Role of Oct-4 during acquisition of developmental competence in mouse oocyte. Zuccotti M et al. Knowledge of what determines the developmental competence of oocytes during folliculogenesis is poor. This review, through the analysis of the expression profile of developmentally competent or incompetent mouse oocytes, summarizes the results of recent studies showing that the Oct-4 transcription factor regulating the expression of Stella and Foxj2 at the Nanog locus could play a pivotal role in the establishment of the oocyte's developmental competence.
Expression regulated by
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Ovarian localization
Oocyte, Granulosa
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Oct-4 regulates the expression of Stella and Foxj2 at the Nanog locus: implications for the developmental competence of mouse oocytes. Zuccotti M et al. BACKGROUND Our knowledge of what determines the mammalian oocyte developmental competence is meagre. By comparing the transcriptional profiles of developmentally competent surrounded nucleolus (SN) and incompetent not surrounded nucleolus (NSN) mouse MII oocytes, we recently demonstrated that Oct-4 and Stella are key factors in the establishment of the oocytes' developmental competence. METHODS Using RT-PCR, microarray and immunocytochemistry assays, we analysed expression of genes and proteins in oocytes isolated throughout folliculogenesis and classified based on their SN- or NSN-type of chromatin organization. RESULTS We show that: (1) Oct-4 and Stella are expressed concurrently at the beginning of oocytes' growth and only in SN oocytes; (2) Germ Cell Nuclear Factor is a putative regulator of Oct-4 expression in MII oocytes; (3) the function of Oct-4 is directed at the Nanog locus, regulating the expression of Stella and Foxj2. CONCLUSIONS (1) A number of factors that act upstream and downstream of Oct-4 emerge as candidate players in the acquisition of the oocyte's developmental competence; (2) we define molecular markers that identify a specific group of ovarian oocytes (SN) that have a potential to acquire developmental competence; (3) the presence of SN and NSN oocytes in human ovaries extends the interest of these results to the field of human reproduction.
Follicle stages
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Fhx (Foxj2) expression is activated during spermatogenesis and very early in embryonic development. Granadino B et al. FHX (FOXJ2) is a recently characterized human fork head transcriptional activator that binds DNA with a dual sequence specificity. We have cloned the cDNA for the mouse orthologue Foxj2 and characterized its expression in the gonads and along the early pre-implantation development of the mouse. In the testis, Foxj2 is expressed from pachytene spermatocytes to round spermatids, but not in spermatogonia. In addition to the germ lineage, only Sertoli cells of the testis showed expression of Foxj2. In the ovary, only granulosa cells of the follicles express the factor. Neither mature spermatozoa nor oocytes showed expression of Foxj2. Foxj2 expression is early activated in zygotic development, being detected since as early as 8-cell stage embryos. Both cell layers of the blastocyst: the trophectoderm (TE) and the inner cell mass (ICM), express Foxj2.