MOUSE X-CHROMOSOME INACTIVATION

在早期哺乳动物发育过程中建立的X染色体失活， 在女性胚胎细胞中，除了一条X染色体外，其他所有染色体都沉默了。 然而，逃避失活的基因散布在X染色体上， 染色体其中一些基因的异常表达可能解释了 特纳综合征与缺少一条X染色体的关系。我们 先前的研究已经揭示了人类和小鼠之间的主要差异 在基因的位置和X-失活状态方面。这项建议 利用小鼠系统跟踪X染色体失活和逃逸的时间 在发育过程中，确定基因的X失活状态 与其位置的关系，并检查剂量的演变 赔偿 具体来说，我们计划（l）构建转基因小鼠， 插入到Hprt基因中的报告序列，所述Hprt基因受到X 失活和Smcx基因逃逸。报告蛋白的表达来 在开发过程中将遵循序列。我们还将继续 研究一种逃避X染色体失活的转基因。 其次，我们计划（2）构建带有报告序列的转基因小鼠 插入灭活中心的不同位置， X染色体失活的扩散。一种平行的方法是测定 X连锁基因的等位基因特异性表达。 第三，我们计划（3）预先定义重排的程度 通过将Clcn 4基因定位到一只小鼠的X染色体上来检测 一个物种，但在另一个常染色体。Clcn 4的表达研究将 以确定剂量补偿的后果。 最后，我们计划（4）确定小鼠基因的X失活状态 使用先前开发的X-常染色体易位系统。本研究 结合详细的基因图谱，将显示是否有基因逃脱， X失活位于特定的结构域。 实验计划基于基因的表达和定位研究 与那些受到X灭活的相比， 失活，应进一步阐明X-失活的过程 性染色体的扩散、维持和进化。

X inactivation, established during early mammalian development, results in the silencing of all but one X chromosome in cells of female embryos. However, genes that escape inactivation are interspersed on the X chromosome. The unusual expression of some of these genes may explain the association of Turner syndrome with the lack of one X chromosome. Our previous studies have uncovered major differences between human and mouse in terms of location and X-inactivation status of genes. This proposal exploits mouse systems to follow the timing of X inactivation and escape during development, to determine the X-inactivation status of genes in relation to their location and to examine evolution of dosage compensation. Specifically, we plan (l) to construct transgenic mice that contain reporter sequences inserted in the Hprt gene that is subject to X inactivation and the Smcx gene that escapes. Expression of the reporter sequences will be followed during development. We will also continue studies of a transgene that escapes X inactivation. Second, we plan (2) to construct transgenic mice with reporter sequences inserted at different locations from the inactivation center to follow spreading of X inactivation. A parallel approach will be to assay for allele-specific expression of X-linked genes by in situ hybridization. Third, we plan (3) to define the extent of a rearrangement previously detected by mapping of the Clcn4 gene to the X chromosome in one mouse species but to an autosome in another. Expression studies of Clcn4 will be done to determine the consequences of dosage compensation. Finally we plan (4) to determine the X-inactivation status of mouse genes using an X-autosome translocation system developed previously. This study in conjunction with detailed mapping will show whether genes that escape X inactivation are located in specific domains. The experiments planned based on expression and mapping studies of genes that escape X inactivation in comparison to those subject to inactivation, should further elucidate the processes of X-inactivation spreading and maintenance and of evolution of the sex chromosomes.