Hosogane Masaki, Bosu Lena, Fukumoto Emiko, Yamada Hidetoshi, Sato Soichiro, Nakayama Keiko
Department of Cell Proliferation, United Center for Advanced Research and Translational Medicine, Graduate School of Medicine, Tohoku University, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi, 980-8575, Japan.
Genes Cells. 2017 Apr;22(4):360-375. doi: 10.1111/gtc.12482. Epub 2017 Mar 14.
Geminin is implicated in regulation of the cell cycle and differentiation. Although loss of Geminin triggers unscheduled DNA rereplication as a result of interruption of its interaction with Cdt1 in some somatic cancer cells, whether such cell cycle regulation also operates in embryonic stem cells (ESCs) has remained unclear. To characterize the Geminin-Cdt1 axis in ESCs and compare it with that in somatic cells, we established conditional knockout (KO) of Geminin in mouse ESCs and mouse embryonic fibroblasts (MEFs). Geminin KO ESCs manifest a large flattened morphology, develop polyploidy accompanied by DNA damage and G -M checkpoint activation, and subsequently undergo apoptosis. Rereplication in Geminin KO ESCs was attenuated by inhibition of G -M checkpoint signaling or by expression of wild-type Geminin, but not by expression of a Geminin mutant that does not bind to Cdt1, indicating the importance of sequestration of Cdt1 by Geminin in G phase. In contrast, Geminin KO MEFs did not manifest disturbance of the cell cycle unless they were treated to force abnormal accumulation of Cdt1. Together, our results indicate that Geminin is a key inhibitor of Cdt1 in mouse ESCs, but that it plays a backup role in MEFs to compensate for accidental up-regulation of Cdt1.
Geminin参与细胞周期调控和分化过程。尽管在某些体细胞癌中，Geminin的缺失因其与Cdt1相互作用的中断而引发了异常的DNA再复制，但这种细胞周期调控在胚胎干细胞（ESC）中是否也起作用仍不清楚。为了描述ESC中Geminin - Cdt1轴的特征并将其与体细胞中的进行比较，我们在小鼠ESC和小鼠胚胎成纤维细胞（MEF）中建立了Geminin的条件性敲除（KO）模型。Geminin敲除的ESC呈现出大而扁平的形态，出现多倍体并伴有DNA损伤和G - M期检查点激活，随后发生凋亡。抑制G - M期检查点信号或表达野生型Geminin可减弱Geminin敲除ESC中的再复制现象，但表达不与Cdt1结合的Geminin突变体则无此效果，这表明Geminin在G期隔离Cdt1具有重要作用。相比之下，Geminin敲除的MEF除非经过处理导致Cdt1异常积累，否则不会出现细胞周期紊乱。总之，我们的结果表明，Geminin是小鼠ESC中Cdt1的关键抑制剂，但在MEF中它起到备用作用，以补偿Cdt1的意外上调。
