Expression analysis of selected immune-relevant genes in channel catfish during Edwardsiella ictaluri infection

Catfishes: A global review of the literature

This study aims to elucidate the evolution of catfish research publications over recent decades, identify emerging research clusters, examine keyword patterns, determine major contributors (including authors, organizations, and funding agencies), and analyze their collaborative networks and citation bursts on a global scale. The USA, Brazil, China, and India collectively contribute approximately 67% of the total catfish research publications, with a marked increase in prevalence since 2016. The most frequently occurring and dominant keywords are "channel catfish" and "responses," respectively. Intriguingly, our findings reveal 28 distinct article clusters, with prominent clusters including "yellow catfish," "channel catfish", "pectoral girdle," "African catfish", "Rio Sao Francisco basin," "Edwardsiella ictaluri," and "temperature mediated". Concurrently, keyword clustering generates seven main clusters: "new species", "growth performance", "heavy metal", "gonadotropin-releasing", "essential oil", and "olfactory receptor". This study further anticipates future research directions, offering fresh perspectives on the catfish literature landscape. To the best of our knowledge, this is the first article to conduct a comprehensive mapping review of catfish research publications worldwide.

Genome-wide characterization of integrin (ITG) gene family and their expression profiling in half-smooth tongue sole (Cynoglossus semilaevis) upon Vibrio anguillarum infection

Integrins (ITGs) are transmembrane heterodimer receptors with ITGα subunit and ITGβ subunit, participating in various physiological processes, including immunity. At present, systematic research on ITGs in teleost is scarce, especially in half-smooth tongue sole (Cynoglossus semilaevis). In this study, a set of 28 ITG genes in half-smooth tongue sole have been identified and characterized. The phylogenetic analysis showed that ITGα and ITGβ subunits were respectively classified into five and two clusters, consistent with previous studies. The selection pressure analysis indicated that most of ITG genes were under purifying selection, except for ITGα11b and ITGαL with positive selection. The expression profiles of eight selected ITG genes, including ITGα1, ITGα5, ITGα8, ITGα11, ITGβ1, ITGβ2, ITGβ3, and ITGβ8, were analyzed in healthy tissues and after infection with Vibrio anguillarum, revealed their implications in immune response. The study provided a comprehensive characterization and expression analysis of ITG genes in half-smooth tongue sole, setting a solid foundation for further functional studies and promising potential in disease control.

Effects of dietary supplementation of Pseudomonas aeruginosa FARP72 on the immunomodulation and resistance to Edwardsiella tarda in Pangasius pangasius

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Pseudomonas aeruginosa FARP72 (PA) supplemented diet impacts the innate immunity.

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Innate immune responses of P. pangasius are differentially stimulated by PA diet.

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It improved the resistance of P. pangasius against E. tarda infection significantly.

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IL-1β & C3 genes upregulated significantly in kidney of PA diet-fed challenged fish.

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Highest upregulation of transferrin seen in liver of PA diet-fed challenged fish.

Edwardsiella tarda is one of the serious bacterial pathogens infecting both cultured and wild catfish urging an immediate need for effective protection strategies. This study assessed the effects of dietary supplementation of Pseudomonas aeruginosa FARP72 at 10⁸ cells/g feed (PA diet) for 30 days on the innate immunity parameters, viz., respiratory oxidative burst (ROB) activity, lysozyme, ceruloplasmin, myeloperoxidase, in-vitro nitric oxide (NO) production in addition to the expression of immune genes encoding interleukin-1β, C3 and transferrin in yellowtail catfish Pangasius pangasius and their resistance to Edwardsiella tarda challenge at a sub-lethal dose of 1.50 × 10⁷ cells/fish. A significant increase in the innate immunity parameters was noted in PA diet-fed catfish on 30 dpf compared to the control. Post E. tarda challenge, the levels of immune parameters increased significantly and peaked at 5 dpi irrespective of feeding to confer protection against E. tarda. Their levels, however, decreased on and from 10 dpi. The results on the expression of immune genes encoding interleukin-1β, C3 and transferrin in the kidney and liver tissue samples of PA diet-fed P. pangasius upon challenge with E. tarda further confirmed the ability of P. aeruginosa to stimulate primary immune organs at the gene level. The effects of feeding P. aeruginosa FARP72 on the immune functions of catfish as examined by the functional immune assays, thus, demonstrating the innate immune responses of catfish that are differentially stimulated by the PA diet. The findings of our study would help evolve management strategies to confer protection against E. tarda infection in commercial catfish aquaculture.

Survival and gene expression responses in immune challenged larval lake sturgeon

Larval lake sturgeon, Acipenser fulvescens, reared in hatcheries for stock enhancement of wild populations may be susceptible to early opportunistic bacterial infection. Thus, we examined survival and whole-body mRNA expression of both stress- and immune-related genes (MyD88, IL-1β, StAR, GR1, and HSP70) in 30 days post fertilization larval lake sturgeon following immune challenge with lipopolysaccharides (LPS). Larval sturgeon were exposed to 0, 25, 50, 100, 150, and 200 μg ml^-1 LPS and sampled after 30 min, 4 h, and 48 h. Mortality was zero in 0 and 25 μg ml^-1 LPS; 37.5% in 50 μg ml^-1 LPS and 100% in the higher concentrations. Expression of MyD88 and StAR mRNA were positively correlated and increased with time in the 50 μg ml^-1 LPS treatment. There was an influence of both treatment and time on IL-1β mRNA, with expression 10-fold higher than controls after 4 h. Expression of HSP70 mRNA was suppressed within 30 min of 50 μg ml^-1 LPS exposure and remained so throughout the time course. Correlated mRNA expression of GR1 with MyD88, StAR and IL-1β suggests a potential relationship between the innate immune and glucocorticoid responses of larval lake sturgeon during this early developmental stage. Data presented suggest that larval lake sturgeon largely responded with predicted changes in gene expression of immune related and stress response genes following LPS challenge. This study provides a foundation for future research examining the effects of hatchery and naturally occurring stressors on the immune responses of larval lake sturgeon.

Genome-wide identification of Hsp70 genes in channel catfish and their regulated expression after bacterial infection

Heat shock proteins 70/110 (Hsp70/110) are a family of conserved ubiquitously expressed heat shock proteins which are produced by cells in response to exposure to stressful conditions. Besides the chaperone and housekeeping functions, they are also known to be involved in immune response during infection. In this study, we identified 16 Hsp70/110 geness in channel catfish (Ictalurus punctatus) through in silico analysis using RNA-Seq and genome databases. Among them 12 members of Hsp70 (Hspa) family and 4 members of Hsp110 (Hsph) family were identified. Phylogenetic and syntenic analyses provided strong evidence in supporting the orthologies of these HSPs. In addition, we also determined the expression patterns of Hsp70/110 genes after Flavobacterium columnare and Edwardsiella ictaluri infections by meta-analyses, for the first time in channel catfish. Ten out of sixteen genes were significantly up/down-regulated after bacterial challenges. Specifically, nine genes were found significantly expressed in gill after F. columnare infection. Two genes were found significantly expressed in intestine after E. ictaluri infection. Pathogen-specific pattern and tissue-specific pattern were found in the two infections. The significantly regulated expressions of catfish Hsp70 genes after bacterial infections suggested their involvement in immune response in catfish.

Biology of Bony Fish Macrophages

Macrophages are found across all vertebrate species, reside in virtually all animal tissues, and play critical roles in host protection and homeostasis. Various mechanisms determine and regulate the highly plastic functional phenotypes of macrophages, including antimicrobial host defenses (pro-inflammatory, M1-type), and resolution and repair functions (anti-inflammatory/regulatory, M2-type). The study of inflammatory macrophages in immune defense of teleosts has garnered much attention, and antimicrobial mechanisms of these cells have been extensively studied in various fish models. Intriguingly, both similarities and differences have been documented for the regulation of lower vertebrate macrophage antimicrobial defenses, as compared to what has been described in mammals. Advances in our understanding of the teleost macrophage M2 phenotypes likewise suggest functional conservation through similar and distinct regulatory strategies, compared to their mammalian counterparts. In this review, we discuss the current understanding of the molecular mechanisms governing teleost macrophage functional heterogeneity, including monopoetic development, classical macrophage inflammatory and antimicrobial responses as well as alternative macrophage polarization towards tissues repair and resolution of inflammation.

The effects of feeding β-glucan to Pangasianodon hypophthalmus on immune gene expression and resistance to Edwardsiella ictaluri

Pangasianodon hypophthalmus (striped catfish) is an important aquaculture species and intensification of farming has increased disease problems, particularly Edwardsiella ictaluri. The effects of feeding β-glucans on immune gene expression and resistance to E. ictaluri in P. hypophthalmus were explored. Fish were fed 0.1% fungal-derived β-glucan or 0.1% commercial yeast-derived β-glucan or a basal control diet without glucan. After 14 days of feeding, the mRNA expression of immune genes (transferrin, C-reactive protein, precerebellin-like protein, Complement C3 and factor B, 2a MHC class II and interleukin-1 beta) in liver, kidney and spleen were determined. Following this fish from each of the three diet treatment groups were infected with E. ictaluri and further gene expression measured 24 h post-infection (h.p.i.), while the remaining fish were monitored over 2 weeks for mortalities. Cumulative percentage mortality at 14 days post-infection (d.p.i.) was less in β-glucan fed fish compared to controls. There was no difference in gene expression between dietary groups after feeding for 14 days, but there was a clear difference between infected and uninfected fish at 24 h.p.i., and based on principal component analysis β-glucans stimulated the overall expression of immune genes in the liver, kidney and spleen at 24 h.p.i.

Antimicrobial responses of teleost phagocytes and innate immune evasion strategies of intracellular bacteria

During infection, macrophage lineage cells eliminate infiltrating pathogens through a battery of antimicrobial responses, where the efficacy of these innate immune responses is pivotal to immunological outcomes. Not surprisingly, many intracellular pathogens have evolved mechanisms to overcome macrophage defenses, using these immune cells as residences and dissemination strategies. With pathogenic infections causing increasing detriments to both aquacultural and wild fish populations, it is imperative to garner greater understanding of fish phagocyte antimicrobial responses and the mechanisms by which aquatic pathogens are able to overcome these teleost macrophage barriers. Insights into the regulation of macrophage immunity of bony fish species will lend to the development of more effective aquacultural prophylaxis as well as broadening our understanding of the evolution of these immune processes. Accordingly, this review focuses on recent advances in the understanding of teleost macrophage antimicrobial responses and the strategies by which intracellular fish pathogens are able to avoid being killed by phagocytes, with a focus on Mycobacterium marinum.

Characterization of four heat-shock protein genes from Nile tilapia (Oreochromis niloticus) and demonstration of the inducible transcriptional activity of Hsp70 promoter

Heat-shock proteins (Hsps), known as stress proteins and extrinsic chaperones, play important roles in the folding, translocation, and refolding/degradation of proteins. In this study, we identified four Hsps in Nile tilapia (Oreochromis niloticus), which display conserved Hsp characteristics in their predicted amino acid sequences. Further analyses on the structures, homology, and phylogenetics revealed that the four Hsps belong to Hsp70 family. One of them does not contain introns and is named Hsp70, while all the other three contain introns and are named Hsc70-1, Hsc70-2, and Hsc70-3. Expressions of the four Hsp proteins were observed in all examined tissues. Six hours after infection of Streptococcus agalactiae in Nile tilapia, the expression of Hsp70 was significantly increased in the liver, head kidney, spleen and gill, while Hsc70s' expression was unchanged in all examined tissues except the head kidney that showed significantly reduced expression of both Hsc70-2 and Hsc70-3. These results suggest that Hsp70 may participate in the defense against S. agalactiae infection. We then isolated the promoter of Hsp70 gene and inserted it into the donor plasmid of Tgf2 transposon system containing green fluorescent protein (GFP) gene. The plasmid was microinjected into zebrafish embryos, where the expression of GFP was induced by heat shock, S. agalactiae immersion challenge, indicating that the isolated Hsp70 promoter has transcriptional activity and is inducible by both heat shock and bacterial challenge. This promoter may facilitate the future construction of disease-resistant transgenic fish. The work also contributes to the further study of immune response of tilapia after bacterial infection.

Comparative analysis of the acute response of zebrafish Danio rerio skin to two different bacterial infections

Skin is an important innate immune organ in fish; however, little is known about the skin's immune response to infectious pathogens. We conducted a comparative analysis of the acute immune response of Zebrafish Danio rerio skin against gram-positive (Staphylococcus chromogenes) and gram-negative (Citrobacter freundii) bacterial infections. Gene expression profiles induced from the two different infections were identified by microarray hybridization, with many genes demonstrating an acute immune response in the skin. Differentially expressed genes were mainly involved in response to stress and stimulus, complement activation, acute-phase response, and defense and immune response. Compared with transcription patterns of skin from the two infections, a similar innate immunity (e.g., transferrin, coagulation factor, complements, and lectins) was observed but with different acute-phase genes (e.g., ceruloplasmin, alpha-1-microglobulin, vitellogenin, and heat shock protein). These results suggest that the skin of fish plays an important role in the innate immune responses to bacterial infection.

Gene expression profiling in the skin of zebrafish infected with Citrobacter freundii

Skin is considered the largest immunologically active organ, but its molecular mechanism remains unclear in fish. Here, Affymetrix Zebrafish GeneChip was used to assess gene expression in the skin of zebrafish (Danio rerio) infected with the bacterium Citrobacter freundii. The results showed that 229 genes were differentially expressed, of which 196 genes were upregulated and 33 genes were downregulated. Gene Ontology and KEGG pathway analyses indicated 88 genes significantly associated with skin immunity involved in complement activation and acute phase response, defense and immune response, response to stress and stimulus, antigen processing and presentation, cell adhesion and migration, platelet activation and coagulation factors, regulation of autophagy and apoptosis. When compared with transcriptional profiles of previously reported carp (Cyprinus carpio) skin, a similar innate immunity (e.g., interferon, lectin, heat shock proteins, complements), and several different acute phase proteins (transferrin, ceruloplasmin, vitellogenin and alpha-1-microglobulin, etc.) were detected in zebrafish skin. The validity of the microarray results was verified by quantitative real-time PCR analysis of nine representative genes. This is first report that skin play important roles in innate immune responses to bacterial infection, which contribute to understanding the defense mechanisms of the skin in fish.

Transcriptional profiles of multiple genes in the anterior kidney of channel catfish vaccinated with an attenuated Aeromonas hydrophila

A total of 22 uniquely expressed sequence tags (ESTs) were identified from channel catfish anterior kidney subtractive cDNA library at 12 h post vaccination with an attenuated Aeromonas hydrophila (AL09-71 N+R). Of the 22 ESTs, six were confirmed to be significantly (P < 0.05) induced by the vaccination. Of 88 channel catfish genes selected from literature, 14 were found to be significantly (P < 0.05) upregulated by the vaccination. The transcriptional levels of the total 20 genes induced by the vaccination were then compared to that induced by the virulent parent A. hydrophila (AL09-71) at different time points. At 3 h post vaccination (hpv) or infection (hpi), Na(+)/K(+) ATPase α subunit was upregulated the most. At 6 and 12 hpv or hpi, hepcidin and interleukin-1β were induced the highest. At 24 hpv or hpi, hepcidin was upregulated the most, followed by lysozyme c. At 48 hpi, lysozyme c and hepcidin were significantly induced. When vaccinated fish were challenged by AL09-71, relative percent of survival of vaccinated fish were 100% at 14 days post vaccination (dpv). Transcriptional levels of toll-like receptor 5 and hepcidin were significantly upregulated in vaccinated fish at 14 dpv. Taken together, our results suggest that vaccination with attenuated A. hydrophila mimics infection by live bacteria, inducing multiple immune genes in channel catfish.

Natural history of SLC11 genes in vertebrates: tales from the fish world

BACKGROUND

The SLC11A1/Nramp1 and SLC11A2/Nramp2 genes belong to the SLC11/Nramp family of transmembrane divalent metal transporters, with SLC11A1 being associated with resistance to pathogens and SLC11A2 involved in intestinal iron uptake and transferrin-bound iron transport. Both members of the SLC11 gene family have been clearly identified in tetrapods; however SLC11A1 has never been documented in teleost fish and is believed to have been lost in this lineage during early vertebrate evolution. In the present work we characterized the SLC11 genes in teleosts and evaluated if the roles attributed to mammalian SLC11 genes are assured by other fish specific SLC11 gene members.

RESULTS

Two different SLC11 genes were isolated in the European sea bass (Dicentrarchus. labrax), and named slc11a2-α and slc11a2-β, since both were found to be evolutionary closer to tetrapods SLC11A2, through phylogenetic analysis and comparative genomics. Induction of slc11a2-α and slc11a2-β in sea bass, upon iron modulation or exposure to Photobacterium damselae spp. piscicida, was evaluated in in vivo or in vitro experimental models. Overall, slc11a2-α was found to respond only to iron deficiency in the intestine, whereas slc11a2-β was found to respond to iron overload and bacterial infection in several tissues and also in the leukocytes.

CONCLUSIONS

Our data suggests that despite the absence of slc11a1, its functions have been undertaken by one of the slc11a2 duplicated paralogs in teleost fish in a case of synfunctionalization, being involved in both iron metabolism and response to bacterial infection. This study provides, to our knowledge, the first example of this type of sub-functionalization in iron metabolism genes, illustrating how conserving the various functions of the SLC11 gene family is of crucial evolutionary importance.

Characterization of two heat shock proteins (Hsp70/Hsc70) from grass carp (Ctenopharyngodon idella): evidence for their differential gene expression, protein synthesis and secretion in LPS-challenged peripheral blood lymphocytes

Two cDNAs, encoding the stress-inducible 70-kDa heat shock protein (Hsp70) and the constitutively expressed 70-kDa heat shock cognate protein (Hsc70), were isolated from grass carp. The Hsp70 and Hsc70 cDNAs were 2250 bp and 2449 bp in length and contained 1932 bp and 1953 bp open reading frames, respectively. Tissue distribution results showed that Hsp70/Hsc70 was highly expressed in gill, kidney, head kidney and peripheral blood lymphocytes (PBLs). Using grass carp PBLs as a cell model, effects of lipopolysaccharide (LPS) on the mRNA and protein levels of Hsp70/Hsc70 were examined. In this case, LPS increased the mRNA expression of Hsp70 in a time- and dose-dependent manner, but had no effect on Hsc70 mRNA expression. In agreement with this, LPS elevated the intracellular Hsp70 markedly, but not the Hsc70 protein levels in parallel experiments. Furthermore, Hsp70 protein was also detected in culture medium. Moreover, inhibition of LPS on Hsp70 release in a time-dependent manner was observed, indicating that there may be a dynamic balance between Hsp70 stores and Hsp70 release in grass carp PBLs following exposure to LPS. Taken together, these results not only shed new insights into the different regulations of LPS on Hsp70/Hsc70 gene expression, protein synthesis and release, but also provide a basis for further study on the functional role of Hsp70 in fish immune response.

Expression profiles of toll-like receptors in anterior kidney of channel catfish, Ictalurus punctatus (Rafinesque), acutely infected by Edwardsiella ictaluri

Using quantitative PCR (QPCR), the relative transcriptional levels of five toll-like receptors (TLR2, TLR3, TLR5, TLR20a and TLR21) were studied in the channel catfish, Ictalurus punctatus (Rafinesque), under uninfected and acutely infected conditions [1-, 2-, 4-, 6-, 12-, 24-, 36- and 48-h post-injection (hpi)]. Under uninfected conditions, the transcriptional levels of the five TLRs were significantly lower than that of 18S rRNA (P < 0.001). QPCR results also revealed that the transcriptional levels of TLR20a and TLR5 were higher than those of TLR2, TLR3 or TLR21. The transcriptional level of TLR3 was significantly lower than that of the other four TLRs (P < 0.001). However, when channel catfish were acutely infected by Edwardsiella ictaluri through intraperitoneal injection, the transcriptional levels of TLRs increased significantly (P < 0.005) at 6 hpi. Among the five TLRs studied, the transcriptional levels of TLR3, TLR5 and TLR21 were never significantly lower than under uninfected conditions (P = 0.16, 0.27 and 0.19, respectively), suggesting these three TLRs might play important roles in host defence against infection by E. ictaluri. The amount of E. ictaluri in the anterior kidney increased at 12 and 24 hpi but decreased at 36 and 48 hpi. Our results suggest that TLRs are important components in the immune system in the channel catfish, and their rapid transcriptional upregulation (within 6 hpi) in response to acute E. ictaluri infection might be important for survival from enteric septicaemia of catfish.

Variation in susceptibility to Henneguya ictaluri infection by two species of catfish and their hybrid cross

Proliferative gill disease (PGD) in channel catfish Ictalurus punctatus is caused by the myxozoan parasite Henneguya ictaluri. There is no effective treatment for PGD, and mortalities can exceed 50% in severe outbreaks. One approach to controlling losses would be to utilize a less susceptible ictalurid species in pond culture; alternatively, one could identify the traits that convey resistance and exploit them in a selective breeding program. Challenge studies have found less severe inflammatory responses in the gill tissue of blue catfish I. furcatus and fewer mortalities than in channel catfish. However, it remains unclear whether infection and subsequent plasmodial development progress the same way in the two species. To investigate this, we compared the dynamics of H. ictaluri infection in blue catfish, channel catfish, and channel catfish x blue catfish hybrids in continuous long-term (5-7-d) and short-term (24-h) pond challenges. After long-term challenge, 66.2% of the channel catfish and 63.6% of the hybrid catfish developed characteristic PGD lesions, compared with 3.7% of the blue catfish. Quantitative polymerase chain reaction analysis detected H. ictaluri in larger percentages of channel and hybrid catfish than blue catfish (98.7% and 95.7% versus 45.9%), with significantly greater parasite DNA equivalents in channel and hybrid catfish than blue catfish. Similar findings were obtained in the short-term exposures. Histologically, channel and hybrid catfish developed severe PGD accompanied by large numbers of developing plasmodia. While mild PGD was observed in some blue catfish, the progression of lesions lagged behind that in channel and hybrid catfish. Most importantly, developing plasmodia were not observed in blue catfish, and parasite DNA was not detected 14 d after removal from the source of infection. Our findings indicate that the resistance of blue catfish to H. ictaluri infection can be overcome by large numbers of infective actinospores but that infection appears to be eliminated before plasmodial development occurs.