Identification of chemokines and a chemokine receptor in cichlid fish, shark, and lamprey

Lympho-Hematopoietic Microenvironments and Fish Immune System

In the last 50 years information on the fish immune system has increased importantly, particularly that on species of marked commercial interest (i.e., salmonids, cods, catfish, sea breams), that occupy a key position in the vertebrate phylogenetical tree (i.e., Agnatha, Chondrichtyes, lungfish) or represent consolidated experimental models, such as zebrafish or medaka. However, most obtained information was based on genetic sequence analysis with little or no information on the cellular basis of the immune responses. Although jawed fish contain a thymus and lympho-hematopoietic organs equivalents to mammalian bone marrow, few studies have accounted for the presumptive relationships between the organization of these cell microenvironments and the known immune capabilities of the fish immune system. In the current review, we analyze this topic providing information on: (1) The origins of T and B lymphopoiesis in Agnatha and jawed fish; (2) the remarkable organization of the thymus of teleost fish; (3) the occurrence of numerous, apparently unrelated organs housing lympho-hematopoietic progenitors and, presumably, B lymphopoiesis; (4) the existence of fish immunological memory in the absence of germinal centers.

CXC chemokines and their receptors in black rockfish (Sebastes schlegelii): Characterization, evolution analyses, and expression pattern after Aeromonas salmonicida infection

Chemokines are crucial regulators of cell mobilization for development, homeostasis, and immunity. Chemokines signal through binding to chemokine receptors, a superfamily of seven-transmembrane domain G-coupled receptors. In the present study, seventeen CXC chemokine ligands (SsCXCLs) and nine CXC chemokine receptors (SsCXCRs) were systematically identified from Sebastes schlegelii genome. Phylogeny, synteny, and evolutionary analyses were performed to annotate these genes, indicating that the tandem duplications (CXCL8, CXCL11, CXCL32, CXCR2, and CXCR3), the whole genome duplications (CXCL8, CXCL12, CXCL18, and CXCR4), and the teleost-specific members (CXCL18, CXCL19, and CXCL32) led to the expansion of SsCXCLs and SsCXCRs. In addition, SsCXCLs and SsCXCRs were ubiquitously expressed in nine examined healthy tissues, with high expression levels observed in head kidney, liver, gill and spleen. Moreover, most SsCXCLs and SsCXCRs were significantly differentially expressed in head kidney, liver, and gill after Aeromonas salmonicida infection, and exhibited tissue-specific and time-dependent manner. Finally, protein-protein interaction network (PPI) analysis indicated that SsCXCLs and SsCXCRs interacted with a few immune-related genes such as interleukins, cathepsins, CD genes, and TLRs, etc. These results should be valuable for comparative immunological studies and provide insights for further functional characterization of chemokines and receptors in teleost.

The evolution and functional characterization of CXC chemokines and receptors in lamprey

Chemokines are a large family of soluble peptides guiding cell migration in development and immune defense. They interact with chemokine receptors and are essential for the coordination of cell migration in diverse physiological processes. The CXC subfamily is one of the largest groups in the chemokine family and consists of multiple members. In this study, we identified homologues of three chemokine ligands (CXCL8, CXCL_F5 and CXCL12) and two CXC receptor like molecules (CXCR_L1 and CXCR_L2) in lamprey. Sequence analysis revealed that they share the same genomic organization with their counterparts in jawed vertebrates but synteny was not conserved. Lamprey CXCL8 and CXCL12 have four conserved cysteine residues whilst the CXCL_F5 has two additional cysteine residues. In addition, CXCL_F5 is evolutionarily related to the fish specific CXC chemokine groups previously identified and contains multiple cationic aa residues in the extended C- terminal region. The two CXCRs possess seven transmembrane domains and conserved structural elements for receptor activation and signaling, including the DRYXXI(V)Y motif in TM2, the disulphide bond connecting ECL2 and TM3, the WXP motif in TM6 and NPXXY motif in TM7. The identified CXC chemokines and receptors were constitutively expressed in tissues including the liver, kidney, intestine, heart, gills, supraneural body and primary leukocytes, but exhibited distinct expression patterns. Relatively high expression was detected in the gills for CXCL8, CXCL_F5 and CXCR_L1 and in the supraneural body for CXCL12 and CXCR_L2. All the genes except CXCL12 were upregulated by stimulation with LPS, pokeweed and bacterial infection, and the CXCL8 and CXCL_F5 was induced by poly (I:C). Functional analysis showed that the CXCL8 and CXCL_F5 specifically interacted with CXCR_L1 and CXCR_L2, respectively. Our results demonstrate that the CXC chemokine system had diversified in jawless fish.

Molecular Characterization and Chemotactic Function of CXCL8 in Northeast Chinese Lamprey (Lethenteron morii)

Chemokine-induced chemotaxis of leukocytes is an important part of the innate immunity and has been shown to mediate inflammation in all groups of jawed vertebrates. For jawless vertebrates, hagfish leukocytes are known to show chemotaxis toward mammalian complement anaphylotoxin and Gram-negative bacteria lipopolysaccharide. However, whether chemokines mediate chemotaxis of leukocytes in jawless vertebrates has not been conclusively examined. Here, we show C-X-C motif chemokine ligand 8 (CXCL8, also named interleukin 8) of the Northeast Chinese lamprey (Lethenteron morii) (designated as LmCXCL8) induces chemotaxis in its leukocytes. We identified LmCXCL8 and found it possesses the characteristic N-terminal cysteine residues and GGR (Gly-Gly-Arg) motif. The Lmcxcl8 gene was found to be expressed in all examined tissues, and its expression was inducible in the lamprey challenged by an infectious bacterium, Pseudomonas aeruginosa. A recombinant LmCXCL8 protein elicited concentration-dependent chemotaxis in peripheral blood leukocytes isolated from the Northeast Chinese lamprey. Based on these results, we conclude that LmCXCL8 is a constitutive and inducible acute-phase cytokine that mediates immune defense and trace the chemotactic function of chemokine to basal vertebrates.

Identification and expression analysis of 19 CC chemokine genes in orange-spotted grouper (Epinephelus coioides)

In this study, we describe 19 different CC chemokine genes from the orange-spotted grouper, Epinephelus coioides, identified by the analysis of the spleen transcriptome. Multiple sequence alignment of the 19 CC chemokines showed that although two genes, EcSCYA115 and EcSCYA117, shared 80% amino acid similarity (72% identity), the majority exhibited low similarity to each other. Phylogenetic analysis divided the 19 CC chemokines into six major groups. Tissue distribution analysis by RT-PCR showed that most of these chemokines were ubiquitously expressed in the 9 examined tissues, whereas some exhibited tissue-preferential expression patterns. For example, EcSCYA103 was preferentially expressed in fin and gill; EcSCYA109 in head kidney and spleen; EcSCYA114 in fin, gill, and liver; and EcSCYA119 in fin and stomach. Quantitative RT-PCR showed that after challenge with grouper iridovirus (GIV), four of the 19 CC chemokine genes, EcSYCA102, EcSYCA103, EcSYCA116, and EcSYCA118, were highly induced in the spleen. The expression of these four genes could also be upregulated by LPS and poly (I:C) challenges, suggesting that these four genes might be involved in immune response against invading pathogens.

A role for the CXCR4-CXCL12 axis in the little skate, Leucoraja erinacea

The interaction between C-X-C chemokine receptor type 4 (CXCR4) and its cognate ligand C-X-C motif chemokine ligand 12 (CXCL12) plays a critical role in regulating hematopoietic stem cell activation and subsequent cellular mobilization. Extensive studies of these genes have been conducted in mammals, but much less is known about the expression and function of CXCR4 and CXCL12 in non-mammalian vertebrates. In the present study, we identify simultaneous expression of CXCR4 and CXCL12 orthologs in the epigonal organ (the primary hematopoietic tissue) of the little skate, Leucoraja erinacea. Genetic and phylogenetic analyses were functionally supported by significant mobilization of leukocytes following administration of Plerixafor, a CXCR4 antagonist and clinically important drug. Our results provide evidence that, as in humans, Plerixafor disrupts CXCR4/CXCL12 binding in the little skate, facilitating release of leukocytes into the bloodstream. Our study illustrates the value of the little skate as a model organism, particularly in studies of hematopoiesis and potentially for preclinical research on hematological and vascular disorders.

Evolution of Alternative Adaptive Immune Systems in Vertebrates

Adaptive immunity in jawless fishes is based on antigen recognition by three types of variable lymphocyte receptors (VLRs) composed of variable leucine-rich repeats, which are differentially expressed by two T-like lymphocyte lineages and one B-like lymphocyte lineage. The T-like cells express either VLRAs or VLRCs of yet undefined antigen specificity, whereas the VLRB antibodies secreted by B-like cells bind proteinaceous and carbohydrate antigens. The incomplete VLR germline genes are assembled into functional units by a gene conversion-like mechanism that employs flanking variable leucine-rich repeat sequences as templates in association with lineage-specific expression of cytidine deaminases. B-like cells develop in the hematopoietic typhlosole and kidneys, whereas T-like cells develop in the thymoid, a thymus-equivalent region at the gill fold tips. Thus, the dichotomy between T-like and B-like cells and the presence of dedicated lymphopoietic tissues emerge as ancestral vertebrate features, whereas the somatic diversification of structurally distinct antigen receptor genes evolved independently in jawless and jawed vertebrates.

Identification and expression analysis of three XCR1-like receptors from Epinephelus coioides after Cryptocaryon irritans infection

The unique receptor XCR1 of the XC subfamily of chemokines is specially expressed in CD8α-like dendritic cells. This receptor has one ligand in mice (XCL1) and two ligands in humans (XCL1 and XCL2). In mammals, the XCR1-XCL1 complex performs a vital role in regulating the localization and function of T cells, dendritic cells, and other cell types. In this study, three XCR1-like receptors (EcXCR1, EcXCR1L, and EcCCR12) were identified from a transcriptome database of orange-spotted grouper. The open reading frames (ORFs) of EcXCR1, EcXCR1L, and EcCCR12 predictably encode 337, 348, and 358 amino acids, respectively. All receptors are seven trans-membrane proteins, and contain conserved functional regions, and conserved sites, that are crucial for the role of chemokine receptors in mammals. Conserved features include four cysteine residues in the extracellular regions, a "DRY" motif in the second intracellular loop, and common characteristics at the N-terminus that are important for ligand interaction. In healthy grouper, EcXCR1, EcXCR1L, and EcCCR12 were broadly expressed in all the tissues tested. EcXCR1 was expressed at high levels in the liver, and EcXCR1L, and EcCCR12 in the thymus. After grouper infection with Cryptocaryon irritans, EcXCR1 and EcCCR12 were up-regulated in the skin and the spleen, and EcCCR12 in the skin, gill, and spleen. EcXCR1L expression changed only slightly. These results imply that EcXCR1 and EcCCR12 may be involved in host defense against parasite infection. A polyclonal antibody was produced against EcCCR12, and used to detect EcCCR12-positive cells in peripheral blood. These results will contribute considerably to elucidate the biological role of piscine XCR1-like receptors and their ligands system in the future.

Explaining the Paucity of Intratumoral T Cells: A Construction Out of Known Entities

This essay addresses the question of how tumors escape control by the immune system. The literature strongly points to inadequate accumulation of T cells among cancer cells as being the proximate cause, but this observation has no acceptable explanation as yet. An approach to this problem is adopted wherein the chemokines and chemokine receptors that normally mediate the trafficking of T cells to inflamed tissues are reviewed and considered in the context of their relative levels of expression in a transplanted colorectal tumor model. This method of reasoning-consistent with Bertrand Russell's (1985) advice, "Whenever possible, substitute constructions out of known entities for inferences to unknown entities"-leads to the proposal that signaling via the chemokine receptor, CXCR4, impairs the function of CXCR3 on the immune cells that are responsible for suppressing the growth of cancers.

Molecular and functional roles of 6C CC chemokine 19 in defense system of striped murrel Channa striatus

In this study, we have reported the molecular information of chemokine-19 (Chem19) from striped murrel Channa striatus (Cs). CsCC-Chem19 cDNA sequence was 555 base pair (bp) in length which is 68bp 5' untranslated region (UTR), 339bp translated region and 149bp 3' UTR. The translated region is encoded for a polypeptide of 112 amino acids. CsCC-Chem19 peptide contains a signal sequence between 1 and 26 and an interleukin (IL) 8 like domain between 24 and 89. The multiple sequence alignment showed a 'DCCL' motif, an indispensable motif present in all CC chemokines which was conserved throughout the evolution. Phylogenetic tree showed that CsCC-Chem19 formed a cluster with chemokine 19 from fishes. Secondary structure of CsCC-Chem19 revealed that the peptide contains maximum amount of coils (61.6%) compared to α-helices (25.9%%) and β-sheet (12.5%). Further, 3D analysis indicated that the cysteine residues at 33, 34, 59 and 75 making the disulfide bridges as 33 = 59 and 34 = 75. Significantly (P < 0.05) highest CsCC-Chem19 mRNA expression was observed in blood and it was up-regulated upon fungus and bacterial infection. Utilizing the coding region of CsCC-Chem19, recombinant CsCC-Chem19 protein was produced. The recombinant CsCC-Chem19 protein induced the cellular proliferation and respiratory burst activity of C. striatus peripheral blood leukocytes (PBL) in a concentration dependent manner. Moreover, the chemotactic activity showed that the recombinant CsCC-Chem19 significantly (P < 0.05) enhanced the movement of PBL of C. striatus. Conclusively, CsCC-Chem19 is a 6C CC chemokine having an ability to perform both inflammatory and homeostatic functions. However, further research is necessary to understand the potential of 6C CC chemokine 19 of C. striatus, particularly their regulatory ability on different cellular components in the defense system.

A CXC chemokine gene, CXCL12, from rock bream, Oplegnathus fasciatus: Molecular characterization and transcriptional profile

Chemokines are small, structurally related chemotactic cytokines characterized by the presence of conserved cysteine residues. In the present study, we identified the cDNA of a CXC chemokine from Oplegnathus fasciatus, designated as OfCXCL12. An open reading frame of 297 bp encoded a 98 amino acid peptide with a putative signal peptide of 23 amino acids. The CXC family-specific small cytokine domain (SCY), which is highly conserved among vertebrates, was located between residues 29 and 87. The characteristic conserved cysteine residues in the CXC motif of OfCXCL12 were separated by tyrosine (Y). Similar to other vertebrate CXCL12 proteins, OfCXCL12 also lacked the ELR motif and hence belongs to ELR(-) subfamily. Phylogenetic analysis revealed two distinct clades, consisting of fish and tetrapod CXCL12 homologs. Constitutive expression with significantly higher levels of OfCXCL12 mRNA transcription was detected in immune-related organs, including the head kidney, spleen, and kidney. Infection with bacterial and viral agents led to significant upregulation of mRNA expression in both the head kidney and spleen, in a stimulant-specific manner. Stimulation of peripheral blood leukocytes by the mitogen concanavalin-A significantly induced OfCXCL12 transcription. Results from the present study suggest an important role for OfCXCL12 in immune defense against bacterial and viral infection in rock bream.

CsCCL17, a CC chemokine of Cynoglossus semilaevis, induces leukocyte trafficking and promotes immune defense against viral infection

CC chemokines are the largest subfamily of chemokines, which are important components of the innate immune system. To date, sequences of several CC chemokines have been identified in half-smooth tongue sole (Cynoglossus semilaevis); however, the activities and functions of these putative chemokines remain unknown. Herein, we characterized a CC chemokine, CsCCL17, from tongue sole, and examined its activity. CsCCL17 contains a 303 bp open reading frame, which encodes a polypeptide of 100 amino acids with a molecular mass of 12 kDa CsCCL17 is phylogenetically related to the CCL17/22 group of CC chemokines and possesses the typical arrangement of four cysteines and an SCCR motif found in known CC chemokines. Under normal physiological conditions, CsCCL17 expression was detected in spleen, liver, heart, gill, head kidney, muscle, brain, and intestine. When the fish were infected by bacterial and viral pathogens, CsCCL17 expression was significantly up-regulated in a time-dependent manner. Chemotactic analysis showed that recombinant CsCCL17 (rCsCCL17) induced migration of peripheral blood leukocytes. A mutagenesis study showed that when the two cysteine residues in the SCCR motif were replaced by serine, no apparent chemotactic activity was observed in the mutant protein rCsCCL17M. rCsCCL17 enhanced the resistance of tongue sole against viral infection, but rCsCCL17M lacked this antiviral effect. Taken together, these findings indicate that CsCCL17 is a functional CC chemokine with the ability to recruit leukocytes and enhance host immune defense in a manner that requires the conserved SCCR motif.

Identification and expression analysis of an atypical chemokine receptor-2 (ACKR2)/CC chemokine binding protein-2 (CCBP2) in rainbow trout (Oncorhynchus mykiss)

Atypical chemokine receptors (ACKRs) have emerged as key components of the chemokine system, with an essential regulatory function in innate and adaptive immune responses and inflammation. In mammals ACKR2 is a 'scavenging' receptor for inflammatory CC chemokines and plays a central role in the resolution of in vivo inflammatory responses. An ACKR2 like gene has been identified and cloned in rainbow trout (Teleostei) in the present study, enabling the further identification of this molecule in another group of ray-finned teleost fish (Holostei), in a lobe-finned fish (Sarcopterygii-coelacanth), and in reptiles. The identity of these ACKR2 molecules is supported by their conserved structure, and by phylogenetic tree and synteny analysis. Trout ACKR2 is highly expressed in spleen and head kidney, suggesting a homeostatic role of this receptor in limiting the availability of its potential ligands. Trout ACKR2 expression can be modulated in vivo by bacterial and parasitic infections, and in vitro by PAMPs (poly I:C and peptidoglycan) and cytokines (IL-6, TNF-α, IFN-γ and IL-21) in a time dependent manner. These patterns of expression and modulation suggest that trout ACKR2 is regulated in a complex way and has an important role in control of the chemokine network in fish as in mammals.

The CXC chemokine receptors of fish: Insights into CXCR evolution in the vertebrates

This article will review current knowledge on CXCR in fish, that represent three distinct vertebrate groups: Agnatha (jawless fishes), Chondrichthyes (cartilaginous fishes) and Osteichthyes (bony fishes). With the sequencing of many fish genomes, information on CXCR in these species in particular has expanded considerably. In mammals, 6 CXCRs have been described, and their homologues will be initially reviewed before considering a number of atypical CXCRs and a discussion of CXCR evolution.

Characterization of a novel CC chemokine CCL4 in immune response induced by nitrite and its expression differences among three populations of Megalobrama amblycephala

A novel CC chemokine gene, chemokine CC motif ligand 4 (CCL4), was isolated from Megalobrama amblycephala. The full-length cDNA was 913 bp, encoding 94 amino acid residues. The deduced amino acid sequence possessed the typical arrangement of four cysteines as found in other known CC chemokines. The expression of M. amblycephala CCL4 during the early development showed the mRNA levels before hatching and at 62 h post fertilized (hpf) were significantly higher than other post-hatching stages (P < 0.05). Besides, it was widely expressed in all detected tissues with the highest transcription in liver, followed by intestine, spleen and gill, where a larger number of immune cells including lymphocytes and macrophages are present. Our findings had fully confirmed that CCL4 expression was strongly induced in vitro and quickly up-regulated after nitrite stress, then substantially altered in all tested tissues, supporting a potential pro-inflammatory function. We also indicated that inflammation effect might firstly happen in blood after nitrite stress. Furthermore, the tissue expression differences of CCL4 among three natural populations revealed that CCL4 mRNA in Yuni Lake population was obviously higher than the other two populations, Liangzi Lake population and Poyang Lake population, which will provide valuable insights into breeding strategies for selecting population with better immune property of M. amblycephala.

CXC chemokine ligand 12 (CXCL12) and its receptor CXCR4

Chemokines were recognized originally for their ability to dictate the migration and activation of leukocytes. However, CXC chemokine ligand 12 (CXCL12, also known as stromal cell-derived factor-1) and its receptor CXCR4 are the first chemokine and receptor that have been shown to be critical for developmental processes, including homing and maintenance of hematopoietic stem cells (HSCs), production of immune cells, homing of primordial germ cells (PGCs), cardiogenesis, arterial vessel branching in some organs, and appropriate assemblies of particular types of neurons. This review focuses on the pathophysiological relevance of CXCL12-CXCR4 signaling in mammals.

Immunological role of C4 CC chemokine-1 from snakehead murrel Channa striatus

In this study, we have reported a cDNA sequence of C4 CC chemokine identified from snakehead murrel (also known as striped murrel) Channa striatus (named as CsCC-Chem-1) normalized cDNA library constructed by Genome Sequencing FLX™ Technology (GS-FLX™). CsCC-Chem-1 is 641 base pairs (bp) long that contain 438 bp open reading frame (ORF). The ORF encodes a polypeptide of 146 amino acids with a molecular mass of 15 kDa. The polypeptide contains a small cytokine domain at 30-88. The domain carries the CC motif at Cys(33)-Cys(34). In addition, CsCC-Chem-1 consists of another two cysteine residues at C(59) and C(73), which, together with C(33) and C(34), make CsCC-Chem-1 as a C4-CC chemokine. CsCC-Chem-1 also contains a 'TCCT' motif at 32-35 as CC signature motif; this new motif may represent new characteristic features, which may lead to some unknown function that needs to be further focused on. Phylogenitically, CsCC-Chem-1 clustered together with CC-Chem-1 from rock bream Oplegnathus fasciatus and European sea bass Dicentrarchus labrax. Significantly (P<0.05) highest gene expression was noticed in spleen and is up-regulated upon fungus (Aphanomyces invadans), bacteria (Aeromonas hydrophila) and virus (poly I:C) infection at various time points. The gene expression results indicate the influence of CsCC-Chem-1 in the immune system of murrel. Overall, the gene expression study showed that the CsCC-Chem-1 is a capable gene to increase the cellular response against various microbial infections. Further, we cloned the coding sequence of CsCC-Chem-1 in pMAL vector and purified the recombinant protein to study the functional properties. The cell proliferation activity of recombinant CsCC-Chem-1 protein showed a significant metabolic activity in a concentration dependent manner. Moreover, the chemotaxis assay showed the capability of recombinant CsCC-Chem-1 protein which can induce the migration of spleen leukocytes in C. striatus. However, this remains to be verified further at molecular and proteomic level.

Phylogenetic analysis of vertebrate CXC chemokines reveals novel lineage specific groups in teleost fish

In this study, we have identified 421 molecules across the vertebrate spectrum and propose a unified nomenclature for CXC chemokines in fish, amphibians and reptiles based on phylogenetic analysis. Expanding on earlier studies in teleost fish, lineage specific CXC chemokines that have no apparent homologues in mammals were confirmed. Furthermore, in addition to the two subgroups of the CXCL8 homologues known in teleost fish, a third group was identified (termed CXCL8_L3), as was a further subgroup of the fish CXC genes related to CXCL11. Expression of the CXC chemokines found in rainbow trout, Oncorhynchus mykiss, was studied in response to stimulation with inflammatory and antiviral cytokines, and bacterial. Tissue distribution analysis revealed distinct expression profiles for these trout CXC chemokines. Lastly three of the trout chemokines, including two novel fish specific CXC chemokines containing three pairs of cysteines, were produced as recombinant proteins and their effect on trout leucocyte migration studied. These molecules increased the relative expression of CD4 and MCSFR in migrated cells in an in vitro chemotaxis assay.

Molecular identification and expression analysis of the CC chemokine gene in rock bream (Oplegnathus fasciatus) and the biological activity of the recombinant protein

We identified the CC chemokine cDNA designated as RbCC1 (CC chemokine 1 in rock bream, Oplegnathus fasciatus), which was isolated using expressed sequence tag (EST) analysis of a lipopolysaccharide (LPS)-stimulated rock bream liver cDNA library. The full-length RbCC1 cDNA (850 bp) contained an open reading frame (ORF) of 366 bp encoding 122 amino acids. Results from our phylogenetic analysis demonstrated that the RbCC1 was closest relationship to the orange-spotted grouper and Mi-iyu croaker CC chemokines located within the fish CC chemokine group. RbCC1 was significantly expressed in the intestine, spleen, liver, and PBLs (peripheral blood leukocytes). Rock bream PBLs were stimulated with several mitogens, LPS and Con A/PMA which significantly induced the expression of RbCC1 mRNA in the PBLs. The RbCC1 mRNA expression in several tissues under conditions of bacterial and viral challenge was examined. The experimental challenge revealed that the kidney and spleen of fish infected with Streptococcus iniae showed the most significant increases in RbCC1 expression compared to the control. In the case of RSIV infection, the RbCC1 mRNA expression was markedly up-regulated in the liver. In this study, recombinant RbCC1 (approximately 53 kDa) was produced using an Escherichia coli expression system followed by purification. Subsequently, the addition of purified rRbCC1 was examined to investigate the impact on the proliferative and chemotactic activity on kidney leukocytes from rock bream. The results demonstrated that the rRbCC1 induces significant biological activity on kidney leukocyte proliferation and attraction at concentrations in the range of 10-300 μg/mL and suggests that rRbCC1 could be utilized as an immune-stimulant and/or molecular adjuvant to enhance the immune effects of vaccines.

Molecular characterization, phylogenetic analysis and expression patterns of five protein arginine methyltransferase genes of channel catfish, Ictalurus punctatus (Rafinesque)

Protein arginine methylation, catalyzed by protein arginine methyltransferases (PRMT), has recently emerged as an important modification in the regulation of gene expression. In this communication, we identified and characterized the channel catfish orthologs to human PRMT 1, 3, 4 and 5, and PRMT4 like. Each PRMT nucleic acid sequence has an open reading frame (ORF) and 3'-untranslated regions. Each ORF appears to encode 361, 587 and 458 amino acid residues for PRMT1, PRMT4 and variant, respectively. The partial ORF of PRMT3 and PRMT5 encode 292 and 563 amino acids, respectively. By comparison with the human counterparts, each channel catfish PRMT also has conserved domains. For expression profile, the channel catfish PRMT1 transcript was detected by RT-PCR in spleens, anterior kidneys, livers, intestines, skin and gills of fish examined. Except in liver, the PRMT3 transcript was detected in all catfish tissues examined. However, the PRMT4 cDNA was detected in livers from all three catfish and gills from two fish, but not other tissues. This information will enable us to further elucidate PRMT functions in channel catfish.

The chemokine CXCL12 is essential for the clearance of the filaria Litomosoides sigmodontis in resistant mice

Litomosoides sigmodontis is a cause of filarial infection in rodents. Once infective larvae overcome the skin barrier, they enter the lymphatic system and then settle in the pleural cavity, causing soft tissue infection. The outcome of infection depends on the parasite's modulatory ability and also on the immune response of the infected host, which is influenced by its genetic background. The goal of this study was to determine whether host factors such as the chemokine axis CXCL12/CXCR4, which notably participates in the control of immune surveillance, can influence the outcome of the infection. We therefore set up comparative analyses of subcutaneous infection by L. sigmodontis in two inbred mouse strains with different outcomes: one susceptible strain (BALB/c) and one resistant strain (C57BL/6). We showed that rapid parasite clearance was associated with a L. sigmodontis-specific CXCL12-dependent cell response in C57BL/6 mice. CXCL12 was produced mainly by pleural mesothelial cells during infection. Conversely, the delayed parasite clearance in BALB/c mice was neither associated with an increase in CXCL12 levels nor with cell influx into the pleural cavity. Remarkably, interfering with the CXCL12/CXCR4 axis in both strains of mice delayed filarial development, as evidenced by the postponement of the fourth molting process. Furthermore, the in vitro growth of stage 4 filariae was favored by the addition of low amounts of CXCL12. The CXCL12/CXCR4 axis thus appears to have a dual effect on the L. sigmodontis life cycle: by acting as a host-cell restriction factor for infection, and as a growth factor for worms.

VLR-based adaptive immunity

Lampreys and hagfish are primitive jawless vertebrates capable of mounting specific immune responses. Lampreys possess different types of lymphocytes, akin to T and B cells of jawed vertebrates, that clonally express somatically diversified antigen receptors termed variable lymphocyte receptors (VLRs), which are composed of tandem arrays of leucine-rich repeats. The VLRs appear to be diversified by a gene conversion mechanism involving lineage-specific cytosine deaminases. VLRA is expressed on the surface of T-like lymphocytes; B-like lymphocytes express and secrete VLRB as a multivalent protein. VLRC is expressed by a distinct lymphocyte lineage. VLRA-expressing cells appear to develop in a thymus-like tissue at the tip of gill filaments, and VLRB-expressing cells develop in hematopoietic tissues. Reciprocal expression patterns of evolutionarily conserved interleukins and chemokines possibly underlie cell-cell interactions during an immune response. The discovery of VLRs in agnathans illuminates the origins of adaptive immunity in early vertebrates.

Chemokines in teleost fish species

Chemokines are chemoattractant cytokines defined by the presence of four conserved cysteine residues which in mammals can be divided into four subfamilies depending on the arrangement of the first two conserved cysteines in their sequence: CXC (α), CC (β), C and CX(3)C classes. Evolutionarily, fish can be considered as an intermediate step between species which possess only innate immunity (invertebrates) and species with a fully developed acquired immune network such as mammals. Therefore, the functionality of their different immune cell types and molecules is sometimes also intermediate between innate and acquired responses. The first chemokine gene identified in a teleost was a rainbow trout (Oncorhynchus mykiss) chemokine designated as CK1 in 1998. Since then, many different chemokine genes have been identified in several fish species, but their role in homeostasis and immune response remains largely unknown. Extensive genomic duplication events and the fact that chemokines evolve more quickly than other immune genes, make it very difficult to establish true orthologues between fish and mammalian chemokines that would help us with the ascription of immune roles. In this review, we describe the current state of knowledge of chemokine biology in teleost fish, focusing mainly on which genes have been identified so far and highlighting the most important aspects of their expression regulation, due to the great lack of functional information available for them. As the number of chemokine genes begins to close down for some teleost species, there is an important need for functional assays that may elucidate the role of each of these molecules within the fish immune response.

A family tree of vertebrate chemokine receptors for a unified nomenclature

Chemokines receptors are involved in the recruitment of various cell types in inflammatory and physiological conditions. There are 23 known chemokine receptor genes in the human genome. However, it is still unclear how many chemokine receptors exist in the genomes of various vertebrate species other than human and mouse. Moreover, the orthologous relationships are often obscure between the genes of higher and lower vertebrates. In order to provide a basis for a unified nomenclature system of the vertebrate chemokine receptor gene family, we have analysed the chemokine receptor genes from the genomes of 16 vertebrate species, and classify them into 29 orthologous groups using phylogenetic and comparative genomic analyses. The results reveal a continuous gene birth and death process during the vertebrate evolution and an interesting evolutionary history of the chemokine receptor genes after the emergence in agnathans.

Cloning, characterization, and expression analysis of a CC chemokine gene from turbot (Scophthalmus maximus)

The chemokines are a superfamily of chemotactic cytokines playing an important role in leukocyte chemotaxis. Here, a turbot head kidney cDNA library was constructed in which KC70 was identified as a CC chemokine. Unknown 5' and 3' parts of the cDNA were amplified by 5' and 3' rapid amplification of cDNA ends (RACE). The complete cDNA of KC70 contains a 59-bp 5' UTR, a 336-bp ORF, and a 152-bp 3' UTR. Four exons and three introns were identified in KC70. Phylogenetic analysis showed that KC70 was similar to CCL19. In normal turbot KC70 was expressed in all tissues except brain and skin. Infection of turbot with pathogenic bacteria significantly increased expression of KC70 in the liver. Expression of KC70 in head kidney first increased and then decreased after bacterial challenge. No significant change was observed in the spleen after bacterial challenge. During embryonic development, KC70 was highly expressed after the gastrula stage. These results indicated KC70 plays important and multiple roles in turbot immune response.

The first non-mammalian CXCR5 in a teleost fish: molecular cloning and expression analysis in grass carp (Ctenopharyngodon idella)

Background

Chemokines, a group of small and structurally related proteins, mediate chemotaxis of various cell types via chemokine receptors. In mammals, seven different CXC chemokine receptors denoted as CXCR1 to CXCR7 have been reported. However, the chemokine receptor CXCR5 has not been reported in other vertebrates.

Results

In the present study, the genomic sequence of CXCR5 was isolated from the grass carp Ctenopharyngodon idella. The cDNA sequence of grass carp CXCR5 (gcCXCR5) consists of 1518 bp with a 43 bp 5' untranslated region (UTR) and a 332 bp 3' UTR, with an open reading frame of 1143 bp encoding 381 amino acids which are predicted to have seven transmembrane helices. The characteristic residues (DRYLAIVHA) and conserved cysteine residues are located in the extracellular regions and in the third to seventh transmembrane domains. The deduced amino acid sequence shows 37.6-66.6% identities with CXCR5 of mammals, avian and other fish species. The grass carp gene consists of two exons, with one intervening intron, spaced over 2081 bp of genomic sequence. Phylogenetic analysis clearly demonstrated that the gcCXCR5 is clustered with those in other teleost fish and then in chicken and mammals. Real-time PCR analysis showed that gcCXCR5 was expressed in all tested organs/tissues and its expression level was the highest in trunk kidney, followed by in the spleen. The expression of gcCXCR5 was significantly modulated by immunostimulants such as peptidoglycan (PGN), lipopolysaccharide (LPS), polyinosinic-polycytidylic acid sodium salt (Poly I:C) and phytohaemagglutinin (PHA).

Conclusion

The cDNA and genomic sequences of CXCR5 have been successfully characterized in a teleost fish, the grass carp. The CXCR5 has in general a constitutive expression in organs/tissues examined, whereas its expression was significantly up-regulated in immune organs and down-regulated in brain, indicating its potential role in immune response and central nervous system.

Sequence analysis, characterization and mRNA distribution of channel catfish (Ictalurus punctatus Rafinesque, 1818) chemokine (C-X-C motif) receptor 4 (CXCR4) cDNA

Chemokine receptor CXCR4, a member of the G protein-coupled receptor superfamily, binds selectively CXCL12. This protein plays many important roles in immunological as well as pathophysiological functions. In this study, we identified and characterized the channel catfish CXCR4 transcript. The full-length nucleic acid sequence of channel catfish CXCR4 cDNA comprised of 1994 nucleotides, including an open reading frame, which appears to encode a putative peptide of 357 amino acid residues with a calculated molecular mass of 40.1kDa. By comparison with the human counterpart, the channel catfish CXCR4 peptide can be divided into domains, including seven transmembrane domains, four cytoplasmic domains, and four extracellular domains. The CXCR4 transcript was detected in spleen, anterior kidney, liver, intestine, skin and gill of all catfish examined in this study. Because four CXCL of channel catfish have been identified, the result provides valuable information for further exploring the channel catfish chemokine signalling pathways and their roles in immune responses to infection.

Evolution of genetic networks underlying the emergence of thymopoiesis in vertebrates

About 500 million years ago, a new type of adaptive immune defense emerged in basal jawed vertebrates, accompanied by morphological innovations, including the thymus. Did these evolutionary novelties arise de novo or from elaboration of ancient genetic networks? We reconstructed the genetic changes underlying thymopoiesis by comparative genome and expression analyses in chordates and basal vertebrates. The derived models of genetic networks were experimentally verified in bony fishes. Ancestral networks defining circumscribed regions of the pharyngeal epithelium of jawless vertebrates expanded in cartilaginous fishes to incorporate novel genes, notably those encoding chemokines. Correspondingly, novel networks evolved in lymphocytes of jawed vertebrates to control the expression of additional chemokine receptors. These complementary changes enabled unprecedented Delta/Notch signaling between pharyngeal epithelium and lymphoid cells that was exploited for specification to the T cell lineage. Our results provide a framework elucidating the evolution of key features of the adaptive immune system in jawed vertebrates.

Extensive expansion and diversification of the chemokine gene family in zebrafish: identification of a novel chemokine subfamily CX

Background

The chemokine family plays important roles in cell migration and activation. In humans, at least 44 members are known. Based on the arrangement of the four conserved cysteine residues, chemokines are now classified into four subfamilies, CXC, CC, XC and CX3C. Given that zebrafish is an important experimental model and teleost fishes constitute an evolutionarily diverse group that forms half the vertebrate species, it would be useful to compare the zebrafish chemokine system with those of mammals. Prior to this study, however, only incomplete lists of the zebrafish chemokine genes were reported.

Results

We systematically searched chemokine genes in the zebrafish genome and EST databases, and identified more than 100 chemokine genes. These genes were CXC, CC and XC subfamily members, while no CX3C gene was identified. We also searched chemokine genes in pufferfish fugu and Tetraodon, and found only 18 chemokine genes in each species. The majority of the identified chemokine genes are unique to zebrafish or teleost fishes. However, several groups of chemokines are moderately similar to human chemokines, and some chemokines are orthologous to human homeostatic chemokines CXCL12 and CXCL14. Zebrafish also possesses a novel species-specific subfamily consisting of five members, which we term the CX subfamily. The CX chemokines lack one of the two N-terminus conserved cysteine residues but retain the third and the fourth ones. (Note that the XC subfamily only retains the second and fourth of the signature cysteines residues.) Phylogenetic analysis and genome organization of the chemokine genes showed that successive tandem duplication events generated the CX genes from the CC subfamily. Recombinant CXL-chr24a, one of the CX subfamily members on chromosome 24, showed marked chemotactic activity for carp leukocytes. The mRNA was expressed mainly during a certain period of the embryogenesis, suggesting its role in the zebrafish development.

Conclusion

The phylogenic and genomic organization analyses suggest that a substantial number of chemokine genes in zebrafish were generated by zebrafish-specific tandem duplication events. During such duplications, a novel chemokine subfamily termed CX was generated in zebrafish. Only two human chemokines CXCL12 and CXCL14 have the orthologous chemokines in zebrafish. The diversification observed in the numbers and sequences of chemokines in the fish may reflect the adaptation of the individual species to their respective biological environment.

Description of a fugu CXC chemokine and two CXC receptor genes, and characterization of the effects of different stimulators on their expression

The primary structures of a CXC chemokine (CXCL8) and two CXC receptors (CXCR) have been characterized in fugu, Takifugu rubripes. Unlike mammalian and avian species, CXCL8 of teleosts including fugu lacks the ELR motif that appears to be important in ligand/receptor interactions on neutrophils. Genomic organization shows that fugu CXCL8 gene consists of four exons and three introns. As in other vertebrates, two CXCR genes isolated from fugu encode proteins CXCR1 and CXCR2 that possess characteristic seven transmembrane domains. Each receptor consists of two exons separated by an intron. Synteny analysis indicates that these two CXCRs were derived from whole genome duplication in teleosts, differing from mammalian CXCR1 and CXCR2. All of these genes are primarily expressed in the lymphoid tissues. Immune stimulation with PHA showed that the expression of both CXCL8 and CXCRs in PBL are upregulated even after only a short time period, but downregulated by LPS stimulation, implying that these genes are involved in the regulation of the immune response in fugu.

Cloning, expression and functional analysis of a novel-chemokine gene of Japanese flounder, Paralichthys olivaceus, containing two additional cysteines and an extra fourth exon

A CC chemokine gene (JFCCL3) was cloned and sequenced from Japanese flounder, Paralichthys olivaceus. The JFCCL3 cDNA contains an open reading frame of 288 nucleotides encoding 95 amino acid residues. The predicted amino acid sequence of JFCCL3 showed the conserved cysteine of the beta chemokine plus two additional cysteines. The genomic sequence consists of two isoforms: JFCCL3.1 and JFCCL3.2 with sizes of 1.8 and 1.2kb, respectively. Both isoforms contain three introns and four exons. RT-PCR showed that JFCCL3 is constitutively expressed in most tissues including lymphoid organs. Using quantitative real-time RT-PCR, the highest expression of JFCCL3 transcripts was observed in PBLs at 3h post-stimulation with Con A/PMA and at 1h post-stimulation with LPS. A phylogenetic analysis showed that JFCCL3 is more closely related to fractalkines than to other mammalian beta chemokines. A chemotaxis assay showed that recombinant JFCCL3 protein has bioactivity for Japanese flounder leukocyte attraction at concentrations from 0.01 to 10 microg/ml.

Evolution of CC chemokines in teleost fish: a case study in gene duplication and implications for immune diversity

Chemokines are a superfamily of cytokines responsible for regulating cell migration under both inflammatory and physiological conditions. CC chemokines are the largest subfamily of chemokines, with 28 members in humans. A subject of intense study in mammalian species, the known functional roles of CC chemokines ligands in both developmental and disease conditions continue to expand. They are also an important family for the study of gene copy number variation and tandem duplication in mammalian species. However, little is known regarding the evolutionary origin and status of these ligands in primitive vertebrates such as teleost fish. In this paper, we review the evolution of the teleost fish CC chemokine gene family, noting evidence of widespread tandem gene duplications and examining the implications of this phenomenon on immune diversity. Through extensive phylogenetic analysis of the CC chemokine sets of four teleost species, zebrafish, catfish, rainbow trout, and Atlantic salmon, we identified seven large groups of CC chemokines. It appeared that several major groups of CC chemokines are highly related including the CCL19/21/25 group, the CCL20 group, CCL27/28 group, and the fish-specific group. In the three remaining groups that contained the largest number of members, the CCL17/22 group, the MIP group, and the MCP group, similarities among species members were obscured by rapid, tandem duplications that may contribute to immune diversity.

The first non-mammalian CXCR3 in a teleost fish: Gene and expression in blood cells and central nervous system in the grass carp (Ctenopharyngodon idella)

A novel fish chemokine receptor gene, chemokine (C-X-C motif) receptor 3 (CXCR3)-like was isolated from the grass carp Ctenopharyngodon idella, with its full-length genomic sequence. The cDNA of grass carp CXCR3-like (gcCXCR3-like) consists of 1261 bp with a 49 bp 5'-UTR and a 189bp 3'-UTR. An open reading frame of 1023 bp encodes a 341-amino acid peptide, with seven transmembrane helices. The deduced amino acid sequence showed the same sequence identities (37.8%) with its counterparts in goat and human. The gcCXCR3-like gene consists of two exons, with one intervening intron, spaced over approximately 2 kb of genomic sequence. Phylogenetic analyses clearly demonstrated that the gcCXCR3-like resembles the CXCR3s of other vertebrates. Real-time PCR analysis showed that gcCXCR3-like was expressed in all tested organs except heart and the expression level of gcCXCR3-like was highest in brain. Flow cytometric analyses showed the positive rate of labelled leukocytes from the healthy grass carp was 17.3%, and the labelled leukocytes were divided into three types by cell sorting. Immunohistochemical localization revealed that gcCXCR3-like expressed in whole brain regions including cerebel, diencephalon, medulla oblongata, optic lobe, and rhinencephalon, and that the labelled leukocytes are actually populations of monocyte and/or phagocyte, lymphocyte and the granulocyte. It is considered that fish CXCR expression and their function may need to be investigated in both nervous and immune systems.

The G protein-coupled receptor subset of the chicken genome

G protein–coupled receptors (GPCRs) are one of the largest families of proteins, and here we scan the recently sequenced chicken genome for GPCRs. We use a homology-based approach, utilizing comparisons with all human GPCRs, to detect and verify chicken GPCRs from translated genomic alignments and Genscan predictions. We present 557 manually curated sequences for GPCRs from the chicken genome, of which 455 were previously not annotated. More than 60% of the chicken Genscan gene predictions with a human ortholog needed curation, which drastically changed the average percentage identity between the human–chicken orthologous pairs (from 56.3% to 72.9%). Of the non-olfactory chicken GPCRs, 79% had a one-to-one orthologous relationship to a human GPCR. The Frizzled, Secretin, and subgroups of the Rhodopsin families have high proportions of orthologous pairs, although the percentage of amino acid identity varies. Other groups show large differences, such as the Adhesion family and GPCRs that bind exogenous ligands. The chicken has only three bitter Taste 2 receptors, and it also lacks an ortholog to human TAS1R2 (one of three GPCRs in the human genome in the Taste 1 receptor family [TAS1R]), implying that the chicken's ability and mode of detecting both bitter and sweet taste may differ from the human's. The chicken genome contains at least 229 olfactory receptors, and the majority of these (218) originate from a chicken-specific expansion. To our knowledge, this dataset of chicken GPCRs is the largest curated dataset from a single gene family from a non-mammalian vertebrate. Both the updated human GPCR dataset, as well the chicken GPCR dataset, are available for download.

Man and chicken are very different, but how is that difference related to our respective gene repertoire? The authors studied the family of G protein–coupled receptors (GPCRs), which in man contains about 791 proteins. These are found in the cell membrane, where they recognize substances, thereby functioning as mediators of signals across the cellular membrane. GPCRs respond to physiologically important substances such as hormones and neurotransmitters. In this paper, the publicly available genomic sequence from the domestic chicken is used to identify the entire repertoire of GPCRs in this species. The authors found 557 GPCRs and compared the chicken and human receptors; they concluded that out of the 328 chicken receptors that are not involved in olfaction, more than 250 have a corresponding human receptor. The majority of the differences between the chicken and man are within three groups of GPCRs—the receptors for olfaction, bitter taste, and the receptors involved in the immune system. The chicken GPCR sequences obtained here will be useful for identification of GPCRs in other species that are more distantly related to man, such as fish or insects. The domestic chicken represents the leading experimental model among the avian species and also serves as an important source of food worldwide.

Molecular Networks Orchestrating GALT Development

During evolution, the development of secondary lymphoid organs has evolved as a strategy to promote adaptive immune responses at sites of antigen sequestration. Mesenteric lymph nodes (LNs) and Peyer's patches (PPs) are localized in proximity to mucosal surfaces, and their development is coordinated by a series of temporally and spatially regulated molecular events involving the collaboration between hematopoietic, mesenchymal, and, for PPs, epithelial cells. Transcriptional control of cellular differentiation, production of cytokines as well as adhesion molecules are mandatory for organogenesis, recruitment of mature leukocytes, and lymphoid tissue organization. Similar to fetal and neonatal organogenesis, lymphoid tissue neoformation can occur in adult individuals at sites of chronic stimulation via cytokines and TNF-family member molecules. These molecules represent new therapeutic targets to manipulate the microenvironment during autoimmune diseases.

Defining the origins and evolution of the chemokine/chemokine receptor system

The chemokine system has a critical role in mammalian immunity, but the evolutionary history of chemokines and chemokine receptors are ill-defined. We used comparative whole genome analysis of fruit fly, sea urchin, sea squirt, pufferfish, zebrafish, frog, and chicken to identify chemokines and chemokine receptors in each species. We report 127 chemokine and 70 chemokine receptor genes in the 7 species, with zebrafish having the most chemokines, 63, and chemokine receptors, 24. Fruit fly, sea urchin, and sea squirt have no identifiable chemokines or chemokine receptors. This study represents the most comprehensive analysis of the chemokine system to date and the only complete characterization of chemokine systems outside of mouse and human. We establish a clear evolutionary model of the chemokine system and trace the origin of the chemokine system to approximately 650 million years ago, identifying critical steps in their evolution and demonstrating a more extensive chemokine system in fish than previously thought.

Cloning of iNOS in the small spotted catshark (Scyliorhinus canicula)

The first cartilaginous fish iNOS gene has been cloned in the small spotted catshark, Scyliorhinus canicula. The cDNA was 4568 bp long, with a 3375 bp open reading frame encoding a protein of 1125 amino acids and a predicted molecular mass of 127.8 kDa. The catshark translation had 77% amino acid similarity with chicken iNOS and 70-73% similarity with known teleost i NOS molecules. The various co-factor binding sites were well conserved, with the calmodulin site hydrophobicity profile noticeable more similar to tetrapod molecules than teleost molecules. The catshark iNOS transcript was not typically expressed constitutively, with the exception of the gills. Clear induction of the gene was seen in splenocytes after exposure to Vibrio anguillarum in vivo, and after stimulation with LPS in vitro. iNOS message was first seen 2 h after stimulation, and was still apparent 24 h post-stimulation, the last timing studies. Poly I:C was also able to induce iNOS transcript expression in splenocytes, albeit at a later timing (i.e.24 h). Such findings suggest a role for this molecule in the non-specific defences of cartilaginous fish as seen in other vertebrate groups.

Organization, alternative splicing, polymorphism, and phylogenetic position of lamprey CD45 gene

CD45 of jawed vertebrates is a receptor-type protein tyrosine phosphatase regulating lymphocyte development and activation. To shed light on the evolution of the CD45 gene, the organization of its orthologue in the lamprey, a jawless vertebrate, was determined. Compared to its mammalian and fugu counterparts, the lamprey gene was found to be lacking several exons in the segment encoding the extracellular part of the protein. In consequence, this part contains only one instead of the two or three fibronectin type III domains typical of the mammalian molecules. The lamprey transcripts of the CD45 gene occur in several variants originating by alternative splicing, including some not observed previously in other vertebrates. Most remarkable of these are splice variants generated by the use of intra-exonic splicing signals and thus lacking one half, one third, or two thirds of an exon and yet apparently translated in the correct reading frame. The lamprey gene contains polymorphic sites not only in the segment encoding the extracellular portion but also in the segment specifying the cytoplasmic part of the molecule. Polymorphism is generated by both mutations and recombination. Some of the alleles may have persisted long enough to represent transspecies polymorphism presumably maintained by positive selection. Phylogenetic analysis suggests that ancestors of the CD45 gene may have existed before the divergence of coelomate from pseudocoelomate metazoans.

In silico identification and expression analysis of 12 novel CC chemokines in catfish

Chemokines, a superfamily of chemotactic cytokines involved in recruitment, activation, and adhesion of a variety of leukocyte types to inflammatory foci, are a crucial component of the immune system of Sarcopterygiian vertebrates. Although all mammalian chemokines are believed to have been found, the status of these molecules in Actinopterygii was unknown until recently. The identification of chemokines in fish species has been complicated by low sequence conservation and confusion over expected numbers. Earlier discoveries of single fish chemokines coupled with rapidly expanding genetic resources in these species have recently provided a foundation for large-scale in silico discoveries of these important immune regulators. We report here the identification and expression analysis of 12 new CC chemokine sequences from catfish. When added to our previous report of 14 catfish CC chemokines, the number of CC chemokines in catfish now stands at 26, two more than known from humans. Establishing orthologous relationships among the majority of catfish CC chemokines, a newly available set of chicken CC chemokines, and their mammalian counterparts remain difficult, suggesting high levels of duplication and divergence within individual species.

Comparison of select innate immune mechanisms of fish and mammals

The study of innate immunity has become increasingly popular since the discovery of homologs of many of the innate immune system components and pathways in lower organisms including invertebrates. As fish occupy a key position in the evolution of the innate and adaptive immune responses, there has been a great deal of interest regarding similarities and differences between their defense mechanisms and those of higher vertebrates. This review focuses on describing select mechanisms of the innate immune responses of fish and the implications for evolution of immunity in higher vertebrates.

Isolation and characterization of CXC receptor genes in a range of elasmobranchs

The CXC group of chemokines exert their cellular effects via the CXCR group of G-protein coupled receptors. Six CXCR genes have been identified in humans (CXCR1-6), and homologues to some of these have been isolated from a range of vertebrate species. Here we isolate and characterize CXCR genes from a range of elasmobranch species. One CXCR1/2 gene fragment isolated from Scyliorhinus caniculus (lesser spotted catshark), and two CXCR1/2 copies from each of the elasmobranchs, Cetorhinus maximus (basking shark), Carcharodon carcharias (great white shark), and Raja naevus (cuckoo ray), exhibit high similarity to both CXCR1 and CXCR2. The two copies evident in the cuckoo ray and lamniform sharks provide strong evidence of CXCR1/2 lineage specific duplication in rays and sharks. A CXCR fragment isolated from Lamna ditropis (salmon shark) shows high similarity to a range of CXCR4 genes and strong clustering with CXCR4 gene homologues was apparent during phylogenetic reconstruction.

The descent of the antibody-based immune system by gradual evolution

The antibody-based immune system (AIS) is one of many means by which organisms protect themselves against pathogens and parasites. The AIS is present in jawed vertebrates (gnathostomes) but absent in all other taxa, including jawless vertebrates (agnathans). We argue that the AIS has been assembled from elements that have primarily evolved to serve other functions and incorporated existing molecular cascades, resulting in the appearance of new organs and new types of cells. Some molecules serving other functions have been appropriated by the AIS, whereas others have been modified to serve new functions, either after the duplication of their encoding genes or through the acquisition of an additional function without gene duplication. A few molecules may have been created de novo. The deployment and integration of the ready-made elements gives the impression of a sudden origin of the AIS. In reality, however, the AIS is an example of an organ system that has evolved gradually through a series of small steps over an extended period.

Molecular cloning and preliminary expression analysis of banded dogfish (Triakis scyllia) CC chemokine cDNAs by use of suppression subtractive hybridization

Suppression subtractive hybridization was carried out by using cDNAs of peripheral white blood cells (PWBCs) of banded dogfish (Triakis scyllia) after phorbol 12-myristate 13-acetate (PMA) stimulation. The Trsc-SCYA107, MIP3alpha1 and MIP3alpha2 clones contained an open reading frame encoding 97, 99 and 97 amino acids, respectively. Comparison of the deduced amino acids showed that the banded dogfish MIP3alpha1 and MIP3alpha2 sequences shared 42.3% and 40.0% identity with human SCYA20, respectively, while the Trsc-SCYA107 sequence shared 50.6, 44.2 and 42.0% identity with the catshark (Scyliorhinus canicula) Scca-SCYA107, rainbow trout (Oncorhynchus mykiss) CK4A and CK4B, respectively. The genomic sequences of banded dogfish Trsc-SCYA107, MIP3alpha1 and MIP3alpha2 contain four exons and three introns, and MIP3alpha1 and MIP3alpha2 shared the same intron/exon organization with that of human. The MIP3alpha1 and MIP3alpha2 genes of lipopolysaccharide (LPS)-unstimulated banded dogfish were expressed in gill, kidney and liver, while Trsc-SCYA107 mRNA was detected in various tissues except for brain. However, the constitutive expression of MIP3alpha2 gene was much lower than the Trsc-SCYA107 and MIP3alpha1 genes. RT-PCR analysis of the Trsc-SCYA107 expression in tissues of LPS-stimulated fish showed enhanced expression at 24 h poststimulation in the gill, heart, leydig, spleen and testes, while the expression of MIP3alpha1 and MIP3alpha2 was not influenced by LPS-stimulation in vivo. Furthermore, a relative increase in the expression of the Trsc-SCYA107 and MIP3alpha2 genes in PWBCs was observed at 1-12 h poststimulation with PMA and LPS, with maximal expression observed at 3 h, while MIP3alpha1 expression was observed at 3-12 h poststimulation only with PMA.

Prototypic T cell receptor and CD4-like coreceptor are expressed by lymphocytes in the agnathan sea lamprey

All jawed vertebrates have highly diverse lymphocyte receptors, which allow discrimination between self and nonself antigens as well as the recognition of potential pathogens. Key elements of the anticipatory recombinatorial immune system in jawed vertebrates are the TCR, Ig, and MHC genes, but their ancestral genes have not been found in more basal vertebrates. In this study, we extended our analysis of the transcriptome of lymphocyte-like cells in the lamprey to identify the TCR-like and CD4-like genes. The structural features of these genes and their preferential expression in lymphocytes make them attractive candidates for ancestral TCR and CD4 genes. The TCR-like gene contains both V (variable) and J (joining) sequences in its first exon and exists as a single-copy gene that is invariant. Thus, the TCR-like gene cannot account for the receptor diversity that is required for the immune responses reported for lamprey, but it could have been easily modified to serve as an evolutionary precursor of modern TCR and Ig genes.

Transcriptome analysis of hagfish leukocytes: a framework for understanding the immune system of jawless fishes

Jawless fishes occupy a critical phylogenetic position in understanding the origin of the adaptive immune system. Here, we performed large-scale expressed sequence tag analysis of leukocytes isolated from the inshore hagfish Eptatretus burgeri. Although we found many immunity-related genes such as those involved in lymphocyte or hematopoietic cell signaling and development as well as cytokine and cytokine receptor genes, MHC molecules or antigen receptors were not identified. We characterized two hagfish cDNAs that closely resembled mammalian proteins with essential roles in adaptive immunity, one encoding a GATA3-like molecule and another encoding a Bruton's tyrosine kinase (Btk)-like molecule. The GATA3-like gene of hagfish was equidistant from GATA3 and GATA2 in jawed vertebrates. Similarly, the hagfish Btk-like molecule was not Btk itself, but qualified as a pre-duplicated form of Btk and Bmx in jawed vertebrates. In total, our work provides circumstantial evidence that adaptive immunity is unique to jawed vertebrates.

Identification of a novel Japanese flounder (Paralichthys olivaceus) CC chemokine gene and an analysis of its function

A cDNA of Japanese flounder (Paralichthys olivaceus) CC chemokine designated as Paol-SCYA104 was cloned and sequenced. The cDNA contains an opening reading frame of 315 nucleotides encoding 104 amino acid residues. The full gene was cloned and sequenced from a BAC library. It has a length of approximately 750 bp from the start codon to the stop codon and is composed of four exons and three introns. Four cysteine residues are conserved in the same positions as those of mammalian and fish CC chemokines. Paol-SCYA104 gene was expressed in several organs, including peripheral blood leukocytes (PBLs), head kidney, trunk kidney, and spleen. The recombinant Paol-SCYA104 was expressed in Escherichia coli and the expressed protein was partially purified. The recombinant Paol-SCYA104 was able to attract Japanese flounder PBLs in a microchemotaxis chamber. On the other hand, a negative control, the fraction of the control cells carrying an expression vector lacking the Paol-SCYA104 cDNA, did not show chemotactic activity. These results indicate that Paol-SCYA104 probably acts as a CC chemokine.

Molecular evolution of CXC chemokines: extant CXC chemokines originate from the CNS

The mammalian CXC chemokine system comprises 16 ligands and six receptors, and its actions stretch well beyond the immune system. Recent elucidation of the pufferfish genome, a representative of an evolutionary ancient vertebrate class, has enabled analysis of the mammalian CXC chemokine system in a phylogenetic context. Comparison of the phylogenies of vertebrate CXC chemokines revealed that fish and mammals have found different solutions to similar problems, grafted on the same basic structural motif. Phylogenetic analyses showed that the large, highly redundant CXC chemokine family is a very recent phenomenon that is exclusive to higher vertebrates. Moreover, its ancestral role is found within the central nervous system and not within the immune system.