Fig. 4. Altered expression of Ap-2 in the premigratory neural crest of Msx1/2 mutant embryos. (A-F) Whole-mount in situ hybridization analysis of pharyngeal arch development. Ap-2, Dlx5, and Twist expression was unaltered in pharyngeal arches in Msx1/2 mutant embryos (B,D,F) compared with controls (A,C,E). (G,H) Wnt1-Cre/R26R neural crest lineage tracer analysis at E9.5. There was no gross deficiency of neural crest in Msx1/2 mutants (H). Cardiac neural crest cells emigrate into the outflow tract (oft) in both control (G) and mutant (H). Reduced ß-galactosidase staining was evident in the peripharyngeal region (bracket) and in the stream of neural crest from r6 and r7 (arrowhead) in the mutant embryo. These differences may be due to the delayed timing of crest migration. (I-P) Analysis of premigratory and migratory neural crest development. Enlarged views of squares in I,J,M and N are shown in K,L,O and P. Expression of Ap-2 was significantly reduced in the neural fold caudal to the preotic sulcus in the mutant (arrowheads in L,P). (Q-T) In wild-type, the expression of Msx1 and Msx2 overlapped with that of Ap-2 at E8.5. pos, preotic sulcus; br1, first pharyngeal arch; br2, second pharyngeal arch. Scale bars: in B (for A,B), D (for C,D), F (for E,F), H (for G,H), J (for I,J), N (for M,N), S (for Q-T), 0.2 mm; in L (for K,L), P (for O,P), 0.1 mm.