Myosin Quality Control Systems in Zebrafish Skeletal Muscle Development

Abstract

In order to maintain homeostasis, defective proteins must be identified, removed, and replaced. In skeletal muscle, failures in this process can lead to a variety of incurable muscle diseases (myopathies), many of which are fatal. While aspects of protein turnover have been studied widely, the protein turnover process in skeletal muscle is still incompletely understood, especially with respect to the motor protein, myosin. By studying the assembly and maintenance of the basic unit of striated muscle, the sarcomere, we aim to elucidate the components involved and the mechanism controlling muscle myosin quality control in skeletal muscle.Zebrafish make an excellent model system to study sarcomere protein turnover due to their ability to survive with myopathies that are fatal in other organisms. Using two different zebrafish lines, steif, and herzschlag, we and others show that steif sarcomeres fail to assemble myosin thick filaments due to a loss of a critical component (Etard et al., 2007), while herzschlag sarcomeres degrade over time as a consequence of muscle contractions. Transmission electron microscopy coupled with H&E staining revealed a slow muscle atrophy specific to herzschlag embryos. To identify factors involved in response to myosin damage during assembly or maintenance, we have screened through candidate genes, myosin chaperones and muscle specific E3 enzymes, using in situ hybridization and qPCR. Our data indicates a division of function where specific E3 enzymes and myosin chaperones respond to myosin damage exclusively during assembly, while other E3 enzymes respond to myosin damage during sarcomere maintenance. Pharmaceutical inhibition of the proteasome shifts this response in steif embryos, but not herzschlag, suggesting an interconnected network of protein quality control during myosin assembly. Together, this work helps highlight potential therapeutic targets to treat myosin turnover related myopathies.Support or Funding InformationNSERCThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.