Fig. 5. Immunostaining of proneural transcription factors in the olfactory epithelia of normal embryos at E18.5 (A-C), and of mice with inactivation either of the Wt1(-KTS) (D-F) or the Wt1(+KTS) (G-I) splice variant. Expression of the mammalian homologue of achaete-scute complex, Mash1 (Ascl1), was reduced in the olfactory epithelia of Wt1(+KTS)-deficient mice (G). The basic helix-loop-helix transcription factor neurogenin1, which is activated by Mash1 (Cau et al., 1997), was detected in fewer olfactory epithelial cells in embryos with lack of the Wt1(+KTS) product (H) compared with wild-type (B) and Wt1(-KTS)-deficient (E) mice. By comparison, only subtle differences in the expression of Pou4f1 were detectable between the different groups (E,F,I). Scale bars: 50 µm.