Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts, United States of America.
PLoS Genet. 2023 Jan 27;19(1):e1010627. doi: 10.1371/journal.pgen.1010627. eCollection 2023 Jan.
Programmed DNA double-strand break (DSB) formation is essential for achieving accurate chromosome segregation during meiosis. DSB repair timing and template choice are tightly regulated. However, little is known about how DSB distribution and the choice of repair pathway are regulated along the length of chromosomes, which has direct effects on the recombination landscape and chromosome remodeling at late prophase I. Here, we use the spatiotemporal resolution of meiosis in the Caenorhabditis elegans germline along with genetic approaches to study distribution of DSB processing and its regulation. High-resolution imaging of computationally straightened chromosomes immunostained for the RAD-51 recombinase marking DSB repair sites reveals that the pattern of RAD-51 foci throughout pachytene resembles crossover distribution in wild type. Specifically, RAD-51 foci occur primarily along the gene-poor distal thirds of the chromosomes in both early and late pachytene, and on both the X and the autosomes. However, this biased off-center distribution can be abrogated by the formation of excess DSBs. Reduced condensin function, but not an increase in total physical axial length, results in a homogeneous distribution of RAD-51 foci, whereas regulation of H3K9 methylation is required for the enrichment of RAD-51 at off-center positions. Finally, the DSB recognition heterodimer cKU-70/80, but not the non-homologous end-joining canonical ligase LIG-4, contributes to the enriched off-center distribution of RAD-51 foci. Taken together, our data supports a model by which regulation of the chromatin landscape, DSB levels, and DSB detection by cKU-70/80 collaborate to promote DSB processing by homologous recombination at off-center regions of the chromosomes in C. elegans.
程序性 DNA 双链断裂 (DSB) 的形成对于在减数分裂过程中实现染色体的准确分离至关重要。DSB 修复的时间和模板选择受到严格调控。然而,对于 DSB 在染色体上的分布以及修复途径的选择如何受到调控,我们知之甚少,而这直接影响着重组景观和前期 I 期的染色体重塑。在这里,我们利用秀丽隐杆线虫生殖系减数分裂的时空分辨率以及遗传方法来研究 DSB 处理的分布及其调控。通过对 RAD-51 重组酶标记 DSB 修复位点进行免疫染色的计算拉直染色体的高分辨率成像显示,整个粗线期 RAD-51 焦点的模式类似于野生型中的交叉分布。具体而言,RAD-51 焦点主要出现在早期和晚期粗线期染色体的基因贫乏的远端三分之一处,并且出现在 X 染色体和常染色体上。然而,这种偏心分布的偏置可以通过过多 DSB 的形成而被消除。降低凝聚酶的功能,而不是增加总物理轴长,会导致 RAD-51 焦点的均匀分布,而 H3K9 甲基化的调控对于 RAD-51 在偏心位置的富集是必需的。最后,DSB 识别异源二聚体 cKU-70/80,但不是非同源末端连接的典型连接酶 LIG-4,有助于 RAD-51 焦点在偏心位置的富集分布。总之,我们的数据支持了一个模型,即染色质景观、DSB 水平和 cKU-70/80 对 DSB 的检测的调控协同作用,促进了同源重组在 C. elegans 染色体的偏心区域的 DSB 处理。