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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Structure of the polycrystalline zeolite catalyst IM-5 solved by enhanced charge flipping     

Baerlocher C  Gramm F  Massüger L  McCusker LB  He Z  Hovmöller S  Zou X 《Science (New York, N.Y.)》2007,315(5815):1113-1116

Despite substantial advances in crystal structure determination methodology for polycrystalline materials, some problems have remained intractable. A case in point is the zeolite catalyst IM-5, whose structure has eluded determination for almost 10 years. Here we present a charge-flipping structure-solution algorithm, extended to facilitate the combined use of powder diffraction and electron microscopy data. With this algorithm, we have elucidated the complex structure of IM-5, with 24 topologically distinct silicon atoms and an unusual two-dimensional medium-pore channel system. This powerful approach to structure solution can be applied without modification to any type of polycrystalline material (e.g., catalysts, ceramics, pharmaceuticals, complex metal alloys) and is therefore pertinent to a diverse range of scientific disciplines.  相似文献   

Extrusion of cells with inappropriate Dpp signaling from Drosophila wing disc epithelia     

Shen J  Dahmann C 《Science (New York, N.Y.)》2005,307(5716):1789-1790

Decapentaplegic (Dpp) is a signaling molecule that controls growth and patterning of the developing Drosophila wing. Mutant cells lacking Dpp signal transduction have been shown to activate c-Jun amino-terminal kinase (JNK)-dependent apoptosis and to be lost from the wing disc epithelium. These observations have led to the hypothesis that Dpp promotes cell survival by preventing apoptosis. Here, we show that in the absence of JNK-dependent apoptosis, mutant cells lacking Dpp signal transduction can survive; however, they are still lost from the wing disc epithelium. This loss correlates with extensive cytoskeletal changes followed by basal epithelial extrusion. We propose that Dpp promotes cell survival within disc epithelia by affecting cytoskeletal organization.  相似文献   

Comment on "On the origin of interictal activity in human temporal lobe epilepsy in vitro"     

Wozny C  Kivi A  Lehmann TN  Dehnicke C  Heinemann U  Behr J 《Science (New York, N.Y.)》2003,301(5632):463; author reply 463

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