Nora Virus VP4b and ORF1 Circulate in Hemolymph of Infected D. melanogaster with Coordinate Expression of Vago and Vir-1

Abstract

Study of the novel RNA virus, Nora virus, which is a persistent, picorna-like virus that replicates in the gut of Drosophila melanogaster offers insight into human innate immunity and other picorna-like viruses. Nora virus infection leads to a locomotor abnormality and upregulation of two candidate target proteins, Vago and Virus-induced RNA 1 (Vir-1). These proteins are uncharacterized in response to Nora virus. We hypothesize that Nora virus is circulating in the hemolymph of Nora virus-infected D. melanogaster, allowing for migration beyond the primary site of replication in the gut. Analysis by qRT-PCR demonstrated biphasic viral load and corresponding vago and vir-1 transcription levels, suggesting transcription of vago and vir-1 occurs in response to viral infection. However, Vir-1 is also present in virus-free D. melanogaster suggesting basal expression or alternative functions. Presence of Nora virus RNA and the Viral Protein 4b (VP4b), in hemolymph of infected D. melanogaster supports the hypothesized circulation of Nora virus in the hemolymph. The study suggests that impaired locomotor function may be due to transport of Nora virus from the gut to the brain via the hemolymph.

Single domain von Willebrand factor type C “cytokines” and the regulation of the stress/immune response in insects

“…Interestingly, Vago expression was not induced by the Toll, Imd, or Jak-STAT pathways and the finding that neither Ago-2 nor R2D2, the other major components of the siRNA pathway, were required for Vago induction led the authors to hypothesize that Dicer-2 has an additional function distinct from the RNAi mechanism (Deddouche et al, 2008). Also in the case of Nora virus infection, Vago expression was induced, thus supporting its cytokine-like function (Cordes et al, 2013;Macke et al, 2020).…”

“…In fly mutants for the gene cactus , the Drosophila ortholog of the NF‐κB inhibitor in the Toll pathway, Vago does not become induced in contrast to mutants for Relish (Imd pathway) in which antiviral resistance against DCV or SINV was not compromised (Deddouche et al, 2008). Vago , among other genes, was also found to be induced in response to infection with the picorna‐like virus Nora virus that replicates primarily in the gut tissue and causes persistent infection in D. melanogaster (Cordes et al, 2013; Macke et al, 2020).…”

Drosophila as a Model for Human Viral Neuroinfections

“…While infection did not impact lifespan, climbing (geotaxis) assays in Nora virus (and DCV) infected flies were significantly impaired compared with uninfected controls. It is postulated that Nora virus may impact fly brain function as a result of Nora virus trafficking from the primary site of infection in the gut through circulation in infected hemolymph [ 195 ]. Nora virus-infected D. melanogaster also show enhanced immune-related gene expression over time, with enhancement of Toll, IMD and hematopoiesis genes, in conjunction with decreased RNAi-related genes [ 196 ].…”

Cellular and molecular organization of the Drosophila foregut

“…The Drosophila PV synthesizes a major digestive product, the multilayered peritrophic matrix (PM) that likewise remains between consumed items and enterocytes as food passes through the gut ( 9 ). The foregut epithelium and the PM restrict pathogens, promote digestion, and provide additional physiological benefits ( 10 – 12 ).…”