Abstract
Encephalopathy in sheep was at first described in Ireland in 1732 and was called scrapie. Ancient DNA in archaeogenetics represents an effective method to evaluate the ancestral pedigree of living animals and track evolutionary changes occurred between the past and the present day. Since several point mutations are today widely described in modern scrapie, no data about both sequence and frequency are still available for the prion protein (PrP) gene in ancient breeds. In order to evaluate whether the haplotypes distribution in ancient sheep differed from those of the modern population we evaluated polymorphism at four well know codons of the Prp Open Reading Frame. In the present work, we collected 37 medieval sheep bone remains found at the Calathamet (n = 11), Palazzo Bonagia (n = 12) and Palazzo Steri (n = 14) Sicilians archeological sites and dated back between 9th - 15th century. Single nucleotide polymorphisms (SNPs) at codons 136, 141, 154 and 171 of the prion protein (PrP) were investigated using cycle sequencing. Sequenom Mass ARRAYiPLEX platform confirmed the results for 5 individuals out of 37. Cycle sequencing showed at all samples the AA136LL141RR154QQ171 (hereafter ALRQ/ALRQ) genotype except at 2 individuals showing the very susceptible genotype VLRQ/VLRQ (n = 1) and the resistant (ALRR/ ALRR) (n = 1) respectively. Supported by a high incidence of susceptible genotype to prion infection we concluded that presumably scrapie was already widespread enough in the medieval Sicily. Moreover, we described conceivable scenarios that could have underlain evolutionary changes in the medieval sheep population.
Highlights
Scrapie or prion disease belongs to the transmissible spongiform encephalopathies (TSEs) together with bovine spongiform encephalopathy (BSE) in cattle and chronic wasting disease (CWD) in deer
The aim of this study was to assess the allelic pattern at codons 136, 141, 154 and 171 in order to estimate whether scrapie was already infectious in medieval era
We presumed genetic forces driving evolutionary changes occurred in the ancestral sheep population
Summary
Scrapie or prion disease belongs to the transmissible spongiform encephalopathies (TSEs) together with bovine spongiform encephalopathy (BSE) in cattle and chronic wasting disease (CWD) in deer. The ARR/ARR is associated with a high resistant genotype to natural scrapie [7] [9] [10], while AHQ haplotype is associated only in some breeds with the resistance to disease [11]. When DNA are well preserved, direct sequencing represents definitely the most reliable and powerful tools to decode ancient genes and to track genetic variability along the time-scale. In line with this premises, we thought the PrP gene as a target of possible evolutionary pressure reflecting the characteristics of living animals
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