X-CHROMOSOME INACTIVATION AND IMPRINTING IN TRANSGENICS

哺乳动物雌性体内的剂量补偿是通过 两条X染色体中的一条在发育早期失活。这个 失活事件包括X染色体的大部分基因， 但不包括参与X-Y配对和重组的一小部分区域。 一旦建立，不活跃状态就是克隆遗传的，并且 稳定，除非在雌性生殖系中重新激活 失活的X染色体是卵子发生的重要组成部分。分子 X失活启动的基础，失活扩散到所有人 但X的特定区域，以及X在卵子发生中的重新激活是 知之甚少，但染色质构象和DNA的差异 甲基化也有牵连。 现在越来越明显的是，可能有10%的哺乳动物 基因组的功能取决于它是否是遗传的 母性的或父性的。建立这种差异的过程 基于亲本起源的功能称为印记。一批 人类基因显然容易受到印记的影响，有几种疾病是 由于亲本来源的不同，它们的表达有表型上的差异。 对人类脆性X连锁精神发育迟滞综合征的研究表明 这种突变可能涉及雌性生殖系的印记；一个错误 在正常的X染色体失活-再激活循环中是可疑的。 在常染色体中已经在分子水平上证明了印记 小鼠的基因和转基因，似乎涉及差异 在某些情况下，甲基化。特定X连锁基因的印记有 还没有在分子水平上描述；这种现象必须是 演示以了解可能存在的印记 人类脆性X-智力低下的表现 综合症。 我们研究X染色体失活和印迹的方法 利用在X染色体上插入外源基因的转基因小鼠 染色体作为模型系统。使用该系统，我们希望(1) 确定哪些常见的分子与X失活相关 (甲基化，DNase I抗性)对这一过程很重要， 仅与失活相关，(2)确定是否 X连锁的转基因在染色质或染色体中有不同的表达、组织 当遗传自父本或母本时甲基化，以及(3)至 确定失活的X染色体是否 卵原细胞在染色质或染色质中有不同的表达、组织 与活性X上的甲基化进行比较。

Dosage compensation in mammalian females is accomplished by the inactivation of one of the two X chromosomes in early development. The inactivation event encompasses most of the genes of the X chromosome, excluding but a small region involved in X-Y pairing and recombination. Once established, the inactive state is clonally inherited and quite stable, except in the female germline in which reactivation of the inactive X chromosome is an essential part of oogenesis. The molecular basis of initiation of X inactivation, spreading of inactivation to all but specific regions of the X, and reactivation of the X in oogenesis is poorly understood, but differences in chromatin conformation and DNA methylation have been implicated. It is now becoming apparent that perhaps ten percent of the mammalian genome functions differently depending on whether it was inherited maternally or paternally. The process of establishing this differential function based on parental origin is termed imprinting. A number of human genes are clearly subject to imprinting, and several diseases are phenotypically different in their expression due to parental origin. Studies of the human fragile X-linked mental retardation syndrome suggest that the mutation may involve imprinting in the female germline; an error in the normal X-chromosome inactivation-reactivation cycle is suspected. Imprinting has been demonstrated at the molecular level in autosomal genes and transgenes of mice, and appears to involve differential methylation in some cases. Imprinting of specific X-linked genes has not yet been described at a molecular level; this phenomenon must be demonstrated in order to understanding the imprinting that may be responsible for expression of the human fragile X-mental retardation syndrome. Our approach to the study of X-chromosome inactivation and imprinting utilizes transgenic mice having a foreign gene inserted on the X chromosome as a model system. Using this system, we hope to (1) determine which of the usual molecular correlates of X inactivation (methylation, DNase I resistance) are important to the process and which are merely correlated with inactivation, (2) to determine whether or not X-linked transgenes are differently expressed, organized in chromatin or methylated when inherited from the male or female parent, and (3) to determine whether or not the X chromosome which was inactivated in oogonial cells is differently expressed, organized in chromatin or methylated compared to the one that was on the active X.