The objectives of this proposal are to investigate the molecular genetic and developmental mechanisms that regulate myosin heavy chain (MHC) isoform structure and function in Drosophila. Unlike other organisms studied, Drosophila has only a single muscle MHC gene, but this single gene encodes multiple MHC protein isoforms by a process of complex, developmentally regulated alternative RNA splicing. The Drosophila MHC gene has five sets of alternatively splice exons that are differentially expressed in different larval and adult muscle types. These alternatively spliced exons are particularly interesting because they encode defined protein domains in the MHC head and hinge regions as well as the carboxyl terminus. These domains are hypothesized to be important determinants of the distinct contractile activities of specialized muscle types, including control of ATP binding and ATPase activity, actin/myosin cross bridge formation, myosin light chain binding, MHC head movement, and myosin filament assembly. Genetic, biochemical and transgenic experiment are proposed to investigate the muscle-specific functions of the variant protein domains in MHC isoforms generated by alternative exon splicing. These approaches will also be used to investigate the roles of intron and exon DNA sequences and RNA and protein splicing factors in the regulated splicing of specific exon sequences into MHC isoforms expressed in functionally specialized muscles such as the indirect flight muscle. %%% The proposed studies undertake to reveal the functions of specific variants of MHC in specialized contractile activities of different skeletal muscle types and to define fundamental developmental and molecular mechanisms that control alternative RNA splicing. This alternative splicing gives rise to a family of proteins with different properties from a single gene.
