Xist expression and macroH2A1.2 localisation in mouse primordial and pluripotent embryonic germ cells
Xist expression and macroH2A1.2 localisation in mouse primordial and pluripotent embryonic germ cells
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DOI：
10.1046/j.1432-0436.2002.690415.x
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发表时间：
2002-01-01
期刊：
影响因子：
2.9
通讯作者：
Brockdorff, N
中科院分区：
文献类型：
--
作者：
Nesterova, TB;Mermoud, JE;Brockdorff, N
雌性哺乳动物X染色体失活的分子机制涉及非编码RNA Xist及其反义配偶体Tsix。在X染色体失活之前，这些RNA以不稳定的形式从所有X染色体转录，在早期胚胎和未分化的胚胎干细胞（ES）中都是如此。在分化后，来自所有等位基因的这些不稳定转录物的表达被沉默，并且Xist RNA在失活的X染色体上特异性地变得稳定。这种表达模式在随后的体细胞分裂中得以维持。一旦建立，X染色体的失活状态是非常稳定的，这是XX原始生殖细胞（PGC）进入生殖嵴时发生的唯一自然情况。为了深入了解X的再激活过程，我们分析了Xist基因的表达，使用RNA FISH在PGCs和PGCs衍生的胚胎生殖（EG）细胞。XX EG细胞显示从两个X染色体表达不稳定的Xist/Tsix。相比之下，在XX PGC的任何阶段均未检测到不稳定的Xist/Tsix转录本。相反，在11.5和13.5 dpc（X染色体再活化发生的时期）之间从生殖嵴分离的XX PGC的比例显示稳定的Xist RNA在一个X上积累。这些细胞的数量逐渐减少，并在13.5 dpc时几乎消失。作为失活状态的晚期标志物，我们分析了组蛋白H2 A变体macroH2A1.2的定位。尽管在PGCs中观察到macroH2A1.2表达，但在任何阶段均未检测到显著的非活性X定位。我们讨论这些结果的背景下，了解X染色体的再激活。
The molecular mechanism underlying X chromosome inactivation in female mammals involves the non-coding RNAs Xist and its antisense partner Tsix. Prior to X inactivation, these RNAs are transcribed in an unstable form from all X chromosomes, both in the early embryo and in undifferentiated embryonic stem (ES) cells. Upon differentiation, the expression of these unstable transcripts from all alleles is silenced, and Xist RNA becomes stabilised specifically on the inactivating X chromosome. This pattern of expression is then maintained throughout subsequent somatic cell divisions. Once established, the inactive state of the X chromosome is remarkably stable, the only natural case of reactivation occurring in XX primordial germ cells (PGCs) when they enter the genital ridge. To gain insight into the X reactivation process, we have analysed Xist gene expression using RNA FISH in PGCs and also in PGC-derived embryonic germ (EG) cells. XX EG cells were shown to express unstable Xist/Tsix from both X chromosomes. In contrast, no unstable Xist/Tsix transcripts were detected in XX PGCs at any stage. Instead, a proportion of XX PGCs isolated from the genital ridge between 11.5 and 13.5 dpc (the period during which X chromosome reactivation occurs) showed an accumulation of stable Xist RNA on one X. The number of these cells decreased progressively and was nearly extinguished by 13.5 dpc. As a late marker for the inactive state, we analysed localisation of the histone H2A variant macroH2A1.2. Although macroH2A1.2 expression was observed in PGCs, no significant localisation to the inactive X was detected at any stage. We discuss these results in the context of understanding X chromosome reactivation.