ANALYSIS OF MUSCLE CREATINE-KINASE GENE REGULATORY ELEMENTS IN SKELETAL AND CARDIAC MUSCLES OF TRANSGENIC MICE

Regulatory regions of the mouse muscle creatine kinase (MCK) gene, pre viously discovered by analysis in cultured muscle cells, were analyzed in transgenic mice, The 206-bp MCK enhancer at nt -1256 was required for high-level expression of MCK-chloramphenicol acetyltransferase fus ion genes in skeletal and cardiac muscle; however, unlike its behavior in cell culture, inclusion of the l-kb region of DNA between the enha ncer and the basal promoter produced a 100-fold increase in skeletal m uscle activity, Analysis of enhancer control elements also indicated m ajor differences between their properties in transgenic muscles and in cultured muscle cells, Transgenes in which the enhancer right E box o r CArG element were mutated exhibited expression levels that were indi stinguishable from the wild-type transgene, Mutation of three conserve d E boxes in the MCK 1,256-bp 5' region also had no effect on transgen e expression in thigh skeletal muscle expression, All of these mutatio ns significantly reduced activity in cultured skeletal myocytes, Howev er, the enhancer AT-rich element at nt -1195 was critical for expressi on in transgenic skeletal muscle, Mutation of this site reduced skelet al muscle expression to the same level as transgenes lacking the 206-b p enhancer, although mutation of the AT-rich site did not affect cardi ac muscle expression, These results demonstrate clear differences betw een the activity of MCK regulatory regions in cultured muscle cells an d in whole adult transgenic muscle. This suggests that there are alter native mechanisms of regulating the MCK gene in skeletal and cardiac m uscle under different physiological states.