Abstract
AbstractThe analysis of age-dependent DNA methylation changes is a valuable tool in epigenetic research and forensic genetics. With some exceptions, most studies in the past concentrated on the analysis of blood, buccal, and saliva samples. Another important sample type in forensic investigations is hair, where age-dependent DNA methylation has not been investigated so far. In this pilot study a deeper look was taken at the possibilities and challenges of DNA methylation analysis in hair. The DNA methylation of selected age-dependent 5’-C-phosphate-G‑3’ (CpG) sites were characterized for their potential use as a biomarker for age prediction using plucked hair samples and massive parallel sequencing. Plucked hair roots of 49 individuals were included in the study. The DNA methylation of 31 hairs was successfully analyzed. The DNA methylation pattern of 10 loci, including ELOVL2, F5, KLF14, and TRIM59, was determined by amplicon-based massive parallel sequencing. Age-dependent changes were found for several markers. The results demonstrate the possible use of already established age-dependent markers but at the same time they have tissue/cell type-specific characteristics. Special challenges such as low amounts of DNA and degraded DNA as well as the possible heterogeneous cellular composition of plucked hair samples, have to be considered.
Highlights
The analysis ofDNA methylation(DNAm) is an interesting forensic tool for applications, such as age prediction and tissue or body fluid determination [30]
The collected hairs can originate from different phases of the hair cycle, as human hair growth is not synchronized, which may result in varying DNAm patterns [16, 24]
The Y axis was adjusted to the range of observed DNAm values and a linear regression line included cells obtained by plucking varies and that multiple cell types, such as keratinocytes, melanocytes, mesenchymal cells, as well as stem cells can be included in the analysis of plucked hairs [27]
Summary
The analysis ofDNA methylation(DNAm) is an interesting forensic tool for applications, such as age prediction and tissue or body fluid determination [30]. Other tissues were examined and some of the commonly used DNAm markers were found to be age-dependent in multiple tissues, of which some showed very tissue-specific changes with age [3, 13,14,15, 23] Another important trace found at crime scenes is hair that has not yet been considered for age prediction using DNAm analysis. In forensics, the term “hair” often refers to the hair shaft only or to a hair shaft with a root without any (detailed) specification of the presence of attached cells; having a look at the total hair follicle, nuclear DNA can derive from multiple cell origins developed from different germ layers: undifferentiated cells, dermal fibroblasts, melanocytes and differentiating keratinocytes in the bulb as well as cells of the inner and outer root sheath, stem cells in the bulge and fully differentiated keratinocytes (dead cells, trichocytes) [25, 27, 29]. The majority of epithelial structures from the hair follicle and part of the bulge containing the stem cells for keratinocyte and melanocyte production, remain attached to the plucked hair but not all of the connective tissues [11]
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