Transition Metal Regulation of Oocyte Maturation

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The objective of this research proposal is to understand the role of zinc in the control of oocyte maturation. Zinc is one of the most widely utilized metals in biological systems and is an essential co-factor in hundreds of transcription factors, phosphatases, kinases, and metalloenzymes. Management of zinc homeostasis is tightly regulated and over twenty zinc-specific transporters are conserved across mammalian genomes. Three of these zinc-transporting proteins are highly enriched in the mouse oocyte and fertilized egg relative to more than 60 other tissues. Our preliminary findings suggest that three physiological processes may depend on zinc as a specific regulatory factor. Using zinc-specific fluorophores, we have identified the granulosa cells as a source of free zinc and predict that zinc is transported to the oocyte through zinc transport proteins present in the transzonal projections connecting these two cells during follicle development. Secondly, removal of zinc during in vitro maturation of oocytes blocks expansion of the surrounding cumulus cells and causes symmetric cytokinesis of the oocyte rather than asymmetric polar body extrusion. These phenotypes are rescued by exogenous zinc. Finally, delivery of zinc to meiotically mature eggs results in parthenogenic activation. These studies suggest a previously unrecognized link between zinc-dependent signaling pathways and oocyte maturation and are the focus of this application. Our overall hypothesis is that the completion of oocyte maturation in the follicle and transition to a meiotically competent egg depends on zinc regulation and oocyte-enriched zinc-specific receptors. This hypothesis is addressed in three interiinked experimental aims by a highly interdisciplinary team that bridges reproductive science, chemical biology and biophysics. While the phenomenological evidence underlying the proposal strongly supports a regulatory role for zinc in oocyte function, biochemical mechanisms are just beginning to emerge in the literature and from our own preliminary data. The results of studies proposed by this project will provide an innovative new model for oocyte development, and add new member(s) to the family of inorganic signaling molecules (such as Ca2+, NO, 02, and C02) that control fundamental cellular and developmental processes.