Unravelling the evolution of antiviral sensors and response systems in animals using the phylum Cnidaria

Project Information

AntiViralEvo

Grant agreement ID: 863809

DOI

10.3030/863809

Project closed

EC signature date 30 January 2020

Start date 1 May 2020

End date 30 September 2025

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 998 750,00

EU contribution

€ 1 998 750,00

Coordinated by

THE HEBREW UNIVERSITY OF JERUSALEM
Israel

Periodic Reporting for period 4 - AntiViralEvo (Unravelling the evolution of antiviral sensors and response systems in animals using the phylum Cnidaria)

Reporting period: 2024-11-01 to 2025-09-30

Summary of the context and overall objectives of the project

Viruses represent a major threat to animal health, yet the evolutionary origins of antiviral immune mechanisms remain poorly understood because vertebrates and invertebrates rely on markedly different defense strategies. This project investigated how antiviral immunity evolved by studying a non-bilaterian animal, the sea anemone Nematostella vectensis, which diverged from bilaterian animals more than 600 million years ago.
The project demonstrated that Nematostella mounts a complex intracellular antiviral immune response that combines features previously thought to be exclusive to either vertebrates or invertebrate bilaterians. Specifically, we showed that viral double-stranded RNA triggers gene expression programs resembling both the interferon-based antiviral response of vertebrates and components of the RNA interference (RNAi) pathways found in insects and worms. Functional genetic and biochemical experiments revealed that retinoic acid-inducible gene I-like receptors (RLRs), which detect viral RNA in vertebrates, are essential for initiating antiviral responses in Nematostella.
In addition, we characterized the RNAi response in this species and found that exposure to viral RNA induces the production of short interfering RNAs that mediate sequence-specific target silencing, but without the secondary amplification typical of antiviral RNAi in many invertebrates. This indicated that RNAi in Nematostella functions as a transient antiviral mechanism that likely acts in parallel with RLR-based innate immune signaling.
Together, these findings established that key components of antiviral immunity originated before the split between cnidarians and bilaterian animals and that early animals possessed a more sophisticated and modular antiviral defense system than previously assumed. By uncovering the deep evolutionary roots and diversification of antiviral mechanisms, this project reshaped our understanding of immune system evolution and highlighted the value of non-traditional model organisms for revealing fundamental biological principles.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The mechanisms for sensing and defeating RNA viruses vastly differ between vertebrate and invertebrate bilaterian animals which hinders our understanding of their evolutionary origin. In this project we characterized the gene expression response (i.e. which genes are activated and inactivated) to a common viral mimic, double-stranded RNA, in a non-bilaterian animal, the cnidarian Nematostella vectensis. Strikingly, we revealed that the innate immune response of Nematostella displays similarities to both invertebrate and vertebrate systems as we find activation of distinct components similar to those found in the interferon system of vertebrates and also to those found in the RNA interference system of flies and worms. This result suggests an ancient origin of these antiviral immune mechanisms and that the last common ancestor of cnidarians and bilaterian animals had a highly sophisticated antiviral system inside its cells. Unexpectedly, after cnidarians separated from the rest of animals, ancient vertebrates and invertebrates lost parts of their antiviral immune systems, whereas cnidarians retained the ancestral complexity. Further, the results of our biochemical and genetic assays indicate that the retinoic acid-inducible gene I-like receptors (RLRs), known to detect viral double-stranded RNA in vertebrates and worms, are essential to initiate the antiviral immune response in Nematostella. Altogether, we provided functional evidence that the RLR-mediated sensing of viral RNA originated before the split of cnidarians from other animals more than half a billion years ago.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

As stated above, the results obtained in this project revealed unexpected complexity of the ancient antiviral immune system in animals. This is an important progress in our understanding of this topic. On a more technical aspect, we developed and generated transgenic lines of Nematostella that express reporter genes under a highly ubiquitous promoter, which is an important research tool in this system. Further, we generated transgenic lines of the same species that utilize this promoter for over-expressing a Nemaotstella receptor of viral double-stranded RNA (RLR) with a peptide tag that enables its efficient biochemical isolation and detection. We used this important tool for testing and characterizing the biochemical traits of this receptor. Lastly, we generated several mutant lines of Nematostella that are defective in different immune-related genes that are essential for antiviral response. In this project we have learned many important details about the evolution of antiviral immunity in animals and that we have developed cutting-edge transgenic tools as well as mutants in Nematostella that will benefit the scientific community using this species as a lab model organism for understanding the evolutionary biology of immune response in animals.

Sea anemones of the species Nematostella vectensis express a red protein under ubiquitous promoter