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.
- Inositol triphosphate receptor
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)