Belew Mezmur D, Chien Emilie, Wong Matthew, Michael W Matthew
Department of Biological Sciences, Molecular and Computational Biology Section, University of Southern California, Los Angeles, CA, 90089, USA.
G3 (Bethesda). 2024 Oct 3;14(12). doi: 10.1093/g3journal/jkae236.
In C. elegans, the germline is specified via a preformation mechanism that relies on the PIE-1 protein's ability to globally silence mRNA transcription in germline precursor cells, also known as the P lineage. Recent work from our group has identified additional genome silencing events in C. elegans during oogenesis and in starved L1 larvae, and these require the condensin II complex, topoisomerase II (TOP-2), and components of the H3K9me/heterochromatin pathway. Interestingly, silencing in oocytes also requires PIE-1, but this is not the case in starved L1s. Here, we ask if additional genome silencing components besides PIE-1 are required to repress gene expression in the P lineage of early embryos, and we find that condensin II and TOP-2 are required and the H3K9me/heterochromatin pathway is not. We show that depletion of TOP-2/condensin II activates the normally suppressed RNA polymerase II to inappropriately transcribe somatic genes in the P lineage. We also present evidence that while both PIE-1 and TOP-2/condensin II are required for genome silencing in the P lineage, PIE-1 can silence transcription independently of TOP-2/condensin II when misexpressed in somatic cells. Thus, in oocytes, all three genome silencing systems (TOP-2/condensin II, H3K9me, and PIE-1) are operational while in both early embryos and starved L1s two of the three are active. Our data show that multiple, redundantly acting genome silencing mechanisms act in a mix and match manner to repress transcription at different developmental stages in the C. elegans germline.
在秀丽隐杆线虫中，生殖系是通过一种预成型机制确定的，该机制依赖于PIE-1蛋白在生殖系前体细胞（也称为P系）中全局沉默mRNA转录的能力。我们小组最近的研究发现，秀丽隐杆线虫在卵子发生过程中和饥饿的L1幼虫中存在额外的基因组沉默事件，这些事件需要凝聚素II复合物、拓扑异构酶II（TOP-2）以及H3K9me/异染色质途径的成分。有趣的是，卵母细胞中的沉默也需要PIE-1，但饥饿的L1幼虫则不然。在这里，我们探讨除了PIE-1之外，是否还需要其他基因组沉默成分来抑制早期胚胎P系中的基因表达，我们发现凝聚素II和TOP-2是必需的，而H3K9me/异染色质途径则不需要。我们表明，TOP-2/凝聚素II的缺失会激活通常被抑制的RNA聚合酶II，从而在P系中不恰当地转录体细胞基因。我们还提供证据表明，虽然PIE-1和TOP-2/凝聚素II对于P系中的基因组沉默都是必需的，但当PIE-1在体细胞中错误表达时，它可以独立于TOP-2/凝聚素II沉默转录。因此，在卵母细胞中，所有三种基因组沉默系统（TOP-2/凝聚素II、H3K9me和PIE-1）都在起作用，而在早期胚胎和饥饿的L1幼虫中，三种系统中的两种是活跃的。我们的数据表明，多种冗余作用的基因组沉默机制以混合搭配的方式在秀丽隐杆线虫生殖系的不同发育阶段抑制转录。
