Functional analysis of the Myostatin gene promoter in sheep.

Compared with the understanding for the functional mechanism of the myostatin gene, little is known about the regulatory mechanism of the myostatin gene transcription and expression. To better understand the function of the myostatin gene promoter (MSTNpro) in the transcriptional regulation of the myostatin gene and to further investigate the transcriptional regulation mechanism of the myostatin gene, the promoter region of the myostatin gene in sheep has been cloned in our recent study (AY918121). In this study, the wild (W) type MSTNPro(W)-EGFP vectors and E-box (E) (CANNTG) mutant (M) type MSTNPro(E(3+5+7)M)-EGFP vectors were constructed and the transcriptional regulation activities were compared by detecting the fluorescent strength of EGFP (enhanced green fluorescent protein) in C2C12 myoblasts (or myotubes) and sheep fibroblasts transfected with the vectors. Results showed that the 0.3-1.2 kb sheep myostatin promoter could activate the transcription and expression of EGFP gene in C2C12 myoblasts to different extent and the 1.2 kb promoter was the strongest. However, fluorescence was not observed in the sheep fibroblasts transfected with the 1.2 kb sheep myostatin promoter. These results suggested that the specific nature of the myostatin gene expression in skeletal muscle was attributed to the specific nature of the myostatin promoter activity. The increasing growth density of C2C12 myoblasts inhibited the transcriptional regulation activity of the wild type sheep myostatin promoter by a mechanism of feedback. The transcriptional regulation activity of the 1.2 kb wild type sheep myostatin promoter increased significantly after C2C12 myoblasts were differentiated, while the activity of 1.2 kb E(3+5+7)-mutant type myostatin promoter had no obvious change. This result suggested that MyoD may be responsible for the difference of the myostatin gene transcription and expression between growing and differentiating conditions by binding to E-box of the myostatin promoter.