Dynamic subcellular localization of estrogen receptor alpha during the first two cleavages of mouse preimplantation embryos

Zygotic gene activation (ZGA) is one of the most important events after mouse fertilization, but the mechanisms underpinning it are still unclear. Estrogen receptor alpha (ERα) is a versatile player in animal development. Our preliminary studies showed that ERα-specific antagonists blocked mouse 2-cell development and inhibited ZGA related gene expression, indicating an indispensable role of maternal ERα in early mouse preimplantation embryo development (PED). Here, we performed immunostaining detection to investigate the cell cycle specific subcellular localization of ERα, and serine 118 phosphorylated ERα (pERα-S118), during the first two cleavages of mouse PED. Our results showed that ERα nuclear localization appeared at 1-cell S-phase, disappeared at metaphase, and reappeared since the G1 phase of 2-cell embryos. Nuclear expression of pERα-S118 started at the 1-cell S-phase, but was absent at the G1 phase of 2-cell embryos, and reappeared since the 2-cell S-phase. Interestingly, pERα-S118 showed a dynamic expression pattern among nuclear, nuclear surface, cytoplasm and cell membrane. These results indicate that maternal derived ERα might still function in the first two cleavages of mouse PED, during which ZGA occurs.