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B B Blomberg

Publications and source records attributed to B B Blomberg.

8 recordsLinked to original sources
PubMed1997

The 14.1 surrogate light chain promoter has lineage- and stage-restricted activity.

The 14.1 surrogate light chain protein is expressed on human pre-B lymphocytes in association with Vpre-B and the mu Ig heavy chain to form the pre-B receptor. The 14.1 chain has also been called the lambda (lambda)-like (LL) protein and is homologous to murine lambda5. The 14.1(IGLL1) gene is expressed in a lineage- and stage-restricted manner. To understand the molecular mechanism of the 14.1 gene tissue- and stage-specific expression, we analyzed the 5'-flanking region and characterized the promoter for this gene. In this report, we identify two DNase I-hypersensitive sites located at 2.6 kilobases (HSS 1) and 0.2 kilobases (HSS 1) upstream of 14.1 exon 1. These hypersensitive sites are present in pre-B lymphocyte cell lines, but absent in mature B and T cell lines. We have used RNase protection analysis to localize the 5' major transcriptional start site and rapid amplification of 5' cDNA ends to identify multiple start sites within the TATA-less, GC-rich 14.1 promoter. The region encompassing HSS 2 was analyzed for promoter activity. Transfection of cell lines with a series of truncated segments of the 5' flanking region linked to the luciferase reporter gene revealed that the 14.1 promoter is lineage- and stage-specific, and we localized this activity to positions +150 to +227 relative to the 5' major transcriptional start site.

B-Lymphocytes↗
PubMed1995

Identification and localization of a developmental stage-specific promoter activity from the murine lambda 5 gene.

The lambda 5 protein is expressed in pre-B cells in association with VpreB and mu-heavy chains, and is critical for differentiation to the B cell stage. Pre-B cell-specific expression of the lambda 5 and VpreB genes is regulated at the level of transcription initiation. In this report, we have identified several DNase l-hypersensitive sites 2.5- to 6.0-kb downstream of the lambda 5 gene, which are present in the pre-B cell line 70Z/3, but not in the myeloma cell line j558L. These sites, however, were shown to have no transcriptional enhancer activity as measured by transient transfection. Enhancer activity was identified within a 361-bp fragment (-296 to +65, where +1 is the major 5' transcription initiation site) upstream of the mouse lambda 5 gene. This activity is orientation and position independent, and is also tissue and differentiation stage specific (active in pre-B but not B and T cells). Deletion constructs indicate that three adjacent areas (-210 to -169, -153 to -64, and -64 to -22) are all necessary for enhancer activity. Pre-B cell-specific promoter activity was shown to reside within the -219 to +109 fragment. Basal promoter activity resides within the -64 to +109 fragment, but is not tissue specific or stage specific. A negative element within the -101 to -64 region is active in all lymphoid cell lines tested and therefore cannot by itself be responsible for the tissue and stage specificity. The data indicate that the elements responsible for the enhancer activity (-210 to -22) are part of the lambda 5 gene promoter and likely confer the tissue and stage specificity via positive elements within the -210 to -22 region.

Animals↗
PubMed1993

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.

Amino Acid Sequence↗
PubMed1991

Identification and localization of an enhancer for the human lambda L chain Ig gene complex.

A strong transcriptional enhancer was identified for the human lambda L chain Ig gene complex. Enhancer activity was measured by activation of the chloramphenicol acetyl transferase (CAT) gene in a transient assay using both mouse and human B lymphoid cell lines. The smallest fragment identified with enhancer activity was 111 bp, which resides 11.7 kb downstream (3') of C lambda 7, a constant region gene we have recently isolated and identified as functional in the human population. Enhancer activity is orientation independent, tissue specific (active in all B cell lines tested and not in a T cell line), and independent of NF kappa B, similar to the mouse lambda enhancers recently reported. The human lambda enhancer is active in both mouse and human B cell lines; interestingly, the mouse lambda enhancers are active in mouse lines but not in a human B cell line. DNA sequence comparison of the mouse and human lambda enhancers indicates a higher degree of homology (average of 72.5%) within the 111-bp enhancer core region identified here than for the remaining flanking sequence compared (average of 42%). This discovery of an enhancer in the human lambda locus (HuE lambda), which is clearly distinct from that of the H and L chain loci, will help to determine the mechanism for the ordered expression and rearrangement of these gene complexes in B cell ontogeny. The presence of only one enhancer in the human C lambda complex 3' of all the C genes suggests that the evolutionary duplication of the L locus differs from that seen in mouse; in mouse the duplication unit was JCJC-enhancer, whereas the human JC lambda s duplicated without the enhancer.

Animals↗
PubMed1989

Nuclear disintegration of target cells by killer B lymphocytes from tumor-bearing mice.

Normal murine B lymphocytes are not known to be effectors of the Fc receptor-mediated, antibody-dependent cellular cytotoxicity (ADCC). In contrast, we report here that highly purified splenic B cells from mammary tumor-bearing mice develop the potential of lysing antibody-coated target cells. These lymphocytes are characterized by being G-10 nonadherent, nylon wool adherent, sIg+, FcR+, Thy 1.2-, asialo GM1-, and the immunoglobulin heavy-chain genes of both chromosomes are rearranged. The lytic reaction is characterized by a noninterdigitating binding and by the appearance of endocytotic vesicles in the target cells. Nuclear disintegration occurs 18 h after initial effector-target cell conjugate formation. At such time, only minor cytoplasmic membrane alterations are evident. The emergence of killer B cells in tumor-bearing hosts indicates that all lymphoreticular cell types bearing Fc receptors are capable of mediating ADCC.

Animals↗
PubMed1988

Intergenic exchange maintains identity between two human lambda light chain immunoglobulin gene intron sequences.

Evidence for gene conversion or unequal double crossover in the human lambda light chain immunoglobulin locus is presented. The high level of J2C2-J3C3 intron cross-hybridization, the identity of the J lambda and J lambda 3 coding and intron sequences, the presence of multiple base differences between the C lambda 2 and C lambda 3 coding regions, and the presence of both the unconverted and converted alleles in the normal gene pool, suggest that a recombinational event has resulted in the conversion of the J lambda 2 coding and intron sequences to those of J lambda 3 and its flanking sequences. Intergenic exchanges, such as the one described here, may provide a mechanism to maintain sequence homogeneity and functionality among the duplicated members of the human lambda gene family.

Amino Acid Sequence↗
PubMedDate not supplied

The human lambda immunoglobulin enhancer is controlled by both positive elements and developmentally regulated negative elements.

We have recently reported the localization of the first transcriptional enhancer in the human lambda (lambda) immunoglobulin light chain locus. Enhancer activity was contained on a 1.2 kb SstI fragment, with partial activity retained on a core 111 bp PstI-SstI fragment. This enhancer is located 11.7 kb downstream of C lambda 7, the most 3' lambda constant region gene. Using a chloramphenicol acetyl transferase (CAT) assay system, we have now determined the boundaries of the complete enhancer and find it is two- to four-fold as active as the core fragment in both pre-B and B cell lines. Interestingly, a larger fragment, containing the complete enhancer as well as 5' and 3' flanking sequences has four- to eight-fold reduced activity when tested in pre-B cell lines, but full activity in B cell lines. This suggests the presence of developmentally regulated negative elements flanking the human lambda enhancer which prevent or reduce its activity at a developmentally incorrect time. By using in vivo footprinting we have begun to examine the protein interactions within this enhancer in a more physiologically relevant manner and have identified motifs which are shared with the murine lambda enhancers, as well as motifs unique to the human lambda enhancer.

Animals↗