Diversity of myosin heavy chain gene sequences and patterns of expression

Abstract

Myosin heavy chain (MHC) is a major component of the contractile apparatus in skeletal muscle. There are at least six distinct MHC isoforms that are expressed in skeletal muscle during development which are encoded by separate genes. Molecular probes that correspond to each of the isoforms can be used as tools to understand what role multiple isoforms play in skeletal muscle development and muscle function. I have isolated cDNA clones that correspond to three developmentally regulated human skeletal muscle MHC isoforms: embryonic, perinatal and one of the several fast MHCs. Gene-specific probes for five MHC genes have been generated and used to study the patterns of MHC mRNA expression in tissue and in cultured muscle cells. Embryonic MHC mRNA is expressed in fetal skeletal but not in adult muscle, whereas, the fast skeletal MHC is expressed in both human fetal (21 weeks of gestation) and adult skeletal muscle.;I have also examined the expression of MHC in cultured human fetal and adult skeletal muscle cells. At least four distinct MHC genes are expressed in fetal muscle cell cultures. The expression of embryonic and perinatal MHC mRNAs appear to be temporally regulated. The expression of embryonic and two fast MHC mRNAs have been examined in satellite cell cultures. The temporal pattern of expression of each of these mRNAs during following differentiation appears to be distinct.;Genomic sequences that contain the human embryonic MHC gene were also characterized in order to study the organization of a human MHC gene. The human embryonic MHC gene appears to have the same intron-exon structure as its rat counterpart. The sequences as well as the positions of the introns and exons of the two genes are well conserved. Human skeletal muscle myosin heavy chain genes have been mapped to a cluster on chromosome 17 (Leinwand et al., 1983. Science 221:766-9). In order to examine the organization of the human skeletal muscle gene cluster, nine clones were isolated from a human genomic YAC library and were analyzed PCR. Eight clones contained the 3{dollar}\sp\prime{dollar} half of the embryonic MHC gene. One YAC also contains the gene that encodes AS8 MHC.