The NCK and ABI adaptor genes in catfish and their involvement in ESC disease response

The effects of primary and secondary bacterial exposure on the seahorse (Hippocampus erectus) immune response

Evolutionary adaptations in the Syngnathidae teleost family (seahorses, pipefish and seadragons) culminated in an array of spectacular morphologies, key immune gene losses, and the enigmatic male pregnancy. In seahorses, genome modifications associated with immunoglobulins, complement, and major histocompatibility complex (MHC II) pathway components raise questions concerning their immunological efficiency and the evolution of compensatory measures that may act in their place. In this investigation heat-killed bacteria (Vibrio aestuarianus and Tenacibaculum maritimum) were used in a two-phased experiment to assess the immune response dynamics of Hippocampus erectus. Gill transcriptomes from double and single-exposed individuals were analysed in order to determine the differentially expressed genes contributing to immune system responses towards immune priming. Double-exposed individuals exhibited a greater adaptive immune response when compared with single-exposed individuals, while single-exposed individuals, particularly with V. aestuarianus replicates, associated more with the innate branch of the immune system. T. maritimum double-exposed replicates exhibited the strongest immune reaction, likely due to their immunological naivety towards the bacterium, while there are also potential signs of innate trained immunity. MHC II upregulated expression was identified in selected V. aestuarianus-exposed seahorses, in the absence of other pathway constituents suggesting a possible alternative or non-classical MHC II immune function in seahorses. Gene Ontology (GO) enrichment analysis highlighted prominent angiogenesis activity following secondary exposure, which could be linked to an adaptive immune process in seahorses. This investigation highlights the prominent role of T-cell mediated adaptive immune responses in seahorses when exposed to sequential foreign bacteria exposures. If classical MHC II pathway function has been lost, innate trained immunity in syngnathids could be a potential compensatory mechanism.

Genome-wide comparative analysis of DNAJ genes and their co-expression patterns with HSP70s in aestivation of the sea cucumber Apostichopus japonicus

DNAJ proteins function as co-chaperones of HSP70 and play key roles in cell physiology to promote protein folding and degradation, especially under environmental stress. Based on our previous study on HSP70, a systematic study of DNAJ was performed in sea cucumber Apostichopus japonicus using the transcriptomic and genomic data, identifying 43 AjDNAJ genes, including six AjDNAJA genes, eight AjDNAJB genes, and 29 AjDNAJC genes. Slight expansion and conserved genomic structure were observed using the phylogenetic and syntenic analysis. Differential period-specific and tissue-specific expression patterns of AjDNAJs were observed between adult and juvenile individuals during aestivation. Strong tissue-specific expression correlations between AjDNAJ and AjHSP70 genes were found, indicating that the involvements of AjHSP70IVAs in the aestivation of sea cucumbers were regulated by AjDNAJs. Several key genes with significant expression correlations, such as AjDNAJB4L and AjHSP70IVAs, were suggested to function together under heat stress. Together, these findings provide early insight into the involvement of AjDNAJs in the aestivation and their roles as co-chaperones of AjHSP70s.

Characterization of CD3γ/δ+ cells in grass carp (Ctenopharyngodon idella)

CD3 is an essential component of the TCR-CD3 complex which plays a key role in adaptive immunity. Non-mammalian CD3 complex consists of CD3γ/δ, CD3ε and CD3ζ subunits. In this study, homologues of CD3γ/δ and CD3ε (termed CiCD3γ/δ and CiCD3ε) have been identified in grass carp (Ctenopharyngodon idella). Like their counterparts from other vertebrates, the CiCD3γ/δ and CiCD3ε are clustered in the same locus in the genome and encode proteins which are structurally conserved, comprising a signal peptide, an extracellular domain, a transmembrane domain and a cytoplasmic tail containing two ITAM motifs. Sequence analyses identified two novel conserved motifs in the cytoplasmic tail of CiCD3γ/δ and CiCD3ε, one is composed of an arginine and lysine motif (RK or RR) at the C terminus of CiCD3γ/δ and a proline rich domain (PxxPxP/Q) located at the N terminus of ITAM motifs of CiCD3ε. Both genes were highly expressed at the mRNA level in the spleen and gills of healthy fish and could be modulated by infection of Flavobacterium columnare and grass carp reovirus. A monoclonal antibody against the CiCD3γ/δ (GC38T) was produced and showed good reactivity with the native molecule in Western blotting analysis and flow cytometry. The CiCD3γ/δ⁺ cells were analysed in the primary leucocytes, accounting for 5.5% of lymphocytes isolated from spleen, 4.5% from head kidney and 2.8% from peripheral blood. The CiCD3γ/δ⁺ cells were localized in the gills and head kidney by fluorescent confocal microscopy.

A Review of Molecular Responses of Catfish to Bacterial Diseases and Abiotic Stresses

Catfish is one of the major aquaculture species in the United States. However, the catfish industry is threatened by several bacterial diseases such as enteric septicemia of catfish (ESC), columnaris disease and Aeromonas disease, as well as by abiotic stresses such as high temperature and low oxygen. Research has been conducted for several decades to understand the host responses to these diseases and abiotic stresses. With the development of sequencing technologies, and the application of genome-wide association studies in aquaculture species, significant progress has been made. This review article summarizes recent progress in understanding the molecular responses of catfish after bacterial infection and stress challenges, and in understanding of genomic and genetic basis for disease resistance and stress tolerance.

Genome-wide association analysis of intra-specific QTL associated with the resistance for enteric septicemia of catfish

Disease resistance is one of the most important traits for aquaculture industry. For catfish industry, enteric septicemia of catfish (ESC), caused by the bacterial pathogen Edwardsiella ictaluri, is the most severe disease, causing enormous economic losses every year. In this study, we used three channel catfish families with 900 individuals (300 fish per family) and the 690K catfish SNP array, and conducted a genome-wide association study to detect the quantitative trait loci (QTL) associated with ESC resistance. Three significant QTL, with two of located on LG1 and one on LG26, and three suggestive QTL located on LG1, LG3, and LG21, respectively, were identified to be associated with ESC resistance. With a well-assembled- and -annotated reference genome sequence, genes around the involved QTL regions were identified. Among these genes, 37 genes had known functions in immunity, which may be involved in ESC resistance. Notably, nlrc3 and nlrp12 identified here were also found in QTL regions of ESC resistance in the channel catfish × blue catfish interspecific hybrid system, suggesting this QTL was operating within both intra-specific channel catfish populations and interspecific hybrid backcross populations. Many of the genes of the Class I MHC pathway, for mediated antigen processing and presentation, were found in the QTL regions. The positional correlation found in this study and the expressional correlation found in previous studies indicated that Class I MHC pathway was significantly associated with ESC resistance. This study validated one QTL previously identified using the second and fourth generation of the interspecific hybrid backcross progenies, and identified five additional QTL among channel catfish families. Taken together, it appears that there are only a few major QTL for ESC disease resistance, making marker-assisted selection an effective approach for genetic improvements of ESC resistance.

JAK and STAT members in channel catfish: Identification, phylogenetic analysis and expression profiling after Edwardsiella ictaluri infection

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway is one of the main pleiotropic cascades used to transmit information from extracellular receptors to the nucleus, which results in DNA transcription and expression of genes involved in immunity, proliferation, differentiation, migration, apoptosis, and cell survival. Members of JAK family and STAT family have been extensively studied in different mammalian species because of their important roles in innate and adaptive immune responses. However, they have not been systematically studied among teleost fish species. In this study, five JAK family members and eight STAT family members were identified and characterized from channel catfish. Phylogenetic analysis was conducted to properly annotate these genes. Syntenic analysis was also conducted to establish orthology, and confirm the results from phylogenetic analysis. Compared to mammals, more members of the JAK and STAT family were identified in channel catfish genome. Expression of JAK and STAT family members was detected in healthy catfish tissues, but was induced in gill, liver, and intestine after bacterial challenge. Notably, the significant upregulation of STAT1b gene in catfish liver, gill and intestine after Edwardsiella ictaluri infection supported the notion that high STAT1 expression are involved in defense against pathogens. Collectively, the increased expression of JAK and STAT members in tested tissues suggested their crucial function in defending the host against pathogen invasion.

The CC and CXC chemokine receptors in channel catfish (Ictalurus punctatus) and their involvement in disease and hypoxia responses

Chemokines are vital regulators of cell mobilization for immune surveillance, inflammation, and development. Chemokines signal through binding to their receptors that are a superfamily of seven-transmembrane domain G-coupled receptors. Recently, a complete repertoire of both CC and CXC chemokines have been identified in channel catfish, but nothing is known about their receptors. In this study, a set of 29 CC chemokine receptor (CCR) genes and 8 CXC chemokine receptor (CXCR) genes were identified and annotated from the channel catfish genome. Extensive phylogenetic and comparative genomic analyses were conducted to annotate these genes, revealing fish-specific CC chemokine receptors, and lineage-specific tandem duplications of chemokine receptors in the teleost genomes. With 29 genes, the channel catfish genome harbors the largest numbers of CC chemokine receptors among all the genomes characterized. Analysis of gene expression after bacterial infections indicated that the chemokine receptors were regulated in a gene-specific manner. Most differentially expressed chemokine receptors were up-regulated after Edwardsiella ictaluri and Flavobacterium columnare infection. Among which, CXCR3 and CXCR4 were observed to participate in immune responses to both bacterial infections, indicating their potential roles in catfish immune activities. In addition, CXCR3.2 was significantly up-regulated in ESC-susceptible fish, and CXCR4b was mildly induced in ESC-resistant fish, further supporting the significant roles of CXCR3 and CXCR4 in catfish immune responses. CXCR4b and CCR9a were both up-regulated not only after bacterial infection, but also after hypoxia stress, providing the linkage between bacterial infection and low oxygen stresses. These results should be valuable for comparative immunological studies and provide insights into their roles in disease and stress responses.