Department of Molecular and Cellular Biology, Genetics Graduate Group, University of California, Davis, California 95616, USA.
Genetics. 2010 Mar;184(3):613-28. doi: 10.1534/genetics.109.110338. Epub 2009 Dec 14.
In many organisms, female and male meiosis display extensive sexual dimorphism in the temporal meiotic program, the number and location of recombination events, sex chromosome segregation, and checkpoint function. We show here that both meiotic prophase timing and germ-line apoptosis, one output of checkpoint signaling, are dictated by the sex of the germ line (oogenesis vs. spermatogenesis) in Caenorhabditis elegans. During oogenesis in feminized animals (fem-3), a single pair of asynapsed autosomes elicits a checkpoint response, yet an unpaired X chromosome fails to induce checkpoint activation. The single X in males and fem-3 worms is a substrate for the meiotic recombination machinery and repair of the resulting double strand breaks appears to be delayed compared with worms carrying paired X chromosomes. Synaptonemal complex axial HORMA domain proteins, implicated in repair of meiotic double strand breaks (DSBs) and checkpoint function, are assembled and disassembled on the single X similarly to paired chromosomes, but the central region component, SYP-1, is not loaded on the X chromosome in males. In fem-3 worms some X chromosomes achieve nonhomologous self-synapsis; however, germ cells with SYP-1-positive X chromosomes are not preferentially protected from apoptosis. Analyses of chromatin and X-linked gene expression indicate that a single X, unlike asynapsed X chromosomes or autosomes, maintains repressive chromatin marks and remains transcriptionally silenced and suggests that this state locally precludes checkpoint signaling.
在许多生物体中，雌性和雄性减数分裂在时间减数分裂程序、重组事件的数量和位置、性染色体分离和检查点功能方面表现出广泛的性别二态性。我们在这里表明，在秀丽隐杆线虫中，减数分裂前期时间和生殖细胞凋亡（检查点信号的一个输出）都由生殖系（卵发生与精子发生）的性别决定。在雌性化动物（fem-3）的卵发生过程中，一对未配对的常染色体引发检查点反应，但未配对的 X 染色体未能诱导检查点激活。雄性和 fem-3 蠕虫中的单个 X 是减数分裂重组机制的底物，并且似乎与携带配对 X 染色体的蠕虫相比，修复由此产生的双链断裂被延迟。联会复合体轴 HORMA 结构域蛋白参与减数分裂双链断裂（DSB）的修复和检查点功能，类似于配对染色体一样组装和解体，但中央区域成分 SYP-1 不在雄性的 X 染色体上加载。在 fem-3 蠕虫中，一些 X 染色体实现了非同源自我联会；然而，具有 SYP-1 阳性 X 染色体的生殖细胞并未优先免受凋亡。对染色质和 X 连锁基因表达的分析表明，单个 X 与未配对的 X 染色体或常染色体不同，保持抑制性染色质标记并保持转录沉默，这表明这种状态局部阻止了检查点信号。
