Drosophila myosin mutants model the disparate severity of type 1 and type 2B distal arthrogryposis and indicate an enhanced actin affinity mechanism

Yiming Guo,Sanford I Bernstein,Alice Huang,Karen H Hsu,Jennifer A Suggs,Douglas M Swank,Kaylyn M Bell,William A Kronert,Floyd Sarsoza

doi:10.1186/s13395-020-00241-6

Yiming Guo, Sanford I Bernstein + Show 7 more

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https://doi.org/10.1186/s13395-020-00241-6

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Abstract

BackgroundDistal arthrogryposis (DA) is a group of autosomal dominant skeletal muscle diseases characterized by congenital contractures of distal limb joints. The most common cause of DA is a mutation of the embryonic myosin heavy chain gene, MYH3. Human phenotypes of DA are divided into the weakest form–DA1, a moderately severe form–DA2B (Sheldon-Hall Syndrome), and a severe DA disorder–DA2A (Freeman-Sheldon Syndrome). As models of DA1 and DA2B do not exist, their disease mechanisms are poorly understood.MethodsWe produced the first models of myosin-based DA1 (F437I) and DA2B (A234T) using transgenic Drosophila melanogaster and performed an integrative analysis of the effects of the mutations. Assessments included lifespan, locomotion, ultrastructural analysis, muscle mechanics, ATPase activity, in vitro motility, and protein modeling.ResultsWe observed significant defects in DA1 and DA2B Drosophila flight and jump ability, as well as myofibril assembly and stability, with homozygotes displaying more severe phenotypes than heterozygotes. Notably, DA2B flies showed dramatically stronger phenotypic defects compared to DA1 flies, mirroring the human condition. Mechanical studies of indirect flight muscle fibers from DA1 heterozygotes revealed reduced power output along with increased stiffness and force production, compared to wild-type controls. Further, isolated DA1 myosin showed significantly reduced myosin ATPase activity and in vitro actin filament motility. These data in conjunction with our sinusoidal analysis of fibers suggest prolonged myosin binding to actin and a slowed step associated with Pi release and/or the power stroke. Our results are supported by molecular modeling studies, which indicate that the F437I and A234T mutations affect specific amino acid residue interactions within the myosin motor domain that may alter interaction with actin and nucleotide.ConclusionsThe allele-specific ultrastructural and locomotory defects in our Drosophila DA1 and DA2B models are concordant with the differential severity of the human diseases. Further, the mechanical and biochemical defects engendered by the DA1 mutation reveal that power production, fiber stiffness, and nucleotide handling are aberrant in F437I muscle and myosin. The defects observed in our DA1 and DA2B Drosophila models provide insight into DA phenotypes in humans, suggesting that contractures arise from prolonged actomyosin interactions.

Highlights

Distal arthrogryposis (DA) is a group of autosomal dominant skeletal muscle diseases characterized by congenital contractures of distal limb joints
Distal arthrogryposis (DA) is a group of autosomal dominant skeletal muscle disorders characterized by nonprogressive congenital contractures in at least two body sites, primarily the upper and lower limbs, which result in camptodactyly and clubfeet [1–3]
The goal of this study was to produce Drosophila models of myosin-based DA1 and DA2B in order to define their phenotypic defects, to examine whether the disparate disease states are mirrored in the disease models and to gain insights into the mechanism of the disease process

Summary

Introduction

Distal arthrogryposis (DA) is a group of autosomal dominant skeletal muscle diseases characterized by congenital contractures of distal limb joints. Distal arthrogryposis (DA) is a group of autosomal dominant skeletal muscle disorders characterized by nonprogressive congenital contractures in at least two body sites, primarily the upper and lower limbs, which result in camptodactyly and clubfeet [1–3]. In addition to these common manifestations, facial abnormalities frequently occur. DA2A or Freeman-Sheldon Syndrome (OMIM 193700 http://www.omim.org) is a severe form of the disease characterized by clubfeet, clenched fists, scoliosis, and distinctive facial abnormalities, including a very small mouth, pinched lips, and H-shaped dimpling of the chin (DA2A was recently suggested to be renamed to Freeman-Burian Syndrome [6]).

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