Expressed Alu elements show high tissue specificity. (A) Venn diagram showing expressed Alu elements defined using RAMPAGE data in cell lines (red), primary cells (green), and tissues (blue). (B) Histogram showing counts of Alu elements expressed in different numbers of biosamples. Note that Alu elements identified in three or more biosamples were defined as robustly expressed Alu elements (robust Alu elements). (C) Dendrogram resulting from agglomerative hierarchical clustering of tissue biosamples based on their Alu expression. Each leaf of the tree represents one RAMPAGE tissue sample, and subtrees dominated by one tissue type are highlighted. (D) Correlation matrix of expressed Alu elements across libraries belonging to 13 tissues of four individuals. Note that correlations between biosamples in the same tissue but from different individuals are significantly higher than correlations between biosamples from the same individual but different tissues. Wilcoxon rank-sum test P-values are shown.
