So, you've died. Your heart's stopped pumping, your brain's stopped thinking and, yes, your hair and nails have stopped growing. And yet, despite all this, your genes are still hard at work. Why?
Gene expression — the process by which information stored in DNA is used to create proteins and other molecules — has been shown to continue in the human body after blood stops flowing, sometimes for several days, according to previous research. This cellular skeleton-crew is responsible for shutting down your immune system, metabolism, cell production and other key processes.
And, according to a new paper published Feb. 13 in Nature Communications, watching the activity of these genes in the dead could reveal valuable insights to the living. In the paper, an international team of researchers suggests that monitoring gene expression in various tissues of recently deceased bodies can provide a shockingly accurate timestamp of when that person died. [The Science of Death: 10 Tales from History]
"We found that many genes change expression over relatively short post-mortem intervals, in a largely tissue specific manner," study author Pedro G. Ferreira, a researcher at the Institute of Molecular Pathology and Immunology at the University of Porto in Portugal, said in a statement. By learning to recognize when and where these gene changes occur after an individual dies, researchers may be able to develop models that can accurately estimate time of death.
Scientists can monitor gene expression in various cells by looking at molecules called RNA transcripts, which copy segments of DNA to create proteins. In the new study, researchers analyzed RNA transcription data from more than 7,000 tissue samples collected from 540 deceased donors, including samples from donors' brains, skin and most major organs. The researchers also compared blood samples taken before and after death from select donors, providing the researchers opportunities for direct comparison between pre- and post-mortem gene expression.
"Immediately following death (and up to seven consecutive hours) we observe an increase in the expression of many genes, and a decrease in the expression of a few," the researchers wrote. Most changes occurred between 7 and 14 hours after death, and stabilized significantly within 24 hours.
Using this RNA transcription data, the researchers developed tissue-specific models to predict how much time had elapsed since an individual's death — also known as the post-mortem interval. By averaging the results from each tissue, the researchers found their model could accurately predict the post-mortem interval within about 10 minutes of the actual time, the researchers wrote.
"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," lead author Roderic Guigó, a coordinator of the Bioinformatics and Genomics Program at the Center for Genomic Regulation in Barcelona, told the BBC. "Longer post-mortem intervals, not only 24 hours, the age of the individual, the cause of death — all of these will need to be taken into account if we are to convert this into a useful tool."
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