Sequencing Hair Shafts

Hair shafts are a promising source of ancient DNA. Long-term hair survival occurs in a variety of natural environments, and large quantities are present in taxonomic collections representing most extant, and many recently extinct, mammalian taxa. Most hair-based genetic studies have used roots, instead of shafts, as a DNA source, primarily because hair shafts consist of dead keratinized cells that contain relatively low levels of DNA. However, several studies have reported shafts as a viable source of modern and ancient mitochondrial DNA. Furthermore, several properties of shafts suggest that they constitute an attractive DNA source for SBS (sequencing-by-synthesis). First, their relative abundance (when present) renders them preferable to bones, because the destructive nature of bone sampling can lead to the loss of important morphological information. Second, turnover of keratinocytes in the hair bulb is exceedingly high, second only to that of cells in the gut epithelium. Therefore, baseline mitochondrial levels in these cells (and thus the precortical cells that develop into the bulk of the shaft) may be higher than those in other tissues commonly used for ancient DNA analyses. Third, even when degraded, shafts are resistant to contamination from exogenous DNA such as bacteria, blood, and skin cells.

Our earlier work showed that hair shafts are a good source of mitochondrial and nuclear DNA from woolly mammoths. However, for the following reasons it remained to be tested whether hair shafts work well for sequencing other species.

The current study shows that adequate amounts of DNA can be obtained from tiny quantities of hair shafts from museum specimens stored under diverse conditions. However, although our method worked in two cases, it failed to produce useful DNA for two other specimens.