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5?ml/well) [http://www.selleckchem.com/products/BIBW2992.html Selleck BIBW2992] uncoated plates (Nunclon) in sphere-forming medium containing either 10?ng/ml FGF2 (human recombinant; Sigma) or 10?ng/ml EGF (mouse submaxillary; Sigma). After a week in vitro, the number of neurospheres was counted as an in vitro index of the in vivo neural progenitor cell population. Capacity of the neural progenitors to self-renew and expand in vitro was established by first passaging the free-floating primary neurospheres, then dissociating the spheres into single cell suspensions at a density of 50?cells/��l, and finally reculturing the cells for 1?week to form secondary neurospheres. The activity of tertiary sphere formation was also examined as described. Spheres?>?200?��m in diameter and [http://www.selleckchem.com/products/BKM-120.html NVP-BKM120 cell line] were performed to calculate P values. To evaluate the effect of Shh on neural progenitors during late gestational stages, we investigated those cell lineages responsive to endogenous Hh signaling using an inducible genetic labeling system (Ahn and Joyner, 2005?and?Yu et al., 2009). Analysis of LacZ activity at E14.5 revealed that early onset (E11.5) Hh-responsive cell lineages develop into the VZ and SVZ proliferating cells in the LGE and MGE (Figs. S1A-D). Late-onset (E12.5 and E13.5) Hh-responsive lineages were also observed in the ventral telencephalon (data not shown), while no contribution of lacZ-expressing cells was observed in the cortex (data not shown). Consistently, Ptch1-lacZ expression was not detected in the cortex, but was present in the LGE and MGE ( Figs. S1E,F). These results suggest that high levels of endogenous Hh signaling affect only neural progenitors in the LGE and MGE. To then evaluate the role of endogenous Shh signaling [http://en.wikipedia.org/wiki/SWAP70 SWAP70] during cortical development, we observed cortical neural progenitors in the Shh?/? telencephalon at E13.5. Although relatively normal cortical layer patterning has been observed previously in Shh?/? telencephalon ( Rash and Grove, 2007), defects in neural progenitor development have not yet been characterized. We checked the proliferation of cortical IPCs expressing T-brain gene-2 (Tbr2) protein in the mutant cortex. Tbr2 is specifically expressed in IPCs of the developing cortex and is required for the specification of IPCs ( Sessa et al., 2008). In the thicker and smaller cortex of Shh?/? mutants, the total number of Tbr2-expressing (Tbr2+) cells was significantly reduced ( Figs.?1A,B,E), although the density of Ki67-expressing (Ki67+) cells per counting area in the Shh?/? cortex was not significantly different from wild-type cortex ( Figs.?1A,B, data not shown). Notably, the mutant VZ showed an obvious reduction in mitotic Tbr2+ cortical IPCs (Ki67+ Tbr2+ cells) ( Figs.?1A�CD,F). These results suggest that VZ progenitors can develop to Tbr2+ IPCs without Shh signal inputs.