Is there life after death? This certainly is one of humanity’s oldest questions and has been the target of several religious, philosophic and scientific hypotheses and tales throughout time. Now, scientists have discovered that at least part of animal’s life machinery continues to work for up to four days after what we now consider as death – and it has nothing to do with zombies or spirits either.
Alex Pozhitkov and his group developed a research driven by the curiosity in the processes of shutting down a complex biological system. They studied activity patterns of genes through postmortem time in two species: zebrafish and mouse.
We tend to see death as a gradual disengagement and loss of regulatory functions, like a car running out of gas. “For a short time, engine pistons will move up and down and spark plugs will spark – but eventually the car will grind to a halt and ‘die'”, Pozhitkov’s group says in their article. Unexpectedly, they found that hundreds of genes not just continue to be expressed, but present more intense activity (they are “upregulated”) after organismal death. “This finding is surprising because in our car analogy, one would not expect window wipers to suddenly turn on and the horn to honk several days after running out of gas”, they say.
A living biological system is a product of self-organizing processes, regulated by networks of genes transcription and proteins translation. Even genes expressed after death seem to make it in non-random way, suggesting that some kind of global regulation network is still operating. Increased expression occurred, for example, in genes related to stress, immunity, development and cancer, following different timing patterns.
Why specifically these genes are turned on after death is an interesting question from now on. One possibility is that upregulating stress and immunity genes could be an organism’s last attempt to reestablish equilibrium, favoring healing or “resuscitation” after severe injury. Alternatively, it may occur due to fast deterioration of important inhibitors of these genes. That might be the case of the unexpected postmortem increase in activity of development genes. Such genes’ activities are essential at early stages of organism’s development, when in fetal stage. After organismal death, they pass through progressive activation, suggesting that they are no longer silenced.
Many questions in evolution of these processes also remain to be investigated, since genes’ increased activity offers no obvious benefit to a dead organism. Anyway, since some genes’ increased activity after death occurred in both the zebrafish and the mouse, it is reasonable to suggest that a similar phenomenon is displayed by other animals.
When scientists better explore how these results are comparable to what occurs in humans, it can lead to plentiful practical uses. For example, we could better estimate the time of death in forensic investigations. Another important possibility in medicine is to improve organ transplantation techniques. Nowadays, transplanted individuals have increased risk to develop cancer. One of the possible reasons for this, demonstrated by this research, is that cancer related genes are also upregulated after death. With more investigations on it, we can better understand timing pattern of these genes’ activation and possibly establish an optimum timing for organ’s removal.
Peter Noble, one of the authors of the research, said to ScienceMag: “the headline of this study is that we can probably get a lot of information about life by studying death”.
Bruna de Oliveira Cassettari
Pozhitkov A. E. et al. Thanatotranscriptome: genes actively expressed after organismal death. bioRxiv preprint (2016). DOI: http://dx.doi.org/10.1101/05830
Mitch Leslie. ‘Undead’ genes come alive days after life ends. ScienceMag (2016). DOI: 10.1126/science.aaf5802