| Co-Investigator(Kenkyū-buntansha) |
SAKAMOTO Takashi Tokyo University of Fisheries, Faculty of Fisheries, Assistant Professor, 水産学部, 助手 (40313390)
YOSHIZAKI Goro Tokyo University of Fisheries, Faculty of Fisheries, Assistant Pr。fessor, 水産学部, 助手 (70281003)
YAMASHITA Hichiaki National Research Institute of Fisheries Science, Senior Researcher Tokyo University of Fisheries, Faculty of Fisheries, Associate Professor, 水産学部, 助教授
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| Research Abstract |
Apoptosis, or programmed cell death, is a process of cell death which is implicated in the natural ontogenesis and differentiation of tissues as well as the elimination of cells that have been irreversibly damaged by environmental stress, including high temperatures. This research revealed that apoptosis is involved in the gonadal sex differentiation of some fish species, particularly those in which the gonads pass through an ambisexual (intersex) stage prior to actual differentiation into ovaries and testes. For example, in ie zebrafish, the degeneration and disappearance of female germinal and somatic elements from the gonads of the genetic males during testicular differentiation was shown to be through apoptosis. We also elucidated the ability of various environmental factors to induce apoptosis in fish embryos and characterized the molecular cascade leading to cellular apoptosis. Ln species with thermolabile sex differentiation (TSD) such as pejerrey, it was shown that apoptosis oc
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curs in the gonads of larvae subjected to heat-stress and, therefore, that this is a plausible mechanism to explain sex determination at different temperatures. Fish germ cells were found to be particularly sensitive to heat. Meanwhile, we examined other molecular, biochemical and cellular pathways that could act in concert with apoptosis to induce gonadal sex differentiation. These included the differential expression of P450c aromatase, a steroidogenic enzyme necessary for the production of estrogen, and the expression of estrogen receptors α and β genes at different temperatures in pejerrey. This study also revealed that brain (GnRH) and pituitary (GtH1 and GtH2) hormones are produced already before sex differentiation and show differential abundance at feminizing and masculinizing temperatures, suggesting a role in the regulation of gonadal steroidogenesis during TSD. Ln addition, we developed methods to distinguish germ cells form somatic cells using the vasa gene promoter in rainbow trout and gilthead sea bream as wd as sex linked markers to identify the genotypic sex in rainbow trout and pejerrey. Less
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