Seasonal variation and hormonal regulation of genes involved in gonadal development in goldfish

In mammals, the Y-chromosome-linked SRY gene initiates the pathway that turn the indifferent gonad into testes. However, the SRY gene is not present in fish, and multiple sex determination mechanisms have been found within the same families and genera of fishes. Since a number of genes related to the control of sexual development have been identified in mammals, it would be interesting to examine the role of these genes during fish gonadal development. In addition, gonadal sex differentiation in fish is highly susceptible to hormone manipulation suggesting that reproductive hormones can play an important role in gonadal sex differentiation and development in these animals.;In this thesis, I have demonstrated 1) seasonal reproductive changes in basal expression levels of genes known to be important in gonadal development of mammalian models in adult goldfish tissues; 2) tissue specific ontological changes in mRNA expression levels of GTHs, GnRHs, GnRH receptors and activin from juvenile to adult goldfish; 3) sex-specific responses to hormonal treatments in the expression of genes important for gonadal development in goldfish gonads; and, 4) differential regulation and ovarian follicular size dependence of expression of genes of interest by reproductive hormones (GnRHs, GTH and gonadal steroids) and these responses are dependent on the size of the ovarian follicles. Results of this thesis provide comprehensive informations on the expression patterns of genes that are important in gonadal development in goldfish. These information are very valuable for fish reproductive studies.;The major goal of this thesis is to attempt to examine/understand the control of gonadal differentiation and development in goldfish. Goldfish is a representative member of cyprinids and a common model in the study of seasonal reproductive cycles in fish. Using QPCR methods and tissue culture approaches, two underlying hypotheses were examined: 1) Genes that are important in gonadal differentiation and development in mammalian models are also important in regulating gonadal development in goldfish, and their expression should change accordingly at different times of the seasonal reproductive cycle. 2) Reproductive hormones (GnRHs, GTH, testosterone and 17beta-estradiol) regulate the expression of genes that are important in gonadal differentiation and development in goldfish.