Role of myocyte-specific enhancer-binding factor (MEF-2) in transcriptional regulation of the alpha-cardiac myosin heavy chain gene.

The intergenic region between the mouse alpha-cardiac myosin heavy chain and beta-myosin heavy chain genes has previously been shown to direct expression of the bacterial chloramphenicol acetyltransferase reporter gene in transgenic mice in a tissue-specific manner. Sequence analyses located a putative myocyte-specific enhancer-binding factor (MEF-2) site situated in the regulatory region of this gene proximal to the start site of transcription. The role of this element in directing the cardiac compartment-specific expression of the transgene was assessed. The polymerase chain reaction was used to perform substitution mutagenesis of the MEF-2 binding site, and lack of MEF-2 binding was confirmed by gel retardation assays. The resultant construct was used to generate transgenic mice. Surprisingly, transgene expression was not down-regulated, but was significantly increased in the hearts of the MEF-2 mutant mice. In addition, cardiac-specific expression of the transgene was perturbed with significant levels of ectopic expression occurring in the aorta.