Abstract
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.
Highlights
Grown mammalian oocytes are arrested at the diplotene stage of the first meiotic prophase within ovarian follicles, which is called germinal vesicle (GV) stage
We inhibited Protein kinase D (PKD) family activity to explore the roles of PKD in porcine oocytes and we showed that PKD served as a key regulator for proper spindle organization and actin assembly for polar body extrusion of porcine oocytes
We first examined the existence of PKD and our results showed that PKD protein expressed in porcine oocytes (Figure 1A)
Summary
Grown mammalian oocytes are arrested at the diplotene stage of the first meiotic prophase within ovarian follicles, which is called germinal vesicle (GV) stage. Microtubules form a specialized bipolar-shaped spindle at the center of oocyte at the metaphase I (MI) stage, and the accurate establishment of the meiotic spindle drives the congression of chromosomes at the equatorial plate [1]. The inter-chromosomal microtubules form the central spindle to lead chromosomes segregation during anaphase I (AI) in oocytes [2]. Actin filaments accumulated both at the cytoplasm and cortex of oocytes, and are directly involved in pushing meiotic spindle to the cortex during meiosis I, which maintain asymmetric spindle positioning at metaphase II (MII) [3, 4]. At the telophase I (TI) stage, the special actin-based cortical bulges and the meiotic spindle midzone induces the formation of cytokinetic furrows for pinching off a polar body [5,6,7]
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