|Other Abstract||Considered as the pivotal axis in the regulation of sexual maturation, Hypothalamic-Pituitary-Gonad(HPG) axis has been studied thoroughly in the teleosts. In addition, there are evidences showing that Growth Hormone/Insulin-like growth factor(GH/IGF) axis also involve in the process of gonad development.
For a better understanding of the relationship between the HPG axis and GH/IGF axis and the function of GH/IGF axis in the regulation of gonad development, the expression of sGnRH, cGnRH, GtH α subunit, GtH-I β subunit, GtH-II β subunit, GH, growth hormone receptor (GHR), IGF-1 were detected in carp embryos. Development in 20 hours post fertilization (hpf) and 23hpf was critical for carp embryos, as most of genes analyzed were first detectable at 20hpf or 23hpf. GHR and IGF-1 were all first expressed prior to GH. The differences in the timing of the expression in GH and IGF mRNA may suggest that IGF gene expression is not GH-dependent. Additionally, the timing of the expression of GtH α subunit, GtH-I β subunit, GtH-II β subunit were unsynchronized in embryos. At the same time, non-transgenic (wild-type) carp and growth hormone transgenic carp were examined for pituitary, liver and gonad mRNA levels. GtH-I β subunit, GtH-II β subunit, GH mRNA levels in the pituitary and GHR, Insulin-like growth factor-1(IGF-1) mRNA levels in the liver show a clear seasonal pattern, increasing in spring during sexual maturation. GHR mRNA levels in liver were higher in transgenic than non-transgenic carp, while GtH-I βsubunit mRNA levels in pituitary were higher in non-transgenic than transgenic carp. These data reveal the stimulation effects of GH in the expression of GHR in liver and the feedback regulation of GtH-I βsubunit production in the presence of constitutive GH overexpression in transgenic carp. In addition, the expression pattern of IGF-1 shows differences between two age groups: IGF-1 mRNA levels in liver of one-year old carp were higher in non-transgenic than transgenic carp. Contrarily, in two-year old carp IGF-1 mRNA levels in liver were higher in transgenic than non-transgenic carp. What’s more, GHR expression was identified in gonad, suggesting the possibility of direct action of GH in gonad. In liver, there was a relationship between the expression of GHR and IGF-1. These results suggest that GH involves in the process of gonad development by the regulation of HPG axis and GH/IGF axis.|