The source of RNA is a special issue for studies of gene expression in the brain. Commonly, postmortem brain tissue is used for the transcriptome profiling. In contrast to the relative stability of the carrier of the genetic information, DNA, RNA molecules, as temporal functional products of the realization of genetic information, are characterized by a short life-span. A special set of enzymes--ribonucleases, or RNases--are responsible for the fast degradation of RNA in vivo. This enzymatic utilization of RNAs might continue for a time after death, also postmortem chemical and thermal processes might lead to the rapid postmortem degeneration of RNAs. RNA degradation leading to qualitative and quantitative changes in the composition of the transcriptome is one of the main problems in the reliable detection of whole-genome expression profiles. Thus the nature and effects of pre- and postmortem conditions on RNA in brain tissue – such as the condition of the patient prior to death and the postmortem interval (the time that has elapsed since a person has died, PMI) – are the special subject of investigations.
