Multiple regions of the porcine α-skeletal actin gene modulate muscle-specific expression in cell culture and directly injected skeletal muscle

Transcriptional regulation of the porcine alpha-skeletal actin gene was investigated by comparative transient transfection assays in cultured mammalian cells and by direct DNA injection in skeletal muscle. Intron I sequences were necessary to direct high-level, cell-specific porcine alpha-skeletal actin expression in C2C12 myotubes, but they inhibited transcription in skeletal muscle. A 5' distal sequence (-1929 to -550), had enhancer-like activity in C2C12 myotubes and directly injected muscle, and inhibited transcription in Hela cells. In contrast, a central region (-550 to -388) enhanced basal transcription in directly injected muscle, but not in C2C12 myotubes. A distal regulatory element localized to the 3' untranslated region modulated SV40 promoter activity only in cell culture studies. These results suggest that the intragenic and 3' distal regulatory element may be differentially utilized during differentiation and maturation of skeletal muscle. All three regions decreased SV40 promoter activity in Hela cells, suggesting that they play a role in defining tissue-specific expression of porcine a-skeletal actin. Furthermore, different regulatory programs of a-skeletal actin expression appear to exist in these two experimental systems.