PDF(Pubmed)
Abstract：
Somatostatin (SST) plays diverse physiological roles in vertebrates, particularly in regulating growth hormone secretion from the pituitary. While the function of SST as a neuromodulator has been studied extensively, its role in fish and mammalian reproduction remains poorly understood. To address this gap, we investigated the involvement of the somatostatin system in the regulation of growth and reproductive hormones in tilapia. RNA sequencing of mature tilapia brain tissue revealed the presence of three SST peptides: SST6, SST3, and low levels of SST1. Four different isoforms of the somatostatin receptor (SSTR) subfamily were also identified in the tilapia genome. Phylogenetic and synteny analysis identified tiSSTR2-like as the root of the tree, forming two mega clades, with SSTR1 and SSTR4 in one and SSTR2a, SSTR3a, and SSTR5b in the other. Interestingly, the tiSSTR-5 isoforms 5x1, 5x2, and 5x3 were encoded in the sstr3b gene and were an artifact of misperception in the nomenclature in the database. RNA-seq of separated pituitary cell populations showed that SSTRs were expressed in gonadotrophs, with sstr3a enriched in luteinizing hormone (LH) cells and sstr3b significantly enriched in follicle-stimulating hormone (FSH) cells. Notably, cyclosomatostatin, an SSTR antagonist, induced cAMP activity in all SSTRs, with SSTR3a displaying the highest response, whereas octreotide, an SSTR agonist, showed a binding profile like that observed in human receptors. Binding site analysis of tiSSTRs from tilapia pituitary cells revealed the presence of canonical binding sites characteristic of peptide-binding class A G-protein-coupled receptors. Based on these findings, we explored the effect of somatostatin on gonadotropin release from the pituitary in vivo. Whereas cyclosomatostatin increased LH and FSH plasma levels at 2 h post-injection, octreotide decreased FSH levels after 2 h, but the LH levels remained unaffected. Overall, our findings provide important insights into the somatostatin system and its mechanisms of action, indicating a potential role in regulating growth and reproductive hormones. Further studies of the complex interplay between SST, its receptors, and reproductive hormones may advance reproductive control and management in cultured populations.
摘要：
生长抑素（SST）在脊椎动物中发挥着不同的生理作用，特别是调节垂体分泌的生长激素。虽然SST作为神经调质的功能已被广泛研究，它在鱼类和哺乳动物繁殖中的作用仍然知之甚少。为了解决这个差距，我们研究了生长抑素系统在罗非鱼生长和生殖激素调节中的作用。成熟罗非鱼脑组织的RNA测序显示存在三种SST肽:SST6、SST3和低水平的SST1。在罗非鱼基因组中还鉴定了生长抑素受体（SSTR）亚家族的四种不同亚型。系统发育和同种学分析确定tiSSTR2样作为树的根，形成两个巨型分支，与SSTR1和SSTR4在一个和SSTR2a，SSTR3a,和SSTR5b在另一个。有趣的是,tiSSTR-5同工型5x1,5x2和5x3在sstr3b基因中编码,是数据库命名法中的误认产物.分离的垂体细胞群的RNA-seq显示SSTRs在促性腺激素中表达，sstr3a富含黄体生成素（LH）细胞，sstr3b显着富含卵泡刺激素（FSH）细胞。值得注意的是,环生长抑素,SSTR拮抗剂,在所有SSTR中诱导cAMP活性，SSTR3a显示最高响应，而奥曲肽,一种SSTR激动剂,显示类似于在人类受体中观察到的结合谱。罗非鱼垂体细胞的tiSSTR的结合位点分析显示，存在肽结合A类G蛋白偶联受体特有的经典结合位点。基于这些发现,我们探讨了生长抑素对体内垂体促性腺激素释放的影响。而环生长抑素在注射后2小时增加LH和FSH血浆水平，奥曲肽在2小时后降低FSH水平，但LH水平未受影响。总的来说,我们的发现为生长抑素系统及其作用机制提供了重要的见解，表明在调节生长和生殖激素方面的潜在作用。进一步研究SST之间的复杂相互作用，它的受体，和生殖激素可以促进养殖人群的生殖控制和管理。
