Activation of ras oncogenes preceding the onset of neoplasia   总被引：24，自引：0，他引：24  

R Kumar  S Sukumar  M Barbacid 《Science (New York, N.Y.)》1990,248(4959):1101-1104

The identification of ras oncogenes in human and animal cancers including precancerous lesions indicates that these genes participate in the early stages of neoplastic development. Yet, these observations do not define the timing of ras oncogene activation in the multistep process of carcinogenesis. To ascertain the timing of ras oncogene activation, an animal model system was devised that involves the induction of mammary carcinomas in rats exposed at birth to the carcinogen nitrosomethylurea. High-resolution restriction fragment length polymorphism analysis of polymerase chain reaction-amplified ras sequences revealed the presence of both H-ras and K-ras oncogenes in normal mammary glands 2 weeks after carcinogen treatment and at least 2 months before the onset of neoplasia. These ras oncogenes can remain latent within the mammary gland until exposure to estrogens, demonstrating that activation of ras oncogenes can precede the onset of neoplasia and suggesting that normal physiological proliferative processes such as estrogen-induced mammary gland development may lead to neoplasia if the targeted cells harbor latent ras oncogenes.  相似文献   

运动的连续平直面上边界层流之解的渐近性质     

Sing.  BB Kumar  A. 《湖南农业大学学报(自然科学版)》1989,16(1)

Falkner-Skan方程描述磁场中连续平直面上不可压缩粘性流的边界层流,本文研究此方程初值问题之解的渐近性质。  相似文献   

Apoptosis. A cinderella caspase takes center stage     

Kumar S  Vaux DL 《Science (New York, N.Y.)》2002,297(5585):1290-1291

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Three-dimensional structure of a recombinant gap junction membrane channel     

Unger VM  Kumar NM  Gilula NB  Yeager M 《Science (New York, N.Y.)》1999,283(5405):1176-1180

Gap junction membrane channels mediate electrical and metabolic coupling between adjacent cells. The structure of a recombinant cardiac gap junction channel was determined by electron crystallography at resolutions of 7.5 angstroms in the membrane plane and 21 angstroms in the vertical direction. The dodecameric channel was formed by the end-to-end docking of two hexamers, each of which displayed 24 rods of density in the membrane interior, which is consistent with an alpha-helical conformation for the four transmembrane domains of each connexin subunit. The transmembrane alpha-helical rods contrasted with the double-layered appearance of the extracellular domains. Although not indicative for a particular type of secondary structure, the protein density that formed the extracellular vestibule provided a tight seal to exclude the exchange of substances with the extracellular milieu.  相似文献   

Trace water content of salt in louisiana salt domes     

Knauth LP  Kumar MB 《Science (New York, N.Y.)》1981,213(4511):1005-1007

The trace water content of salt in six Louisiana salt domes has been determined and has been found to be the lowest of any terrestrial rock type. The average water content of normal domal salt is on the order of 0.003 percent by weight, but anomalous zones within salt stocks can have more than ten times this amount. From the average value, the minimum amount of water in liters, W, available to collect around a radioactive waste repository is given as W = 0.28 r(3), where r is the radius in meters of the sphere in which water may be thermally activated to migrate completely to the repository.  相似文献   

Appendage regeneration in adult vertebrates and implications for regenerative medicine     

Brockes JP  Kumar A 《Science (New York, N.Y.)》2005,310(5756):1919-1923

The regeneration of complex structures in adult salamanders depends on mechanisms that offer pointers for regenerative medicine. These include the plasticity of differentiated cells and the retention in regenerative cells of local cues such as positional identity. Limb regeneration proceeds by the local formation of a blastema, a growth zone of mesenchymal stem cells on the stump. The blastema can regenerate autonomously as a self-organizing system over variable linear dimensions. Here we consider the prospects for limb regeneration in mammals from this viewpoint.  相似文献   

Thin Films of n-Si/Poly-(CH3)3Si-Cyclooctatetraene: Conducting-Polymer Solar Cells and Layered Structures     

Sailor MJ  Ginsburg EJ  Gorman CB  Kumar A  Grubbs RH  Lewis NS 《Science (New York, N.Y.)》1990,249(4973):1146-1149

The optical and electronic properties of thin films of the solution-processible polymer poly-(CH(3))(3)Si-cyclooctatetraene are presented. This conjugated polymer is based on a polyacetylene backbone with (CH(3))(3)Si side groups. Thin transparent films have been cast onto n-doped silicon (n-Si) substrates and doped with iodine to form surfacebarrier solar cells. The devices produce photovoltages that are at the theoretical limit and that are much greater than can be obtained from n-Si contacts with conventional metals. Two methods for forming layered polymeric materials, one involving the spincoating of preformed polymers and the other comprising the sequential polymerization of different monomers, are also described. An organic polymer analog of a metal/insulator/metal capacitor has been constructed with the latter method.  相似文献   

Properties of gamma-ray burst progenitor stars     

Kumar P  Narayan R  Johnson JL 《Science (New York, N.Y.)》2008,321(5887):376-379

We determined some basic properties of stars that produce spectacular gamma-ray bursts at the end of their lives. We assumed that accretion of the outer portion of the stellar core by a central black hole fuels the prompt emission and that fall-back and accretion of the stellar envelope later produce the plateau in the x-ray light curve seen in some bursts. Using x-ray data for three bursts, we estimated the radius of the stellar core to be approximately (1 - 3) x 10(10) cm and that of the stellar envelope to be approximately (1 - 2) x 10(11) cm. The density profile in the envelope is fairly shallow, with rho approximately r(-2) (where rho is density and r is distance from the center of the explosion). The rotation speeds of the core and envelope are approximately 0.05 and approximately 0.2 of the local Keplerian speed, respectively.  相似文献   

The ecoresponsive genome of Daphnia pulex     

Colbourne JK  Pfrender ME  Gilbert D  Thomas WK  Tucker A  Oakley TH  Tokishita S  Aerts A  Arnold GJ  Basu MK  Bauer DJ  Cáceres CE  Carmel L  Casola C  Choi JH  Detter JC  Dong Q  Dusheyko S  Eads BD  Fröhlich T  Geiler-Samerotte KA  Gerlach D  Hatcher P  Jogdeo S  Krijgsveld J  Kriventseva EV  Kültz D  Laforsch C  Lindquist E  Lopez J  Manak JR  Muller J  Pangilinan J  Patwardhan RP  Pitluck S  Pritham EJ  Rechtsteiner A  Rho M  Rogozin IB  Sakarya O  Salamov A  Schaack S  Shapiro H  Shiga Y  Skalitzky C  Smith Z  Souvorov A  Sung W 《Science (New York, N.Y.)》2011,331(6017):555-561

We describe the draft genome of the microcrustacean Daphnia pulex, which is only 200 megabases and contains at least 30,907 genes. The high gene count is a consequence of an elevated rate of gene duplication resulting in tandem gene clusters. More than a third of Daphnia's genes have no detectable homologs in any other available proteome, and the most amplified gene families are specific to the Daphnia lineage. The coexpansion of gene families interacting within metabolic pathways suggests that the maintenance of duplicated genes is not random, and the analysis of gene expression under different environmental conditions reveals that numerous paralogs acquire divergent expression patterns soon after duplication. Daphnia-specific genes, including many additional loci within sequenced regions that are otherwise devoid of annotations, are the most responsive genes to ecological challenges.  相似文献   

Analysis of the published calorimetric evidence for electrochemical fusion of deuterium in palladium     

Miskelly GM  Heben MJ  Kumar A  Penner RM  Sailor MJ  Lewis NS 《Science (New York, N.Y.)》1989,246(4931):793-796

Estimates are given of the raw data that are the basis for the claims of excess power production by the electrochemical charging of palladium in deuterium oxide (D(2)O). Calorimetric results are also presented that show no anomalous power production in either 0.1M LiOD/D(2)O or 0.1M LiOH/H(2)O (LiOH is lithium hydroxide). Several possible sources of error in open-system calorimetry are discussed that can confound interpretation of temperature changes in terms of anomalous power production.  相似文献