Fig. 2. Lmx1a regulates mesDA neurogenesis by inducing proneural factor expression and cell growth in their progenitors. (A) The mesDA number (indicated by Th and Lmx1b expressions) is reduced in dreher mutant embryos compared with wild-type embryos at E13.5, but the fate of Lmx1a⁺ neurons is not affected. The intensities of anti-Th and anti-Lmx1b staining were lower in dreher mutants. However, almost all Lmx1a⁺ neurons and neurons generated from ventral midline regions of the mesencephalon, in mutants and wild-type controls, expressed Lmx1b. (B) Neurogenesis in Lmx1a⁺ progenitors is affected by the dreher mutation. The Th⁺ neuron number is severely reduced in dreher mutants at E11.5. Ngn2 and Mash1 expression levels in the Lmx1a⁺ VZ region are reduced and, consistently, the generation of Lmx1a⁺ TuJ1⁺ neurons is less efficient in mutants. Note that reductions in the expression levels of proneural factors are apparent in the medial part of the Lmx1a⁺ domain. (C) Quantification of Lmx1b⁺ neurons in the ventral mesencephalon of wild-type, heterozygous and homozygous dreher mutant embryos at E13.5. (D) Quantification of BrdU-incorporating, Ngn2⁺ and Mash1⁺ cells in Lmx1a⁺ VZ region.