So what would happen if you took the human version of a TNF protein and exposed it to a coral's TNF receptors?
Quistad and his colleagues did just that and watched for the telltale signs of apoptosis. Under a microscope, they saw evidence that the coral cell was breaking down within 10 minutes of exposure to human TNF. A series of other cellular signals associated with apoptosis confirmed it: Human TNF sets into motion programmed cell death in corals.
Next, Quistad and colleagues wondered if coral TNF proteins would trigger apoptosis in human cells. They coaxed E. coli bacteria to express the same TNF proteins produced by corals and exposed them to cultured human tissue. Sure enough, apoptosis occurred in the human cells. Quistad published these results today in the Proceedings of the National Academy of Sciences.
The findings suggest that the pathway by which TNF triggers apoptosis is old. Extremely old.
"The fact that it goes both ways means that these domains haven't changed in half a billion years," Quistad said. "Corals are actually much more similar to humans than we ever realized."
That's interesting from an evolutionary biology perspective, Quistad said, because approximately 542 million years ago, organized life took off in a very big way.
Known as the Cambrian Explosion, this period saw the emergence of the early ancestors of much of the life that exists today, including humans. No one really knows what set off the Cambrian Explosion, but it's possible the evolution of orderly, systematic cell death played a leading role.
|Contact: Beth Chee|
San Diego State University