3' enhancers hs3b/hs4 are dispensable for deregulation in mouse plasmacytomas with T(12;15) translocations.

-deregulating T(12;15) chromosomal translocations are the hallmark cytogenetic abnormalities of murine plasmacytomas (PCTs). In most PCTs, the immunoglobulin heavy chain () locus is broken between the enhancer and the 3' regulatory region (), making the latter the major candidate for orchestrating deregulation. To elucidate the role of the in tumorigenesis, we induced PCTs in transgenic mice deficient for the major enhancer elements, and (hs3b-4).

Transgenes of the mouse immunoglobulin heavy chain locus, lacking distal elements in the 3' regulatory region, are impaired for class switch recombination.

The immunoglobulin heavy (H) chain class switch is mediated by a deletional recombination event between µ and γ, α, or ε constant region genes. This recombination event is upregulated during immune responses by a regulatory region that lies 3' of the constant region genes. We study switch recombination using a transgene of the entire murine H chain constant region locus.

Oncogenic Myc translocations are independent of chromosomal location and orientation of the immunoglobulin heavy chain locus.

Many tumors are characterized by recurrent translocations between a tissue-specific gene and a proto-oncogene. The juxtaposition of the Ig heavy chain gene and Myc in Burkitt's lymphoma and in murine plasmacytoma is a classic example. Regulatory elements within the heavy chain constant region locus are required for Myc translocation and/or deregulation.

Enhancement of antibody class-switch recombination by the cumulative activity of four separate elements.

Class-switch recombination of Ab isotype is mediated by a recombinational DNA deletion event and must be robustly upregulated during Ag-driven differentiation of B cells. The enhancer region 3' of the Cα gene is important for the upregulation of switch recombination. Using a transgene of the entire H chain C region locus, we demonstrate in this study that it is the four 3' enhancer elements themselves (a total of 4.

Excessive amounts of mu heavy chain block B-cell development.

Antigen-independent B-cell development occurs in several stages that depend on the expression of Ig heavy and light chain. We identified a line of mice that lacked mature B cells in the spleen. This mouse line carried approximately 11 copies of a transgene of the murine heavy chain constant region locus, and B-lineage cells expressed excessive amounts of the intracellular μ heavy chain.

Switch recombination and somatic hypermutation are controlled by the heavy chain 3' enhancer region.

Both class switch recombination (CSR) and somatic hypermutation (SHM) require transcription and the trans-acting factor activation-induced cytidine deaminase (AID), and must be up-regulated during antigen-dependent differentiation of B lymphocytes. To test the role of the heavy chain 3' enhancers in both CSR and SHM, we used a BAC transgene of the entire heavy chain constant region locus. Using Cre-loxP recombination to delete a 28-kb region that contains the four known 3' heavy chain enhancers, we isolated lines of BAC transgenic mice with an intact heavy chain locus and paired lines in the same chromosomal insertion site lacking the 3' enhancers.

Induced expression of murine gamma2a by CD40 ligation independently of IFN-gamma.

IgG2a, with gamma2a H chains, is important for protection against viruses and other intracellular pathogens. Although a large portion of IgG2a expression is dependent upon IFN-gamma, some germline transcription and switch recombination to the murine gamma2a H chain gene expression are independent of IFN-gamma. We found that agonistic anti-CD40 Abs injected into IFN-gamma-deficient mice induce a > 200-fold increase in the amount of serum Ig2a, while other Ig isotypes are increased by 16-fold or less.

The 3' end of the heavy chain constant region locus enhances germline transcription and switch recombination of the four gamma genes.

The switch in immunoglobulin (Ig) heavy chain class is preceded by germline transcription and then mediated by a DNA recombination event. To study germline transcription and class switch recombination we used transgenic mice with a 230-kilobase bacterial artificial chromosome that included a rearranged VDJ gene and the entire heavy chain constant region locus. In addition to several lines with intact transgenes, we identified two lines in which the heavy chain locus transgene lacked Calpha and everything 3' of it, including the regulatory elements HS3a, HS1-2, HS3b, and HS4.

Receptors and counterreceptors involved in NK-B cell interactions.

In addition to the well-documented effect of NK cells on B cell differentiation via their ability to secrete IFN-gamma, NK cells can also induce, via direct cell-cell interactions, germline transcripts (Igamma2a) necessary for switch recombination to IgG2a. Analysis of the ligand-receptor pairs that could be involved in this induction revealed that the expression of CD48 on B cells is crucial for the induction. NK cells from mice with targeted deletions of either the CD2 or the CD244 gene, both of which encode ligands for CD48, are compromised in their ability to induce B cell Igamma2a expression.

Germline transcription and switch recombination of a transgene containing the entire H chain constant region locus: effect of a mutation in a STAT6 binding site in the gamma 1 promoter.

The switch (S) in H chain class is preceded by germline transcription and then mediated by a DNA recombination event. One of the impediments toward understanding the mechanism is the lack of a system in which a recombinant DNA molecule undergoes cytokine-regulated class S recombination. To study class S recombination, we used transgenic mice with a 230-kb bacterial artificial chromosome that included a rearranged VDJ gene and the entire murine H chain constant region locus.

A murine model of Nijmegen breakage syndrome.

Nijmegen breakage syndrome (NBS) is a rare autosomal recessive disorder characterized by microcephaly, immunodeficiency, and predisposition to hematopoietic malignancy. The clinical and cellular phenotypes of NBS substantially overlap those of ataxia-telangiectasia (A-T). NBS is caused by mutation of the NBS1 gene, which encodes a member of the Mre11 complex, a trimeric protein complex also containing Mre11 and Rad50.

A DNase I hypersensitive site near the murine gamma1 switch region contributes to insertion site independence of transgenes and modulates the amount of transcripts induced by CD40 ligation.

Several cis-acting elements regulate the expression of germline transcripts of heavy chain constant region genes and their subsequent switch recombination. To study such elements in the murine gamma1 gene, we have utilized a transgenic approach. In this study we focused on a DNase I hypersensitive site (termed 'Site II') that lies about 2 kb 3' of the gamma1 promoter region and I exon, just 5' to the gamma1 switch region.

Cutting edge: IFN-gamma regulated germline transcripts are expressed from gamma2a transgenes independently of the heavy chain 3' enhancers.

Several results indicate that transcriptional enhancers lying 3' of the Calpha gene regulate RNA expression and switch recombination of heavy chain genes. To investigate this regulation we prepared transgenic mice with a 10.5-kb transgene that included the germline form of the murine gamma2alpha gene, including promoter, I, S, and C regions.

Germline transcription and recombination of a murine VDJmudeltagamma1 transgene.

To investigate the regulation of Ig switch recombination, we have constructed mice with a 56 kb VDJmudeltagamma1 transgene. This transgene included an anti-nitrophenyl VDJ segment, Smu, Cmu, Cdelta, Igamma1, Sgamma1, Cgamma1 and the Cgamma1 membrane exons from the murine Igh(a) haplotype. Two founder lines were produced, with very similar characteristics.

Potential regulatory elements for germline transcription in or near murine Sgamma1.

We were interested in identifying cis-acting elements that regulate germline transcription and switch recombination of heavy chain genes. The murine gamma1 heavy chain gene includes two DNase I hypersensitive sites, which may represent protein:DNA interactions important for germline transcription and switch recombination. One DNase hypersensitive site is at the promoter/I exon boundary (termed 'Site I'); we localized a second pair of DNase hypersensitive sites to just 5' of the Sgamma1 region (termed 'Site II').

Interleukin-12 acts as an adjuvant for humoral immunity through interferon-gamma-dependent and -independent mechanisms.

Interleukin-12 (IL-12) is a pivotal cytokine that has dramatic effects on cell-mediated immunity. It is now becoming increasingly recognized that IL-12 also strongly controls humoral immunity. We have investigated the mechanism by which IL-12 induces alterations in antibody isotype expression by determining the influence of IL-12 on in vitro immunoglobulin (Ig) production in polyclonally activated murine spleen cell cultures.

gamma1 heavy chain transgenes are responsive to IFN-gamma repression and CD40 ligation.

The cis-acting elements that regulate production of germ-line transcripts from Ig heavy chain genes and subsequent switch recombination to those genes are poorly defined. We reported that a 17-kb transgene that includes Igamma1, Sgamma1, and Cgamma1 is regulated for germ-line transcription like the endogenous gamma1 gene. Transcripts from such transgenes are expressed only in B cells treated with both LPS and IL-4, and not in B cells treated with LPS alone or in thymocytes or nonlymphoid tissues.

Enhancement of humoral immunity by interleukin-12.

We have found that IL-12 treatment of mice leads to long-lasting enhancement in production of most antibody isotypes in conventional B-cell responses. Initial recruitment of new B-cell clones into the response is mediated by IFN-gamma, but subsequent enhancement of Ig secretion appears to be IFN-gamma-independent. We have further found that activated B cells can directly bind IL-12.

The gamma 1 heavy chain gene includes all of the cis-acting elements necessary for expression of properly regulated germ-line transcripts.

The regulation of heavy chain switch recombination and the production of germ-line transcripts are highly correlated. IL-4 induces the production of murine gamma 1 germ-line transcripts, and much, if not all, of the regulation is transcriptional. We have investigated the cis-acting elements involved in the regulation of expression of germ-line transcripts by preparing transgenes with the gamma 1 locus.

Antigen receptor cross-linking differentially regulates germ-line CH ribonucleic acid expression in murine B cells.

Cytokines are believed to regulate Ig class switching, in part, through selective modulation of germ-line constant heavy (CH) gene transcription. B cell activators such as LPS or activated T cell membranes also influence germ-line CH RNA expression in the absence of exogenous cytokines. In this report we determined whether multivalent Ag receptor cross-linking, utilizing dextran-conjugated anti-IgD Abs (alpha delta-dex), could also regulate germ-line CH RNA expression.

Germline transcripts of the murine immunoglobulin gamma 2a gene: structure and induction by IFN-gamma.

The switch in expression by B cells from IgM to IgG, IgE, or IgA is accomplished by a DNA deletion. The deletion event is regulated, in that specific cytokines direct the B cell to switch to one, or sometimes two, of the six possible murine heavy chain genes. Prior to switch recombination, cytokine treatment also induces the transcription of the constant, switch, and upstream regions of the targeted heavy chain.

mnd2: a new mouse model of inherited motor neuron disease.

The autosomal recessive mutation mnd2 results in early onset motor neuron disease with rapidly progressive paralysis, severe muscle wasting, regression of thymus and spleen, and death before 40 days of age. mnd2 has been mapped to mouse chromosome 6 with the gene order: centromere-Tcrb-Ly-2-Sftp-3-D6Mit4-mnd2-D6Mit 6, D6Mit9-D6Rck132-Raf-1, D6Mit11-D6Mit12-D6Mit14, mnd2 is located within a conserved linkage group with homologs on human chromosome 2p12-p13. Spinal motor neurons of homozygous affected animals are swollen and stain weakly, and electromyography revealed spontaneous activity characteristic of muscle denervation.