Novel messenger RNAs for body fluid identification

In forensic investigations, the identification of the cellular or body fluid source of biological evidence can provide crucial probative information for the court. Messenger RNA (mRNA) profiling has become a valuable tool for body fluid and cell type identification due to its high sensitivity and compatibility with DNA analysis. However, using a single marker to determine the somatic origin of a sample can lead to misinterpretation as a result of cross-reactions. While false positives may be avoided through the simultaneous detection of multiple markers per body fluid, this approach is currently limited by the small number of known differentially expressed mRNAs. Here we characterise six novel mRNAs, partly identified from RNA-Seq, which can supplement existing markers for the detection of circulatory blood, semen (with and without spermatozoa), and menstrual fluid: HBD and SLC4A1 for blood, TNP1 for spermatozoa, KLK2 for seminal fluid, and MMP3 and STC1 for menstrual fluid. Respective expression profiles were evaluated by singleplex endpoint reverse transcription polymerase chain reaction (RT-PCR). HBD, SLC4A1, and KLK2 were specific to their target body fluids. TNP1, MMP3, and STC1 each cross-reacted with two non-target samples; however, these signals were below 350 RFU, not reproducible, and likely resulted from large body fluid inputs. All candidates were more sensitive for the detection of their target body fluids than corresponding well-known mRNAs, in particular those for menstrual fluid. The increased sensitivities were statistically significant, except for KLK2. Thus, the new mRNAs introduced here are promising new targets for improved body fluid profiling.