Characterization of the function and regulation of type-1 inositol 1,4,5-trisphosphate receptor in mouse oocytes and eggs

Given the indispensable role of Ca2+ release in fertilization, the type 1 inositol 1,4,5- trisphosphate receptor (IP3R1) is a key regulatory molecule in mediating the cross-talk between cell cycle progress and the Ca2+ release machinery in mammalian oocytes. The studies in this thesis addressed several important regulatory aspects of the Ca 2+ release activity at fertilization of mammalian eggs. In chapter I, we found that compromised functionality of IP3R1 underlay the defective IP3R1-mediated Ca2+ release in aging eggs. Further, our studies also indicated that modifications on the biochemical status of IP3R1 by incubation with caffeine have positive effects on the Ca2+ release activity and developmental fate of aging mouse eggs. Thus, these results may help facilitate the invention of a cure that could delay/reverse many of age induced detrimental changes thereby restoring the fertilizability of aged eggs. For the next two chapters we mainly focus on the regulatory role of IP3R1 as a significant participant in the early developmental event. Our completed results with the caspase-3 cleaved IP3R1 indicated that the truncated IP3R1 might not play a prominent role affecting the Ca2+ homeostasis during the aging process in mouse oocytes due to its rapid turnover rate. Regardless, we confirmed the leaky property of C-IP3R1 in mouse oocytes and found a novel protective proteolysis pathway in mouse oocytes. Finally development of a system by which we could selectively overexpress IP3R1 phosphorylation mutants allows us to probe important phosphorylation regulatory mechanisms underlying the [Ca2+]i oscillations in mammalian oocytes. Thus the experiments I have done provide valuable information regarding the extensive regulation of the PI pathway, regulation that in aged and non- aged MII eggs, results in a Ca2+ release program that is replete with information.