Immunoglobulin lambda locus

Abstract: B-cell-specific enhancers have been identified in the immunoglobulin lambda locus 3' of each constant-region cluster. These enhancers contain two distinct domains, lambda A and lambda B, which are essential for enhancer function. lambda B contains a near-consensus binding site for the Ets family of transcription factors. In this study, we have identified a B-cell-specific protein complex which binds the lambda B motif of the lambda 2-4 enhancer in vitro and appears necessary for the activity of the enhancer in vivo, since mutations in lambda B which prevent this interaction also eliminate enhancer function. This complex contains PU.1, a member of the Ets family, and a transcriptional activator whose expression is restricted to cells of the hematopoietic system with the exception of T lymphocytes. In addition, it contains a factor which binds specifically to a region adjacent to the PU.1 binding site. This factor cannot bind lambda B autonomously but appears to require interaction with the PU.1 protein to stabilize its association with the DNA. This complex may be identical or related to the PU.1/NF-EM5 complex which interacts with a homologous DNA element in the immunoglobulin kappa 3' enhancer.

Abstract: As a first step toward defining the elements necessary for lambda immunoglobulin gene regulation, DNase I hypersensitive sites were mapped in the mouse lambda locus. A hypersensitive site found 15.5 kb downstream of C lambda 4 was present in all the B-cell but not in the T-cell lines tested. This site coincided with a strong B-cell-specific transcriptional enhancer (E lambda 2-4). This novel enhancer is active in myeloma cells, regardless of the status of endogenous lambda genes, but is inactive in a T-cell line and in fibroblasts. The enhancer E lambda 2-4 functions in the absence of the transcription factor NF kappa B, which is necessary for kappa enhancer function. No evidence could be found for NF kappa B binding by this element. Rearrangement of V lambda 2 to JC lambda 3 or JC lambda genes deletes E lambda 2-4; however, a second strong enhancer was found 35 kb downstream of C lambda 1, which cannot be eliminated by lambda gene rearrangements. The second lambda enhancer (E lambda 3-1) is 90% homologous to the E lambda 2-4 sequence in the region determined to comprise the active enhancer and likewise lacks the consensus binding site for NF kappa B. The data support a model for the independent activation of kappa and lambda gene expression based on locus-specific regulation at the enhancer level.

Abstract: The variant translocation t(8;22) in Burkitt's lymphoma (BL) cells joins band q24 of chromosome 8 distal to the proto-oncogene MYC to the immunoglobulin lambda locus. The distribution of breakpoints on chromosome 8 of 11 cell lines with t(8;22) has been investigated by in situ fluorescence hybridization and pulsed-field gel electrophoresis. We show that these chromosomal breakpoints generally fall within a region of about 300 kb 3' of MYC and that at least 8 out of 11 affect the previously characterized transcriptional unit PVT1. Comparable results were obtained in earlier experiments analyzing the variant t(2;8). Recently, in a series of BL cells carrying t(8;14), breakpoints upstream of MYC have been described at a similar distance. Therefore, our results suggest that deregulation of MYC by the immunoglobulin loci can occur at a distance of up to about 350 kbp of MYC.

Abstract: We have characterized the organization, complexity, and expression of the porcine (Sus scrofa domestica) immunoglobulin lambda (IGL) light chain locus, which accounts for about half of antibody light chain usage in swine, yet is nearly totally unknown. Twenty-two IGL variable (IGLV) genes were identified that belong to seven subgroups. Nine genes appear to be functional. Eight possess stop codons, frameshifts, or both, and one is missing the V-EXON. Two additional genes are missing an essential cysteine residue and are classified as ORF (open reading frame). The IGLV genes are organized in two distinct clusters, a constant (C)-proximal cluster dominated by genes similar to the human IGLV3 subgroup, and a C-distal cluster dominated by genes most similar to the human IGLV8 and IGLV5 subgroups. Phylogenetic analysis reveals that the porcine IGLV8 subgroup genes have recently expanded, suggesting a particularly effective role in immunity to porcine-specific pathogens. Moreover, expression of IGLV genes is nearly exclusively restricted to the IGLV3 and IGLV8 genes. The constant locus comprises three tandem cassettes comprised of a joining (IGLJ) gene and a constant (IGLC) gene, whereas a fourth downstream IGLJ gene has no corresponding associated IGLC gene. Comparison of individual BACs generated from the same individual revealed polymorphisms in IGLC2 and several IGLV genes, indicating that allelic variation in IGLV further expands the porcine antibody light chain repertoire.