Isoform switch of Tks5 is critical for myoblast fusion. (A) Effects of ectopic expression of flag-tagged Tks5α or Tks5αΔPX in day 4 differentiated myoblasts. Cell lysates were immunoblotted with anti-Tks5 SH3 or anti-Flag antibodies, with arrow and arrowhead indicating Tks5α and Tks5αΔPX, respectively. Asterisk shows nonspecific signal of anti-Flag antibody. (B and C) Fusion efficiency of different Tks5 constructs expressing myoblasts. Scale bar, 30 µm. **, P < 0.01; ***, P < 0.001. (D) Effects of ectopic expression of flag-tagged Tks5 in undifferentiated myoblasts. After 48-h transfection, undifferentiated myoblasts were seeded on fibronectin-coated coverslips and stained for actin, Cortactin, and Flag. Maximum-intensity projections are shown. (E) Effects of Tks5αΔPX expression on invadosome formation. Day 3 differentiated myoblasts with Tks5α or Tks5αΔPX expression were seeded on fibronectin-coated coverslips and stained to detect endogenous Dyn2 and F-actin distribution. Scale bars, 10 µm.