Molecular identification of the Kiss2/Kiss1ra system and its potential function during 17alpha-methyltestosterone-induced sex reversal in the orange-spotted grouper, Epinephelus coioides

Abstract

The Kiss1/Kiss1r system is a component of the hypothalamus-pituitary-gonadal (HPG) axis, which plays a crucial role in regulating gonadotropins and gonadotropin-releasing hormone. The sex reversal process is a special reproductive phenomenon regulated by the HPG axis. To better understand the neuroendocrine mechanisms of sex reversal, cDNAs encoding kiss2 and kiss1ra have been cloned and functionally characterized from the orange-spotted grouper Epinephelus coioides, a protogynous hermaphroditic teleost. The core mature peptide (Kiss2-10) of grouper Kiss2 shared high similarity to other KISS orthologs. In phylogenetic analyses, the grouper Kiss was clustered with the teleost Kiss2 clade and termed grouper kiss2. The predicted amino acid sequence of grouper kiss1ra contained three putative glycosylation sites at its N-terminus, showing high similarity to that of other teleosts. Synthesized Kiss2-10 was able to functionally interact with Kiss1ra in cultured COS-7 cells to trigger downstream signaling. Both kiss2 and kiss1ra mRNAs were expressed in all tissues examined, with highest levels in the olfactory bulb and moderate levels in the hypothalamus among brain areas and highest levels in ovary among peripheral tissues. Intraperitoneal injection of Kiss2-10 significantly increased gnrh1 mRNA levels in hypothalamus and follicle-stimulating hormone beta (fshb) mRNA levels in the pituitary at 6 and 12 h postinjection. During the process of sex reversal induced by 17 alpha-methyltestosterone (MT), kiss2 and kiss1ra mRNA expression were significantly decreased in the first week, but kiss2 increased in the fourth week, in accordance with the expression pattern of gnrh1 mRNA in the grouper hypothalamus. This is the first description of the Kiss2/Kiss1ra system during MT-induced sex reversal in orange-spotted grouper.