The cysteine‐rich peptide hepcidin is known to be an antimicrobial peptide and iron transport regulator that has been found in both fish and mammals. Recently, we found two different types (designated Hep‐JF1 and Hep‐JF2) of hepcidin cDNA in the Japanese flounder, Paralichthys olivaceus, by expressed sequence tag analysis. The identity of amino acid sequences between Hep‐JF1 and Hep‐JF2 was 51%. The Hep‐JF1 and Hep‐JF2 genes both consist of three exons and two introns, and both exist as single copies in the genome. The predicted mature regions of Hep‐JF1 and Hep‐JF2 have six and eight Cys residues, respectively. The first Cys residue of Hep‐JF1 was deleted and the second was replaced with Gly. The number and positions of Cys residues in Hep‐JF2 are the same as they are in human Hep. Hep‐JF1 is specifically expressed in liver while the expression of Hep‐JF2 was detected from gill, liver, heart, kidney, peripheral blood leucocytes, spleen and stomach. Gene expression of Hep‐JF1 in liver decreased during experimental iron (iron‐dextran) overload. Expression of Hep‐JF1 in liver was decreased by injecting fish with iron‐dextran and increased by injecting lipopolysaccharide. Iron overload did not significantly affect expression of Hep‐JF2 in liver but it did increase expression of Hep‐JF2 in kidney. Lipopolysaccharide injection increased expression of Hep‐JF2 in both liver and kidney. In liver, some cells expressed both Hep‐JF1 and Hep‐JF2 while some other cells expressed just one of them. Synthesized Hep‐JF2 peptide showed antimicrobial activity, while synthesized Hep‐JF1 peptide did not against several bacteria including fish‐pathogenic bacteria used in this study.
Some strains of Vibrio parahaemolyticus cause acute hepatopancreatic necrosis disease (AHPND) in shrimp. We sequenced 3 AHPND and 3 non-AHPND strains and found that all of them lacked the pathogenicity island relevant to human infection. A unique sequence encoding a type IV pilus/type IV secretion system was found in 3 AHPND strains.
White spot syndrome virus (WSSV) is a crustacean-infecting, double-stranded DNA virus and is the most serious viral pathogen in the global shrimp industry. WSSV is the sole recognized member of the family Nimaviridae, and the lack of genomic data on other nimaviruses has obscured the evolutionary history of WSSV. Here, we investigated the evolutionary history of WSSV by characterizing WSSV relatives hidden in host genomic data. We surveyed 14 host crustacean genomes and identified five novel nimaviral genomes. Comparative genomic analysis of Nimaviridae identified 28 “core genes” that are ubiquitously conserved in Nimaviridae; unexpected conservation of 13 uncharacterized proteins highlighted yet-unknown essential functions underlying the nimavirus replication cycle. The ancestral Nimaviridae gene set contained five baculoviral per os infectivity factor homologs and a sulfhydryl oxidase homolog, suggesting a shared phylogenetic origin of Nimaviridae and insect-associated double-stranded DNA viruses. Moreover, we show that novel gene acquisition and subsequent amplification reinforced the unique accessory gene repertoire of WSSV. Expansion of unique envelope protein and nonstructural virulence-associated genes may have been the key genomic event that made WSSV such a deadly pathogen.
IMPORTANCE WSSV is the deadliest viral pathogen threatening global shrimp aquaculture. The evolutionary history of WSSV has remained a mystery, because few WSSV relatives, or nimaviruses, had been reported. Our aim was to trace the history of WSSV using the genomes of novel nimaviruses hidden in host genome data. We demonstrate that WSSV emerged from a diverse family of crustacean-infecting large DNA viruses. By comparing the genomes of WSSV and its relatives, we show that WSSV possesses an expanded set of unique host-virus interaction-related genes. This extensive gene gain may have been the key genomic event that made WSSV such a deadly pathogen. Moreover, conservation of insect-infecting virus protein homologs suggests a common phylogenetic origin of crustacean-infecting Nimaviridae and other insect-infecting DNA viruses. Our work redefines the previously poorly characterized crustacean virus family and reveals the ancient genomic events that preordained the emergence of a devastating shrimp pathogen.
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