title: Expression of the inclusion body myopathy 3 mutation in Drosophila depresses myosin function and stability and recapitulates muscle inclusions and weakness.
abstract: Hereditary myosin myopathies are characterized by variable clinical features. Inclusion body myopathy 3 (IBM-3) is an autosomal dominant disease associated with a missense mutation (E706K) in the myosin heavy chain IIa gene. Adult patients experience progressive muscle weakness. Biopsies reveal dystrophic changes, rimmed vacuoles with cytoplasmic inclusions, and focal disorganization of myofilaments. We constructed a transgene encoding E706K myosin and expressed it in Drosophila (E701K) indirect flight and jump muscles to establish a novel homozygous organism with homogeneous populations of fast IBM-3 myosin and muscle fibers. Flight and jump abilities were severely reduced in homozygotes. ATPase and actin sliding velocity of the mutant myosin were depressed >80% compared with wild-type myosin. Light scattering experiments and electron microscopy revealed that mutant myosin heads bear a dramatic propensity to collapse and aggregate. Thus E706K (E701K) myosin appears far more labile than wild-type myosin. Furthermore, mutant fly fibers exhibit ultrastructural hallmarks seen in patients, including cytoplasmic inclusions containing aberrant proteinaceous structures and disorganized muscle filaments. Our Drosophila model reveals the unambiguous consequences of the IBM-3 lesion on fast muscle myosin and fibers. The abnormalities observed in myosin function and muscle ultrastructure likely contribute to muscle weakness observed in our flies and patients.
authors.affiliation: Department of Biology and Molecular Biology Institute, San Diego State University, San Diego, CA 92182, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.forename: Girish C
authors.initials: GC
authors.lastname: Melkani
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Suggs
authors.forename: Anju
authors.initials: A
authors.lastname: Melkani
authors.forename: William A
authors.initials: WA
authors.lastname: Kronert
authors.forename: Anthony
authors.initials: A
authors.lastname: Cammarato
authors.forename: Sanford I
authors.initials: SI
authors.lastname: Bernstein
mesh_terms: D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D017124:Conserved Sequence; D003286:Contracture / Q000151:congenital* / Q000235:genetics / Q000503:physiopathology; D004331:Drosophila melanogaster / Q000235:genetics*; D006720:Homozygote; D006801:Humans; D002479:Inclusion Bodies / Q000378:metabolism* / Q000473:pathology; D007700:Kinetics; D008124:Locomotion; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018908:Muscle Weakness / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D009210:Myofibrils / Q000378:metabolism / Q000648:ultrastructure; D018995:Myosin Heavy Chains / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D018979:Myositis, Inclusion Body / Q000151:congenital* / Q000235:genetics / Q000503:physiopathology; D009886:Ophthalmoplegia / Q000235:genetics* / Q000503:physiopathology; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D013696:Temperature
chemical_list: D000199:Actins; D050505:Mutant Proteins; D017301:Ca(2+) Mg(2+)-ATPase; D018995:Myosin Heavy Chains