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Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/24/2014 Publication Date: 12/4/2014 Citation: Cleveland, B.M., Weber, G.M. 2014. Effects of sex steroids on expression of genes regulating growth-related mechanisms in rainbow trout (Oncorhynchus mykiss). General and Comparative Endocrinology. DOI:10.1016/j.ygcen.2014.11.018. Interpretive Summary: In rainbow trout sex steroid production increases significantly during sexual maturation. Estrogen increases in females and promotes weight loss while the male sex steroids (androgens) have positive effects on growth. However, specifically how or why these responses occur is largely unknown. We injected fish with either estrogen or androgens to determine how they impact the regulation of genes related to growth. Collective evidence indicates estrogen negatively affects genes responsible for muscle accretion, in contrast androgens had a positive effect on these same genes. Our results identify mechanisms which are associated with two different growth responses; weight loss and weight gain. These mechanisms can be used as markers for developing feeding strategies, formulating diets, or establishing husbandry practices that optimize growth performance. Technical Abstract: Effects of a single injection of 17-estradiol (E2), testosterone (T), or 5a-dihydrotestosterone (DHT) on expression of genes central to the growth hormone (GH)/insulin-like growth factor (IGF) axis, muscle-regulatory factors, TGF-beta superfamily signaling cascade, and estrogen receptors were determined in rainbow trout (Oncorhynchus mykiss) liver and white muscle tissue. In liver in addition to regulating GH sensitivity and IGF production, sex steroids also affected expression of IGF binding proteins, as E2, T, and DHT increased expression of igfbp2b and E2 also increased expression of igfbp2 and igfbp4. Regulation of this system also occurred in white muscle in which E2 increased expression of igf1, igf2, and igfbp5, suggesting anabolic capacity may be maintained in white muscle in the presence of E2. In contrast, DHT decreased expression of igfbp5. DHT and T decreased expression of myogenin, while other muscle regulatory factors were either not affected or responded similarly for all steroid treatments. Genes within the TGF-beta superfamily signaling cascade responded to steroid treatment in both liver and muscle, suggesting a role for sex steroids in the ability to transmit signals initiated by TGF-beta superfamily ligands, with a greater number of genes responding in liver than in muscle. Estrogen receptors were also regulated by sex steroids, with era1 expression increasing for all treatments in muscle, but only E2- and T-treatment in liver. E2 reduced expression of erb2 in liver. Collectively, these data identify how physiological mechanisms are regulated by sex steroids in a manner that promotes the disparate effects of androgens and estrogens on growth in salmonids. |
