Towards localizing head shots – Forensic sub-differentiation of anatomical brain regions by differential RNA expression

Abstract

The detection of organ tissues, including brain, in even challenged forensic sample material by forensic RNA analysis has become a valid and routinely used method of trace contextualization. However, in cases of severe head traumas dealt by blunt impacts or firearm projectiles, for example in situations when multiple offenders handled different weapons, it can be beneficial for criminal investigations to determine by analysis of traces of biological material which area of the head had been hit (and by whom) by proxy of detecting which part of the brain had been injured. A whole transcriptome analysis employing massive parallel RNA Sequencing of four different anatomical areas of the cerebral cortex (frontal, temporal, parietal, occipital) was performed on a training set of autopsy samples from brain tissue. Applying different bioinformatic classification algorithms brain area specific mRNA candidates were selected and suitable markers were then validated on an independent test set of autopsy brain samples using quantitative RT-PCR. Here we found, that the differences in mRNA transcription of these two markers between the four brain regions were too small and less pronounced to be useful for and applicable in forensic RNA analysis. Hence, we conclude, that sub-differentiation of these brain regions via RNA expression analysis is out of forensic scope.