Larson Braden J, Van Mike V, Nakayama Taylor, Engebrecht JoAnne
Department of Molecular and Cellular Biology, University of California, Davis, California 95616.
Department of Molecular and Cellular Biology, University of California, Davis, California 95616
Genetics. 2016 Aug;203(4):1641-58. doi: 10.1534/genetics.116.191130. Epub 2016 Jun 8.
During meiosis in the heterogametic sex in some species, sex chromosomes undergo meiotic sex chromosome inactivation (MSCI), which results in acquisition of repressive chromatin and transcriptional silencing. In Caenorhabditis elegans, MSCI is mediated by MET-2 methyltransferase deposition of histone H3 lysine 9 dimethylation. Here we examined the meiotic chromatin landscape in germ lines of four Caenorhabditis species; C. remanei and C. brenneri represent ancestral gonochorism, while C. briggsae and C. elegans are two lineages that independently evolved hermaphroditism. While MSCI is conserved across all four species, repressive chromatin modifications are distinct and do not correlate with reproductive mode. In contrast to C. elegans and C. remanei germ cells where X chromosomes are enriched for histone H3 lysine 9 dimethylation, X chromosomes in C. briggsae and C. brenneri germ cells are enriched for histone H3 lysine 9 trimethylation. Inactivation of C. briggsae MET-2 resulted in germ-line X chromosome transcription and checkpoint activation. Further, both histone H3 lysine 9 di- and trimethylation were reduced in Cbr-met-2 mutant germ lines, suggesting that in contrast to C. elegans, H3 lysine 9 di- and trimethylation are interdependent. C. briggsae H3 lysine 9 trimethylation was redistributed in the presence of asynapsed chromosomes in a sex-specific manner in the related process of meiotic silencing of unsynapsed chromatin. However, these repressive marks did not influence X chromosome replication timing. Examination of additional Caenorhabditis species revealed diverse H3 lysine 9 methylation patterns on the X, suggesting that the sex chromosome epigenome evolves rapidly.
在某些物种的异配性别减数分裂过程中，性染色体会经历减数分裂性染色体失活（MSCI），这导致获得抑制性染色质并使转录沉默。在秀丽隐杆线虫中，MSCI由组蛋白H3赖氨酸9二甲基化的MET - 2甲基转移酶沉积介导。在这里，我们研究了四种秀丽隐杆线虫物种生殖系中的减数分裂染色质景观；雷曼隐杆线虫和布伦纳隐杆线虫代表祖先的雌雄异体，而布里格隐杆线虫和秀丽隐杆线虫是两个独立进化出雌雄同体的谱系。虽然MSCI在所有四个物种中都是保守的，但抑制性染色质修饰是不同的，并且与生殖模式无关。与秀丽隐杆线虫和雷曼隐杆线虫生殖细胞中X染色体富含组蛋白H3赖氨酸9二甲基化相反，布里格隐杆线虫和布伦纳隐杆线虫生殖细胞中的X染色体富含组蛋白H3赖氨酸9三甲基化。布里格隐杆线虫MET - 2的失活导致生殖系X染色体转录和检查点激活。此外，在Cbr - met - 2突变体生殖系中，组蛋白H3赖氨酸9二甲基化和三甲基化都减少了，这表明与秀丽隐杆线虫不同，H3赖氨酸9二甲基化和三甲基化是相互依赖的。在未联会染色质减数分裂沉默的相关过程中，布里格隐杆线虫H3赖氨酸9三甲基化在存在未联会染色体的情况下以性别特异性方式重新分布。然而，这些抑制标记并不影响X染色体的复制时间。对其他秀丽隐杆线虫物种的研究揭示了X染色体上不同的H3赖氨酸9甲基化模式，表明性染色体表观基因组进化迅速。
