Circular RNAs of human blood cells, plasma, and plasma subfractions

Abstract

Circular RNAs (circRNAs) are a novel class of regulatory noncoding RNAs with the closed structure of a phosphate–ribose chain. Here, we searched for the characteristic sequences of exon–exon junctions of circular RNAs in high-throughput sequencing data of RNA from human blood cells, plasma, and plasma subfractions. Eighty-eight characteristic junctions of circular RNAs’ exons were identified, eight of which are related to fragments of previously unannotated novel circular human transcripts. The set of 88 circular RNAs identified in human blood was enriched with transcripts of genes encoding transcription factors and proteins involved in biogenesis and transport of membrane vesicles. RT-PCR analysis of circular RNA content in human blood plasma subfractions revealed full-length circular transcripts mostly in fractions of blood plasma membrane particles, such as microvesicles and exosomes. Our results and previously published data suggest that extracellular circular RNAs may be regulators of fundamental cellular processes. The results can be used for the development of novel methods of low invasive diagnostics of human diseases.