Researchers at a biotechnology institute in Cambridge, Massachusetts, studied syncytin, a gene active mainly in placental tissue. It is the envelope gene of HERV-W, a retrovirus of the kind that inserts its own DNA into a host's genome, and they showed its protein fuses cells.
The gene turned out to be a fragment of an ancient retrovirus that infected an ancestor of humans millions of years ago and became a permanent part of the genome. Syncytin makes the protein that fuses placental cells together into the single sheet of tissue separating a fetus's blood supply from the mother's.
Work in mice later found that removing a similar, separately captured gene blocked this fusion and was fatal to the embryo, so a borrowed viral gene is no leftover curiosity. Later research found that different mammal lineages independently captured different retroviral genes for the same placental job, a pattern now considered one of the clearest examples of a virus gene becoming indispensable to its host.
Read the original study
A virus gene, now load-bearing.
Source
- Mi, S., Lee, X., Li, X.-p., Veldman, G. M., Finnerty, H., Racie, L., LaVallie, E., Tang, X.-Y., Edouard, P., Howes, S., Keith, J. C., & McCoy, J. M. (2000). Syncytin is a captive retroviral envelope protein involved in human placental morphogenesis. Nature, 403(6771), 785–789. https://doi.org/10.1038/35001608