The Localization And Function Of SNAIL And SLUG In Mouse Ovaries And Preimplantation Embryos

The pregnancy of mammal depends on the development of ovarian follicles, oocytesmaturation, ovulation, fertilization, embryo development and implantation. These processes areregulated by various genes and signaling molecules. SNAIL and SLUG are zinc-fingertranscription factors which belong to SNAIL superfamily, they participate in the regulation ofcell division, cell survival, mesoderm formation and epithelial-to-mesenchymal transition(EMT) process. Plenty attentions have been paid to the key roles of SNAIL and SLUG in themigratory tissues, including the primitive streak, mesoderm and other organs such as lung,kidney and limb bud. However, little is known about the localization and function of SNAIL orSLUG on the development of mouse ovary and early embryo development. In the present studywe investigated the expression of SNAIL and SLUG in ovaries from neonatal mice andgonadotropin-induced immature mice during follicular maturation, ovulation and luteinizationprocess by using immunohistochemical analysis and Western-blot. Additionally, we examinedthe expression and localization of SNAIL and SLUG during GVBD-stage oocytes and earlyembryo by laser scanning confocal microscopy.Our data demonstrated that there was no SNAIL immunoreactivity except ovarian surfaceepithelial cells on postnatal day1(PD1) and the early development of follicle (PD1-PD5).SNAIL was first evident in the interstitial cells and theca cells at PD6, then it appeared in theoocytes at PD8. After that the expression pattern remained the same in the epithelial cells,interstitial cells, theca cells and oocytes, but never detected in granulosa cells. Different fromSNAIL, SLUG was expressed in oocytes and ovarian surface epithelial cell at PD1, with thedevelopment of follicles, it arised in theca cells and interstitial cells at PD6, but not ingranulosa cells either. The expression of SNAIL and SLUG was similar in hormonallyregulated ovaries. In preantral, antral, and preovulatory follicles, the immunoreactivity of thesetwo transcription factors was apparent in interstitial cells, theca cells and oocytes. We found that both SNAIL and SLUG were evident in CL. As SLUG, the localization was movinggradually from the peripheral region to interior of CL. Accompanying the degeneration of CL,the expression level of SNAIL and SLUG were all decreased. Western-blot was performed todetermine the protein content of SNAIL and SLUG in hormonally regulated ovaries duringfollicular maturation, ovulation, and luteinization process., the volume of SNAIL and SLUGwas same at eight difference stages, include0h，24h,48h after PMSG, and4h,10h,11h,12h,24h after hCG. But the volume of SNAIL and SLUG at hCG-48was both decreased. Thiswas in accord with our immunohistochemical study of gonadotropin-induced immature mice.During early embryo cleavage, SNAIL existed in the nucleus and cytoplasm of embryos exceptnucleolus from germinal vesicle breakdown (GVBD) to8-cell stage, then it localized incytoplasm at morula stage and in nucleus at blastocyst stage. SLUG，the same as SNAIL,existed in the nucleus and cytoplasm of embryos except nucleolus from germinal vesiclebreakdown (GVBD) to8-cell stage, but it was in cytoplasm at morula stage and the wholeblastocyst stage.In conclusion, SNAIL and SLUG may have important role during follicular maturationand early embryo development, but the patterns of expression of SNAIL and SLUG are not allthe same, we speculate that they may have different role in these stages.