MicroRNAs and Body Fluid Identification

MicroRNAs (miRNAs) are small (18-25 nucleotides), non-coding, single-stranded RNA molecules found in plants, animals, and viruses. These molecules play a role in RNA silencing and post-transcriptional regulation of gene expression and, therefore, can be used as a biomarker for body fluid identifications (BFID). While messenger RNA (mRNA) and miRNA demonstrate tissue-specific expression, miRNAs are more stable in compromised samples due to their small size and highly abundant per cell. For these reasons, forensic scientists have looked into these biomolecules for determining the DNA source recovered from casework evidence. Forensic DNA analysis is often performed on many types of substrates such as saliva, semen, venous blood, menstrual blood, tissues, teeth and bone, etc. In some cases, it would be beneficial to know whether the DNA came from a sperm cell versus an epithelial cell, for example. Traditionally, this was done by cutting a vaginal swab in half and smearing one half on a slide to visualize if sperm was present under a microscope. The other half would go onto DNA analysis. This is not ideal because the foreign male DNA could be present in low amounts and half of the material has now been consumed. Therefore, one study looked at co-extraction and co-analysis of DNA and miRNA to obtain an STR profile (for human identification, HID) and determine the origin of that DNA (BFID). They specifically looked at 4 miRNA markers for menstrual blood, venous blood, and semen in a multiplex reaction. Then they amplified the co-extracted DNA with a commercial STR kit. Both amplified products from DNA and miRNA were separated and detected on the same capillary electrophoresis (CE) platform. They were successfully able to determine the source of DNA and the origin of where it came from. Likewise, another study looked at 8 miRNA markers for blood, saliva, semen, and vaginal material using quantitative PCR (qPCR) compared to CE. The results of the study showed that blood and semen were highly distinguishable from the other fluids, but saliva and vaginal fluid have many markers in common. In addition, the CE analysis was able to detect absence or presence of miRNAs like qPCR; however, CE analysis also offers an indication of expression level. In conclusion these studies show the possibility for confirmed BFID with co-analysis of DNA with the potential for an extended panel of markers.

References:

1)     Li Y, Zhang J, Wei W, Wang Z, Prinz M, Hou Y. A strategy for co-analysis of microRNAs and DNA. FSI:Genetics 12 (2014) 24-29.

2)     van der Meer D J, Williams G A. Performing body fluid identification with microRNAs using capillary electrophoresis. FSI: Genetics Supplement Series 5 (2015) e592-e594.