Recovery and stability of RNA in vaginal swabs and blood, semen, and saliva stains

RNA expression patterns, including the presence and relative abundance of particular mRNA species, provide cell and tissue specific information that could be used for body fluid identification. In this report, we address perceived concerns on the stability, and hence recoverability, of RNA in forensic samples. Stains were prepared from blood, saliva, semen, and vaginal secretions and exposed to a range of environmental conditions from 1 to 547 days. The persistence and stability of RNA within each type of body fluid stain were determined by quantitation of total RNA, and reverse transcriptase-polymerase chain reaction (RT-PCR) using eight different mRNA transcripts from selected housekeeping and tissue-specific genes. The results demonstrate that RNA can be recovered from biological stains in sufficient quantity and quality for mRNA analysis. On average, several hundred nanograms of total RNA was recovered from 50-mu L-sized blood and saliva stains, 1 mu g from a 50-mu L semen stain and nearly 70 mu g from a whole vaginal swab. Messenger RNA is detectable in some samples stored at room temperature for at least 547 days. The environmental samples that were protected from direct rain impact exhibited housekeeping and tissue specific mRNA recoverability up to 7 days (saliva and semen), 30 days (blood), or 180 days (vaginal swab). Additionally, rain had a detrimental effect on the recoverability of blood (3 days), saliva (1 day), semen (7 days), and vaginal secretions (3 days) specific transcripts, with one of the mRNA species (the semen marker PRM2) not being detectable after 1 day.