Characterisation of a fourth immunoglobulin light chain isotype in the common carp

Characterization of immunoglobulin light chain utilization and variable family diversity in rainbow trout

This study characterizes immunoglobulin light chain (IgL) expression and variable family usage in rainbow trout. IgL transcripts were generated by 5' RACE from both immune and TNP-KLH immunized fish. Phylogenetic analysis revealed that the IgL variable regions clustered into seven different families: three kappa families (two newly described in this study), three sigma families, and a single lambda family. IgL1 and IgL3 transcripts expressing identical variable regions were identified and genomic analysis revealed that the two isotypes are co-localized on chromosomes 7, 15, 18, and 21 allowing for potential rearrangement between clusters. Fish were immunized with TNP-KLH (n = 5) and percent expression of IgL1, IgL2, IgL3, and IgL4 measured by qRT-PCR from immune tissues and magnetically sorted TNP-specific lymphocyte populations. In all samples IgL1 constituted 80-95% of the transcripts. The percentage of anti-TNP specific IgL1 transcripts was measured in naïve, unsorted, and TNP-specific cell populations of TNP-KLH fish (n = 3) and found to be significantly higher in the TNP positive cell population (21%) compared to the naïve population (1%; p = 0.02) suggesting that there is a selection of TNP specific IgL sequences.

Characterization of a specific monoclonal antibody against immunoglobulin light kappa/L1 chain in olive flounder (Paralichthys olivaceus)

Immunoglobulins (Ig) are heterodimeric proteins that play critical roles in the adaptive immune system of vertebrates. Because of their plasticity, teleostean Igs are more diverse, and thus do not conform to mammalian classifications. Because of this, mammalian-based Ig cell markers cannot be used successfully to study immune responses in fish. There is therefore a need to produce Ig-specific cell markers for fish. Here, we attempted to identify the specific isotype detected by an Ig light chain-specific monoclonal antibody (anti-olive flounder IgL-mAb: M7C3-4) that we had previously produced [11]. Three newly identified sequences of the Ig light chain from olive flounder were classified according to their isotypes. Subsequent analyses revealed that M7C3-4 was able to specifically detect lymphocytes expressing one of the κ chains (Igκ-a) in olive flounder. Interestingly, Igκ-a⁺ B cells were more abundant in spleen and trunk-kidney than in peripheral blood, indicating a distribution different from that of IgM⁺ B cells. Our work reveals interesting aspects of B cell distribution and differentiation, and may aid in the production of suitable and effective cell markers for olive flounder.

Characterization of an IgM-like immunoglobulin from silver catfish (Rhamdia quelen) serum and its use for the production of polyclonal antibodies and development of immunoassays

Abstract: Knowledge on fish immunoglobulin (Ig) characteristics and the availability of monoclonal or polyclonal antibodies to fish Igs are essential to evaluate the humoral immune response and the Ig distribution on leukocyte cells. We demonstrated that silver catfish serum Ig is composed of one immunodominant H chain with approximately 75k Da and one L chain with approximately 28 kDa, similar to human IgM. Rabbit polyclonal antibodies to the catfish IgM-like Ig recognized both the H and L chain and were useful in developing an indirect ELISA to measure the production of antibodies in fish immunized with bovine serum albumin. Dot blot and western blot cross-reactivity studies indicated a wide degree of epitope sharing amongst Ig from several Siluriformes and Characiformes fish indigenous to Brazilian rivers. In these fish species, polyclonal antibodies reacted mostly with the H chain. The results presented here are central to the development of tools and strategies to investigate the antibody production to inoculated antigens and tissue distribution of Ig molecules in native fish species. Furthermore, because of the wide range of cross-reactivity, polyclonal antibodies to silver catfish IgM-like Ig might be used to develop immunoassays to measure the humoral immune response in other fish species.

Preferential combination between the light and heavy chain isotypes of fish immunoglobulins

Immunoglobulin light chain (IgL) is necessary for the assembly of an Ig molecule, which plays important roles in the immune response. IgL genes were identified in various teleost species, but the basic functions of different IgL isotypes and the preferential combination between IgL and IgH (Ig heavy chain) isotypes remain unclear. In the current study, by EST database searching and cDNA cloning in rainbow trout, 8 IgL sequences were obtained, which could be classified into the IgLκF, IgLκG, IgLσ and IgLλ isotypes, respectively. Trout IgL isotypes were highly expressed in the immune-related tissues, and participated in the immune responses in spleen and gut by stimulation with LPS and poly (I:C). The results of FACS and LC-MS/MS indicated that the IgLκG and IgLσ isotypes preferentially bonded with the heavy chains of IgM and IgT, respectively, in trout B cells and serum. In addition, the genomic organization of trout IgL isotypes and the utilization of recombination signal sequences were studied.

Immunoglobulin genes and their transcriptional control in teleosts

Immunoglobulin (Ig), which exists only in jawed vertebrates, is one of the most important molecules in adaptive immunity. In the last two decades, many teleost Ig genes have been identified by in silico data mining from the enormous gene and EST databases of many fish species. In this review, the organization of Ig gene segments, the expressed Ig isotypes and their transcriptional controls are discussed. The Ig heavy chain (IgH) locus in teleosts encodes the variable (V), the diversity (D), the joining (J) segments and three different isotypic constant (C) regions including Cμ, Cδ, and Cζ/τ genes, and is organized as a "translocon" type like the IgH loci of higher vertebrates. In contrast, the Ig light (L) chain locus is arranged in a "multicluster" or repeating set of VL, JL, and CL segments. The IgL chains have four isotypes; two κ L1/G and L3/F), σ (L2) and λ. The transcription of IgH genes in teleosts is regulated by a VH promoter and the Eμ3' enhancer, which both function in a B cell-specific manner. The location of the IgH locus, structure and transcriptional function of the Eμ3' enhancer are important to our understanding of the evolutional changes that have occurred in the IgH gene locus.

Three isotypes of immunoglobulin light chains in large yellow croaker, Pseudosciaena crocea: Molecular cloning, characterization, and expression analysis

Both cDNA library mining and transcriptome analysis were used to obtain 21 immunoglobulin light chain (IgL) sequences for the large yellow croaker, Pseudosciaena crocea. Full-length cDNA sequences are available for 10 of these, and they were identified as belonging to the three IgL isotypes of LycIgL1, LycIgL2, and LycIgL3. The LycIgL1 isotype is most abundant in the large yellow croaker IgL repertoire, as in the other teleosts. Tissue expression profile analysis revealed that the three LycIgL isotypes were constitutively expressed at different abundances in the kidney, spleen, liver, gill, heart, intestine, and muscle, although the heart did not express LycIgL3. Real-time polymerase chain reaction revealed that expression of the three LycIgL isotypes in the kidney and spleen tissues was up-regulated during 72 h of inductions with poly(I:C) or bacterial vaccine at different intensities and in different manners. The LycIgL1 isotype responded to stimulations most intensely in the spleen, while the LycIgL3 isotype responded most quickly in the kidney. Compared to the LycIgL1 and LycIgL3 isotypes, the LycIgL2 isotype responded more slowly and weakly in both tissues. These results indicate different isotypes of LycIgL respond to immune stimuli in the spleen and kidney in an isotypic-specific manner.

Immunoglobulin light chain (IgL) genes in zebrafish: Genomic configurations and inversional rearrangements between (V(L)-J(L)-C(L)) gene clusters

In mammals, Immunoglobulin light chain (IgL) are localized to two chromosomal regions (designated kappa and lambda). Here we report a genome-wide survey of IgL genes in the zebrafish revealing (V(L)-J(L)-C(L)) clusters spanning 5 separate chromosomes. To elucidate IgL loci present in the zebrafish genome assembly (Zv6), conventional sequence similarity searches and a novel scanning approach based on recombination signal sequence (RSS) motifs were applied. RT-PCR with zebrafish cDNA was used to confirm annotations, evaluate VJ-rearrangement possibilities and show that each chromosomal locus is expressed. In contrast to other vertebrates in which IgL exon usage has been studied, inversional rearrangement between (V(L)-J(L)-C(L)) clusters were found. Inter-cluster rearrangements may convey a selective advantage for editing self-reactive receptors and poise zebrafish by virtue of their extensive numbers of V(L), J(L) and C(L) to have greater potential for immunoglobulin gene shuffling than traditionally studied mice and human models.

Diverse immunoglobulin light chain organizations in fish retain potential to revise B cell receptor specificities

We have characterized the genomic organization of the three zebrafish L chain isotypes and found they all differed from those reported in other teleost fishes. Two of the zebrafish L chain isotypes are encoded by two loci, each carrying multiple V gene segments. To understand the derivation of these L chain genes and their organizations, we performed phylogenetic analyses and show that IgL organization can diverge considerably among closely related species. Except in zebrafish, the teleost fish IgL each contain only two to four recombinogenic components (one to three V, one J) and exist in multiple copies. BCR heterogeneity can be generated, but this arrangement apparently provides neither combinatorial diversification nor an opportunity for the secondary rearrangements that, in mammals, take place during receptor editing, a process crucial to the promotion of tolerance in developing lymphocytes. Examination of the zebrafish IgL recombination possibilities gave insight into how the suppression of self-reactivity by receptor editing might be managed, including in miniloci. We suggest that, despite the diverse IgL organizations in early and higher vertebrates, two elements essential to generating the Ab repertoire are retained: the numerous genes/loci for ligand-binding diversification and the potential for correcting unwanted specificities that arise.

Antibody repertoire development in teleosts--a review with emphasis on salmonids and Gadus morhua L

The group of teleosts is highly diverse, comprising more than 23000 extant species. Studies of the teleost antibody repertoire have been conducted in many different species within different orders, though some species and families have been better characterised than others. The Atlantic cod (Gadus morhua L.) and several species within the Salmoninae (e.g. Salmo salar and Oncorynchus mykiss) are among the best-studied teleosts in terms of the antibody repertoire. The estimated size of the repertoire, the organisation of immunoglobulin (IG) gene segments, the expressed IG repertoire, the IgM serum concentration, and the serum antibody responses reveal some fundamental differences between these species. The serum IgM concentration of G. morhua is some ten times higher than that of S. salar, though G. morhua is characterised as a 'low' (or 'non') responder in terms of specific antibody production. In contrast, an antibody response is readily induced in S. salar, although the response is strongly regulated by antigen induced suppression. The IGHD gene of G. morhua has a unique structure, while the IGHM and IGHD genes of S. salar have a characteristic genomic organisation in two parallel loci. In addition, salmonids, express a broad repertoire of IGH and IGI V-region gene segments, while a single V gene family dominates the expressed heavy and light chain repertoire of G. morhua. Little is known about the developing antibody repertoire during ontogeny, in different stages of B-cell maturation, or in separate B-cell subsets. Information on the establishment of the preimmune repertoire, and the possible role of environmental antigens is also sparse.

Channel catfish immunoglobulins: repertoire and expression

The channel catfish, Ictalurus punctatus, is widely recognized as an important model for studying immune responses in ectothermic vertebrates. It is one of the few fish species for which defined viable in vitro culture systems have been established and is currently the only fish species from which a variety of functionally distinct clonal leukocyte lines are available. Moreover, there is a large basis of biochemical and molecular information on the structure and function of catfish immunoglobulins (Igs). Catfish, as other teleosts, have a tetrameric homolog of IgM as their predominant serum Ig plus a homolog of IgD. They also have genetic elements basically similar to those of mammals, which encode and regulate their expression. The catfish Ig heavy (H) chain locus is a translocon-type locus with three Igdelta genes linked to an Igmu gene or pseudogene. The catfish IgH locus is estimated to contain approximately 200 variable (V) region genes representing 13 families as well as at least three diversity (D) and 11 joining (JH) genes. The catfish has two light (L) chain isotypes, F and G, both encoded by loci organized in multiple cassettes of VL-JL-CL with the VL in the opposite transcriptional orientation. Hence, all requisite components for encoding antibodies are present in the catfish, albeit with certain variations. In the future, whether or not additional unique features of Ig function and expression will be found remains to be determined.

Marine organism cell biology and regulatory sequence discoveryin comparative functional genomics

The use of bioinformatics to integrate phenotypic and genomic data from mammalian models is well established as a means of understanding human biology and disease. Beyond direct biomedical applications of these approaches in predicting structure–function relationships between coding sequences and protein activities, comparative studies also promote understanding of molecular evolution and the relationship between genomic sequence and morphological and physiological specialization. Recently recognized is the potential of comparative studies to identify functionally significant regulatory regions and to generate experimentally testable hypotheses that contribute to understanding mechanisms that regulate gene expression, including transcriptional activity, alternative splicing and transcript stability. Functional tests of hypotheses generated by computational approaches require experimentally tractable in vitro systems, including cell cultures. Comparative sequence analysis strategies that use genomic sequences from a variety of evolutionarily diverse organisms are critical for identifying conserved regulatory motifs in the 5′-upstream, 3′-downstream and introns of genes. Genomic sequences and gene orthologues in the first aquatic vertebrate and protovertebrate organisms to be fully sequenced (Fugu rubripes, Ciona intestinalis, Tetraodon nigroviridis, Danio rerio) as well as in the elasmobranchs, spiny dogfish shark (Squalus acanthias) and little skate (Raja erinacea), and marine invertebrate models such as the sea urchin (Strongylocentrotus purpuratus) are valuable in the prediction of putative genomic regulatory regions. Cell cultures have been derived for these and other model species. Data and tools resulting from these kinds of studies will contribute to understanding transcriptional regulation of biomedically important genes and provide new avenues for medical therapeutics and disease prevention.

Characterisation of T cell antigen receptor alpha chain isotypes in the common carp

T cell receptor alpha (TCRalpha) chain has been characterised in several teleost species to date. Here, a reverse transcription-polymerase chain reaction (RT-PCR) strategy was used to isolate cDNA clones encoding TCRalpha chain from an individual of the common carp (Cyprinus carpio.L.). The Valpha sequences identified were most similar to Valpha of other teleosts, and could be classified into as many as 14 Valpha families. For the Jalpha sequences, diversity comparable to that seen in other teleosts could be identified, and the J-region motif was well conserved. The Calpha sequences demonstrated the highest similarity to zebrafish Calpha and possessed a well-conserved transmembrane (TM) region. Two Calpha isotypes with a complete C region were obtained, designated Calpha1 and Calpha2, with approximately 70% similarity at the amino acid level ( approximately 85% identity at the nucleotide level), and, in addition, Calpha2 contained two unique sequences, designated Calpha2a and Calpha2b, with 93% similarity (96% identity). Therefore, the results obtained using an individual clearly showed that carp possesses at least two Calpha loci, possibly as a result of tetraploidisation.