PARENT SESSION
Gonadal Function

THE INVOLVEMENT OF ACTIVIN AND TGF₁ IN THE REGULATION OF TELEOST OVARIAN STEROID PRODUCTION.

Calp, Katie¹, Van Der Kraak, Glen¹, ¹

ABSTRACT- Local ovarian factors have been recognized for their contribution to the regulation of vertebrate ovarian function. Activin and TGF₁, members of the transforming growth factor (TGF) superfamily of polypeptide growth factors, are produced in the mammalian ovary and have been shown to exert their local effects via autocrine/paracrine mechanisms. Activin and its receptors have been cloned in the teleost ovary, and have been shown to exert effects on oocyte maturation. The effects of goldfish recombinant (gr) activin-B, human recombinant (hr) activin-A and hr TGF₁ on teleost ovarian steroidogenesis were investigated using an in vitro incubation system. Vitellogenic or preovulatory full grown (PFG) goldfish follicles were incubated with gr activin-B (5.0 IU/mL), hr activin-A (50 ng/mL) or hr TGF₁ (50 ng/mL) alone, or in the presence of human chorionic gonadotropin (hCG; 1.0 or 10.0 IU/mL). Steroid hormone levels were measured in the incubation medium by RIA. In PFG follicles, both activin-A and TGF₁ significantly decreased gonadotropin (GtH)-stimulated production of 17,20-dihydroxy-4-pregnen-3-one, which is the maturation-inducing hormone in this teleost fish species. Activin-A also significantly decreased GtH-stimulated testosterone production in these follicles. Neither activin-A nor TGF₁ affected GtH-stimulated estradiol production from vitellogenic follicles. This research demonstrates that members of the TGF superfamily are active in the goldfish ovary, exerting differential effects on ovarian steroid production that appear to be related to the stage of ovarian maturity. Members of the TGF superfamily may play an important role in the regulation of teleost ovarian function.

KEY WORDS: activin, TGF₁, teleost, steroidogenesis