为确保雌性动物不会有多余的X-染色体基因产物，每个细胞中两个X-染色体中的一个会被抑制。在胚胎生成过程中，这个X-染色体失活(XCI)过程的有印记形式，会在胚胎发育过程大约“四细胞阶段”在检测出父方X-染色体(Xp)上有Xist RNA的表达之后选择性地将父方X-染色体抑制。之后，XCI的一种胚胎形式会出现在胚胎本身的发育中的胚泡中，随机地使父方或母方X-染色体失去活性。

Shin等人利用小鼠的遗传研究结果发现，“Rnf12/RLIM泛素连接酶”的母方沉积在最初过程的启动中、而不是在之后的随机X-染色体抑制中起关键作用。

英文摘要：

Nature doi:10.1038/nature09457

Maternal Rnf12/RLIM is required for imprinted X-chromosome inactivation in mice
JongDae Shin,Michael Bossenz,Young Chung,Hong Ma,Meg Byron,Naoko Taniguchi-Ishigaki,Xiaochun Zhu,Baowei Jiao,Lisa L. Hall,Michael R. Green,Stephen N. Jones,Irm Hermans-Borgmeyer,Jeanne B. Lawrence& Ingolf Bach

Two forms of X-chromosome inactivation (XCI) ensure the selective silencing of female sex chromosomes during mouse embryogenesis. Imprinted XCI begins with the detection of Xist RNA expression on the paternal X?chromosome (Xp) at about the four-cell stage of embryonic development. In the embryonic tissues of the inner cell mass, a random form of XCI occurs in blastocysts that inactivates either Xp or the maternal X?chromosome (Xm)1, 2. Both forms of XCI require the non-coding Xist RNA that coats the inactive X?chromosome from which it is expressed. Xist has crucial functions in the silencing of X-linked genes, including Rnf12 (refs 3, 4) encoding the ubiquitin ligase RLIM (RING finger LIM-domain-interacting protein). Here we show, by targeting a conditional knockout of Rnf12 to oocytes where RLIM accumulates to high levels, that the maternal transmission of the mutant X?chromosome (Δm) leads to lethality in female embryos as a result of defective imprinted XCI. We provide evidence that in Δm female embryos the initial formation of Xist clouds and Xp silencing are inhibited. In contrast, embryonic stem cells lacking RLIM are able to form Xist clouds and silence at least some X-linked genes during random XCI. These results assign crucial functions to the maternal deposit of Rnf12/RLIM for the initiation of imprinted XCI.