Induro-RT mediated circRNA-sequencing (IMCR-seq) enables comprehensive profiling of full-length and long circular RNAs from low input total RNA.

Circular RNA (circRNA) has recently gained attention for its emerging biological activities, relevance to disease, potential as biomarkers, and promising an alternative modality for RNA vaccines. Nevertheless, sequencing circRNAs has presented challenges. In this context, we introduce a novel circRNA sequencing method called Induro-RT mediated circRNA-sequencing (IMCR-seq), which relies on a group II intron reverse transcriptase with robust rolling circle reverse transcription activity. The IMCR-seq protocol eliminates the need for conventional circRNA enrichment methods such as rRNA depletion and RNaseR digestion yet achieved the highest circRNA enrichment and detected 6-1000 times more circRNAs for the benchmarked human samples compared to other methods. IMCR-seq is applicable to any organism, capable of detecting circRNAs of longer than 7000 nucleotides, and is effective on samples as small as 10 ng of total RNA. These enhancements render IMCR-seq suitable for clinical samples, including disease tissues and liquid biopsies. We demonstrated the clinical relevance of IMCR-seq by detecting cancer-specific circRNAs as potential biomarkers from IMCR-seq results on lung tumor tissues together with blood plasma samples from both a healthy individual and a lung cancer patient. In summary, IMCR-seq presents an efficient and versatile circRNA sequencing method with high potential for research and clinical applications.