Figure 1.

Individual Muscle Bundles Form through Progressive Series of Steps

Dorsal view of control forelimbs from E10.5 (A) to E14.5 (M) embryos. Muscle progenitors are detected by in situ hybridization for MyoD (A) or Myogenin (B, C, G, H, and I) and immunohistochemistry to detect Myosin (E, F, J, K, L, and M). The limbs are oriented from proximal to distal as shown in the schematic E12.5 forelimb (D). Arrow in (C) shows an area devoid of myogenin positive cells. Arrow in (F) represents the beginning of myocyte fusion. Individual muscles are identified and listed in (M).