Temporal mRNA expression of transforming growth factor-beta superfamily members and inhibitors in the developing rainbow trout ovary

Authors: Lankford, Scott; Weber, Gregory - Greg

Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2009
Publication Date: 9/23/2009
Citation: Lankford, S.E., Weber, G.M. 2010. Temporal mRNA expression of transforming growth factor-beta superfamily members and inhibitors in the developing rainbow trout ovary. General and Comparative Endocrinology. 166(2):250-258.

Interpretive Summary: A first step in the production of fish as with any animal is obtaining seedstock. For fish, this requires being able to control the reproduction of the animal so that the animal spawns high quality eggs. At present, little is known about many of the hormones that regulate ovarian development and spawning in fish. This is especially true of growth factors including members of the transforming growth factor-beta (TGF-beta) superfamily. Members of this superfamily are known to have critical roles in ovarian development in mammals including determining how many offspring will be born by determining how many eggs the female will produce to be fertilized. As a first step in understanding these growth factors in fish, we determined if the mRNA for these growth factors were present in the fish ovary and egg. We then determined when levels of the mRNA changes during the reproductive cycle as an indicator of what the growth factors might be regulating. The presence of the mRNAs for growth factors in the ovary, together with different patterns of changes in mRNA levels, suggest the TGF-beta superfamily members help to regulate reproduction in fish. Further study of these growth factors may lead to improved methods of spawning fish or husbandry practices that result in improved egg quality.

Technical Abstract: Members of the transforming growth factor-beta (TGF-beta) superfamily have critical roles in ovarian development in mammals, yet many of these peptides have not been characterized or even identified in fish. Although much is known about the endocrine control of ovarian development in fishes, little is known about the intraovarian functions of TGF-beta superfamily members. We characterized the temporal changes in ovarian mRNA expression of six TGF-beta superfamily members and two TGF-beta superfamily inhibitors, follistatin and BAMBI (bone morphogenetic protein [bmp] and activin membrane-bound inhibitor), during reproductive development in rainbow trout, 'Oncorhynchus mykiss'. For comparison to TGF-beta superfamily member expression patterns, we quantified mRNA changes of insulin-like growth factor (IGF) I and II and five enzymes associated with steroidogenesis, along with plasma levels of three sex steroids, due to their known actions in ovarian regulation in fishes. Expression was measured at six developmental stages [early pre-vitellogenic (Vg), late pre-Vg, early-Vg, mid-Vg, late-Vg and competent] by quantitative, real-time RT-PCR. Maximum expression of bmp4, bmp7 and gdf9 (growth and differentiation factor) mRNAs were during pre-Vg stages. Changes in expression of inhibin alpha and beta-A subunits, as well as follistatin, occurred during early-mid-Vg, which corresponded with increased estradiol-17-beta and testosterone production. Expression of inhibin beta-B subunit mRNA was decreased and BAMBI expression increased in follicles that were competent to respond to the maturation inducing hormone. Differential temporal expression patterns among the transcripts are consistent with disparate roles in regulating ovarian development in fish.