Our long-term goal is to significantly impact the fundamental knowledge of muscle biology and provide new approaches for disease treatment. Striated muscle fibers are large multinucleated cells and possess a highly organized cytoarchitecture containing organelles positioned for optimal muscle function. This positioning is particularly evident in the placement of myonuclei, which reside above the sarcomere at the periphery of the myofiber and are positioned to maximize their internuclear distance. Our objective is the identification of mechanisms responsible for myonuclear movement and positioning. Centrally located myonuclei have been used for decades as a hallmark of muscle disease. However, much remains to be learned about the mechanisms that control myonuclear movement normally and the contribution of aberrant myonuclear position to the etiology and/or progression of muscle disease. Building on our published results over funding period (e.g. Metzger et al., 2012; Folker et al., 2012, 2014; Schulman et al., 2013, 2014; Azevedo et al., 2016; Manhart et al., 2018, 2020; Rosen et al., 2019), our specific aims are to first address mechanistically how tendon and motoneurons signal to the myofiber to fine-tune myonuclear positioning. We identified two signaling pathways at the myotendinous junction that regulate nuclear positioning. Likewise, we will dissect the contribution of the motoneuron to nuclear placement. Secondly, we will examine why muscles fail to function optimally when myonuclei are mispositioned. Muscle physiology will be assayed through testing mitochondrial function via quantification of ATP and ROS levels and by testing neuromuscular communication via electrophysiological approaches. We will also investigate the input to muscle function of specific metabolic and signaling proteins that we identified are misregulated as a result of mispositioned myonuclei. Thirdly, we will push forward our dissection of the myonuclear positioning mechanisms from fly to the human system. We will employ human 3D muscle cultures that are co-cultured with motoneurons to define and then perturb myonuclear movement and positioning as the myofibers develop. Our methodologies take advantage of cutting edge, in vivo time lapse imaging approaches that we have developed in Drosophila and will also apply to human 3D cultures to follow myonuclear movement and cytoskeletal dynamics. We will employ the genetic resources available in Drosophila and human cultures to manipulate genes, processes, and cell types for our analyses. These genetic experiments will be supported by biochemical and cell biological approaches. Together the work outlined in this proposal will shed new light on this little understood, but important area of muscle biology. The results of this research will permit us to highlight genes and mechanisms that are candidates for changes associated with different human muscle diseases.

Public Health Relevance

/Public Health Relevance Statement Our research will impact the knowledge of muscle biology and provide new approaches for human disease treatment. Specifically, we will identify mechanisms responsible for nuclear movement and position to better understand how improper positioning of muscle nuclei occurs and how it impacts normal cell function. The results of this research will highlight genes and cellular mechanisms that may fail to function properly in human muscle diseases.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Research Project (R01)
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Skeletal Muscle and Exercise Physiology Study Section (SMEP)
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Boyce, Amanda T
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Sloan-Kettering Institute for Cancer Research
New York
United States
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Balakrishnan, Mridula; Baylies, Mary K (2018) Myonuclear Positioning and Aneurysms Are LINC'd by Ariande. Dev Cell 45:149-150
Deng, Su; Azevedo, Mafalda; Baylies, Mary (2017) Acting on identity: Myoblast fusion and the formation of the syncytial muscle fiber. Semin Cell Dev Biol 72:45-55
Rosen, Jonathan N; Baylies, Mary K (2017) Myofibrils put the squeeze on nuclei. Nat Cell Biol 19:1148-1150
Deng, Su; Bothe, Ingo; Baylies, Mary (2016) Diaphanous regulates SCAR complex localization during Drosophila myoblast fusion. Fly (Austin) 10:178-86
Azevedo, Mafalda; Schulman, Victoria K; Folker, Eric et al. (2016) Imaging Approaches to Investigate Myonuclear Positioning in Drosophila. Methods Mol Biol 1411:291-312
Bothe, Ingo; Baylies, Mary K (2016) Drosophila myogenesis. Curr Biol 26:R786-91
Deng, Su; Bothe, Ingo; Baylies, Mary K (2015) The Formin Diaphanous Regulates Myoblast Fusion through Actin Polymerization and Arp2/3 Regulation. PLoS Genet 11:e1005381
Dobi, Krista C; Schulman, Victoria K; Baylies, Mary K (2015) Specification of the somatic musculature in Drosophila. Wiley Interdiscip Rev Dev Biol 4:357-75
Schulman, Victoria K; Dobi, Krista C; Baylies, Mary K (2015) Morphogenesis of the somatic musculature in Drosophila melanogaster. Wiley Interdiscip Rev Dev Biol 4:313-34
Kumar, Ram P; Dobi, Krista C; Baylies, Mary K et al. (2015) Muscle cell fate choice requires the T-box transcription factor midline in Drosophila. Genetics 199:777-91

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