In this study, mRNA degradation in fresh and aged body fluid stains (blood, saliva, semen, and vaginal fluid) was analyzed, using next-generation RNA sequencing (RNA-seq).
Forensic applications of RNA analysis have included body fluid identification and analysis of RNA degradation in aged stains as a possible indicator of time. With respect to age estimation of a stain through RNA analysis, a full understanding of the patterns and rates of RNA degradation in postmortem samples and body fluid stains is lacking. In the current study, the global abundance of transcripts present in each of the different stains decreased with time; however, within the global population, specific transcripts disappeared from RNA extracts with differing rates; for example, a positive correlation was observed between the initial abundance of a typical transcript and the time it could no longer be detected in the RNA-seq results. In other words, the greater the initial transcript abundance, the longer it could be detected with RNA-seq. Transcripts, of the same time zero abundance, that nonetheless disappeared from the transcriptome at different time points during storage could be readily identified and were members of transcript groups common to all body fluid stains, as well as groups whose presence was restricted among body fluids. A possible relationship between transcript length and longevity during storage was investigated, and no significant correlation was found. Results of this study will contribute to the understanding of mRNA degradation in forensically relevant body-fluid stains in ways that may lead to developing a tool to estimate the age of a stain at a crime scene. (publisher abstract modified)