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Title: The maturation-inducing hormone 17a-20b-dihydroxy-4pregnen-3-one regulates gene expression of inhibin A and bambi (bone morphogenetic protein and activin membrane bound inhibitor) in the rainbow trout ovary

Author
item Lankford, Scott
item Weber, Gregory - Greg

Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2010
Publication Date: 5/22/2010
Citation: Lankford, S.E., Weber, G.M. 2010. The maturation-inducing hormone 17a-20b-dihydroxy-4pregnen-3-one regulates gene expression of inhibin A and bambi (bone morphogenetic protein and activin membrane bound inhibitor) in the rainbow trout ovary. General and Comparative Endocrinology. 168:369-376.

Interpretive Summary: A first step in the production of fish as with any animal is controlling reproduction so that the animal spawns high quality eggs. Hormone systems are key to controlling reproduction but little is known about many of the hormones that regulate ovarian development and spawning in fish. In fish, almost nothing is known about members of a superfamily of hormones known as the transforming growth factor-b (TGFb) superfamily, and inhibitors that regulate their actions, even though these growth factor hormones are known to have many critical roles in ovarian development in mammals. We characterized changes in TGFb superfamily system genes. The results suggested they might be involved in the regulation of follicle maturation. Follicle maturation is a process that prepares the eggs for spawning and its successful completion greatly affects egg quality. In the present study we determined a key steroid that regulates follicle maturation, referred to as the M-phase inducing hormone (MIH), also regulates gene expression of two superfamily system members, inhibin bA (inhbA) subunit that forms activin A, and bambi (bone morphogenetic protein and activin membrane-bound inhibitor). Activin A has been shown to regulate follicle maturation in some fish species and Bambi functions to inhibit actions of almost all TGFb superfamily members. These data suggest that TGFb superfamily system may be involved in a positive feedback loop that leads to an increase in MIH production. Manipulation of the factors involved in this feedback loop may lead to improved methods for controlling spawning in fish and increase the number of fish producing high quality eggs.

Technical Abstract: Transforming growth factor-beta (TGFb) superfamily members are important paracrine and autocrine regulators of ovarian development and steroidogenesis in mammals and birds, but their reproductive roles in fish are not well understood. The activin system, Tgfb, and bone morphogenetic protein 15 (Bmp15) participate in the regulation of follicle maturation in some fish species. In addition, transcript levels of TGFb superfamily members and their inhibitors, follistatin and bambi (bmp and activin-membrane-bound inhibitor), change in the rainbow trout ovary during reproductive development including the transition from vitellogenesis to follicle maturation. The objective of the present study was to determine if the maturation inducing hormone (MIH) in trout, 17a,20b-dihydroxy-4-pregnen-3-one, regulates gene expression of TGFb superfamily members and their inhibitors. Overnight incubation of isolated follicles competent to resume meiosis in response to the MIH, in control medium, increased transcript levels of inhibin bA subunit (inhba) and decreased levels of bambi suggesting the transcripts are influenced by systemic factors. Incubation with MIH decreased inhba and increased bambi expression levels. Cycloheximide altered responses to isolation and MIH. The MIH was the most potent steroid examined. The responses of the transcripts to incubation with and without MIH were observed in maturationally incompetent follicles although the responses to MIH were greater in competent than incompetent follicles. In summary, MIH regulates inhba and bambi expression in a stage specific manner supporting a role for MIH regulation of the TGFb superfamily system and a role for the TGFb superfamily system in the regulation of follicle maturation in rainbow trout.