The regulation and role of the insulin-like growth factor system in zebrafish (Danio rerio) ovarian development

While the involvement of gonadotropins in regulating oocyte maturation and ovulation is well understood, there is much less known about the role played by peptide hormones synthesized within the ovary. These studies investigate the importance of the insulin-like growth factor (IGF) family in the regulation of ovarian function in the zebrafish. Using RT-qPCR it was demonstrated that IGF ligands and receptors were expressed in the ovary and displayed differential temporal and spatial expression patterns. Addition of human chorionic gonadotropin (hCG) to ovarian follicles incubated in vitro increased IGF-III and IGF-IIb mRNA levels whereas the maturation inducing steroid (17alpha-20beta-P) decreased expression of these genes. Follicles treated with recombinant human IGF-I or IGF-II were stimulated to undergo maturation independently from treatment with hCG or 17alpha-20beta-P. IGF-I also promoted maturational competence and steroidogenesis. These results demonstrate that the IGF system is present in the zebrafish ovary and plays a critical role in promoting oocyte maturation.