ARS | Publication request: Changes in ovarian TGF-beta superfamily mRNA levels during oocyte maturation, and in response to 17,20beta-dihydroxy-4-pregnen-3-one treatment in vivo and in vitro, in rainbow trout

Submitted to: Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 20, 2007
Publication Date: June 3, 2007
Citation: Weber, G.M., Lankford, S. 2007. Changes in ovarian TGF-beta superfamily mRNA levels during oocyte maturation, and in response to 17,20beta-dihydroxy-4-pregnen-3-one treatment in vivo and in vitro, in rainbow trout. Meeting Proceedings pp.287.

Technical Abstract: BACKGROUND: Follicle maturation is a complex process regulated by the coordination of diverse hormones. The mechanisms and extent to which these different hormones interact to induce oocyte maturational competence, production of the maturation-inducing hormone (MIH), and the ability of the MIH to induce the resumption of meiosis is not well understood. Although members of the transforming growth factor-beta (TGF-beta)superfamily, including activin and bone morphogenetic proteins (BMP), have been identified as important regulators of ovarian function in mammals, their actions in the fish ovary have received little attention. METHODS: Blood plasma and ovarian tissues were collected from rainbow trout at various stages of the reproductive cycle, and following injection with sex steroids. Ovarian follicles from fish at various reproductive stages were incubated with graded doses of sex steroids and then collected for mRNA measurement. Ovarian expression of TGF-beta superfamily and related transcripts were measured by RT-qPCR. Sex steroids were measured in the plasma by radioimmunoassay. RESULTS: Ovarian transcripts for BAMBI and activin A were found to increase and decrease respectively as the follicles progressed from obtaining competence to completing germinal vesicle breakdown (GVBD), which is an indicator of the resumption of meiosis. These changes in transcript levels coincided with a decrease in estradiol-17beta and an increase in 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P) concentrations in the plasma. The progestin 17,20beta-P is the putative MIH in rainbow trout. In vitro treatment with 17,20beta-P increased BAMBI and decreased activin A mRNA levels in ovarian tissues. Injections of 17,20beta-P increased BAMBI but did not alter activin A mRNA levels. The responses to 17,20beta-P treatment were specific to this steroid. CONCLUSION: Changes in mRNA levels of activin A and BAMBI during follicle maturation, and in response to the MIH, 17,20beta-P, suggest a role for TGF-beta superfamily peptides in the regulation of follicle maturation in rainbow trout.