Fig. 1

The reported exitron in the CD19 exon 2 is a reverse transcription artifact. a Genome browser view showing cDNA-seq and dRNA-seq data for RNA from a patient-derived xenograft (PDX). Junction reads supporting the reported Δex2part product can be observed in cDNA-seq but are absent in the dRNA-seq. b Schematic of the predicted secondary structure and the direct repeats of the putative intron in CD19 exon 2. c Schematic of the eGFP/mCherry-based reporter to detect splicing of the reported CD19 exitron. d RT-PCR assay characterizing the CD19 transcript isoforms for the wild type version and the variants of the reporter shown in panel c. They include two different point mutants predicted to stabilize the putative hairpin (mut+) or disrupt one of the direct repeats (mut−), as well as the control construct wherein the reported exitron has been deleted at the DNA level (exon2part-del). e Flow cytometry-based assay to characterize splicing of the reported exitron in HEK293T cells. f Genome browser view showing the region of CD19 exon 2. cDNA-seq, dcDNA-seq, and dRNA-seq were performed on the same RNA sample from HEK293T cells expressing the mut+ reporter shown in panel c. Several hundred junction reads supporting exitron excision at the direct repeats in the cDNA-seq and dcDNA-seq data are detected, while none are found in the dRNA-seq