Study On Proteinaceous Infectious Agent In Fishes

Transmissible spongiform encephalopathy (TSE) is infectious diseases caused by proteinaceous infectious agent (Prions). Prions are thought to be composed of a rogue isoform of the endogenous prion protein which was in a large diversity and a wide range of distribution. Fish are beginning to provide useful insights into the roles of PrP in health and disease, as well as the potential risk of prion transmission between fish and mammals.The use of fish in TSE research could significantly improve our basic understanding of prion diseases. Therefore, guppy ( Poecilia reticulate ),grass carp ( Ctenopharyngodon idellus ) and bighead carp ( Aristichthys nobilis ) were selected to study the PrP encoding gene and the structure of their deduced protein. We received the following results:We cloned PrP encoding gene sequences of bighead carp, grass carp and guppy. DNAtools was used to find ORF and the deduced amino acid sequences protein. guppy PrP-1 weighs about 54kilodaltons consisting of 515 amino acid residues, and the pI is about 9.51. Bighead carp PrP-2 weighs 57 kilodaltons consisting of 551 amino acid residues, and the pI is about 9.10. grass carp PrP-2 weighs 56 kilodaltons consisting of 534 amino acid residues, and the pI is about 8.94. Furthermore, sequences analysis also demonstrate that these three PrPC bear the structural signatures of PrP including a disulphide bridge and a glycosyl phosphatidyl inositol anchor site, a glycosylation site, a signal sequence, tandem repeats, a hydrophobic region. We cloned genomic DNA sequences of guppy PrP-1, and found guppy PrP~C is encoded by a single exon.The expression of PrP~C gene was analyzed with RT-PCR. The expression of PrP gene was detected in multiple tissues including eye, brain, intestine, liver, tail and muscle. The expression of PrP gene was at much higher levels in brain than other tissues. The expression of PrP gene under 5‰salinity was at much higher levels. This results that PrP is a endogenous protein which may associate with the response to saline stress.At last we made phylogenetic analysis of the globular domains and the repetitive domains of prion protein between vertebrate classes. Furthermore, we analyzed the risk of prion disease in fish. The use of fish in TSE research will likely uncover novel aspects of prion transmission across a wide range of hosts, relevant to human health. This research provides support for the exploration concerning the evolution and functions of PrPC and the transmissible spongiform encephalopathy (TSE ) existing in fish possibly.