Figure 3.
Cortical preplate neurons lose dorsal characteristics and acquire ventral properties in Ngn mutants. (A–D) Distribution of SCG10 transcripts on frontal sections of E12.5 wild-type and Ngn mutant telencephalon. SCG10+ neurons are found in the telencephalic PP of wild-type embryos (A), Ngn1 mutants (B), Ngn2 mutants (C), and Ngn1;Ngn2 double mutants (D). (E–L) Distribution of Tbr1 transcripts (E–H) and Math2 transcripts (I–L) on frontal sections of E12.5 wild-type and Ngn1 mutant telencephalon, revealing a strong reduction in the expression of these dorsal-specific markers by postmitotic neurons of the dorsal and medial cortex in Ngn2 mutants (arrows, G and K, respectively) and in lateral cortex of Ngn1;Ngn2 double mutants (arrows, H and L, respectively). (M–P) Distribution of Dlx1 transcripts on frontal sections of E12.5 wild-type and Ngn mutant telencephalon. This ventral marker is ectopically expressed by PP neurons in the dorsal cortex of Ngn2 mutant embryos (arrow, O) and in the dorsal and lateral cortex of Ngn1;Ngn2 double mutant embryos (arrow, P). (Q,R) Expression of Dlx1 in the telencephalon of E13.5 wild-type (Q) and Ngn2 mutant (R) embryos, demonstrating that the ectopic expression of Dlx1 has expanded to the medial and lateral cortex in Ngn2 mutant at this stage (arrow, R). (S–V) Expression of Dlx5 (S,T) and GAD67 (U,V) in the telencephalon of E13.5 wild-type and Ngn2 mutant embryos, demonstrating that these genes are also ectopically expressed in Ngn2 mutant cortex at this stage (arrow, T and V, respectively). High-magnification views of Math2 (purple) and Dlx1 (orange) expression in the dorsal cortex of E13.5 wild-type (W) and Ngn2 mutant (X) embryos. Math2 and Dlx1 are not coexpressed in the Ngn2 mutant cortex, indicating that mutant PP neurons adopt either a dorsal or a ventral fate. The same mis-specification of cortical neurons was observed in Ngn2neo and Ngn2lacZKI homozygous mutants.