An ancient anthozoan protein reveals an alternative evolutionary path of antiviral signaling
The innate immune system is the frontier defense for animals to survive in their nonstop struggle against viral infections. This continuous condition forced animals to evolve a broad repertoire of innate immune pathways to defend against viruses. Different bilaterian animals rely on a variety of components to mediate the immune response against these viral infections. This diversity masks the system's ancestral state. In this study, we focus on homologs of the vertebrate viral RNA sensors RIG-I-like Receptors RLRa and RLRb and Mitochondrial Antiviral Signaling Protein MAVS of Nematostella vectensis. We show that the knockdown of Nematostella RLRb and MAVS, but not RLRa, leads to a significant decrease in the expression levels of homologs of immune-related genes after microinjection of double-stranded RNA, dsRNA viral, RNA mimic. Moreover, we knocked out these genes using CRISPR, and we demonstrated that the RLRb and MAVS mutant lines exhibited weaker responses to dsRNA challenge compared to wild-type animals. Overall, the results of this study give us new insight into the mode of action of RLRs and MAVS to activate the immune system in cnidarians and reveal a mode of action that is conserved with their vertebrate homologs.