Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109, USA.
Trends Genet. 2011 Oct;27(10):411-21. doi: 10.1016/j.tig.2011.06.007. Epub 2011 Jul 21.
The unique segregation of homologs, rather than sister chromatids, at the first meiotic division requires the formation of crossovers (COs) between homologs by meiotic recombination in most species. Crossovers do not form at random along chromosomes. Rather, their formation is carefully controlled, both at the stage of formation of DNA double-strand breaks (DSBs) that can initiate COs and during the repair of these DSBs. Here, we review control of DSB formation and two recently recognized controls of DSB repair: CO homeostasis and CO invariance. Crossover homeostasis maintains a constant number of COs per cell when the total number of DSBs in a cell is experimentally or stochastically reduced. Crossover invariance maintains a constant CO density (COs per kb of DNA) across much of the genome despite strong DSB hotspots in some intervals. These recently uncovered phenomena show that CO control is even more complex than previously suspected.
在第一次减数分裂中，同源染色体而非姐妹染色单体的独特分离需要通过减数重组在大多数物种中形成同源染色体之间的交叉（COs）。CO 不会随机沿着染色体形成。相反，它们的形成受到严格控制，包括在可以引发 CO 的 DNA 双链断裂（DSBs）形成阶段以及在这些 DSBs 的修复过程中。在这里，我们回顾了 DSB 形成的控制以及最近发现的两个 DSB 修复控制：CO 动态平衡和 CO 不变性。当细胞中的总 DSB 数量实验或随机减少时，CO 动态平衡保持每个细胞的 CO 数量不变。尽管在某些区间存在强烈的 DSB 热点，但 CO 不变性在基因组的大部分区域保持恒定的 CO 密度（每千碱基对 DNA 的 COs）。这些最近发现的现象表明，CO 控制比之前怀疑的更为复杂。
