An ancient retrovirus that's been integrated into the human genome appears to become reactivated during embryonic development to help ward off other viral invaders, Carl Zimmer writes at the New York Times.
Stanford University's Joanna Wysocka and her colleagues report in Nature that the HERVK retrovirus is activated at the eight-cell stage of embryogenesis and remains active through implantation. When the HERVK Rec protein is overexpressed in a cell line, the researchers note, it leads to an increased amount of IFITM1 on cell surfaces, which inhibits viral infection, suggesting that that viral expression protects embryos from infection by other viruses.
Additionally, as Rec also binds cellular RNAs and affects their ribosome occupancy, the virus could also guide embryonic development, the researchers add.
This reactivation of viral genes during embryonic development seems to be "part of the program," Wysocka tells Zimmer.
The Francis Crick Institute's Jonathan Stoye calls the study "thought worthy," but tells Zimmer it suggests, but doesn't prove, that the retroviral genes are conferring a benefit on human embryos. He says they could just be acting as "very successful parasites."