Yu K L, He M L, Chik C C, Lin X W, Chang J P, Peter R E
Department of Zoology, The University of Hong Kong, Hong Kong, China.
Gen Comp Endocrinol. 1998 Dec;112(3):303-11. doi: 10.1006/gcen.1998.7137.
In goldfish (Carassius auratus), two distinct forms of gonadotropin-releasing hormone (GnRH), namely, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), have been identified in the brain using chromatographic, immunological, and molecular cloning approaches. These two native GnRHs act on specific receptors in the anterior pituitary to stimulate the synthesis and release of gonadotropins and growth hormone in goldfish. To evaluate the potential roles of sGnRH and cGnRH-II in both neural and reproductive tissues in goldfish, we studied the mRNA expression of sGnRH, cGnRH-II, and GnRH receptor (GnRH-R) in discrete brain areas, pituitary, ovary, and testis by a combined reverse transcription-polymerase chain reaction (RT-PCR) and Southern blot analysis. Total RNA was extracted from various tissues of sexually recrudescent male and female goldfish and RT-PCR was performed with primers specific for GnRH-R complementary DNA (cDNA), sGnRH cDNA, cGnRH-II cDNA-1, and cDNA-2. Results showed that GnRHs and GnRH-R mRNAs are differentially distributed in the brain. In the goldfish brain, sGnRH mRNA was predominantly expressed in the forebrain areas (olfactory bulb, telencephalon, and hypothalamus) whereas cGnRH-II mRNA-1 were expressed in all brain areas including olfactory bulbs and optic tectum-thalamus. The expression level of cGnRH-II mRNA-2 was much lower than that of cGnRH-II mRNA-1 in the brain. On the other hand, GnRH-R mRNA was expressed in all brain regions and pituitary. In the ovary and testis, GnRH-R mRNA, sGnRH mRNA, and cGnRH-II mRNA-1, but not cGnRH-II mRNA-2, are expressed. Sequence analysis of the PCR products showed that nucleotide sequences of GnRH-R in gonads are identical with that in the brain and pituitary. The coexistence of GnRHs and GnRH-R mRNAs in both neural and gonadal tissues supports the notion that sGnRH and cGnRH-II may act as neurotransmitters and/or neuromodulators in the brain and as autocrine and/or paracrine hormones in gonadal tissues in addition to their established neuroendocrine roles at the pituitary of goldfish.
在金鱼（Carassius auratus）中，利用色谱、免疫和分子克隆方法，已在脑中鉴定出两种不同形式的促性腺激素释放激素（GnRH），即鲑鱼GnRH（sGnRH）和鸡GnRH-II（cGnRH-II）。这两种天然的GnRH作用于垂体前叶的特定受体，以刺激金鱼中促性腺激素和生长激素的合成与释放。为了评估sGnRH和cGnRH-II在金鱼神经组织和生殖组织中的潜在作用，我们通过逆转录-聚合酶链反应（RT-PCR）和Southern印迹分析相结合的方法，研究了离散脑区、垂体、卵巢和睾丸中sGnRH、cGnRH-II和GnRH受体（GnRH-R）的mRNA表达。从性成熟的雄性和雌性金鱼的各种组织中提取总RNA，并使用针对GnRH-R互补DNA（cDNA）、sGnRH cDNA、cGnRH-II cDNA-1和cDNA-2的特异性引物进行RT-PCR。结果表明，GnRH和GnRH-R mRNA在脑中的分布存在差异。在金鱼脑中，sGnRH mRNA主要在前脑区域（嗅球、端脑和下丘脑）表达，而cGnRH-II mRNA-1在包括嗅球和视顶盖-丘脑在内的所有脑区表达。cGnRH-II mRNA-2在脑中的表达水平远低于cGnRH-II mRNA-1。另一方面，GnRH-R mRNA在所有脑区和垂体中均有表达。在卵巢和睾丸中，表达GnRH-R mRNA、sGnRH mRNA和cGnRH-II mRNA-1，但不表达cGnRH-II mRNA-2。PCR产物的序列分析表明，性腺中GnRH-R的核苷酸序列与脑和垂体中的相同。GnRH和GnRH-R mRNA在神经组织和性腺组织中的共存支持了这样一种观点，即除了它们在金鱼垂体中已确定的神经内分泌作用外，sGnRH和cGnRH-II在脑中可能作为神经递质和/或神经调节剂，在性腺组织中作为自分泌和/或旁分泌激素。
