Final Report Summary - ANTIVIRALRNAI (RNAi-mediated viral immunity in insects)
Since the discovery of RNAi in 1998 and of its multiple roles in cellular homeostasis, we have witnessed a new way of thinking, conceiving and perceiving gene regulation. When RNAi was shown to be antiviral, first in plants in 1997 and later in nematodes and in insects, a new and intriguing phase opened up in host-pathogen relationships and immunity: a new “nucleic-acid based” immune system was discovered and awaits to be unravelled.
Important viral infectious diseases, such as dengue and chikungunya, are transmitted to humans by insect vectors. One of the key factors that modulates whether an insect is competent or not to transmit a given pathogen is its innate immune response. Understanding how the infection is controlled within the insect before crossover to the human host could generate new strategies to disrupt pathogen transmission. Arboviruses (for arthropod-borne viruses) are maintained in a transmission cycle between hematophagous insect vectors and arthropods in general, and vertebrate hosts. Within their insect vector, arboviruses encounter several anatomical and immunological barriers: RNA interference (RNAi) is the major antiviral defence mechanism in insects. The small interfering RNA (siRNA) pathway constitutes a hallmark of the insect antiviral RNAi response. During the siRNA response, the defence mechanism is activated by cleavage of viral double-stranded RNA (dsRNA) into 21 nucleotide (nt) viral small interfering RNAs (vsiRNA) by Dicer-2 (Dcr-2). Once produced, vsiRNAs guide the sequence-specific recognition and cleavage of viral target RNAs by an Argonaute-2 (AGO-2)-containing RNA induced silencing complex (RISC).
An ideal model system to study antiviral immunity and host-pathogen relationships should combine a genetically tractable small animal with a virus capable of naturally infecting it. Using Drosophila as a model system and an array of viruses naturally infecting it, we have performed work key to redefine and understand better the principles of the antiviral RNAi response: we obtained evidence that antiviral immunity in Drosophila requires systemic RNA interference spread (Nature, 2009); that RNAi and reverse transcription control virus persistence in insects (Nat Immunol, 2013); that RNAi is the main antiviral response against (+) and (-) strand RNA viruses and DNA viruses in insects (PNAS, 2010 and 2012); that arboviruses generate piRNAs in mosquito cells as part of the antiviral response (PLoS ONE, 2012). We have also contributed to the exploitation of high throughput sequencing data by developing software for in silico reconstruction of viral genomes from small RNAs (J Virol, 2011).
These discoveries, allowed us to set the basis to tackle an ambitious research program that have changed our way of understanding today invertebrate immunity.
Important viral infectious diseases, such as dengue and chikungunya, are transmitted to humans by insect vectors. One of the key factors that modulates whether an insect is competent or not to transmit a given pathogen is its innate immune response. Understanding how the infection is controlled within the insect before crossover to the human host could generate new strategies to disrupt pathogen transmission. Arboviruses (for arthropod-borne viruses) are maintained in a transmission cycle between hematophagous insect vectors and arthropods in general, and vertebrate hosts. Within their insect vector, arboviruses encounter several anatomical and immunological barriers: RNA interference (RNAi) is the major antiviral defence mechanism in insects. The small interfering RNA (siRNA) pathway constitutes a hallmark of the insect antiviral RNAi response. During the siRNA response, the defence mechanism is activated by cleavage of viral double-stranded RNA (dsRNA) into 21 nucleotide (nt) viral small interfering RNAs (vsiRNA) by Dicer-2 (Dcr-2). Once produced, vsiRNAs guide the sequence-specific recognition and cleavage of viral target RNAs by an Argonaute-2 (AGO-2)-containing RNA induced silencing complex (RISC).
An ideal model system to study antiviral immunity and host-pathogen relationships should combine a genetically tractable small animal with a virus capable of naturally infecting it. Using Drosophila as a model system and an array of viruses naturally infecting it, we have performed work key to redefine and understand better the principles of the antiviral RNAi response: we obtained evidence that antiviral immunity in Drosophila requires systemic RNA interference spread (Nature, 2009); that RNAi and reverse transcription control virus persistence in insects (Nat Immunol, 2013); that RNAi is the main antiviral response against (+) and (-) strand RNA viruses and DNA viruses in insects (PNAS, 2010 and 2012); that arboviruses generate piRNAs in mosquito cells as part of the antiviral response (PLoS ONE, 2012). We have also contributed to the exploitation of high throughput sequencing data by developing software for in silico reconstruction of viral genomes from small RNAs (J Virol, 2011).
These discoveries, allowed us to set the basis to tackle an ambitious research program that have changed our way of understanding today invertebrate immunity.