Meeting Abstract

11.5  Thursday, Jan. 3  Gender-specific expression of multiple reproductive and somatic growth-related genes and effects of 17β-estradiol in the male tilapia (Oreochromis mossambicus) DAVIS, L.K.*; HIRANO, T.; GRAU, E.G.; Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe lkdavis@hawaii.edu

Gene multiplicity, derived from duplication and subsequent functionalization of genes, has enabled teleosts to evolve new or derived roles for multiple gene forms. This study describes the simultaneous and differential regulation of multiple forms of reproductive- and growth-related genes, including three vitellogenins (Vg), and two receptors for estrogen (ER), and growth hormone (GHR) in male, female, and 17β-estradiol (E₂)-treated male tilapia (Oreochromis mossambicus). Plasma Vg levels and hepatic expression of Vgs A-C and ERα increased significantly in E₂-treated males 48 h after injection (5 µg/g), whereas E₂ reduced expression of ERβ, both GHRs, and insulin-like growth factor-I (IGF-I) and plasma IGF-I. In the testes, ERα gene transcripts were significantly increased by E₂, while expression of the other genes was not. All three Vg genes were detected at low levels in the testes, but their expression was not altered by E₂. Expression of genes for the GH/IGF-I axis was higher in the ovary than in the testes, suggesting roles for a localized ovarian GH/IGF-I axis. Plasma IGF-I, Vg and patterns of hepatic expression of E₂-injected male tilapia were similar to those seen in females, whereas E₂ did not affect gene expression in the testes to the same extent. The energetic cost of vitellogenesis in females may be compensated by suppression of somatic growth, modulated by the liver. This shift of energy utilization away from growth and towards reproduction (ie. egg production) may be a key mechanism behind the sexual dimorphism often seen in fish. Supported by EPA STAR Fellowship (FP-91642801-1) to L.K.D. and NSF Grant (IOB05-17769) and USDA CREES Grant (2005-35206-15285) to E.G.G.