Baarends Willy M, Wassenaar Evelyne, Hoogerbrugge Jos W, Schoenmakers Sam, Sun Zu-Wen, Grootegoed J Anton
Department of Reproduction and Development, Erasmus MC-University Medical Center, Rotterdam, The Netherlands.
J Cell Sci. 2007 Jun 1;120(Pt 11):1841-51. doi: 10.1242/jcs.03451. Epub 2007 May 8.
Mono-ubiquitylated H2A marks the transcriptionally silenced XY body during male meiotic prophase. Concomitant with H2A(K119ub1), the ubiquitin-conjugating enzyme HR6B is also enriched on the XY body. We analyzed H2A and H2B ubiquitylation in Hr6b-knockout mouse spermatocytes, but no global changes were detected. Next, we analyzed phosphorylation of the threonine residues T120 and T119 that are adjacent to the K119 and K120 target sites for ubiquitylation in H2A and H2B, respectively. In wild-type cells, H2A(T120ph) and H2B(T119ph) mark meiotically unpaired and silenced chromatin, including the XY body. In Hr6b-knockout spermatocytes, the H2B(T119ph) signal was unchanged, but H2A(T120ph) was enhanced from late pachytene until metaphase I. Furthermore, we found increased H3(K4) dimethylation on the X and Y chromosomes of diplotene Hr6b-knockout spermatocytes, persisting into postmeiotic round spermatids. In these cells, the X and Y chromosomes maintained an unchanged H3(K9m2) level, even when this modification was lost from centromeric heterochromatin. Analysis of gene expression showed derepression of X chromosome genes in postmeiotic Hr6b-knockout spermatids. We conclude that HR6B exerts control over different histone modifications in spermatocytes and spermatids, and that this function contributes to the postmeiotic maintenance of X chromosome silencing.
单泛素化的H2A在雄性减数分裂前期标记转录沉默的XY体。与H2A（K119ub1）相伴，泛素结合酶HR6B也在XY体上富集。我们分析了Hr6b基因敲除小鼠精母细胞中H2A和H2B的泛素化情况，但未检测到整体变化。接下来，我们分析了苏氨酸残基T120和T119的磷酸化情况，它们分别与H2A和H2B中泛素化的K119和K120靶位点相邻。在野生型细胞中，H2A（T120ph）和H2B（T119ph）标记减数分裂时未配对且沉默的染色质，包括XY体。在Hr6b基因敲除的精母细胞中，H2B（T119ph）信号未改变，但H2A（T120ph）从粗线期后期到中期I增强。此外，我们发现双线期Hr6b基因敲除精母细胞的X和Y染色体上H3（K4）二甲基化增加，并持续到减数分裂后圆形精子细胞。在这些细胞中，即使着丝粒异染色质上这种修饰消失，X和Y染色体的H3（K9m2）水平仍保持不变。基因表达分析显示减数分裂后Hr6b基因敲除精子细胞中X染色体基因去抑制。我们得出结论，HR6B对精母细胞和精子细胞中不同的组蛋白修饰发挥调控作用，且该功能有助于减数分裂后X染色体沉默的维持。
