Genetics and Developmental Biology Unit and Mammalian Developmental Epigenetics Group, Institut Curie, PSL Research University, CNRS UMR3215, INSERM U934, 75248 Paris, France; email:
Current affiliation: Developmental Biology Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.
Annu Rev Genet. 2018 Nov 23;52:535-566. doi: 10.1146/annurev-genet-120116-024611. Epub 2018 Sep 26.
In somatic nuclei of female therian mammals, the two X chromosomes display very different chromatin states: One X is typically euchromatic and transcriptionally active, and the other is mostly silent and forms a cytologically detectable heterochromatic structure termed the Barr body. These differences, which arise during female development as a result of X-chromosome inactivation (XCI), have been the focus of research for many decades. Initial approaches to define the structure of the inactive X chromosome (Xi) and its relationship to gene expression mainly involved microscopy-based approaches. More recently, with the advent of genomic techniques such as chromosome conformation capture, molecular details of the structure and expression of the Xi have been revealed. Here, we review our current knowledge of the 3D organization of the mammalian X-chromosome chromatin and discuss its relationship with gene activity in light of the initiation, spreading, and maintenance of XCI, as well as escape from gene silencing.
在雌性有袋类哺乳动物的体细胞核中，两条 X 染色体呈现出非常不同的染色质状态：一条 X 染色体通常是常染色质，转录活跃，而另一条则大多处于沉默状态，并形成一种细胞学上可检测到的异染色质结构，称为巴氏小体。这些差异是在雌性发育过程中由于 X 染色体失活（XCI）而产生的，几十年来一直是研究的焦点。最初，为了定义失活 X 染色体（Xi）的结构及其与基因表达的关系，主要采用基于显微镜的方法。最近，随着染色体构象捕获等基因组技术的出现，Xi 的结构和表达的分子细节已经被揭示。在这里，我们回顾了我们目前对哺乳动物 X 染色体染色质三维组织的认识，并讨论了其与基因活性的关系，重点是 XCI 的起始、扩散和维持，以及逃避基因沉默。
