Health Physics     

Hull AP 《Science (New York, N.Y.)》1963,142(3588):73-74

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Role of histone H3 lysine 27 methylation in X inactivation   总被引：1，自引：0，他引：1  

Plath K  Fang J  Mlynarczyk-Evans SK  Cao R  Worringer KA  Wang H  de la Cruz CC  Otte AP  Panning B  Zhang Y 《Science (New York, N.Y.)》2003,300(5616):131-135

The Polycomb group (PcG) protein Eed is implicated in regulation of imprinted X-chromosome inactivation in extraembryonic cells but not of random X inactivation in embryonic cells. The Drosophila homolog of the Eed-Ezh2 PcG protein complex achieves gene silencing through methylation of histone H3 on lysine 27 (H3-K27), which suggests a role for H3-K27 methylation in imprinted X inactivation. Here we demonstrate that transient recruitment of the Eed-Ezh2 complex to the inactive X chromosome (Xi) occurs during initiation of X inactivation in both extraembryonic and embryonic cells and is accompanied by H3-K27 methylation. Recruitment of the complex and methylation on the Xi depend on Xist RNA but are independent of its silencing function. Together, our results suggest a role for Eed-Ezh2-mediated H3-K27 methylation during initiation of both imprinted and random X inactivation and demonstrate that H3-K27 methylation is not sufficient for silencing of the Xi.  相似文献   

Implications for mantle dynamics from the high melting temperature of perovskite     

van Keken PE  Yuen DA  van den Berg AP 《Science (New York, N.Y.)》1994,264(5164):1437-1439

Recent studies have implied that (Mg, Fe)SiO(3)-perovskite, a likely dominant mineral phase in the lower mantle, may have a high melting temperature. The implications of these findings for the dynamics of the lower mantle were investigated with the use of numerical convection models. The results showed that low homologous temperatures (0.3 to 0.5) would prevail in the modeled lower mantle, regardless of the effective Rayleigh number and internal heating rates. High-temperature ductile creep is possible under relatively cold conditions. In models with low rates of internal heating, local maxima of viscosity developed in the mid-lower mantle that were similar to those obtained from inversion of geoid, topography, and plate velocities.  相似文献   

A SIMPLE GAS GENERATOR FOR LABORATORY USE     

Harrison AP 《Science (New York, N.Y.)》1922,56(1445):287-288

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Environment. Environmental monitoring network for India     

Sundareshwar PV  Murtugudde R  Srinivasan G  Singh S  Ramesh KJ  Ramesh R  Verma SB  Agarwal D  Baldocchi D  Baru CK  Baruah KK  Chowdhury GR  Dadhwal VK  Dutt CB  Fuentes J  Gupta PK  Hargrove WW  Howard M  Jha CS  Lal S  Michener WK  Mitra AP  Morris JT  Myneni RR  Naja M  Nemani R  Purvaja R  Raha S  Vanan SK  Sharma M  Subramaniam A  Sukumar R  Twilley RR  Zimmerman PR 《Science (New York, N.Y.)》2007,316(5822):204-205

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Formation of a nematic fluid at high fields in Sr3Ru2O7     

Borzi RA  Grigera SA  Farrell J  Perry RS  Lister SJ  Lee SL  Tennant DA  Maeno Y  Mackenzie AP 《Science (New York, N.Y.)》2007,315(5809):214-217

In principle, a complex assembly of strongly interacting electrons can self-organize into a wide variety of collective states, but relatively few such states have been identified in practice. We report that, in the close vicinity of a metamagnetic quantum critical point, high-purity strontium ruthenate Sr3Ru2O7 possesses a large magnetoresistive anisotropy, consistent with the existence of an electronic nematic fluid. We discuss a striking phenomenological similarity between our observations and those made in high-purity two-dimensional electron fluids in gallium arsenide devices.  相似文献   

The Miller volcanic spark discharge experiment     

Johnson AP  Cleaves HJ  Dworkin JP  Glavin DP  Lazcano A  Bada JL 《Science (New York, N.Y.)》2008,322(5900):404

Miller's 1950s experiments used, besides the apparatus known in textbooks, one that generated a hot water mist in the spark flask, simulating a water vapor-rich volcanic eruption. We found the original extracts of this experiment in Miller's material and reanalyzed them. The volcanic apparatus produced a wider variety of amino acids than the classic one. Release of reduced gases in volcanic eruptions accompanied by lightning could have been common on the early Earth. Prebiotic compounds synthesized in these environments could have locally accumulated, where they could have undergone further processing.  相似文献   

Sustainability. Paying for ecosystem services--promise and peril     

Kinzig AP  Perrings C  Chapin FS  Polasky S  Smith VK  Tilman D  Turner BL 《Science (New York, N.Y.)》2011,334(6056):603-604

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Proteoglycan-specific molecular switch for RPTPσ clustering and neuronal extension     

Coles CH  Shen Y  Tenney AP  Siebold C  Sutton GC  Lu W  Gallagher JT  Jones EY  Flanagan JG  Aricescu AR 《Science (New York, N.Y.)》2011,332(6028):484-488

Heparan and chondroitin sulfate proteoglycans (HSPGs and CSPGs, respectively) regulate numerous cell surface signaling events, with typically opposite effects on cell function. CSPGs inhibit nerve regeneration through receptor protein tyrosine phosphatase sigma (RPTPσ). Here we report that RPTPσ acts bimodally in sensory neuron extension, mediating CSPG inhibition and HSPG growth promotion. Crystallographic analyses of a shared HSPG-CSPG binding site reveal a conformational plasticity that can accommodate diverse glycosaminoglycans with comparable affinities. Heparan sulfate and analogs induced RPTPσ ectodomain oligomerization in solution, which was inhibited by chondroitin sulfate. RPTPσ and HSPGs colocalize in puncta on sensory neurons in culture, whereas CSPGs occupy the extracellular matrix. These results lead to a model where proteoglycans can exert opposing effects on neuronal extension by competing to control the oligomerization of a common receptor.  相似文献   

SCHOOL GRADES--TO WHAT TYPE OF DISTRIBUTION SHALL THEY CONFORM?     

Weiss AP 《Science (New York, N.Y.)》1912,36(926):403-407

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