Cloning of transforming growth factor-β1 (TGF-β1) and its type II receptor from zebrafish ovary and role of TGF-β1 in Oocyte maturation

TGF-beta is a multifunctional factor involved in regulating a variety of cellular activities. In mammals, TGF-beta is known to regulate reproduction, including ovarian functions. The role of TGF-beta in lower vertebrates, such as fish, is poorly understood. To examine the role of TGF-beta in fish reproduction, cDNAs encoding TGF-beta1 and the type II TGF-beta receptor ( TbetaRII) were cloned from the zebrafish ovary using PCR-based strategies. The mature peptide region of the zebrafish TGF-beta1 shows 70-85% identity with TGF-beta1 from other species. The zebrafish TbetaRII cDNA sequence is the first to be reported from a fish species, and it shows a high level of conservation at the kinase domain. Using RT-PCR, we have detected mRNA expression of TGF-beta1, TbetaRII, as well as its downstream signaling molecules Smad2, 3, and 4 in ovarian follicles at different stages of development. In addition, we have examined the effect of TGF-beta1 on oocyte maturation. TGF-beta1 significantly inhibited both gonadotropin- and 17alpha, 20beta-dihydroxyprogesterone-induced oocyte maturation in a dose- and time-dependent manner. These findings demonstrate, for the first time, that TGF-beta1 plays a role in regulating oocyte maturation in fish and suggest that a TGF-beta/Smad signaling pathway is present in the zebrafish ovary.