Identification of three developmentally controlled isoforms of human myosin heavy chains.

A set of cDNA clones coding for myosin heavy chains (MHC) was isolated from a human fetal skeletal muscle library. We have demonstrated by restriction mapping and nucleotide sequence analysis that the cDNAs represent three distinct transcripts, presumably the products of different genes. Furthermore, the pattern of mRNA expression indicates that the corresponding genes are regulated in a tissue-specific and developmental-stage-specific manner. While the cDNA clone gtMHC-V exhibits extensive sequence similarity to the rat beta-myosin heavy chain, the two other clones, gtMHC-F and gtMHC-E are very similar to the rat genes encoding the perinatal and embryonic myosin heavy chains, respectively. The mRNA corresponding to clone gt-MHC-V is highly expressed in heart and adult fast skeletal muscle and to a lesser extent in fetal skeletal muscle and adult slow skeletal muscle. The mRNAs corresponding to clones gtMHC-F and gtMHC-E are abundantly present in fetal skeletal muscle and are not present or barely detectable in heart and adult skeletal muscle.