During infusion, mice were treated with tamoxifen to acutely label cells in which the Hh pathway was active. YFP labeling in vehicle-infused mice was predominantly ventral, demonstrating that pump installation alone did not alter the pattern of Hh signaling ( Figures 5A and 5E). We observed increased GFAP labeling after all pump implantations, likely due selleck chemicals to increased numbers of reactive astrocytes. Administration of either cyclopamine or 5E1 antibody reduced the number of YFP-positive cells in the ventral SVZ, confirming that YFP labeling was dependent on pathway activation ( Figures 5B, 5C, 5F, and 5G). SAG infusion resulted in a dramatic increase in YFP-positive cells, both GFAP-positive and –negative, in the

ventral SVZ, but did not significantly alter the pattern of YFP labeling in the dorsal SVZ ( Figures 5D and 5H). Infusion of cyclopamine,

5E1, or SAG may also affect SVZ cell survival or proliferation, as suggested by previous experiments in which Smoothened was ablated in the SVZ (Balordi and Fishell, 2007b). Staining for the proliferation marker Ki67 indicated that large changes in proliferation did not occur during the time frame of this experiment. In both controls and SAG-infused animals, we observed small populations of YFP-positive cells in the dorsal SVZ. Most of these cells were GFAP negative and Dcx positive, suggesting that they correspond to young migrating neurons (Figure 5 and data not shown). We cannot exclude Talazoparib nmr that a small subpopulation of Gli1-expressing type B or C cells are present in dorsal regions. The regional difference in Gli1 distribution remains after agonist infusion, suggesting that additional cell-intrinsic factors may affect the ability of dorsal cells to activate Adenosine the Hh pathway. While high Hedgehog pathway activity was required for the production of particular types of neuronal progeny, this observation did not necessarily indicate that Hedgehog signaling had an instructive role in cell fate. To investigate

this possibility, we performed targeted injections of Ad:GFAPpCre virus in SmoM2-YFP; R26R mice ( Mao et al., 2006). The Ad:GFAPp-Cre virus, in which Cre recombinase expression is driven by the murine GFAP promoter, results in recombination in primary progenitors (type B cells) within this region ( Merkle et al., 2007). In these animals, Cre-mediated recombination causes the expression of SmoM2, a constitutively active mutant of Smo, and activation of the Hh pathway. By injecting Ad:GFAPpCre in the dorsal SVZ of SmoM2-YFP; R26R animals, we activated the Hh pathway to high levels in a ligand-independent, cell-intrinsic fashion while simultaneously labeling these cells with β-galactosidase. This allowed us to follow the labeled progeny of these infected stem cells. Remarkably, while expression of the SmoM2 protein is sufficient to drive rapid tumorigenesis in other contexts ( Schüller et al.