Expression and distribution of the zinc finger protein, SNAI3, in mouse ovaries and pre-implantation embryos

The Snail gene family includes Snai1, Snai2, and Snai3 that encode zinc finger-containing transcriptional repressors in mammals. The expression and localization of SNAI1 and SNAI2 have been studied extensively during folliculogenesis, ovulation, luteinization, and embryogenesis in mice. However, the role of SNAI3 is unknown. In this study, we investigated the expression of SNAI3 during these processes. Our immunohistochemistry data showed that SNAI3 first appeared in oocytes by postnatal day (PD) 9. Following this, SNAI3 was found to be expressed consistently in theca and interstitial cells, along with oocytes. In gonadotropin-treated immature mice, the expression of SNAI3 did not change significantly during follicular development. The expression of SNAI3 was reduced during ovulation, after which it increased gradually during luteinization. Similar results were obtained from western blot analyses. Furthermore, real-time polymerase chain reaction (RT-PCR) analyses revealed varying mRNA levels of different Snail factors at a given time in gonadotropin-induced ovaries. During early embryo cleavage, SNAI3 was localized to the nucleus, except the nucleolus at the germinal vesicle and one-cell stages. From two- to eight-cell stages, SNAI3 was localized only to the nucleolus. Thereafter, SNAI3 was detected only in the cytoplasm, except during the blastocyst stage when it was localized to the nucleus of the trophectoderm and the inner cell mass. RT-PCR results showed that the expression of Snail superfamily genes was decreased during the blastocyst stage. From the eight-cell to morula stage, when compaction occurs that is a prerequisite for blastocyst formation, Snai3 mRNA was expressed at very low levels and was opposite to the highest expression level of the compaction-related gene, E-cadherin, at the eight-cell stage. Taken together, our results suggest that SNAI3 likely plays some roles during folliculogenesis, luteinization, and early embryonic development.