Cloning and expression of tachykinins and their association with kisspeptins in the brains of zebrafish

Abstract

The tachykinins are a family of neuropeptides, including substance P (SP), neurokinin A (NKA), and neurokinin B (NKB), that are encoded by the tac1 (SP and NKA) or tac2/3 (NKB) genes. Tachykinins are widely distributed in the central nervous system and have roles as neurotransmitters and/or neuromodulators. Recent studies in mammals have demonstrated the coexpression of NKB and kisspeptin and their comodulatory roles over the control of reproduction. We have recently identified two kisspeptin-encoding genes, kiss1 and kiss2, in teleosts. However, such relationship between tachykinins and kisspeptins has not been demonstrated in non-mammalian species. To determine the involvement of tachykinins in the reproduction in teleosts, we identified tac1 and two tac2 (tac2a and tac2b) sequences in the zebrafish genome using in silico data mining. Zebrafish tac1 encodes SP and NKA, whereas the tac2 sequences encode NKB and an additional peptide homologous to NKB (NKB-related peptide). Digoxigenin in situ hybridization in the brain of zebrafish showed tac1 mRNA-containing cells in the olfactory bulb, telencephalon, preoptic region, hypothalamus, mesencephalon, and rhombencephalon. The zebrafish tac2a mRNA-containing cells were observed in the preoptic region, habenula, and hypothalamus, whereas the tac2b mRNA-containing cells were predominantly observed in the dorsal telencephalic area. Furthermore, we examined the coexpression of tachykinins and two kisspeptin genes in the brain of zebrafish. Dual fluorescent in situ hybridization showed no coexpression of tachykinins mRNA with kisspeptins mRNA in hypothalamic nuclei or the habenula. These results suggest the presence of independent pathways for kisspeptins and NKB neurons in the brain of zebrafish.

Goldfish neurokinin B: Cloning, tissue distribution, and potential role in regulating reproduction

“…Our findings support the role of NKBs as neuroendocrine regulators of reproduction in fish. In contrast to mammals, which have only one TAC3 gene, goldfish and zebrafish (Biran et al, 2012;Ogawa et al, 2012;Zhou et al, 2012) have two TAC3 genes, consistent with the notion that there was a teleost-specific genome duplication event (Christoffels et al, 2004). The two goldfish TAC3 genes are predicted to generate four mature NKB peptides.…”

“…Increasing evidence supports a critical role of the NKB/NK3R system in mammalian reproduction (Corander et al, 2010;Ramaswamy et al, 2010Ramaswamy et al, , 2011Topaloglu et al, 2009); however, studies on NKBs in lower vertebrates are limited to zebrafish (Biran et al, 2012;Ogawa et al, 2012;Zhou et al, 2012). In the present study, we cloned and characterized two goldfish TAC3 cDNAs, determined their mRNA expression patterns and regulation in the brain and pituitary and examined the effects of in vivo administration of NKBs on GnRH and gonadotropin subunit mRNA expression.…”

“…Recently, several groups, including ours, have characterized the TAC3/TACR3 signaling pathway in zebrafish (Biran et al, 2012;Ogawa et al, 2012;Zhou et al, 2012). In this study, we used goldfish as a model to further investigate the role of NKBs in fish reproduction.…”

Cholinergic left-right asymmetry in the habenulo-interpeduncular pathway

“…The dHbL was implicated in mediating fear responses of zebrafish (57) comparable to the role of the rodent medial dorsal (SP) subnucleus, suggesting functional homology between these brain regions. However, because tac1 transcripts were not detected in the zebrafish Hb (58) and their cholinergic nature was also unresolved (13)(14)(15), functional comparisons with the mammalian Hb were incomplete.…”

Direct Regulation of Gonadotropin Release by Neurokinin B in Tilapia (Oreochromis niloticus)

“…The mammalian TAC1 and TAC4 give rise to 2 active neuropeptides, whereas the TAC3 is the only TAC that give rise to only 1 neuropeptide, namely NKB (17). We have recently identified genes encoding NKB (tac3a/b) and tac3r from many fish species, and cloned 2 tac3 cDNA forms from zebrafish (18,19). Phylogenetic analyses showed that piscine and mammalian Tac3 genes arise from 1 lineage (18).…”