Induction of spermatogenesis in Japanese eel by recombinant goldfish gonadotropins
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We previously demonstrated the biological activities of single-chain recombinant gonadotropins (scGTHs) of goldfish Carrassius auratus follicle-stimulating hormone (scFSH) and luteinizing hormone (scLH), produced by a baculovirus–silkworm larvae system, by using in vivo bioassays with some fishes including Japanese eel Anguilla japonica. Among the bioassays, we succeeded in induction of spermatogenesis of sexually immature male Japanese eels by both scFSH and scLH, especially resulting in the occurrence of spermatozoa in scLH-administered males. However, those recombinant hormones did not induce enlargement of testes. In order to further confirm the potency of recombinant GTHs for use in aquaculture species, we administered scFSH and scLH to males of Japanese eel at higher dosage and frequency (eight times with 2–5 days interval) than those of the previous study (five or six times with 7 days intervals), including combination of scFSH and scLH administration (scFSH–scLH). Gonadosomatic indices (GSI) of scLH- and scFSH–scLH-administered males were larger than those of initial control males and of control males that were injected with saline. Enlargement of testes was also confirmed by measurement of testicular lobe size in scFSH-, scLH-, and scFSH–scLH-administered males. By histological observation, occurrence of spermatozoa was confirmed in scLH- and scFSH–scLH-administered eels. Although milt production was not induced, higher dosage and frequency of scGTH administration was effective in promoting testicular development of immature eels. Thus, single-chain fish GTHs produced by the baculovirus–silkworm larvae system could be a useful tool for promotion of gonadal maturation in aquaculture fishes.
KeywordsFSH Goldfish Gonadotropin Japanese eel LH Recombinant hormone Single-chain Spermatogenesis
We thank Professor Robert W. Ridge, Department of Life Science, International Christian University, for critical reading of the manuscript. We also thank Dr. Goro Yoshizaki and Dr. Tetsuro Morita of the Department of Marine Sciences, Tokyo University of Marine Science and Technology, for their technical assistances and valuable advice. This study was supported in part by a Grants-in-Aid from the Japan Society for the Promotion of Science for Scientific Research (MK, YH) and grants from the Ministry of Education, Sports, Science, and Technology for the Academic Frontier Project (2003–2007), International Christian University.
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