Preservation of ancient DNA in thermally damaged archaeological bone

Relationship Between Amplicon Size and Heat Conditions in Polymerase Chain Reaction Detection of DNA Degraded by Autoclaving

This study examined the influence of heat exposure on DNA samples during polymerase chain reaction (PCR) detection. In this study, λDNA samples, as model DNA, were exposed to 105°C for 3-90 minutes or to 105°C-115°C for 15 minutes by autoclaving. The exposed samples were subjected to real-time PCR using nine primer sets with amplicon sizes of 45-504 bp. Regarding DNA samples exposed to 105°C by autoclaving, the data showed negative correlations between the logarithm of λDNA concentration (log λDNA) calculated using real-time PCR and exposure duration and a good relationship between the slope of the regression line and amplicon size. Regarding λDNA samples exposed to heat for 15 minutes, the data showed negative correlations between the log λDNA and exposure temperature and a good relationship between the slope of the regression line and amplicon size. These results showed that the equations used in this study could predict the degree of degradation in λDNA samples by autoclaving, and the PCR detection levels of the DNA at each amplicon size.

A fresh perspective on infrared spectroscopy as a prescreening method for molecular and stable isotopes analyses on ancient human bones

Following the development of modern genome sequencing technologies, the investigation of museum osteological finds is increasingly informative and popular. Viable protocols to help preserve these collections from exceedingly invasive analyses, would allow greater access to the specimens for scientific research. The main aim of this work is to survey skeletal tissues, specifically petrous bones and roots of teeth, using infrared spectroscopy as a prescreening method to assess the bone quality for molecular analyses. This approach could overcome the major problem of identifying useful genetic material in archaeological bone collections without resorting to demanding, time consuming and expensive laboratory studies. A minimally invasive sampling of archaeological bones was developed and bone structural and compositional changes were examined, linking isotopic and genetic data to infrared spectra. The predictive model based on Infrared parameters is effective in determining the occurrence of ancient DNA (aDNA); however, the quality/quantity of aDNA cannot be determined because of the influence of environmental and local factors experienced by the examined bones during the burial period.

MTaxi: A comparative tool for taxon identification of ultra low coverage ancient genomes

A major challenge in zooarchaeology is to morphologically distinguish closely related species' remains, especially using small bone fragments. Shotgun sequencing aDNA from archeological remains and comparative alignment to the candidate species' reference genomes will only apply when reference nuclear genomes of comparable quality are available, and may still fail when coverages are low. Here, we propose an alternative method, MTaxi, that uses highly accessible mitochondrial DNA (mtDNA) to distinguish between pairs of closely related species from ancient DNA sequences. MTaxi utilises mtDNA transversion-type substitutions between pairs of candidate species, assigns reads to either species, and performs a binomial test to determine the sample taxon. We tested MTaxi on sheep/goat and horse/donkey data, between which zooarchaeological classification can be challenging in ways that epitomise our case. The method performed efficiently on simulated ancient genomes down to 0.3x mitochondrial coverage for both sheep/goat and horse/donkey, with no false positives. Trials on n=18 ancient sheep/goat samples and n=10 horse/donkey samples of known species identity also yielded 100% accuracy. Overall, MTaxi provides a straightforward approach to classify closely related species that are difficult to distinguish through zooarchaeological methods using low coverage aDNA data, especially when similar quality reference genomes are unavailable. MTaxi is freely available at https://github.com/goztag/MTaxi.

Whole mitochondrial genomes assembled from thermally altered forensic bones and teeth

The recovery and analysis of genetic material obtained from thermally altered human bones and teeth are increasingly important to forensic investigations, especially in cases where soft-tissue identification is no longer possible. Although little is known about how these fire-related processes affect DNA degradation over time, next-generation sequencing technology in combination with traditional osteobiographical applications may provide us clues to these questions. In this study, we compare whole mitochondrial genome data generated using two different DNA extraction methods from 27 thermally altered samples obtained from fire victims (Maricopa County, Arizona) . DNA extracts were converted to double-stranded DNA libraries and enriched for whole mitochondrial DNA (mtDNA) using synthetic biotinylated RNA baits, then sequenced on an Illumina MiSeq. We processed the mitochondrial data using an in-house computational pipeline (MitoPipe1.0) composed of ancient DNA and modern genomics applications, then compared the resulting information across the two extraction types and five burn categories. Our analysis shows that DNA fragmentation increases with temperature, but that the acute insult from fire combined with the lack of water is insufficient to produce 5' and 3' terminal deamination characteristic of ancient DNA. Our data also suggest an acute and significant point of DNA degradation between 350 °C and 550 °C, and that the likelihood of generating high quality mtDNA haplogroup calls decreases significantly at temperatures > 550 °C. This research is part of a concerted effort to understand how fire affects our ability to generate genetic profiles suitable for forensic identification purposes.

Modern, archaeological, and paleontological DNA analysis of a human-harvested marine gastropod (Strombus pugilis) from Caribbean Panama

Although protocols exist for the recovery of ancient DNA from land snail and marine bivalve shells, marine conch shells have yet to be studied from a paleogenomic perspective. We first present reference assemblies for both a 623.7 Mbp nuclear genome and a 15.4 kbp mitochondrial genome for Strombus pugilis, the West Indian fighting conch. We next detail a method to extract and sequence DNA from conch shells and apply it to conch from Bocas del Toro, Panama across three time periods: recently-eaten and discarded (n = 3), Late Holocene (984-1258 before present [BP]) archaeological midden (n = 5), and mid-Holocene (5711-7187 BP) paleontological fossil coral reef (n = 5). These results are compared to control DNA extracted from live-caught tissue and fresh shells (n = 5). Using high-throughput sequencing, we were able to obtain S. pugilis nuclear sequence reads from shells across all age periods: up to 92.5 thousand filtered reads per sample in live-caught shell material, 4.57 thousand for modern discarded shells, 12.1 thousand reads for archaeological shells, and 114 reads in paleontological shells. We confirmed authenticity of the ancient DNA recovered from the archaeological and paleontological shells based on 5.7× higher average frequency of deamination-driven misincorporations and 15% shorter average read lengths compared to the modern shells. Reads also mapped to the S. pugilis mitochondrial genome for all but the paleontological shells, with consistent ratios of mitochondrial to nuclear mapped reads across sample types. Our methods can be applied to diverse archaeological sites to facilitate reconstructions of the long-term impacts of human behaviour on mollusc evolutionary biology.

Macroscopic determination of the pre-burning condition of human remains recovered from an unusual forensic context: A case report

Understanding the taphonomic process of burning allows forensic practitioners to better interpret remains and reconstruct the burning incident in a medicolegal investigation. This can yield critical information, especially when other details, such as the biological profile, are obscured by fire. A forensic case involving human remains recovered within a Greek Orthodox cemetery that exhibited a distinctive pattern of differential burning is reported. The bones exhibited a range of differential burning in a pattern inconsistent with the anatomical position of the remains during heat exposure. No macroscopic signs of skeletal trauma or evidence of dismemberment were present on the remains. The pre-burning condition of the bones was inferred based on the presence of the differential burning and its localization identified through analysis of a suite of macroscopic heat-induced traits, as well as consideration of the forensic context. The anthropologists concluded that the bones were skeletonized prior to burning and that the remains were once interred or stored in an ossuary and were likely burned in a ritualistic manner, given the artifacts present and the conspicuous location of the burn area. This case highlights the practical experience required of forensic practitioners encountering burned remains and the necessity of understanding fire as a taphonomic agent that can be analyzed to determine pre-burning condition and the scenario of the burning event in a medicolegal investigation. Furthermore, this case underscores the achievability of pre-burning condition determination using macroscopic traits alone, even when there is a paucity of skeletal elements in the inventory. Due to knowledge of the funerary customs of modern-day Greece, the practitioners were able to interpret the origin of the remains, thereby this paper provides insight into a geographically specific forensic context.

Genome-Wide DNA from Degraded Petrous Bones and the Assessment of Sex and Probable Geographic Origins of Forensic Cases

The acquisition of biological information and assessment of the most probable geographic origin of unidentified individuals for obtaining positive identification is central in forensic sciences. Identification based on forensic DNA, however, varies greatly in relation to degradation of DNA. Our primary aim is to assess the applicability of a petrous bone sampling method in combination with Next Generation Sequencing to evaluate the quality and quantity of DNA in taphonomically degraded petrous bones from forensic and cemetery cases. A related aim is to analyse the genomic data to obtain the molecular sex of each individual, and their most probable geographic origin. Six of seven subjects were previously identified and used for comparison with the results. To analyse their probable geographic origin, samples were genotyped for the 627.719 SNP positions. Results show that the inner ear cochlear region of the petrous bone provides good percentages of endogenous DNA (14.61–66.89%), even in the case of burnt bodies. All comparisons between forensic records and genetic results agree (sex) and are compatible (geographic origin). The application of the proposed methodology may be a powerful tool for use in forensic scenarios, ranging from missing persons to unidentified migrants who perish when crossing borders.

An interdisciplinary study around the reliquary of the late cardinal Jacques de Vitry

The reliquary of Jacques de Vitry, a prominent clergyman and theologian in the early 13th century, has experienced several transfers over the last centuries, which seriously question the attribution of the remains to the late Cardinal. Uncertainty about the year of his birth poses an additional question regarding his age at death in 1240. The reliquary, located in the Saint Marie d'Oigines church, Belgium, was reopened in 2015 for an interdisciplinary study around his relics as well as the Treasure of Oignies, a remarkable cultural heritage notably built from Jacques de Vitry's donation. Anthropological, isotopic and genetic analyses were performed independently on the remains found in the reliquary. Results of the analyses provided evidence that the likelihood that these remains are those of Jacques de Vitry is very high: the remains belong to the same human male individual and the historical tradition about his age is confirmed. In addition, a separate relic (left tibia) was analysed and found to match with the remains of the reliquary (right tibia). The unique Jacques de Vitry's mitre, made of parchment, was sampled non-destructively and the extracted parchment collagen was analysed by a proteomic method in order to determine the animal species. The results showed that, surprisingly, not all parts of the mitre were made from the same species. All together, these findings are expected to fertilize knowledge carried by historical tradition around the relics of Jacques de Vitry and his related cultural heritage.

Novel Substrates as Sources of Ancient DNA: Prospects and Hurdles

Following the discovery in the late 1980s that hard tissues such as bones and teeth preserve genetic information, the field of ancient DNA analysis has typically concentrated upon these substrates. The onset of high-throughput sequencing, combined with optimized DNA recovery methods, has enabled the analysis of a myriad of ancient species and specimens worldwide, dating back to the Middle Pleistocene. Despite the growing sophistication of analytical techniques, the genetic analysis of substrates other than bone and dentine remain comparatively "novel". Here, we review analyses of other biological substrates which offer great potential for elucidating phylogenetic relationships, paleoenvironments, and microbial ecosystems including (1) archaeological artifacts and ecofacts; (2) calcified and/or mineralized biological deposits; and (3) biological and cultural archives. We conclude that there is a pressing need for more refined models of DNA preservation and bespoke tools for DNA extraction and analysis to authenticate and maximize the utility of the data obtained. With such tools in place the potential for neglected or underexploited substrates to provide a unique insight into phylogenetics, microbial evolution and evolutionary processes will be realized.

Paleomicrobiology of Human Tuberculosis

Tuberculosis is a significant global disease today, so understanding its origins and history is important. It is primarily a lung infection and is transmitted by infectious aerosols from person to person, so a high population density encourages its spread. The causative organism is Mycobacterium tuberculosis, an obligate pathogen in the M. tuberculosis complex that also contains closely related species, such as Mycobacterium bovis, that primarily infect animals. Typical bone lesions occur in about 5% of untreated infections. These can be recognized in historical and archaeological material, along with nonspecific paleopathology such as new bone formation (periostitis), especially on ribs. Based on such lesions, tuberculosis has been found in ancient Egypt, pre-Columbian America, and Neolithic Europe. The detection of M. tuberculosis ancient DNA (aDNA) by using PCR led to the development of the new field of paleomicrobiology. As a result, a large number of tuberculosis cases were recognized in mummified tissue and bones with nonspecific or no lesions. In parallel with these developments, M. tuberculosis cell wall lipid biomarkers have detected tuberculosis suggested by paleopathology and confirmed aDNA findings. In well-preserved cases, molecular typing has identified M. tuberculosis lineages and genotypes. The current interest in targeted enrichment, shotgun sequencing, and metagenomic analysis reveals ancient mixed infections with different M. tuberculosis strains and other pathogens. Identification of M. tuberculosis lineages from samples of known age enables the date of the emergence of strains and lineages to be calculated directly rather than by making assumptions on the rate of evolutionary change.

A new model for ancient DNA decay based on paleogenomic meta-analysis

The persistence of DNA over archaeological and paleontological timescales in diverse environments has led to a revolutionary body of paleogenomic research, yet the dynamics of DNA degradation are still poorly understood. We analyzed 185 paleogenomic datasets and compared DNA survival with environmental variables and sample ages. We find cytosine deamination follows a conventional thermal age model, but we find no correlation between DNA fragmentation and sample age over the timespans analyzed, even when controlling for environmental variables. We propose a model for ancient DNA decay wherein fragmentation rapidly reaches a threshold, then subsequently slows. The observed loss of DNA over time may be due to a bulk diffusion process in many cases, highlighting the importance of tissues and environments creating effectively closed systems for DNA preservation. This model of DNA degradation is largely based on mammal bone samples due to published genomic dataset availability. Continued refinement to the model to reflect diverse biological systems and tissue types will further improve our understanding of ancient DNA breakdown dynamics.

Demonstration of Protein-Based Human Identification Using the Hair Shaft Proteome

Human identification from biological material is largely dependent on the ability to characterize genetic polymorphisms in DNA. Unfortunately, DNA can degrade in the environment, sometimes below the level at which it can be amplified by PCR. Protein however is chemically more robust than DNA and can persist for longer periods. Protein also contains genetic variation in the form of single amino acid polymorphisms. These can be used to infer the status of non-synonymous single nucleotide polymorphism alleles. To demonstrate this, we used mass spectrometry-based shotgun proteomics to characterize hair shaft proteins in 66 European-American subjects. A total of 596 single nucleotide polymorphism alleles were correctly imputed in 32 loci from 22 genes of subjects' DNA and directly validated using Sanger sequencing. Estimates of the probability of resulting individual non-synonymous single nucleotide polymorphism allelic profiles in the European population, using the product rule, resulted in a maximum power of discrimination of 1 in 12,500. Imputed non-synonymous single nucleotide polymorphism profiles from European-American subjects were considerably less frequent in the African population (maximum likelihood ratio = 11,000). The converse was true for hair shafts collected from an additional 10 subjects with African ancestry, where some profiles were more frequent in the African population. Genetically variant peptides were also identified in hair shaft datasets from six archaeological skeletal remains (up to 260 years old). This study demonstrates that quantifiable measures of identity discrimination and biogeographic background can be obtained from detecting genetically variant peptides in hair shaft protein, including hair from bioarchaeological contexts.

Barcoding the largest animals on Earth: ongoing challenges and molecular solutions in the taxonomic identification of ancient cetaceans

Over the last few centuries, many cetacean species have witnessed dramatic global declines due to industrial overharvesting and other anthropogenic influences, and thus are key targets for conservation. Whale bones recovered from archaeological and palaeontological contexts can provide essential baseline information on the past geographical distribution and abundance of species required for developing informed conservation policies. Here we review the challenges with identifying whale bones through traditional anatomical methods, as well as the opportunities provided by new molecular analyses. Through a case study focused on the North Sea, we demonstrate how the utility of this (pre)historic data is currently limited by a lack of accurate taxonomic information for the majority of ancient cetacean remains. We then discuss current opportunities presented by molecular identification methods such as DNA barcoding and collagen peptide mass fingerprinting (zooarchaeology by mass spectrometry), and highlight the importance of molecular identifications in assessing ancient species' distributions through a case study focused on the Mediterranean. We conclude by considering high-throughput molecular approaches such as hybridization capture followed by next-generation sequencing as cost-effective approaches for enhancing the ecological informativeness of these ancient sample sets.This article is part of the themed issue 'From DNA barcodes to biomes'.

Determination of the ruminant origin of bone particles using fluorescence in situ hybridization (FISH)

Molecular biology techniques such as PCR constitute powerful tools for the determination of the taxonomic origin of bones. DNA degradation and contamination by exogenous DNA, however, jeopardise bone identification. Despite the vast array of techniques used to decontaminate bone fragments, the isolation and determination of bone DNA content are still problematic. Within the framework of the eradication of transmissible spongiform encephalopathies (including BSE, commonly known as "mad cow disease"), a fluorescence in situ hybridization (FISH) protocol was developed. Results from the described study showed that this method can be applied directly to bones without a demineralisation step and that it allows the identification of bovine and ruminant bones even after severe processing. The results also showed that the method is independent of exogenous contamination and that it is therefore entirely appropriate for this application.

The half-life of DNA in bone: measuring decay kinetics in 158 dated fossils

Claims of extreme survival of DNA have emphasized the need for reliable models of DNA degradation through time. By analysing mitochondrial DNA (mtDNA) from 158 radiocarbon-dated bones of the extinct New Zealand moa, we confirm empirically a long-hypothesized exponential decay relationship. The average DNA half-life within this geographically constrained fossil assemblage was estimated to be 521 years for a 242 bp mtDNA sequence, corresponding to a per nucleotide fragmentation rate (k) of 5.50 × 10(-6) per year. With an effective burial temperature of 13.1°C, the rate is almost 400 times slower than predicted from published kinetic data of in vitro DNA depurination at pH 5. Although best described by an exponential model (R(2) = 0.39), considerable sample-to-sample variance in DNA preservation could not be accounted for by geologic age. This variation likely derives from differences in taphonomy and bone diagenesis, which have confounded previous, less spatially constrained attempts to study DNA decay kinetics. Lastly, by calculating DNA fragmentation rates on Illumina HiSeq data, we show that nuclear DNA has degraded at least twice as fast as mtDNA. These results provide a baseline for predicting long-term DNA survival in bone.

Site-specific deamidation of glutamine: a new marker of bone collagen deterioration

RATIONALE

Non-enzymatic deamidation accumulates in aging tissues in vivo and has been proposed to be potentially useful as a molecular clock. The process continues post mortem, and here we explore the increase in levels of deamidation in archaeological collagen, as measured during Zooarchaeology by Mass Spectrometry (ZooMS) analysis.

METHODS

With the high sensitivity of current generation mass spectrometers, ZooMS provides a non-destructive and highly cost-effective method to characterise collagen peptides. Deamidation can be detected by mass spectrometry as a +0.984 Da mass shift; therefore, aside from its original purpose, peptide mass-fingerprinting for bone identification, ZooMS concurrently yields a 'thermal indicator' of the samples.

RESULTS

By analysis of conventional ZooMS spectra, we determined the deamidation rate for glutamine residues in 911 bone collagen samples from 50 sites, with ages varying from medieval to Palaeolithic. The degree of deamidation was compared to diagenetic parameters and nearby sequence properties.

CONCLUSIONS

The extent of deamidation was found to be influenced more by burial conditions and thermal age than, for example, chronological age, the extent of bioerosion or crystallinity. The method lends itself mostly to screening heterogenic deposits of bone to identify outliers.

Ancient human DNA

The contribution of palaeogenetic data to the study of various aspects of hominin biology and evolution has been significant, and has the potential to increase substantially with the widespread implementation of next generation sequencing techniques. Here we discuss the present state-of-the-art of ancient human DNA analysis and the characteristics of hominin aDNA that make sequence validation particularly complex. A brief overview of the development of anthropological palaeogenetic analysis is given to illustrate the technical challenges motivating recent technological advancements.

Evaluating the impact of post-mortem damage in ancient DNA: a theoretical approach

The growth of ancient DNA research has offered exceptional opportunities and raised great expectations, but has also presented some considerable challenges. One of the ongoing issues is the impact of post-mortem damage in DNA molecules. Nucleotide alterations and DNA strand breakages lead to a significant decrease in the quantity of DNA molecules of useful length in a sample and to errors in the final DNA sequences obtained. We present a model of age-dependent DNA damage and quantify the influence of that damage on subsequent steps in the sequencing process, including the polymerase chain reaction and cloning. Calculations using our model show that deposition conditions, rather than the age of a sample, have the greatest influence on the level of DNA damage. In turn, this affects the probability of interpreting an erroneous (possessing damage-derived mutations) sequence as being authentic. We also evaluated the effect of post-mortem damage on real data sets using a Bayesian phylogenetic approach. According to our study, damage-derived sequence alterations appear to have little impact on the final DNA sequences. This indicates the effectiveness of current methods for sequence authentication and validation.

Ancient mitogenomics

The mitochondrial genome has been the traditional focus of most research into ancient DNA, owing to its high copy number and population-level variability. Despite this long-standing interest in mitochondrial DNA, it was only in 2001 that the first complete ancient mitogenomic sequences were obtained. As a result of various methodological developments, including the introduction of high-throughput sequencing techniques, the total number of ancient mitogenome sequences has increased rapidly over the past few years. In this review, we present a brief history of ancient mitogenomics and describe the technical challenges that face researchers in the field. We catalogue the diverse sequencing methods and source materials used to obtain ancient mitogenomic sequences, summarise the associated genetic and phylogenetic studies that have been conducted, and evaluate the future prospects of the field.