Science Roundup - The monthly review of Science highlights for AAAS members

This month in Science Roundup:

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The Sea Urchin Genome
Special online collection >>

The sea urchin has been a major experimental model for over a century, contributing to fundamental principles of cell biology, developmental biology, and gene regulation. In the 10 Nov 2006 issue, Science and it online companion Signal Transduction Knowledge Environment (STKE) described the sequencing of the genome of the purple sea urchin Strongylocentrotus purpuratus and new insights into the animal’s evolution and development. A Research Article and Report in Science detailed the sea urchin genome and transcriptome, while Review and Perspective articles explored the ecological role of purple sea urchins, genomic insights into their complex immune systems, and paleogenomic studies of sea urchins and their spiny skinned relatives. Articles in STKE looked at the signaling mechanisms involved in sea urchin embryogenesis. Also on Science Online, videos featuring sea urchin biologist D. McClay highlighted the historical significance of the sea urchin; an interactive poster offered additional images, movies, and a collection of Web resources; and a podcast segment featured an interview with project leader E. H. Davidson about the genome sequencing effort.


Assessing Marine Diversity Loss

Marine ecosystems provide a wide variety of goods and services including vital food resources and waste detoxification. Although factors such as pollution and habitat destruction are known to contribute to marine biodiversity loss at local scales, the importance of biodiversity changes at the ecosystem level remain poorly understood. In a Research Article in the 3 Nov. 2006 Science , Worm et al. analyzed local experiments, long-term regional time series, and global fisheries data to quantify how loss of marine diversity has affected the functioning and stability of marine ecosystems and the services upon which humans depend. Overall, their results indicate that marine diversity loss is accelerating on a global scale and increasingly impairing the ocean’s capacity to provide food, maintain water quality, and recover from perturbations. At the current loss rate, the team estimates that all commercial fish and invertebrate species will collapse by 2048. Despite this gloomy outlook, the available data suggest that these trends are reversible. Closing fisheries and establishing marine protected areas, for example, boosted the species richness in these regions by 23% on average and these increases in biodiversity were associated with large increases in fisheries productivity. An accompanying News story by E. Stokstad highlighted the study.


Cooler, Longer Life

Restricting dietary caloric intake has been shown to prolong life span in a variety of organisms, and in mammals the resultant lowering of core body temperature (CBT) has been offered as one possible explanation. In a Report in the 3 Nov 2006 Science , Conti et al. investigated whether a cooler body temperature alone can lead to longer life. The team genetically engineered mice to overexpress uncoupling protein 2 (UCP-2) -- a protein involved in converting ATP to heat rather than energy -- in a brain region that senses and controls body temperature, much like a thermostat. Overexpression of the protein effectively heated up the brain’s thermostat, and essentially tricked the rest of the body into cooling down by 0.3 to 0.5 degrees Celsius. These "cool mice" were fed the same amount of food as control mice, but showed increased energy efficiency and a greater median lifespan -- a 12% increase in males and a 20% increase in females. In humans, that would correspond to a life span extension of 7 to 8 years. The results suggest that lower body temperature accounts for at least some of the age-fighting effects of calorie restriction. An accompanying Perspective by C. B. Saper considered whether mild hypothermia might be easier to tolerate than a lifetime of starvation as a way to increase longevity.


Clues to Plant Nutrition

Reducing world hunger will require improvements in agriculture that include increasing the nutritional value of dietary staples. Two Reports in the 24 Nov 2006 Science offered new insights into how plants store and mobilize nutrients, that could aid the development of nutrient-enriched crops. In plants, iron is required for photosynthesis and respiration, but too much of this nutrient can be toxic. In a study using the model plant Arabidopsis thaliana , Kim et al. ( published online 2 Nov ) found that in seeds, iron is preferentially sequestered in the vacuoles of embryonic vascular cells by a protein transporter. Vacuoles may thus provide a way to enrich the iron content of grains. In a related study, Uauy et al. found that a gene in wild wheat increases its protein, zinc, and iron content, but that this gene has lost its function in domesticated wheat varieties. Inserting the wild gene into cultivated wheat could therefore potentially improve the nutritional content of the grain. A related Perspective by J. D. Gitlin underscored the importance of advances in basic plant sciences to efforts to eradicate child malnutrition.


Typhoid Sleuthing

The bacterium Salmonella Typhi causes 21 million cases of typhoid fever and 200,000 deaths per year, predominantly in impoverished populations in southern Asia , Africa , and South America . Notoriously, Typhi can be "carried" by individuals who can shed high levels of the bacteria for decades without any clinical symptoms of disease. In a Report in the 24 Nov 2006 Science , Roumagnac et al. elucidated the evolutionary history of this pathogen through genetic analysis of 105 Typhi strains from around the world. The continued existence of the ancestral strain and many of its direct descendents, point to a neutral population structure (no selective advantage of one genotype over another) that has evolved over the last 10,000 to ~50,000 years . Mutation analysis suggests that Typhi spread globally during acute epidemics followed by prolonged persistence in asymptomatic human carriers. The team also reports that the widespread use of fluoroquinolone antibiotics has led to the expansion of drug-resistant strains, which are hampering efforts to combat typhoid fever particularly in southern Asia . Senior researcher M. Achtman discussed the details of the study and the implications for future public health campaigns in a segment of the 24 Nov podcast.


Money Matters

The material benefits of money in everyday modern life are innumerable, but can money directly affect our psychological state and behavior? In a Report in the 17 Nov 2006 Science Vohs et al. described the results of nine experiments, which suggest that even thinking about money changes behavior in reliable ways. The experiments involved exposing volunteers to the idea of money (e.g., by asking them to read essays about money, or unscramble phrases with money-related words) and then comparing their behavior in certain tasks with that of volunteers in a control group who had not had the same exposure. The researchers found that in all of the experiments, subjects who had been "primed" with money behaved in a more self-sufficient fashion than control subjects primed with neutral concepts. Namely, money-primed subjects were less likely to ask for help in solving problems, to offer help to another person, or to make monetary donations. Moreover, participants primed with money preferred to play alone, work alone, and put more physical distance between themselves and a new acquaintance. As noted in an accompanying Perspective by C. B. Burgoyne and S. E. G. Lea, gaining a more comprehensive understanding of the causes and effects of behavior toward money could lead to new insights about human happiness and well-being.


The Right Combination
Inroduction to the special issue >>

Composite materials are put together from two or more components that remain distinct or separate within the final product. In a special section of the 17 Nov 2006 Science , three articles looked at contemporary composite materials from three different perspectives. A Perspective by P.J. Hogg described the use of composites in crafting energy-absorbing armor to protect vehicles and people from projectiles, impacts, and crashes. A Review by Cox and Yang discussed the improving accuracy of models and simulations in predicting fracture patterns and other types of damage in tough structural composites and Balazs et al. explored efforts to mix polymers and nanoparticles to produce new flexible composites with advantageous electrical, optical, or mechanical properties.

Also of materials science interest, a special News Focus celebrated the 20th anniversary of the discovery of high-temperature superconductors -- materials through which electrons mysteriously pair and glide at temperatures as high as 138 kelvin. A related collection of articles in ScienceCareers.org explored career prospects in high-temperature superconductivity.


Early Hominin Diet

About 2.4 to 1.4 million years ago, our earliest stone tool-making ancestors Homo habilis and H. erectus shared the southern African savanna with other early hominins commonly referred to as "robust" australopithecines or Paranthropus species. But these species died out 1 million to 1.4 million years ago and their extinction is often attributed to their low-nutrient, high-fiber diet, which may have been too specialized to allow them to cope with the changing environment. Now, in a Report in the 10 Nov 2006 Science Sponheimer et al. present new data obtained from the large molar teeth of the 1.8 million-year-old P. robustus that suggest that the eating habits of these ancestral hominins were more varied than previously thought (listen to the related podcast segment). The team used a minimally invasive technique called laser ablation to etch the tooth enamel of several fossil teeth, followed by isotope analysis. Because different plants absorb carbon dioxide for photosynthesis differently, the team was able to determine what types of vegetation the hominins ate based on the ratio of carbon isotopes in their teeth. The analysis revealed that in addition to the expected diet of woody fruits, shrubs and herbs, P. robustus diversified its menu to include savanna-based foods such as grasses or animals eating those plants, depending on the season. This suggests that other biological or social factors may be needed to explain the extinction of Paranthropus . An accompanying Perspective by S. M. Ambrose highlighted the study.


Reassessing Ice Mass Loss

Remote-sensing data and models indicate that in recent years, the Greenland Ice Sheet has been rapidly thinning at its margins while growing in its interior. These changes and the potential impact of even a small loss of ice mass on sea level, particularly on low-lying island and coastal regions, underscore the importance of methods for directly observing variations in ice sheet mass. In a Report in the 24 Nov 2006 Science (published online 19 Oct), Lutchke et al. reported results from an analysis of data collected by GRACE (Gravity Recovery and Climate Experiment) -- a pair of satellites that can follow melting by measuring tiny variations in gravity caused by the redistribution of Earth’s mass. Like other studies, the team found that Greenland is losing ice at alarming rate. They determined that the ice sheet has lost about 100 gigatons of ice per year between 2003 and 2005, as compared to the average ice loss rate of about 12 Gt of ice per year for the decade between 1992 and 2002. However, this estimate is much less than other recent rate calculations, which are closer to 240 Gt of ice per year for the same period. An accompanying Perspective by A. Cazenave stressed the importance of further research to improve estimates of Greenland and Antarctica ice mass balance and models of ice sheet dynamics in response to climate change.


When Rocks Melt and Freeze

Two Reports in Science this month shed light on how rocks behave at both extremes of the temperature spectrum. The results from these studies have implications for understanding deep-Earth processes and the effects of climate warming in ice-rich regions.

--Schiano et al. (10 Nov 2006) investigated how silicate melts (molten rock in Earth’s mantle) and other geophysical fluids form and migrate through their solid source rocks. Their results show that when driven by a temperature gradient, small amounts of silicate melt can move through the mineral matrix rather than along crystal edges, but that bubbles of carbon dioxide-rich fluids remain stuck in place. This so-called transcrystalline melt migration affects the separation of mantle melts and the composition of fluid inclusions trapped within rock crystals. As noted in an accompanying Perspective by M. Holness the new work poses interesting questions about how we read the rock record to interpret what happens in the deep Earth.

--Murton et al. (17 Nov 2006) meanwhile showed that contrary to common perception, the fracturing of rocks in the cold is not typically caused by the expansion of water upon freezing. Rather, data from experiments simulating the freezing and thawing permafrost indicate that rock fracture results from a process called ice segregation. As a freezing front moves through rock, it squeezes water from its pores into pockets where lenses or layers of ice form, thus causing the rock to crack. In warming climates, such fracturing may increasingly destabilize permafrost in polar regions. An accompanying Perspective by B. Hallet highlighted the study.


Cosmic Shock Waves

Galaxies are not spread out evenly throughout the universe, but rather are clumped together in massive clusters separated by vast cosmic voids. These clusters form as galaxies move through space and draw in surrounding clouds of dust and gas by gravitational force, sometimes colliding at speeds of up to a few thousand kilometers per second. In a Report in the 3 Nov 2006 Science , Bagchi et al. reported the detection of giant, radio-emitting ringlike structures at the outskirts of a galaxy cluster that may trace the elusive shock waves caused by such energetic mergers and collisions. The structures are made of streams of magnetically charged particles and extend some 6 million light years around a galaxy cluster called Abell 3376, located more than 600 million light years away. Radio traces picked up by the Very Large Array telescope indicate that electrons and other particles are spiraling inside the rings so fast that it is as if they are being propelled by a giant linear accelerator. This suggests that a tremendous source of energy, like that of a comic shock wave, may be powering them. The radio sources may also represent the acceleration sites of the still-mysterious ultra-high-energy cosmic rays. An accompanying Perspective by T. A. Ensslin and a related ScienceNOW story by P. Berardelli (published 2 Nov) highlighted the discovery.


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In Science ’s STKE

Phosphoinositides and Cellular Stress

Phosphoinositides regulate numerous cellular processes required for growth, proliferation, and motility. Whereas phosphoinositide signal transduction pathways within the cytosol have been well characterized, nuclear signaling pathways remain poorly understood. In a Perspective published 7 Nov 2006 in Science ’s Signal Transduction Knowledge Environment (STKE), Bunce et al. highlighted new results that demonstrate a role for nuclear phosphoinositides in cellular stress response pathways. In response to stressors such as UV irradiation or oxidative stress, a kinase called PIPKIIbeta is phosphorylated thereby inhibiting its lipid kinase activity and resulting in increased nuclear levels of its preferred substrate phosphatidylinositol 5-phosphate (PI5P). The accumulation of PI5P in turn recruits the tumor suppressor protein ING2 to chromatin, facilitating ING2’s ability to alter the transcriptional activity of target genes and modulate processes such as apoptosis. It is not yet clear exactly how PI5P accumulation results ING2 activation. Nevertheless, the findings highlight a previously uncharacterized function for phosphoinositides and implicate their metabolism in signaling pathways critical for cell survival.


Also in STKE this month:

--C. Cho and B.E. Ehrlich discussed the inositol 1,4,5-trisphosphate receptor, which is responsible for the initiation of intracellular calcium signaling, and it regulators (28 Nov 2006)
--M.H.H. Schmidt and I. Dikic described new insights into ubiquitin signaling pathways (21 Nov 2006)



This month’s Science Roundup is sponsored by AAAS:
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