circRNA enrichment occurs in platelets but not megakaryocytes. (A-D) Adapted University of California Santa Cruz screen shots for 4 genes with extreme circRNA enrichment in platelets. Each panel shows RNAseq read abundance in a single platelet total RNA sample (F1), together with the position and abundance of back-splice exon junctions in the same sample. The intron-exon structure is shown below, with exons known to contribute to circRNAs shown in red. CircRNA structures present in the sample together with back-splice frequencies are also shown (for PHC3, only structures with ≥10 back-splice reads are shown). Above each panel, the gene names, cytogenetic locations, coding strand, and scale in kilobases are indicated. (E-F) Expression levels of circRNAs relative to linear RNAs from the same loci in platelets and cultured megakaryocytes, normalized to the housekeeping pool (−∆∆CT values).