Recycling of graphite during Himalayan erosion: a geological stabilization of carbon in the crust     

Galy V  Beyssac O  France-Lanord C  Eglinton T 《Science (New York, N.Y.)》2008,322(5903):943-945

At geological time scales, the role of continental erosion in the organic carbon (OC) cycle is determined by the balance between recent OC burial and petrogenic OC oxidation. Evaluating its net effect on the concentration of carbon dioxide and dioxygen in the atmosphere requires the fate of petrogenic OC to be assessed. Here, we report a multiscale (nanometer to micrometer) structural characterization of petrogenic OC in the Himalayan system. We show that graphitic carbon is preserved and buried in marine sediments, while the less graphitized forms are oxidized during fluvial transport. Radiocarbon dating indicates that 30 to 50% of the carbon initially present in the Himalayan rocks is conserved during the erosion cycle. Graphitization during metamorphism thus stabilizes carbon in the crust over geological time scales.  相似文献   

Neutrophil extracellular traps kill bacteria   总被引：5，自引：0，他引：5  

Brinkmann V  Reichard U  Goosmann C  Fauler B  Uhlemann Y  Weiss DS  Weinrauch Y  Zychlinsky A 《Science (New York, N.Y.)》2004,303(5663):1532-1535

Neutrophils engulf and kill bacteria when their antimicrobial granules fuse with the phagosome. Here, we describe that, upon activation, neutrophils release granule proteins and chromatin that together form extracellular fibers that bind Gram-positive and -negative bacteria. These neutrophil extracellular traps (NETs) degrade virulence factors and kill bacteria. NETs are abundant in vivo in experimental dysentery and spontaneous human appendicitis, two examples of acute inflammation. NETs appear to be a form of innate response that binds microorganisms, prevents them from spreading, and ensures a high local concentration of antimicrobial agents to degrade virulence factors and kill bacteria.  相似文献   

Elucidation of the small RNA component of the transcriptome   总被引：3，自引：0，他引：3  

Lu C  Tej SS  Luo S  Haudenschild CD  Meyers BC  Green PJ 《Science (New York, N.Y.)》2005,309(5740):1567-1569

Small RNAs play important regulatory roles in most eukaryotes, but only a small proportion of these molecules have been identified. We sequenced more than two million small RNAs from seedlings and the inflorescence of the model plant Arabidopsis thaliana. Known and new microRNAs (miRNAs) were among the most abundant of the nonredundant set of more than 75,000 sequences, whereas more than half represented lower abundance small interfering RNAs (siRNAs) that match repetitive sequences, intergenic regions, and genes. Individual or clusters of highly regulated small RNAs were readily observed. Targets of antisense RNA or miRNA did not appear to be preferentially associated with siRNAs. Many genomic regions previously considered featureless were found to be sites of numerous small RNAs.  相似文献   

Flexible control of mutual inhibition: a neural model of two-interval discrimination     

Machens CK  Romo R  Brody CD 《Science (New York, N.Y.)》2005,307(5712):1121-1124

Networks adapt to environmental demands by switching between distinct dynamical behaviors. The activity of frontal-lobe neurons during two-interval discrimination tasks is an example of these adaptable dynamics. Subjects first perceive a stimulus, then hold it in working memory, and finally make a decision by comparing it with a second stimulus. We present a simple mutual-inhibition network model that captures all three task phases within a single framework. The model integrates both working memory and decision making because its dynamical properties are easily controlled without changing its connectivity. Mutual inhibition between nonlinear units is a useful design motif for networks that must display multiple behaviors.  相似文献   

Control of crystal size and lattice formation by starmaker in otolith biomineralization     

Söllner C  Burghammer M  Busch-Nentwich E  Berger J  Schwarz H  Riekel C  Nicolson T 《Science (New York, N.Y.)》2003,302(5643):282-286

The stone-like otoliths from the ears of teleost fishes are involved in balance and hearing and consist of calcium carbonate crystallites embedded in a protein framework. We report that a previously unknown gene, starmaker, is required in zebrafish for otolith morphogenesis. Reduction of starmaker activity by injection of modified antisense oligonucleotides causes a change in the crystal lattice structure and thus a change in otolith morphology. The expression pattern of starmaker, along with the presence of the protein on the growing otolith, suggest that the expression levels of starmaker control the shape of the otoliths.  相似文献   

Simple solutions: concentrations in the surface region     

Christian SD  Tucker EE 《Science (New York, N.Y.)》1977,198(4313):210

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Paleo-Eskimo mtDNA genome reveals matrilineal discontinuity in Greenland     

Gilbert MT  Kivisild T  Grønnow B  Andersen PK  Metspalu E  Reidla M  Tamm E  Axelsson E  Götherström A  Campos PF  Rasmussen M  Metspalu M  Higham TF  Schwenninger JL  Nathan R  De Hoog CJ  Koch A  Møller LN  Andreasen C  Meldgaard M  Villems R  Bendixen C  Willerslev E 《Science (New York, N.Y.)》2008,320(5884):1787-1789

The Paleo-Eskimo Saqqaq and Independence I cultures, documented from archaeological remains in Northern Canada and Greenland, represent the earliest human expansion into the New World's northern extremes. However, their origin and genetic relationship to later cultures are unknown. We sequenced a mitochondrial genome from a Paleo-Eskimo human by using 3400-to 4500-year-old frozen hair excavated from an early Greenlandic Saqqaq settlement. The sample is distinct from modern Native Americans and Neo-Eskimos, falling within haplogroup D2a1, a group previously observed among modern Aleuts and Siberian Sireniki Yuit. This result suggests that the earliest migrants into the New World's northern extremes derived from populations in the Bering Sea area and were not directly related to Native Americans or the later Neo-Eskimos that replaced them.  相似文献   

In vivo activation of the p53 pathway by small-molecule antagonists of MDM2     

Vassilev LT  Vu BT  Graves B  Carvajal D  Podlaski F  Filipovic Z  Kong N  Kammlott U  Lukacs C  Klein C  Fotouhi N  Liu EA 《Science (New York, N.Y.)》2004,303(5659):844-848

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Polarized notum activation at wounds inhibits Wnt function to promote planarian head regeneration   总被引：2，自引：0，他引：2  

Petersen CP  Reddien PW 《Science (New York, N.Y.)》2011,332(6031):852-855

Regeneration requires initiation of programs tailored to the identity of missing parts. Head-versus-tail regeneration in planarians presents a paradigm for study of this phenomenon. After injury, Wnt signaling promotes tail regeneration. We report that wounding elicits expression of the Wnt inhibitor notum preferentially at anterior-facing wounds. This expression asymmetry occurs at essentially any wound, even if the anterior pole is intact. Inhibition of notum with RNA interference (RNAi) causes regeneration of an anterior-facing tail instead of a head, and double-RNAi experiments indicate that notum inhibits Wnt signaling to promote head regeneration. notum expression is itself controlled by Wnt signaling, suggesting that regulation of feedback inhibition controls the binary head-tail regeneration outcome. We conclude that local detection of wound orientation with respect to tissue axes results in distinct signaling environments that initiate appropriate regeneration responses.  相似文献   

Effect of wnt-1 and related proteins on gap junctional communication in Xenopus embryos     

Olson D  Christian J  Moon R 《Science (New York, N.Y.)》1991,252(5009):1173-1176

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