Abstract：Abstract Growth and reproduction are closely related in fish. Herely, the hormone cross-talk between the two systems in the gonad has been analyzed with Common carp (Cyprinus carpio) and growth hormone (gh) transgenic common carp by using real qRT-PCR, immunofluorescence, in situ hybridization, and in vitro incubation. The expression of gonadotropin hormone alpha (gthα), follicle-stimulating hormone beta (fshβ), luteinizing-stimulating hormone beta (lhβ), gonadotropin-releasing hormone 3 (gnrh3), growth hormone receptor (ghr) and 4 GnRH receptor mRNA were detected in testis and ovary of common carp. Immunofluorescence showed that GTHα and LHβ were localized mainly in the somatic cells and primary sperm cells of the gonads. In vitro incubation of ovary fractions with GnRH confirmed the existence of gonadal GnRH-GtH paracrine system, which was independent of the hypothalamus-pituitary-gonad axis. The expression levels of gnrh3, gthα, fshβ and lhβ mRNA were significantly different in the gonad of GH-transgenic carp when compared with non-transgenic carp. Further analysis in vitro showed that GH up-regulated the expression of gnrh3, gthα, fshβ and lhβ in the ovarian GnRH-GtH system at primary growth stages. But the signals were inhibited in the ovarian at the secondary growth stages. Our results confirmed the GnRH-GtH paracrine system in gonad and uncovered its important role in the interaction between growth and reproduction in common carp, which provides scientific data to reveal the regulation mechanism between growth and reproduction in fish.
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