Baiting ancient DNA with RNA

A new paper by Meredith Carpenter and colleagues describes a novel method that can greatly enrich the yield of DNA from ancient samples:

Most ancient specimens contain very low levels of endogenous DNA, precluding the shotgun sequencing of many interesting samples because of cost. Ancient DNA (aDNA) libraries often contain <1% endogenous DNA, with the majority of sequencing capacity taken up by environmental DNA. Here we present a capture-based method for enriching the endogenous component of aDNA sequencing libraries. By using biotinylated RNA baits transcribed from genomic DNA libraries, we are able to capture DNA fragments from across the human genome. We demonstrate this method on libraries created from four Iron Age and Bronze Age human teeth from Bulgaria, as well as bone samples from seven Peruvian mummies and a Bronze Age hair sample from Denmark. Prior to capture, shotgun sequencing of these libraries yielded an average of 1.2% of reads mapping to the human genome (including duplicates). After capture, this fraction increased substantially, with up to 59% of reads mapped to human and enrichment ranging from 6- to 159-fold. Further- more, we maintained coverage of the majority of regions sequenced in the precapture library. Intersection with the 1000 Genomes Project reference panel yielded an average of 50,723 SNPs (range 3,062147,243) for the postcapture libraries sequenced with 1 million reads, compared with 13,280 SNPs (range 21773,266) for the precapture libraries, increasing resolution in population genetic analyses. Our whole-genome capture approach makes it less costly to sequence aDNA from specimens containing very low levels of endogenous DNA, enabling the analysis of larger numbers of samples.

The paper includes a very interesting discussion of the relative costs of different capture methods that have been applied to ancient specimens. There is also this, in the acknowledgements:

Portions of this manuscript are subject to one or more patents pending.

UPDATE (2013-11-03): Oops. The “less-than” sign is a special character in HTML that I didn’t escape out of the quote; sorry I left the incomplete quote up so long but I was out of town. Fixed now.

Reference:

Carpenter, M. et al. (2013). Pulling out the 1%: Whole-Genome Capture for the Targeted Enrichment of Ancient DNA Sequencing Libraries, The American Journal of Human Genetics, http://dx.doi.org/10.1016/j.ajhg.2013.10.002