title: Molecular characterization and expression analyses of cDNAs encoding the thioredoxin-interacting protein and selenoprotein P genes and histological changes in Nile tilapia (Oreochromis niloticus) in response to silver nanoparticle exposure.
abstract: Herein, Nile tilapia thioredoxin-interacting protein (On-TXNIP) and selenoprotein P (On-SEPP) cDNAs were cloned and characterized. The full-length On-TXNIP cDNA contained 2 arrestin domains, 2 conserved cysteine residues that bind to thioredoxin to inhibit thioredoxin function, and 2 PPXY motifs, which negatively regulate the protein by stimulating binding to E3 ubiquitin ligase. The On-SEPP cDNA contained 17 selenocysteines (Sec) encoded by the TGA codon, which can be recognized as either a stop codon or a Sec codon. The On-SEPP cDNA also carried 2 typical SECIS elements located in the 3'UTR that are important for selenocysteine translation. Evolutionary analyses of both the On-TXNIP and On-SEPP genes revealed that these genes are closely related to the TXNIP and SEPP genes in zebrafish (Danio rerio), with amino acid similarities of 91.8% and 61.9%, respectively. A normal tissue distribution analysis indicated that the On-TXNIP and On-SEPP genes were ubiquitously expressed in all tissues examined, and the highest expression levels of these genes were observed in peripheral blood leukocytes (PBLs) and the trunk kidney, respectively. The expression levels of On-TXNIP and On-SEPP transcripts were acutely and chronically analyzed following the injection of fish with 1, 10 or 100mg/kg silver nanoparticles (Ag NPs). Significant up-regulation of On-TXNIP and On-SEPP transcripts was observed in the liver, spleen, and head kidney at the early phase of Ag NP exposure (hours 6 through 48). Down-regulation of On-SEPP transcripts was clearly observed in the liver at weeks 1 to 4. Histopathology analysis demonstrated that the fish livers exhibited a dramatic infiltration of Kupffer cells, elevated bi-nucleated cells, expanded sinusoidal blood congestion and severe necrosis in a dose-dependent manner. Based on these findings, coupling of the expression analysis of these two cellular stress response genes and histopathological observation of fish exposed to Ag NPs should be reliable for the assessment of Ag NP contamination in teleost fish.
authors.affiliation: Toxicology Graduate Program, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.
authors.forename: Kubpaphas
authors.initials: K
authors.lastname: Thummabancha
authors.affiliation: Department of Biology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.
authors.forename: Nuttaphon
authors.initials: N
authors.lastname: Onparn
authors.affiliation: Laboratory of Aquatic Animal Health Management, Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok 10900, Thailand. Electronic address: ffispssp@ku.ac.th.
authors.forename: Prapansak
authors.initials: P
authors.lastname: Srisapoome
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D017124:Conserved Sequence; D015536:Down-Regulation; D029941:Fish Proteins / Q000235:genetics* / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D053768:Metal Nanoparticles / Q000009:adverse effects* / Q000737:chemistry; D008969:Molecular Sequence Data; D009928:Organ Specificity; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051140:Selenoproteins / Q000235:genetics* / Q000378:metabolism; D012834:Silver / Q000494:pharmacology*; D013879:Thioredoxins / Q000378:metabolism; D017210:Tilapia
chemical_list: D002352:Carrier Proteins; D029941:Fish Proteins; D012333:RNA, Messenger; D051140:Selenoproteins; D012834:Silver; D013879:Thioredoxins
keywords: Gene expression; Histopathology; Nile tilapia; Selenoprotein P; Silver nanoparticles; Thioredoxin-interacting protein