Humans No Longer Have Ancient Defense Mechanism Against Viruses

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Insects and plants have an important ancient defence mechanism that helps them to fight viruses. This is encoded in their DNA. Scientists have long assumed that vertebrates – including humans – also had this same mechanism. But researchers at KU Leuven have found that vertebrates lost this particular asset in the course of their evolution.

The possibilities encoded in our DNA are expressed via RNA. Conversely, RNA interference (RNAi) can also suppress the expression of a specific gene. Insects and plants use this RNAi mechanism to defend themselves against viruses, among other things. With a little help, insects and plants can even be made resistant to certain diseases through this RNAi mechanism. Examples include so-called genetically modified crops.

Credit: KU Leuven

It seems only logical to assume, then, that humans can be protected against specific diseases in a similar way. However, past experiments to this effect have proven to be a challenge. Researchers from the Animal Physiology and Neurobiology unit at KU Leuven have now shown why this is the case.

KU Leuven researcher Niels Wynant studied Argonaute proteins, which play an important role in the RNAi process. “In a first stage, we compared the DNA of more than 40 living organisms from various important animal groups. It’s the first time that such a diverse group was studied. It didn’t take us long to find the Argonaute proteins in these organisms. We also discovered the existence of three distinct types of Argonautes, each with a specific biological role,” Wynant explains.

“Two out of these three types are especially important for our research: AGO1 and AGO2. The AGO1 family plays a role in regulating its own gene expression. These proteins help to determine which characteristics encoded in the DNA are actually expressed. The AGO2 family takes care of the defence against viruses. However, we didn’t find these AGO2 proteins in vertebrates.”

Citation: The evolution of animal Argonautes: evidence for the absence of antiviral AGO Argonautes in vertebrates. Niels Wynant, Dulce Santos & Jozef Vanden Broeck  Scientific Reports
DOI:10.1038/s41598-017-08043-5