Changes in ovarian expression of TGF-b superfamily and steroid synthesis related mRNAs in response to 17,20b-dihydroxy-4-pregnen-3-one treatment in vivo in rainbow trout (Oncorhynchus mykiss)
Members of the transforming growth factor-b (TGF-b) superfamily of peptides including activins, inhibins and bone morphogenetic proteins (BMP) have been identified as important regulators of ovarian development and steroidogenesis in mammals and birds. Their actions in fish have received little attention. In the present study we injected adult female rainbow trout with either vehicle, estradiol-17b (E2), testosterone (T), progesterone (P4) or 17,20b-dihydroxy-4-pregnen-3-one (17,20b-P) and 1 day later collected ovarian fragments for measurement of TGF-b superfamily and steroid synthesis related mRNA levels by RT-qPCR. Ovarian levels of BAMBI (BMP and activin membrane-bound inhibitor) and steroid acute regulatory protein (StAR) transcripts were increased in response to 17,20b-P and P4, but not E2 or T. The increase in StAR suggests the 17,20 b-P, the putative maturation inducing hormone (MIH) in rainbow trout, may increase the rate of its own production. Increased expression of BAMBI may attenuate actions of TGF-b superfamily peptides in the regulation of steroidogenesis if BAMBI functions in fish as it does in mammals.