How many times have you watched a murder mystery show where the detective strolls into the murder scene and inspects the victim’s body for just a few moments before confidently declaring the time of death? This may not come as a surprise, but in real life it’s not that simple. In the first few hours, time of death is usually estimated by taking into account physiological factors, like body temperature, rigor mortis and skin discolouration. However, these methods are still largely unreliable and inaccurate, as they can be influenced by a number of factors including the ambient conditions, cause of death, body structure, body location, and drug consumption. Researchers have been searching for ways to make estimating time of death more accurate, and one of these new methods involves looking not just at the body as a whole, but analysing what is inside cells at the molecular level.
Our genetic information is stored in cells as DNA. In order for that information to actually do something, in needs to be read. When DNA is read it is transcribed into RNA, which is then translated into proteins that undertake some action in the cell. When a tissue dies, the cells in that tissue undergo changes in gene expression. A team of researchers in Portugal and Spain has looked at how gene expression changes after death by analysing RNA levels in pre-mortem and post-mortem samples. They found that each tissue exhibits specific changes in gene expression that is not consistent with random RNA degradation but actually a result of active and ongoing gene regulation, even after the organism dies. These changes are speculated to be caused by low oxygen as the blood supply to the tissue is lost. Each tissue type has its own unique pattern of changes in gene expression over time since death. From this, the researchers built a model that can be used to estimate time of death by looking at RNA levels in tissues that are likely to be found in a forensics scenario, including fat, lung, skin and thyroid tissue. They also found no impact of cause of death on their estimates. This technique could not only improve time-of-death estimates in forensic pathology, but also assist researchers working with post-mortem tissue samples and have implications for organ preservation and transplantations. Also, if you’re curious as to how forensic scientists determine time of death after days, or even weeks and months, check out this article on forensic entomology.
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Emi Schutz Archives
March 2018
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