Homozygosity for prion protein alleles encoding glutamine-171 renders sheep susceptible to natural scrapie.

Abstract

Natural scrapie has been viewed both as a recessive trait and as a contagious disease modulated by a host locus. To address this conundrum, we determined the structure of the sheep prion protein (PrP) gene, which contains three exons and extends over 20 kb of DNA. In the United States 86.4% of scrapie cases occur in Suffolk sheep, and within this breed 49__.6% (+_s.D., n=69) of healthy animals carry one or more PrP alleles encoding Arg (R)-171. Four scrapie-affected sheep were homozygous for wild-type PrP open reading frames encoding the alternative Gin (Q)-171 allele. Analysis of additional cases revealed that all were Q/Q-171 homozygotes (n= 31), yielding a probability of 0.000004 that PrP genotype is unrelated to susceptibility. These data imply that homozygosity for Q-171 codons is necessary but not sufficient for the development of natural scrapie, echo reports of recessive manifestation, and parallel over-representation of PRNP codon 129 homozygotes in Crentzfeldt-Jakob disease of humans. Whereas progress has been substantial regarding experimental scrapie in rodents, the occurrence and spread of disease in flocks of sheep has remained enigmatic. Appreciation of the relationship between codon 171 genotype and susceptibility may help define the molecular basis of natural scrapie.

Evidence for protein X binding to a discontinuous epitope on the cellular prion protein during scrapie prion propagation

“…In sheep, the substitution of a basic residue at position 171 probably prevents scrapie through a dominant-negative mechanism similar to that postulated for a basic residue at 219 protecting humans from CJD. With few exceptions, only sheep that are Q͞Q at 171 develop scrapie; sheep that are Q͞R or R͞R are resistant (31)(32)(33)(34)(35)(36)(37)(38)(39). These findings suggest that R171 creates a PrP C molecule in sheep that acts as a dominant negative in preventing PrP Sc formation (Fig.…”

Characterization of the Bovine Prion Protein Gene: The Expression Requires Interaction between the Promoter and Intron.

“…The 5' non-coding region of the bovine PrP gene consists of three exons, like the mouse, rat and sheep PrP genes, contrasting to the two exons of the hamster and human PrP genes [3,28,30,38,39]. The 5'-flanking region of the bovine PrP gene shows an 89% homology with that of the sheep gene and only about a 46-62% homology with those of the mouse, rat, hamster and human PrP genes.…”

“…The nucleotide sequences of the potential promoter regions of the PrP gene in some animal species have been reported [3,28,30,38,39]. However, no precise analysis of the promoter function has been reported, except for the rat PrP gene [30], so that the mechanisms controlling PrP gene expression are still poorly understood.…”

Biology of PrPsc Accumulation in Two Natural Scrapie-Infected Sheep Flocks

“…a,b DNA sequencing followed PCR amplification using primers specific for the entire PrPcoding sequence, as described previously. 38 Immunohistochemical detection of PrP sc . Single-label immunohistochemistry for PrP sc was performed on formalinfixed, paraffin-embedded tissues using heat-induced antigen retrieval and 90% formic acid pretreatment as described previously.…”