemics spread and how aspects of H5N1 virus biology may contribute to infection and transmissibility. A special online portal ( http://www.sciencemag.org/marketing/influenza/ ) offered access to previous Science articles that provide additional perspective on the flu crisis, as well as three articles from the Science Classic archive dating from 1918 and 1919 that provide contemporary thoughts on the great 1918 flu pandemic. Finally, a special podcast devoted to influenza featured interviews with Science News writers and scientists on topics related to the special section ( http://www.sciencemag.org/about/podcast.dtl ).

 

Malaria-Free Mosquitoes

Efficient strategies to control malaria will benefit from a better understanding of what happens to the malaria parasites in their wild-mosquito vectors. Now a Report in the 28 Apr 2006 Science reveals that nature already has some built-in resistance mechanisms. Riehle et al. ( http://www.sciencemag.org/cgi/content/short/312/5773/577 ) examined wild mosquitoes fed on the blood of people from Mali who were naturally infected with the human malaria parasite Plasmodium falciparum and identified a small cluster of genes that affect the insects' ability to resist the parasite. One gene on the "resistance island" called APL1 appears to play a particularly important role; when its action was blocked using RNA interference, mosquitoes became vulnerable to infection. Interestingly, this gene encodes a protein that is similar to molecules involved in natural pathogen resistance mechanisms in plants and mammals. As noted in an accompanying News story by M. Enserink ( http://www.sciencemag.org/cgi/content/short/312/5773/514a ), the team's finding that a large proportion of insects remained uninfected despite being fed infected blood suggests that mosquito resistance to the malaria parasite is much more common that previously thought.

 

Regenerating the Liver

The liver has a remarkable capacity to regenerate after severe injury or surgery, even after two-thirds of the organ has been removed. Two studies reported in Science this month revealed two factors found, unexpectedly, to be important for liver regrowth (see the News story by G. Vogel in the 14 Apr issue; http://www.sciencemag.org/cgi/content/short/312/5771/178a ).

--Lesurtel et al. ( 7 Apr 2006; http://www.sciencemag.org/cgi/content/short/312/5770/104 ) reported that in mice, regeneration of damaged liver tissue requires the neurotransmitter serotonin carried by circulating blood platelets. Mice with impaired platelet function had a drastically reduced ability to regenerate their livers, but when treated with a drug that binds serotonin receptors, liver cell proliferation was restored. Liver regeneration in mice lacking peripheral serotonin was also restored when their platelets were reloaded with serotonin. Serotonin receptor agonists may thus be a therapeutic option for aiding liver tissue recovery.

--Huang et al. ( 14 Apr 2006; http://www.sciencemag.org/cgi/content/short/312/5771/233 ) reported that an increase in bile acids stimulates liver regeneration in mice and requires the nuclear bile acid receptor FXR. Bile acids help digest fat, but are toxic outside the digestive system -- and a healthy liver normally removes them from the blood. The researchers therefore propose that FXR monitors the level of bile acids passing through the liver and, when the levels get too high, triggers the proliferation of new liver cells until the organ can handle the bile load.

 

Ecological Networks and Coevolution

Mutualistic interactions between plants and animals have played a major role in shaping biodiversity. However, most studies of coevolution have focused on interactions between pairs or small groups of species, and have ignored the wider network of interactions at the level of the ecological community. In a study reported in the 21 Apr 2006 Science, Bascompte et al. ( http://www.sciencemag.org/cgi/content/short/312/5772/431 ) took a quantitative approach to investigate how coevolutionary interactions are shaped within species-rich communities. Drawing on data from tropical rain forests to artic ecosystems, the team analyzed a large set of mutualistic interactions between plants and their free-living pollinators and seed-dispersal agents. Their analysis shows that mutualistic networks are dominated by weak, asymmetric interactions, in which one partner in each mutualism depends strongly on the other while the other is only weakly dependent. For example, a plant might rely heavily on one bird species to disperse its seeds, but that same bird might consume fruits and subsequently disperse seeds from a variety of plant species. Using a simple model, the researchers further showed that over time, this asymmetry may enhance long-term species coexistence and thus help to maintain biodiversity. As noted in an accompanying Perspective by J. N. Thompson ( http://www.sciencemag.org/cgi/content/short/312/5772/372 ), such studies are "part of a growing realization that much of the diversification of life is about the diversification of interactions through ongoing coevolution."

 

Cooperation and Punishment

Understanding the circumstances under which people cooperate is a complex matter that has challenged evolutionary, behavioral, and economic researchers for decades. Particularly difficult to deconstruct are so-called "public-goods" problems, which involve situations in which individuals incur a cost to create a benefit for the group (modern examples might include recycling, voting, or giving blood). In a Report in the 7 Apr 2006 Science, Gürerk et al. ( http://www.sciencemag.org/cgi/content/short/312/5770/108 ) offered new insight into what drives cooperation in large groups. In an experimental game, individuals were asked to choose between two artificial societies. In one society, players could contribute money to a group project and the sum of all contributions was divided evenly amongst all players. The second society was similar except that after players contributed, they were allowed to pay to punish (reduce the payoff of) players who did not contribute equally. After each of 30 rounds of play, players were allowed to choose their society for the next round. The researchers found that most people initially picked the first society, which does not permit punishment and tolerates freeloaders. But as successive rounds of the game were played, cooperation broke down in that group and nearly all players came to appreciate the greater rewards of the other society, which enabled higher total payoffs despite the individual cost of punishing freeloaders. An accompanying Perspective by J. Henrich ( http://www.sciencemag.org/cgi/content/short/312/5770/60 ) highlighted the study.

 

Tools for Biochemistry
http://www.sciencemag.org/sciext/biochemtools/

Researchers at the frontiers of biochemistry are seeking quantitative information about how proteins and other macromolecules function inside living cells. In a special collection of articles published with the 14 Apr 2006 issue, Science and its online companion the Signal Transduction Knowledge Environment ( STKE; http://stke.sciencemag.org/ ) described technological advances that are making their work possible. Review and Perspective articles in Science explored fluorescent probes and techniques to determine protein expression; single-molecule imaging techniques to follow gene expression and cellular metabolism; NMR methods that allow internal motions to be probed with high time and spatial resolution; and recent progress in mass spectroscopy, which is allowing not only the identification of proteins, but characterization of their modifications and analysis of their concentrations. Related research papers demonstrated the power of some of these tools, as well as computational methods, in studies of protein dynamics. Finally, STKE offered a Review on the challenges of fluorescence resonance energy transfer (or FRET) -- an imaging technique used to measure protein-protein interactions in living cells -- and a Protocol for monitoring real-time trafficking of a specific type of glutamate receptor.

 

Fuel From Shuffled Carbon?

When oil is refined into gasoline, long-chain hydrocarbons (alkanes) are broken down into medium-sized hydrocarbons which can form easily flowing liquid fuel. But the refining process also generates a lot of shorter chains, which are much less useful for engine applications. Now, a Report by Goldman et al. ( http://www.sciencemag.org/cgi/content/short/312/5771/257 ) in the 14 Apr 2006 Science has unveiled a dual catalyst system that can stitch together these shorter alkanes, transforming undesirable byproducts into hydrocarbons suitable for transportation fuel. The first catalyst breaks hydrogen atoms off a few of the chains at a time, producing reactive double bonds (as opposed to the unreactive single bonds that hold alkanes together). Next, a second catalyst scrambles these chains at the double bonds, rearranging the number of carbon atoms in them. The first catalyst then replaces the hydrogen atoms onto the new rearranged molecules, returning them back to their hydrocarbon form, but with different sizes. Starting with hexane (a six-carbon chain), the researchers showed that one catalyst combination yielded mostly 10-carbon chains, an ideal component of ultraclean diesel. As noted in an accompanying News story by R. F. Service ( http://www.sciencemag.org/cgi/content/short/312/5771/175a ), the new catalysts still work too slowly for commercial use, but they could one day transform gasoline into a form of renewable energy.

 

Imitating Insect Eyes

Insect eyes are called compound eyes because they contain thousands of integrated optical units called ommatidia, each of which functions as a separate visual receptor. Each miniature eye points in a different direction and collects incident light from a narrow angular range, thereby contributing to the eye's wide field of view and super-fast ability to detect motion and recognize images. In a remarkable example of bio-inspired technology, a Report by Jeong et al. ( http://www.sciencemag.org/cgi/content/short/312/5773/557 ) in the 28 Apr 2006 Science now describes the creation of an artificial compound eye that shows optical properties comparable to those of the eye of a honeybee. Using a combination of micro- and nanofabrication techniques, the researchers used flexible polymers to build artificial ommatidia, each with a microlens connected to a tube-like "waveguide" that directs light down to an optoelectronic imaging device. Each ommatidium was then arranged over a polymer dome to mimic the curvature of a natural insect eye. Such artificial compound eyes hold great potential for a broad range of applications, from medical diagnostics and light-field photography to military surveillance imaging.

 

Aegean History Revised

The second millennium BC saw the development of several major civilizations in the Aegean (Greece, Crete, and Anatolia) and on Cyprus that became integrated into the ancient cultures of the Near East and Egypt. Archaeologists have used similarities among artifacts to help understand how these cultures were connected at various points in time, but chronologies for some periods remain ambiguous. Now, two radiocarbon studies reported in the 28 Apr 2006 Science revise the inferred relations among these cultures and Egyptian and Near Eastern historical dates. One critical tie point is the age of the Santorini volcanic eruption, which flung ash across the eastern Mediterranean. Dates from pottery artifacts have placed the event at roughly 1500 B.C., whereas radiocarbon dates indicate it was 100 to 150 years earlier. In a Brevia article, Friedrich et al. ( http://www.sciencemag.org/cgi/content/short/312/5773/548 ) described their discovery of a single olive tree buried alive by the massive eruption, radiocarbon dating of which constrains the eruption date to the range 1627-1600 B.C. This result fits into the chronology presented by Manning et al. ( http://www.sciencemag.org/cgi/content/short/312/5773/565 ) which is based a large number of radiocarbon dates from 1700 to 1400 BC and now shifts the Aegean record about 100 years earlier. Among the many implications of these results is that the famed New Palace culture of Crete was contemporaneous with the Levant culture, not with the subsequent New Kingdom period of Egypt as had been previously inferred. An accompanying News story by M. Balter ( http://www.sciencemag.org/cgi/content/short/312/5773/508 ) highlighted the findings.

 

Dating the Drake Passage

Over the past 50 million years, Earth's climate has undergone a stepwise shift from "greenhouse" to "icehouse". Dramatic change occurred some 34 million years ago when rapid cooling swept over the Antarctic, transforming lush forests into glaciers. The opening of the Drake Passage -- the waterway between the southern tip of South America and Antartica -- is believed to have influenced this cooling period because it enabled the development of the Antarctic Circumpolar Current (ACC). However, estimates of the age of the passage range from 49 million years ago to 17 million years ago, so it has been difficult to assess what role the opening played in climate change. Now, a Report by Scher and Martin ( http://www.sciencemag.org/cgi/content/short/312/5772/428 ) in the 21 Apr 2006 Science presents new evidence from fossil fish teeth that narrows the estimate considerably. Fish teeth have been shown to absorb the rare-earth element neodymium as they settle to the ocean floor. Interestingly, the proportion of two neodymium isotopes differs between Pacific and Atlantic seawater, because the isotopic ratios in rock surrounding the two ocean basins are different. The researchers were thus able to find traces of Pacific water leaking through the Drake Passage about 41 million years ago. This event long preceded opening of the last ocean gateway to Antarctica -- the Tasmanian Gateway -- around 35 million years ago, and glaciation of the continent. An accompanying News story by R. A. Kerr ( http://www.sciencemag.org/cgi/content/short/312/5772/350a ) highlighted the Report.

 

San Francisco Earthquake Centennial

On 18 April 1906, the vast San Andreas Fault yielded to tectonic forces, creating a magnitude 7.9 earthquake that rattled coastal northern California. The rupture spread north and south at speeds exceeding 3 kilometers per second, and its effects were felt as far north as Oregon and as far east as Nevada. In the 14 April 2006 Science, a pair of Perspective articles marked the 100th anniversary of the great 1906 San Francisco quake -- and discussed what we have learned since then about quake dynamics and earthquake-proof building design. W. L. Ellsworth ( http://www.sciencemag.org/cgi/content/short/312/5771/203 ) emphasized that although the 1906 event "broke the dawn for earthquake science," the subsequent simple models of cyclical fault rupture have not yielded useful predictions. Long-term studies of earthquake physics are crucial if we hope to improve long-term forecasts and seismic-hazard assessments. M. C. Comerio ( http://www.sciencemag.org/cgi/content/short/312/5771/204 ) reflected on improvements in earthquake-resistant design, noting that architects and engineers are now aided by new tools that can measure ground shaking and mathematical models to analyze and predict structural behavior. These and other technologies may help reduce the economic cost of earthquake damage to new and existing building in developed countries, but low-tech solutions for structures in the developing world are still sorely needed.

 

Optical Schrödinger Kittens

Particles such as atoms can be in two or more different quantum states at the same time, but an object made of a large number of atoms, such as a cat, can clearly not be in two different states. Or can it? Schrödinger's cat is a thought experiment designed to illustrate this paradox. Clearly, we cannot know whether a cat hidden inside a box is dead or alive -- yet according to quantum physics, the cat must exist in a quantum superposition of the "dead" and "alive" states simultaneously until observation or measurement (opening the box) narrows the possible states to one. Quantum information processing will require the reliable preparation of such quantum states of matter. But while these are easy to specify theoretically, experimental realization of such states has been difficult. Now, in a Report in the 7 Apr 2006 Science (published online 9 Mar 2006), Ourjoumstev et al. ( http://www.sciencemag.org/cgi/content/short/312/5770/83 ) have reported on the production of a small Schrödinger cat state, or Schrödinger kitten, in the form of a tiny light pulse. The achieved this feat by subtracting a single photon from a squeezed laser pulse beam and further showed that the kitten states can be grown into bigger cats through a suitable amplification and distillation process. An accompanying Perspective by N. Gisin ( http://www.sciencemag.org/cgi/content/short/312/5770/63 ) highlighted the Report.