Zombie Genes

 

Geneticists usually concern themselves with gene expression in living organisms. This makes perfect sense. What is the point of checking out genes when you are dead? Received wisdom suggests that all genetic expression stops when an organism dies. Of course when you die, and I'm talking about brain death, not all  cells in a body die immediately. After death cellular activity starts to wind down as cells deplete oxygen and energy resources. Some cells can be alive several days after death.

Work on Zebra fish and mice have shown some startling and largely unexpected results. Just an aside, Zebra fish and mice are often used for genetic research because both these species have been studied for a number of years and their respective genomes are well characterised. Researchers looked at a number of genes involved in various cellular processes such as the inflammatory response, the immune response and genes involved in development and cancer. Some of these genes were still active four days after death. Individual cells are not aware of the organism's death but they do 'sense' that something is amiss and this triggers a stress response. In other circumstances this response is adaptive and useful and helps to combat physiological and metabolic challenges. Therefore, the up regulation of genes involved in the inflammatory response should come as no surprise. What did surprise the scientists was the 'switching on' of genes usually only expressed during early development. These are genes that are active during foetal gestation and during the critical developmental stage just after birth. Normally these genes become dormant during the rest of the organism's life. The expression of these genes, in death, appears paradoxical. 

Also of interest was the observation that certain genes involved in some cancers are switched on. This has important implications for donor organs and may explain, to some degree at least, why recipients of donor organs have an increased cancer incidence. However, it has to be acknowledged that the anti-rejection drugs designed to suppress the immune system have an important role in the development of cancer in transplant patients. Even so, an understanding of genetic events during death can help to mitigate, at least, some of the cancer related problems associated with organ transplantation.

Genetic post-mortem changes could help establish the time of death in murder cases. Genetic expression profiles follow a well defined sequence after death which could allow the highly accurate determination of the time of death, even within minutes. This of course has utility in the medico-legal world. 

We are indeed living in interesting times. The increase in our genetic knowledge and technology is occurring at a giddy pace. As a geneticist in the twilight of his career I'm well aware that I will miss out on most of the wondrous advances happening, on almost a daily basis, in my profession. Tis nearly time for me to retire and spread out my dotage in the home for 'Bewildered Cytogeneticists'. A new generation is poised, and eager, to takeover and replace weary old bones. Now, isn't that the sad truth- or is it?