排序方式: 共有149条查询结果,搜索用时 15 毫秒
141.
The human fossil assemblage from the Mladec Caves in Moravia (Czech Republic) has been considered to derive from a middle or later phase of the Central European Aurignacian period on the basis of archaeological remains (a few stone artefacts and organic items such as bone points, awls, perforated teeth), despite questions of association between the human fossils and the archaeological materials and concerning the chronological implications of the limited archaeological remains. The morphological variability in the human assemblage, the presence of apparently archaic features in some specimens, and the assumed early date of the remains have made this fossil assemblage pivotal in assessments of modern human emergence within Europe. We present here the first successful direct accelerator mass spectrometry radiocarbon dating of five representative human fossils from the site. We selected sample materials from teeth and from one bone for 14C dating. The four tooth samples yielded uncalibrated ages of approximately 31,000 14C years before present, and the bone sample (an ulna) provided an uncertain more-recent age. These data are sufficient to confirm that the Mladec human assemblage is the oldest cranial, dental and postcranial assemblage of early modern humans in Europe and is therefore central to discussions of modern human emergence in the northwestern Old World and the fate of the Neanderthals. 相似文献
142.
Genome-wide association study and mouse model identify interaction between RET and EDNRB pathways in Hirschsprung disease 总被引:13,自引:0,他引:13
Carrasquillo MM McCallion AS Puffenberger EG Kashuk CS Nouri N Chakravarti A 《Nature genetics》2002,32(2):237-244
Genetic studies of Hirschsprung disease, a common congenital malformation, have identified eight genes with mutations that can be associated with this condition. Mutations at individual loci are, however, neither necessary nor sufficient to cause clinical disease. We conducted a genome-wide association study in 43 Mennonite family trios using 2,083 microsatellites and single-nucleotide polymorphisms and a new multipoint linkage disequilibrium method that searches for association arising from common ancestry. We identified susceptibility loci at 10q11, 13q22 and 16q23; the gene at 13q22 is EDNRB, encoding a G protein-coupled receptor (GPCR) and the gene at 10q11 is RET, encoding a receptor tyrosine kinase (RTK). Statistically significant joint transmission of RET and EDNRB alleles in affected individuals and non-complementation of aganglionosis in mouse intercrosses between Ret null and the Ednrb hypomorphic piebald allele are suggestive of epistasis between EDNRB and RET. Thus, genetic interaction between mutations in RET and EDNRB is an underlying mechanism for this complex disorder. 相似文献
143.
Erik?WeberEmail author Jeroen?Van?Bouwel Robrecht?Vanderbeeken 《Foundations of Science》2005,10(4):437-454
In the literature on scientific explanation two types of pluralism are very common. The first concerns the distinction between
explanations of singular facts and explanations of laws: there is a consensus that they have a different structure. The second
concerns the distinction between causal explanations and uni.cation explanations: most people agree that both are useful and
that their structure is different. In this article we argue for pluralism within the area of causal explanations: we claim that the structure of a causal explanation depends on the causal structure of the
relevant fragment of the world and on the interests of the explainer. 相似文献
144.
Carlton VE Harris BZ Puffenberger EG Batta AK Knisely AS Robinson DL Strauss KA Shneider BL Lim WA Salen G Morton DH Bull LN 《Nature genetics》2003,34(1):91-96
Familial hypercholanemia (FHC) is characterized by elevated serum bile acid concentrations, itching, and fat malabsorption. We show here that FHC in Amish individuals is associated with mutations in tight junction protein 2 (encoded by TJP2, also known as ZO-2) and bile acid Coenzyme A: amino acid N-acyltransferase (encoded by BAAT). The mutation of TJP2, which occurs in the first PDZ domain, reduces domain stability and ligand binding in vitro. We noted a morphological change in hepatic tight junctions. The mutation of BAAT, a bile acid-conjugating enzyme, abrogates enzyme activity; serum of individuals homozygous with respect to this mutation contains only unconjugated bile acids. Mutations in both TJP2 and BAAT may disrupt bile acid transport and circulation. Inheritance seems to be oligogenic, with genotype at BAAT modifying penetrance in individuals homozygous with respect to the mutation in TJP2. 相似文献
145.
在地图学中,地图投影是指建立地球表面上一点与投影平面上点之间的一一对应关系。地图投影的目的是通过将不可展的球面投影到一个可展曲面上,然后将该曲面展开成为一个平面,来保证空间信息在地域上的连续性、完整性和可测度性。根据美国著名地图投影专家J.P.Snyder统计,世界上地图投影种类现有256种。 相似文献
146.
Ichthyostega was the first Devonian tetrapod to be subject to a whole-body reconstruction. It remains, together with Acanthostega, one of only two Devonian tetrapods for which near-complete postcranial material is available. It is thus crucially important for our understanding of the earliest stages of tetrapod evolution and terrestrialization. Here we show a new reconstruction of Ichthyostega based on extensive re-examination of original material and augmented by recently collected specimens. Our reconstruction differs substantially from those previously published and reveals hitherto unrecognized regionalization in the vertebral column. Ichthyostega is the earliest vertebrate to show obvious adaptations for non-swimming locomotion. Uniquely among early tetrapods, the presacral vertebral column shows pronounced regionalization of neural arch morphology, suggesting that it was adapted for dorsoventral rather than lateral flexion. 相似文献
147.
Augmentation of tumor angiogenesis by a Myc-activated microRNA cluster 总被引:28,自引:0,他引:28
Dews M Homayouni A Yu D Murphy D Sevignani C Wentzel E Furth EE Lee WM Enders GH Mendell JT Thomas-Tikhonenko A 《Nature genetics》2006,38(9):1060-1065
Human adenocarcinomas commonly harbor mutations in the KRAS and MYC proto-oncogenes and the TP53 tumor suppressor gene. All three genetic lesions are potentially pro-angiogenic, as they sustain production of vascular endothelial growth factor (VEGF). Yet Kras-transformed mouse colonocytes lacking p53 formed indolent, poorly vascularized tumors, whereas additional transduction with a Myc-encoding retrovirus promoted vigorous vascularization and growth. In addition, VEGF levels were unaffected by Myc, but enhanced neovascularization correlated with downregulation of anti-angiogenic thrombospondin-1 (Tsp1) and related proteins, such as connective tissue growth factor (CTGF). Both Tsp1 and CTGF are predicted targets for repression by the miR-17-92 microRNA cluster, which was upregulated in colonocytes coexpressing K-Ras and c-Myc. Indeed, miR-17-92 knockdown with antisense 2'-O-methyl oligoribonucleotides partly restored Tsp1 and CTGF expression; in addition, transduction of Ras-only cells with a miR-17-92-encoding retrovirus reduced Tsp1 and CTGF levels. Notably, miR-17-92-transduced cells formed larger, better-perfused tumors. These findings establish a role for microRNAs in non-cell-autonomous Myc-induced tumor phenotypes. 相似文献
148.
Barouch DH Liu J Li H Maxfield LF Abbink P Lynch DM Iampietro MJ SanMiguel A Seaman MS Ferrari G Forthal DN Ourmanov I Hirsch VM Carville A Mansfield KG Stablein D Pau MG Schuitemaker H Sadoff JC Billings EA Rao M Robb ML Kim JH Marovich MA Goudsmit J Michael NL 《Nature》2012,482(7383):89-93
Preclinical studies of human immunodeficiency virus type 1 (HIV-1) vaccine candidates have typically shown post-infection virological control, but protection against acquisition of infection has previously only been reported against neutralization-sensitive virus challenges. Here we demonstrate vaccine protection against acquisition of fully heterologous, neutralization-resistant simian immunodeficiency virus (SIV) challenges in rhesus monkeys. Adenovirus/poxvirus and adenovirus/adenovirus-vector-based vaccines expressing SIV(SME543) Gag, Pol and Env antigens resulted in an 80% or greater reduction in the per-exposure probability of infection against repetitive, intrarectal SIV(MAC251) challenges in rhesus monkeys. Protection against acquisition of infection showed distinct immunological correlates compared with post-infection virological control and required the inclusion of Env in the vaccine regimen. These data demonstrate the proof-of-concept that optimized HIV-1 vaccine candidates can block acquisition of stringent, heterologous, neutralization-resistant virus challenges in rhesus monkeys. 相似文献
149.
Genome divergence in two Prochlorococcus ecotypes reflects oceanic niche differentiation 总被引:1,自引:0,他引:1
Rocap G Larimer FW Lamerdin J Malfatti S Chain P Ahlgren NA Arellano A Coleman M Hauser L Hess WR Johnson ZI Land M Lindell D Post AF Regala W Shah M Shaw SL Steglich C Sullivan MB Ting CS Tolonen A Webb EA Zinser ER Chisholm SW 《Nature》2003,424(6952):1042-1047
The marine unicellular cyanobacterium Prochlorococcus is the smallest-known oxygen-evolving autotroph. It numerically dominates the phytoplankton in the tropical and subtropical oceans, and is responsible for a significant fraction of global photosynthesis. Here we compare the genomes of two Prochlorococcus strains that span the largest evolutionary distance within the Prochlorococcus lineage and that have different minimum, maximum and optimal light intensities for growth. The high-light-adapted ecotype has the smallest genome (1,657,990 base pairs, 1,716 genes) of any known oxygenic phototroph, whereas the genome of its low-light-adapted counterpart is significantly larger, at 2,410,873 base pairs (2,275 genes). The comparative architectures of these two strains reveal dynamic genomes that are constantly changing in response to myriad selection pressures. Although the two strains have 1,350 genes in common, a significant number are not shared, and these have been differentially retained from the common ancestor, or acquired through duplication or lateral transfer. Some of these genes have obvious roles in determining the relative fitness of the ecotypes in response to key environmental variables, and hence in regulating their distribution and abundance in the oceans. 相似文献