A person whose heart and brain are no longer functioning and whose respiratory and circulatory systems have stopped working is declared dead, but does this mean that life no longer exists when the body has shut down?
Apparently no. Findings of new research offer evidence that many genes remain active days following clinical death. Some genes were even found to have increased their activity when the body's biological processes are believed to have stopped.
While these zombie genes won't bring back the dead to life, the discovery has important implications such as in the field of medicine where it could shed light on cancer risks faced by organ transplant patients.
Prompted by earlier research that identified genes in human cadavers that were still active more than 12 hours after death, Peter Noble, from the University of Washington, and colleagues conducted a study of gene activity in dead mice and zebrafish.
The researchers identified more than 1,000 genes that are still working days after death. The genes also do not happen to have just survived longer than the rest of the body. Some of them activated after death.
By looking at fluctuation levels of messenger RNA (mRNA) present in the zebrafish and mice up to 96 hours after they died, researchers found evidence that the activities of some genes increased in the first 24 hours after the animals died.
Higher levels of mRNA in a cell means there are more genes that are currently active because the RNA molecules tell the genes which proteins need to be produced by which cells.
Many of the identified postmortem genes are useful during emergencies firing up the immune system and counteracting stress but some of these genes have surprising functions. Developmental genes that sculpt the embryo, for instance, were found to activate after death.
Noble and colleagues said that this could be because the cellular conditions of the newly dead organisms are comparable to those of embryos.
Genes that promote cancer were also found to become more active after death, which could explain why organ transplant patients who receive organs from the recently deceased have increased risk for cancer. A 2015 study has shown that organ transplant patients are four times more likely to develop melanoma.
Pacific University molecular pharmacologist Ashim Malhotra, who was not part of the study, said it is crucial to know what happens to organs following death particularly if these organs will be used for transplant.
"The headline of this study is that we can probably get a lot of information about life by studying death," Noble said.