Long dsRNAs promote an anti-viral response in Pacific oyster hampering ostreid herpesvirus 1 replication

Abstract

Double stranded RNA-mediated genetic interference (RNAi) is a widely used reverse genetic tool for determining the loss-of-function phenotype of a gene. Here, the possible induction of an immune response by long dsRNA was tested in a marine bivalve, i.e. Crassostrea gigas, as well as the specific role of the subunit 2 of the nuclear factor κB inhibitor (IκB2). This gene is a candidate of particular interest for functional investigations in the context of massive mortality oyster events as Cg-IκB2 mRNA levels exhibited significant variation depending on the amount of ostreid herpesvirus 1 (OsHV-1) DNA detected. In the present study, dsRNAs targeting Cg-IκB2 and Green Fluorescence Protein genes were injected in vivo into oysters before being challenged by OsHV-1. Survival appeared close to 100% in both dsRNA injected conditions associated with a low detection of viral DNA and a low expression of a panel of 39 OsHV-1 genes as compared to infected control. Long dsRNA molecules, both Cg-IκB2- and GFP-dsRNA, may have induced an anti-viral state controlling the OsHV-1 replication and precluding the understanding of the Cg-IκB2 specific role. Immune-related genes including Cg-IκB1, Cg-Rel1, Cg-IFI44, Cg-PKR, and Cg-IAP appeared activated in dsRNA-injected condition potentially hampering viral replication and thus conferring a better resistance to OsHV-1 infection. We revealed that long dsRNA-mediated genetic interference triggered an anti-viral state in the oyster, emphasizing the need of new reverse genetics tools for assessing immune gene function and avoiding off-target effects in bivalves

Host‐microbiota interactions shed light on mortality events in the striped venus clam Chamelea gallina

“…Although multiple infections involving a virus cannot be excluded in C. gallina , the down‐regulation in both mortality sites of putative Interferon‐induced protein 44‐like (IFI44), a key element for effective antiviral defense in bivalve species (Olicard, Renault, Torhy, Benmansour, & Bourgougnon, ; Pauletto et al, ; Renault, Faury, Barbosa‐Solomieu, & Moreau, ; Segarra et al, ) and the significant down‐regulation of several pathways typically involved in virus response suggests that viral replications should be excluded in C. gallina . Furthermore, the absence of viral detection in the histological analysis carried out in our study supports the premise that viral replication is not at the root of C. gallina mortality as recently proposed in C. gigas (De Lorgeril et al, ).…”

Antiviral Defense and Innate Immune Memory in the Oyster

“…Poly(I:C) is a synthetic double-stranded RNA (dsRNA) molecule that has been widely used as a viral mimic in mammalian and fish models to activate the type I interferon pathway [ 15 , 40 , 41 ]. Intramuscular injection of poly(I:C) and other long dsRNA molecules induce an antiviral response in C. gigas that hampers OsHV-1 replication [ 42 , 43 , 44 , 45 ]. Oysters have a RIG-1 like receptor (RLR) pathway that senses cytoplasmic poly(I:C) and transmits signals via mitochondrial antiviral protein (MAVS) to activate NF-κB [ 46 ].…”

“…This phenomenon of improved survival upon secondary exposure to OsHV-1 is termed immune priming to distinguish the innate memory from the mechanistically different adaptive immunity in vertebrates [ 86 , 87 ]. Several studies have shown immune priming with ribonucleic acids of different structures (single or double-stranded) or various lengths (300 bp to 8000 bp) can elicit a protective antiviral response in C. gigas against subsequent challenge with OsHV-1 [ 42 , 43 , 44 , 45 ]. This protection is long-lasting, persisting for at least five months, and the enhanced survival was validated on a shellfish farm exposed to naturally reoccurring episodes of OsHV-1 [ 44 ].…”

Transgenerational plasticity and antiviral immunity in the Pacific oyster (Crassostrea gigas) against Ostreid herpesvirus 1 (OsHV-1)

“…A core set of genes expressed in response to OsHV-1 infection has been identified in adults (He et al, 2015;Rosani et al, 2015) and larvae (Zhang et al, 2015), and differences in antiviral gene expression in C. gigas primed with poly(I:C) (Green and Montagnani, 2013;Green et al, 2015b), and their progeny (Green et al, 2016) following inoculation with OsHV-1 have been characterized. Stimulation with double-stranded RNA, such as poly(I:C), induces the expression of antiviral effector genes (Green et al, 2014b), for at least seven days (Green et al, 2014a), and this response appears to inhibit OsHV-1 replication (Lafont et al, 2017;Pauletto et al, 2017). Do C. gigas offspring produced from parents stimulated with poly(I:C) also have elevated expression of antiviral effector genes?…”

“…Experimental studies using a heterologous immune-priming model provide evidence of immune plasticity in C. gigas to OsHV-1 infection (Green and Montagnani, 2013;Green et al, 2015b;Lafont et al, 2017;Pauletto et al, 2017). The immune system of C. gigas can be primed with synthetic virus-associated molecular patterns (i.e.…”