Neurokinin B in a flatfish species, the half-smooth tongue sole (Cynoglossus semilaevis), and its potential role in reproductive functions

Abstract

Although recent studies have revealed its involvement in fish reproduction, the physiological role of neurokinin B (NKB), which is encoded by the tachykinin 3 (tac3) gene, is still largely unclear in teleosts, with most researches on the orders Perciformes and Cypriniformes. In the current study we identified the tac3 gene in a representative species of Pleuronectiformes, the half-smooth tongue sole. The full-length cDNA sequence of tongue sole tac3 was 742 base pairs (bp) in length with an open reading frame of 372 bp that encoded a 123-amino acids preprohormone. The TAC3 precursor contained NKB and an additional peptide NKB-related peptide (NKBRP), both of which had an –FVGLM motif at the C-termini. Tissue distribution analysis indicated that tac3 transcripts were highly expressed in the brain, intestine and gonads of both sexes, and to a lesser extent in other tissues. Among various brain regions, tac3 transcripts were most abundant in the hypothalamus. In addition, the expression profiles of tac3 mRNA were also evaluated along the brain-pituitary-gonadal axis during tongue sole ovarian maturation. The brain tac3 mRNA levels remained unchanged, however, in both pituitary and ovary, the mRNA expression of tac3 increased significantly to the maximal levels at stage III and then declined back to basal levels. Taken together, our results encompass the first study reporting the existence of tac3 gene in a flatfish species and suggest its possible involvement in the control of reproduction in the half-smooth tongue sole.