Characterization of the genomic region containing the Shadow of Prion Protein (SPRN) gene in sheep

In order to characterize the genomic region containing SPRN in sheep, a BAC mini-contig was built, covering approximately 200,000 bp and containing the genes ECHS1, PAOX, MTG1, SPRN, LOC619207, CYP2E1 and at least partially SYCE1. FISH mapping of the two most exterior BAC clones of the contig positioned this contig on Oari22q24. A fragment of 4,544 bp was also sequenced, covering the entire SPRN gene and 1206 bp of the promoter region. In addition, the transcription profile of SPRN in 21 tissues was determined by RT-PCR, showing high levels in cerebrum and cerebellum, and low levels in testis, lymph node, jejunum, ileum, colon and rectum.Annotation of a mini-contig including SPRN suggests conserved linkage between Oari22q24 and Hsap10q26. The ovine SPRN sequence, described for the first time, shows a high level of homology with the bovine, and to a lesser extent with the human SPRN sequence. In addition, transcription profiling in sheep reveals main expression of SPRN in brain tissue, as in rat, cow, man and mouse.TSEs are a group of fatal neurodegenerative diseases, caused by prions (PrPSc). These infectious particles are alternatively folded forms of the endogenous protein PrPC, encoded by PRNP [1,2]. Conversion of PrPC into PrPSc requires the presence of PrPSc and probably also of a not identified species-specific protein, 'protein X' [3,4].In sheep, TSE susceptibility is influenced by polymorphisms of the PRNP gene, with the alleles coding for alanine, arginine and arginine at positions 136, 154 and 171 of the prion protein associated with a high resistance to classical scrapie and BSE [5]. Nevertheless, this resistance is not absolute, since it has been shown that atypical scrapie can occur in sheep with the genotype ARR/ARR [6-11], sheep with this genotype can be artificially infected with BSE [12] and infectivity has been detected in the spleen of an ARR/ARR sheep, experimentally infected with BSE [13]. Moreover, the presumed resistance of ARR/ARR sheep might