Heatmaps of enrichment of the binding motifs of activator TFs across nine cell types and four regions. Shading indicates log2 enrichment of motifs in sequences of the specified cell and region. (Clustering was done using SE DHS motifs). To improve visualization of the heatmaps, the original set of motifs is pruned through a strategy that includes removing any motifs for which the corresponding TF fails to be significantly expressed in any of the nine cell types. This pruning strategy reduces the motif set to primarily include motifs of activator and master factors. The remaining motifs are clustered and ordered by exemplar-based agglomerative clustering on the log2 enrichment values across the nine cell types (“Methods”). Groups or families of motifs are manually labeled on the left side. Black boxes highlight cell-specific motif enrichment clusters.