Throughout their meiotic maturation in most mammals, oocytes are arrested twice, prophase I and metaphase II. Being released from these arrests, transient or oscillation of intracellular Ca2+ concentration is observed in the ooplasm, which is not answered in relation to the specific role in the resumption of meiotic arrest. Recently, Ca2+/calmodulin-dependent protein kinase II (CaM KII) has been known as a Ca2+ oscillation decoder from the in vitro experiment. CaM KII is multifunctional serine/threonine kinase observed in most cells. Present studies were performed to investigate the role of CaM KII during resumption of meiotic arrest and activation in vitro of mouse oocytes. It was questioned whether CaM KII might be involved in the meiotic resumption of mouse oocytes. Compared to the control, both of CaM KII inhibitors, KN-93 and KN-62, significantly inhibited germinal vesicle breakdown (GVBD) of mouse oocytes in a dose-dependent manner. As the concentration of KN-93 increased, concomitant decrease of intracellular Ca2+ concentration ([Ca2+]i) was also observed using confocal laser scanning microscope (CLSM) and an intracellular Ca2+ indicator, fluo 3-AM. When GVBD oocytes were treated with 6% ethanol, small [Ca2+]i transient was observed in oocytes bathed with Ca2+-free medium and large increase was observed in oocytes bathed with Ca2+-containing medium, suggesting that [Ca2+]i transient could happen from intracellular Ca2+ store as well as Ca2+ influx through Ca2+-channel on the oolemma. However, KN-93 inhibited the [Ca2+]i transient of GVBD oocytes in both cases. Using monoclonal antibodies against α-subunit of CaM KII, tubulin and microtubule-assocaited proteins (MAPs), CaM KII has been colocalized on the spindle with tubulin and MAPs. The present study also demonstrated the presence of α-subunit of CaM KII in heart, kidney, testes, ovary as well as in brain of the mouse. In ovarian follicles, CaM KII was expressed in granulosa cells and oocytes. Based on overall the above results, followings are suggested. First, CaM KII might be involved in the regulatory mechanism of meiotic resumption. Second, CaM KII might play a regulatory role in the stabilization of microtubule.

• Sook Young Yoon(Fertility Center of CHA Gangnam Medical Center, CHA University)
• Dawon Kang(Department of Physiology and Institute of Health Sciences, Gyeongsang National University School of Medicine)