Ouro-seq: Improved Recovery of Full-Length circRNAs from Samples with Limited RNA Content Using Short-Amplicon Suppression

Circular RNAs (circRNAs) represent an emerging class of RNAs with potential roles in disease pathogenesis and promising biomarker applications. However, their detection in samples with limited RNA content, such as liquid biopsies, remains challenging due to extremely low abundance. Here, we introduce Ouro-seq, a novel long-read sequencing protocol optimized for full-length circRNA recovery. We applied Ouro-seq to urine and self-sampled cervical swab (CVS) samples from cervical cancer patients and plasma from lung cancer patients and healthy controls. Our approach significantly outperformed conventional methods, recovering 2-5 times more and substantially longer circRNA molecules. Unexpectedly, while plasma samples predominantly contained exonic circRNAs, urine and CVS were dominated by previously under characterized intergenic circRNA. We identified extensive alternative circularization and splicing events. Functional annotation revealed distinct specialization patterns among circRNA subtypes, with exonic circRNAs exhibiting enhanced miRNA sponging potential and circRNAs from unplaced genomic scaffolds showing greater peptide-coding capacity. This study significantly advances our understanding of circRNA biology in liquid biopsies and establishes Ouro-seq as a valuable tool for comprehensive circRNA characterization with potential applications in biomarker discovery and disease monitoring.

• Type: RNASeq
• Archive: European Genome-phenome Archive (EGA)