Biran, J., Palevitch, O., Ben-Dor, S., and Levavi-Sivan, B. (2012) Neurokinin Bs and neurokinin B receptors in zebrafish-potential role in controlling fish reproduction. Proceedings of the National Academy of Sciences of the United States of America. 109(26):10269-10274.
The endocrine regulation of vertebrate reproduction is achieved by the coordinated actions of several peptide neurohormones,
tachykinin among them. To study the evolutionary conservation and physiological functions of neurokinin B (NKB), we identified
tachykinin (tac) and tac receptor (NKBR) genes from many fish species, and cloned two cDNA forms from zebrafish. Phylogenetic analysis showed that piscine
Tac3s and mammalian neurokinin genes arise from one lineage. High identity was found among different fish species in the region
encoding the NKB; all shared the common C-terminal sequence. Although the piscine Tac3 gene encodes for two putative tachykinin
peptides, the mammalian ortholog encodes for only one. The second fish putative peptide, referred to as neurokinin F (NKF),
is unique and found to be conserved among the fish species when tested in silico. tac3a was expressed asymmetrically in the habenula of embryos, whereas in adults zebrafish tac3a-expressing neurons were localized in specific brain nuclei that are known to be involved in reproduction. Zebrafish tac3a mRNA levels gradually increased during the first few weeks of life and peaked at pubescence. Estrogen treatment of prepubertal
fish elicited increases in tac3a, kiss1, kiss2, and kiss1ra expression. The synthetic zebrafish peptides (NKBa, NKBb, and NKF) activated Tac3 receptors via both PKC/Ca2+ and PKA/cAMP signal-transduction pathways in vitro. Moreover, a single intraperitoneal injection of NKBa and NKF significantly
increased leuteinizing hormone levels in mature female zebrafish. These results suggest that the NKB/NKBR system may participate
in neuroendocrine control of fish reproduction.