Alok D, Hassin S, Sampath Kumar R, Trant J M, Yu K, Zohar Y
Center of Marine Biotechnology, University of Maryland Biotechnology Institute, 701 E. Pratt Street, Baltimore, MD 21202, USA.
Mol Cell Endocrinol. 2000 Oct 25;168(1-2):65-75. doi: 10.1016/s0303-7207(00)00317-8.
Gonadotropin-releasing hormones (GnRHs) bind to the specific receptor present on the gonadotrophs to activate the synthesis and release of gonadotropins (follicle stimulating hormone or FSH and luteinizing hormone or LH), which in turn control gonadal maturation, gametogenesis and gamete release. Perciform species have three endogenous GnRHs. The main objective of this study was to characterize the gonadotropin-releasing hormone receptor (GnRH-R) present in the pituitary of a perciform species, striped bass (Morone saxatilis) and demonstrate how it interacts with its potential ligand. In this study, a cDNA for GnRH-R from the pituitaries of striped bass was cloned. The cloned cDNA has an open reading frame (ORF) that codes for a 419 amino acids peptide. Like other G-protein coupled receptors including the non-mammalian GnRH-Rs, the peptide has seven putative transmembrane domains and a C-terminal tail. Comparative analysis of the amino acid sequence of striped bass (stb) GnRH-R shows 38-87% similarity with the known GnRH-Rs. A Northern blot analysis revealed a single GnRH-R transcript in the pituitary; however, its expression in various extrapituitary tissues was demonstrated by a reverse-transcription-PCR (RT-PCR). Functionally, upon induction by endogenous forms of GnRHs (seabream, chicken II and salmon GnRHs) and a mammalian GnRH-agonist, the recombinant stbGnRH-R mediated a reporter gene (luciferase) activity in a fish cell line (CHSE-214). A real-time relative quantitation method established that significantly higher (P<0.05) levels of stbGnRH-R mRNA were present in the pituitaries of striped bass with advanced stages of ovarian development, compared to the pituitaries of fish with less developed ovaries.
促性腺激素释放激素（GnRHs）与促性腺细胞上存在的特定受体结合，以激活促性腺激素（促卵泡激素或FSH和促黄体生成素或LH）的合成与释放，而促性腺激素又反过来控制性腺成熟、配子发生和配子释放。鲈形目物种有三种内源性GnRHs。本研究的主要目的是鉴定一种鲈形目物种条纹鲈（Morone saxatilis）垂体中存在的促性腺激素释放激素受体（GnRH-R），并证明其如何与其潜在配体相互作用。在本研究中，克隆了条纹鲈垂体中GnRH-R的cDNA。克隆的cDNA有一个编码419个氨基酸肽的开放阅读框（ORF）。与包括非哺乳动物GnRH-Rs在内的其他G蛋白偶联受体一样，该肽有七个推定的跨膜结构域和一个C末端尾巴。条纹鲈（stb）GnRH-R氨基酸序列的比较分析显示，与已知的GnRH-Rs有38 - 87%的相似性。Northern印迹分析显示垂体中有单一的GnRH-R转录本；然而，通过逆转录PCR（RT-PCR）证明了其在各种垂体外组织中的表达。在功能上，在内源性形式的GnRHs（黑鲷、鸡II型和鲑鱼GnRHs）和一种哺乳动物GnRH激动剂的诱导下，重组stbGnRH-R在鱼类细胞系（CHSE-214）中介导了报告基因（荧光素酶）活性。一种实时相对定量方法确定，与卵巢发育较差的鱼的垂体相比，卵巢发育晚期的条纹鲈垂体中stbGnRH-R mRNA水平显著更高（P<0.05）。
