Activity of multiple light chain genes in murine myeloma cells producing a single, functional light chain

Introduced T cell receptor variable region gene segments recombine in pre-B cells: evidence that B and T cells use a common recombinase

We have recently proposed that a common recombinase performs all of the many variable region gene assembly events in B and T cells, and that the specificity of these joining events is mediated by regulating the "accessibility" of the involved gene segments. To test this possibility, we have introduced "accessible" T cell receptor (TCR) variable region gene segments into a pre-B cell line capable of recombining endogenous and transfected immunoglobulin (Ig) variable region gene segments. Although the corresponding "inaccessible" endogenous TCR gene segments do not rearrange in this line or in B cells in general, the introduced TCR gene segments join very frequently and, in fact, closely resemble introduced Ig gene segments in their recombination characteristics. These observations suggest a new role for conventional Ig transcriptional enhancers--recombinational enhancement. Our studies provide insight into additional aspects of the joining mechanism such as N region insertion, aberrant joining, and recombination-recognition sequence requirements for joining.

The level of lambda 1 light chain expression in the mouse reflects the probability of rearrangement of the relevant gene

The predominance of kappa over lambda light chain expression in mice can either reflect the probability of rearrangement of the relevant locus or be the result of antigen-driven clonal expansion. To discriminate between these two possibilities we determined, by limiting dilution analysis, the frequencies of kappa- and lambda-producing cells in B lymphocytes generated in vitro from bone marrow pre-B cells. The frequencies obtained in these cultures are not significantly different from those obtained with mature spleen cells. In addition, Southern blot analysis of bone marrow-derived and splenic cell DNA revealed that in both populations the extent of B lymphocytes having undergone lambda 1 gene rearrangement does not exceed 4%. These results, therefore, establish that in the mouse the low level of lambda light chain expression directly reflects the probability of rearrangement of the relevant locus.

Lack of isotype exclusion and expression of aberrant lambda light chain on secreted MOPC-315 myeloma proteins

The presence of aberrant lambda 1 light (L) chain fragment (lambda 1 F) on the secreted myeloma protein of MOPC-315 has been demonstrated by serological and immunochemical methods. We developed a highly sensitive radioimmunoassay that utilizes exquisitely specific xenogeneic anti-lambda 1 antibodies to detect the minute amounts of lambda 1 F on lambda 2-bearing MOPC-315 myeloma proteins. In addition, structural evidence that lambda 1 F is present on MOPC-315 myeloma protein was demonstrated by subjecting 125I-labeled MOPC-315 myeloma protein to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions followed by autoradiography. The relative amounts of lambda 1 F and lambda 2-chain on MOPC-315 myeloma were measured by two independent methods. The molar ratio of lambda 1 F to lambda 2 was calculated to be 1:68 by radioimmunoassay and 1:80 by analytical SDS-PAGE. This represents the first demonstration that an aberrant L-chain fragment combines with a heavy chain and is secreted in association with antigen-binding myeloma proteins. The implications of these results on L-chain isotype exclusion are discussed.

The c-myc oncogene driven by immunoglobulin enhancers induces lymphoid malignancy in transgenic mice

Transgenic mice bearing the cellular myc oncogene coupled to the immunoglobulin mu or kappa enhancer frequently develop a fatal lymphoma within a few months of birth. Since the tumours represent represent both immature and mature B lymphocytes, constitutive c-myc expression appears to be highly leukaemogenic at several stages of B-cell maturation. These myc mice should aid study of lymphoma development, B-cell ontogeny and immunoglobulin regulation.

C mu-containing transcripts initiate heterogeneously within the IgH enhancer region and contain a novel 5'-nontranslatable exon

Transcriptional competence of the immunoglobulin heavy-chain locus (IgH) is established at an early stage of lymphoid cell development, leading to the appearance of RNA components, previously called C mu RNA1 or sterile-mu RNA2, which contain constant-region sequences but lack variable-region sequences. These components are of two types: those which initiate in the D region of alleles that have undergone DJH (diversity-joining region) rearrangement (D mu transcripts) and those which initiate within the JH-C mu intron (hereafter termed I mu transcripts). In pre-B and early B cells, D mu and I mu transcripts are nearly as abundant as the messenger RNA encoding mu heavy chain. The D mu transcripts are spliced into RNAs containing D, JH and C mu sequences, and in some, but not all, cases these RNAs are translated into D mu proteins. To establish whether the I mu transcripts have any translational potential and to elucidate the structure of their promoter region, we have determined their transcription initiation sites and their mode of splicing. As reported here, by using sequence analysis of cloned I mu complementary DNAs, primer extension and S1 nuclease mapping, we have found that these transcripts have remarkable 5' heterogeneity: there are more than five distinct start sites spanning a region of 44 nucleotides that is located downstream of an octanucleotide found in all variable-region promoters. Such imprecise initiation may result from the lack of a well-defined TATAA motif and the unusual proximity of the octanucleotide to the enhancer region. Approximately 700 nucleotides downstream from these initiation sites, a cryptic splice site is used to create a nontranslatable exon ('nontron') which is joined to the C mu 1 domain. The properties of the nontron may be important for the mechanism of allelic exclusion.

Linkage of a 7S RNA sequence and kappa light chain genes in the mouse

A mouse 7S RNA cDNA plasmid clone was employed to identify and map DNA restriction fragment variants using recombinant inbred (RI) and congenic mouse strains. More than a dozen such restriction variants were identified and mapped to different regions of the mouse genome. One such variant, designated Rn7s-6, showed close linkage to the Ly-2,3-Igk-V (T lymphocyte antigens 2 and 3, kappa immunoglobulin variable region) cluster of markers on chromosome 6. No recombinants were detected among three of these markers in 59 RI strains. On the basis of these data, the Rn7s-6 sequence may be placed within 1.3 centimorgans of Ly-3 and one of the Igk-V-region markers, Igk-Ef1. Two mouse stocks with previously identified crossovers within the Ly-2,3-Igk-V region were used to sublocalize Rn7s-6. The results are consistent with the gene order (Ly-2, Ly-3)-(Rn7s-6, Igk-Ef1)-Igk-Ef2. Several mouse plasmacytomas, known to have various parts of the kappa chain complex deleted, retain the Rn7s-6 sequence. The Rn7s-6 variant is a plus/minus variant; no sequence allelic to Rn7s-6 is found in inbred strains that share the Ly-3a-Igk-Ef1a haplotype.

Regulated progression of a cultured pre-B-cell line to the B-cell stage

The variable (V) regions of heavy and light immunoglobulin chains are encoded by multiple germline DNA elements which are assembled into complete variable-region genes in precursor(pre-) B lymphocytes. The heavy-chain V region (VH) is assembled from three separate germline DNA elements, the variable (VH), diversity (D) and joining (JH) segments; whereas light-chain variable regions of either the kappa or lambda type are assembled from two elements, the VL and JL. Analysis of tumour cell lines or sorted cell populations which represent early and late pre-B cells has suggested that heavy-chain assembly and expression generally precedes that of light chains; but, primarily because of the lack of appropriate model systems to study the phenomenon, the mechanism and significance of this apparently orderly differentiation process are much debated. Here we describe for the first time a transformed cell line, 300-19, which sequentially undergoes all of the immunoglobulin gene rearrangement and expression events associated with the differentiation of pre-B cells to surface immunoglobulin-positive B lymphocytes. Analysis of the in vitro differentiation of 300-19 cells provides direct evidence for distinct differentiation phases of first VH and subsequently VL assembly during B-cell differentiation. Furthermore, these analyses suggest that the mu heavy chain, resulting from a productive VHDJH rearrangement, has both a positive and a negative regulatory role in mediating this ordered differentiation process, that is, signalling the cessation of VH gene assembly and simultaneously signalling the onset of VL assembly.

Deletions of kappa chain constant region genes in mouse lambda chain-producing B cells involve intrachromosomal DNA recombinations similar to V-J joining

We isolated and characterized the germ-line counterpart of a DNA segment designated RS (for recombining sequence), that is frequently recombined in mouse lambda light chain-producing B lymphocytes. Using Southern blot analyses of myelomas and mouse-Chinese hamster fusion cell lines, we found that RS DNA sequences are located on mouse chromosome 6, evidently more than 15 kilobases downstream of the kappa light-chain locus. We find that a typical recognition site for Ig gene recombination is situated within germ-line RS sequences near the recombination points observed in at least two lambda chain-producing cell lines. This represents a complete and functional Ig recognition site that is not directly associated with Ig genes. We also characterized a recombined RS segment isolated from the cell line BM18-4.13.9. This recombined segment has a variable region kappa light chain gene (V kappa) joined directly to RS sequences. Our results suggest that the deletion of the kappa light chain constant region (C kappa) exon in many lambda chain-producing B cells is the result of RS recombination and that C kappa deletion may be mediated by the same processes as antibody gene V-J joining (J = joining segment gene). We discuss the potential biological significance of RS DNA recombination in B-cell maturation.

Genes encoding the T-cell receptor alpha and beta subunits are transcribed in an ordered manner during intrathymic ontogeny

To further characterize sequential events involved in activation of genes encoding the T-cell receptor (a complex of T3 molecules and a disulfide-linked heterodimer designated Ti, T3-Ti) for antigen and the major histocompatibility complex during intrathymic ontogeny, cDNA probes specific for Ti alpha and Ti beta subunits were used for transcriptional analysis. Ti beta transcript levels were minimal in stage I thymocytes, maximal in stage II thymocytes, and intermediate in state III thymocytes. In contrast, Ti alpha transcriptional activity was virtually undetectable in stage I, was low in stage II, and achieved high levels only in the stage III compartment. Analysis of tumor populations derived from individual stages of thymic differentiation confirmed these observations and demonstrated that clonal stage I-II cells often express Ti beta RNA in the absence of Ti alpha RNA. The latter was not a consequence of functional Ti alpha-subunit isotypy because each of 13 interleukin 2-dependent T-cell clones, including inducer, suppressor, and cytotoxic T cells, contain transcripts that hybridize with the Ti alpha probe. From these data it is concluded that Ti beta gene activation precedes Ti alpha gene activation. Moreover, the high level of Ti beta mRNA preceding Ti alpha mRNA expression implies that Ti beta mRNA and/or its protein products may regulate Ti alpha gene transcription.

A uniform deleting element mediates the loss of kappa genes in human B cells

Human immunoglobulin light-chain genes become rearranged in an ordered fashion during pre-B-cell development such that rearrangement generally occurs in kappa genes before lambda genes (refs 1,2). This ordered process includes an unanticipated deletion of the constant kappa (C kappa) gene and kappa enhancer sequence which precedes lambda rearrangement, and the site of this deletional recombination was located 3' to the joining (J kappa) segments in 75% of cases studied. We have now characterized the recombinational element responsible for this event on three separate alleles and found them to be identical. This kappa-deleting element recombined site-specifically with a palindromic signal (CACAGTG) located in the J kappa-C kappa intron. All losses of C kappa genes in other human B cells were mediated by this determinant, including the 25% of instances when this element recombined with sequences 5' to J kappa. In contrast, the kappa-deleting element remained in its germline form on all successful kappa-producing alleles. Moreover, kappa loss is an evolutionarily conserved event, as the kappa-deleting element appears to be the human homologue of the murine RS sequence. Our results suggest that this element may help ensure isotypic and allelic exclusion of light chains and may be involved in the ordered use of human light-chain genes.

Cloning and sequencing of a rearranged V lambda gene from a Burkitt's lymphoma cell line expressing kappa light chains

We have cloned and sequenced a rearranged V lambda gene from a Burkitt's lymphoma cell line PA682(PB). This cell line has two rearranged kappa loci and has been shown to be expressing kappa light chains. This V lambda gene has been identified as a member of the V lambda subgroup III gene family based on the homology of the predicted amino acid sequence of PAV lambda with the reported sequences of the V lambda protein DEL of subgroup III. Nine cross-hybridizing bands have been detected on Southern blots and the chromosomal orientation of the V lambda subgroup III gene family has been determined in relation to the V lambda subgroup I gene family. Although the PAV lambda rearrangement has occurred via a legitimate V-J joining and a normal size transcript is detected on Northern blots, the nucleotide sequence reveals a high level of mutations resulting in multiple termination signals within the V gene coding sequence and only a truncated V lambda protein can be translated. This confirms previous observations that although multiple light chain genes may be transcribed, only one functional light chain protein can be synthesized.

Aberrant recombination events in B cell lines derived from a kappa-deficient human

We have analyzed the structure of Ig kappa chain genes in B cell lines derived from a human individual who cannot synthesize any kappa chains, and whose Igs all contain lambda chains (1). We have characterized secondary DNA recombination events at two kappa alleles which have undergone misaligned V-J recombinations. One such secondary recombination has joined the flanking sequences of a V kappa and a J kappa 2 gene segment as if it were the reciprocal product of a V-J kappa 2 recombination, and resulted in the displacement of the recombined VJ kappa 1 gene segments from the C kappa locus. The non-rearranged form of the V kappa fragment which had recombined with the J kappa 2 flank was cloned. Nucleotide sequencing of this fragment identified a V kappa gene that differed by at least 38% from all previously sequenced human V kappa genes. The other V-J kappa segment analyzed has undergone a secondary recombination at a different site from that described above, at a site within the intervening sequence between the J kappa and C kappa gene segments, similar to the location of secondary recombinations which have occurred in lambda + B cell lines from mice and humans (2,3). These results prove that multiple recombinations can occur at one J kappa-C kappa locus.

Transmission and expression of a specific pair of rearranged immunoglobulin mu and kappa genes in a transgenic mouse line

Two genes that code for a hapten-specific immunoglobulin M (IgM) have been introduced into the mouse germ line. The transgenic antibody represents 10-50% of the serum IgM and is expressed on the membrane of B cells. B-cell hybridoma lines show that a negative feedback inhibition of mu and kappa transgenic products on the immunoglobulin heavy-chain rearrangement is possible.

Nonfunctional immunoglobulin light chain transcripts in two IgE-producing rat immunocytomas; implications for the allelic exclusion and transcription activation processes

The rearrangement and expression of immunoglobulin light-chain genes have been studied in two IgE-producing immunocytomas, IR2 and IR162. In the IR2 tumor only one of the kappa-chain alleles is rearranged, expressing a full-length kappa-chain polypeptide. In IR162 one of the kappa-chain alleles is functionally rearranged, expressing a 1200-nucleotide (nt) long mRNA, which encodes a functional 23-kDal kappa-chain polypeptide. The second kappa-chain allele is aberrantly rearranged; i.e., a different V region is connected to a position that is located between the J cluster and the C kappa exon. Two mRNAs which are 750 and 850 nt are transcribed from the aberrantly rearranged allele, both of which appear to encode a 12-kDal polypeptide consisting of a signal sequence that is connected directly to the C region. The levels of expression from the two kappa-chain alleles are approximately the same, suggesting that no specific mechanism exists to suppress expression of a nonfunctional allele. The rat genome contains a single lambda-chain locus which includes two C-region exons. Although this locus remains in the germ-line configuration in the IR2 and the IR162 tumors, transcripts from the C lambda I and C lambda II regions were detected at a low level in both tumors. These transcripts were detected in RNA from the immunocytomas but not in rat liver RNA indicating that expression is tissue-specific. They lacked V-region sequences and resemble so-called sterile transcripts which are expressed at a low level from unrearranged mu- and kappa-chain genes.

Allelic exclusion and control of endogenous immunoglobulin gene rearrangement in kappa transgenic mice

Hybridomas were produced from spleen cells of kappa transgenic mice to investigate expression of the transgenic kappa gene, its effect on allelic exclusion and its effect on the control of light-chain gene rearrangement and expression. Our results show that the transgene is expressed normally and that the production of a complete immunoglobulin molecule turns off light-chain gene rearrangement.

Insertion of N regions into heavy-chain genes is correlated with expression of terminal deoxytransferase in B cells

The variable regions of immunoglobulin heavy chains are encoded in the germ line by three discrete DNA segments: VH (variable) elements, D (diversity) elements and JH (joining) elements. During the differentiation of B lymphocytes, individual segments from each group are brought together by recombination to form the complete VHDJH variable region. To understand these processes better, we have now isolated and sequenced molecular clones representing intermediates (DJH fusions) and final products (VH-to-DJH joins) of heavy-chain gene rearrangement in two cell lines that represent analogues of cells at early stages of B-lymphocyte differentiation. Heavy-chain gene assembly in one cell line but not in the other is accompanied by the appearance of short nucleotide insertions at the recombinational junctions. The generation of such insertions is positively correlated with the expression of terminal deoxynucleotidyl transferase in these lines.

Introduction of a mu immunoglobulin gene into the mouse germ line: specific expression in lymphoid cells and synthesis of functional antibody

A functionally rearranged mu heavy chain immunoglobulin (lg) gene was introduced into the germ line of mice. The mu gene encodes a polypeptide which, combined with lambda 1 light chains, shows a specificity for binding the hapten NP. Four transgenic mice harboring 20-140 copies of the foreign mu gene expressed the gene specifically in spleen, lymph node, and thymus at a high level. Purified surface lg-positive B cells, Lyt 2-positive mature T cells, and thymocytes transcribed the foreign mu gene at a similarly high level, suggesting that control of lg gene rearrangement might be the only mechanism that determines the specificity of heavy chain gene expression within the lymphoid cell lineage. No transcription of the foreign mu gene was detected in nonlymphoid tissues with the exception of the heart which expressed the gene at a low level. The transgenic mice had up to 400-fold elevated serum levels of NP binding antibody, which contained a heavy chain with the characteristics of the foreign mu gene. The serum levels of endogenous heavy and light chains in transgenic mice appeared to be the same as in normal mice.

The structure, rearrangement and expression of D beta gene segments of the murine T-cell antigen receptor

It has been postulated that the variable region of the beta-polypeptide of the murine T-cell antigen receptor is encoded by three distinct germ-line gene segments--variable (V beta), diversity (D beta) and joining (J beta)--that are rearranged to generate a V beta gene. Germ-line V beta and J beta gene segments have been isolated previously. Here we report the isolation and characterization of two germ-line D beta gene segments that have recognition signals for DNA rearrangement strikingly similar to those found in the three immunoglobulin gene families and in V beta and J beta gene segments. The D beta and J beta segments can join in the absence of V beta gene segment rearrangement and these rearranged sequences are transcribed in some T cells.

Cloning of terminal transferase cDNA by antibody screening

A cDNA library was prepared from a terminal deoxynucleotidyltransferase-containing thymoma in the lambda phage vector lambda gt11. By screening plaques with anti-terminal transferase antibody, positive clones were identified of which some had beta-galactosidase-cDNA fusion proteins identifiable after electrophoretic fractionation by immunoblotting with anti-terminal transferase antibody. The predominant class of cross-hybridizing clones was determined to represent cDNA for terminal transferase by showing that one representative clone hybridized to a 2200-nucleotide mRNA in close-matched enzyme-positive but not to enzyme-negative cells and that the cDNA selected a mRNA that translated to give a protein of the size and antigenic characteristics of terminal transferase. Only a small amount of genomic DNA hybridized to the longest available clone, indicating that the sequence is virtually unique in the mouse genome.

Models for the rearrangements of immunoglobulin genes: a computer view

Substantial data on the rearrangements of immunoglobulin genes in mouse and man have been available since 1981. Various models have been proposed to interpret these data, but none have been quantitatively tested. We use computer simulations to pinpoint some key features in this system.

Ordered rearrangement of immunoglobulin heavy chain variable region segments

The immunoglobulin heavy chain variable region is encoded as three separate libraries of elements in germ-line DNA: VH, D and JH. To examine the order and regulation of their joining, we have developed assays that distinguish their various combinations and have used the assays to study tumor cell analogs of B-lymphoid cells as well as normal B-lymphoid cells. Abelson murine leukemia virus (A-MuLV) transformed fetal liver cells - the most primitive B-lymphoid cell analog available for analysis - generally had DJH rearrangements at both JH loci. These lines continued DNA rearrangement in culture, in most cases by joining a VH gene segment to an existing DJH complex with the concomitant deletion of intervening DNA sequences. None of these lines or their progeny showed evidence of VHD or DD rearrangements. Heavy chain-producing tumor lines, representing more mature stages of the B-cell pathway, and normal B-lymphocytes had either two VHDJH rearrangements or a VHDJH plus a DJH rearrangement at their two heavy chain loci; they also showed no evidence of VHD or DD rearrangements. These results support an ordered mechanism of variable gene assembly during B-cell differentiation in which D-to-JH rearrangements generally occur first and on both chromosomes followed by VH-to-DJH rearrangements, with both types of joining processes occurring by intrachromosomal deletion. The high percentage of JH alleles remaining in the DJH configuration in heavy chain-producing lines and, especially, in normal B-lymphocytes supports a regulated mechanism of heavy chain allelic exclusion in which a VHDJH rearrangement, if productive, prevents an additional VH-to-DJH rearrangement.

Immunoglobulin gene 'remnant' DNA--implications for antibody gene recombination

Many immunoglobulin (Ig)-producing cells retain the DNA that separates Ig variable (V) and constant (C) region genes in the germline. This "remnant" DNA must be moved during the recombination process that joins V and C genes via a joining (J) segment. We have analyzed remnant DNAs in several Ig-producing cell lines. The nucleotide sequences of kappa (kappa) light chain remnant DNAs indicate close relationships to V-J joining. We find fused V kappa and J kappa recognition sequences in five remnant DNAs, suggesting reciprocal relationships to the fused V kappa and J kappa segments produced by V-J joining. However, of sixteen plasmacytoma remnant DNAs analyzed, all involve only recombination with J kappa l. Thus, in most cell lines, remnant DNAs are not directly reciprocal to recombined kappa-genes. On the other hand, our analyses of some myelomas do indicate indirect relationships between remnant DNAs and kappa-genes. Our results suggest that multiple steps of DNA recombination occur during Ig-gene rearrangement. Because remnant DNA joining sites do not exhibit the flexibility that has been observed in Ig-gene V-J joining, our findings also suggest that the joining mechanism may involve endonuclease, exonuclease and ligase activities.

Site-specific recombination between immunoglobulin D and JH segments that were introduced into the genome of a murine pre-B cell line

A recombinant plasmid containing the herpes simplex virus thymidine kinase (tk) gene, flanked on one side by two murine immunoglobulin heavy chain diversity (D) elements and on the other by two murine immunoglobulin heavy chain joining (JH) elements, was introduced into a tk- variant of a pre-B cell line transformed by Abelson murine leukemia virus. The four possible site-specific joining events between the D and JH segments within the integrated construct occurred frequently during passage of the cloned line under nonselective conditions, and deletion of the internal tk gene as a result of these joining events was, by far, the predominant mechanism of resistance to BUdR within this line. These studies demonstrate that a precise chromosomal location is not essential for the assembly of D and JH elements and provide a model system for mechanistic and genetic studies of this recombination process.

Novel kappa light-chain gene rearrangements in mouse lambda light chain-producing B lymphocytes

The genes that encode the immunoglobulin proteins made by B lymphocytes are made up of segments that are separately encoded in the germ-line genome and brought together by recombination during B-cell ontogeny. There are two types of immunoglobulin light chain, kappa and lambda, but only a single type is expressed in individual B cells. It is thought that kappa gene recombination precedes lambda gene recombination during B-cell ontogeny. We describe here unusual recombinations that have occurred in two lambda-producing B-cell lines and suggest that they are involved in the developmental switch from kappa to lambda gene expression in maturing B cells. These recombinations involve the J kappa-C kappa introns of V-J joined but nonfunctional kappa genes and a sequence that in the germ line occurs downstream of the C kappa exon (called RS, for recombining sequence).

Antigen binding to lymphoid cells from unimmunized mice. VII. Restriction of antigen-binding capacity by maturing B lymphocytes

Neonatal spleen populations have been studied for antigen-binding capacity in an attempt to determine if the frequency of double antigen-binding cells changes as the population matures. Just after birth, the frequencies of total ABC, double ABC and Ig-bearing cells were similar to the frequencies seen in the adult bone marrow. During the first week after birth, the proportion of total ABC and Ig-bearing cells rose sharply so that by 8 days after birth, these cells were about half of adult levels. The proportion of total double ABC, after a brief rise at day 1, remained constant throughout the test period. Thus, the proportion of total ABC which are doubles gradually decreases with age. Sedimentation velocity studies indicate that double ABC's tend to co-sediment with cells which require a period of maturation before they can respond to a thymus-independent antigen in irradiated hosts. Single ABC, on the other hand, tend to co-sediment with cells which are immediately responsive to antigen, or require a shorter maturational period before they become responsive to antigen. All of these data, taken together with our other work, suggest the possibility that multiple ABC are clonally-derived lymphocyte populations which become more restricted in their antigen-binding capacity as they mature.

High frequency of lambda gene activation in bone marrow pre-B cells

The frequency of lambda light chain (L) producing cells in immunoglobulin-producing cells that have been generated in vitro from bone marrow pre-B cells was investigated. The frequency of lambda-producing cells obtained in such a culture was three- to eightfold higher than that observed in the culture of mature spleen B cells. These results suggest that the activation of lambda gene at pre-B cell stage occurs far more frequently than the frequency presumed from the percentage of lambda-bearing cells in mature B cells.

Transposition and amplification of oncogene-related sequences in human neuroblastomas

We have cloned a 2.0-kb EcoRI fragment of human genomic DNA (NB-19-21) which has homology to the v-myc oncogene but is distinct from the classical c-myc gene. This sequence is amplified from 25- to 700-fold in eight of nine tested human neuroblastoma cell lines which contain either homogeneously staining regions or double minutes (HSRs or DMs), the caryological manifestations of amplified genes. In the remaining line, the c-myc proto-oncogene is amplified approximately 30-fold. NB-19-21 hybridizes to a 3.2-kb cytoplasmic, poly(A)+ RNA species that is abundant only in lines in which the sequence is amplified. We propose that the gene encoding the NB-19-21-related RNA species may represent a new oncogene, which we call N-myc. NB-19-21 derives from chromosome 2; but in the five HSR-containing lines that have amplified this sequence, none has HSRs on chromosome 2. NB-19-21 is associated with DMs in a DM-containing line. A second, randomly cloned, amplified DNA segment from the HSR of one of the neuroblastoma lines is amplified in a subset of the lines in which NB-19-21 is amplified. In addition, this probe identifies a novel joint in the amplification unit of one line relative to that of the others. We suggest that, in the eight lines which have amplified NB-19-21, the amplification units are overlapping, but not identical, and that transposition of the common sequences may occur prior to amplification.

Suppressor T cell action inhibits the expression of an excluded immunoglobulin gene

Cells of the murine plasmacytoid line MOPC-315 synthesize two distinct immunoglobulin light chains: a normal lambda II protein, which is incorporated into secretory and surface-bound immunoglobulin, and a truncated, nonfunctional lambda I protein found only in the cytoplasm. Idiotype-specific suppressor T lymphocytes selectively inhibit the expression of both lambda II- and lambda I-specific messenger RNA by MOPC-315 cells. This finding demonstrates that phenotypically excluded light chain genes can be subject to immunoregulatory control and suggests that the expression of divergent lambda isotypes may be coordinately regulated in immunoglobulin-secreting cells.

Nucleotide sequence of a region downstream of the mouse CK immunoglobulin gene

2318 bp downstream of the CK (1) gene segment were sequenced in a clone (L1-D) derived from mouse liver DNA. The 966 bp at the 5' side of this stretch were found to be identical to a sequence which had been determined previously in a myeloma T derived clone, i.e. no somatic mutations had occurred in the transition from the germline to the rearranged configuration. The remaining 1352 bp had not been known and extend the sequenced part of the mouse JK-CK region to about 7.5 kb. Within the newly sequenced area three BspRI sites have been located which were used in chromatin studies (Weischet et al., accompanying publications). In L1-D sequences have been found which are possible targets of aberrant recombination events.

Chance, necessity and antibody gene dynamics

Early in their development B lymphocytes commit themselves to the expression of only one immunoglobulin light-chain gene and only one heavy-chain gene out of the large numbers of available loci. Here I shall present the view that the initial selection of loci for expression is made by chance, whereas the exclusion of other loci from expression is a necessity imposed by the physiology of lymphocyte development.

Construction of a modular dihydrofolate reductase cDNA gene: analysis of signals utilized for efficient expression

Dihydrofolate reductase (DHFR) modular genes have been constructed with segments containing the adenovirus major late promoter, a 3' splice site from a variable region immunoglobulin gene, a DHFR cDNA, and portions of the simian virus 40 (SV40) genome. DNA-mediated transfer of these genes transformed Chinese hamster ovary DHFR- cells to the DHFR+ phenotype. Transformants contained one to several copies of the transfected DNA integrated into the host genome. Clones subjected to growth in increasing concentrations of methotrexate eventually gave rise to lines containing several hundred copies of the transforming DNA. Analysis of the DHFR mRNA produced in amplified lines indicated the following. (i) All clones utilize the adenovirus major late promoter for transcription initiation. (ii) A hybrid intron formed by the 5' splice site of the adenovirus major late leader and a 3' splice site from a variable-region immunoglobulin gene is properly excised. (iii) The mRNA is not efficiently polyadenylated at sequences in the 3' end of the DHFR cDNA but rather uses polyadenylation signals downstream from the DHFR cDNA. Three independent clones produce a DHFR mRNA containing SV40 or pBR322 and SV40 sequences, and the RNA is polyadenylated at the SV40 late polyadenylation site. Another clone has recombined into cellular DNA and apparently uses a cellular sequence for polyadenylation. Introduction of a segment containing the SV40 early polyadenylation signal into the 3' end of the DHFR cDNA gene generated a recombinant capable of transforming cells to the DHFR+ phenotype with at least a 10-fold increase in efficiency, demonstrating the necessity for an efficient polyadenylation signal. Attachment of a DNA segment containing the transcription enhancer (72-base pair repeat) of SV40 further increased the biological activity of the modular DHFR gene 50- to 100-fold.

Sequential generation of antibody diversity during B-cell development

It has become increasingly apparent that generation of and variation in antigen-combining sites of antibodies occurs sequentially during B-cell development. Allelic and isotypic exclusion mechanisms ensure that a B cell produces antibody molecules having a single kind of combining site. A major reason for evolution of mechanisms which result in asynchronous formation of functional H and L chain genes may be the need for allelic and isotypic exclusion; but this may not be the only advantage of asynchronous formation of H and L chain genes. The evolution of mechanisms causing nonjunctional somatic mutation late in B cell development - only after antigen exposure apparently - may result from the biological advantages of: (1) 'fine tuning' of the combining site; (2) a response to an anti-idiotype regulatory network, or (3) expanded memory.

The genetic control of antibody formation

Studies of the molecular biology of lymphoid cells have markedly increased our understanding of how millions of different antibodies can be synthesized by a single animal. To date, the most detailed understanding has been achieved for the mouse, primarily because of the relatively greater experimental availability of this species. These studies, as well as those involving other species, have shown that the complete genes for antibody polypeptide chains are assembled from disparate genetic elements which are originally widely separated in the genome. The assembly process itself, together with the coding information present in the germ line genetic elements, contributes to the diversity of structure (and thus combining specificities) shown by mature antibody molecules. Specifically, the diversity of structure characteristic of antibody variable regions is due to three distinct mechanisms: innate variability of germ line genes; mismatching of individual gene segments during their somatic rearrangement leading to junctional diversity; and somatic mutation in variable region genetic material during or after the rearrangement. These processes lead to the wide array of combining specificities that permit the humoral immune system of a mature animal to interact with essentially any non-self antigen which it encounters. Complex genetic rearrangements are also responsible for the class switching phenomenon long known to be characteristic of the humoral immune response. A form of homologous recombination between constant region genes, possibly mediated by specific "switching" enzymes, is now believed to be involved in this phenomenon. It is also currently believed that the restriction of gene rearrangement processes to one of the two possible chromosomes of a diploid pair in each cell is responsible for the phenomenon of allelic exclusion that has long been associated with the normal functioning of mammalian B-cells.

Construction of a modular dihydrofolate reductase cDNA gene: analysis of signals utilized for efficient expression

Dihydrofolate reductase (DHFR) modular genes have been constructed with segments containing the adenovirus major late promoter, a 3' splice site from a variable region immunoglobulin gene, a DHFR cDNA, and portions of the simian virus 40 (SV40) genome. DNA-mediated transfer of these genes transformed Chinese hamster ovary DHFR- cells to the DHFR+ phenotype. Transformants contained one to several copies of the transfected DNA integrated into the host genome. Clones subjected to growth in increasing concentrations of methotrexate eventually gave rise to lines containing several hundred copies of the transforming DNA. Analysis of the DHFR mRNA produced in amplified lines indicated the following. (i) All clones utilize the adenovirus major late promoter for transcription initiation. (ii) A hybrid intron formed by the 5' splice site of the adenovirus major late leader and a 3' splice site from a variable-region immunoglobulin gene is properly excised. (iii) The mRNA is not efficiently polyadenylated at sequences in the 3' end of the DHFR cDNA but rather uses polyadenylation signals downstream from the DHFR cDNA. Three independent clones produce a DHFR mRNA containing SV40 or pBR322 and SV40 sequences, and the RNA is polyadenylated at the SV40 late polyadenylation site. Another clone has recombined into cellular DNA and apparently uses a cellular sequence for polyadenylation. Introduction of a segment containing the SV40 early polyadenylation signal into the 3' end of the DHFR cDNA gene generated a recombinant capable of transforming cells to the DHFR+ phenotype with at least a 10-fold increase in efficiency, demonstrating the necessity for an efficient polyadenylation signal. Attachment of a DNA segment containing the transcription enhancer (72-base pair repeat) of SV40 further increased the biological activity of the modular DHFR gene 50- to 100-fold.

Multiple immunoglobulin heavy-chain gene transcripts in Abelson murine leukemia virus-transformed lymphoid cell lines

Lymphoid cells transformed by Abelson murine leukemia virus (A-MuLV) contain three classes of RNA transcripts from immunoglobulin mu genes. P mu-mRNAs (productive) correspond to the normal 2.7-kilobase (kb) membrane (mu m) and 2.4-kb secreted (mu s) mu mRNA species both in size and coding capacity and occur at approximately equal abundance in most mu-positive (pre-B-like) A-MuLV transformants. A mu-mRNAs (aberrant) generally fall into one of two categories--aberrantly small 2.3-kb mu m and 2.0-kb mu s mRNAs which encode aberrantly small mu polypeptide chains, or normal-sized, V H-containing mu RNAs which do not encode immunologically identifiable mu polypeptide chains. In one case, the latter type of A mu-mRNA was demonstrated to result from an in-phase termination codon in the D segment of the mu mRNA. Also, most, if not all, A-MuLV transformants express members of a 3.0 to 1.9-kb set of C mu-containing, but V H-negative S mu-RNAs (for sterile), the expression of which may occur simultaneously with but independently of P mu-mRNAs or A mu-mRNAs. The S mu-RNA sequences do not encode immunologically identifiable mu chains and can be produced by cells with unrearranged heavy-chain alleles, such as T-lymphocytes, although the structure of the S mu-RNAs from T-lymphoid cells appears to be different from that of B-lymphoid cell S mu-RNAs. Certain A-MuLV transformants also express gamma-RNA sequences that are probably analogous to the three different forms of mu RNA. These data support the concept that heavy-chain allelic exclusion, like that of light chains, is not mediated by control at the DNA or RNA levels but is probably a consequence of feedback control from cytoplasmic mu chains.

Normal human B cells display ordered light chain gene rearrangements and deletions

Human kappa-producing B cell lines and leukemias retain their excluded lambda light chain genes in the germ line configuration, whereas transformed lambda-producing B cells uniformly rearrange or delete their kappa genes (12). Whether the unexpected lambda gene recombinations within malignant lambda-producing B cells reflect a normal developmental process or are secondary to transformation and specific chromosomal translocations was uncertain. To resolve this issue, we purified circulating lambda-bearing B cells from a normal individual to 97% purity by using a series of negative selection steps and a final positive selection on a cell sorter. Over 95% of the collective kappa genes in these lambda B cells were no longer in their germ line form, with the majority (60%) deleted and the remainder present but in a rearranged state. The chromosomal loss of the germ line kappa genes included the joining (J kappa) segments as well as the constant (C kappa) region, yet the particular variable (V kappa) gene family studied was spared. In addition, the incidence of kappa gene deletions was higher in long-term than in freshly transformed lambda B cell lines. This implies that the deletion of aberrantly rearranged kappa genes may occur as a second event. Such a mechanism would serve to eliminate aberrant transcripts and light chain fragments that might interfere with the synthesis and assembly of effective immunoglobulin molecules. Thus, despite the nearly equal usage of kappa and lambda light chain genes in man, there appears to be a sequential order to their expression during normal B cell ontogeny in which kappa gene rearrangements precede those of lambda.

Continuing kappa-gene rearrangement in a cell line transformed by Abelson murine leukemia virus

A cell line transformed by Abelson murine leukemia virus, called PD, is capable of carrying out kappa-gene rearrangement while growing in culture. Subclones of PD have diverse kappa-gene structures, and some derivatives show evidence of continued joining activity after as many as three subclonings. Analysis of PD sublineages has shown that a rearranged chromosome can undergo secondary kappa-gene rearrangements, producing either a new rearrangement or a deletion of C kappa. Although the PD line actively rearranges its kappa genes, its rearranged heavy-chain genes show little variation, and there is no rearrangement of lambda genes. In PD subclones, DNA fragments representing the reciprocal product of kappa-gene rearrangement are often evident, and they may undergo either further rearrangement or deletion. The implications of multiple rearrangements on a single chromosome and of the maintenance of reciprocal fragments are considered in the context of a model that postulates that the V kappa and J kappa segments are not all organized in the DNA in the same transcriptional direction, leading to inversions rather than deletions during joining.

Truncated mu chain in a Burkitt lymphoma line (P3HR-1) and its fate in various hemapoietic somatic cell hybrids

Hybrids obtained by the fusion of PUT, an ouabain and TG-resistant subline of the Burkitt lymphoma(BL)-derived P3HR-1 line, with hemopoietic cells of various differentiation types were tested for their membrane and intracellular immunoglobulin expression. PUT cells carry no membrane immunoglobulin, but contained intracellular 61K mu chain and kappa chain. The PUTKO-1 hybrid, derived from the fusion of PUT with the erythroleukemia line K562 contains no detectable immunoglobulin. NAMPUT, a hybrid between PUT and the IgM-lambda-producing BL line Namalwa, synthetizes cellular mu, lambda and kappa chains, but its surface-Ig is exclusively mu-lambda. Two different mu chains could be detected, both precipitated by either anti-mu or anti-lambda sera. Immunoprecipitation with anti-kappa precipitated neither kappa nor mu. PUTRAL was derived by fusing PUT with Rael, an unusual surface-IgG-lambda-carrying BL line. In this hybrid, the ability to synthesize gamma and lambda chains has been eclipsed, but two mu chains are present: one corresponding to the truncated 61K chain of PUT, and a normal-sized 74K. Between 20 and 30% of the cells stain for surface IgM.

Somatic DNA rearrangement generates functional rat immunoglobulin kappa chain genes: the J kappa gene cluster is longer in rat than in mouse

The kappa immunoglobulin (Ig) genes from rat kidney and from rat myeloma cells were cloned and analyzed. In kidney DNA one C kappa species is observed by Southern blotting and cloning in phage vectors; this gene most likely represents the embryonic configuration. In the IR52 myeloma DNA two C kappa species are observed: one in the same configuration seen in kidney and one which has undergone a rearrangement. This somatic rearrangement has brought the expressed V region to within 2.7 kb 5' of the C kappa coding region; the rearrangement site is within the J kappa cluster which we have mapped. The rat somatic Ig rearrangement, therefore, closely resembles that seen in mouse Ig genes. In the rat embryonic fragment two J kappa segments were mapped at 2 and 4.3 kb 5' from the C kappa coding region. Therefore, the rat J kappa cluster extends over about 2.3 kb, a region much longer than the 1.4 kb of the mouse and human J kappa clusters. In the region between C kappa and the expressed J kappa of IR52 myeloma DNA, and XbaI site present in the embryonic kappa gene has been lost. A somatic mutation has therefore occurred in the intervening sequence DNA approx. 0.7 kb 3' from the V/J recombination site. Southern blots of rat kidney DNA hybridized with different rat V kappa probes showed non-overlapping sets of bands which correspond to different subgroups, each composed of 8-10 closely related V kappa genes.

Multiple immunoglobulin heavy-chain gene transcripts in Abelson murine leukemia virus-transformed lymphoid cell lines

Lymphoid cells transformed by Abelson murine leukemia virus (A-MuLV) contain three classes of RNA transcripts from immunoglobulin mu genes. P mu-mRNAs (productive) correspond to the normal 2.7-kilobase (kb) membrane (mu m) and 2.4-kb secreted (mu s) mu mRNA species both in size and coding capacity and occur at approximately equal abundance in most mu-positive (pre-B-like) A-MuLV transformants. A mu-mRNAs (aberrant) generally fall into one of two categories--aberrantly small 2.3-kb mu m and 2.0-kb mu s mRNAs which encode aberrantly small mu polypeptide chains, or normal-sized, V H-containing mu RNAs which do not encode immunologically identifiable mu polypeptide chains. In one case, the latter type of A mu-mRNA was demonstrated to result from an in-phase termination codon in the D segment of the mu mRNA. Also, most, if not all, A-MuLV transformants express members of a 3.0 to 1.9-kb set of C mu-containing, but V H-negative S mu-RNAs (for sterile), the expression of which may occur simultaneously with but independently of P mu-mRNAs or A mu-mRNAs. The S mu-RNA sequences do not encode immunologically identifiable mu chains and can be produced by cells with unrearranged heavy-chain alleles, such as T-lymphocytes, although the structure of the S mu-RNAs from T-lymphoid cells appears to be different from that of B-lymphoid cell S mu-RNAs. Certain A-MuLV transformants also express gamma-RNA sequences that are probably analogous to the three different forms of mu RNA. These data support the concept that heavy-chain allelic exclusion, like that of light chains, is not mediated by control at the DNA or RNA levels but is probably a consequence of feedback control from cytoplasmic mu chains.

Immunoglobulin heavy-chain expression and class switching in a murine leukaemia cell line

A cell line that switches from mu to gamma 2b synthesis during growth in culture uses the same VH region for both heavy chains but retains two copies of the Cmu gene. This suggests that the mu to gamma 2b class switch can occur, at least in part, by an RNA processing mechanism. Regulatory variants of this cell line lose constitutive mu-chain synthesis but simultaneously acquire lipopolysaccharide (LPS)-inducible synthesis of that chain. This co-variation is allele-specific and is correlated to a large deletion of DNA in the JH--Cmu intron.