To further confirm that the regulation of circPOLR2B by YTHDC1 is mediated by m6A methylation, dot blot assays were performed and revealed that, compared with that in HA, the m6A methylation level of circRNAs in GBM cells increased and the upregulation was more distinct in GSCs, indicating that m6A modification of circRNAs may widely exist in GBM cells and GSCs (Fig. S3F). The gene discussed is YTHDC1; the disease is glioblastoma.