Maternal Oct-4 is a potential key regulator of the developmental competence of mouse oocytes

We report that: 1) the transcription factor Oct-4 is absent in MIINSN oocytes, accounting for 2) the down-regulation of Stella, a maternal-effect factor required for the oocyte-to-embryo transition and of which Oct-4 is a positive regulator; 3) eighteen Oct-4-regulated genes are up-regulated in MIINSN oocytes and are part of gene expression networks implicated in the activation of adverse biochemical pathways such as oxidative phosphorylation, mitochondrial dysfunction and apoptosis.The down-regulation of Oct-4 plays a crucial function in a sequence of molecular processes that leads to the developmental arrest of MIINSN oocytes. The use of a model study in which the MII oocyte ceases development consistently at the 2-cell stage has allowed to attribute a role to the maternal Oct-4 that has never been described before. Oct-4 emerges as a key regulator of the molecular events that govern the establishment of the developmental competence of mouse oocytes.The early stages of mammalian development are sustained by the presence of transcripts and proteins that have been produced and stored in the oocyte during folliculogenesis. This supply is used by the morula stage in sheep and rabbit preimplantation embryos; the 4- to 8-cell stage in humans and the 2-cell stage in the mouse, at which time zygotic gene activation (ZGA) occurs and novel transcripts and proteins are expressed by the embryonic genome [reviewed in [1,2]]. What is the exact maternal contribution during this period of transition from a maternal to an embryonic control of development, and how the maternal legacy of transcripts and proteins is orchestrated through the first mitotic divisions prior to ZGA, remains unclear. An altered maternal contribution to a correct expression of zygotic genes leads to a developmental block at the time of ZGA [1,2].This developmental block is a feature of a group of fully grown antral oocytes present in the mammalian ovary. Based on their chromatin organisation, antral oocytes