From the time we see Bambi’s mom bite the dust, we all know what death is. At least, we think we do. But the simple definition of death—that the body stops working—doesn’t take into account how weird our bodies actually are.
“We really know nothing about what happens when you die,” says Peter Noble, a former professor at the University of Alabama. Noble knows firsthand that surprises await scientists studying the end of life: he helped discover that long-dormant genes can spring into action hours or even days after an organism dies.
A gene is a set of chemical instructions, made of DNA, telling the body how to do something. When a gene is activated, those chemical instructions get transcribed by our RNA, and our cells can then use that copied sequence as a scaffold to build complex molecules. If a gene is a recipe in a cookbook, activation is writing down the list of ingredients so you can buy them and get cooking.
Noble and colleagues at the University of Washington were testing a technique for measuring gene activity. As a control, they analyzed tissues from recently-dead zebrafish, expecting to see a steady decrease in new copies of genes as cellular activity tapered off. And that’s what they found — with some notable exceptions. After the zebrafish were dead, around one percent of their genes sprang to life, as though the cells were preparing to build something.
The idea that genes would activate after an organism’s death was unheard of, so the researchers wrote it off as a mistake with their instrumentation. But repeated tests, in fish and then in mice, continued to bear out the impossible: genes activating hours, or even days, after an organism died.
The scientists’ findings were met with skepticism, until a group of researchers led by Roderic Guigó at Barcelona’s Centre for Genomic Regulation also found post-mortem gene activity, this time in humans. “We were saved when the group from the Barcelona genome institute covered the paper on humans, because they … proved the same thing,” says Noble.
Guigó and his team were studying gene regulation by analyzing tissues from people who donated their bodies after death. Their work was already underway when Noble’s paper was published, so they weren’t surprised by his team’s findings. “It was more or less what we were seeing,” says Guigó.
These discoveries could give us a better understanding of how genes work when we’re still alive, and they might help improve medical procedures like organ transplants. “Knowing how organs change on a molecular level after the death of the body … could maybe help to improve the practices for organ transplantation or organ preservation,” says Guigó.
The other big potential application of their studies, say Guigó and Noble, is in forensic science. The researchers found that different genes activate at different time intervals after death—one might regularly kick in six hours post-mortem, whereas another might fire up 24 hours later. Forensic scientists might be able to apply this information to make more accurate estimates of time of death.
But while this discovery opens up new possibilities for medical science, the biggest question posed by the research—why some of our genes activate after we die—remains a mystery. Noble thinks clues may lie in the kinds of genes that are reanimating. Though none of the zombie genes seem to make any physical changes after death, many of them are related to activities that are normally closely regulated or inhibited. This includes the gene that tells cells to produce the beginnings of a spinal column — once you’ve already got a spine, you no longer need to grow a new one.
Other genes that activate after death are related to cancers. Perhaps in the absence of other genes that normally inhibit them, these genes seize the opportunity to reactivate, like teens throwing a party when their parents are out of town.
While the reason for the reactivation of these genes remains elusive, what’s clear is that death is a more nuanced process than previously thought. Death doesn’t mean that all the billions of cells in our bodies stop working, it just means that they stop working together. The hours and days during which these connections fall apart and life fizzles out are a new frontier for science.
“I call it the twilight of death, going from the organism’s death as a whole versus what happens to individual cells,” says Noble. “Where [is] the breakdown between cells and the whole functioning organism? That’s a big question. No one knows.”