Komatsu Masanori, Sato Yoichi, Negami Tatsuki, Terada Tohru, Sasaki Osamu, Yasuda Jumpei, Arakawa Aisaku, Yoshida Chikara, Takahashi Hideaki, Malau-Aduli Aduli E O, Suzuki Keiichi, Shimizu Kentaro
Animal Breeding Research Group, NARO Institute of Livestock and Grassland Science, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki 305-0901, Japan
Animal Industry Research Institute, Iwate Agricultural Research Center (IARC), Takizawa, Iwate 020-0173, Japan.
G3 (Bethesda). 2014 Dec 23;5(2):271-9. doi: 10.1534/g3.114.016105.
Ghrelin and the ghrelin receptor (GHSR1a) are involved in growth hormone secretion, food intake, and several other important functions. Ghrelin acts on GHSR1a and induces signal transduction via the Gαq subunit. In our previous study, we identified the DelR242 (3R) allele, a truncated 3-arginine residue (3R) [major type: 4 arginine residues (4R)] of the third intracellular loop of GHSR1a, with a high frequency in Japanese Shorthorn bulls (0.43) but with a low frequency in other cattle breeds (0.00-0.09). To further investigate the reasons for the higher frequency of the 3R allele, we performed several experiments. In this study, we found a significant sex difference in the frequency of the 3R allele. Statistical analysis revealed a significant overdominance effect of the DelR242 locus on growth in Japanese Shorthorn weaner bulls. However, additive/dominance/overdominance effects of the 3R allele on carcass traits in adult steers and dams were not significant. The mode of the overdominance effect was estimated to be solely controlled by the single DelR242 locus without any other linked loci using linkage disequilibrium analysis in GHSR1a. These results indicated that 4R/3R heterozygotes had a selective advantage in weaner bulls because of their higher average daily gain than homozygotes. We discussed possible molecular mechanisms involved in the overdominance effect of the DelR242 locus on these traits in weaner bulls using a structural model of the complex consisting of a GHSR1a dimer and Gαq.
胃饥饿素和胃饥饿素受体（GHSR1a）参与生长激素分泌、食物摄入及其他多种重要功能。胃饥饿素作用于GHSR1a，并通过Gαq亚基诱导信号转导。在我们之前的研究中，我们鉴定出了DelR242（3R）等位基因，它是GHSR1a第三个细胞内环的截短型3个精氨酸残基（3R）[主要类型：4个精氨酸残基（4R）]，在日本短角牛公牛中频率较高（0.43），而在其他牛品种中频率较低（0.00 - 0.09）。为了进一步探究3R等位基因频率较高的原因，我们进行了多项实验。在本研究中，我们发现3R等位基因频率存在显著的性别差异。统计分析表明，DelR242位点对日本短角断奶公牛的生长具有显著的超显性效应。然而，3R等位基因对成年阉牛和母牛胴体性状的加性/显性/超显性效应并不显著。使用GHSR1a中的连锁不平衡分析估计，超显性效应模式仅由单个DelR242位点控制，不存在任何其他连锁位点。这些结果表明，4R/3R杂合子断奶公牛由于其平均日增重高于纯合子而具有选择优势。我们使用由GHSR1a二聚体和Gαq组成的复合物的结构模型，讨论了DelR242位点对断奶公牛这些性状的超显性效应可能涉及的分子机制。
