The frequency of multiple recombination events occurring at the human Ig kappa L chain locus

Products of Ig kappa L chain gene rearrangement in a variety of human B cell samples were investigated by sequential Southern blot hybridization analysis. By application of four region-specific probes (C kappa, J kappa, U' kappa and kappa de) a complete spectrum of kappa rearrangements, including both predicted and novel products, were detected. Nearly 30% of the products detected reflect multiple recombination of the kappa locus. The kappa-deleting element was responsible for 70% of the multiple rearrangements that were detected. Interestingly, eight kappa-expressing samples exhibited rearrangement of the kappa-deleting element. The remaining multiple recombination products were characteristic of double V kappa-J kappa rearrangement. This frequency reveals that secondary V-J rearrangement may significantly contribute to the expression of kappa L chains in humans.     

Evolution of human immunoglobulin kappa J region genes

Immunoglobulin kappa chain variable region genes are assembled from two discontinuous DNA segments, a V and a J gene. The J region genes, in addition to encoding amino acid positions 96-108 of the kappa polypeptide chain, also provide sequences required for both DNA and RNA splicing reactions. For purposes of evolutionary comparison and to establish the complexity of the kappa J region locus in man, we have determined an approximately 3000 basepair nucleotide sequence in a cloned human DNA fragment that encodes the germline distinct J region segments. Significant blocks of homology have been tightly maintained between this region and an analogous segment of the mouse genome. In particular, the short sequences, GGTTTTTGT and CACTGTG, thought to be involved in V-J recombination, are the most highly conserved regions (97% homology). In addition, from heteroduplex data and computer analysis of the nucleotide sequences, it is clear that the mouse J3 sequence, a pseudogene, is not present in the human cluster. This can be explained by a duplication event in the mouse J region gene cluster that may have been the result of unequal crossing over between homologous chromosomes.     

Studies on the immunoglobulin V kappa locus in human lymphoid cell lines

DNA digests of 16 human lymphoid cell lines were studied in blot hybridization experiments with probes from V kappa genes and their immediate neighborhood as well as with single or low-copy probes from intergenic regions. The patterns were compared with those of placenta DNA digests in which the kappa genes are in the germline configuration. The differences of patterns which were detected with the first type of hybridization probes can be attributed to V kappa--J kappa rearrangements or to restriction site polymorphisms between individuals. Some of the pattern differences observed with the second type of probes can be interpreted best as arising from deletions of parts of the kappa locus. Such deletions may be individual variations but they may also be caused by the V kappa-J kappa rearrangement process. The results obtained with one particular probe which was derived from a nonduplicated part of the kappa locus allow some conclusions as to the mechanism of the V kappa--J kappa rearrangement: the genomic situation in some lymphoid cell lines can be explained by an inversion while in other cell lines clearly deletions have occurred. The observations are in agreement with the inversion-deletion mechanism of V kappa--J kappa rearrangement as proposed by Lewis et al. (1982, 1984).     

The human V kappa locus. Characterization of extended immunoglobulin gene regions by cosmid cloning

As part of the ongoing work in our laboratory on the structural organization of the human V kappa locus we screened cosmid libraries with V kappa gene probes and obtained numerous V kappa gene-containing cosmid clones. Several genomic regions of the V kappa locus were reconstructed from overlapping cosmid inserts and were extended by one step of chromosomal walking. The regions that are called Wa, Wb, Oa, Ob and Ob' comprise about 370 kb (10(3) bases) of DNA and contain 24 V kappa genes and pseudogenes. The V kappa genes belong to the three dominant subgroups (V kappa I, V kappa II, V kappa III) and are arranged to form mixed clusters with members of the different subgroups being intermingled with each other. The distances between the genes range from 1 to 15 kb. Three genes of the Wa and Wb regions that were sequenced turned out to be pseudogenes. Terminal parts of the regions Wa and Ob that do not contain V kappa genes of one of the known subgroups may represent extended spacer regions within the V kappa locus. Wa and Wb are duplicated regions located at different positions of the locus. Region Wb was found to comprise inversely repeated sections of at least 14 kb each that contain V kappa genes oriented in opposite polarity. This finding is consistent with inversion-deletion models of V-J joining; it also shows that the V kappa locus contains not only unique and duplicated but also triplicated parts. The data on the W and O regions are discussed together with those on the L regions and on other regions established in our laboratory. Although the picture of the human V kappa locus with, to date, about 70 different non-allelic V kappa genes is still incomplete, some general features with respect to the organization of the genes and the limited duplication of genomic regions have emerged.     

Targeted disruption of the porcine immunoglobulin kappa light chain locus

Inactivation of the endogenous pig immunoglobulin (Ig) loci, and replacement with their human counterparts, would produce animals that could alleviate both the supply and specificity issues of therapeutic human polyclonal antibodies (PAbs). Platform genetics are being developed in pigs that have all endogenous Ig loci inactivated and replaced by human counterparts, in order to address this unmet clinical need. This report describes the deletion of the porcine kappa (??) light chain constant (C??) region in pig primary fetal fibroblasts (PPFFs) using gene targeting technology, and the generation of live animals from these cells via somatic cell nuclear transfer (SCNT) cloning. There are only two other targeted loci previously published in swine, and this is the first report of a targeted disruption of an Ig light chain locus in a livestock species. Pigs with one targeted C?? allele (heterozygous knockout or ±) were bred together to generate C?? homozygous knockout (?/?) animals. Peripheral blood mononuclear cells (PBMCs) and mesenteric lymph nodes (MLNs) from C?? ?/? pigs were devoid of ??-containing Igs. Furthermore, there was an increase in lambda (??) light chain expression when compared to that of wild-type littermates (C?? +/+). Targeted inactivation of the Ig heavy chain locus has also been achieved and work is underway to inactivate the pig lambda light chain locus.     

Hypersensitive site 4 of the human beta globin locus control region.

The Locus Control Region (LCR) of the human beta globin gene domain is defined by four erythroid-specific DNasel hypersensitive sites (HSS) located upstream of this multigene cluster. The LCR confers copy number dependent high levels of erythroid specific expression to a linked transgene, independent of the site of integration. To assess the role of the individual hypersensitive sites of the LCR, we have localized HSS4 to a 280bp fragment that is functional both in murine erythroleukaemia (MEL) cells and in transgenic mice. This fragment coincides with the major area of hypersensitivity 'in vivo' and contains a number of DNasel footprints. Bandshift analysis shows that these footprints correspond to binding sites for the erythroid specific proteins GATA1 and NF-E2 and a number of ubiquitous proteins, including jun/fos, Sp1 and TEF2.     

A complex translocation at the murine kappa light-chain locus.

We have previously reported that a segment of DNA from a murine plasmacytoma comprises DNA from three chromosomes, the immunoglobulin kappa light-chain locus on chromosome 6, the S mu locus on chromosome 12, and a region on chromosome 15. We now report that the reciprocal product contains DNA from only the kappa locus and chromosome 15 and not from S mu. We conclude that a complex series of events, including both a transposition of DNA and a translocation between chromosomes, generated these imperfect reciprocal products.     

Assignment of human phosphoribosylglycinamide synthetase locus to region 21q221

Summary The enzymatic activity of phosphoribosylglycinamide synthetase (GARS) has been studied in several cases of partial monosomies and full and partial trisomies 21. An excess of GARS activity was found in regular trisomy 21 with a trisomy 21/normal ratio equal to 1.55. A 0.99 ratio was found in 21q2121pter monosomy; a 0.54 ratio was found in 21qter21q22 monosomy; a 0.88 ratio, in 21q2121pter trisomy, and a 1.46 ratio, in 21q22.1 trisomy. Consequently, the GARS gene locus, assigned to chromosome 21, could be localized in subband 21q22.1.     

Long-distance control of origin choice and replication timing in the human beta-globin locus are independent of the locus control region

DNA replication in the human beta-globin locus is subject to long-distance regulation. In murine and human erythroid cells, the human locus replicates in early S phase from a bidirectional origin located near the beta-globin gene. This Hispanic thalassemia deletion removes regulatory sequences located over 52 kb from the origin, resulting in replication of the locus from a different origin, a shift in replication timing to late S phase, adoption of a closed chromatin conformation, and silencing of globin gene expression in murine erythroid cells. The sequences deleted include nuclease-hypersensitive sites 2 to 5 (5'HS2-5) of the locus control region (LCR) plus an additional 27-kb upstream region. We tested a targeted deletion of 5'HS2-5 in the normal chromosomal context of the human beta-globin locus to determine the role of these elements in replication origin choice and replication timing. We demonstrate that the 5'HS2-5-deleted locus initiates replication at the appropriate origin and with normal timing in murine erythroid cells, and therefore we conclude that 5'HS2-5 in the classically defined LCR do not control replication in the human beta-globin locus. Recent studies also show that targeted deletion of 5'HS2-5 results in a locus that lacks globin gene expression yet retains an open chromatin conformation. Thus, the replication timing of the locus is closely correlated with nuclease sensitivity but not globin gene expression.     

The structural repertoire of the human V kappa domain.

In humans, the gene for the V kappa domain is produced by the recombination of one of 40 functional V kappa segments and one of five functional J kappa segments. We have analysed the sequences of these germline segments and of 736 rearranged V kappa genes to determine the repertoire of main chain conformations, or canonical structures, they encode. Over 96% of the sequences correspond to one of four canonical structures for the first antigen binding loop (L1) and one canonical structure for the second antigen binding loop (L2). Junctional diversity produces some variation in the length of the third antigen binding loop (L3) and in the identity of residues at the V kappa-J kappa join. However, this is limited and 70% of the rearranged sequences correspond to one of three known canonical structures for the L3 region. Furthermore, we show that the canonical structures selected during the primary response are conserved during affinity maturation: the key residues that determine the conformations of the antigen binding loops are unmutated or undergo conservative mutation. The implications of these results for immune recognition are discussed.     

Evolutionary relationship between human and mouse immunoglobulin kappa light chain variable region genes

Similar to the Igh-V multigene family, the human or mouse Igk-V repertoirer is a distorted continuum of homologous genes that may be grouped into families displaying >80% nucleic acid sequence similarity among their members. systematic interspecies sequence comparisons reveal that most human Igk-V gene families exhibit clear homology to mouse Ogk-V families (sequence similarity >74%). A hypothetical phylogenetic tree of Igk-V genes predicts that a minimum of seven Igk-V genes/families predate mammalian radiation. In two cases, several interrelated mouse Igk-V families exhibit phylogenetic equidistance with just one human Igk-V family, implying a more pronounced divergence for the elevated number of Igk-V gene families in the mouse. Mouse-human Igk-V comaprisons, moreover, illustrate how expansion, contraction, and perhaps deletion of Igk-V gene families shape the Igk-V repertoire during mammalian evolution.