REGULATION OF SITE-SPECIFIC GONADOTROPIN-RELEASING HORMONE GENE EXPRESSION IN TILAPIA

促性腺激素释放激素（GnPH）是所有脊椎动物中控制生殖的关键激素。在进化过程中，GnRH肽经历了基因复制和结构变化，产生了多种分子形式的GnRH。脊椎动物物种，包括灵长类动物和人类，在个体大脑中有一个以上的GnRH变体。几个种类的小骨虾有三种GnRH分子变体;在终末神经（鲑鱼GnRH），视前区（海鸟GnRH）和中脑被盖（鸡GnRH II）。在鱼，罗非鱼，我们的特点是初级结构，并证明了神经元含有三种GnRH分子形式有不同的胚胎起源。我们利用已知的GnRHcDNA序列构建了特异性的GnRH信使RNA探针，并成功地将其用于罗非鱼脑中GnRH的定位。在本研究中，使用定量放射性原位杂交，我们研究了去势和类固醇替代治疗对终末神经，视前和中脑GnRH mRNA合成的影响。终末神经GnRH神经元受睾酮的正调节，受三碘甲腺原氨酸的负调节;视前GnRH神经元受雌激素和睾酮的调节，但不受酮睾酮（非芳香化雄激素）的调节。目前的研究强调，中脑GnRH神经元是不敏感的性类固醇激素，表明一个迄今未知的调节机制可能会操作这些细胞。终末神经和视前GnRH神经元受雌激素途径的影响。

Gonadotropin-releasing hormone (GnPH) is a pivotal hormone in the control of reproduction in all vertebrates. During evolution, GnRH peptide underwent gene duplication and structural changes to give rise to multiple molecular forms of GnRHs. Vertebrate species, including primates and humans have more than one GnRH variant in individual brains. Several species of bonyfish have three molecular variants of GnRH; in the terminal nerve (salmon GnRH), preoptic area (seabream GnRH) and midbrain tegmentum (chicken GnRH II). In fish, tilapia Oreochromis niloticus, we have characterized the primary structure and demonstrated that neurons containing the three GnRH molecular forms have different embryonic origins. Further, we speculate that the three GnRH molecules might have different functions and different regulatory mechanisms.We have constructed specific GnRH messenger RNA probes from known GnRH cDNA sequences, and have used them successfully to localize GnRHs in the brain of tilapia. In the present study, using quantitative radioactive in situ hybridization, we examined the effects of castration and steroid replacement therapy on the terminal nerve, preoptic and midbrain GnRH mRNA synthesis. The terminal nerve GnRH neurons are positively regulated by testosterone and negatively by triiodothyronine ; and preoptic GnRH neurons by estrogen and testosterone but not ketotestosterone (nonaromatizable androgen). The present study emphasizes that the midbrain GnRH neurons are insensitive to sex steroids, indicating an as yet unknown regulatory mechanism may operate these cells. The terminal nerve and preoptic GnRH neurons are under the influence of an estrogenic pathway.