A search for additional circRNAs with the expected properties of miRNA sponges. (A) Frequency of AGO2-crosslinking clusters observed in circRNAs compared with that of clusters observed in their neighboring exons (left). See Figure 4E for color keys. For comparison, the analysis was repeated for a negative control, IGF2BP1 (right). No significant difference was observed between circular exons and their neighboring exons (P > 0.1, paired Mann-Whitney test). (B) Numbers of AGO2-crosslinking clusters assigned to individual miRNA families. The number of crosslinking clusters was tallied for each circRNA-miRNA pair, and the distribution of values is plotted. The outlying CDR1as-miR-7 pair is indicated. (C) Numbers of 7- and 8-nucleotide sites for individual miRNA families found within each circRNA. The number of sites was tallied for each circRNA-miRNA pair, and the distribution of values is plotted. The black curve indicates the averaged results when repeating the analysis 1,000 times using different permutations of the site sequences. The two outlying pairs are indicated. (D) Numbers of miRNA target sites in CDR1as and top-ranking ZNF circRNAs. (E) Part of the ZNF91 locus containing the circRNA. miR-23 and miR-296 seed matches are indicated.