Meeting Abstract

29.7  Jan. 5  Seasonal Pituitary mRNA Expression of Steroidogenic Factor-1 and a Splice-Variant during Ovarian Steroidogenesis and Development in Channel Catfish, Ictalurus punctatus SMALL, B.C.*; MURDOCK, C.A.; USDA-ARS Catfish Genetics Research Unit, MS; Jacksonville State University, AL bsmall@msa-stoneville.ars.usda.gov

Steroidogenic factor-1 (SF-1) is an orphan nuclear receptor that regulates steroidogenesis at multiple levels of the reproductive axis. Recently, channel catfish SF-1 (Genbank accession no: DQ000612) and a corresponding splice variant (SF-1b; DQ291133) were cloned in our laboratory. The spice variant has a 372 bp addition, resulting in the induction of an early termination codon into the open reading frame. In the present study, the seasonal regulation of channel catfish SF-1 and the SF-1b mRNA expression in the pituitaries of reproductively mature females was monitored via monthly sampling of pond-reared fish. Tissue collection began in April, prior to the natural spawning season, and continued on a monthly basis until May of the following year. Expression analyses were conducted using real-time quantitative RT-PCR to measure SF-1 and SF-1b mRNA levels in total RNA isolated from pituitaries. Concurrent measurements of estradiol, testosterone, and gonadosomatic index were also conducted. Gonadosomatic index decreased rapidly between June and August then increased steadily until the following May. No significant correlations between circulating estradiol or testosterone and SF-1 or SF1b were observed. Pituitary mRNA levels of SF-1 were approximately ten-fold higher than SF-1b levels; however, the seasonal patterns of expression were similar, with peak expression occurring at the start of the natural spawning season. A second increase in SF-1 and SF-1b expression was observed in September and August, respectively. Although, no correlations were observed between SF-1 or SF1-b levels and circulating steroid concentrations, the patterns of expression suggest roles for SF-1 and SF-1b at the start of seasonal ovarian development and again prior to final oocyte maturation.