Fig. 8. mRNA in situ hybridization at E9.5 demonstrates loss of Tbx1 expression in the core of the first and second arch in mutant (B) when compared with control (arrows A). In addition there was no expression in the area of the third arch artery (arrowheads, compare A with B). Expression of dHAND was maintained or expanded in Fgf8 mutants (D,F) compared with wild type (C,E). Frontal view of first arch reveals possible expansion of dHAND in Fgf8 mutants (G,H). Expression of Dlx2, (I,J) Msx1 (K,L) and Gli1 (M,N) were reduced or absent in the arches (arrows), particularly in PA2 with very distal sparing in PA1.