(A–Diii) Wt (A–Aiii, C–Ciii) and TEAD1-Tg (B–Biii, D–Diii) SC numbers and proliferation were assessed. Postnatal day 12 (PN 12d, A–Biii) and day 20 (PN 20d, C–Diii) are represented in IF images. Pax7 (green) alone is shown in A, B, C, and D, and combined with DAPI (blue) and laminin (red) in the merged images Ai, Bi, Ci, Di. EdU (red) alone is represented in Aii, Bii, Cii, Dii and combined with Pax7 (green) in merged images Aiii, Biii, Ciii, Diii, arrows indicate nuclei labeled with both EdU and Pax7 while arrowheads are Pax7 positive nuclei that show no EdU label. (E–G) Numbers of SCs normalized to total myofibers per image is quantified for PN 10d, 12d, 14d, and 20d Wt or TEAD1-Tg TA sections (E). Fold increase in SC numbers in TEAD1-Tg TA sections compared to Wt was quantified for PN 10d, 12d, 14d, and 20d (F). Fold increase in percent EdU positive SCs in TEAD1-Tg TA sections compared to Wt was quantified for PN 12d and 20d (G). (H–J) Apoptosis rates of SCs were assessed for PN 14d. Representative images for Wt (H) and TEAD1-Tg muscle (I) show Pax7 (green) and TUNEL (red) stained nuclei (blue). Percent of SCs that were TUNEL positive or negative was quantified (J). n > 3 mice for all measurements, p<0.05 represented by (*), p<0.005 represented by (**), p<0.0005 represented by (***).