Phosphatidyl-inositol-3-kinase (PI3K)/AKT regulation is involved in oocyte developmental competence

INTRODUCTION We recently demonstrated that somatic follicular cells finely regulate the translation of stored mRNAs during oocyte maturation. Amphiregulin and other EGF-like peptides expressed by follicular cells trigger the translation of specific transcripts in the oocyte, seemingly by indirect activation of the PI3K/AKT/mTOR cascade. The present study aims to better characterize the role of PI3K/AKT during oocyte maturation by using a genetic model where Pten (phosphatase and tensin homologue), which negatively regulates PI3K, is specifically ablated in oocytes. MATERIALS AND METHODS Cumulus-oocyte-complexes were collected from 21-days-old Ptenfl/fl:ZP3-CRE mice after PMSG-priming. AKT phosphorylation was assessed by western-blot. Translational activity was measured by luciferase assay after intraoocyte injection of dual luciferase translation reporters. Developmental competence was assessed by in vitro maturation and fertilization (IVM-IVF). Oocyte diameter and the kinetics of meiotic resumption were also analyzed. RESULTS In Ptenfl/fl:ZP3-CRE oocytes AKT was phosphorylated to the same extent in GV stage oocytes and after 2.5h culture either with or without amphiregulin, while AKT in wild type oocytes was only transiently phosphorylated after 2.5h culture with amphiregulin. Similarly, the specific translation of the luciferase reporters was no longer dependent on amphiregulin in Ptenfl/fl:ZP3-CRE oocytes. Pten conditional knock-out oocytes also showed a higher developmental competence after IVM-IVF. Oocyte diameter and the re-entry into cell-cycle were not affected. DISCUSSION Our results demonstrate that PI3K/AKT activation is a key factor for oocyte developmental competence and confirm its involvement in downstream signaling regulating the execution of the oocyte translational program during maturation.