Characterization of Nuclei Shapes in Hair Roots

Abstract

In a previous study, 4′,6-diamidino-2-phenylindole (DAPI), a minor groove DNA binding dye, was successfully evaluated as a method to stain nuclei in hair roots for successful nuclear DNA analysis. The DAPI-stained nuclei were visualized and counted through high-magnification fluorescence microscopy. A variety of nuclei shapes (area and circularity) and sizes were identified. In this study, we illustrate examples of what forensic examiners can expect when visualizing DAPI-stained hair roots. The diversity of nuclei shapes and sizes described here can serve as a practical guide to assist forensic examiners in conducting examination of DAPI-stained hair roots and DAPI-stained nuclei counting. Awareness of different nuclei shapes, the general shape of nuclei at the peripheries of soft tissue, nuclei orientation, the developmental and mechanical forces that shape nuclei, peripheral distortion challenges, nuclear stain intensity, and potential overlap of nuclei allows examiners to better distinguish true nuclei from staining artifacts or other features that have no consequence in nuclear DNA analysis. Consequently, all the nuclei present in a hair root may not be visible and nuclei count should be approximated because the exact number may not be known with certainty. All the above highlight the importance and justify why examiners are recommended to use the expression “DAPI-stained visible nuclei” when reporting nuclei count results. Despite the existence of uncertainty in the nuclei counting process, the best estimate of the number of visible nuclei in a hair will help route hair samples for the appropriate DNA analysis and increase the success rate of nuclear DNA analysis of hairs in forensics.