Fig. 1. Impaired development of Th-positive mesDA neurons in Ngn2 mutant mice. (A-C) In the VM Ngn2 (red) was expressed in part of the VZ lying immediately above the Nurr1-expressing mesDA neuron precursors (green, A). A few single Ngn2-positive cells were seen to co-express Nurr1 (arrow, B,C). (D-I) At E11.5-E15.5, the number of Th-positive cells in the VM was dramatically reduced, by approx 90%, in the homozygous (–/–) Ngn2 mutants (E,G,I), compared with the wild-type (WT, +/+) mice (D,F,H). The remaining Th-positive cells were located at the lateral edges of the mesDA neuron domain, whereas the medial portion was almost completely devoid of Th-positive cells. (J-M) Parallel sections stained for Aadc and Vmat2 showed the same degree of cell loss, with positive cells remaining in the same lateral population. (N,O) At later embryonic stages (E17.5), more Th-positive neurons had been generated in the Ngn2 mutant and the difference between wild type and Ngn2 mutants with respect to both the number and distribution of Th-positive neurons was less pronounced. Scale bars: 50 µm in A; 100 µm in D-O.