The effect of M ‐phase stage‐dependent kinase inhibitors on inositol 1,4,5‐trisphosphate receptor 1 ( IP 3 R1 ) expression and localization in pig oocytes

At fertilization, inositol 1,4,5‐trisphosphate receptor type 1 ( IP 3 R1 ) has a crucial role in Ca 2+ 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 U 0126 (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.