A full-length cDNA encoding mouse utrophin with an N-terminal FLAG epitope tag was inserted between the cytomegalovirus (CMV) minimal promoter and polyadenylation signal, all downstream of the tetracycline operator (tetracycline responsive element). Tissue-specific tetracycline transactivator (tTA) or reverse transactivator (rtTA) expression from a second transgene permits regulation of utrophin expression by administration of doxycycline in drinking water. (J:80809)