Differential DNA Preservation of Thermally Altered Tissue and Bone

Recovering high-quality DNA from thermally altered human remains poses a significant challenge for research and law enforcement agencies due to high levels of DNA degradation resulting from exposure to extremely high temperatures (e.g., fire). The current standard practice for the DNA identification of badly burned skeletal remains is to extract DNA from dense cortical bone collected from recovered skeletal elements. Some of the problems associated with this method are that it requires specialized equipment and training, is highly invasive (involving the physical destruction of sample material), time-consuming, and does not reliably guarantee the successful identification of the remains in question. At low-medium levels of thermal exposure, charred tissue is often adhered to these skeletal remains and typically discarded. In cases where burned/charred tissue is recoverable, it has the potential to be a more efficient alternative to the sampling of cortical bone. However, little has been done to test the viability of thermally altered soft tissue in terms of DNA identification to date. Burned/charred tissue was collected from skeletal samples provided by the University of Tennessee Forensic Anthropology Center, as a part of a controlled burn from donor individuals, for downstream laboratory processing and DNA analysis as part of the Stone Lab (Arizona State University, School of Human Evolution and Social Change). DNA from this charred tissue was extracted using the Qiagen DNeasy Blood and Tissue Kit, and resulting yields were quantified via fluorometry using the Qubit Fluorometer 2.0 and Agilent TapeStation 4200 High-Sensitivity D5000 assay. It was found that between the temperatures of ~200-300 ℃ (burn category 2) and ~300-350 ℃ (burn category 3), tissue was the most efficient extraction type, especially from tissue taken from the surface of the ilium and the rib. As for bone, both the Dabney and the Loreille protocol performed similarly, so choice in extraction type comes down to personal preference, type of equipment on hand, and training. Although, for samples with low input material, the Dabney protocol is optimal.