XIST GENE AND ITS ROLE IN X-INACTIVATION

X-失活是一种顺式限制剂量补偿， 雌性哺乳动物的染色体。 尽管许多研究小组做出了努力， 关于它的机制和基因的数量， 涉案 我们已经分离出一个人类基因（XIST），它映射到Xq 13， X-失活中心（XIC）的最小缺失间隔 被映射。 该基因编码许多可变剪接的 转录本只表达自失活的X染色体。 因此，它在染色体正常个体中的表达是女性- 特定. 最近，我们克隆了XIST小鼠同源物（Xist），发现 它映射到小鼠X-失活中心（X控制元件： Xce）区域，并且其表达在小鼠中也是雌性特异性的。 XIST基因，因为它的定位分配和其独特的模式， 表达，是一个很好的工具来研究X-失活。 整个 鼠Xist基因，包括启动子区，将被表征， 测序 人类和小鼠基因之间的序列比较将是 为了找到同源性区域， 保守的功能域。 表达XIST的时间将是 在小鼠胚胎中测定，以测试转录是否 在X失活发生时启动。 XIST分析 基因及其表达将在染色体 导致缺乏X-灭活的异常， Xce基因座的突变。 涉及敲除的功能实验 XIST基因将在培养细胞和胚胎细胞中进行， 小鼠胚胎干细胞（ES细胞）用于转基因动物的创建。 我们还计划分离出覆盖整个 X-失活中心在人体中已定位的定位间隔 和鼠标。 酵母人工染色体（YAC）、粘粒和λ噬菌体 利用XIST作为探针，已经从这两种基因组中分离出了基因组克隆， 人和小鼠文库，并将用作 染色体步移 我们对XIST的研究主要集中在X-失活方面 中心区域可能会导致识别的功能 这一独特的基因，并确定其在X-失活的作用。 X染色体失活的分子基础的解开， 能够关闭数千个基因， 只有一对同源染色体，肯定会导致 基因调控新机制的鉴定 表情

X-inactivation is the cis-limited dosage compensation of one of the pair of chromosomes in female mammals. Despite the effort of many research groups, very little has been learned about its mechanism and the number of genes involved. We have isolated a human gene (XIST) which maps to Xq13 within the smallest deletion interval where the X-inactivation center (XIC) has been mapped. The gene encodes for a number of alternatively spliced transcripts expressed exclusively from the inactive X chromosomes. Consequently its expression in chromosomally normal individuals is female- specific. Recently, we have cloned the XIST mouse homolog (Xist) and found that it maps to the mouse X-inactivation center (X controlling element: Xce) region and that its expression is also female-specific in the mouse. The XIST gene because of its mapping assignment and its unique pattern of expression, is an excellent tool to study X-inactivation. The entire murine Xist gene, including the promotor region, will be characterized and sequenced. Sequence comparison between the human and mouse genes will be performed in order to find regions of homology which may represent conserved functional domains. The timing of expression of XIST will be determined in mouse embryos in order to test whether transcription initiates at the time when X-inactivation occurs. Analysis of the XIST gene and its expression will be performed in individuals with chromosome abnormalities resulting in lack of X-inactivation and in mice bearing mutations of the Xce locus. Functional experiments involving knock-out of the XIST gene will be performed in both cultured cells and in embryonal stem (ES) cells from mouse embryos for the creation of transgenic animals. We also plan to isolate overlapping DNA fragments spanning the entire mapping interval where the X-inactivation center has been mapped in human and mouse. Yeast artificial chromosome (YAC), cosmid and lambda phage genomic clones have already been isolated, using XIST as a probe, from both human and mouse libraries and will be used as starting points for chromosome walking. Our studies on the XIST are on the X-inactivation center region will possibly lead to the identification of the function of this unique gene and to the determination of its role in X-inactivation. The unraveling of the molecular basis of X-inactivation, a phenomenon capable of turning off thousands of genes and of acting specifically on only one of the pair of two homologous chromosomes, will certainly lead to the identification of novel mechanisms for the regulation of gene expression.