Date Published: December 14, 2018
Publisher: Impact Journals
Author(s): Yu Zhang, Hong-Hui Wang, Xiang Wan, Yao Xu, Meng-Hao Pan, Shao-Chen Sun.
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.
Fully grown mammalian oocytes are arrested at the diplotene stage of the first meiotic prophase within ovarian follicles, which is also called germinal vesicle (GV) stage. In order to produce fertilizable female gametes, these oocytes must undergo well-regulated meiotic maturation, including meiosis resumption, proper apparatus assembly and arrangement, as well as first polar body (PBI) extrusion. A combination of cytoskeleton, including microtubules and actin filaments is pivotal for the success meiosis of oocytes. 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 . Then the inter-chromosomal microtubules form the central spindle to lead chromosomes segregation during anaphase I (AI) in oocytes . 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 also 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 [5–7].
In the present study, we explored the functions of PKD during porcine oocyte meiotic maturation. We showed that PKD was critical for meiosis resumption, spindle organization and actin microfilament assembly, which eventually affected PBI extrusion during porcine oocyte maturation.