The build up to this can be seen here: viewtopic.php?f=12&t=15797&p=321710#p321710
Moved due to an inappropriate thread title (which cannot be editted once posted.) If anyone would like any particular posts above thread placed here please PM me and I’ll copy and paste where appropriate. Anyway, back to LuckyR’s post:
Here is an entertaining synopsis geared to the lay public:
The Virus and the Placenta
Boston in the mid-1990s was humming with the activity of the Human Genome Project. Sequencing technologies had advanced to the point where scientists were incorporating gene discovery into even the most basic research. Since the American courts had thus far allowed companies to patent the genes they discovered, companies like the Genetics Institute (now a part of Pfizer) saw a chance to cash in. There, molecular biologist John McCoy was looking for proteins secreted by cells since they seemed good targets for developing potential drugs.
All was going as planned until McCoy’s bioinformatics specialist Steve Howes rushed into his lab in 1997 to show him the sequence of a gene they called syncytin, which their work showed was secreted by placenta tissue.
Before McCoy could go public with his discovery, he needed to figure out exactly what syncytin did, a job he passed to bench scientist Sha Mi, who everyone called Misha. Misha’s experiments seemed to be going as planned until, a few months later, she, too, rushed into McCoy’s lab with findings of her own.
Syncytin is produced only by certain cells in the placenta, and it directs the formation of the cellular boundary between the placenta and maternal tissue. Approximately one week after fertilization, the egg, now a hollow ball of cells called a blastocyst, implants itself into the uterus, stimulating the formation of the placenta, which provides the fetus with oxygen and nutrients while removing carbon dioxide and other wastes. It also serves as a barrier to prevent infection and keep maternal and fetal blood separate. (Mixing the two could cause a fatal autoimmune response.) The cells in the outer layer of the blastocyst form the outer layer of the placenta, and those in direct contact with the uterus are the only ones that made syncytin.
When the scientists looked closer at the DNA sequence of syncytin, they found that it was nearly identical to a viral protein called env that caused the virus to fuse with its host cell. In the placenta, syncytin performed helped the fetus fuse with its mother. At last McCoy, Howe, and Mi knew what syncytin did.
“This was a bona fide retroviral envelope protein that had somehow been captured during evolution and been trained to operate in human biology,” McCoy says.
The two other retroviral genes next to syncytin, gag and pol, were completely non-functional, McCoy says. Only env remained intact. “Everything else about that retrovirus had been trashed,” he says. The team published a paper in Nature in 2000.
“An important step in mammalian evolution was accomplished by capturing this viral envelope gene,” McCoy says. “There’s plenty of examples of viruses picking up human genes, but this is one of the first examples of the reverse.”
Humans aren’t the only species with a placenta, however. All mammals have placentas, including marsupials and egg-laying mammals. Although all of these mammals have a syncytin gene, they don’t all have the same syncytin gene. The syncytin produced by mice is completely different from the two syncytins found in humans and other primates. At numerous points in mammalian evolution, symbiotic retroviruses entered the genome and steered different groups of mammals along different evolutionary paths, according to a 2012 paper in PNAS by virologist Harmit Malik at the Fred Hutchinson Cancer Research Center in Seattle. Nor was syncytin the only driver