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971.
Castets M Broutier L Molin Y Brevet M Chazot G Gadot N Paquet A Mazelin L Jarrosson-Wuilleme L Scoazec JY Bernet A Mehlen P 《Nature》2012,482(7386):534-537
The role of deleted in colorectal carcinoma (DCC) as a tumour suppressor has been a matter of debate for the past 15 years. DCC gene expression is lost or markedly reduced in the majority of advanced colorectal cancers and, by functioning as a dependence receptor, DCC has been shown to induce apoptosis unless engaged by its ligand, netrin-1 (ref. 2). However, so far no animal model has supported the view that the DCC loss-of-function is causally implicated as predisposing to aggressive cancer development. To investigate the role of DCC-induced apoptosis in the control of tumour progression, here we created a mouse model in which the pro-apoptotic activity of DCC is genetically silenced. Although the loss of DCC-induced apoptosis in this mouse model is not associated with a major disorganization of the intestines, it leads to spontaneous intestinal neoplasia at a relatively low frequency. Loss of DCC-induced apoptosis is also associated with an increase in the number and aggressiveness of intestinal tumours in a predisposing APC mutant context, resulting in the development of highly invasive adenocarcinomas. These results demonstrate that DCC functions as a tumour suppressor via its ability to trigger tumour cell apoptosis. 相似文献
972.
对分离自四川省卧龙保护区大熊猫肠道的6株大肠杆菌的抗生素抗性与质粒的关系进行了研究,结果显示:6株大肠杆菌中都存在不同大小的质粒DNA;采用SDS高温法处理每株大肠杆菌后,有2类质粒在琼脂糖凝胶上的条带数减少,菌株的抗生素抗性水平也有所降低,有2株菌的某些抗生素抗性完全消失;将分离自6株大肠杆菌的质粒转化大肠杆菌JM109,获得1个氨苄青霉素抗性转化子.这些结果表明,大熊猫肠道中的大肠杆菌的抗生素抗性与它们含有的质粒有关. 相似文献
973.
Pennacchio LA Ahituv N Moses AM Prabhakar S Nobrega MA Shoukry M Minovitsky S Dubchak I Holt A Lewis KD Plajzer-Frick I Akiyama J De Val S Afzal V Black BL Couronne O Eisen MB Visel A Rubin EM 《Nature》2006,444(7118):499-502
Identifying the sequences that direct the spatial and temporal expression of genes and defining their function in vivo remains a significant challenge in the annotation of vertebrate genomes. One major obstacle is the lack of experimentally validated training sets. In this study, we made use of extreme evolutionary sequence conservation as a filter to identify putative gene regulatory elements, and characterized the in vivo enhancer activity of a large group of non-coding elements in the human genome that are conserved in human-pufferfish, Takifugu (Fugu) rubripes, or ultraconserved in human-mouse-rat. We tested 167 of these extremely conserved sequences in a transgenic mouse enhancer assay. Here we report that 45% of these sequences functioned reproducibly as tissue-specific enhancers of gene expression at embryonic day 11.5. While directing expression in a broad range of anatomical structures in the embryo, the majority of the 75 enhancers directed expression to various regions of the developing nervous system. We identified sequence signatures enriched in a subset of these elements that targeted forebrain expression, and used these features to rank all approximately 3,100 non-coding elements in the human genome that are conserved between human and Fugu. The testing of the top predictions in transgenic mice resulted in a threefold enrichment for sequences with forebrain enhancer activity. These data dramatically expand the catalogue of human gene enhancers that have been characterized in vivo, and illustrate the utility of such training sets for a variety of biological applications, including decoding the regulatory vocabulary of the human genome. 相似文献
974.
When two superconductors are electrically connected by a weak link--such as a tunnel barrier--a zero-resistance supercurrent can flow. This supercurrent is carried by Cooper pairs of electrons with a combined charge of twice the elementary charge, e. The 2e charge quantum is clearly visible in the height of voltage steps in Josephson junctions under microwave irradiation, and in the magnetic flux periodicity of h/2e (where h is Planck's constant) in superconducting quantum interference devices. Here we study supercurrents through a quantum dot created in a semiconductor nanowire by local electrostatic gating. Owing to strong Coulomb interaction, electrons only tunnel one-by-one through the discrete energy levels of the quantum dot. This nevertheless can yield a supercurrent when subsequent tunnel events are coherent. These quantum coherent tunnelling processes can result in either a positive or a negative supercurrent, that is, in a normal or a pi-junction, respectively. We demonstrate that the supercurrent reverses sign by adding a single electron spin to the quantum dot. When excited states of the quantum dot are involved in transport, the supercurrent sign also depends on the character of the orbital wavefunctions. 相似文献
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979.
聋哑大学生思想政治教育方法途径初探 总被引:2,自引:0,他引:2
聋哑学生的教育是我国社会主义教育事业的一个组成部分。对高等特殊教育聋哑学生身心特点进行分析,得出对聋哑学生思想政治教育采取的教学方法,加强聋哑大学生的课外思想教育活动,把他们培养成德、智、体全面发展并具有良好心理素质的社会主义事业接班人和建设者。 相似文献
980.
张德全 《科技情报开发与经济》2003,13(3):169-170
渠道混凝土防渗节水工程是提高农田灌溉面积,减少水资源浪费的有效措施之一,文章提出了混凝土防渗节水设计的具体内容,包括混凝土水灰比的设计,不同砂粒的最佳搭配,骨料的最佳选择及最佳灰砂比的确定,以及根据裂缝,温度,湿度对混凝土的影响所应采取的相应防治措施。 相似文献