Figure 3.

In the limb Pax3⁺ somitic cells, but not Pax7⁺ somitic cells are required for embryonic myogenesis, while Pax7⁺ cells are required for fetal myogenesis. (A–C) E12.5 Pax3^Cre/+;R26R^DTA/+ hindlimb sections show a complete loss of Pax7⁺ progenitors (A), MyoD⁺ myoblasts (B), and myosin⁺ myofibers (C), indicating a complete loss of embryonic limb myogenesis when Pax3⁺ cells are ablated. (D,E) E14.5 Pax7^iCre/+;R26R^DTA/+ hindlimb sections show a normal pattern of embryonic MyoD⁺ myoblasts (D) and myosin⁺ myofibers (E) when Pax7⁺ cells are ablated. P0 Pax7^iCre/+;R26R^DTA/+ shank cross-section shows a basic muscle pattern (H,I), but muscles contain fewer laminin⁺ myofibers with a higher proportion of slow myosin⁺ myofibers compared with control Pax7^iCre/+;R26R^+/+ sections (F,G).