title: In vivo assessment of contractile strength distinguishes differential gene function in skeletal muscle of zebrafish larvae.
abstract: The accessible genetics and extensive skeletal musculature of the zebrafish make it a versatile and increasingly used model for studying muscle contraction. We here describe the development of an in vivo assay for measuring the contractile force of intact zebrafish at the larval stage. In addition, as proof of applicability, we have used this assay to quantify contractile strength of zebrafish larvae in a morphant model of deranged rbfox function. Average maximum tetanic (180 Hz) whole body forces produced by wild-type larvae at 2, 3, 4, and 5 days postfertilization amounted to 3.0, 7.2, 9.1, and 10.8 mN, respectively. To compare at potentially different stages of muscle development, we developed an immunohistological assay for empirically determining the cross-sectional area of larval trunk skeletal muscle to quantify muscle-specific force per cross-sectional area. At 4-5 days postfertilization, specific force amounts to ∼ 300 mN/mm(2), which is similar to fully developed adult mammalian skeletal muscle. We used these assays to measure contractile strength in zebrafish singly or doubly deficient for two rbfox paralogs, rbfox1l and rbfox2, which encode RNA-binding factors shown previously to modulate muscle function and muscle-specific splicing. We found rbfox2 morphants produce maximal tetanic forces similar to wild-type larvae, whereas rbfox1l morphants demonstrate significantly impaired function. rbfox1l/rbfox2 morphants are paralyzed, and their lack of contractile force production in our assay suggests that paralysis is a muscle-autonomous defect. These quantitative functional results allow measurement of muscle-specific phenotypes independent of neural input.
authors.affiliation: Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio;
authors.forename: Brit L
authors.initials: BL
authors.lastname: Martin
authors.affiliation: Department of Molecular Genetics, The Ohio State University, Columbus, Ohio;
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Gallagher
authors.affiliation: Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio;
authors.forename: Neha
authors.initials: N
authors.lastname: Rastogi
authors.affiliation: Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio; Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio;
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Davis
authors.affiliation: Department of Neuroscience, The Ohio State University, Columbus, Ohio; and.
authors.forename: Christine E
authors.initials: CE
authors.lastname: Beattie
authors.affiliation: Department of Molecular Genetics, The Ohio State University, Columbus, Ohio; Department of Biological Chemistry and Pharmacology, The Ohio State University, Columbus, Ohio.
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Amacher
authors.affiliation: Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio; Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio; janssen.10@osu.edu.
authors.forename: Paul M L
authors.initials: PM
authors.lastname: Janssen
mesh_terms: D019412:Anatomy, Cross-Sectional; D000818:Animals; D007814:Larva / Q000502:physiology; D009119:Muscle Contraction / Q000235:genetics*; D024510:Muscle Development / Q000235:genetics*; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D012313:RNA / Q000096:biosynthesis; D016601:RNA-Binding Proteins / Q000502:physiology; D015027:Zebrafish / Q000502:physiology*; D029961:Zebrafish Proteins / Q000502:physiology
chemical_list: D016601:RNA-Binding Proteins; C472413:Rbfox1l protein, zebrafish; D029961:Zebrafish Proteins; D012313:RNA
keywords: contraction; muscle; rbfox1; rbfox2; zebrafish