Differential neuroendocrine regulation of follicle-stimulating hormone and luteinizing hormone in Atlantic cod and GFP-transgenic medaka.

This project investigates how pituitary gonadotrope cells develop and mature during puberty, and how the two gonadotropins, FSH and LH, are differentially regulated. Puberty is regulated by the brain-pituitary-gonad axis. Forebrain GnRH binds to specific receptors on pituitary gonadotropes, thereby stimulating synthesis and release of two distinct gonadotropins, FSH and LH, which again stimulate gonadal development. Increased release of GnRH from hypothalamus and functional maturation of gonadotropes are probably key factors in pubertal development, but the triggering mechanism(s) are not known in any vertebrate. Furthermore, the differential regulation of FSH and LH is not well understood. Teleosts are useful models for studying puberty in that they have separate cells producing FSH and LH, in contrast to mammals that only have one gonadotrope cell type producing both hormones. Two different models will be used: The economically important Atlantic cod, and 2 newly developed transgenic lines of medaka, wh ere green fluorescent protein (GFP) is coupled to the promoters of FSH and LH, respectively, enabling isolation of FSH- and LH-producing gonadotropes directly from a pituitary primary culture. We will trace the development of GFP-medaka gonadotropes in vi vo. Furthermore, large-scale gene expression studies and electrophysiological / imaging analyses will be performed on the two models to identify differential membrane properties, intracellular signaling pathways, and gene expression patterns in FSH- and L H-producing gonadotropes before and after puberty. The combination of molecular and electrophysiological methods planned in this project will be powerful tools for obtaining new insight into puberty regulation in fish.