Researchers at the Francis Crick Institute (UK) have found a vital mechanism, previously thought to have disappeared as mammals evolved, that helps protect mammalian stem cells from RNA viruses such as SARS-CoV-2 and Zika virus. The scientists suggest this could one day be exploited in the development of new antiviral treatments. On infecting a host, a virus enters cells in order to replicate. For most cells in mammals, the first line of protection are proteins, called interferons. Stem cells, however, lack the ability to trigger an interferon response and there has been uncertainty about how they protect themselves. In their study, published in the July 9, 2021 issue of Science, the Crick scientists analyzed genetic material from mouse stem cells and found it contains instructions to build a protein, named antiviral Dicer (aviD), which cuts up viral RNA and so prevents RNA viruses from replicating. This form of protection is called RNA interference, which is the method also used by cells in plants and invertebrates. The article is titled “An Isoform of Dicer Protects Mammalian Stem Cells Against Multiple RNA Viruses.”