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M Nagae, T Todo, K Gen, Y Kato, G Young, S Adachi, and K Yamauchi


cDNAs encoding the glycoprotein hormone α- and gonadotropin (GTH) IIβ-subunits of Japanese eel (Anguilla japonica) pituitary were cloned using the polymerase chain reaction. The nucleotide sequence of the glycoprotein hormone α-subunit cDNA was 364 base pairs (bp) long, encoding 117 amino acids, and that of the GTH IIβ-subunit cDNA was 433 bp long, encoding 140 amino acids. The deduced amino acid sequence of each mature subunit showed high homology with those of other teleosts, indicating that the structure of GTH subunits has been conserved during the evolution of teleosts. Changes in the expression of these subunit genes during ovarian development induced artificially by the injection of chum salmon pituitary homogenate were examined using Northern blot analysis. Glycoprotein hormone α-subunit mRNA increased almost linearly during ovarian development, whereas GTH IIβ-subunit mRNA was detected only at the late vitellogenic and migratory nucleus stages. These data indicate that eel GTH II is synthesized mainly at the late vitellogenic and migratory nucleus stages, and suggest that GTH II plays an important role in final oocyte maturation of Japanese eel. Changes in the expression of glycoprotein hormone α- and GTH IIβ-subunits mRNA correlate with the serum estradiol-17β (E2) and testosterone profile during ovarian development. The increase in mRNA of both subunits is probably due to positive feedback of E2 and testosterone produced by ovarian follicles in response to the GTH contained in chum salmon pituitary homogenate.

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JQ Jiang, DS Wang, B Senthilkumaran, T Kobayashi, HK Kobayashi, A Yamaguchi, W Ge, G Young, and Y Nagahama

The Japanese eel (Anguilla japonica) and Nile tilapia (Oreochromis niloticus) 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) cDNAs were isolated from their respective testes cDNA libraries. The cDNAs predict two peptides of 436 and 406 amino acid residues that share about 42% homology with mammalian 11beta-HSD type 2 proteins. Analysis of the tissue distribution pattern by RT-PCR reveals that 11beta-HSD2 is expressed in a wide variety of tissues in tilapia, with higher expression in kidney and gill of both sexes, and with the highest expression in testis. 11beta-Dehydrogenase activity of the eel 11beta-HSD2 was confirmed by demonstrating the conversion of cortisol to cortisone by the recombinant protein after transient expression of this cDNA clone in COS-1 cells. Bands of approximately 2.7 and approximately 3.8 Kb were detected in Northern blot of eel and tilapia testes respectively, which is consistent with the cloned cDNA sizes of the two species. Northern blot analysis also revealed that the expression of the eel testis 11beta-HSD2 gene could be induced by human chorionic gonadotropin (hCG) injection, implying a role of 11beta-HSD2 in hCG-induced 11-ketotestosterone production and spermatogenesis in the Japanese eel.