Fig. 5. Molecular changes in the second branchial arch of conventional and tamoxifen-induced Hoxa2 mutant embryos. (A-L) Whole-mount in situ hybridization on wild-type (A,D,G,J), Hoxa2^–/– (B,E,H,K) and TM-treated Hoxa2^flox/flox;Cre-ERT2 (C,F,I,L) 10.5 dpc embryos using Alx4 (A-C), Bapx1 (D-F), Msx1 (G-I) and Six2 (J-L) antisense probes. Hoxa2^flox/flox;Cre-ERT2 homozygous mutant embryos were collected 24 hours or 12 hours (inset in L) after TM treatment. Arrows show Alx4, Bapx1 and Six2 ectopic expression, as well as Msx1 downregulation in the second arch of both Hoxa2^–/– and TM-treated Hoxa2^flox/flox;Cre-ERT2 mutant embryos. (M-O) Whole-mount in situ hybridization on wild-type (M), Hoxa2^–/– (N) and TM-treated Hoxa2^flox/flox;Cre-ERT2 (O) 11.5 dpc embryos with a Six2 probe. The Hoxa2^flox/flox;Cre-ERT2 mutant embryo in O was treated at 10.5 dpc. Arrows show ectopic expression in the second arch of both Hoxa2^–/– and Hoxa2^flox/flox;Cre-ERT2 embryos. BA1, first branchial arch; BA2, second branchial arch.