Parallel ClickSeq and Nanopore sequencing elucidates the rapid evolution of defective-interfering RNAs in Flock House virus

Dicer-2-Dependent Generation of Viral DNA from Defective Genomes of RNA Viruses Modulates Antiviral Immunity in Insects

The RNAi pathway confers antiviral immunity in insects. Virus-specific siRNA responses are amplified via the reverse transcription of viral RNA to viral DNA (vDNA). The nature, biogenesis, and regulation of vDNA are unclear. We find that vDNA produced during RNA virus infection of Drosophila and mosquitoes is present in both linear and circular forms. Circular vDNA (cvDNA) is sufficient to produce siRNAs that confer partially protective immunity when challenged with a cognate virus. cvDNAs bear homology to defective viral genomes (DVGs), and DVGs serve as templates for vDNA and cvDNA synthesis. Accordingly, DVGs promote the amplification of vDNA-mediated antiviral RNAi responses in infected Drosophila. Furthermore, vDNA synthesis is regulated by the DExD/H helicase domain of Dicer-2 in a mechanism distinct from its role in siRNA generation. We suggest that, analogous to mammalian RIG-I-like receptors, Dicer-2 functions like a pattern recognition receptor for DVGs to modulate antiviral immunity in insects.

The potential impact of nanopore sequencing on human genetics

Nanopore sequencing has been available to researchers for a little over 3 years. Recently, the milestone of sequencing and assembling a human genome on this platform was achieved for the first time. Significant improvements to the platform in yield and accuracy, coupled with higher throughput nanopore sequencers, mean that human genome sequencing at scale is now possible. Here, a brief recent history of the nanopore platform is provided, key papers and innovations are highlighted and some of the challenges for the future are discussed.

Metagenomic arbovirus detection using MinION nanopore sequencing

With its small size and low cost, the hand-held MinION sequencer is a powerful tool for in-field surveillance. Using a metagenomic approach, it allows non-targeted detection of viruses in a sample within a few hours. This study aimed to determine the ability of the MinION to metagenomically detect and characterise a virus from an infected mosquito. RNA was extracted from an Aedes notoscriptus mosquito infected with Ross River virus (RRV), converted into cDNA and sequenced on the MinION. Bioinformatic analysis of the MinION reads led to detection of full-length RRV, with reads of up to 2.5kb contributing to the assembly. The cDNA was also sequenced on the MiSeq sequencer, and both platforms recovered the RRV genome with >98% accuracy. This proof of concept study demonstrates the metagenomic detection of an arbovirus, using the MinION, directly from a mosquito with minimal sample purification.