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1 Laboratory of Reproductive Biology, Department of Developmental Biology, National Institute for Basic Biology, Okazaki 444-8585, Japan
2 Core Research for Evolutional Science and Technology (CREST), Kawaguchi, Saitama 332-0012, Japan
3 Department of Molecular Biomechanics, Graduate University for Advanced Studies, Okazaki 444-8585, Japan
4 Faculty of Life Sciences, Southwest China Normal University, 400715, Chongqing, P.R. China
5 Department of Animal Sciences, School of Life Sciences, University of Hyderabad, P.O. Central University, Gachibowli, Hyderbad 500 046, Andhra Pradesh State, India
6 National Research Institute of Aquaculture, Tamaki, Mie 516-0423, Japan
(Requests for offprints should be addressed to Y Nagahama; Email: nagahama{at}nibb.ac.jp)
In order to elucidate the roles of 17ß-HSDs in fish gonadal steroidogenesis, three types of 17ß-HSDs (17ß-HSD1, 17ß-HSD8 and putative 17ß-HSD12) were cloned and characterized from the Nile tilapia, Oreochromis niloticus. The cloned cDNAs of 17ß-HSD type 1, 8 and 12 were 1504, 1006 and 1930 bp long, with open reading frames encoding proteins of 289, 256 and 314 aminoacids, respectively. Tissue distribution pattern analyzed by RT-PCR and Northern blot showed that 17ß-HSD1 was dominantly expressed in the ovary, while the putative 17ß-HSD12, one of the two duplicates found in fish, is a male specific enzyme and expressed exclusively in testis (detected by RT-PCR only). On the other hand, 17ß-HSD8 was expressed in the brain, gill, heart, liver, intestine, gonad, kidney and muscle of both male and female. Enzymatic assays of the three types of 17ß-HSDs were performed using recombinant proteins expressed in E. coli or HEK 293 cells. Tilapia 17ß-HSD1 expressed in E. coli had the preference for NADP(H) as cofactor and could catalyze the inter-conversion between estrone and estradiol efficiently as well as the inter-conversion between androstenedione and testosterone, but less efficiently. Tilapia 17ß-HSD8 recombinant protein expressed in HEK 293 cells could catalyze the conversion of testosterone to androstenedione, as well as the inter-conversion between estrone and estradiol. However, the putative 17ß-HSD12 expressed in E. coli or in HEK 293 cells showed no conversion to any of the four substrates tested in this study. Based on enzyme characterization and tissue distribution, it is plausible to attribute crucial roles to 17ß-HSDs in the gonadal steroidogenesis of teleosts.
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