Alexander Pozhitkov, first author of the study, wondered how long it takes for all cellular processes to end. To begin exploring the question, he teamed up with Peter Noble, who previously studied the behavior of microbes on and in the body following death. Together, they developed a microarray technique called Gene Meter to study the thanatotranscriptome, or post-mortem gene expression levels in newly dead zebrafish and mice.
Conventional microarray qualifies gene expression by normalizing expression profiles against microarray databases. “The major problem with this is you do not know how each probe behaves,” Pozhitkov said. On the other hand, Gene Meter calibrates the microarray probes in a dilution series, allowing a researcher to match the expression patterns to get a magnified range of expression profiles—like the death transcriptome. “It’s like calibrating a pH meter.”
Using this technique, the team found that hundreds of genes are active following death, some showing expression within half-an-hour and others turning on 24, 48, or even 96 hours later. These late expressing genes were involved in stress, immunity, inflammation, apoptosis, transport, development, epigenetic regulation, and cancer.
Because new molecules are synthesized so long after death, the authors suggest that cells maintain sufficient energy and resources for self-organizing processes. “We presume to understand the major biosynthetic and metabolic pathways. So when a system is shutting down, the shut-down has to be predictable in the light of these known pathways,” explained Pozhitkov.
The technique and the results may eventually prove useful for forensic scientists who need to determine time of death, but also show potential for testing the quality of organ transplants, for example, exploring donor rejection rates or cancer incidence in recipients.