Zombie Genes: Study Finds Gene Activity After Death

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Thought your body completely stops working after death? Not so according to a new study on postmortem gene activity. A study led by a computational biologist named Roderic Guigó with the Genotype-Tissue Expression pilot (GTEx) has been studying tissue samples from hundreds of people in order to measure gene activity after death. The team looked at 9000 samples to determine the differences in postmortem gene activity.

An earlier 2016 study had already found that gene activity in animals can carry on for days after death. Scientists had expected that genes would stop functioning after death, but found instead that some genes actually increase in activity. Gene activity was found to persist in animals even up to four days after death.

Scientists were also surprised to find which genes became more active. One particular set of genes that reactivated were those that help to form the embryo. Another set of genes that tend to promote the growth of cancer also reignited, perhaps explaining why those who undergo organ transplants face higher cancer risks. Some of these changes are hard to explain or understand, but Guigó believes some changes can be traced to a lack of oxygen following the cessation of blood flow through the body.

At the time of the 2016 study scientists anticipated that the findings could help them to better preserve organs for donation and make the process safer. They also believed the study could help to better understand gene networks and even pinpoint the time of death of murder victims. Now, Guigó’s study seems to be confirming some of their hypotheses.

Technology Changing the Game

As technology advances, so does our understanding of the human body. The human genome wasn’t even fully mapped until 2003 with the help of computer software. Likewise the GTEx study made use of specialized computer software designed by Guigó and his team.

One would expect that genes decrease in activity after death, but that’s not the case. Computer scientist Ilias Tagkopoulos explained to Science Mag, “At a cellular level, death is a cascade of events affecting biological processes at different timescales.” The computer software confirmed not only that gene activity can carry on, but also found that not all genes see congruent increase or decrease in activity, even genes in the same part of the body. For example, in human blood, the software found a decrease in activity in genes related to metabolism and immune function, but an increase in activity related to stress response. Guigó’s team hopes their software can help to map and study their unexpected changes.

Problems with the Study of Genes

Most samples are taken after death, limiting the ability of scientists to study healthy genes. It’s simply not possible to get a hunk of healthy, fresh human heart to study. Most scientists rely not only on samples taken after death, but these samples are usually stored for hours or even days after death before scientists are able to look at them.

To circumvent some of these issues, Guigó’s study relied on samples taken within 24 hours of death, as well as blood samples taken before death.

So What?

The scientists found that the changes in gene activity are different depending on the kind of tissue being studied. Spleen and brain samples see little gene activity after death, while gene activity quickly changes after death in over 600 different muscle genes, allowing future scientists to target their genetic studies to certain regions of the body.

These findings could have a huge impact on determining the time of death of murder victims. The software found that the bulk of gene activity, whether an increase or a decrease, happens between 7-14 hours after death. Gene activity seems to balance out around 14 hours after death. According to Guigó, time of death is best estimated using tissue samples from the thyroid and lungs.

Although these findings could make waves in the field of forensics, Guigó insists that the research into post mortem gene activity has not yet come that far, “At this point, our program is an academic exercise.”

Another issue with the study is that analyzing these tissue samples is still quite expensive, but the more tissue analyzed the more precise the results. The downside is that the more tissue that needs to be analyzed, the more costly doing so would be.

Guigó has warned, however, that the scientists working on this study have yet to come up with a tool that could actually be used in forensic cases, “We conclude there is a signature or a fingerprint in the pattern of gene expression after death that could eventually be used in forensic science, but we don’t pretend we have now a method that can be used in the field.”

Guigó is also optimistic that his findings in gene activity after death don’t end here. He holds a hypothesis that examining postmortem gene activity may even lead to being able to determine the cause of death just from looking at genes.

On a larger scale, genes make up virtually all life on earth. Understanding genes helps us to understand life on earth. Better understanding the human genome specifically could have unpredictable benefits to diagnosing and treating diseases.

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