Novel Polymorphisms and Genetic Characteristics of the Shadow of Prion Protein Gene (<i>SPRN</i>) in Cats, Hosts of Feline Spongiform Encephalopathy

Prion diseases are transmissible spongiform encephalopathies (TSEs) caused by pathogenic prion protein (PrP^Sc) originating from normal prion protein (PrP^C) and have been reported in several types of livestock and pets. Recent studies have reported that the shadow of prion protein (Sho) encoded by the shadow of prion protein gene (<i>SPRN</i>) interacts with prion protein (PrP) and accelerates prion diseases. In addition, genetic polymorphisms in the <i>SPRN</i> gene are related to susceptibility to prion diseases. However, genetic polymorphisms in the feline <i>SPRN</i> gene and structural characteristics of the Sho have not been investigated in cats, a major host of feline spongiform encephalopathy (FSE). We performed amplicon sequencing to identify feline <i>SPRN</i> polymorphisms in the 623 bp encompassing the open reading frame (ORF) and a small part of the 3′ untranslated region (UTR) of the <i>SPRN</i> gene. We analyzed the impact of feline <i>SPRN</i> polymorphisms on the secondary structure of <i>SPRN</i> mRNA using RNAsnp. In addition, to find feline-specific amino acids, we carried out multiple sequence alignments using ClustalW. Furthermore, we analyzed the N-terminal signal peptide and glycosylphosphatidylinositol (GPI)-anchor using SignalP and PredGPI, respectively. We identified three novel SNPs in the feline <i>SPRN</i> gene and did not find strong linkage disequilibrium (LD) among the three SNPs. We found four major haplotypes of the <i>SPRN</i> polymorphisms. Strong LD was not observed between <i>PRNP</i> and <i>SPRN</i> polymorphisms. In addition, we found alterations in the secondary structure and minimum free energy of the mRNA according to the haplotypes in the <i>SPRN</i> polymorphisms. Furthermore, we found four feline-specific amino acids in the feline Sho using multiple sequence alignments among several species. Lastly, the N-terminal signal sequence and cutting site of the Sho protein of cats showed similarity with those of other species. However, the feline Sho protein exhibited the shortest signal sequence and a unique amino acid in the omega-site of the GPI anchor. To the best of our knowledge, this is the first report on genetic polymorphisms of the feline <i>SPRN</i> gene.