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.