Kusakabe Makoto, Ishikawa Asano, Kitano Jun
Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba 277-8564, Japan.
Ecological Genetics Laboratory, National Institute of Genetics, Shizuoka 411-8540, Japan.
Gen Comp Endocrinol. 2014 Sep 1;205:197-206. doi: 10.1016/j.ygcen.2014.06.017. Epub 2014 Jun 25.
Relaxin (RLN) is a hormone that was originally identified as a regulator of pregnancy and reproduction. However, recent mammalian studies have demonstrated that relaxins also have potent osmoregulatory actions. In mammals, six relaxin family peptides have been identified: RLN1/2, RLN3, insulin-like peptide (INSL) 3, INSL4, INSL5, and INSL6. Previous genome database searches have revealed that teleosts also possess multiple relaxin family genes. However, the functions of these relaxin family peptides in teleosts remain unclear. In order to gain insight into the osmoregulatory functions of teleost relaxins, we studied the relaxin family peptides in euryhaline three-spined sticklebacks (Gasterosteus aculeatus), which have diversified into a variety of ecotypes. Rln3a, rln3b, and rln transcripts were abundant in the stickleback brain, whereas insl5b transcript levels were highest in the intestine among tissues. Seawater challenge experiments showed that transcript levels of rln3a, rln3b, and rln in the brain changed significantly after seawater transfer. Particularly, rln3b showed different patterns of temporal changes between anadromous and stream-resident morphs. The transcript levels of relaxin family peptide receptors, rxfp1, rxfp2b, rxfp3-2a, and rxfp3-2b, did not exhibit substantial changes in the brain, although these were constantly higher in the anadromous morph than the stream-resident morph. These results suggest that stickleback relaxin systems are differentially regulated by salinity signals, at least at the transcriptional level, and anadromous and stream-resident morphs differ in relaxin signaling pathways. The differences in the expression of relaxin-related genes between these two morphs provide a foundation for further exploration of the osmoregulatory function of relaxins in teleosts.
松弛素（RLN）是一种最初被确定为妊娠和生殖调节因子的激素。然而，最近的哺乳动物研究表明，松弛素也具有强大的渗透调节作用。在哺乳动物中，已鉴定出六种松弛素家族肽：RLN1/2、RLN3、胰岛素样肽（INSL）3、INSL4、INSL5和INSL6。先前的基因组数据库搜索显示，硬骨鱼也拥有多个松弛素家族基因。然而，这些松弛素家族肽在硬骨鱼中的功能仍不清楚。为了深入了解硬骨鱼松弛素的渗透调节功能，我们研究了广盐性三刺鱼（Gasterosteus aculeatus）中的松弛素家族肽，该物种已分化为多种生态型。Rln3a、rln3b和rln转录本在三刺鱼脑中含量丰富，而insl5b转录本水平在各组织中以肠道最高。海水应激实验表明，海水转移后，脑中rln3a、rln3b和rln的转录本水平发生了显著变化。特别是，rln3b在溯河洄游型和溪流定居型之间表现出不同的时间变化模式。松弛素家族肽受体rxfp1、rxfp2b、rxfp3-2a和rxfp3-2b的转录本水平在脑中没有表现出实质性变化，尽管在溯河洄游型中这些水平始终高于溪流定居型。这些结果表明，三刺鱼的松弛素系统至少在转录水平上受到盐度信号的差异调节，并且溯河洄游型和溪流定居型在松弛素信号通路方面存在差异。这两种形态之间松弛素相关基因表达的差异为进一步探索硬骨鱼中松弛素的渗透调节功能奠定了基础。
