Conservation between human and mouse circRNAs. (A) Analysis of enrichment in circRNAs from human orthologs of mouse genes for which circRNAs were found. Only the mouse genes that had one-to-one human orthologs were considered. (B) Extent to which mouse circRNAs align with human circRNA loci. (C) An example of conserved circRNAs, which derives from human PHF21A and mouse Phf21a loci. (D) Relationship between average circular fractions observed for circRNAs conserved in human and mouse (n = 130). Spearman’s rank correlation coefficient is shown. (E) Sequence conservation for the conserved circRNAs, compared with that of their neighboring exons. Distributions are of average mammalian phyloP scores for each of the three codon positions in circular exons and their neighboring linear exons. No significant difference was observed at any of the three positions (P > 0.1, paired Mann-Whitney test).