Ancient DNA: The quest for the best

Eva-Maria Geigl (1) , Thierry Grange (2)

1 IJM (UMR_7592) - Institut Jacques Monod
2 EMSI - Ecole de Management des Systèmes d'Information

It is the dream of all researchers working with ancient DNA to identify prior to DNA extraction from bone the specimens or specific zones within them that contain the most and highest proportion of endogenous DNA. Since it impacts the sacrifice of precious ancient specimens and the financial support needed for the analyses, the question is of high importance to the scientific field of paleogenomics. The "Holy Grail" of paleogenomics was reached when Cristina Gamba and collaborators discovered that it was in the petrosal part of the temporal bone, the densest part of the mammalian skeleton, where DNA is exceptionally well preserved. As a consequence, osteological collections experienced a rush from paleogenomicists to "harvest" these precious bone parts. In this issue of Molecular Ecology Resources, Alberti and colleagues (2018) describe the discovery of another promising source of relatively well preserved endogenous DNA, the outermost layer of cortical bone, that they had identified through computed tomography (CT scans). These bones being larger and more abundant than petrous bones, this discovery increases markedly the source material for high quality paleogenomic studies and releases the pressure on osteological collections. KEYWORDS Ancient DNA, DNA preservation, taphonomy, bone Paleogenomics, or the analysis of DNA preserved in biological material from the past, mainly bones, contributes greatly to the study of the recent evolutionary history of humans, human and animal migrations, domestication processes, past population dynamics, and the impact of climate change on past biodiversity, to name just a few. The primary source of these studies, however, is limited in number. Moreover, paleogenomic analyses being costly, and the failure rate due to insufficient DNA preservation high, researchers in the field were seeking for the "Holy Grail" since the initial proposition of differential DNA preservation in molecular preservation niches (Geigl 2002). Empirical considerations and observations motivated ancient DNA researchers to privilege the most compact bones for their studies. Gamba et al. (2014) pushed this logic to its ultimate limit and discovered that the most compact bone of the mammalian skeleton, the petrosal part of the temporal bone, is by far the best source of endogenous DNA from ancient bones. Since then, our scientific community could verify the truth and robustness of this observation that has transformed the field of paleogenomics to a point that a joke dates studies before 2014 to BP (before petrous). In the present study, Alberti et al. (2018) used CT scans to identify the most compact parts of bones. This allowed them to refine the identification of the zones within the petrosal to be the most compact and favorable for DNA preservation. Most importantly, however, they identified a part of ancient

Domaines: Sciences du Vivant [q-bio]; Génétique; Biodiversité et Ecologie; Génomique, Transcriptomique et Protéomique [q-bio.GN]; Anthropologie biologique; Environnement et Société; Evolution [q-bio.PE]; Systématique, phylogénie et taxonomie

Eva-Maria Geigl, Thierry Grange. Ancient DNA: The quest for the best. Molecular Ecology Resources, 2018, 18 (6), pp.1185-1187. ⟨10.1111/1755-0998.12931⟩. ⟨hal-02396328⟩