Activation of immunoglobulin control elements in transgenic mice

Properties of hybridomas generated by spleen cells of IL-4- and IL-13-knockout mice

Interleukin-4 (IL-4)- and IL-13-knockout mice were immunized with murine recombinant IL-4 or IL-13, and spleen cells were fused with P3X63-Ag8.653 myeloma cells. Selection of the antigen-positive hybridomas was fulfilled in the presence of IL-6 containing thymic stroma cell supernatant (TSS). All of the selected anti- IL-4- and anti-IL-13-specific hybridoma clones (eight and 10, respectively) required the presence of TSS (0.5-2.5%) for their cloning, stable growth in large-scale cultures, and production of monoclonal antibodies (MAbs). Several of the anti-IL-4-specific clones were adapted to growth without TSS. However, the loss of antibody-secreting capacity in the process of adaptation to TSS-free growth was detected. The data demonstrate that cytokine-deficient mice technology can be used for generation of MAbs to autologous cytokines.

Cytokine-deficient mice as a model for generation of autologous anti-cytokine monoclonal antibodies

The possibility of inducing immune responses to murine interleukin-4 (IL-4) and IL-13 and generating anti-cytokine monoclonal antibodies (mAbs) was studied in IL-4- and IL-13-knockout mice. The minimal doses of IL-4 or IL-13 that could induce significant anti-cytokine responses with titers of 5000-10,000 were 20 microg per injection with the total doses of 100 microg. The highest titers in a range of 20,480-40,960 were achieved by triple immunization of IL-13-knockout mice with 30 microg of IL-13 per injection. Anti-IL-4 mAbs were generated at an antibody serum titer about 400; however, only 0.5% of primary hybridoma clones were anti-IL-4-positive. Anti-IL-13 cell fusions were successful at titers of 20,480 and 40,960 with 50% of the primary clones positive. Both hybridomas secreted low-affinity IgMkappa mAbs and were IL-6-dependent. These data demonstrate that IL-4- and IL-13-deficient mice may develop high polyclonal immune responses to "syngeneic" murine cytokines but fail to generate high-affinity mAbs at the tested conditions.

Effect of the Emu IgH enhancer on expression of a GFP reporter gene in transfected B cells and transgenic mice

Transgenic mice were generated to identify the first B cell maturation stage showing expression of an immunoglobulin transcriptional enhancer element (Emu)-green fluorescent protein (GFP) transgene, and to check the ability of the Emu element to behave as a locus control region. Flow cytometry experiments indicated that stably transfected 18-81 cells (a murine pre-B cell line) and A20 cells (a murine IgM(+) B cell line) maintained a constant GFP expression for several months in culture. Contrasting with in vitro results, flow cytometry experiments did not highlight GFP(+) B cells in spleen and bone marrow of Emu-GFP transgenic mice and no GFP transcripts were detected by Northern blot and reverse transcriptase polymerase chain reaction analysis. In transgenic mice, the lack of GFP expression seemed related to transgene DNA methylation occurring within all organs. Our results show dramatic differences for expression of the Emu-GFP transgene in vitro and in vivo. Despite that Emu was reported to efficiently control the in vivo expression of other associated transgenes, it is not sufficient to sustain GFP expression in transgenic mice and to counteract developmental silencing programs that occur in the embryo.

Cux/CDP homeoprotein is a component of NF-muNR and represses the immunoglobulin heavy chain intronic enhancer by antagonizing the bright transcription activator

Nuclear matrix attachment regions (MARs) flanking the immunoglobulin heavy chain intronic enhancer (Emu) are the targets of the negative regulator, NF-muNR, found in non-B and early pre-B cells. Expression library screening with NF-muNR binding sites yielded a cDNA clone encoding an alternatively spliced form of the Cux/CDP homeodomain protein. Cux/CDP fulfills criteria required for NF-muNR identity. It is expressed in non-B and early pre-B cells but not mature B cells. It binds to NF-muNR binding sites within Emu with appropriate differential affinities. Antiserum specific for Cux/CDP recognizes a polypeptide of the predicted size in affinity-purified NF-muNR preparations and binds NF-muNR complexed with DNA. Cotransfection with Cux/CDP represses the activity of Emu via the MAR sequences in both B and non-B cells. Cux/CDP antagonizes the effects of the Bright transcription activator at both the DNA binding and functional levels. We propose that Cux/CDP regulates cell-type-restricted, differentiation stage-specific Emu enhancer activity by interfering with the function of nuclear matrix-bound transcription activators.

Identification and functional characterization of a highly conserved sequence in the intron of the kappa light chain gene

A highly conserved 225 bp sequence was identified within the J-C intron of the murine kappa light-chain immunoglobulin gene and its nuclear protein-binding and regulatory function were examined. The binding of nuclear proteins to this fragment was found to reflect the differentiation state of the cell used to prepare the nuclear extracts and three different complexes are seen with this fragment: CI, CII and CIII. CIII is present in all cell types. CI is present in fibroblasts, T cells and early B cells, but not mature B cells. Moreover, nuclear extracts prepared from the early pre-B cell line, 70Z/3, that was treated with agents which activate kappa gene transcription have a reduced ability to form CI. Therefore, the presence of CI correlates with the absence of kappa gene transcription. CII is present in all stages of B cell development, however its composition changes with B cell maturation. Contained within the 225 bp element is the ets family-binding motif GGAA and the B-cell-and-macrophage-specific family member, PU.1 binds this sequence and participates in CII formation. The 225 bp fragment showed modest augmentation of expression in CAT reporter constructs containing the heavy chain enhancer (HCE) and a light chain promoter in the plasmacytoma, S194, and uninduced 70Z/3 cells and mediated a small but reproducible response to IFN-gamma in 70Z/3 cells. Thus, the 225 bp sequence contained within the J-C intron may function as a regulatory element for kappa light chain gene expression.

Mouse interleukin-2 receptor alpha gene expression. Delimitation of cis-acting regulatory elements in transgenic mice and by mapping of DNase-I hypersensitive sites

The alpha chain of the interleukin-2 receptor (IL-2R alpha) is a key regulator of lymphocyte proliferation. To analyze the mechanisms controlling its expression in normal cells, we used the 5'-flanking region (base pairs -2539/+93) of the mouse gene to drive chloramphenicol acetyltransferase expression in four transgenic mouse lines. Constitutive transgene activity was restricted to lymphoid organs. In mature T lymphocytes, transgene and endogenous IL-2R alpha gene expression was stimulated by concanavalin A and up-regulated by IL-2 with very similar kinetics. In thymic T cell precursors, IL-1 and IL-2 cooperatively induced transgene and IL-2R alpha gene expression. These results show that regulation of the endogenous IL-2R alpha gene occurs mainly at the transcriptional level. They demonstrate that cis-acting elements in the 5'-flanking region present in the transgene confer correct tissue specificity and inducible expression in mature T cells and their precursors in response to antigen, IL-1, and IL-2. In a complementary approach, we screened the 5' end of the endogenous IL-2R alpha gene for DNase-I hypersensitive sites. We found three lymphocyte specific DNase-I hypersensitive sites. Two, at -0.05 and -5.3 kilobase pairs, are present in resting T cells. A third site appears at -1.35 kilobase pairs in activated T cells. It co-localizes with IL-2-responsive elements identified by transient transfection experiments.

Lymphocyte expression in transgenic trout by mouse immunoglobulin promoter/enhancer

Two groups of transgenic rainbow trout (Oncorhynchus mykiss, Walbaum) have been produced and compared. One group harbored the reporter gene of chloramphenicol acetyltransferase (CAT) associated with mouse immunoglobulin (Ig) promoter/enhancer (pUCL-CAT-E). The other group carried the same reporter gene under the control of the cytomegalovirus promoter/enhancer (pCMV-CAT). Slot blot analysis of DNA from blood cells and other tissues from pUCL-CAT-E fish showed variation of copy number between the major tissues but not between red and white blood cells. Southern blot analysis indicated that multiple copies organized in concatemers were incorporated into the genome. The pCMV-CAT fish had a pronounced expression of CAT in both white and red blood cells. In contrast, activity of CAT was found in the white blood cells of all pUCL-CAT-E fish but not in their red blood cells. Expression in white blood cells was found preferentially in sIg+ cells, indicating that B cells are the major expressors. High expression was also found in spleen and kidney, but the activity found in thymocytes was equal to the background level. Analysis of some major tissues showed high white blood cell expression associated with low tissue expression, except that liver (known to contain lymphoid tissue in fish) was higher. Thus the regulatory elements of the Ig gene from mouse induce a tissue-specific expression in fish.