The Relationship Between Evi-1 Expression And Mouse Follicular Development

The ecotropic viral integration site-1gene (Evi-1) was first identified as a common site of retroviral integration invirally induced myeloid tumors of AKXD mice. Evi-1 is shown to be highly expressed in human myeloid leukemias and myelodysplastic syndromes by chromosomal rearrangements involving3q26, to which Evi-1 is mapped. It is an important regulator of the transforming growth factor beta superfamily and antagonize the effects of TGF-β. Mice lacking Evi-1 die within the first few weeks of life with multiple defects in embryonic development. Several studies have demonstrated that Evi-1 is expressed in many embryonic and adult mouse tissues. However, little is known about its role in ovarian function. The roles of the TGF-βsuperfamily in ovarian functions and theactivity of Evi-1 as a repressor of TGF-βsignaling indicate the possibility that Evi-1 may play some roles in ovarian follicle development. Thus,the purpose of this study was to localize the Evi-1 protein in the ovaries and to further explore its biological function in the regulation of folliculogenesis.The results showed that :1. The localization of Evi-1 protein was in the cytoplasm of oocytes and not in theca cells, granulosa cells and the nucleus of oocyte.2. Expression of Evi-1 protein during postnatal ovarian follicular development: We found that Evi-1 was highly expressed in the cytoplasm of oocytes in primordial and primary follicles on PD1 and PD6. In the preantral follicles from PD10 to PD 16, Evi-1 immunostaining maintained an intermediate level in oocytes. Evi-1 expression was low in early antral follicles on PD23.3. Expression of Evi-1 protein after gonadotropin treatment: Evi-1 was still localized in the cytoplasm of oocytes. After PMSG treatment for 24h, Evi-1 immunostaining was mainly in the oocytes,but at a lower level than that in PD 23. After hCG treatment for 4h and 11h, Evi-1 level was even lower in oocytes in large antral follicles. In small follicles, the intensity of staining for the Evi-1 in oocytes was higher than in large antral follicles.There was no detectable Evi-1 immunostaining in corpora lutea after hCG 24h.4. Expression of Evi-1 protein during the estrous cycle: In the ovaries from cycling mice, the immunostaining of Evi-1 was seen in small follicles and the expression of Evi-1 protein was still localized in the oocyte. At diestrus and estrus,strong signal was detected in oocytes in small follicle and faint staining was observed at proestrus and metestrus compared with diestrus and estrus.5. Expression of Evi-1 mRNA and ovulation related genes in gonadotropin-induced immature mice: Real-time PCR was performed to examine the relationship between Evi-1 mRNA and ovulation related genes (Ptgs2, Tnfaip6, Has2, Cd44, C1qbp). At 4h after hCG treatment, Evi-1 mRNA was down-regulated whereas ovulation related genes were up-regulated.Overall,the results indicate that Evi-1 is expressed in a stage-specific manner during ovarian follicular development and may play some roles in early follicledevelopment.