This article provides background information, methodology, and findings for a study that examined whether RNA, which decomposes quickly, can provide information on a sample's age.
Background information notes that although DNA is housed in the nucleus of the cell, the molecular machinery responsible for protein assembly is housed outside the nucleus. For the critical instructions to exit the nucleus, they must be transcribed to a temporal molecule called RNA, which, due to its small size, can travel outside the nucleus. Just as all the cell's DNA is called the "genome," all of the transcribed RNA molecules are called its "transcriptome." Since it comes directly from DNA, the transcriptome has the potential to identify individuals, reconstruct phenotypes, and suggest ancestry, just as does DNA; and RNA can potentially identify tissue and fluid types. A major complication with the transcriptome regarding its forensic value, however, is its rapid degradation. The study reported in this article examined what determines the rate of RNA decay and whether this rate is different for different genes; and if so, why. The research team collected specimens of blood, saliva, semen, and vaginal fluids. From zero to 360 days after collection, RNA was isolated from the samples and sequenced, using a Next-Generation Sequencing (NGS) system. The study determined that different fluids generally had different RNA transcripts, or if the same, at different amounts; however, even when comparable in both identity and amount at time zero, they would disappear at different rates. From these findings, the study argues that forensic scientists could identify when a particular body fluid was deposited at a crime scene.