The effect of M-phase stage-dependent kinase inhibitors on inositol 1,4,5-trisphosphate receptor 1 (IP3R1) expression and localization in pig oocytes

At fertilization, inositol 1,4,5-trisphosphate receptor type 1 (IP(3)R1) has a crucial role in Ca2+ release in mammals. Expression levels, localization and phosphorylation of IP(3)R1 are important for its function, but it still remains unclear which molecule(s) regulates IP(3)R1 behavior in pig oocytes. We examined whether there was a difference in localization of IP(3)R1 after in vitro or in vivo maturation of pig oocytes. In mouse oocytes, large clusters of IP(3)R1 were formed in the cortex of the oocyte except in a ring-shaped band of cortex adjacent to the spindle. However, no such clusters of IP(3)R1 were observed in pig oocytes and there was no difference in its localization between in vitro and in vivo matured oocytes. We next tried to clarify which factor(s) regulates IP(3)R1 localization, phosphorylation and expression using M-phase stage-dependent kinase inhibitors. Our results show that treatments with roscovitine (p34(cdc2) kinase inhibitor) or U0126 (mitogen-activated protein kinase inhibitor) did not affect IP(3)R1 expression or localization in pig oocytes, although the latter strongly inhibited phosphorylation. However, treatment with BI-2536, an inhibitor of polo-like kinase 1 (Plk1), dramatically decreased the expression level of IP(3)R1 in pig oocytes in a dose-dependent manner. From these results, it is suggested that Plk1 is involved in the regulation of IP(3)R1 expression in pig oocytes.