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a Inland Station, National Research Institute of Aquaculture, Tamaki, Mie 519-0423, Japan
b National Research Institute of Aquaculture, Nansei, Mie 519-0196, Japan
c Laboratory of Molecular Endocrinology, School of Fisheries Sciences, Kitasato University, Sanriku, Iwate 022-0101, Japan
ABSTRACT
Two distinct gonadotropins (GTHs) have been demonstrated in a number of teleost fishes. Although the physiological roles of GTHs have been extensively studied in salmonids, little is known about their biological functions in nonsalmonid fishes. In this study, to elucidate the role of GTH-I and GTH-II in reproduction, we cloned the
-glycoprotein subunit (GSU) and gonadotropin ß subunits (Iß and IIß) of red seabream using the 5'- and 3'-RACE methods and used these cDNA probes to reveal changes in mRNA levels of each subunit during sexual maturation of both male and female red seabream. The nucleotide sequences of GSU, Iß, and IIß are 629, 531, and 557 base pairs long, encoding peptides of 117, 120, and 146 amino acids, respectively. The deduced amino acid sequence of each mature subunit showed high homology with those of other teleosts. Northern blot analysis showed that Iß mRNA levels of males increase in association with gonadal development, whereas those of females remain low throughout sexual maturation, indicating sexual dimorphism in the expression pattern of Iß. In contrast, IIß mRNA levels of both sexes are maintained at high levels from the beginning of gametogenesis to spawning season. These results are different than those of salmonids and suggest that GTH-I may have important roles in male, but not female, gametogenesis. GTH-II may be involved in regulation of early and late gametogenesis in both male and female red seabream.
First decision: 20 December 1999.
1 Financially supported in part by a grant-in-aid from the Ministry of Agriculture, Forestry and Fisheries (ED-00-11-3-1).
2 Correspondence. FAX: 81 596 58 6413; kgen{at}ss.nria-tmk.affrc.go.jp
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