Typically, when a person’s heart stops beating, they’re pronounced dead. But don’t tell that to their genes, some of which only come to life two days after they’ve kicked the bucket.
In fact, hundreds of genes suddenly started churning out messenger RNA, which sends a signal to various cellular machines to start making the stuff of life, such as proteins. Peter Noble and Alex Pozhitkov, both at the University of Washington, discovered this life-after-death scenario in mice and zebrafish. They released their results recently on the BioRxiv, a prepublication server.
Here’s Anna Williams, reporting for New Scientist:
Hundreds of genes with different functions “woke up” immediately after death. These included fetal development genes that usually turn off after birth, as well as genes that have previously been associated with cancer. Their activity peaked about 24 hours after death.
It takes time for the DNA to be unraveled by proteins called histones, according to Noble. As it unravels, genes that were previously silent, such as those involved in embryological development, may become active again as the genes that are used to suppress them break down.
“You’d think that when something dies, that everything would be turned off and everything would be silent, but that’s not the case,” Noble told NOVA Next. “In complex organisms, when we suddenly die, it takes awhile for the [DNA] complexes to break down, and they reach many barriers.”
Though the study focused on mice and zebrafish, the two organisms are commonly used in genetic studies as models for humans.
These findings could change the way that organ transplants are handled.
For example, liver transplant patients tend to have much higher rates of cancer, and up until now this was thought to be an immune response.
“Our results suggest it may not be [an immune response],” Noble said. “It may be just the fact that cancer genes are turned on at death as a natural phenomenon.”
With this knowledge, scientists could test an organ for active cancer genes before transplant occurs, drastically reducing the chances of cancer in the new recipient.
For most genes, overall mRNA levels should decrease over time after death. However, in 548 zebrafish genes and 515 mouse genes, mRNA levels peaked after death. This meant that the decaying bodies had enough excess energy for these genes to switch on and continue functioning long after the animal died.
The big question following these findings is why these specific genes turn on after the heart has stopped beating. One hypothesis, Noble and Pozhitkov said, is that the body using the last of its energy to heal itself, similar to what happens while someone is alive.
The second hypothesis researchers have for why this may be happening has to do with how DNA unravels following death.
Photo credit: Juan Eduardo Donoso / Flickr (CC BY-NC-ND 2.0)