DNA dies

Some genes only come to life after death

Even if the brain is dead, many genes are not yet; on the contrary, they then become active.

"A person is dead when the diagnosis of brain death and its documentation have been completed and the last doctor involved puts his signature on the diagnosis protocol." This is how the German Medical Association defines it, the Supreme Medical Council of Austria does it similarly: "The person is dead, when the entire brain (= cerebrum, cerebellum and brain stem) has failed. ”The definition is controversial, but medicine needs clarity, especially transplant medicine needs it, it needs to know when to remove tissue or organs.

But there can still be life in them when the brain has long ceased to work, more than that, there it can only become active or some genes can. Peter Noble (University of Washington, Seattle) noticed this when he analyzed the Thanatos transcriptome in dead zebrafish and mice: Thanatos is death, and the transcriptome contains the transcription of genetic information from DNA into RNA. Some genes of humans already know that this can continue after death. But Noble first takes a look at whole organisms. Two years ago he checked which bacteria were still active in cadavers, and now he has just looked at the genomes, “out of pure curiosity to see what happens when you die”.

What happens when you die?

With zebrafish and mice a lot happens (in advance on bioRxiv 10.46.): 548 or 515 genes became active or more active, very different ones, some have to do with stress and inflammation, others with the immune system, others promote cancer, and some are even genes that play a role in embryonic development. “You don't have the language,” reports Noble, but it doesn't stay away for long: Developmental genes are probably active because other genes that have blocked their activity are no longer active themselves.

The activities came very differently in fish and mice and at different times, some even four days after death. “We had thought that you could compare the death of a vertebrate with a car running out of fuel: the pistons move a little, then everything stops,” explains Noble: “But what we saw would be analogous of the car as if the horn were suddenly honking long after its 'death'. "

The metaphor may allude to the alarm signal contained in Noble's finding: If genes that promote cancer awaken after death, cancer could be found in transplants that were removed after brain death was diagnosed. But the finding is not only important for medicine, which has to do with life, but also for those who track down the dead, the forensic one: With analyzes of the Thanatos transcriptome, times of death could be determined more precisely than with today's methods that are being developed Noble in a parallel work, which he also makes available in advance on bioRxiv.

("Die Presse", print edition, June 24, 2016)