Tạp chí khoa học số 2006-08-25

25 August 2006 | $10 www.sciencemag.org SCIENCE VOL 313 25 AUGUST 2006 1009 CONTENTS CONTENTS continued >> DEPARTMENTS 1015 Science Online 1016 This Week in Science 1020 Editors’ Choice 1022 Contact Science 1023 NetWatch 1025 Random Samples 1041 Newsmakers 1060 AAAS News & Notes 1145 New Products 1146 Science Careers >> Editorial p. 1019; News story p. 1034; Book Review p. 1046; Review p. 1061 EDITORIAL 1019 What’s a Wetland, Anyhow? by Donald Kennedy and Brooks Hanson >> Freshwater Resources section p. 1067 1034 INTRODUCTION A Thirsty World 1067 REVIEWS Global Hydrological Cycles and World Water Resources 1068 T. Oki and S. Kanae The Challenge of Micropollutants in Aquatic Systems 1072 R. P. Schwarzenbach et al. PERSPECTIVES Waterborne Infectious Diseases—Could They Be Consigned 1077 to History? A. Fenwick Seeking Sustainability: Israel’s Evolving Water Management 1081 Strategy A. Tal NEWS Running Out of Water—and Time 1085 Desalination Freshens Up 1088 SPECIAL SECTION Freshwater Resources Volume 313, Issue 5790 NEWS OF THE WEEK Pushed by an Outsider, Scientists Call for Global Plan 1026 to Share Flu Data Perelman Declines Math’s Top Prize; Three Others 1027 Honored in Madrid Okounkov, Tao, and Werner Capture Fields Medals, ‘Math’s Nobels’ Skeptics Seek to Slay the ‘Hobbit,’ Calling Flores 1028 Skeleton a Modern Human After 2 Millennia on Ice, a Nomad Resurfaces 1029 SCIENCESCOPE 1029 At International AIDS Conference, Big Names 1030 Emphasize Big Gaps Scientists Derive Line From Single Embryo Cell 1031 NASA Chief Blasts Science Advisers, Widening Split 1032 With Researchers New in Nanotech: Self-Folding Delivery Boxes 1032 Satellite’s X-ray Vision Clinches the Case for 1033 Dark Matter NEWS FOCUS Going Against the Flow 1034 Controversial Rivers Project Aims to Turn India’s Fierce Monsoon Into a Friend >> Freshwater Resources section p. 1067 One Year After, New Orleans Researchers Struggle 1038 to Rebuild Sharpening Up Models for a Better View of the 1040 Atmosphere COVER Raindrops are a welcome source of freshwater replenishment. Nonetheless, maintaining a clean and plentiful water supply remains a worldwide concern. A special section beginning on page 1067 highlights some of the scientific and engineering challenges in managing this vital and increasingly scarce resource. Photo: Getty Images 1011 CONTENTS continued >> CONTENTS LETTERS Preserving the Jarawa’s Future S. Corry 1043 Ice Sheets and Sea Level J. Oerlemans, D. Dahl-Jensen, V. Masson-Delmotte Response J. T. Overpeck et al. CORRECTIONS AND CLARIFICATIONS 1045 BOOKS ET AL. When the Rivers Run Dry Water—The Defining Crisis 1046 of the Twenty-First Century F. Pearce, reviewed by S. L. Postel >> Freshwater Resources section p. 1067 BROWSINGS 1047 Exceeding Our Grasp Science, History, and the 1047 Problem of Unconceived Alternatives P. K. Stanford, reviewed by T. Lewens EDUCATION FORUM Teaching and Assessing Knowledge Integration 1049 in Science M. C. Linn, H S. Lee, R. Tinker, F. Husic, J. L. Chiu PERSPECTIVES Are Global Conservation Efforts Successful? 1051 A. S. L. Rodrigues Unraveling Gut Inflammation 1052 W. Strober >> Report p. 1126 Growing Apart in Lock Step 1054 J. J. Lissauer >> Report p. 1107 Crafting the Pieces of the Diversity Jigsaw Puzzle 1055 R. L. Kitching >> Reports pp. 1112 and 1115 Surface Transfer Doping of Semiconductors 1057 J. Ristein ZAP and ZIP, a Story to Forget 1058 T. V. P. Bliss, G. L. Collingridge, S. Laroche >> Research Article p. 1093; Report p. 1141 TECHNICAL COMMENT ABSTRACTS CELL BIOLOGY Comment on “Cell Type Regulates Selective 1045 Segregation of Mouse Chromosome 7 DNA Strands in Mitosis” J. E. Haber full text at www.sciencemag.org/cgi/content/full/313/5790/1045b Response to Comment on “Cell Type Regulates Selective Segregation of Mouse Chromosome 7 DNA Strands in Mitosis” A. J. S. Klar and A. Armakolas full text at www.sciencemag.org/cgi/content/full/313/5790/1045c REVIEW OCEAN SCIENCE Trajectory Shifts in the Arctic and Subarctic 1061 Freshwater Cycle B. J. Peterson et al. >> Freshwater Resources section p. 1067 BREVIA PALEONTOLOGY An Aegialodontid Upper Molar and the Evolution 1092 of Mammal Dentition A. V. Lopatin and A. O. Averianov An early mammal found in Russia shows that a distinctive dental pattern of marsupials and placental animals had evolved by 130 million years ago. RESEARCH ARTICLE NEUROSCIENCE Learning Induces Long-Term Potentiation in the 1093 Hippocampus J. R. Whitlock, A. J. Heynen, M. G. Shuler, M. F. Bear Rapid learning in rats strengthens synapses in the hippocampus of the brain, confirming that synaptic long-term potentiation underlies learning in vivo. >> Perspective p. 1058; Report p. 1141 SCIENCE EXPRESS www.sciencexpress.org BIOCHEMISTRY Structure of the Exon Junction Core Complex with a Trapped DEAD-Box ATPase Bound to RNA C. B. F. Andersen et al. A structure of a complex that binds to new mRNA reveals how two proteins inhibit the ATPase activity of an RNA helicase to ensure tight binding. 10.1126/science.1131981 GEOCHEMISTRY Oxygen Isotope Variation in Stony-Iron Meteorites R. C. Greenwood, I. A. Franchi, A. Jambon, J. A. Barrat, T. H. Burbine Oxygen isotope measurements show that two similar groups of stony meteorites have different origins and that one likely comes from the asteroid Vesta. 10.1126/science.1128865 PHYSICS Tunable Quasi–Two-Dimensional Electron Gases in Oxide Heterostructures S. Thiel, G. Hammerl, A. Schmehl, C. W. Schneider, J. Mannhart Application of an electric field can tune the conductance of the interface region between layered oxides by orders of magnitude. 10.1126/science.1131091 IMMUNOLOGY Reversal of the TCR Stop Signal by CTLA-4 H. Schneider et al. A protein responsible for preventing unwanted immune responses discourages extended liaisons between activated immune cells. 10.1126/science.1131078 www.sciencemag.org SCIENCE VOL 313 25 AUGUST 2006 www.sciencemag.org SCIENCE VOL 313 25 AUGUST 2006 1013 CONTENTS continued >> REPORTS PHYSICS Superfluidity of Grain Boundaries and Supersolid 1098 Behavior S. Sasaki et al. Experiments show that superfluid flow along grain boundaries in solid 4 He may explain its supersolid behavior. APPLIED PHYSICS Detection, Stimulation, and Inhibition of Neuronal 1100 Signals with High-Density Nanowire Transistor Arrays F. Patolsky et al. With an array of silicon nanowire field-effect transistors, the activity at up to 50 locations along an axon of a cortical rat neuron can be recorded and modified. CHEMISTRY Discrete Sandwich Compounds of Monolayer 1104 Palladium Sheets T. Murahashi et al. A compound containing three or five metal atoms, instead of the usual one, between two hydrocarbon layers challenges the boundary between discrete molecules and layered solids. ASTRONOMY Forced Resonant Migration of Pluto’s Outer 1107 Satellites by Charon W. R. Ward and R. M. Canup The orbits of Pluto’s two small moons can be explained if they corotated with the larger moon, Charon, following an impact in which the three moons were created. >> Perspective p. 1054 CLIMATE CHANGE Ice Record of δ 13 C for Atmospheric CH 4 Across the 1109 Younger Dryas–Preboreal Transition H. Schaefer et al. Carbon isotopes in ice methane did not vary near the end of the last deglaciation when atmospheric methane levels rose, implying that clathrates were not the methane source. PALEONTOLOGY Decoupled Plant and Insect Diversity After the 1112 End-Cretaceous Extinction P. Wilf, C. C. Labandeira, K. R. Johnson, B. Ellis After the end-Cretaceous extinction, plants diversified without many insects in some places, whereas elsewhere insect herbivores diversified despite few plant species. >> Perspective p. 1055 ECOLOGY Why Are There So Many Species of Herbivorous 1115 Insects in Tropical Rainforests? V. Novotny et al. The number of insect species in tropical and temperate forests is determined by the diversity of tree species. >> Perspective p. 1055 BOTANY Brassinosteroids Regulate Dissociation of BKI1, a 1118 Negative Regulator of BRI1 Signaling, from the Plasma Membrane X. Wang and J. Chory A steroid hormone signaling pathway in plants is activated when an inhibitor is displaced from the cell membrane. CELL SIGNALING ATM Engages Autodegradation of the E3 Ubiquitin 1122 Ligase COP1 After DNA Damage D. Dornan et al. After a cell experiences DNA damage, the enzyme that normally tags a tumor suppressor for degradation is inhibited, allowing accumulation of the tumor suppressor. MICROBIOLOGY Symbiotic Bacteria Direct Expression of an 1126 Intestinal Bactericidal Lectin H. L. Cash et al. The cells that line the intestine secrete a small molecule that binds to resident bacteria through a peptidylglycan interaction and kills them. >> Perspective p. 1052 DEVELOPMENTAL BIOLOGY Individual Cell Migration Serves as the Driving 1130 Force for Optic Vesicle Evagination M. Rembold, F. Loosli, R. J. Adams, J. Wittbrodt High-resolution imaging of cells in living fish shows that migrating cells form the eye by acting individually rather than collectively. MOLECULAR BIOLOGY 1134 Argonaute Slicing Is Required for Heterochromatic Silencing and Spreading D. V. Irvine et al. In RNA interference, genes are silenced through base-pairing of small interfering RNAs with RNA, presumably transcribed from the silenced region. MEDICINE Chemical Chaperones Reduce ER Stress and Restore 1137 Glucose Homeostasis in a Mouse Model of Type 2 Diabetes U. Özcan et al. Small-molecule drugs that help to fold and process proteins correct type 2 diabetes in a mouse model, providing a new lead for the treatment of human diabetes. NEUROSCIENCE Storage of Spatial Information by the Maintenance 1141 Mechanism of LTP E. Pastalkova et al. Maintenance of spatial memories in the rat brain can be reversed by inhibition of long-term synaptic potentiation in the rat brain. >> Perspective p. 1058; Research Article p. 1093 SCIENCE (ISSN 0036-8075) is published weekly on Friday, except the last week in December, by the American Association for the Advancement of Science, 1200 New York Avenue, NW, Washington, DC 20005. Periodicals Mail postage (publication No. 484460) paid at Washington, DC, and additional mailing offices. Copyright © 2006 by the American Association for the Advancement of Science. The title SCIENCE is a registered trademark of the AAAS. Domestic individual membership and subscription (51 issues): $139 ($74 allocated to subscription). 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Authorization to photocopy material for internal or personal use under circumstances not falling within the fair use provisions of the Copyright Act is granted by AAAS to libraries and other users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that $18.00 per article is paid directly to CCC, 222 Rosewood Drive, Danvers, MA 01923. The identification code for Science is 0036-8075. Scienceis indexed in the Reader’s Guide to Periodical Literature and in several specialized indexes. CONTENTS www.sciencemag.org SCIENCE VOL 313 25 AUGUST 2006 1015 ONLINE SCIENCE’S STKE www.stke.org SIGNAL TRANSDUCTION KNOWLEDGE ENVIRONMENT PERSPECTIVE: Multifunctional Potassium Channels— Electrical Switches and Redox Enzymes, All in One S. H. Heinemann and T. Hoshi A potassium channel subunit acts as a redox enzyme that can modulate channel inactivation. PROTOCOL: Real-Time Measurements of Protein Affinities on Membrane Surfaces by Fluorescence Spectroscopy F. Philip and S. Scarlata Find out how to quantify protein interactions using FRET. SCIENCENOW www.sciencenow.org DAILY NEWS COVERAGE Ant Takes a Bite out of Speed Record Quick-fire chompers accelerate hunting, hasten retreat. Premature Births Linked to Gene Variant Finding may explain higher incidence of preemies in African-American population. Not a Drop to Drink Report finds global freshwater supplies dwindling faster than thought. >> Freshwater Resources section p. 1067 SCIENCE CAREERS www.sciencecareers.org CAREER RESOURCES FOR SCIENTISTS GLOBAL: Special Feature—Seeing the World Through Science R. Arnette Scientists describe their most memorable conference experiences. MISCINET: Educated Woman, Chapter 54—Phoenix Rising M. P. DeWhyse Micella takes us through the excitement of dissertation defense day. UK: Eng.D.—An Applied Doctorate L. Blackburn In the United Kingdom, professional doctorate degrees provide an alternative to the Ph.D. CANADA: A New University Means New Jobs in Ontario A. Fazekas Established in 2003, the University of Ontario Institute of Technology is still hiring science faculty. MISCINET: Is There an M.D./Ph.D. in My Future? MentorDoctor Team The team advises an undergraduate interested in practicing medicine and research. Scientific conference on ice. Separate individual or institutional subscriptions to these products may be required for full-text access. www.sciencemag.org Channel or enzyme? Breakneck biting. separated by a barrier of solid helium and pro- pose a model in which superflow along grain boundaries in the solid accounts for the observed mass transport. Freshen This The Nordic and Atlantic Subpolar Oceans of the Northern Hemisphere became less saline during the past half-century, and Peterson et al. (p. 1061) address the problem of the origin of the necessary freshwater inputs. They examined how precipitation onto the ocean, river discharge, glacial melt, and sea ice melt have changed recently in comparison to a baseline from 1936 to 1955. This understanding is par- ticularly important in light of projections of a continued increase in precipitation in high northern latitudes and the critical role that this region is thought to play in regulating ocean circu- lation and global climate. Neuronal Stimulation and Recording It would be useful to interrogate or modify the electrophysiology of neurons in detail. One prom- ising approach is to use small field-effect transis- tors (FETs). Patolsky et al. (p. 1100) assembled arrays of p- and n-type silicon nanowires and then used polylysine patterning to direct the growth of rat cortical neurons on the wires so that the dendrites and axons of a single neuron could be stimulated or interrogated at up to 50 loca- tions along one axon in physiological media. The action potentials induced with the usual glass microelectrode or with the nanowire transistors were comparable, and the nanowire junctions A Sandwich with Extra Palladium In the 50 years since Wilkinson’s characterized ferrocene, chemists have manipulated nearly every metal in the periodic table into a sandwich between planar cyclic aromatic hydrocarbons. However, despite the available space between the flanking rings, the central com- pounds have almost never contained more than one metal cen- ter. Murahashi et al. (p. 1104) prepared and characterized a com- pound with three pal- ladium atoms sand- wiched between tropylium rings, and another with five palladium atoms sandwiched between naphthacenes. The structures present an inter- esting boundary case between discrete mole- cules and layered solids. Supersolid Flow in Grain Boundaries? When two reservoirs of a liquid are brought together, their levels will equilibrate to a com- mon level. Recent experiments have found evidence of “supersolid” behavior in solid 4 He, where superfluid-like mass flow through the solid was observed. How a solid can flow like a superfluid has been controversial. Sasaki et al. (p. 1098, published online 3 August; see the 4 August news story by Cho) reexamined mass flow between two reservoirs of superfluid 4 He could be used to inhibit signals as well as meas- ure propagation speeds. Migrating Moons Pluto’s two recently discovered moons travel in orbits that appear to be influenced by the largest satellite, Charon. The two moons’ orbits are circu- lar and coplanar with that of Charon, which sug- gests that they formed in a common impact as opposed to being captured independently. How- ever, all three moons lie at large distances from Pluto, so if they were formed together in a collision they must have migrated outward. Ward and Canup (p. 1107, published online 6 July; see the Perspective by Lissauer) propose that the two moons were created in the same impact that pro- duced Charon. To avoid the disruption of the sys- tem as it expanded, the two small moons remained in corotation resonances with Charon. Corotation type resonances, similar to those that constrain Neptune’s ring arcs, would not have altered the eccentricities of the satellites after capture. Moderate Methane Changes The atmospheric concentration of methane, a powerful greenhouse gas that is also a useful tracer of global carbon cycling, varied dramati- cally between cold and warm periods of Earth history during the past 800,000 years. The causes of these variations are still unclear. Schaefer et al. (p. 1109) analyzed West Green- land ice to develop a record of the stable iso- topic composition of the carbon in atmospheric methane at the end of the last deglaciation, when the concentration of methane in the EDITED BY STELLA HURTLEY AND PHIL SZUROMI 25 AUGUST 2006 VOL 313 SCIENCE www.sciencemag.org 1016 CREDITS (TOP TO BOTTOM): M. JANDA (2005); MURAHASHI ET AL. Ecology Then and Now Plants and their insect predators form a complex and evolving ecosystem (see the Perspective by Kitching). Wilf et al. (p. 1112) show that the Cretaceous-Paleogene extinction complicated plant-insect coevolution for perhaps several million years. In one location after the extinction, a limited species of leaves reveal diverse insect predation. In another, many species of leaves show limited types of predation. Thus, in some locations, plants seemed to have evolved without much insect predation, while in others, insects evolved despite limited plant diversity. In con- trast, Novotny et al. (p. 1115) compared present-day insect host speci- ficity and diversity on phylogenetically comparable sets of plants in trop- ical and temperate forests. Coexistence of numerous herbivore species in tropical forests did not seem to reflect narrower niches; instead, herbi- vore species richness appeared to be driven by plant diversity. www.sciencemag.org SCIENCE VOL 313 25 AUGUST 2006 1017 This Week in Science atmosphere increased from 500 to 750 parts per billion in less than 200 years. The carbon-isotopic composition of methane changed remarkably little, implying that the methane was being released from tropical wetlands rather than ocean clathrates. Linking LTP with Learning and Memory The phenomenon of synaptic long-term potentiation (LTP) was discovered more than 30 years ago in the hippocampus. Although it is commonly thought that hippocampal LTP is induced by learn- ing, there has not been a direct demonstration (see the Perspective by Bliss et al.). Whitlock et al. (p. 1093) recorded field potentials from multiple sites in hippocampal area CA1 before and after single-trial inhibitory avoidance learning. Field potentials increased on a subset of the electrodes, and these could be specifically related to the learning event. Pastalkova et al. (p. 1141) reversed hippocampal LTP in freely moving animals using a cell-permeable inhibitor of a protein kinase. Reversal was accompanied by a complete disruption of previously acquired long-term memory in a place avoidance task, even when the kinase inhibitor was infused only during the consolidation interval. This result suggests that LTP was necessary for storing spatial information. Dealing with DNA Damage Cells need to be able to respond to DNA damage to restrict its consequences for the organism as a whole. Dornan et al. (p. 1122) found a new target for the protein kinase ATM (which when mutated causes ataxia telangiectasia, a disease that renders patients sensitive to ionizing radiation and an increased risk of cancer). ATM is activated in response to DNA damage and phosphorylates COP1, an E3 ubiquitin ligase that controls ubiquitination and degradation of the key tumor suppressor protein p53. This phosphorylation appears to cause COP1 to turn on itself, mediating its own autoubiquitina- tion and consequent degradation, leading to the accumulation of p53. In tissue cultures, this phos- phorylation event appears to be necessary for p53-dependent tumor suppressor activity in response to DNA damaging agents. Getting to Grips with Gut Flora All mammals rely on a factory of symbiotic microorganisms living in the gut to help process nutri- ents into usable forms, but if these bacteria escape containment, they can trigger damaging inflam- matory responses. Mammals use several adaptive and innate systems to keep the gut flora in check, including microbicidal peptide defensins, lysozymes, and lectins. Cash et al. (p. 1126; see the Perspective by Strober) have discovered that the expression of a carbohydrate-binding protein—a lectin—is induced by the intestinal microbial population from Paneth cells in the crypts. This lectin is among the most highly expressed proteins in the small intestine, recognizes peptidoglycan, and is directly bactericidal. Indeed sufferers of inflammatory bowel disease tend to express elevated levels of C-type lectins. Fish Eyes Cell movements and molecular factors direct organ develop- ment. Rembold et al. (p. 1130) used high-resolution in vivo imaging to reconstruct eye morphogenesis at the single-cell level in wild-type, mutant, and mosaic fish. Hundreds of cells representing retinal progenitor cells and presumptive fore- brain cells are tracked simultaneously. The analyses indicate that retinal progenitor cells actively migrate during optic vesicle evagination and that the optic vesicle forms from individual cell movements, not tissue movements. Diabetes—An Unfolding Story Obesity triggers stress in the endoplasmic reticulum (ER), a network of intracellular membranes involved in protein folding and trafficking. That ER stress in turn disrupts insulin signaling. Ozcan et al. (p. 1137) investigated whether a class of small-molecule drugs that normalize ER function, called “chemical chaperones,” might have therapeutic benefits in type 2 diabetes. These drugs were found to correct hyperglycemia and restore insulin sensitivity in genetically obese and diabetic mice, sug- gesting that they merit further study as a potential therapy for human diabetes. CREDIT: REMBOLD ET AL./PETRA RIEDINGER, EMBL HEIDELBERG PUT YOURSELF IN THE PICTURE. 2007 AAAS Annual Meeting 15-19 February, San Francisco “Science and Technology for Sustainable Well-Being” “To raise newquestions, new possibilities, to regard old problems from a new angle, requires creative imagination and marks rea l advance in science.” Albert Einstein _ > Put yourself in the picture by presentingaposter at the AAAS Student Poster Session. It provides a great opportunity to present yourresearch and offers anexcellent venuefo r extended informal discussion with meeting attendees. Accepted posters will belisted in the 2007 AAAS Meeting Poster Book. Winners will be published in Science. Fr ee registration opportunities are avail- able as are travel assistance grants, please see the Web sitefor futher details. Deadline forsubmi ssion: Monday, 13 November 2006. See the Web sitefor full details: www.aaasmeeting.org/student. www.aaasmeeting.org/student Call for Entries Student Poster Competition www.sciencemag.org SCIENCE VOL 313 25 AUGUST 2006 1019 CREDIT: GETTY IMAGES EDITORIAL What’s a Wetland, Anyhow? ANYONE INTERESTED IN WATER AND ENVIRONMENTAL SCIENCE SHOULD STUDY THE U.S. Supreme Court’s opinion—or, more precisely, its three rather different opinions—in the recent case called Rapanos vs. United States. Don’t tune out if you’re in Asia, Europe, or else- where, because this is NOT merely a domestic issue! Water quality is critical internationally, improvements in water quality have been a major source of global public health benefits (see the special section, p. 1067), and U.S. regulatory approaches are sometimes copied elsewhere. Here’s what the Court was facing. The Clean Water Act mandates that the U.S. Army Corps of Engineers issue regulations defining what fits under the act’s umbrella term “waters of the United States.” The Court of Appeals for the Sixth Circuit had upheld federal jurisdiction over Michigan wetlands in Rapanos, finding that there were hydrologic connections between the site and nearby ditches and drains, and thence to navigable waters. Defendants appealed to the Supreme Court, which issued its opinions on 19 June 2006. The Court’s fundamental split will surprise few. Justice Scalia, repre- senting the views of Roberts, Alito, Thomas, and himself, offered a very restrictive definition of wetlands: They must have surface connections to navigable waters. That view would have stripped regulatory protection from lands historically treated as wetlands by the Corps of Engineers. On the other side, Justice Stevens, for Souter, Ginsberg, and Breyer, favored a definition that includes groundwater with a significant nexus of connection to more distant navigable waters. Justice Kennedy wrote the decisive opinion, in effect bouncing the matter back to the appellate court. His position favored the “significant nexus” view, adding that the determination would essentially be a scientific matter, within the proper scope of the regulatory agency’s authority. That leaves the matter approxi- mately where it was, but the tone of the opinions is revealing with respect to the depth and tenor of the disagreement on the Court. There are jabs and needles everywhere. Stevens said that Scalia’s opinion “disregards its own obligation to interpret laws rather than make them.” The Chief Justice’s separate opinion criticized the Corps for failing to issue regulatory revisions after an earlier Court decision, saying that it had an “essentially boundless view of the scope of its power.” Scalia, in what reads like a dissenting opinion, said that the Stevens definition of wetlands was “beyond parody.” Ouch. This case also signals how different justices might apply science as a guide to decision-making. “Beyond parody” might also fit Scalia’s effort to define terms used in hydrology. His search for commonplace labels as proxies for scientific definitions must have left his copy of Webster’s Dictionary dog-eared from overuse; the text cites it over and over again. His opinion shows no awareness of what hydrologic investigations have demonstrated about the interconnectedness of ground and surface waters. Neither is there any suggestion that groundwater moves (it does) or that it regularly feeds surface streams or lakes, often keeping these waters flowing between rainstorms. The essential message is: “If you can’t see it, it doesn’t matter.” There is a missing precedent here. An earlier Supreme Court case, Borden Ranch and Tsakopoulos vs. U.S. Army Corps of Engineers and U.S. Environmental Protection Agency, ended in a 4-4 tie, thereby letting stand a decision that fined Tsakopoulos for a plowing technique that the government said would damage the underlying wetland. Ironically, Kennedy had recused himself because he knew Tsakopoulos. Given his views in Rapanos, he would likely have sided with the government, creating a precedent that might have moved the Court not to hear Rapanos. Two take-home lessons seem clear. First, Kennedy is knowledgeable about environmental science; Scalia has little knowledge or perhaps only little interest. Second, despite the meager opportunity for direct scientific input to the Court, concerned scientists could help federal agencies work out realistic scientific standards for defining a “significant nexus” and get those into the Code of Federal Regulations. They might also be useful in the next big case, when the Court will decide whether carbon dioxide is a pollutant under the Clean Air Act. Perhaps they could give the justices something more scientifically helpful than Webster. – Donald Kennedy and Brooks Hanson 10.1126/science.1132934 Donald Kennedy is the Editor-in-Chief of Science. Brooks Hanson is Deputy Editor for physical sciences at Science. inverse relation between solution depth and growth rates. Overall, these results clarify the means of controlling the growth of amorphous mineral phases, of interest both in natural processes and in materials fabrication. — MSL Phys. Rev. Lett. 97, 45503 (2006). PROTEOMICS You Are What You Eat Plant biomass contains a lower percentage of N than animal biomass because plants have rela- tively more carbohydrate and less pro- tein. To look more deeply at elemental aspects, Elser et al. compared the pro- teomes of nine plants and nine ani- mals. The proteomes of plants were found to have a lower N content than those of animals; on average, animals had 7% more N atoms per amino acid. Furthermore, N content is related to overall gene expression level in such a way that, on average, plants have a lower N content in genes that are more highly expressed, whereas no discernible correlation with expression existed in the animal proteomes. These findings may reflect an eco-physiological selec- tion away from the use of N-rich amino acids in plants, perhaps as a result of a greater sensitivity to limiting N supplies. — LMZ Mol. Biol. Evol. 23, 10.1093/molbev/msl068 (2006). 25 AUGUST 2006 VOL 313 SCIENCE www.sciencemag.org 1020 CREDITS (TOP TO BOTTOM): BARCIA ET AL., J. EXP. MED. 203, 10.1084/JEM.20060420 (2006); DR. RICHARD KESSEL & DR. GENE SHIH EDITORS’CHOICE CHEMISTRY Bounding Biomineralization Many organisms build skeletons or shells out of calcium carbonate, either by localizing its crystal- lization or by stabilizing the otherwise short-lived amorphous form. In general, control of this process has been attributed to a mix of proteins, polymers, and magnesium ions on the assumption that each plays roughly the same role in inhibiting the nucleation and growth of crystalline calcite. DiMasi et al. have used in situ synchrotron x-ray reflectivity to distinguish the roles played by these different substances. Specifically, they monitored the formation of amorphous calcium carbonate films on monolayers of arachidic acid placed against a subphase of saturated aqueous calcium bicarbonate, while varying the concen- tration of additives, including MgCl 2 and the sodium salt of poly(acrylic acid)—a model of nat- urally occurring aspartate in proteins. The mag- nesium ions were found to introduce an induction period, delaying the onset of film formation, but had little influence on the subsequent growth of the film. Changing the polymer concentration also did not affect the growth rate of the films but did affect the lifetime of the metastable amor- phous phase before it crystallized or redissolved into the solution. Finally, by varying the trough depth, the authors could tune the path length for the diffusion of carbon dioxide during film for- mation; this component of the study revealed an IMMUNOLOGY Synapse Formation in the Brain A productive meeting of a T cell and an antigen-presenting cell results in the formation of an immunological synapse between the membranes of the two cells, a crucial step in promoting T cell activation. Concentrated within synapses are the adhesion protein LFA1, T cell receptors, peptide-MHC com- plexes, and downstream signalling components. Two concentric domains of the synapse have been characterized: peripheral and central supramolecular activation clusters (pSMACs and cSMACs). Although both domains can be observed in vitro, difficulty seeing them in vivo has prompted discussion of their importance in effective immune responses. Using a rat model with a doc- umented immune response to virally infected astrocytes in the brain, Barcia et al. found that both CD4 + and CD8 + T cells were required for clearance of infected cells, although only CD8 + cells entered the brain parenchyma to establish close contact with astrocytes. These contacts exhibited features characteristic of immune synapse formation, including recruitment and phosphorylation of the intracellular tyrosine kinases Lck and ZAP70 and a membrane reorganization into intimate three-dimensional apposition. More striking was the detection of cSMAC- and pSMAC-like regions, defined by the central and peripheral distributions of the T cell receptor and LFA1, respectively. Typical synapse structures were seen both before and during the immune-mediated clearance of infected astrocytes, suggesting their direct involvement in the antiviral response. — SJS J. Exp. Med. 203, 10.1084/jem.20060420 (2006). A CD8 + T cell (red) embrac- ing an astrocyte (magenta). BIOPHYSICS Sensory Discrimination An attractive (or noxious) signal might come from any direction, so how can a single cell remain on the lookout in all directions? Escherichia coli are known to cope by inter- spersing periods of directional swimming with tumbling, which reorients them randomly. The single-celled slime mold Dictyostelium lives socially and has taken advan- tage of this lifestyle to appor- tion the community’s detectors to cover all points of the compass. Samadani et al. show that single Dic- tyostelium cells respond reproducibly (as assessed by the angular location of a cAMP-sensing compo- nent) to 10 trials of a fixed pulse of cAMP, yet this angle varies over more than 180° when measured across 40 cells. Nevertheless, the population response, summed over orientation and magnitude, yields a peak unerringly directed at the origin of the pulse. Each cell’s innate inclination can be modeled as a function of (i) the overall mobilization of sensor components, (ii) the degree to which the components are distributed EDITED BY GILBERT CHIN AND JAKE YESTON A group of Dictyostelium. . $10 www.sciencemag.org SCIENCE VOL 313 25 AUGUST 2006 1009 CONTENTS CONTENTS continued >> DEPARTMENTS 1015 Science Online 1016 This Week in Science 1020 Editors’ Choice 1022 Contact Science 1023. discourages extended liaisons between activated immune cells. 10.1126 /science. 1131078 www.sciencemag.org SCIENCE VOL 313 25 AUGUST 2006 www.sciencemag.org SCIENCE VOL 313 25 AUGUST 2006 1013 CONTENTS continued. identification code for Science is 0036-8075. Scienceis indexed in the Reader’s Guide to Periodical Literature and in several specialized indexes. CONTENTS www.sciencemag.org SCIENCE VOL 313 25 AUGUST