Figure 8 .

Neurog1 ^−/− and Neurog1/2 ^−/− olfactory sensory neurons express mature markers but fail to innervate olfactory bulb. (A) to (H) Coronal sections of the embryonic day (E) 18.5 OB showing expression of GAP43 (red, A to D) and OMP (green, E to H) with DAPI (blue, A to H) in wild-type (A,E), Neurog1^−/− (B,F), Neurog2^KI/KI (C,G) and Neurog1/2^−/− (D,H) embryos. Yellow arrows denote loss of OSN innervation of the OB in Neurog1^−/− and Neurog1/2^−/− (B,D,F,H) embryos. (I) to (T) Expression of odorant receptors L45 (I) to (L), M72 (M) to (P) and P2 (Q) to (T) in E18.5 wild-type (I,M,Q), Neurog1^−/− (J,N,R), Neurog2^KI/KI (K,O,S) and Neurog1/2^−/− (L,P,T) embryos. Note that the lack of an apparent OB in Neurog1^−/− sections is because the OB is shortened along the proximodistal axis, and hence does not fill the rostral-most part of the cavity in the skull, where OR expression levels are the highest (J,N,R). GAP43, growth-associated protein 43; OB, olfactory bulb; OE, olfactory epithelium; OMP, olfactory marker protein; OSN, olfactory sensory neuron. Scale bars: 500 μm (A) to (T).