Gene expression after death: a new research field

Transcriptomics is the study of mRNA expressed through the genes of an organism. According to a new study in transcriptomics, researchers at the University of Washington (Seattle, USA) have demonstrated that gene expression is not abruptly switched off immediately after death and can, in fact, be observed 48 to 96 hours after a living organism has been declared dead. Using microarray-based gene expression profiling, a sudden decrease of total mRNA abundance was observed in zebrafish 12 hours postmortem. Slightly different patterns were observed when using mRNA extracted from mouse brain and liver. Total mRNA abundance in mouse brain increased in the first hour and then gradually decreased over the next 48 hours. Finally, a slow and gradual decrease in total mRNA abundance was seen in mouse liver. Expression of 548 zebrafish genes and 515 mouse genes was found to be significantly up-regulated after death of healthy adults suggesting that the transcription machinery has still access to sufficient energy sources and is still very much functional even long after death.

Scientists determined that the up-regulation of these genes was not random, that discernible patterns could be seen in both organisms, and that genes could be grouped in categories such as apoptosis, inflammation, immunity, or stress. It can be hypothesized that the over-expression of these genes is a response mechanism to cope with a new environment, a sort of physiological process that unnecessarily facilitates healing after severe damage. Genes involved in embryonic development, epigenetic regulation, and cancer are also of particular of interest as their expression seems to peak about 24-48 hours after death. These genes might help us understand their implication in the postmortem up-regulation of genes, which would be otherwise absent or silent in a living organism. Although some studies showed the expression of genes involved in wound healing after death in humans who had suffered from multiple trauma, further research will be required in order to determine whether similar profiles exist in human samples.

Thanatotranscriptomics is clearly a new and promising concept, albeit spine-chilling. Investigations conducted by forensic scientists might be facilitated by this discovery as they will be able to determine time since death more precisely, in terms of hours rather than days. Finally, the study of these genes may also offer additional insight as to why people receiving organ transplants are more likely to develop cancer.
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