"生存还是毁灭",发育还是阻滞--小鼠早胚体外发育2-细胞阻滞产生机制初析

在体外培养条件下，小鼠受精卵往往经一次分裂后就停滞在２－细胞，不能完成到达囊胚的后续发育过程，称作２－细胞阻滞。氧自由基伤害、培养液成分不平衡等外界因素都能引起阻滞。小鼠的２－细胞阻滞现象受细胞质内母型物质制约，具有品系依赖性。在阻滞品系小鼠胚胎的细胞质内可能缺乏某些重要的蛋白因子，在无外源信号的培养体系内不能继续分裂。发生阻滞的胚胎细胞内ＭＰＦ前体物虽然储备充足，但因无法去磷酸化激活而最终导致发

"To be or not to be", to develop or to be blocked- The mechanism of 2-cell block in the early mouse embryo cultured in vitro

When mouse embryos are cultured from 1-cell stage in vitro, they generally fail to undergo a second cleavage and are arrested at 2-cell stage, which is know as the "2-cell block". Abnormal conditions in the cultural medium such as oxygen-free radical damage and environment imbalance may cause block. The phenomenon of "2-cell block" is strain dependent, and is maternally restricted by cytoplasm. Deficiency in the cytoplasm of some important proteins and absence of external signals from the cultural medium are also two of the reasons for 2-cell block. Mouse embryos arrested at 2-cell stage contain sufficient amount of inactive pre-MPF. The cleavage is inhibited by the inability to dephosphorylate and activate pre-MPF in the second cell cycle. Suppression of initial zygotic gene activation (ZGA) induction is involved in the 2-cell block of mouse embryos in vitro. The critical period for 2-cell stage arrest correlates with the initial phase of ZGA. Normal regulation of ZGA by zygotic clock may be prevented because of unfavourable environment, absence of external signals and deficiency of some important proteins in the cytoplasm. And the activation of MPF is the downstream event of ZGA. In summary, the block of early development is mainly due to the failure of ZGA in cultured embryos.