Fig. 4. Ngn1 function is required for the expression of a subset of transcriptional regulators expressed in basal progenitors. Expression of NeuroD (A-A''), Phd1 (B-B''), Ebf1 (C-C'') and Lhx2 (D-D'') analysed by in situ hybridisation on sections of wild-type (A-D), Mash1 mutant (A'-D') and Ngn1 mutant (A''-D'') OE at E12.5. In wild-type OE, NeuroD is expressed in basal progenitors and only transiently in differentiating neurons (A) (Cau et al., 1997), while Phd1, Ebf1 and Lhx2 are expressed both in dividing basal progenitors and in post-mitotic OSNs (B-D; data not shown). Expression of the four genes is abolished in Mash1 mutants OE (because of the loss of both basal progenitors and post-mitotic neurons in these mutants) except in restricted areas that maintain neurogenesis (A'-D'). In contrast, expression of Ebf1 and Lhx2 is maintained in basal progenitors in Ngn1 mutant OE (C'',D''), while expression of NeuroD and Phd1 is missing (A'',B''). Ebf1 is also expressed in the mesenchyme surrounding the OE. Scale bar, 25 µm.
