BAVARIAN RESEARCH ASSOCIATION PRIONS
Erl 2 BSE Genomics C
The aim of the study was the identification of DNA polymorphisms in the bovine prion protein gene. These polymorphisms were analyzed in control and BSE animals to identify polymorphisms with relevance to resistance/susceptibility to BSE infection and which potentially could be used for specific breeding of more resistant cows similar to the European sheep breeding program of scrapie resistant animals. Thereby, breed specific differences should be considered. In contrast to human and sheep, only a few polymorphisms leading to non-synonymous amino acid exchanges are known within the prion protein gene. As none of the identified polymorphisms within the coding region exhibited significant association to BSE susceptibility, we and other scientists investigated the promoter region surrounding exon 1 of the prion protein gene PRNP. This region was suggested to influence the expression of the gene. The analysis led to the isolation of several polymorphisms both, single nucleotide and insertion/¬deletion polymorphisms (SNPs and indels). Breed specific comparative genotyping of these polymorphisms resulted in a significantly different distribution in control and German BSE animals. To investigate the influence of different variants of these polymorphisms on gene expression naturally occurring as well as artificial constructed combinations of polymorphisms (haplotypes) were cloned in expression vectors and transfected into neuronal cells. A specific combination of 12 polymorphisms resulted in a significantly reduced expression level compared to all other haplotypes. Interestingly this low expressing haplotype was underrepresented in the BSE group of all breeds compared to control animals. This observation is in good agreement with previous investigations in mice. Analysis of transgenic and knock out mice showed that endogenous prion protein is necessary for infection and that the incubation time strongly depends on the amount of endogenous prion protein. We identified a haplotype in bovine animals, which potentially reduces the probability to get infected by BSE due to reduced expression of endogenous prion protein. Less amount of endogenous prion protein reduce the chance to get misfolded following contact to a misfolded and aggregated PrPsc due to a BSE-infection. Therefore for the first time, there is a possibility to breed animals, which probably develop a higher resistance to BSE infections. To finally proof our results the genotype/phenotype correlation of animals orally infected with BSE in the pathogenesis study in Riems is currently under investigation.