Cloning and analysis of transcripts and genes encoding fish-specific proteins related to PrP

We report cloning and tissue expression of transcripts of a fourth fish-specific gene (SPRNB) encoding a prion protein (PrP)-related protein (Shadoo2) from two species, Cyprinus carpio (carp) and Danio rerio (zebrafish), as well as gene or partial transcript sequences identified by in silico searches of public databases from Gasterosteus aculeatus (stickleback), Oryzias latipes (medaka fish) and Salmo salar (salmon). We also present an up-to-date summary of current knowledge of the other three PrP-related genes and transcripts (PrP-like protein, PrP1 and PrP2) encoded exclusively in fish genomes, including some additional transcripts we identified by in silico searches. We compare levels of protein-sequence conservation among the different genes within given fish species, and among given genes in different fish species, and analyse the gene structures and contexts (flanking genes) where genomic sequence is available. These analyses show remarkably high divergences of sequences and expression patterns for proteins in distant fish, such as Fugu and zebrafish, leaving open the question of how varied their functions may be.