Extensive and heterogeneous viral circular RNA production during Zika virus infection

Circular RNAs (circRNAs) are covalently closed RNA molecules with regulatory functions. Although virus-derived circRNAs (vcircRNAs) are well characterized in DNA viruses, their occurrence in RNA viruses remains poorly understood. Recent reports in coronaviruses and hepatitis C virus suggest that vcircRNA production extends beyond nuclear-replicating viruses. Here, we show that Zika virus (ZIKV), a vector-borne orthoflavivirus, produces vcircRNAs during infection of neural stem cells. Using a custom computational pipeline optimized for viral back-splice junction detection, we identified at 72 hours post infection a core set of 113 putative vcircRNAs shared across three biological replicates and distributed throughout the viral genome. Eight candidates spanning different genomic regions and abundance levels were experimentally validated by rolling-circle reverse transcription and Nanopore sequencing. These findings provide the first evidence of vcircRNA production in an orthoflavivirus, suggesting that circular RNA biogenesis may represent a previously underappreciated feature of RNA virus biology.