Fig. 4. Malformations of proximal but not distal appendicular skeletal structures in Pbx1^-/- embryos. (A) Immunohistochemical analysis using anti-Pbx1b (Pbx1b) or anti-Meis (Meis) antibodies on transverse sections of limb buds from E11.5 wild-type and Pbx1^-/- embryos. Diffuse nuclear expression (brown) of Pbx1b and Meis is detected in superimposable domains confined to the proximal limb buds of wild-type embryos. In limb buds of Pbx1^-/- embryos, both nuclear and cytoplasmic expression of Pbx1b is absent, while Meis protein expression is unperturbed. (B) Skeletal structures in right forelimb of wild-type (left) and Pbx1^-/- (right) E16 embryos. The morphologies of the limbs with associated scapulae and clavicles dissected free from embryos are shown in lateral views. In the Pbx1^-/- embryo, there is hypoplasia of the superior scapular border (1), acromial spine and process (2), and coracoid process (3). The clavicle is shortened and attenuated (4). The humerus is shorter, distorted and thinned proximally; its head is fused to the glenoid cavity (5) and coracoid process (3) and continuous with the inferior border of the scapula (7). The cartilaginous core of the deltoid tuberosity is nonconjoined (6). The cartilages of the distal forelimb are spared. acromial process, ap; acromial spine, as; coracoid process, cp; clavicle, cv; deltoid tuberosity, dt; glenoid process, gf; humerus, h; humeral head, hh; manus, ms; radius, r; scapula, scp; ulna, u. (C) Lateral views show the morphology of the pelvic girdle, with malformed and rudimentary ilium (2), ischium (3) and pubis (4), in the Pbx1^-/- hindlimb (right). The os coxae-femur articulation (1) is fused. The hindlimb malformation also affects the femur, which is shorter and distorted proximally (5) in the Pbx1^-/- embryo, while the cartilaginous structures of the distal hindlimb are spared. acetabular fossa, af; femoral head, fh; femur, f; fibula, fl; greater trocanter, gt; ilium, il; pubis, pb; pes, ps; patella, pt; tibia, t.