Modular organization of phylogenetically conserved domains controlling developmental regulation of the human skeletal myosin heavy chain gene family.

The mammalian skeletal myosin heavy chain locus is composed of a six-membered family of tandemly linked genes whose complex regulation plays a central role in striated muscle development and diversification. We have used publicly available genomic DNA sequences to provide a theoretical foundation for an experimental analysis of transcriptional regulation among the six promoters at this locus. After reconstruction of annotated drafts of the human and murine loci from fragmented DNA sequences, phylogenetic footprint analysis of each of the six promoters using standard and Bayesian alignment algorithms revealed unexpected patterns of DNA sequence conservation among orthologous and paralogous gene pairs. The conserved domains within 2.0 kilobases of each transcriptional start site are rich in putative muscle-specific transcription factor binding sites. Experiments based on plasmid transfection in vitro and electroporation in vivo validated several predictions of the bioinformatic analysis, yielding a picture of synergistic interaction between proximal and distal promoter elements in controlling developmental stage-specific gene activation. Of particular interest for future studies of heterologous gene expression is a 650-base pair construct containing modules from the proximal and distal human embryonic myosin heavy chain promoter that drives extraordinarily powerful transcription during muscle differentiation in vitro.