Shox2 deficiency results in shortened limbs. Alizarin red (bone, red) - Alcian blue (cartilage, blue) staining on E16.5 WT (A) and Shox2 mutant (B) embryos revealed a severe shortening of Shox2 mutant fore-(D) and hindlimbs (F) compared to the wildtype (C, E). The proximal skeletal elements humerus and femur are particularly affected and show no ossification (arrows). The more distal parts of the Shox2−/− limbs (radius, ulna, tibia, and fibula) are only slightly shortened compared to the wildtype. h, humerus; r, radius; f, femur; fi, fibula; t, tibia; u, ulna.