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Myomaker is a membrane activator of myoblast fusion and muscle formation



Fusion of myoblasts is essential for the formation of multi-nucleated muscle fibres. However, the identity of muscle-specific proteins that directly govern this fusion process in mammals has remained elusive. Here we identify a muscle-specific membrane protein, named myomaker, that controls myoblast fusion. Myomaker is expressed on the cell surface of myoblasts during fusion and is downregulated thereafter. Overexpression of myomaker in myoblasts markedly enhances fusion, and genetic disruption of myomaker in mice causes perinatal death due to an absence of multi-nucleated muscle fibres. Remarkably, forced expression of myomaker in fibroblasts promotes fusion with myoblasts, demonstrating the direct participation of this protein in the fusion process. Pharmacological perturbation of the actin cytoskeleton abolishes the activity of myomaker, consistent with previous studies implicating actin dynamics in myoblast fusion. These findings reveal a long-sought myogenic fusion protein that controls mammalian myoblast fusion and provide new insights into the molecular underpinnings of muscle formation.

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Figure 1: Muscle-specific expression of myomaker.
Figure 2: Myomaker is essential for skeletal muscle development.
Figure 3: Control of myoblast fusion by myomaker.
Figure 4: Myomaker is expressed on the cell membrane of myoblasts.
Figure 5: Myomaker participates in the myoblast membrane fusion reaction.

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We thank J. Cabrera for graphics, the Transgenic Technology Center at University of Texas Southwestern Medical Center for embryonic stem cell injections, J.A. Richardson for histology and the University of Texas Southwestern Live Cell Imaging Facility (K. Luby-Phelps and A. Budge) for microscopy and live cell-imaging assistance. We thank D. Rosenbaum, W. Snell, S. Schmid, J. Seemann and members of the Olson laboratory for scientific discussions. D.P.M. was financed by a National Institutes of Health National Research Service Award Fellowship (F32AR05948403). This work was supported by grants from the National Institutes of Health (HL-077439, HL-111665, HL093039 and U01-HL-100401) and the Robert A. Welch Foundation (grant 1-0025) (to E.N.O.).

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Authors and Affiliations



D.P.M. and E.N.O. conceived the project and designed the experiments. D.P.M., J.R.O., L.B.S., S.B. and J.M.S. performed experiments. D.P.M. and R.B.-D. wrote the animal protocol. D.P.M. and E.N.O. analysed the data and prepared the manuscript.

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Correspondence to Eric N. Olson.

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The authors declare no competing financial interests.

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Supplementary Figures

This file contains Supplementary Figures 1-8. (PDF 9769 kb)

Time-lapse microscopy of C2C12 myoblasts infected with GFP and Myomaker

C2C12 cells were infected with GFP and Myomaker retrovirus and induced to differentiate. This video depicts a myoblast fusing to a myoblast (arrowhead) and fusion of two myotubes (arrows). Myomaker not only increases myoblast-myotube fusion, but also myotube-myotube fusion. The video represents 32 hours of culture, beginning 48 hours after differentiation. Frames are 15 minutes apart and video speed is 3 frames/second. (MOV 11306 kb)

Myomaker-infected fibroblasts fusing to muscle cells

10T½ fibroblasts were infected with GFP and Myomaker. C2C12 myoblasts were infected with dsRed and then mixed with the GFP+Myomaker-infected fibroblasts and induced to differentiate. Red/Green chimeric myotubes, generated from the fusion of myoblasts and fibroblasts, can be visualized fusing with a C2C12 cell (red arrow) and fibroblasts (green arrows). The video represents 40 hours of culture, beginning 48 hours after differentiation. Frames are 15 minutes apart and video speed is 3 frames/second. (MOV 27854 kb)

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Millay, D., O’Rourke, J., Sutherland, L. et al. Myomaker is a membrane activator of myoblast fusion and muscle formation. Nature 499, 301–305 (2013).

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