title: Knockdown of fast skeletal myosin-binding protein C in zebrafish results in a severe skeletal myopathy.
abstract: Myosin-binding protein C (MyBPC) in the muscle sarcomere interacts with several contractile and structural proteins. Mutations in the cardiac isoform (MyBPC-3) in humans, or animal knockout, are associated with cardiomyopathy. Function of the fast skeletal isoform (MyBPC-2) in living muscles is less understood. This question was addressed using zebrafish models, combining gene expression data with functional analysis of contractility and small-angle x-ray diffraction measurements of filament structure. Fast skeletal MyBPC-2B, the major isoform, was knocked down by >50% using morpholino antisense nucleotides. These morphants exhibited a skeletal myopathy with elevated apoptosis and up-regulation of factors associated with muscle protein degradation. Morphant muscles had shorter sarcomeres with a broader length distribution, shorter actin filaments, and a wider interfilament spacing compared with controls, suggesting that fast skeletal MyBPC has a role in sarcomere assembly. Active force was reduced more than expected from the decrease in muscle size, suggesting that MyBPC-2 is required for optimal force generation at the cross-bridge level. The maximal shortening velocity was significantly increased in the MyBPC-2 morphants, but when related to the sarcomere length, the difference was smaller, reflecting that the decrease in MyBPC-2B content and the resulting myopathy were accompanied by only a minor influence on filament shortening kinetics. In the controls, equatorial patterns from small-angle x-ray scattering revealed that comparatively few cross-bridges are attached (as evaluated by the intensity ratio of the 11 and 10 equatorial reflections) during active contraction. X-ray scattering data from relaxed and contracting morphants were not significantly different from those in controls. However, the increase in the 11:10 intensity ratio in rigor was lower compared with that in controls, possibly reflecting effects of MyBPC on the cross-bridge interactions. In conclusion, lack of MyBPC-2 results in a severe skeletal myopathy with structural changes and muscle weakness.
authors.affiliation: Department of Physiology and Pharmacology, Department of Cell and Molecular Biology, and Department of Women's and Children's Health, Karolinska Institutet, SE 171 77 Stockholm, Sweden.
authors.forename: Mei
authors.initials: M
authors.lastname: Li
authors.affiliation: Department of Physiology and Pharmacology, Department of Cell and Molecular Biology, and Department of Women's and Children's Health, Karolinska Institutet, SE 171 77 Stockholm, Sweden.
authors.forename: Monika
authors.initials: M
authors.lastname: Andersson-Lendahl
authors.affiliation: Department of Physiology and Pharmacology, Department of Cell and Molecular Biology, and Department of Women's and Children's Health, Karolinska Institutet, SE 171 77 Stockholm, Sweden.
authors.forename: Thomas
authors.initials: T
authors.lastname: Sejersen
authors.affiliation: Department of Physiology and Pharmacology, Department of Cell and Molecular Biology, and Department of Women's and Children's Health, Karolinska Institutet, SE 171 77 Stockholm, Sweden anders.arner@ki.se.
authors.forename: Anders
authors.initials: A
authors.lastname: Arner
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D017209:Apoptosis; D017353:Gene Deletion; D009135:Muscular Diseases / Q000235:genetics* / Q000378:metabolism; D012518:Sarcomeres / Q000378:metabolism* / Q000473:pathology; D024744:Skeletal Muscle Myosins / Q000235:genetics / Q000378:metabolism*; D015027:Zebrafish
chemical_list: D000199:Actins; D024744:Skeletal Muscle Myosins