Auto-fluorescence emitted from the cell residues preserved in human tissues of medieval Korean mummies

As a significant association has been established between residual ancient DNA (aDNA) and histological preservation, the morphological identification or confirmation of preserved cell residue in ancient tissues would greatly facilitate aDNA studies and enhance the definitiveness of their conclusions. However, morphological differentiation of cell residue from other tissue structures has always been difficult, even for experienced histologists, due to the severe degradation of cells over long burial durations. In the present study, using a fluorescence microscopy equipped with a specific type of filter set (excitation filter, 510-550 nm; dichroic mirror, 570 nm; emission filter, approximately 590 nm), we found that certain structures in well-preserved mummified tissues emitted auto-fluorescence. Those structures were actually cell residues (e.g. fragmented DNA), laser capture microdissection and Quantifiler kit analysis having shown that preservation of nuclear DNA correlates with auto-fluorescence emission in laser capture microdissection-captured areas. Detection of auto-fluorescence could be an effective means of identifying cell residues in ancient tissue, enabling selection of the well-preserved samples necessary in successful aDNA studies.