Figure 2: Efficient fusion requires myomaker expression in both fusing cells but myomerger in one fusing cell.

(a) Diagram showing the cell mixing approach to assess fusion between the populations of fibroblasts. Co-localization of GFP and NLS-TdTomato (NLS-Tom) in the nucleus represents fusion (arrows). Representative images demonstrate fusion of myomaker⁺ myomerger⁺ GFP⁺ fibroblasts with myomaker⁺ NLS-Tom⁺ fibroblasts but not myomerger⁺ NLS-Tom⁺ fibroblasts. (b) Quantification of the percent of GFP⁺ NLS-Tom⁺ syncytia and the percent of nuclei in syncytia (n=3). Dotted line on right panel represents fusion achieved when both cells express both myomaker and myomerger (from Fig. 1b). (c) Heterologous fusion experiment between C2C12 myoblasts and GFP⁺ fibroblasts infected with either empty, myomaker or myomerger. Representative immunofluorescent images to visualize co-localization of myosin and GFP (arrows), indicating fusion. Quantification of the percentage of GFP⁺ myosin⁺ cells (n=3). Data are presented as mean±s.e.m. *P<0.05 compared with myomerger⁺ NLS-Tom⁺ fibroblasts in b or empty in c. #P<0.05 between myomaker and myomerger. An unpaired t-test was used to determine significance. Scale bars, 50 μm (a), 100 μm (c).