Abstract
Mummified remains have long attracted interest as a potential source of ancient DNA. However, mummification is a rare process that requires an anhydrous environment to rapidly dehydrate and preserve tissue before complete decomposition occurs. We present the whole-genome sequences (3.94 X) of an approximately 1600-year-old naturally mummified sheep recovered from Chehrābād, a salt mine in northwestern Iran. Comparative analyses of published ancient sequences revealed the remarkable DNA integrity of this mummy. Hallmarks of postmortem damage, fragmentation and hydrolytic deamination are substantially reduced, likely owing to the high salinity of this taphonomic environment. Metagenomic analyses reflect the profound influence of high-salt content on decomposition; its microbial profile is predominated by halophilic archaea and bacteria, possibly contributing to the remarkable preservation of the sample. Applying population genomic analyses, we find clustering of this sheep with Southwest Asian modern breeds, suggesting ancestry continuity. Genotyping of a locus influencing the woolly phenotype showed the presence of an ancestral ‘hairy’ allele, consistent with hair fibre imaging. This, along with derived alleles associated with the fat-tail phenotype, provides genetic evidence that Sasanian-period Iranians maintained specialized sheep flocks for different uses, with the ‘hairy’, ‘fat-tailed’-genotyped sheep likely kept by the rural community of Chehrābād's miners.
Highlights
Metagenomic analyses reflect the profound influence of high-salt content on decomposition; its microbial profile is predominated by halophilic archaea and bacteria, possibly contributing to the remarkable preservation of the sample
In 1993, a remarkably preserved human body dating to approximately 1700 years Before Present (BP) was discovered in the Douzlakh salt mine near Chehrabad village in the Zanjan Province of northwest Iran [1,2,3]
The leg was possibly discarded during food preparation activities, as both sheep and goat were likely used as provisioning for Sasanian-period miners; equines may have been used as beasts of burden [16]
Summary
In 1993, a remarkably preserved human body dating to approximately 1700 years Before Present (BP) was discovered in the Douzlakh salt mine near Chehrabad village in the Zanjan Province of northwest Iran [1,2,3]. The leg was possibly discarded during food preparation activities, as both sheep and goat were likely used as provisioning for Sasanian-period miners; equines may have been used as beasts of burden [16]. By this time, sheep were an established commodity for their meat and secondary products such as wool fibre, which was widespread by the fourth millennium BCE and showed regional specialization by the third millennium BCE [17]. We find unusual survival patterns of endogenous DNA given its distance from the equator, implying that exceptional preservation of nucleic acid integrity was afforded by the unique saltrich environment This enables characterization of the mummy skin metagenome and population genomic profiling of this sheep in the context of modern breeds. We genotype the antisense EIF2S2 retrogene insertion within the 30 UTR of the IRF2BP2 gene that influences the woolly phenotype and is derived relative to the ancestral coarse ‘hairy’ coat [19], in tandem with fibre analysis using scanning electron microscopy (SEM)
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