Biran Jakob, Golan Matan, Mizrahi Naama, Ogawa Satoshi, Parhar Ishwar S, Levavi-Sivan Berta
Department of Animal Sciences (J.B., M.G., N.M., B.L.-S.), The Robert H. Smith Faculty of Agriculture, Food, and Environment, Hebrew University of Jerusalem, Rehovot 76100, Israel; and Brain Research Institute (S.O., I.S.P.), Monash University Sunway Campus, Jalan Lagoon Selatan, Bandar Sunway, Selangor 46150, Malaysia.
Endocrinology. 2014 Dec;155(12):4831-42. doi: 10.1210/en.2013-2114. Epub 2014 Sep 11.
Neurokinin B (NKB) was recently identified as a key regulator of reproduction in mammals and fish. Fish were found to possess a specific novel neurokinin termed NKF. To study the role of NKB/NKF in the regulation of fish reproduction and to investigate the role of NKB/NKF and their receptors in the piscine pituitary, we have identified the NKB/tachikinin 3 receptor (tac3r) system in tilapia. Bioinformatics and phylogenetic analyses have demonstrated that the tilapia holds 1 putative tac3 gene and 2 NKB receptor genes (tac3ra and tac3rb) that clustered with other piscine Tac3 and NKB receptor lineages. Furthermore, we found that in African cichlids, NKB peptides differ from other vertebrate NKBs in their C-terminal sequence, possessing isoleucine instead of valine as the X in the NKB FXGLM-NH2-terminal consensus sequence. Signal transduction analysis demonstrated that tilapia NKB (tiNKB), tiNKF, and human NKB activated both CRE-luc and SRE-luc transcriptional activity of both tilapia and human NKB receptors. Two hours after ip injection of tiNKB, the plasma levels of both FSH and LH were increased, whereas tiNKF was more effective in increasing LH levels. However, tiNKB was more effective than tiNKF in increasing both FSH and LH from tilapia pituitary dispersed cells. Using in situ hybridization and fluorescent immunohistochemistry, we have shown that LH cells possess tac3, tac3ra, and tac3rb mRNAs, whereas FSH cells possess mainly tac3rb and tac3ra and tac3 to a much lesser extent. These results suggest that the members of the NKB/tac3r system may serve as paracrine/autocrine regulators of gonadotropin release in fish pituitary.
神经激肽B（NKB）最近被确定为哺乳动物和鱼类生殖的关键调节因子。人们发现鱼类拥有一种名为NKF的特定新型神经激肽。为了研究NKB/NKF在鱼类生殖调节中的作用，并探讨NKB/NKF及其受体在鱼类垂体中的作用，我们在罗非鱼中鉴定了NKB/速激肽3受体（tac3r）系统。生物信息学和系统发育分析表明，罗非鱼有1个推定的tac3基因和2个NKB受体基因（tac3ra和tac3rb），它们与其他鱼类的Tac3和NKB受体谱系聚集在一起。此外，我们发现，在非洲丽鱼科鱼类中，NKB肽在其C端序列上与其他脊椎动物的NKB不同，在NKB FXGLM-NH2端共有序列中，其X为异亮氨酸而非缬氨酸。信号转导分析表明，罗非鱼NKB（tiNKB）、tiNKF和人类NKB均可激活罗非鱼和人类NKB受体的CRE-荧光素酶和SRE-荧光素酶转录活性。腹腔注射tiNKB两小时后，促卵泡激素（FSH）和促黄体生成素（LH）的血浆水平均升高，而tiNKF在提高LH水平方面更有效。然而，在从罗非鱼垂体分散细胞中提高FSH和LH水平方面，tiNKB比tiNKF更有效。通过原位杂交和荧光免疫组织化学，我们发现LH细胞含有tac3、tac3ra和tac3rb mRNA，而FSH细胞主要含有tac3rb和tac3ra，tac3的含量则少得多。这些结果表明，NKB/tac3r系统的成员可能作为鱼类垂体中促性腺激素释放的旁分泌/自分泌调节因子。
