Yoon Sang-Wook, Kim Dae-Kwan, Kim Keun Pil, Park Kyung-Soon
1 Department of Life Science, Chung-Ang University , Seoul, Korea.
Stem Cells Dev. 2014 Nov 15;23(22):2700-11. doi: 10.1089/scd.2014.0129. Epub 2014 Aug 18.
Homologous recombination (HR) maintains genomic integrity against DNA replication stress and deleterious lesions, such as double-strand breaks (DSBs). Rad51 recombinase is critical for HR events that mediate the exchange of genetic information between parental chromosomes in eukaryotes. Additionally, Rad51 and HR accessory factors may facilitate replication fork progression by preventing replication fork collapse and repair DSBs that spontaneously arise during the normal cell cycle. In this study, we demonstrated a novel role for Rad51 during the cell cycle in mouse embryonic stem cells (mESCs). In mESCs, Rad51 was constitutively expressed throughout the cell cycle, and the formation of Rad51 foci increased as the cells entered S phase. Suppression of Rad51 expression caused cells to accumulate at G2/M phase and activated the DNA damage checkpoint, but it did not affect the self-renewal or differentiation capacity of mESCs. Even though Rad51 suppression significantly inhibited the proliferation rate of mESCs, Rad51 suppression did not affect the replication fork progression and speed, indicating that Rad51 repaired DNA damage and promoted DNA replication in S phase through an independent mechanism. In conclusion, Rad51 may contribute to G2/M transition in mESCs, while preserving genomic integrity in global organization of DNA replication fork.
同源重组（HR）可维持基因组完整性，抵御DNA复制应激以及诸如双链断裂（DSB）等有害损伤。Rad51重组酶对于真核生物中介导亲代染色体间遗传信息交换的HR事件至关重要。此外，Rad51和HR辅助因子可通过防止复制叉崩溃来促进复制叉的推进，并修复在正常细胞周期中自发出现的DSB。在本研究中，我们证明了Rad51在小鼠胚胎干细胞（mESC）细胞周期中的新作用。在mESC中，Rad51在整个细胞周期中持续表达，并且随着细胞进入S期，Rad51焦点的形成增加。抑制Rad51表达会导致细胞在G2/M期积累并激活DNA损伤检查点，但不影响mESC的自我更新或分化能力。尽管抑制Rad51会显著抑制mESC的增殖速率，但抑制Rad51并不影响复制叉的推进和速度，这表明Rad51通过独立机制修复DNA损伤并促进S期的DNA复制。总之，Rad51可能有助于mESC中的G2/M转换，同时在DNA复制叉的整体组织中保持基因组完整性。
