Fig. 2. Functional redundancy between Lrp5 and Lrp6 in the limb. (A-C) Dorsal views of skeletal preparations of 18.5 dpc forelimbs stained with Alizarin Red showing regions of ossification in Lrp5^+/- (A), Lrp5^-/- (B) and Lrp5^+/-;Lrp6^+/- (C) littermates. Arrows show ossification centers in the phalanx that are lost in Lrp5^-/- and Lrp5^+/-;Lrp6^+/- forelimbs. (D,E) Ventral views of adult forelimbs showing loss of a post-axial digit (arrow) in Lrp5^+/-;Lrp6^+/- mice (E) compared with a wild-type littermate (D). (F,G) Side views of newborn pups showing normal limbs (F) compared with defects in a Lrp5^-/-;Lrp6^+/- mutant littermate (G). (H-M) Skeletal preparations of newborn limbs stained with Alizarin Red and Alcian Blue to indicate bone and cartilage formation, respectively. Lrp5^-/-;Lrp6^+/- forelimbs (I,J) and hindlimbs (L,M) show severe defects compared with a wild-type forelimb (H) and hindlimb (K). The mutant forelimb in I is from the newborn pictured in G.