A novel method for the simultaneous co-isolation of DNA and mRNA for forensic casework samples

Current DNA and mRNA co-isolation methods proposed for the analysis of forensic casework
samples involve the physical separation of the DNA and mRNA phases. Whilst this separation is
useful, it does lead to increased opportunities for contamination as there are now two down-stream
work processes. Also, the scientist’s opinion as to the attribution of a DNA profile to a particular
body fluid would not be particularly robust. Furthermore, these methods often use hazardous
chemicals such as phenol/chloroform and are time costly.
The use of silica-coated and oligo-dT coated magnetic beads offers a co-isolation method that delays
the separation of the DNA and the mRNA phases, thus reducing the opportunities for down-stream
contamination. The magnetic beads method does not use any hazardous chemicals, thus offering
safer and faster co-isolation. The aim was to develop a novel co-isolation technique that was at least
comparable to the single isolation methods of DNA and mRNA.
Saliva and blood stains were collected using buccal swabs and the finger prick method, respectively.
The DNA/mRNA was extracted by a combination of silica coated magnetic beads and oligo-dT coated
magnetic beads. The isolated and purified sample underwent nucleic acid quantification using a
Nano-drop spectrophotometer. Analysis of the DNA phase was carried out using the Qiagen ESSPlex
investigator on an ABI 310 genetic analyser. The mRNA phase underwent reverse transcription
before undergoing PCR targeting body fluid specific mRNA markers. The mRNA amplicons were
visualised using a 2% agarose gel. The DNA results acquired from this co-isolation method were then
compared to the DNA results obtained from using single isolation method. A successful co-isolation
method is one that does not adversely affect the quality of the DNA result.