CHARACTERIZATION OF A CARDIAC-SELECTIVE AND DEVELOPMENTALLY UP-REGULATED PROMOTER IN TRANSGENIC MICE

Transcriptional regulatory mechanisms which mediate cardiac-specific g ene expression have not yet been completely understood(1). Potential c ardiac-specific promoter sequences, sharing similar protein binding mo tives, show either coexpression in skeletal muscle(2), local restricti on to the atrium(3) or late onset of expression during fetogenesis(4). Based on in situ hybridization studies that indicated the expression of the cardiac myosin-light-chain-2 (MLC-2) gene in ventricular myocar dium and in the lower outflow tract, a model system for selective targ eting of foreign genes to the heart of transgenic mice has been develo ped. The regulatory promoter element was derived from the rat cardiac MLC-2 gene(5). 2100 bp of the 5' regulatory MLC-2 sequences were found to drive constitutive cardiac expression of a firefly luciferase repo rter gene from early tubular heart formation. During ventricular loop and septum formation luciferase activity was 10-fold upregulated in co mparison to steady-state levels observed 10 days after birth. No lucif erase activity was detectable in any other muscle or non-muscle tissue of transgenic mice. These data suggest that the 2.1 kb DNA sequences of the 5' flanking region of the cardiac MLC-2 gene contain sufficient regulatory elements for a selective gene expression in cardiac myocyt es from embryogenesis. The transgenic model should aid in determining the influences of pathogenic gene products on developing and mature he art muscle to elucidate the etiology of myocardial diseases such as ca rdiomyopathies.