Fig. 7. Phenotypes produced by misexpressing HOXD13, HOXD13(I47L) and HOXD13(IQN) in developing chick limbs. Frontal views of stage 32-34 hindlimbs stained with Alcian Blue, showing the injected right limb on the right and the uninjected opposite limb on the left. Ti, tibia; Fi, fibula; t, tibiale; f, fibulare. (A) Embryo injected with RCAS-HOXD13, showing normal phalanges but mild shortening of the proximal cartilages, especially the femur and tibia, resulting in an abnormal articulation between the fibula and fibulare (arrowhead). (B,C) Embryos injected with RCAS-HOXD13(I47L), showing normal phalanges (the embryo in C was the only one out of 38 with a rudimentary extra digit (asterisked), but marked shortening of the proximal cartilages, particularly the tibia, which has a rounded morphology, and extra cartilages in the zeugopod (arrowheads). (D,E) Embryos injected with RCAS-HOXD13(IQN), showing normal phalanges but marked shortening of the proximal cartilages, especially the femur and tibia (again resulting in an abnormal articulation between the fibula and fibulare; upper arrowheads), and also the metatarsals (lower arrowheads).