Inhibition of protein kinase D disrupts spindle formation and actin assembly during porcine oocyte maturation

Protein kinase D (PKD) subfamily which includes PKD1, PKD2 and PKD3 is a novel family of serine/threonine kinases. PKD has been widely implicated in the regulation of multiple physiological effects including immune responses, apoptosis and cell proliferation. However, the roles of PKD in oocytes have not been fully clarified. In this study we investigated the regulatory functions of PKD during porcine oocyte maturation. Our results indicated that PKD expressed in porcine oocytes and the inhibition of PKD family activity led to the failure of meiosis resumption and the first polar body extrusion. Further analysis indicated that the spindle assembly and chromosome alignment were disrupted after PKD family inhibition, and this might be through its regulatory role on MAPK phosphorylation. We also found that PKD phosphorylated cofilin for actin assembly, which further affected cortical actin distribution, indicating the roles of PKD family on cytoskeleton. In addition, a decreased expression of PKD in postovulatory aging porcine oocytes was observed, which might connect PKD with cytoskeleton defects in aged oocytes. Taken together, these results suggest that PKD possesses important functions in porcine oocyte maturation by regulating spindle organization and actin assembly.