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Phosphorylation of inositol 1,4,5-triphosphate receptor 1 during in vitro maturation of porcine oocytes

Ito, Junya, Yoshida, Tomoko, Kasai, Yasushi, Wakai, Takuya, Parys, Jan B., Fissore, Rafael A., Kashiwazaki, Naomi
Animal science journal = 2010 v.81 no.1 pp. 34-41
calcium, calcium signaling, epitopes, inositols, meiosis, mice, mitogen-activated protein kinase, mitogen-activated protein kinase kinase kinase, oocytes, phosphorylation, swine
During fertilization in mammalian species, a sperm-induced intracellular Ca²⁺ signal ([Ca²⁺]i) mediates both exit of meiosis and oocyte activation. Recently, we demonstrated in mouse oocytes that the phosphorylation levels of inositol 1,4,5 trisphosphate receptor type1 (IP₃R1), the channel responsible for Ca²⁺ release and oscillations during fertilization, changed during maturation and fertilization. Therefore, we examined the expression and phosphorylation of IP₃R1 during in vitro maturation of pig oocytes. Here, our present study shows that expression of IP₃R1 protein did not change during maturation, although the phosphorylation status of the receptor, specifically at an MPM-2 epitope, did. We found that while at the beginning of maturation IP₃R1 lacked MPM-2 immunoreactivity, it became MPM-2 reactive by 24 h and reached maximal reactivity by 36 h. Interestingly, the acquisition of MPM-2 reactivity coincided with the activation of p34cdc² kinase and mitogen-activated protein kinase (MAPK), which are involved in meiotic progression. Following completion of maturation, inactivation of MAPK by U0126 did not affect IP₃R1 phosphorylation, although inactivation of p34cdc² kinase by roscovitine dramatically reduced IP₃R1 phosphorylation. Neither inhibitor affected total expression of IP₃R1. Altogether, our results show that IP₃R1 undergoes dynamic phosphorylation during maturation and this might underlie the generation of oscillations at fertilization.