Phosphorylation of histone H3 on Ser10 by auto-phosphorylated PAK1 is not essential for chromatin condensation and meiotic progression in porcine oocytes

BACKGROUND: The p21-activated kinase 1 (PAK1) is essential for mitosis and plays an important role in the regulation of microtubule assembly during oocyte meiotic maturation in mice; however, little is known about its role in porcine oocytes. RESULT: Total p21-activated kinase 1 (PAK1) and phosphorylated PAK1 at Thr423 (PAK1(Thr423)) were consistently expressed in porcine oocytes from the germinal vesicle (GV) to the second metaphase (MII) stages, but phosphorylation of histone H3 at Ser10 (H3(Ser10)) was only expressed after the GV stage. Immunofluorescence analysis revealed that PAK1(Thr423) and H3(Ser10) colocalized on chromosomes after the GV stage. Blocking of endogenous PAK1(Thr423) by injecting a specific antibody decreased the phosphorylation level of H3(Ser10); however, it had no impact on chromatin condensation, meiotic progression, cleavage rate of blastomeres or the rate of blastocyst formation. CONCLUSION: Phosphorylation of PAK1(Thr423) is a spontaneous activation process and the activated PAK1(Thr423) can promote the phosphorylation of H3(Ser10); however, this pathway is not required for meiotic maturation of porcine oocytes or early embryonic development.