Endocrine Control of Fish Reproduction

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Reproduction is a complex process that requires precise control by various signaling molecules, such as hormones and growth factors. A key event in female reproduction is the growth of oocytes (increase in size) and their maturation into fertilizable eggs. The overall goal of my NSERC-funded research program is to determine how hormones produced from the pituitary gland work with hormones and growth factors produced within the ovary to regulate oocyte development. We showed that several members of the transforming growth factor-beta (TGF-beta) family regulate oocyte maturation in the zebrafish ovary. More recently, we described key cellular pathways that mediate the effects of these growth factors in the ovary. In addition, we have identified additional members of the TGF-beta family, Nodal-related 1 (Ndr1) and Ndr2, and a group of small RNAs, named microRNAs, as potential regulators of oocyte growth and maturation. In the next five years, we will continue to use zebrafish as a model to study how oocyte growth and maturation are regulated by integrative functioning of hormones, growth factors and microRNAs. ***Two specific aims are proposed:***1) Roles of the Nodal signaling pathway:***Nodal signals, Ndr1 and Ndr2, play critical roles during embryonic development. However, their function in the adult ovary is not known. Our recent findings suggest that the Nodal signals may promote early oocyte growth but inhibit oocyte maturation. In this study, we will first increase or decrease the amount of Ndr1 and Ndr2 production within the ovary and observe how this affect oocyte growth and hormones-induced oocyte maturation. We will also study the intracellular signaling pathways that mediate Ndr1 and Ndr2 actions in the ovary. ***2) Roles of microRNAs***MicroRNAs are important regulators of physiological processes. Their functions in oocyte growth and maturation are poorly understood. Our recent studies suggest that microRNAs produced from follicular cells (cells that surround oocytes) may be important for oocyte growth and maturation. To test this possibility, we will first inhibit the expression of genes that encode for the enzymes involved in microRNA production and determine if oocyte growth and maturation are affected by loss of these genes. We will then test the effects of several microRNAs in modulating growth factor signaling and oocyte development.***The proposed studies will provide new insights into the regulation of oocyte growth and maturation. They will enhance our overall understanding of vertebrate reproduction. These studies may also have impacts on women's reproductive health and fertility. Finally, understanding how fish reproduction is regulated has potential applications in aquaculture.