Dead But Not Entirely

Dead But Not Entirely
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By Drs. David Niesel and Norbert Herzog

Scientists have been using various techniques to determine which of the 22,000 human genes are used in response to various situations, for example during infection or after exposure to a toxin. These studies provide insights into the mechanisms the body uses to respond to insults and can lead to the development of new therapeutics and medical interventions. A recent study explored what happens to gene expression when an organism dies. Surprisingly, some genes are actually turned on. Nature can be unpredictable!

Genes encoded in our DNA are regulated by a variety of mechanisms and the DNA is read by enzymes called RNA polymerases. They transcribe the DNA into a molecule called RNA which then serves as the template for proteins. The total complement of RNA made in a cell is called the transcriptome. The transcriptome of a dead organism is called the Thanatotranscriptome, thanatos, is Greek for death.

In this new study, RNA production was monitored in zebra fish and mice at various times after death. Surprisingly, 1063 genes produced more RNA from 0.5 to 96 hours after death. The RNAs specified proteins that affect the body's response to stress, immunity, inflammation, cell death, cellular transport, embryogenesis and cancer.

You might ask why would this study be done. One reason is understanding how nature works, and also, what happens when a very complex natural system such as a human body shuts down? It is not like a car that runs out of gas and the pistons continue to go up and down before the car stops, it is much more complicated. With the finding that some genes are turned on, it is like the engine trying to restart itself even with having no gas. The body has a complex system of checks and balances that keep us functioning properly and they kick in to try and "right the ship".

Similar genes were activated in the mice and Zebrafish. This implies that there may be a generalizable gene response to death in all animals. Cells in a dead body initiate processes that normally would help or heal after infection or injury but death is an insult an organism that cannot recover from. The expression of genes used in embryogenesis could reflect a relaxation of the tight controls on genes that could lead to uncontrolled growth and cancer in a living mature organism. The fact that new RNA is produced up to 48 hours after death, suggests that cells retain sufficient energy and resources to keep going, at least for a while. This research has implications for organ transplantation where organs are harvested from a person who has recently died. What are the consequences of these changes in gene expression on the success of the transplant and the future health of the recipient? Could they develop cancer from the activation of embryonic genes that drive cell growth and division? So the hunt for "Zombie Genes" may not be so farfetched after all. Don't worry, there still is no way that humans can return from death as Zombies to devour humans, with a special fondness for devouring brains, despite their popularity as entertainment.

Medical Discovery News is hosted by professors Norbert Herzog at Quinnipiac University, and David Niesel of the University of Texas Medical Branch. Learn more at

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