Protein kinase B (PKB/Akt) is required for the completion of meiosis in mouse oocytes

Akt, also known as protein kinase B, is implicated in many cellular processes. Akt is phosphorylated at two residues, Thr308 and Ser473. Thr308-phosphorylated Akt is present in pericentriolar materials, while localization of Ser473-phosphorylated Akt was similar to that of microtubules in metaphase oocytes. Spindles were shorter and aberrant in oocytes injected with Thr308- or Ser473-phosphorylated Akt antibodies. Specifically, Thr308- and Ser473-phosphorylated Akts function individually and are both necessary to assemble the metaphase II (MII) spindle. Moreover, the functions of Thr308- and Ser473-phosphorylated Akts differ in MII oocytes. Although oocytes exhibited second polar body (PB2) emission after the injection of a peptide for Thr308, the chromosomal alignment and microtubular organization were aberrant. In contrast, the injection of a peptide for Ser473 caused a failure of PB2 emission. These results suggest that Thr308- and Ser473-phosphorylated Akts are individually involved in fertilization to complete meiosis, including different roles (i.e., Ser473-phosphorylated Akts are involved in PB2 emission, whereas Thr308-phosphorylated Akts regulate the organization of microtubules).