In teleosts, ghrelin plays an important role in body weight gain. This hormone has been used in functional studies on food intake and foraging-related behaviors. However, the regulatory role of its 5′ flanking and coding regions is unknown. To examine the effects of single nucleotide polymorphisms (SNPs) in the ghrelin gene of Nile tilapia, we cloned sequences of its 5′ flanking and coding regions to analyze the regulatory elements binding sites and nonsynonymous mutation sites, and screened the SNPs in these two regions to find their association with mRNA expression levels and superior growth traits. No SNPs loci were found in the coding region. However, a SNPs locus (C−226 T) was identified in the amplified 5′ flanking region, for which we analyzed the distribution of three genotypes (CC, CT and TT) at frequencies of 17.80 %, 50.00 % and 32.14 %, respectively. TT is associated with an increased number of putative octamer transcription factor 1 binding sites (from 2 to 3); the TT genotype also exhibited more superior growth traits (body weight, total length, standard length, body depth) than either the CC and CT genotypes. Expression of ghrelin mRNA in Nile tilapia with the TT genotype was significantly up-regulated ( < 0.05) compared with the CC genotype. Thus, the polymorphism at the ghrelin locus C−226T is associated with superior growth in Nile tilapia, rendering the C−226T locus a potential marker for future selection of breeding stock to improve the quality and growth rate of farmed fish.

中文翻译：

---

Ghrelin基因单核苷酸多态性及其对尼罗罗非鱼生长的影响


在硬骨鱼中，生长素释放肽在体重增加中起着重要作用。这种激素已用于食物摄入和觅食相关行为的功能研究。然而，其 5' 侧翼和编码区的调节作用尚不清楚。为了研究尼罗罗非鱼ghrelin基因单核苷酸多态性（SNP）的影响，我们克隆了其5'侧翼区和编码区的序列，分析了调控元件结合位点和非同义突变位点，并筛选了这两个区域的SNP寻找它们与 mRNA 表达水平和优良生长性状的关联。编码区未发现 SNP 位点。然而，在扩增的 5' 侧翼区域中发现了一个 SNP 位点（C−226 T），我们分析了该位点的三种基因型（CC、CT 和 TT）的分布，频率分别为 17.80 %、50.00 % 和 32.14 % 。 TT 与假定的八聚体转录因子 1 结合位点数量增加相关（从 2 个增加到 3 个）； TT基因型还表现出比CC和CT基因型更优越的生长性状（体重、总长度、标准长度、体高）。与 CC 基因型相比，TT 基因型尼罗罗非鱼 ghrelin mRNA 表达显着上调（ < 0.05）。因此，生长素释放肽基因座 C−226T 的多态性与尼罗罗非鱼的优良生长相关，使 C−226T 基因座成为未来选择种鱼以提高养殖鱼的质量和生长速度的潜在标记。