Isolation and characterization of the mouse cardiac myosin heavy chain genes

Two mouse genomic libraries were probed in order to isolate the murine cardiac myosin heavy chain (MHC) genes. Two overlapping cosmid clones that encode the cardiac genes were isolated. One of them encompasses the entire alpha-cardiac MHC gene, its 5'-flanking region and approximately 10 kilobase pairs (kb) of the 3'-end of the beta-cardiac MHC gene which we determined is located approximately 4 kb upstream of the alpha-cardiac MHC gene. Four clones isolated from a bacteriophage library were found to overlap with the 5'-region of the cosmid clones, and sequence analysis confirmed that the 5'-end of the beta-cardiac MHC gene was contained within one of the clones. Primer extension and polymerase chain reaction (PCR) analyses were used to define the transcriptional start site and the 5'-organization of the alpha-cardiac MHC gene. This region exhibits greater than 90% homology to the corresponding nucleotides of the rat alpha-cardiac MHC gene. To assess the importance of the intergenic region in directing expression of the alpha-cardiac MHC gene, a fragment containing the 3'-end of the beta-cardiac gene and the 5'-end of the alpha-cardiac gene was linked to a chloramphenicol acetyltransferase gene and used to generate transgenic mice. Analyses of the chloramphenicol acetyltransferase (CAT) activity in two lines indicate that the intergenic region is sufficient to properly direct expression in a tissue-specific manner.