Fig. 9.

Scheme of the divergent genetic systems that control the Hand2-Shh morphoregulatory system and the proximal skeleton in fore- and hindlimb buds. (A) Axial Hox9 genes regulate the Hand2-Shh pathway during initiation of forelimb bud development. The present study reveals the hindlimb-specific regulation of the common Hand2-Shh pathway by Islet1. (B) A forelimb-field specific gene, Tbx5, is required for development of the shoulder girdle. The present study reveals that development of different segments of the pelvic girdle is controlled by either Islet1 or Pitx1.