Control of Neural Stem Cells Figure 1. Activated Hh pathway leads to neocortical defects in Ptc1Lox/Lox;NestinCre dorsal brain. In situ hybridisation on E14.5 sagittal sections demonstrating that both Ptc1 (A, B, Ai, Bi) and Gli1 (C, D, Ci, Di) transcripts are upregulated in VZ of Ptc1Lox/Lox;NestinCre neocortex compared to wild type Ptc1Lox/Lox littermate. (Ai–Di): shows a higher magnification of the wild type and mutant neocortex in A–D (boxed area). E: Taqman RT-PCR for detection of total Ptc1 transcript in microdissected VZ of wild type and mutant neocortex. The expression of Ptc1 was upregulated in E14.5 Ptc1Lox/Lox;NestinCre VZ compared to Ptc1Lox/Lox VZ, due to negative feedback mechanism. The data was normalised based on the expression of Gapdh and is presented as three independent pooled samples of each genotype. (F, G): Haematoxylin and Eosin stained coronal sections of E14.5 neocortex. Ptc1Lox/Lox;NestinCre neocortex is extensively folded and GE are distorted compared to Ptc1Lox/Lox (F). The regions of thickened neuroepithelium in the mutant are not consistent even in the same rostral/caudal plane (arrows) with regions of normal thickness also present (arrowheads). Scale bars (A–D, F–G), 100 mm; (Ai–Di), 50 mm. Abbreviations: CP, choroid plexus; GE, ganglionic eminence; LV, lateral ventricle; NC, neocortex; VZ, ventricular zone. doi:10.1371/journal.pone.0014680.g001 cortical VZ neural progenitors at low levels that are sufficient to reduce the Hh pathway activity and a consequence of Ptc1 inactivation is the generation of a robust physiological cell- autonomous Hh response. Defects were observed in dorsal forebrain and midbrain development in Ptc1Lox/Lox;NestinCre embryos beginning at E11.5 (data not shown). In E14.5 Ptc1Lox/Lox;NestinCre embryos, the neocortex, hippocampus, medial pallium and the ganglionic eminences were distorted. In contrast to the smooth surface of the Ptc1Lox/Lox neocortex (Fig. 1F), the neuroepithelial surface of the Ptc1Lox/Lox;NestinCre neocortex (Fig. 1G) was extensively irregular and folded. This results in regions of decreased cortical thickness and regions of folding. This irregularity was apparently not associated with differences in the rostral/caudal positioning (Fig. S2A–F). PLoS ONE | www.plosone.org 4 February 2011 | Volume 6 | Issue 2 | e14680