Myostatin（growth/differentiation factor 8, 第八生長分化因子）為TGF-β superfamily 的成員之一。文獻指出myostatin能抑制骨骼肌細胞的生長，且在動物體內利用基因工程的方法調此蛋白質表現，就能促進動物的生長性能。本研究目的是探討myostatin在骨骼肌發育中所扮演的角色，以及利用非基因工程的方法調節myostatin於動物體內的表現，期望提高動物的生長性能。利用Baculovirus表現系統製造並純化myostatin重組蛋白質；再將myostatin重組蛋白質加至培養中的L8肌原母細胞（myoblast），結果發現myostatin重組蛋白質抑制L8肌原母細胞的分裂與分化；也抑制L8肌肉細胞（myotube）總蛋白質合成速率，且其同時抑制肌肉細胞內肌纖維與非肌纖維蛋白質之合成，但L8 肌肉細胞總蛋白質的分解速率則不受到myostatin重組蛋白質影響。在動物實驗中，利用反轉錄連鎖反應法（RT-PCR）發現myosatin基因表現於骨骼肌、心臟及肝臟，其中於骨骼肌內的表現量隨著年齡增加有提高的趨勢。此外本研究亦利用非基因工程的方法來調節動物體內myostatin的表現以促進動物的生長性能，方法為注射myostatin胜?以誘發母鼠產生其抗體後，再與以配種；懷孕的過程中，母鼠體內的myostatin抗體可以穿過胎盤進入胎兒，使產下的仔鼠體內擁有來自母鼠的myostatin抗體。結果顯示，來自母鼠的myostatin抗體能中和仔鼠體內myostatin，進而促進仔鼠的生長性能；分析仔鼠的體組成，發現粗蛋白質顯著較對照組為高，但粗脂肪則有顯著減少。綜合上述研究結果，myostatin在肌肉生成（myogenesis）或肌肉蛋白質的合成均扮演一個負調控角色（negative regulator），且誘發母體產生myostain抗體後能顯著促進子代的生長性能；未來此法若能應用於畜產動物的生長上，除了方法簡單便利外，更重要的是在過程中並未使用任何令人擔憂的基因工程法。 Myostatin (growth/differentiation factor 8) is a member of transforming growth factor β superfamily. It is reported myostatin is a negative regulator of skeletal muscle growth. Genetic strategies were used to demonstrate that down-regulation of myostatin enhanced growth performance in mice. The goals of this study were to investigate the role of myostatin in skeletal muscle development and the application of myostatin in animal growth. Two major approaches were used in this study. First, recombinant myostatin protein was expressed and purified from a baculovirus expression system. In the L8 culture system, recombinant myostatin protein inhibited the proliferation and differentiation of L8 myoblasts. In addition, recombinant myostatin inhibited total protein synthesis in L8 myotubes; however, protein degradation was not altered by myostatin. The inhibition of total protein synthesis was attributed to the inhibition of both myofibrillar and non-myofibrillar protein synthesis. We also found that myostatin is expressed not only in skeletal muscle but also in liver and heart, and myostatin expressed in muscle is associated with aging in mice. Second, maternal immunization against myostatin was attempted to enhance the growth performance in offspring. Female mice were immunized with myostatin peptides before mating. The maternal antibodies could be transferred to offspring, and resulted in enhanced the growth performance, reduced fat content and increased crude protein in offspring. It is concluded that myostatin plays a crucial roles in myogenesis and regulation of protein synthesis, and maternal myostatin immunization enhances the growth performance of offspring. In conclusion, it is a convenient way to improve the livestock growth performance by controlling myostatin activity.
