Cloning of the bovine prion-like Shadoo (SPRN) gene by comparative analysis of the predicted genomic locus
SPRN is a new prion-like gene coding for Sho, a protein with significant similarity to PrP. SPRN was initially described in zebrafish; however, the strong evolutionary conservation led to the hypothesis that SPRN might be the ancestral prion-like gene. We mapped SPRN in Bos taurus by comparative analysis of the locus and of the predicted flanking genes. BACs, spanning the whole SPRN genomic locus, were assigned to BTA26q23 by radiation hybrid mapping and fluorescent in situ hybridization (FISH). Sequencing of five genes flanking SPRN, namely, ECHS1, PAOX, MTG1, SPRN, and CYP2E1, high-resolution FISH on mechanically stretched chromosomes, and combed BAC DNA allowed us to establish their order and reciprocal orientation. The results confirmed that BTA26q23 corresponds to HSA10q24.3–26.3, which is the site where the human SPRN is located. The gene order in Bos taurus is the same as in man, cen-ECHS1-PAOX-MTG1-SPRN-CYP2E1-tel, but PAOX has a different orientation in the two species. SPRN has the typical two-exon PRNP arrangement, with the CDS fully contained within exon 2; furthermore, it codes for a 143-amino-acid protein with 74.8% identity and 84.7% similarity with the human PRNP. RT-PCR and Northern blot analysis showed that SPRN is expressed at high levels in brain and less in testis and lung.