Fig. 2. Skeletal analysis of vertebral patterning defects. Cervical region of whole-mount mouse skeletal preparations from (A) wild-type, (B) LRE^+/-, (C) LRE+RARE^+/-, (D) Cdx1^+/-, (E) RARE^-/-, (F,I) LRE^-/-, (G,J) LRE+RARE^-/- and (H) Cdx1^-/- offspring. Note the C2 to C1 transformations evidenced by a broader C2 neural arch and an ectopic anterior arch of the atlas (^*AAA in C-E). Anterior transformation of C1 was assessed by loss of the anterior arch of the atlas and anterior malposition (C1 arrow in F,G,H) and fusion with the basioccipital bone (small bracket in F,G,I). Anterior transformation of C2, C3 and C7 are denoted "C1", "C2" and "C6", respectively, in F-H as determined by morphological criteria as described in Material and methods. A partial rib associated with presumptive T1, which did not reach the sternum, is indicated by the short arrow (F,H). Fusions between adjacent vertebrae in LRE and LRE+RARE-null mutants are indicated by the long bracket (I,J). AAA, anterior arch of the atlas; ^*AAA, ectopic anterior arch of the atlas; TA, tuberculum anterior; C, cervical vertebrae; T, thoracic vertebrae. Quotation marks indicate presumptive anterior transformations.