Depletion of maternal SMC2 results in developmental arrest at the 1-cell stage
We further investigated the early embryo developmental competence both by observing in vitro and in vivo culture of fertilized eggs, and parthenogenetically activated (PA) eggs.
We mated Smc2flox /flox and Smc2flox /flox Gdf9Cre females with wild-type males, and then embryos were isolated on embryonic day 0.5 (E0.5) and cultured in vitro (Fig. 3A and B). We found that most of the SMC2-/+ embryos were arrested at the 1-cell stage. After 48 h of culture, most of the SMC2+/+embryos developed to the 4-8-cell stages, while SMC2-/+ fertilized eggs were still arrested at the 1-cell stage.
Further, we isolated the embryos on E1.5 to eliminate the possibility ofin vitro culture interference, and found that SMC2-/+ embryos were arrested at the 1-cell stage, while all the SMC2+/+ embryos reached the 2-cell stage.
Next, we examined the development of PA eggs. Following PA, the activation rate ofSmc2flox /flox Gdf9Cre oocytes decreased to some extent; compared with the control group, they arrested at the 1-cell stage (Fig. 3C). The chromosome decondensation in SMC2-null MII oocytes resulted in chromatid separation defects (Fig. 3D). The separated chromosomes were still connected by thin threads of decondensed chromatin.
Taken together, the maternal SMC2 was required for embryo development beyond the zygote stage.