de Napoles Mariana, Mermoud Jacqueline E, Wakao Rika, Tang Y Amy, Endoh Mitusuhiro, Appanah Ruth, Nesterova Tatyana B, Silva Jose, Otte Arie P, Vidal Miguel, Koseki Haruhiko, Brockdorff Neil
Developmental Epigenetics Group, MRC Clinical Sciences Centre, ICFM, Hammersmith Hospital, DuCane Road, London W12 ONN, United Kingdom.
Dev Cell. 2004 Nov;7(5):663-76. doi: 10.1016/j.devcel.2004.10.005.
In many higher organisms, 5%-15% of histone H2A is ubiquitylated at lysine 119 (uH2A). The function of this modification and the factors involved in its establishment, however, are unknown. Here we demonstrate that uH2A occurs on the inactive X chromosome in female mammals and that this correlates with recruitment of Polycomb group (PcG) proteins belonging to Polycomb repressor complex 1 (PRC1). Based on our observations, we tested the role of the PRC1 protein Ring1B and its closely related homolog Ring1A in H2A ubiquitylation. Analysis of Ring1B null embryonic stem (ES) cells revealed extensive depletion of global uH2A levels. On the inactive X chromosome, uH2A was maintained in Ring1A or Ring1B null cells, but not in double knockout cells, demonstrating an overlapping function for these proteins in development. These observations link H2A ubiquitylation, X inactivation, and PRC1 PcG function, suggesting an unanticipated and novel mechanism for chromatin-mediated heritable gene silencing.
在许多高等生物中，5% - 15%的组蛋白H2A在赖氨酸119位点发生泛素化修饰（uH2A）。然而，这种修饰的功能以及参与其建立的相关因子尚不清楚。在此，我们证明uH2A存在于雌性哺乳动物的失活X染色体上，并且这与属于多梳抑制复合物1（PRC1）的多梳蛋白家族（PcG）蛋白的募集相关。基于我们的观察结果，我们测试了PRC1蛋白Ring1B及其密切相关的同源物Ring1A在H2A泛素化中的作用。对Ring1B基因敲除胚胎干细胞（ES细胞）的分析显示，整体uH2A水平大幅降低。在失活X染色体上，uH2A在Ring1A或Ring1B基因敲除细胞中得以维持，但在双敲除细胞中则不然，这表明这些蛋白在发育过程中具有重叠功能。这些观察结果将H2A泛素化、X染色体失活和PRC1 PcG功能联系起来，提示了一种意想不到的新型染色质介导的可遗传基因沉默机制。
