PRION ISOLATE SPECIFIED ALLOTYPIC INTERACTIONS BETWEEN THE CELLULAR AND SCRAPIE PRION PROTEINS IN CONGENIC AND TRANSGENIC MICE

Different prion isolates, often referred to as ''strains,'' present an enigma because considerable evidence argues that prions are devoid of nucleic acid. To investigate prion diversity, we inoculated three ''s trains'' of prions into congenic and transgenic mice harboring variabl e numbers of two different alleles, designated a and b, of the prion p rotein (PrP) structural gene, Prn-p. The length of the incubation time was inversely related to the number of Prn-p(a) genes in mice inocula ted with the Rocky Mountain Laboratory (RML) prion strain. Results wit h mice lacking this locus (Prn-p(0/0)) and transgenic mice argue that long incubation times are not a dominant trait as thought for many yea rs, but rather they are due to reduced levels of the substrate PrPC-A (cellular isoform of PrP, allotype A) in (Prn-p(a) x Prn-p(b))F-1 mice . In contrast, the Prn-p(a) gene extended incubation times in mice ino culated with the 87V and 22A prion strains, whereas the Prn-p(b) gene was permissive. Experiments with the 87V isolate suggest that a geneti c locus distinct from Prn-p controls deposition of the scrapie isoform of PrP (PrPSc) and attendant neuropathology. Each prion isolate produ ced distinguishable patterns of PrPSc accumulation in brain; of note, the patterns in Prn-p(a) and Prn-p(b) congenic mice inoculated with RM L prions were more different than those in congenic Prn-p(b) mice with RML or 22A prions. Our results suggest that scrapie ''strain-specific '' incubation times can be explained by differences in the relative ef ficiency of allotypic interactions that lead to conversion of PrPC int o PrPSc.