 This month in Science Roundup: Sponsored by:
  Feeding the FutureSpecial Online Collection Feeding the 9 billion people expected to inhabit our planet by 2050 will be an unprecedented challenge. In the 12 Feb 2010 Science, a special section explored the obstacles to achieving global food security and some promising solutions that science and technology can offer. News articles introduced farmers and researchers who are finding ways to boost harvests, especially in the developing world. And Reviews, Perspectives, and an online audio interview provided a broader context for the causes and effects of food insecurity and pointed to paths to ending hunger. Also online, a special edition of the podcast included interviews about measuring food insecurity, rethinking agriculture for the 21st century, and freeing up more farmland and food crops by eating less meat; and Science Careers took a look at interdisciplinary careers associated with food security and profiled a plant geneticist who is cultivating a future for peanut farming in Uganda. Metabolic Regulation by Acetylation Like protein phosphorylation, the posttranslational addition of acetyl groups to lysine residues has emerged as a key mechanism in cellular regulation, in particular through the modification of histones and nuclear transcription regulators. Now two Reports in the 19 Feb 2010 Science suggest that acetylation may also help control the function of metabolic enzymes (see the related Perspective by A. Norvell and S.B. McMahon). Zhao et al. found that in human liver cells, a large proportion of enzymes in various metabolic pathways including glycolysis, the urea cycle, and fatty acid metabolism, are acetylated. The team further showed that acetylation regulates various enzymes by distinct mechanisms, directly activating some, inhibiting one, and controlling the stability of another. In a second study, Wang et al. reported that about 90% of the proteins involved in central metabolism in the bacterium Salmonella enterica are acetylated. Moreover, the enzymes are acetylated differentially in response to different carbon sources, concomitantly with changes in cell growth, thereby coordinating metabolic flux with cellular energy status. Taken together, the studies demonstrate that reversible acetylation represents a metabolic regulatory mechanism conserved from bacteria to mammals.  Beneficial Toad TraitsIt takes a special kind of toad to hop around the world, colonizing continent after continent. In a Report in the 5 Feb 2010 Science, Van Bocxlaer et al. analyzed 228 toad species and reconstructed the evolutionary history of various traits linked to toads' geographic ranges. The team came up with a list of seven traits that have likely enabled these amphibians to spread around the globe. One is the ability to live away from water instead of being dependent on damp or wet places to survive. Species with poison glands to deter predators, internal fat-storage organs for energy, large adult size, and large clutch sizes were also found to be particularly widespread. The authors propose that these traits accumulated in the most ancestral toads, creating a "range-expansion phenotype" that enabled their global radiation. An accompanying News story by E. Pennisi noted that knowing what kind of toads spread in the past may help us understand which ones will survive, and potentially become invasive, if transported into a new environment. San Andreas Slip History Data about previous major earthquakes inform us about the behavior of a particular fault and can guide future expectations about the recurrence of large and potentially destructive earthquakes. Two Reports in the 26 Feb 2010 Science (published online 21 Jan) exemplify how high-resolution laser imaging and improved radiocarbon dating techniques are providing new insights into earthquake behavior. Zielke et al. analyzed high-resolution topographic data from of a stretch of southern California's San Andreas Fault known as the Carrizo segment, which show that major surface ruptures, such as the 1857 Fort Tejon earthquake, resulted from slips of only about 5 meters -- much less than previously thought. Grant-Ludwig et al. analyzed the geomorphic features in the Carrizo region, which indicate that several smaller earthquakes have occurred during recent centuries rather than infrequent but larger events. An accompanying Perspective by K. Scharer explained how the new data and interpretations challenge fault behavior models that have been applied to the San Andreas Fault for decades.  From Big Fishes to Big WhalesThe largest living marine vertebrates -- baleen whales and several lineages of sharks and rays -- feed by filtering very small organisms, such as plankton and small fish, from seawater. Two Reports in the 19 Feb 2010 Science shed new light on the evolution of these giant filter feeders (also called planktivores). Friedman et al. reported several new examples of large-bodied filter-feeding fish that populated the seas before modern baleen whales and other contemporary filter feeders. Researchers had believed that these prehistoric bony fish only existed for a short period of time, but analyses of the new fossils -- which have been sitting in museums, either unexamined or misidentified -- show that the creatures actually persisted for more than 100 million years during the Mesozoic (245-65 million years ago). In a second study, Marx and Uhen tested the theory that the evolution of modern whales, dolphins, and porpoises during the Cenozoic, about 30 to 40 million years ago, was controlled by biological and environmental factors. Their analyses show that the diversity of these marine animals indeed parallels the diversity of diatoms -- a common type of phytoplankton -- as well as changes in ocean temperature, as indicated by oxygen stable isotope records. In an accompanying Perspective, L. Cavin discussed how the two studies change our view of the natural history of large marine filter feeders, and raise new questions about their evolutionary drivers. Hotspot Control Genetic recombination -- which involves the breaking and rejoining of DNA strands to produce new combinations of genes -- is an essential biological process among eukaryotes. During mammalian meiosis, the specialized cell division process during which maternal and paternal chromosomes are halved to generate sperm and egg cells, recombination joins together different parts of homologous chromosomes, resulting in genetic variation among offspring. In the 12 Feb 2010 Science, three groups (published online 31 Dec 2009) reported the identification of a mammalian gene -- PR domain containing 9 or Prdm9 -- that controls the extent to which recombination occurs in preferred chromosomal locations know as "hotspots." Parvanov et al. found that in mice, Prdm9 -- which encodes a zinc finger protein that acts as a histone methyltransferase -- is expressed in early meiosis in males and females and that its deficiency results in sterility in both sexes. They also sequenced the gene in both mice and humans and analyzed its sequence variants. Baudat et al. correlated different Prdm9 variants in mice and humans with PRDM9 protein variants with different predicted DNA sequence specificities and different patterns of hotspot "usage" in the genome. Finally, Myers et al. compared the locations of recombination hotspots in the human and chimpanzee genomes and found that a sequence motif previously associated with 40% of human hotspots (and to which the PRDM9 protein binds), does not function in chimpanzees -- and that the recombination process leads to a self-destructive drive in which the very motifs that recruit hotspots are eliminated from our genome. An accompanying Perspective, Cheung et al. noted that the findings open the door to understanding the balance of successful gamete formation and maintenance of genetic diversity.  Ice Age InsightsAbout every 100,000 years, kilometers-thick ice sheets form atop the northernmost reaches of North America, Europe, and Asia and extend well into the mid-latitudes. The ice sheets tie up so much seawater that ocean levels can drop by over 100 meters. Then, after about 90,000 years, the glaciers retreat, sea levels rise, and land reappears, until the next ice age begins. Now, a study in the 12 Feb 2010 Science reports that something very unusual happened about 81,000 years ago, well into the last glacial period: the seas rose. Dorale et al. dated layers of the mineral calcite, which were deposited like bathtub rings on stalactites from pools of water in Mallorca caves, in the western Mediterranean. Because the pools are connected to the sea through underground passages, the layers record sea level at the time they formed. Using this approach, the team inferred that sea level ~81,000 years ago reached more than a meter above its present height, implying less ice on Earth and temperatures as high or higher at that time than today. The new data challenge some of the prevailing assumptions about ice-age theory and the 100,000-year glaciation cycle, but as noted in an accompanying Perspective by R. Lawrence Edwards), "demonstrate once again the rapidity with which large ice sheets can come and go." Quantum Fractals Fractals -- geometric entities whose basic patterns appear similar at all scales -- abound in nature: Galaxies, clouds, mountains, trees, and broccoli are all familiar examples. In the 5 Feb 2010 Science, researchers reported evidence that fractals occur in the quantum realm as well. Quantum particles, such as the electrons surrounding the nuclei of atoms, have a wave nature associated with them that gives rise to interference phenomena much like that found in waves on the surface of water, light waves, or sound waves. Using scanning tunneling microscopy to study the electronic states in the ferromagnetic semiconductor gallium arsenide, Richardella et al. found that as the material nears the metal-insulator transition (where it changes from being an electric conductor to an insulator), the waves associated with individual electrons start to interfere with each other and become fractal in nature. The findings reveal an important role of electron-electron interactions in this magnetic semiconductor, which, over the past decade, has emerged as a promising material for spintronic applications. A Perspective by G.A. Fiete and A. de Lozanne highlighted the study.  Art and Science ConvergeSpecial Issue Introduction The convergence of art and science can successfully convey complex phenomena in spectacular ways and for the past 7 years, Science and the U.S. National Science Foundation have co-sponsored annual challenges to encourage the merger of these disciplines. A special section of the 19 Feb 2010 issue presented the winners and honorable mentions in the 2009 International Science & Engineering Visualization Challenge, which drew 130 entries from 14 countries, 23 U.S. states, and the District of Columbia. The winners -- in categories including illustration, multimedia, informational graphics, and photography -- captured the forces exerted by lung cells, the solution to a mathematical puzzle, the busy lives of cells, the epigenetics of identical twins, how people travel within the United States, the wonder of human brain development, and self-assembling polymers in action. An online slide presentation showcased the awardees, and a podcast interview with two of this year's winners discussed their clever use of 75,000 cable zip ties. Recombinant Infectious Prions Prion diseases are a group of fatal neurodegenerative disorders that include Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy in cows. The prion hypothesis posits that the infectious agent of these diseases is a misfolded form of the normal prion protein (PrP) -- a cell surface protein enriched in the central nervous system -- but definitive proof has been lacking. Now, a study described in the 26 Feb 2010 Science (published online 28 Jan) lends new support to the prion hypothesis. Wang et al. report that mixing recombinant PrP purified from E. coli bacteria with liver RNA and synthetic phospholipids in vitro, produces bona fide infections prions. In addition to displaying characteristic features including resistance to proteinase-K and infectivity in cultured cells, the recombinant prions cause rapid disease progression when injected into wild-type mice, yielding both the behavioral and the neuropathological symptoms of prion disease. An accompanying Perspective by S. Supattapone noted that the study demonstrates the importance of nonproteinaceous cofactors for producing recombinant infectious proteins in vitro.
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