Baarends Willy M, Wassenaar Evelyne, Hoogerbrugge Jos W, van Cappellen Gert, Roest Henk P, Vreeburg Jan, Ooms Marja, Hoeijmakers Jan H J, Grootegoed J Anton
Department of Reproduction and Development, Erasmus University Rotterdam, 3000 DR Rotterdam, The Netherlands.
Mol Cell Biol. 2003 Feb;23(4):1151-62. doi: 10.1128/MCB.23.4.1151-1162.2003.
The ubiquitin-conjugating enzymes HR6A and HR6B are the two mammalian homologs of Saccharomyces cerevisiae RAD6. In yeast, RAD6 plays an important role in postreplication DNA repair and in sporulation. HR6B knockout mice are viable, but spermatogenesis is markedly affected during postmeiotic steps, leading to male infertility. In the present study, increased apoptosis of HR6B knockout primary spermatocytes was detected during the first wave of spermatogenesis, indicating that HR6B performs a primary role during the meiotic prophase. Detailed analysis of HR6B knockout pachytene nuclei showed major changes in the synaptonemal complexes. These complexes were found to be longer. In addition, we often found depletion of synaptonemal complex proteins from near telomeric regions in the HR6B knockout pachytene nuclei. Finally, we detected an increased number of foci containing the mismatch DNA repair protein MLH1 in these nuclei, reflecting a remarkable and consistent increase (20 to 25%) in crossing-over frequency. The present findings reveal a specific requirement for the ubiquitin-conjugating activity of HR6B in relation to dynamic aspects of the synaptonemal complex and meiotic recombination in spermatocytes.
泛素缀合酶HR6A和HR6B是酿酒酵母RAD6在哺乳动物中的两个同源物。在酵母中，RAD6在复制后DNA修复和孢子形成中起重要作用。HR6B基因敲除小鼠可以存活，但减数分裂后阶段的精子发生受到明显影响，导致雄性不育。在本研究中，在精子发生的第一波过程中检测到HR6B基因敲除的初级精母细胞凋亡增加，表明HR6B在减数分裂前期发挥主要作用。对HR6B基因敲除的粗线期细胞核的详细分析显示，联会复合体有重大变化。发现这些复合体更长。此外，我们经常在HR6B基因敲除的粗线期细胞核中发现端粒区域附近的联会复合体蛋白缺失。最后，我们在这些细胞核中检测到含有错配DNA修复蛋白MLH1的位点数量增加，这反映了交叉频率显著且持续增加（20%至25%）。本研究结果揭示了HR6B的泛素缀合活性在精子细胞中联会复合体的动态方面和减数分裂重组方面的特定需求。
