Fig. 6. Ngn1 is redundant with Mash1 for the determination of a subset of olfactory sensory neuron progenitors. Expression of the pan-neuronal marker SCG10 (A-A''',C-C''') and of the progenitor and neuronal marker Ebf1 (B-B''') in the OE (A-A''') and the vomeronasal organ (C-C''') of wild-type (A-C), Mash1 mutant (A'-C'), Ngn1 mutant (A''-C''), and Mash1, Ngn1 double mutant (A'''-C''') embryos at E12.5. Subsets of OSNs differentiate in the absence of Mash1 or Ngn1 function (A',A'',B',B''), while in the absence of both genes, Ebf1-positive progenitors and SCG10-positive OSNs are completely missing (A''',B'''). In contrast, some OSNs persist in the VNO of Mash1, Ngn1 double mutants (C'''). Expression of the Notch ligand Dll1 (D-D''') and the Notch effector Hes5 (E-E''') in wild-type (D,E), Mash1 mutant (D',E'), Ngn1 mutant (D''-E'') and Mash1, Ngn1 double mutants (D'''-E''') in E10.0 olfactory placodes. Dll1 is expressed in isolated cells and Hes5 in cell clusters in wild-type and single mutant placodes, while expression of the two genes is missing in Mash1, Ngn1 double mutant placodes (D''',E'''), indicating that Mash1 and Ngn1 have redundant functions in the determination of placodal progenitors. Scale bars, 25 µm (A-A''',B-B''',C-C'''); 50 µm (D-D''',E-E''').