Fig. 1. Meox1;Meox2 mutants have profound axial skeleton defects. Alcian Blue/Alizarin Red skeletal preparations of neonates. The forelimbs and shoulder girdle have been removed for ease of viewing. In contrast to control littermates (Meox1^+/-;Meox2^+/- A and E, n>6), animals with mutations in both Meox1 and Meox2 genes have defects in the development of the axial skeleton (B-H, n>6). Meox1^-/-;Meox2^+/- display rib fusions and deformations, and vertebral bodies at the lumbar level are split, and tail vertebrae are fused (B,F). Meox1^+/-;Meox2^-/- are less severely affected, there are no rib defects and lumbar vertebrae appear normal, but tail vertebrae are malformed and fused (C,G). Meox1^-/-;Meox2^-/- animals lack an axial skeleton (D,H), there are no ribs and, while ossified, deformed vertebrae are formed at the cervical and thoracic level; more posterior lumbar vertebrae are present only as cartilage condensations at the position expected of the neural arches (arrow in H) and tail vertebrae are completely absent. The sternum develops, albeit abnormally, in the absence of the ribs (arrowhead in D). Normally developed neural arches (na) and vertebral bodies (vb) are identified in E.