Fig. 2. Facial motor neuron specification is normal in Tbx20 conditional mutants. Gene expression profile analysis in transverse sections at r4 (A-N) or flat-mounted hindbrains (O-R). (A,B) Tbx20 cKO mutant mice lack Tbx20 protein in the neural tube. (C,D) Tbx20-null cells are viable and detected by their expression of the non-functional Tbx20 transcript. (E-N) Hoxb1, Math3, Mash1, Isl1, Nkx6.1 and Phox2a are expressed normally in Tbx20 mutants. (O,P) Gata2 expression is normal in Tbx20 mutants, although medial GATA2 labeling in r4 is reduced (dashed line marks the r4/r5 border). (Q,R) Phox2b expression (bracketed) is confined to r4 in Tbx20 mutants, whereas controls exhibit labeling in r4 and r5. The altered Phox2b labeling pattern indicates a cell migration defect. Data are representative of at least twelve sections from at least three embryos of each genotype. Scale bars: in B, 40 µm for A,B; in L, 80 µm for C-L; in N, 160 µm for M,N; in R, 300 µm for O-R.