Production of Animal Models for Marbling by Introducing The Bovine ADAM12 Gene

ADAM12是ADAM（一种崩解素和金属蛋白酶）家族的成员，最近被认为在肌肉形成和脂肪形成中起调节作用。也有报道称，在肌肉组织中特异性表达人ADAM12的转基因小鼠表现出肌内脂肪沉积。由于这些表型与牛肉大理石纹相似，我们通过在肌肉组织中特异性表达牛ADAM12基因的转基因小鼠来建立牛大理石纹动物模型。从牛ADAM12 cDNA中制备了3个转基因（MCK-bADAM12 C3、TRC和MP）。MCK-bADAM12 C3编码一种膜锚定的ADAM12蛋白，由原结构域、金属蛋白酶、崩解素、富含半胱氨酸、跨膜结构域和细胞质尾部组成。MCK-bADAM12 TRC编码一种由整个细胞外结构域组成的分泌型蛋白。mck - badam12mp编码原结构域和金属蛋白酶结构域。这些转基因是由小鼠肌酸激酶（MCK）启动子驱动的，用于肌肉特异性表达。C3、TRC和MP分别获得1个、2个和3个转基因建立者。转基因个体是可育的，并将牛ADAM12基因传递给后代。所有转基因品系在体重和脂肪含量上都与对照组没有差异。然而，TRC和MP转基因小鼠的肌内脂肪沉积比同窝对照增加，而C3转基因小鼠则没有。在TRC和MP转基因小鼠肌肉组织中观察到相似的表型，表明ADAM12金属蛋白酶结构域足以诱导肌内脂肪沉积。

ADAM12 is a member of the ADAM (a disintegrin and metalloprotease) family, and recently has been suggested to function in regulation of myogenesis and adipogenesis. It is also reported that the transgenic mice expressing human ADAM12 specifically in muscle tissue exhibit the intramuscular fat deposition. As these phenotypes are similar to the beef marbling, we produced the transgenic mice expressing the bovine ADAM12 gene specifically in muscle tissue to establish the animal models for marbling.Three transgenes (MCK-bADAM12 C3, TRC and MP) were prepared from the bovine ADAM12 cDNA. MCK-bADAM12 C3 encodes a membrane-anchored ADAM12 protein consisting of the prodomain, the metalloprotasase, disintegrin, cystein-rich, and transmenbrane domains and cytoplasmic-tail. MCK-bADAM12 TRC encodes a secreted-form protein consisting of the whole extracellular domain. MCK-bADAM12 MP encodes the prodomain and the metalloprotease domain.These transgenes are driven by the mouse muscle creatine kinase (MCK) promoter for the muscle-specific expression.One, two and three transgenic founders were obtained for each of transgenes C3, TRC and MP, respectively. Transgenic individuals were fertile and transmitted the bovine ADAM12 genes to the offsprings.All transgenic lines did not differ from littermate controls in body weight and fat content. However, TRC and MP transgenic mice developed the increased intramuscular fat deposition more than littermate controls, but C3 transgenic mice did not.The observation of similar phenotypes between TRC and MP transgenic mice muscle tissues suggested that ADAM12 metalloprotease domain was sufficient to induce the intramuscular fat deposition.