Segment-Specific Kinetics of mRNA, cRNA, and vRNA Accumulation during Influenza Virus Infection

Abstract

ABSTRACT Influenza A virus (IAV) is a segmented negative-sense RNA virus and is the cause of major epidemics and pandemics. The replication of IAV is complex, involving the production of three distinct RNA species, namely mRNA, cRNA, and viral RNA (vRNA), for all eight genome segments. While understanding IAV replication kinetics is important for drug development and improving vaccine production, current methods for studying IAV kinetics have been limited by the ability to detect all three different RNA species in a scalable manner. Here, we report the development of a novel pipeline using total stranded RNA sequencing (RNA-Seq), which we named influenza virus enumerator of RNA transcripts (InVERT), that allows for the simultaneous quantification of all three RNA species produced by IAV. Using InVERT, we provide a full landscape of the IAV replication kinetics and found that different groups of viral genes follow different kinetics. The segments coding for RNA-dependent RNA polymerase (RdRP) produced more vRNA than mRNA, while some other segments (NP, NS, and hemagglutinin [HA]) consistently made more mRNA than vRNA. vRNA expression levels did not correlate with cRNA expression, suggesting complex regulation of vRNA synthesis. Furthermore, by studying the kinetics of a virus lacking the capacity to generate new polymerase complexes, we found evidence that further supports a model in which cRNA synthesis requires newly synthesized RdRP and that incoming RdRP can only generate mRNA. Overall, InVERT is a powerful tool for quantifying IAV RNA species to elucidate key features of IAV replication. IMPORTANCE Influenza A virus (IAV) is a respiratory pathogen that has caused significant mortality throughout history and remains a global threat to human health. Although much is known about IAV replication, the regulation of IAV replication dynamics is not completely understood. This is due in part to both technical limitations and the complicated replication of the virus, which has a segmented genome and produces three distinct RNA species for each gene segment. We developed a new approach that allows the methodical study of IAV replication kinetics, shedding light on many interesting features of IAV replication biology. This study advances our understanding of the kinetics of IAV replication and will help to facilitate future research in the field.