Zombie Genes Awaken

For centuries, people have wondered what happens to us after we die. While the question will likely remain one of the great mysteries of life, scientists have come some way in finding out what happens to organisms on a biological level after death. Research carried out previously has shown that individual cells can survive a long time after an organism dies. But more recently, scientists at the University of Washington, Seattle, have stumbled upon some rather surprising evidence for the continued and even newly awakened activity of genes days after an animal has died.

DNA分子,组成genes, are like a blueprint of biological rules that an organism must follow to function and live. In life, information from genes is processed to form functional gene products like RNA or proteins (a process known as ‘gene expression’). This is governed by complex genetic and epigenetic networks. In death, scientists have been unsure about how gene expression stops occurring – does it waver off slowly, or stop abruptly? Through research that was initially focused on calibrating gene activity data on living samples, the biologists Noble and his colleagues at the University of Washington took a fairly dark turn by testing their experimental approach on post-mortem samples of mice and zebrafish. The researchers measured gene activity by monitoring the levels of messenger RNA present in the mice and fish – with an increase in messenger RNA indicating more active genes. They found that 1063 genes were still active more than 24 hours after the death of the organisms. Not only that, but while some genes dwindled in activity a few hours after death, most in fact increased their activity for up to 4 days after death.

The most abundantly active genes were related to immune functions concerning inflammation. These are genes that would be helpful in emergencies, like helping an organism to fight off an incoming infection. The functions of other active genes proved to be more interesting; for instance, developmental genes were observed to ‘turn on’ (or activate) after death. Developmental genes help to form the embryo – so an increase in activity of these genes is odd since there is no conceivable need of such a function after death. As discussed inScience, perhaps this shows that the cellular conditions in recently-expired organisms resemble those in embryos. Other earlier research suggests that genes are actually turned on and off at the very start of human life as well, to direct early development and embryo formation. This suggests that death might trigger a similar mechanism, that turns genes on and off during early development. Additionally, genes that foster cancerous growth were also remarkably observed to ramp up their activity after death. This could explain why patients who get transplants from a recently deceased donor are more likely to develop cancers. One plausible reason for transplant patients having a high incidence of cancer is that they need to take a lot of drugs daily after the procedure, to make sure their immune systems don’t reject the new organs. Still, the University of Washington researchers argue that activated cancer genes could play a larger part in this than currently realised.

There is also another potential advantage of this research into zombie genes – in forensics. While many biological, chemical and physical indicators can be used to determine the time of death, most of these indicators in forensic analyses of murdered victims, for example, are not very accurate. More often, information from other sources like witness accounts are used to come up with the time of death of a victim – which results in less accurate estimates and a longer post-mortem interval (the elapsed time between death of a person and the start of an official investigation). The experimental method involving measuring gene activity, that has been validated and tested by Noble and his colleagues, can be applied to forensic investigations to accurately predict the time of death of deceased victims.

While these studies have yet to be peer-reviewed, the findings of this genetic research have undeniably stirred up some attention in the scientific community. From this research, scientists may be able to learn more about complex genetic networks and how they unwind when they no longer need to keep an organism functioning. A key unanswered question from this research is how there could be enough energy and resources in the animals’ bodies post-mortem to still carry out gene expression processes. Evidently, this research has significant scope in the biological sciences, particularly its potential in improving transplant diagnostics and forensic investigations. Once again, it is inarguable that studying death can help us to understand life.