Department of Biology, Faculty of Science and Engineering, Konan University, Kobe, Japan.
PLoS One. 2012;7(7):e41955. doi: 10.1371/journal.pone.0041955. Epub 2012 Jul 27.
Gonadotropin-releasing hormone (GnRH) is a neuroendocrine peptide that plays a central role in the vertebrate hypothalamo-pituitary axis. The roles of GnRH in the control of vertebrate reproductive functions have been established, while its non-reproductive function has been suggested but less well understood. Here we show that the tunicate Ciona intestinalis has in its non-reproductive larval stage a prominent GnRH system spanning the entire length of the nervous system. Tunicate GnRH receptors are phylogenetically closest to vertebrate GnRH receptors, yet functional analysis of the receptors revealed that these simple chordates have evolved a unique GnRH system with multiple ligands and receptor heterodimerization enabling complex regulation. One of the gnrh genes is conspicuously expressed in the motor ganglion and nerve cord, which are homologous structures to the hindbrain and spinal cord of vertebrates. Correspondingly, GnRH receptor genes were found to be expressed in the tail muscle and notochord of embryos, both of which are phylotypic axial structures along the nerve cord. Our findings suggest a novel non-reproductive role of GnRH in tunicates. Furthermore, we present evidence that GnRH-producing cells are present in the hindbrain and spinal cord of the medaka, Oryzias latipes, thereby suggesting the deep evolutionary origin of a non-reproductive GnRH system in chordates.
促性腺激素释放激素（GnRH）是一种神经内分泌肽，在脊椎动物下丘脑-垂体轴中起着核心作用。GnRH 在控制脊椎动物生殖功能中的作用已经确立，但其非生殖功能已被提出，但了解较少。在这里，我们展示了无肠类动物文昌鱼在其非生殖幼虫阶段具有贯穿整个神经系统的突出 GnRH 系统。无肠类动物 GnRH 受体在系统发育上与脊椎动物 GnRH 受体最为接近，但对受体的功能分析表明，这些简单的脊索动物已经进化出一种具有多种配体和受体异二聚化的独特 GnRH 系统，从而能够进行复杂的调节。其中一个 gnrh 基因在运动神经节和神经索中显著表达，而运动神经节和神经索是与脊椎动物后脑和脊髓同源的结构。相应地，GnRH 受体基因在胚胎的尾肌和脊索中表达，这两者都是沿着神经索的典型轴向结构。我们的发现表明 GnRH 在无肠类动物中具有新的非生殖作用。此外，我们提供的证据表明，产 GnRH 的细胞存在于斑马鱼（Oryzias latipes）的后脑和脊髓中，这表明在脊索动物中，非生殖 GnRH 系统具有深远的进化起源。
