Investigation of stem cells in adult and prepubertal mouse ovaries

The possible presence of oocyte and granulosa cells originated from stem cells in the adult mammalian ovaries was claimed by some studies which will lead to major changes in reproductive biology and infertility treatments. Purpose of this research is to investigate the possible existence and the location of the potential stem cells in mouse ovaries. In this study, the ovaries from 2-week (pre-puberty) and 8-week (adult) old BALB-C mice were used. For the investigation of the presence of possible stem cells, the expression profiles of three well known stem cell markers, Oct-4, Nanog and Sox2 were determined in the ovaries of two different age groups by real time quantitative RT-PCR (qRT-PCR). Protein expression levels and their localization in the ovary cells were immunohistochemically evaluated on fresh-frozen ovary tissue sections by using monoclonal antibodies specific to Sox2, Nanog and Oct-4. The gene expression levels of Oct-4 and Nanog were found to be significantly differentiated between 2-week old and 8-week old mice whereas no significant difference was observed in the expression level of Sox2 between two age groups. Immunohistochemistry results showed the presence of both Sox2 and Oct-4 protein in the cytoplasm of ovarian epithelial cells, granulosa cells, oocytes and theca cells. Nanog protein was observed only in the nucleus of the oocytes and furthermore the expression of Nanog was higher in eight weeks old samples compared to two weeks old ones according to qRT-PCR results. These results suggest for the first time that Nanog protein is expressed both in adult and pre-puberty mouse ovaries and locate at the nucleus of the oocytes and to the best of our knowledge this is the first study that shows the differential expression of Oct-4, Nanog and Sox2 in pre-puberty and adult mouse ovaries by qRT-PCR. Collectively, our results may suggest that both pre-puberty and adult mice ovaries accommodate cells carrying stem cell features.