豬myostatin基因多態性與生長及屠體性狀相關性探討

Abstract

肌肉抑制生長基因（myostatin gene, MSTN gene）是TGF-β superfamily的成員之一，其功能為抑制肌肉的生長，對於骨骼肌生長的調控十分重要。MSTN基因變異在牛造成「雙肌」的現象；而豬MSTN基因啟動子（promoter）435及447位點（置）的多態性被認為是控制豬mtostatin表現量以及對於肌肉生成影響重要的候選基因標誌。本研究的目的是了解豬myostatin基因啟動子中的遺傳變異、多態性，及其對於豬隻生長及屠體相關性狀的影響。 研究結果顯示，豬MSTN基因啟動子區域435及447位點（置）可分別偵測到AA、AG及GG三種基因型；這兩點的基因型可以組合成MSTN 435GG/447AA, GA/AG, AA/GG, AA/AG, GA/AA, 及 AA/AA 6 種組合基因型；若是分別以haplotype來分析，則有三種haplotype： MSTN 435G/447A (B haplotype)、435A/447G (A haplotype)及435A/447A (C haplotype)；其中MSTN 435AA/447AA 組合基因型及 435A/447A haplotype只在中國豬種及杜洛克豬中發現，而MSTN 435GG/447AA、 GA/AG及AA/GG三種組合基因型，435G/447A、435A/447G兩種haplotype只在藍瑞斯豬及約克夏豬中發現。研究結果顯示，MSTN基因啟動子區域 435及447兩個位點在藍瑞斯豬及約克夏豬中呈現完全連鎖不平衡（complete linkage disequilibrium）的情形，但是在杜洛克豬中則是不完全連鎖不平衡（incomplete linkage disequilibrium）。 生長性狀的相關性研究結果顯示，具有MSTN g.435GG的杜洛克豬個體有較高的平均日增重（average daily gain, ADG）（P < 0.01）、70日齡（P < 0.05）及150日齡體重（P < 0.01），且其達到110 kg所需日齡（P < 0.01）顯著較具有g.435AA基因型的個體早；另一方面，具有g.447AA基因型的杜洛克豬個體有較高的日增重（P < 0.01）、70日齡 （P < 0.01）及150日齡體重（P < 0.01），且其達到110 kg所需日齡（P < 0.01）顯著較具有g.447GG基因型的個體早。屠體性狀的相關性研究結果顯示，具有MSTN g.435GG基因型的個體第十肋及最後腰椎背脂較具有g.435AA基因型的個體為厚（P < 0.05）；而具有g.435AA基因型的個體較具有g.435GG基因型的個體具有較重的前段瘦肉重（P < 0.05）、後段瘦肉重（P < 0.01）、瘦肉總重（P < 0.01）及較高的瘦肉百分比（P < 0.01）；具有MSTN g.447GG基因型的個體，其第十肋背脂（P < 0.01）、第一肋背脂（P < 0.05）、最後肋背脂（P < 0.05）較薄，且後段脂肪（P < 0.05）較少，且有較重的後段瘦肉重（P < 0.01）、瘦肉總重（P < 0.01）及較高的瘦肉百分比（P < 0.01）。 本研究結果顯示，MSTN 435/447或許可用於未來豬隻遺傳育種及選拔計畫的基因標誌（genetic marker）；另外，還可用於區分中國豬種及西方豬種的分子標誌。選拔MSTN g.435G及g.447A交替基因（allele）的豬隻可以提昇日增重、體重及減少達到110 kg所需日齡，而選拔MSTN g.435A及g.447G 交替基因的豬隻則預期可以增加四肢肌肉量、瘦肉總產量及減少背脂厚度。

Myostatin gene (MSTN gene) is a member of the TGF-β superfamily that can inhibit muscle growth. It’s function as essential for regulating skeletal muscle mass. In cattle, mutations and polymorphisms of MSTN gene have been reported that having relations with “double-muscled” phenotype. The polymorphisms in the MSTN promoter region of 435/447 sites have been reported as candidate genetic markers for regulating myostatin expression and also for the myogenic process. The purpose of this study was to determine genetic variations and polymorphisms for the porcine MSTN promoter region of 435/447 two sites and its effects on porcine growth and carcass traits. The results indicated that the MSTN promoter region of 435/447 sites can be detected AA, AG, and GG 3 genotypes, respectively. And they could be divided into 6 combined genotypes: MSTN 435GG/447AA, GA/AG, AA/GG, AA/AG, GA/AA, and AA/AA; and 3 haplotypes: MSTN 435A/447G (A haplotype), 435G/447A (B haplotype), and 435A/447A (C haplotype), respectively. Moreover, we reported that the results of a MSTN 435AA/447AA genotype and 435A/447A haplotype were only found in Chinese pig breeds and Duroc, whereas MSTN 435GG/447AA, GA/AG, and AA/GG 3 genotypes and 435G/447A, 435A/447G two haplotypes were discovered in Landrace and Yorkshire. The findings had demonstrated that we not only found complete linkage disequilibrium in Landrace and Yorkshire, but also discovered new partially incomplete linkage disequilibrium in Duroc. For growth traits test, MSTN g.435GG individuals had significant higher ADG (P < 0.01), body weight at 70 d (P < 0.05), at 150 d (P < 0.01), and were significant lower in age of 110 kg (P < 0.01) than g.435AA individuals in Duroc. On the other hand, g.447AA individuals had a significant higher value for ADG (P < 0.01), body weight at 70 d (P < 0.01) and at 150 d (P < 0.01), and were significant lower value in age days of 110 kg (P < 0.01) than g.447GG individuals. For carcass traits test, the MSTN g.435GG individuals were thicker in carcass backfat at 10th rib and last lumbar (P < 0.05) than g.435AA individuals. And that g.435AA had higher values than g.435GG for anterior-end meat (P < 0.05), posterior-end meat (P < 0.01), total lean weight (P < 0.01), and lean weight percentage (P < 0.01). The MSTN g.447GG individuals had thinner carcass backfat at 10th rib (P < 0.01), 1st rib (P < 0.05), last rib (P < 0.05), and lower posterior-end fat (P < 0.05), but greater in posterior-end meat (P < 0.01), total lean weight (P < 0.01), and lean weight percentage (P < 0.01). In conclusion, the genetic marker of MSTN 435/447 SNPs might be used in porcine breeding and selection programs in the future. It could also be used as specific genetic maker for distinguishing Chinese and western pig breeds. Selection for MSTN g.435G and g.447A allele are expected to increase ADG, body weight and decreasing age of 110 kg, whereas selection for MSTN g.435A and g.447G allele are expected to increase muscle of limb and total meat production, decreasing backfat thickness.