Question

Hormonal Control of Zebrafish Oocyte Maturation

Answer 1

Ovarian differentiation and the processes of follicle development, oocyte maturation and ovulation are complex events, requiring the coordinated action of regulatory molecules. In zebrafish, ovarian development is initiated at 10 days after hatching and fish become sexually mature at 3 months. Adult zebrafish have asynchronous ovaries, which contain follicles of all stages of development. Eggs are spawned daily under proper environmental conditions in a population of zebrafish, with individual females spawning irregularly every 4–7 days in mixed sex conditions. Maximal embryo viability is achieved when sexually isolated females are bred in 10-day intervals.

Similar to other vertebrates, hormones from the hypothalamus–pituitary–gonadal axis play important roles in regulating follicle development. Follicle stimulating hormone (FSH) stimulates estradiol production, which in turn, promotes viteollogenesis. Luteinizing hormone (LH) stimulates the production of 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) or maturation inducing hormone (MIH) which acts through membrane progestin receptors to activate maturation promoting factor, leading to oocyte maturation. In zebrafish have also provided novel insights into the functions of ovary-derived growth factors in follicle development and oocyte maturation. Special emphasis is placed on how follicle development and oocyte maturation in adult females is regulated by gonadotropins, ovarian steroids and growth factors produced by the ovary.