Abstract Insects, especially blow flies, are forensically relevant to determine the minimal postmortem interval (PMI min ), based on the fact that they are usually the first colonisers of a body. By estimating the age of immature blow flies, interferences can be made about the time since death. Whilst morphological parameters are valuable for age estimation of blow fly larvae, gene expression profiling is more applicable for blow fly pupae. Here, the age-dependent changes in the gene expression levels during the development are analysed. 28 temperature-independent markers have already been described for the age estimation of pupae of the forensically important blow fly Calliphora vicina and are analysed by RT-qPCR. To allow simultaneous analysis of these age markers, a multiplex assay was developed in the present study. After reverse transcription, the markers are analysed simultaneously in an endpoint PCR and subsequently separated by capillary electrophoresis (CE). This method is highly attractive due to its quick and easy procedure and interpretation. The present age prediction tool was adapted and validated. The multiplex PCR assay reproduced the same expression profiles as the RT-qPCR assay based on the same markers. The statistical evaluation shows that the new assay has a lower precision but a better trueness for age determination compared to the RT-qPCR assay. Since the new assay is also qualified to estimate the age of C. vicina pupae and is practical, cost-effective and, even more importantly, time-saving, it is attractive for use in forensic casework.
In recent years, forensic mRNA profiling has increasingly been used to identify the origin of human body fluids. By now, several laboratories have implemented mRNA profiling and also use it in criminal casework. In 2018 the FoRNAP (Forensic RNA Profiling) group was established among a number of these laboratories with the aim of sharing experiences, discussing optimization potential, identifying challenges and suggesting solutions with regards to mRNA profiling and casework. To compare mRNA profiling methods and results a collaborative exercise was organized within the FoRNAP group. Seven laboratories from four countries received 16 stains, comprising six pure body fluid / tissue stains and ten mock casework samples. The laboratories were asked to analyze the provided stains with their in-house method (PCR/CE or MPS) and markers of choice. Five laboratories used a DNA/RNA co-extraction strategy. Overall, up to 11 mRNA markers per body fluid were analyzed. We found that mRNA profiling using different extraction and analysis methods as well as different multiplexes can be applied to casework-like samples. In general, high input samples were typed with high accuracy by all laboratories, regardless of the method used. Irrespective of the analysis strategy, samples of low input or mixed stains were more challenging to analyze and interpret since, alike to DNA profiling, a higher number of markers dropped out and/or additional unexpected markers not consistent with the cell type in question were detected. It could be shown that a plethora of different but valid analysis and interpretation strategies exist and are successfully applied in the Forensic Genetics community. Nevertheless, efforts aiming at optimizing and harmonizing interpretation approaches in order to achieve a higher consistency between laboratories might be desirable in the future. The simultaneous extraction of DNA alongside RNA showed to be an effective approach to identify not only the body fluid present but also to identify the donor(s) of the stain. This allows investigators to gain valuable information about the origin of crime scene samples and the course of events in a crime case.
