Isolation of early immunoglobulin lambda-like gene transcripts in human fetal liver

Analysis of the repressor element-1 silencing transcription factor/neuron-restrictive silencer factor occupancy of non-neuronal genes in peripheral lymphocytes from patients with Huntington's disease

We have previously demonstrated that the transcription of neuronal repressor element-1/neuron-restrictive silencer element (RE1/NRSE)-regulated genes is reduced in the brain of subjects with Huntington's disease (HD) as a result of increased binding of the repressor element-1 silencing transcription factor/neuron-restrictive silencer factor (REST/NRSF) to its RE1/NRSE targets. As specific non-neuronal REST/NRSF-regulated genes have been identified in the human genome, we exploited the possibility that the binding of REST/NRSF to its target RE1/NRSE sites may also be altered in the peripheral tissues of HD patients. Our results show that REST/NRSF occupancy is increased in lymphocytes from HD subjects, thus indicating for the first time that the activity of the RE1/NRSE sites is dysfunctional in vivo. Chromatin immunoprecipitation (ChIP) of the RE1/NRSE sites in lymphocytes may therefore be a reproducible, sensitive and specific means of searching for candidate markers of HD onset and progression.

Transgenic human lambda 5 rescues the murine lambda 5 nullizygous phenotype

The human lambda 5 (hu lambda 5) gene is the structural homologue of the murine lambda 5 (m lambda 5) gene and is transcriptionally active in pro-B and pre-B lymphocytes. The lambda 5 and VpreB polypeptides together with the Ig mu H chain and the signal-transducing subunits, Ig alpha and Ig beta, comprise the pre-B cell receptor. To further investigate the pro-B/pre-B-specific transcription regulation of hu lambda 5 in an in vivo model, we generated mouse lines that contain a 28-kb genomic fragment encompassing the entire hu lambda 5 gene. High levels of expression of the transgenic hu lambda 5 gene were detected in bone marrow pro-B and pre-B cells at the mRNA and protein levels, suggesting that the 28-kb transgene fragment contains all the transcriptional elements necessary for the stage-specific B progenitor expression of hu lambda 5. Flow cytometric and immunoprecipitation analyses of bone marrow cells and Abelson murine leukemia virus-transformed pre-B cell lines revealed the hu lambda 5 polypeptide on the cell surface and in association with mouse Ig mu and mouse VpreB. Finally, we found that the hu lambda 5 transgene is able to rescue the pre-B lymphocyte block when bred onto the m lambda 5-/- background. Therefore, we conclude that the hu lambda 5 polypeptide can biochemically and functionally substitute for m lambda 5 in vivo in pre-B lymphocyte differentiation and proliferation. These studies on the mouse and human pre-B cell receptor provide a model system to investigate some of the molecular requirements necessary for B cell development.

μ-Surrogate Light Chain Physicochemical Interactions of the Human PreB Cell Receptor: Implications for VH Repertoire Selection and Cell Signaling at the PreB Cell Stage

The surrogate light chain (SL) composed of the λ-like and VpreB polypeptides is organized as two Ig domains and an extra-loop structure. It associates to the μ-chain in preB cells. We have produced human VpreB, SL, two Fdμ (VH-CH1), and the two corresponding Fab-like (Fdμ-SL) recombinant proteins in baculovirus. The correctness of the general conformation of the proteins was assessed by epitope mapping and affinity measurements using a new batch of anti-VpreB mAbs. Plasmon resonance analysis showed that both VpreB and the entire SL associated with the Fdμ fragments, with Kd values of 3 × 10−8 M for VpreB-Fdμ and of 10−9 to 10−10 M, depending upon the VH, for SL-Fdμ. These results indicate that the λ-like chain, in addition to be covalently bound to the Cμ1 domain, also interacts with the VH domain. Therefore, a dual role of the SL emerges: 1) interaction of the C-domain of λ-like would release the μ-chain from its interaction with binding protein in the endoplasmic reticulum, and 2) interaction of a part of λ-like and most of VpreB would bind to VH, ensuring a “quality control” of the native heavy chain that represents the first step of selection of the B cell repertoire. We also demonstrated that two Fab-like fragments did not interact with each other, suggesting that activation of the cell surface preB receptor does not involve aggregation neither in cis nor in trans of the Fab-like structures.

The organization of the gamma-glutamyl transferase genes and other low copy repeats in human chromosome 22q11

A clone map consisting of YACs, cosmids, and fosmids has been constructed covering low copy repeat regions of human chromosome 22q11. A combination of clone restriction digest analysis, single-copy landmark content analysis, HindIII-Sau3AI fingerprinting, and sequencing of PCR products derived from clones was required to resolve the map in this region. Seven repeat-containing contigs were placed in 22q11, five containing gamma-glutamyl transferase (GGT) sequences described previously. In one case, a single interval at the resolution of the YAC map was shown to contain at least three GGT sequences after higher resolution mapping. The sequence information was used to design a rapid PCR/restriction digest technique that distinguishes the GGT loci placed in the YAC map. This approach has allowed us to resolve the previous cDNA and mapping information relating to GGT and link it to the physical map of 22q11.

Cell surface expression of surrogate light chain (psi L) in the absence of mu on human pro-B cell lines and normal pro-B cells

Surrogate light chains (psi L) encoded by lambda-like (lambda 5) and VpreB genes play a critical role in controlling the early steps of B cell differentiation. We prepared new anti-VpreB monoclonal antibodies (mAb) (3C7/6F6) which preferentially recognize the VpreB epitope at the cell surface of human cell lines that do not express the mu chain. These mAb provide the first characterization of human pro-B cell lines expressing surface psi L. We demonstrate that surface psi L expression is considerably enhanced upon interleukin-7 stimulation and that the psi L complex is formed independently of the Ig alpha/Ig beta heterodimer. Finally, using these antibodies, we confirm the existence of a normal pro-B cell population in human adult bone marrow. These cells are CD34+ CD38+ psi L+, do or do not express CD19, CD10, or both epitopes, and may represent the earliest cell population committed to B cell differentiation.

Composite exon structure of an unusual Ig lambda-like gene located at human 22q11 position

The surrogate light chain, composed of the VpreB and the lambda-like proteins, plays a critical role in controlling the early stages of B lymphocyte development. The lambda-like locus, located on the q11. 2-q11.3 region of human Chromosome (Chr) 22, contains three genes (14.1 Flambda-1, and 16.1) among which only the 14.1 is functional. This gene contains three exons, whereas the others lack exon 1. We have isolated in fetal liver a transcript of the Flambda-1 gene that contains the exon 3 sequence and a long non-Ig related sequence upstream. We show that this sequence resulted from the splicing of three new exons located telomeric to the Flambda-1 gene, highly homologous to beta-glucuronidase exon 11 (Chr 7), to the ABR exon 8 (Chr 17), and to an Expressed Sequence Tag (EST), respectively. We also show that this chimeric transcript is expressed in cells or tissues from various origins. This composite gene structure appears to be a new example of human genome flexibility, which can be explained by mechanisms such as exon shuffling and which results in the emergence of new transcription units inserted in regions involved in translocations.

The human pre-B cell receptor: structural constraints for a tentative model of the pseudo-light (psi L) chain

In human pre-B cells, the mu chain is associated with a surrogate light chain composed of the lambda-like and Vpre-B gene products. This pre-B cell receptor presumably triggers early steps of B cell differentiation, We have determined the NH2-terminal amino acid sequence of the lambda-like chain, showing that the mature chain results from the cleavage of a leader segment of 44 residues, leaving a polypeptide of 169 amino acids having partial features of the Ig light chain domains, with the exception of the first 50 amino acid NH2-terminal region. We have completed the nucleotide sequence of the Vpre-B gene, which appears to contain 126 residues in its mature form of which the 24 COOH-terminal portion was not Ig-related. Analysis of transfectants has provided direct evidence that lambda-like and Vpre-B chains assemble together even in the absence of heavy chain, prompting the search for a structural basis of this interaction. Comparison with the domain organization of the regular Ig lambda chain suggests that most of the psi L chain can be accommodated within a CL-VL-like structure, with an extra "subdomain" contributed by the non-Ig-like portions of both the lambda-like and Vpre-B polypeptides.

Discrete early pro-B and pre-B stages in normal human bone marrow as defined by surface pseudo-light chain expression

Vpre-B and lambda-like genes are selectively expressed in B cell precursors and encode polypeptide chains associated in a mu-pseudo light chain (mu-psi L) complex which is thought to regulate some early steps of B cell differentiation. We have generated anti-Vpre-B monoclonal antibodies which allowed us to identify different steps of differentiation from the pro-B to the immature B cells by following surface expression of Vpre-B, mu and light chains in normal adult human bone marrow. Already present at the surface of a small fraction of B cell progenitors (CD34+/CD19+) the Vpre-B molecule was consistently found coexpressed with CD19 and was also found with the sequentially occurring CD10, CD20, CD21, CD22 and CD5 markers. Three discrete cell types were identified: (i) a subpopulation expressing Vpre-B without mu and which represented an early stage of differentiation, (ii) a minor subpopulation co-expressing Vpre-B and mu without the conventional light chains and (iii) a major subpopulation co-expressing Vpre-B, mu and kappa or lambda chains, considered an intermediate pre-B/B stage. The presence of the psi L chain in various cell subpopulations, in possible association with discrete molecules and/or different contexts, suggests its involvement at several steps of early B cell differentiation.

Physical location of the human immunoglobulin lambda-like genes, 14.1, 16.1, and 16.2

The human immunoglobulin lambda-like (IGLL) genes, which are homologous to the human immunoglobulin lambda (IGL) light chain genes, are expressed only in pre-B cells and are involved in B cell development. Three IGLL genes, 14.1, 16.1, and 16.2 are present in humans as opposed to one, lambda 5 (Igll), found in the mouse. To precisely map the location of the human IGLL genes in relation to each other and to the human IGL gene locus, at 22q11.1-2, a somatic cell hybrid panel and pulsed field gel electrophoresis (PFGE) were used. Hybridization with a lambda-like gene-specific DNA probe to somatic cell hybrids revealed that these genes reside on 22q11.2 between the breakpoint cluster region (BCR) and the Ewing sarcoma breakpoint at 22q12 and that gene 16.1 was located distal to genes 14.1 and 16.2. Gene 14.1 was found by PFGE to be proximal to 16.2 by at least 30 kilobases (kb). A 210 kb Not I fragment containing genes 14.1 and 16.2 is adjacent to a 400 kb Not I fragment containing the BCR locus, which is just distal to the IGL-C (IGL constant region) genes. We have determined that the IGLL genes 14.1 and 16.2 are approximately 670 kb and 690 to 830 kb distal, respectively, to the 3'-most IGL-C gene in the IGL gene locus, IGL-C7. We thus show the first physical linkage of the IGL and the IGLL genes, 14.1 and 16.2. We discuss the relevance of methylation patterns and CpG islands to expression, and the evolutionary significance of the IGLL gene duplications. Consistent with the GenBank nomenclature, these human IGLL genes will be referred to as IGLL1 (14.1), IGLL2 (16.2), and IGLL3 (16.1), reflecting their position on chromosome 22, as established by this report.

Bone marrow cells in X-linked agammaglobulinemia express pre-B-specific genes (lambda-like and V pre-B) and present immunoglobulin V-D-J gene usage strongly biased to a fetal-like repertoire

Expression of Ig and Ig-related genes has been studied in bone marrow cells from two patients with severe form of X-linked agammaglobulinemia (XLA). Phenotypic analysis revealed the presence of pre-B cells, in the absence of mature B cell markers. The pre-B-specific genes, lambda-like and V pre-B, were normally transcribed. Sequence analysis of 48 distinct V-D-J cDNA clones directly derived from XLA bone marrow cells indicated that they had characteristics of an early fetal pre-B repertoire. All VH families were identified, with a strong bias in the gene usage: a few VH genes were largely overexpressed, either germline or slightly mutated; most genes had been located 3' of the VH locus and were also used in fetal liver (8-13 wk of gestation). Short D regions, (resulting from D-D fusion, making usage of all D genes in both orientations with utilization of the three reading frames), restricted N diversity, and a fetal JH usage pattern were also observed. Taken together, our data suggest that the XLA defect does not alter V-D-J rearrangements nor the expression of mu, lambda-like, and V pre-B transcripts and most likely results in a poor efficiency of some critical steps of the B cell maturation.

The surrogate light chain in B-cell development

The proteins encoded by the VpreB and lambda 5 genes associate with each other to form a light (L) chain-like structure, the surrogate L chain. It can form Ig-like complexes with three partners-the classical heavy (H) chain, the DHJHC mu-protein, or the newly discovered p55 chain; these are expressed on the surface of pre-B cells at different stages of development. Here, Fritz Melchers and colleagues review the structures of the VpreB and lambda 5 genes in mouse and their relatives in humans, describe their pattern of expression, and speculate on their possible evolution and functions.

Organization and expression of the pseudo-light chain genes in human B-cell ontogeny

In pre-B cells, the mu chain is expressed at the cell surface in association with a "light chain surrogate" encoded by the V pre-B and the lambda-like genes. This mu-psi-L complex presumably triggers early steps of the B cell differentiation, possibly by controlling the Ig gene rearrangements. In the humans, the lambda-like complex contains 3 genes, located in the 22q11.2-q12.3 band, telomeric to the IGCL locus, with which they share a similar organization, pointing to a common genetic origin. Only one lambda-like gene, 14.1, is functional and specifically expressed with V pre-B in pre-B cells. This expression starts in cells which still have the IGH locus in germline configuration (pro-B stage) and ceases as soon as the IGL loci rearrange. These pre-B specific transcripts provide useful markers of cells of the B lineage in both physiological and pathological situations.

Interrelating B cell subpopulations and environmental regulation with the expression of three tiers of repertoire diversity

The B cell repertoire consists of three tiers of clonotype diversity. One tier, which is the product of H chain V region rearrangements in the absence of N additions, is of limited diversity (less than 10(8) clonotypes) so that clonotypes of this tier would be expected to recur within and among B cells of individuals of an inbred strain. These clonotypes, therefore, could be subjected to, and conserved by, evolutionary selective pressures such as those imposed by ubiquitous bacterial pathogens. The second tier of clonotypes is created by H chain V region rearrangements that include N additions, and is, therefore, exceedingly diverse. Clonotypes of this tier would be unlikely to recur; however, by providing maximal diversity they would ensure protection against a wide spectrum of pathogens. The third tier of diversity is that which is generated by the superimposition of somatic mutations on clonotypes of the other two tiers. This tier of clonotypes is reflective of the refinement of specificities that are destined for expression in memory B cells. B cells exists as three distinct subpopulations, Ly-1 B cells, conventional primary B cells and memory B cells. These subpopulations differ functionally, developmentally, and by the extent to which they are impacted by immunoregulatory processes. Furthermore, B cells of these subpopulations differentially express the three tiers of clonotype diversity.

Surface markers, heavy chain sequences and B cell lineages

A unifying theory of B cell development and lineage commitment is presented. There are two firmly established B lineages: cells which normally arise only from fetal sources and lack N insertions in their rearranged heavy chains; and N-containing cells which arise from adult bone marrow precursors (and perhaps from late fetal sources). Commitment to the expression of CD5 and the capacity for long-life (or self-renewal) are induced as a consequence of sIg cross-linking, typically by a repeating epitope, thymus independent type two antigen. Alternatively, activation resulting from cognate interaction with a helper T cell does not induce CD5 but results in lower expression of J11d. In this case activation occurs in the absence of sIg cross-linking. It is further proposed that differences in the Ig repertoire make it highly likely that fetal/neonatal, but not adult derived B cells will be induced to express CD5. The model offers a plausible explanation for the correlation of CD5 expression and natural autoantibody production by neonatal B cells. Possible sources of pathogenic autoantibody are discussed in the context of this model.

Normal pre-B cells express a receptor complex of mu heavy chains and surrogate light-chain proteins

Precursors of B cells, which constitute a subpopulation of the lymphocytes in bone marrow, can be identified by their surface expression of nonimmunoglobulin markers and the absence of immunoglobulin kappa and lambda light chains. Most pre-B cells synthesize mu heavy chains but, without light-chain partners, these undergo rapid cytoplasmic degradation. In the present study, we demonstrate that late stage pre-B cells, like their neoplastic counterparts, express low levels of a surface receptor composed of mu chains paired with a surrogate light-chain complex formed by Vpre-B and lambda 5-like proteins. The data define a previously suspected but unrecognized stage in normal pre-B-cell differentiation. Expression of a clonally diverse receptor renders this population of immature B-lineage cells potentially vulnerable to clonal selection by antigens and idiotypic interactions.

Early occurrence of immunoglobulin isotype switching in human fetal liver

A cDNA library prepared from a human fetal liver of the first trimester of gestation was screened with Ig C mu, C gamma, C kappa and C lambda probes. Ten heavy chain clones were isolated and characterized by restriction mapping and partial sequencing. The absence of Ig light chain clone and the presence of pre-B-specific lambda-like transcripts suggest that the immune compartment of this cDNA library was mostly derived from pre-B cells. Three transcripts of mu, gamma 2 and gamma 4 isotypes contained a V-D-J-C region with an open reading frame and used members of the VHIV, VHIII and VHI families, respectively. Seven clones were derived from sterile transcripts, one C mu and six C gamma. In addition to C mu exons, the sterile mu transcript contained the 5' flanking germline region. By contrast, the gamma sterile transcripts used a 5' sequence that was spliced from the I gamma 1 region onto the first C gamma 1 exon. In addition several of these transcripts were derived from alternative splicing. The simultaneous expression of both sterile and functional gamma transcripts suggests that the switch mechanism operates in normal fetal liver very early in ontogeny.

The human pre-B-specific lambda-like cluster is located in the 22q11.2-22q12.3 region, distal to the IgC lambda locus

The chromosomal location of the lambda-like gene cluster, a gene family selectively expressed in human pre-B cells, was analyzed by in situ hybridization with a probe specific for the lambda-like genes. This cluster mapped in the q11.2-q12.3 region of chromosome 22. The use of Burkitt lymphoma and myelogenous leukemia cell lines with translocations in the 22q11 region led to a refinement in the location according to the following order: cen----BCRL2, VpreB, IgV lambda 1----BCRL4, IgV lambda----IgC lambda----BCR----BCRL3, lambda-like----tel. Unlike those of the mouse system, the pre-B-specific genes VpreB and lambda-like do not belong to the same transcriptional unit.

Expression of a novel type of immunoglobulin C lambda transcripts in human mature B lymphocytes producing kappa light chains

Ordered rearrangement of immunoglobulin genes (heavy chain then kappa and eventually lambda genes) is observed during B lymphocyte ontogeny. Unexpectedly, we found that human mature B cells producing kappa chains and having germ-line lambda genes contain lambda mRNA consisting of an invariant 5' region (herein termed X) and of one of the classical C lambda exons. The X region of these transcripts originates from a unique exon located 5 kb upstream of the J-C lambda 1 gene segment. X-C lambda mRNA expression occurs without somatic DNA rearrangement. The use of the X DNA fragment as a probe allows definition of a family of human genes that comprises at least four members and includes the first exon of the lambda 14.1 gene. The latter is selectively transcribed in pre-B lymphocytes and directs the synthesis of a lambda-like chain. In contrast, the X-C lambda transcripts do not appear to encode a C lambda-related polypeptide in mature B cells. Thus, despite a 73% homology extending far beyond the exon sequences, the X and lambda 14.1 genes are expressed at different stages of B cell development and might serve different functions.

Biochemical nature of an Fc mu receptor on human B-lineage cells

An IgM-binding protein of approximately 60 kD has been identified on activated B cells, but not on resting and activated T cells, monocytes, or granulocytes. Here, we characterize this IgM-binding protein as a receptor for the Fc portion (CH3 and/or CH4 domains) of IgM molecules (Fc microR). The Fc microR can be expressed as a cell surface activation antigen throughout the pre-B and B cell stages in differentiation. Receptor expression is not directly linked with IgM production, as both mu- pre-B cells and isotype-switched B cells may express the Fc microR. The receptor molecules produced by both pre-B and B cells are identical in size and are characterized as an acidic sialoglycoprotein with O-linked, but no N-linked, oligosaccharide. The Fc microR is anchored to the surface of B-lineage cells via a glycosyl phosphatidylinositol linkage. The Fc microR is thus the third member of a family of Fc receptors expressed on B-lineage cells, and its preferential expression on activated B cells suggests a potential role in the response to antigens.

A mouse monoclonal antibody reactive preferentially with human IgM lambda

In analyzing mouse monoclonal antibodies (mAb) against a human IgM kappa paraprotein, we found an unusual mAb (LP4; gamma 2b kappa isotype) that reacted in an enzyme linked immunosorbent assay with all 5 IgM lambda but not with 8 IgM kappa or other myelomas. Neither isolated mu heavy nor lambda light chains were reactive with LP4 mAb. By immunofluorescence, LP4 mAb identified approximately 30% of IgM+ B cells and approximately 40% of mitogen-stimulated, IgM+ plasma cells from 4-7 normal blood samples. All LP4+ cells were IgM+. Biosynthetic analysis of the plasma cells revealed that LP4 mAb recognized most IgM lambda and a very minor proportion of IgM kappa molecules. This mAb provides a useful marker for the analysis of pre-B and B cell differentiation.

Immunoglobulin lambda light chain evolution: Igl and Igl-like sequences form three major groups

The nucleotide sequences, and the derived protein sequences, of immunoglobulin (Ig) Igl, Igl-like VpreB genes and the protein sequences of Igl-C regions were aligned and compared. A classification of the Igl and Igl-like VpreB sequences into three categories, designated groups I, II, and III, is proposed. Group I contains the human and mouse Igl-like VpreB genes. Group II contains Igl-V genes of the rabbit and the recently described mouse Igl-Vx gene. Group III includes the Igl-V genes, encoding all other known Igl-V region protein sequences, of mouse, rat, human, pig, sheep, and chicken. An evolutionary analysis of the three groups is presented, and suggests that the group III genes are evolving at a faster rate than those of the other groups and that within this group a further subdivision is possible: the V lambda-encoding genes of mouse, rat, and one human subgroup evolve faster than other group III genes. It is suggested that all mammalian species contain Igl-V genes of each group. A similar comparison between the protein sequences encoded by the known Igl-C genes indicates that the duplication of the Igl-J-C gene pairs occurred independently in each species, after mammalian speciation, and that the Igl-V-(J-C)(J-C) gene clusters of the mouse may not have their homologues in other species.