The gene sets constituting pathways relevant to neuronal development and differentiation were retrieved from Molecular Signatures Database (MsigDB 3.0, C2 & C5) [33]. Each pathway-specific data set was analyzed by hierarchical average-linkage clustering. The clustering was performed using Gene Cluster 3.0 (http://bonsai.ims.utokyo.ac.jp/~mdehoon/software/cluster/) or using R programs.