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排序方式: 共有287条查询结果,搜索用时 46 毫秒
31.
Evolution of neoplastic cell lineages in Barrett oesophagus. 总被引:20,自引:0,他引:20
M T Barrett C A Sanchez L J Prevo D J Wong P C Galipeau T G Paulson P S Rabinovitch B J Reid 《Nature genetics》1999,22(1):106-109
It has been hypothesized that neoplastic progression develops as a consequence of an acquired genetic instability and the subsequent evolution of clonal populations with accumulated genetic errors. Accordingly, human cancers and some premalignant lesions contain multiple genetic abnormalities not present in the normal tissues from which the neoplasms arose. Barrett oesophagus (BE) is a premalignant condition which predisposes to oesophageal adenocarcinoma (EA) that can be biopsied prospectively over time because endoscopic surveillance is recommended for early detection of cancer. In addition, oesophagectomy specimens frequently contain the premalignant epithelium from which the cancer arose. Neoplastic progression in BE is associated with alterations in TP53 (also known as p53) and CDKN2A (also known as p16) and non-random losses of heterozygosity (LOH). Aneuploid or increased 4N populations occur in more than 90-95% of EAs, arise in premalignant epithelium and predict progression. We have previously shown in small numbers of patients that disruption of TP53 and CDKN2A typically occurs before aneuploidy and cancer. Here, we determine the evolutionary relationships of non-random LOH, TP53 and CDKN2A mutations, CDKN2A CpG-island methylation and ploidy during neoplastic progression. Diploid cell progenitors with somatic genetic or epigenetic abnormalities in TP53 and CDKN2A were capable of clonal expansion, spreading to large regions of oesophageal mucosa. The subsequent evolution of neoplastic progeny frequently involved bifurcations and LOH at 5q, 13q and 18q that occurred in no obligate order relative to each other, DNA-content aneuploidy or cancer. Our results indicate that clonal evolution is more complex than predicted by linear models. 相似文献
32.
Molecular characterization and expression of the gene encoding human erythroid-potentiating activity 总被引:11,自引:0,他引:11
J C Gasson D W Golde S E Kaufman C A Westbrook R M Hewick R J Kaufman G G Wong P A Temple A C Leary E L Brown 《Nature》1985,315(6022):768-771
Erythropoietin is the primary physiological regulator of erythropoiesis; however, in vitro studies have identified another class of mediators which appear to be important in stimulating erythroid progenitors. These factors have generally been referred to as burst-promoting activities (BPA), because they stimulate the growth of early erythroid progenitors referred to as burst-forming units-erythroid (BFU-E) which give rise to colonies of up to thousands of haemoglobinized cells. We recently reported purification of a burst-promoting activity from medium conditioned by the Mo T-lymphoblast cell line infected with human T-cell lymphotropic virus type II (HTLV-II). This purified glycoprotein of relative molecular mass (Mr) 28,000 also stimulates colony formation by more mature erythroid precursors (CFU-E) and is therefore referred to as erythroid-potentiating activity (EPA). Purified EPA specifically stimulates human and murine cells of the erythroid lineage, unlike murine interleukin-3 (IL-3) which stimulates precursor cells from all haematopoietic lineages. We report here the isolation of a complementary DNA molecular clone encoding EPA and its use in producing EPA in COS (monkey) cells and CHO (Chinese hamster ovary) cells. We also define the organization of the EPA gene in human DNA. 相似文献
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34.
Extensive and coordinated transcription of noncoding RNAs within cell-cycle promoters 总被引:5,自引:0,他引:5
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36.
D E Humphries G W Wong D S Friend M F Gurish W T Qiu C Huang A H Sharpe R L Stevens 《Nature》1999,400(6746):769-772
37.
Human eyes are in constant and rapid motion even when observers try to maintain steady fixation. Also, the visual system has a sluggish temporal response. In combination, these two factors would be expected to blur stimuli and reduce spatial sensitivity. But observers are able to detect a difference in separation of a few seconds of arc between two closely spaced parallel lines. Here we report that even very large amounts of positional jitter of the line pair has minimal impact on this ability. This result is in marked contrast to the deterioration observed when targets are swept linearly across the retina, but is consistent with a system that must ignore oculomotor jitter. To explain these results will require a re-evaluation of current models of position coding in human vision. 相似文献
38.
In the mammalian cortex, glutamate and gamma-aminobutyric acid (GABA) are the principal transmitters mediating excitatory and inhibitory synaptic events. Glutamate activates cation conductances that lead to membrane depolarization whereas GABA controls chloride conductances that produce hyperpolarization. Here we report that the GABAA-activated conductance in hippocampal pyramidal cells is enhanced by glutamate at concentrations below that required for its excitatory action. The GABA-potentiating effect can be induced, with comparable potency, by several glutamate analogues such as quisqualate, N-methyl-D-aspartate (NMDA), kainate and, surprisingly, by D-2-amino-5-phosphonovalerate (APV), an antagonist for NMDA receptors. Data from dose-response curves show that glutamate enhances the GABAA conductance without significantly changing GABA binding affinity. The low concentration of glutamate needed to enhance GABAA responses raises the possibility that glutamate modulates the strength of GABA-mediated transmission in the cortex. 相似文献
39.
河南浮戏山植物区系地理及其近缘关系 总被引:3,自引:0,他引:3
浮戏山有种子植物96科313属552种,区系成分以北温带、泛热带和旧世界温带三种成分为主,其次是东亚和东亚北美间断成分,植物区系具有明显的温带性质。以植物地理成分为指标,将浮戏山和全国其它19个地区进行系统聚类分析,结果表明,浮戏山植物区系成分和与其同处于中纬度地区的河南境内的桐柏山、大别山、小秦岭、老君山及山西中条山山东泰山最为相似,而与高纬度地区的长白山。低纬度地区的广西大瑶山和海南五指山最为 相似文献
40.
用光镜和电镜观察了福建水牛的肉孢子虫形态,证明有两型的孢囊。大型包囊的原级囊壁有菜花状突起,顶端呈树枝状分支,内有环纹小纤丝、微管和电子致密颗粒,经鉴定是梭状肉孢子虫(Sarcocystis fusiformis)。小型包囊有两种,其中一种的囊壁外侧有倾斜的放射状突起条纹,其原级囊壁具有斜状突起的绒毛,鉴定为李氏肉孢子虫(S.Levinei),另一小型包囊的囊壁光滑,无放射状条纹,囊内隔板不明显,所含的慢殖子较少,与李氏肉孢子虫有明显差异,故暂不定种名。 相似文献