Fig. 4. Rspo2 and Lrp6 interact during morphogenesis of the limbs. Alcian Blue and Alizarin Red stained E18.5 right forelimbs (A-F) and left hindlimbs (G-L). Asterisks in A-D and G-J indicate absence of digits. Arrowheads in A and C indicate absence of a radius. Arrow in C indicates malformation of the humerus. Arrowhead in G-I indicate absence of the fibula. Arrow in I indicates absence of the femur.