The first two waves of sensory neurogenesis depend on β-catenin. (A, E, I, L) Illustration of a transverse section at E9 and E10.5, respectively, displaying cells, which contribute to the DRG in red. Green box represents caption area for subfigures B-D, F-H, J-K and M-N, respectively. (B-D, G-H) Double immunohistochemistry for β-gal expressed by the R26R reporter and the sensory neurogenesis transcription factors Neuog2 at E9 or Neurog1 at E10.5, respectively. (B’-D’) Migrating DRG progenitors do not express Neurog2 in either of the two mutant types. (F’-H’) Whereas βcat-Null R26R animals lose expression of Neurog1 in DRG progenitors, progenitors of βcat-Sig R26R animals maintain expression of Neurog1. (J-K, M-N) Double immunohistochemistry for β-gal expressed by the BAT-gal Wnt-reporter and the sensory neurogenesis transcription factors Neurog2 at E9 or Neurog1 at E10.5 as well as Sox10 at both stages, respectively. (J’-J”, K’-K”, M’-M”, N’-N”) corresponding single fluorescence channels of the sections shown in J, K, M and N, respectively. Arrows indicate double positive cells, arrowheads indicate BAT-gal-negative cells within the stained subpopulations. (O) Quantification of Neurogenin-positive cells per R26R-positive cells contributing to the DRG at E9 and E10.5 show an almost complete loss of Neurog2 in both mutants at E9 and a significant reduction of Neurog1 in the βcat-Null R26R mutant at E10.5. (P) Percentage of BAT-gal-positive cells in the subpopulations of DRG precursors shows that only small fraction of the Neurog1 population express BAT-gal, in comparison to the other subpopulations. NT, neural tube; Dashed lines frame in vivo fate mapped cells, * indicates P <0.05; Scale bars: 25 μm. DRG, dorsal root ganglia; E, embryonic day.