In vivo and in vitro analysis of electrical activity-dependent expression of muscle acetylcholine receptor genes using adenovirus.

Acetylcholine receptor (AChR) genes are repressed in extrajunctional domains of adult muscle fiber by neurally evoked electrical activity. Denervation elicits upregulation of AChR gene transcription in extrasynaptic areas. We have used an adenovirus (Ad)-based strategy to analyze in vitro and in vivo the electrical activity-dependent transcription of the chicken AChR alpha 1 subunit gene. The luciferase gene placed under the control of wild-type and mutated fragments of the alpha 1 subunit promoter was inserted in a defective Ad vector designed for the study of transcriptional regulation. Animals were infected by intramuscular injection and in vivo luciferase levels were normalized by coinfection with an Ad vector containing the chloramphenicol acetyltransferase gene driven by an electrical activity-insensitive promoter. Our results demonstrate that although both proximal MyoD binding sites of the alpha 1 promoter are required for muscle-specific expression of the alpha 1 gene, only one is necessary, albeit insufficient, to enhance alpha 1 promoter activity after denervation. Parallel results were obtained with cultured muscle cells in vitro following tetrodotoxin blocking of spontaneous electrical activity. These results substantiate a direct contribution of MyoD factors in electrical activity-dependent regulation of AChR expression and further indicate that Ad-based vectors constitute a powerful tool in the field of transcriptional regulation.