high levels of Shh signaling factors, 74.5 ± 9.4 % of cells were NKX2-1+ compared with 65.2 ± 6.2% in cultures treated with low levels of Shh, though this difference was not statistically significant (Figure 1C). Telencephalic specification was equivalent between conditions, as FOXG1 expression levels were 86 ± 2.8% and 85 ± 1.0% in high and low Shh conditions, respectively (Figure 1F). No NKX2-1+, FOXG1− cells were observed in our cultures and there was no difference in terms of the percentage of SST+ cells or intrinsic factors that would bias these cells to either a dorsal or ventral MGE identity between Shh levels (data not shown) (Flames et al., 2007). However, in 30% of experiments treated with higher levels of Shh agonists, cultures detached from the plate after D24. Since the conditions were otherwise comparable, cultures treated with low levels of Shh signaling factors were used.
