Phosphorylation of YWHAZ at Serine 58 by PKB/Akt is associated with resumption of meiotic arrest in mouse oocytes

Mammalian oocyte maturation is a tightly regulated process essential for successful fertilisation and embryonic development. Meiotic resumption in mammalian oocytes is controlled by various regulatory factors, including the tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein (YWHA/14-3-3). However, the specific functions of individual YWHA isoforms in oocyte meiosis remain poorly understood. In this study, we revealed that knockdown of Ywhaz, one of the isoforms of YWHA, using short interfering RNA (siRNA) or morpholino oligomers (MOs), accelerates meiotic resumption in mouse oocytes. To elucidate the mechanism underlying YWHAZ-mediated meiotic resumption, we thus explored its interactions with potential target proteins. Co-immunoprecipitation and immunofluorescence analyses demonstrated a physical interaction between YWHAZ and phosphorylated CDC25B. Additionally, we identified the protein kinases responsible for YWHAZ phosphorylation at distinct residues. Specifically, JNK1, CSNK1A1/CKIα and protein kinase B (PKB/Akt) were found to phosphorylate YWHAZ at Serine 184/186, Threonine 232 and Serine 58, respectively. Notably, phosphorylation of YWHAZ at serine 58 by PKB/Akt promoted meiotic resumption in mouse oocytes. Furthermore, we found the formation of a heterodimer between YWHAZ and YWHAQ. Our results provide insights into the PKB/Akt-YWHAZ-CDC25B signalling pathway and illuminate the functional influence of YWHAZ phosphorylation in meiotic regulation.