An mRNA and DNA co-isolation method for forensic casework samples

RNA analysis is expected to play an increasingly important role in the area of biomolecular forensic analysis. For example, mRNA expression analysis performed on a total RNA sample isolated from a biological stain may be used to identify the nature of the tissue(s) comprising the stain. Many of the physiological stains encountered at crime scenes involve heterogeneous mixtures of different body fluids (e.g., semen and saliva, semen and vaginal secretions). Separate sampling of these mixed stains from different "geographical" locations of the stains to isolate DNA and RNA could result in a misleading estimate of the ratio of the body fluids present and, in extreme cases, even fail to detect one of the contributors. Thus, a prerequisite for the use of mRNA expression profiling in routine forensic analysis is the ability to co-extract DNA and RNA from the same stain. This article describes an optimized method that was specifically developed to co-extract mRNA and DNA from the same physiological stain and that appears to be sufficiently sensitive and robust for routine forensic use.