Cloning And Characterization Of A Prion Protein Encoding Gene Of Guppy (Poecilia Reticulata) And Expression Analysis

Proteinaceous infectious agent (Prions) is the aggregate of prion protein, which causes transmissible spongiform encephalopathy (TSE). Prion protein is a normal cellular protein with a large diversity and a wide range of distribution. It is highly possible that Prions and TSE could form in cultured fishes, for the processing and raw materials of fish feeds are similar to those of mammals. Guppy (Poecilia reticulata) was selected as the researching material of studying the structure and tissue expression of PrP encoding gene in this study.Following results were obtained:The full length cDNA of a PrP encoding gene of Guppy and the corresponding genomic DNA were cloned. The cDNA was 2,245bp in length and contained an open reading frame (ORF) of 1,545bp. The ORF encoded a protein of 515 amino acids, which held all typical structural characteristics of functional PrP, including a signal sequence, a basic structure, a tandem repeat region, a hydrophobic region, a glycosylation site, a disulphide bridge and a glycosyl phosphatidy inositol anchor site. It retained the same spacial structure as other fish Prions. Acocording to the Neighbor-joining tree of fish PrPs, the Guppy PrPc was assigned to the type 1 of PrP fish Prions (PrP-1). The cloned genomic DNA fragment corresponding to the cDNA was 3,720bp in length, consisting of 2 introns and 2 exons. The PrPC is encoded by a single exon.The expression of PrPC encoding gene in different tissues of Guppy was analyzed with RT-PCR. Although the gene was transcribed in diverse tissues including brain, eye, liver, intestine, muscle and tail, the transcript of the gene was the most abundant in brain. In addition, the transcription of the gene was enhanced by 5‰salinity, implying that it was associated with the response of Guppy to saline stress.