Recently, several authors described the observation that RNA degradation does not correlate with the postmortem interval (PMI), but rather with other parameters like environmental impact and the circumstances of death. Therefore, the question arose if the analysis of gene expression could be a valuable tool in forensic genetics to contribute to the determination of the cause of death. In our study, six human tissues obtained from six individuals with PMI varying between 15 and 118 h were used for total RNA extraction. Quantification was performed using a GAPDH real-time assay, and the quality of mRNA was checked by amplification of different fragment lengths of the GAPDH transcript. In our set of samples, nearly all tissues in all PMI revealed satisfactory results, while skeletal muscle, followed by brain and heart, gave the best results. No correlation between PMI and RNA degradation could be detected, as very good results were observed for all tissues from the individual with the longest PMI. The highly promising results obtained in this study raise hopes that in the near future several fields of forensic investigation may profit from additional information about gene expression patterns and their correlation with pathological findings.

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BackgroundThe Host Cell Reactivation Assay (HCRA) is widely used to identify circumstances and substances affecting the repair capacity of cells, however, it is restricted by the transfection procedure used and the sensitivity of the detection method. Primary skin cells are particularly difficult to transfect, and therefore sensitive methods are needed to detect any variations due to the cell-type or inter-individual differences or changes induced by diverse substances.A sensitive and repeatable method to detect the repair capacity of skin cells would be useful in two different aspects: On the one hand, to identify substances influencing the repair capacity in a positive manner (these substances could be promising ingredients for cosmetic products) and on the other hand, to exclude the negative effects of substances on the repair capacity (this could serve as one step further towards replacing or at least reducing animal testing).ResultsIn this paper, we present a rapid and sensitive assay to determine the repair capacity of primary keratinocytes, melanocytes and fibroblasts based on two wave-length Green Fluorescent Protein (GFP) and DsRed reporter technology in order to test different substances and their potential to influence the DNA repair capacity. For the detection of plasmid restoration, we used FACS technology, which, in comparison to luminometer technology, is highly sensitive and allows single cell based analysis.The usefulness of this assay and studying the repair capacity is demonstrated by the evidence that DNA repair is repressed by Cyclosporin A in fibroblasts.ConclusionsThe methodology described in this paper determines the DNA repair capacity in different types of human skin cells. The described transfection protocol is suitable for the transfection of melanocytes, keratinocytes and fibroblasts, reaching efficacies suitable for the detection of the restored plasmids by FACS technology. Therefore the repair capacity of different cell types can be compared with each other. The described assay is also highly flexible, and the activity of other repair mechanisms can be determined using modifications of this method.

Additional Supporting Information may be found in the online version of this article: Figure S1. Role of SIRT2 in UVB-induced DNA damage repair and apoptosis, and cell proliferation. Appendix S1. Methods. Mitochondrial DNA copy number -but not a mitochondrial tandem CC to TT transition -is increased in sun-exposed skin Abstract: Mitochondrial DNA (mtDNA) mutations are causatively associated with photo-ageing and are used as biomarkers of UV exposure. The most prominent mitochondrial mutation is the common deletion (CD), which is induced in many tissues by oxidative stress. More photo-specific mutations might be CC to TT tandem transitions which arise from UV-induced cyclobutane pyrimidine dimers. As nucleotide excision repair is absent in mitochondria, this DNA damage can presumably not be repaired resulting in high mitochondrial mutation levels. Here, we analysed levels of the CD, a mitochondrial and a chromosomal tandem transition in epidermis and dermis from exposed and less UVexposed skin. We also analysed mtDNA copy number, for which changes as a result of oxidative stress have been described in different experimental settings. Whereas mitochondrial tandem transition levels were surprisingly low with no discernible correlation with UV exposure, mtDNA copy number and CD were significantly increased in UV-exposed samples.