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Regular Article |
a Center of Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore, Maryland 21202
ABSTRACT
In vertebrates, the growth and maturation of the ovarian follicle is dependent on the appropriate dynamics of sex steroid secretion, which is dictated by gene expression of the steroidogenic enzymes. The molecular aspects of steroid regulation are poorly understood in fishes, so as a first step we determined the pattern of expression of four key steroidogenic genes throughout the ovarian cycle in an annually spawning teleost, the channel catfish (Ictalurus punctatus). The abundance of transcripts encoding 3ß-hydroxysteroid dehydrogenase (3ß-HSD) and cholesterol side chain cleavage (P450scc), 17
-hydroxylase/lyase (P450c17), and aromatase (P450arom) were determined by rtqRT-PCR or ribonuclease protection assay and correlated to ovarian growth and plasma titers of estradiol (E2) and testosterone (T) in two populations of catfish. Elevations in transcript abundance for P450c17, P450scc, and P450arom were observed at the onset of ovarian recrudescence and during early vitellogenic growth of the oocytes; however, all three decreased precipitously with the completion of vitellogenesis. Changes in the expression of these genes strongly suggest a direct correlation to E2 and T titers. Alternatively 3ß-HSD transcript abundance was relatively stable throughout the year. This study suggests that the genes encoding the three steroidogenic cytochrome P450s have a similar regulatory mechanism.
1 This research was supported by grants from the United States Department of Agriculture (Enhancing Reproductive Efficiency, grant 94-37203-0761) and Wallenburg Foundation awarded to J.M.T. A portion of this study has been published in the Proceedings of the 6th International Symposium on Reproductive Physiology of Fish, Bergen, Norway, 4–9 July 1999.
2 Correspondence: John M. Trant, Center of Marine Biotechnology, University of Maryland Biotechnology Institute, 701 E. Pratt Street, Baltimore, MD 21202. FAX: 410 234 8896; trant{at}umbi.umd.edu
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