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排序方式: 共有877条查询结果,搜索用时 359 毫秒
811.
Le Fèvre O Paltani S Arnouts S Charlot S Foucaud S Ilbert O McCracken HJ Zamorani G Bottini D Garilli B Le Brun V Maccagni D Picat JP Scaramella R Scodeggio M Tresse L Vettolani G Zanichelli A Adami C Bardelli S Bolzonella M Cappi A Ciliegi P Contini T Franzetti P Gavignaud I Guzzo L Iovino A Marano B Marinoni C Mazure A Meneux B Merighi R Pellò R Pollo A Pozzetti L Radovich M Zucca E Arnaboldi M Bondi M Bongiorno A Busarello G Gregorini L Lamareille F Mathez G Mellier Y Merluzzi P Ripepi V 《Nature》2005,437(7058):519-521
To understand the evolution of galaxies, we need to know as accurately as possible how many galaxies were present in the Universe at different epochs. Galaxies in the young Universe have hitherto mainly been identified using their expected optical colours, but this leaves open the possibility that a significant population remains undetected because their colours are the result of a complex mix of stars, gas, dust or active galactic nuclei. Here we report the results of a flux-limited I-band survey of galaxies at look-back times of 9 to 12 billion years. We find 970 galaxies with spectroscopic redshifts between 1.4 and 5. This population is 1.6 to 6.2 times larger than previous estimates, with the difference increasing towards brighter magnitudes. Strong ultraviolet continua (in the rest frame of the galaxies) indicate vigorous star formation rates of more than 10-100 solar masses per year. As a consequence, the cosmic star formation rate representing the volume-averaged production of stars is higher than previously measured at redshifts of 3 to 4. 相似文献
812.
Nedimović MR Carbotte SM Harding AJ Detrick RS Canales JP Diebold JB Kent GM Tischer M Babcock JM 《Nature》2005,436(7054):1149-1152
The Earth's oceanic crust crystallizes from magmatic systems generated at mid-ocean ridges. Whereas a single magma body residing within the mid-crust is thought to be responsible for the generation of the upper oceanic crust, it remains unclear if the lower crust is formed from the same magma body, or if it mainly crystallizes from magma lenses located at the base of the crust. Thermal modelling, tomography, compliance and wide-angle seismic studies, supported by geological evidence, suggest the presence of gabbroic-melt accumulations within the Moho transition zone in the vicinity of fast- to intermediate-spreading centres. Until now, however, no reflection images have been obtained of such a structure within the Moho transition zone. Here we show images of groups of Moho transition zone reflection events that resulted from the analysis of approximately 1,500 km of multichannel seismic data collected across the intermediate-spreading-rate Juan de Fuca ridge. From our observations we suggest that gabbro lenses and melt accumulations embedded within dunite or residual mantle peridotite are the most probable cause for the observed reflectivity, thus providing support for the hypothesis that the crust is generated from multiple magma bodies. 相似文献
813.
Maskos U Molles BE Pons S Besson M Guiard BP Guilloux JP Evrard A Cazala P Cormier A Mameli-Engvall M Dufour N Cloëz-Tayarani I Bemelmans AP Mallet J Gardier AM David V Faure P Granon S Changeux JP 《Nature》2005,436(7047):103-107
Worldwide, 100 million people are expected to die this century from the consequences of nicotine addiction, but nicotine is also known to enhance cognitive performance. Identifying the molecular mechanisms involved in nicotine reinforcement and cognition is a priority and requires the development of new in vivo experimental paradigms. The ventral tegmental area (VTA) of the midbrain is thought to mediate the reinforcement properties of many drugs of abuse. Here we specifically re-expressed the beta2-subunit of the nicotinic acetylcholine receptor (nAChR) by stereotaxically injecting a lentiviral vector into the VTA of mice carrying beta2-subunit deletions. We demonstrate the efficient re-expression of electrophysiologically responsive, ligand-binding nicotinic acetylcholine receptors in dopamine-containing neurons of the VTA, together with the recovery of nicotine-elicited dopamine release and nicotine self-administration. We also quantified exploratory behaviours of the mice, and showed that beta2-subunit re-expression restored slow exploratory behaviour (a measure of cognitive function) to wild-type levels, but did not affect fast navigation behaviour. We thus demonstrate the sufficient role of the VTA in both nicotine reinforcement and endogenous cholinergic regulation of cognitive functions. 相似文献
814.
Veazey RS Klasse PJ Schader SM Hu Q Ketas TJ Lu M Marx PA Dufour J Colonno RJ Shattock RJ Springer MS Moore JP 《Nature》2005,438(7064):99-102
Human immunodeficiency virus type 1 (HIV-1) continues to spread, principally by heterosexual sex, but no vaccine is available. Hence, alternative prevention methods are needed to supplement educational and behavioural-modification programmes. One such approach is a vaginal microbicide: the application of inhibitory compounds before intercourse. Here, we have evaluated the microbicide concept using the rhesus macaque 'high dose' vaginal transmission model with a CCR5-receptor-using simian-human immunodeficiency virus (SHIV-162P3) and three compounds that inhibit different stages of the virus-cell attachment and entry process. These compounds are BMS-378806, a small molecule that binds the viral gp120 glycoprotein and prevents its attachment to the CD4 and CCR5 receptors, CMPD167, a small molecule that binds to CCR5 to inhibit gp120 association, and C52L, a bacterially expressed peptide inhibitor of gp41-mediated fusion. In vitro, all three compounds inhibit infection of T cells and cervical tissue explants, and C52L acts synergistically with CMPD167 or BMS-378806 to inhibit infection of cell lines. In vivo, significant protection was achieved using each compound alone and in combinations. CMPD167 and BMS-378806 were protective even when applied 6 h before challenge. 相似文献
815.
Neurotoxic esterase: not so toxic? 总被引:2,自引:0,他引:2
O'Callaghan JP 《Nature genetics》2003,33(4):437-438
816.
Dodé C Levilliers J Dupont JM De Paepe A Le Dû N Soussi-Yanicostas N Coimbra RS Delmaghani S Compain-Nouaille S Baverel F Pêcheux C Le Tessier D Cruaud C Delpech M Speleman F Vermeulen S Amalfitano A Bachelot Y Bouchard P Cabrol S Carel JC Delemarre-van de Waal H Goulet-Salmon B Kottler ML Richard O Sanchez-Franco F Saura R Young J Petit C Hardelin JP 《Nature genetics》2003,33(4):463-465
We took advantage of overlapping interstitial deletions at chromosome 8p11-p12 in two individuals with contiguous gene syndromes and defined an interval of roughly 540 kb associated with a dominant form of Kallmann syndrome, KAL2. We establish here that loss-of-function mutations in FGFR1 underlie KAL2 whereas a gain-of-function mutation in FGFR1 has been shown to cause a form of craniosynostosis. Moreover, we suggest that the KAL1 gene product, the extracellular matrix protein anosmin-1, is involved in FGF signaling and propose that the gender difference in anosmin-1 dosage (because KAL1 partially escapes X inactivation) explains the higher prevalence of the disease in males. 相似文献
817.
Mutations in PCSK9 cause autosomal dominant hypercholesterolemia 总被引:22,自引:0,他引:22
Abifadel M Varret M Rabès JP Allard D Ouguerram K Devillers M Cruaud C Benjannet S Wickham L Erlich D Derré A Villéger L Farnier M Beucler I Bruckert E Chambaz J Chanu B Lecerf JM Luc G Moulin P Weissenbach J Prat A Krempf M Junien C Seidah NG Boileau C 《Nature genetics》2003,34(2):154-156
Autosomal dominant hypercholesterolemia (ADH; OMIM144400), a risk factor for coronary heart disease, is characterized by an increase in low-density lipoprotein cholesterol levels that is associated with mutations in the genes LDLR (encoding low-density lipoprotein receptor) or APOB (encoding apolipoprotein B). We mapped a third locus associated with ADH, HCHOLA3 at 1p32, and now report two mutations in the gene PCSK9 (encoding proprotein convertase subtilisin/kexin type 9) that cause ADH. PCSK9 encodes NARC-1 (neural apoptosis regulated convertase), a newly identified human subtilase that is highly expressed in the liver and contributes to cholesterol homeostasis. 相似文献
818.
Vanhamme L Paturiaux-Hanocq F Poelvoorde P Nolan DP Lins L Van Den Abbeele J Pays A Tebabi P Van Xong H Jacquet A Moguilevsky N Dieu M Kane JP De Baetselier P Brasseur R Pays E 《Nature》2003,422(6927):83-87
Human sleeping sickness in east Africa is caused by the parasite Trypanosoma brucei rhodesiense. The basis of this pathology is the resistance of these parasites to lysis by normal human serum (NHS). Resistance to NHS is conferred by a gene that encodes a truncated form of the variant surface glycoprotein termed serum resistance associated protein (SRA). We show that SRA is a lysosomal protein, and that the amino-terminal alpha-helix of SRA is responsible for resistance to NHS. This domain interacts strongly with a carboxy-terminal alpha-helix of the human-specific serum protein apolipoprotein L-I (apoL-I). Depleting NHS of apoL-I, by incubation with SRA or anti-apoL-I, led to the complete loss of trypanolytic activity. Addition of native or recombinant apoL-I either to apoL-I-depleted NHS or to fetal calf serum induced lysis of NHS-sensitive, but not NHS-resistant, trypanosomes. Confocal microscopy demonstrated that apoL-I is taken up through the endocytic pathway into the lysosome. We propose that apoL-I is the trypanosome lytic factor of NHS, and that SRA confers resistance to lysis by interaction with apoL-I in the lysosome. 相似文献
819.
Hjorth J Sollerman J Møller P Fynbo JP Woosley SE Kouveliotou C Tanvir NR Greiner J Andersen MI Castro-Tirado AJ Castro Cerón JM Fruchter AS Gorosabel J Jakobsson P Kaper L Klose S Masetti N Pedersen H Pedersen K Pian E Palazzi E Rhoads JE Rol E van den Heuvel EP Vreeswijk PM Watson D Wijers RA 《Nature》2003,423(6942):847-850
Over the past five years evidence has mounted that long-duration (>2 s) gamma-ray bursts (GRBs)-the most luminous of all astronomical explosions-signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like 'bumps' in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the 'collapsar' model. 相似文献
820.
The organization of neurons into columns is a prominent feature of central nervous system structure and function. In many regions of the central nervous system the grouping of neurons into columns links cell-body position to axonal trajectory, thus contributing to the establishment of topographic neural maps. This link is prominent in the developing spinal cord, where columnar sets of motor neurons innervate distinct targets in the periphery. We show here that sequential phases of Hox-c protein expression and activity control the columnar differentiation of spinal motor neurons. Hox expression in neural progenitors is established by graded fibroblast growth factor signalling and translated into a distinct motor neuron Hox pattern. Motor neuron columnar fate then emerges through cell autonomous repressor and activator functions of Hox proteins. Hox proteins also direct the expression of genes that establish motor topographic projections, thus implicating Hox proteins as critical determinants of spinal motor neuron identity and organization. 相似文献