Gene expression profiles during RA-mediated differentiation. Gene expression levels were examined at six time points (0 h, 6 h, 1 day, 2 days, 3 days and 5 days) after addition of RA to each neuroblastoma culture. Heat map representation of genes differentially expressed in the indicated cell lines stimulated with RA is shown in the presence or absence of a PI3K inhibitor. Genes are clustered according to hierarchical clustering with Pearson’s correlation. A colour-coded scale (green, down-regulation; red, up-regulation) for percentage expression is indicated at the top of the figure. Cluster A includes genes that were down-regulated by LY294002 in RA-treated SH-SY5Y-A cells. Genes in the cluster were further classified into two subgroups: neural genes; and genes related to other functions. Genes selected in Figure 6 are marked in blue on the right side of the heat map of cluster A.