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J Schwager

Publications and source records attributed to J Schwager.

32 records · Page 2Linked to original sources
PubMed1989

Genetic basis of the antibody repertoire in Xenopus: analysis of the Vh diversity.

The Xenopus IgH locus includes various variable (VH) families, several putative diversity (DH) and at least seven joining (JH) elements, but--although structurally very similar to the mammalian locus--it contributes to a restricted antibody repertoire. The largest three VH families contain 15-30 VH elements which are interspersed at the VHI-VHII and VHII-VHIII boundaries. Twenty-nine genomic and eight expressed VH regions have been sequenced. Each VH family has distinct promoter elements with up to three octamers (ATGCCTAAAT) in either orientation. The incidence of pseudogenes ranges from less than 15% in VHI and VHII to approximately 50% in VHIII, consistent with their relative expression. CDR1 and CDR2 show low overall diversity with nucleotide divergence limited to parts of the CDRs. Randomly selectedly VH elements share CDR1 and CDR2, in some cases also with expressed VH regions. Thus, the complexity of VH elements is not maximal. Patterns of sequence similarities or identities indicate recombination or gene conversion events; sets of direct and inverted repeats flank the sites of, or lie within FR or CDR sequences where these genetic events may occur. Restricted antibody diversity in Xenopus seems therefore to be at least partially related to low complexity of VH elements, frequence of pseudogenes and expression regulated by specific promoter elements; diversity may potentially be increased by (non)homologous recombination events.

Amino Acid Sequence↗
PubMed1989

Evolution of immunoglobulin genes: VH families in the amphibian Xenopus.

We have isolated multiple independent cDNA clones that represent mRNA sequences of immunoglobulin heavy chains from the spleen of adult Xenopus laevis. These cDNA clones contained constant (C) region sequences that were either Cmu or a separate C region sequence believed to be Cnu. In individual cDNA clones the C region sequences were associated with independent heavy-chain variable region (VH) sequences that were classifiable into five distinct families. Genomic Southern blotting analyses with family-specific probes indicated that the haploid genome contains a minimum of 80 VH gene segments, a number similar to that found in various mammalian species. Multiple JH and putative DH segments were also identified (J, joining; D, diversity). Analyses of 13 independent VHDJH junctions suggest that combinatorial and junctional diversification mechanisms probably arose early in vertebrate evolution. Finally, comparison of Xenopus VH sequences to those from other vertebrates indicated conservation of V region framework residues that are responsible for the tertiary structure of the Fv throughout evolution.

Amino Acid Sequence↗
PubMed1988

Organization and rearrangement of immunoglobulin M genes in the amphibian Xenopus.

Sequences of immunoglobulin (Ig) cDNA clones of Xenopus laevis show that at least three different VH families are expressed in association with different JH elements and different isotypes of Ig constant regions. In genomic Southern blot analysis, the VH probes for each family hybridize to a distinct set of multiple DNA fragments. In contrast, the genomic JH elements and the IgM constant region gene are localized in a single DNA fragment of approximately 15 kb. Genomic VH elements contain regulatory sequences similar to those in VH genes of shark, fish and mammals and have a leader peptide sequence that contains an intron; they encode the VH region until residue 95 and have heptamer--23-bp--nonamer motifs similar to the rearrangement signal sequences (RSS) in all other vertebrate VH elements. The six genomic JH elements so far sequenced have a nonamer--23-bp--heptamer motif at their 5' end. These RSS motifs imply the existence of DH elements. The comparison of cDNA clones that contain similar constant regions but different VH regions or JH elements suggest rearrangement events. This is shown by Southern blot analysis of erythrocyte and B cell DNA with a JH probe. Thus, the overall organization of the Xenopus Ig gene locus is similar to that of mammals but strikingly different from shark.

Amino Acid Sequence↗
PubMed1988

Amino acid sequence of heavy chain from Xenopus laevis IgM deduced from cDNA sequence: implications for evolution of immunoglobulin domains.

Present understanding of the evolution of immunoglobulins is derived almost entirely from studies of a few mammalian species. To obtain information about immunoglobulin genes in Xenopus laevis, a cDNA library was prepared in the expression vector lambda gt11 from mitogen-stimulated splenocytes of this species. Of approximately equal to 50,000 clones screened, 18 were found to express IgM epitopes. One of these, lambda XIg14, hybridized with RNA of RNA of approximately equal to 2 kilobases from splenocytes. The insert of this clone appears to encode a variable region and part of a mu constant region; that of another clone, lambda XIg8, appears to encode a variable region and a complete mu constant region. Both inserts contain sequence corresponding to the three gene segments (VH, DH, and JH) that encode heavy-chain variable regions. The heavy-chain constant region (CH) encoded by lambda XIg8 has the characteristic features of C mu, including a four-domain structure and a carboxyl-terminal tail. The amino acid sequences of two mu-chain peptides agree with the cDNA sequence. The identity in amino acid sequence between the corresponding Xenopus and mouse C mu domains ranges from 31 to 47%. The C mu domains vary in the extent to which their sequences resemble the sequences of other immunoglobulins, consistent with previous suggestions that the immunoglobulin domains have an independent evolutionary history.

Amino Acid Sequence↗
PubMed1985

Anti-immunoglobulin M induces both B-lymphocyte proliferation and differentiation in Xenopus laevis.

Anti-IgM induced the proliferation of spleen lymphocytes of the amphibian Xenopus laevis as determined by 3H-thymidine uptake. The responding cells were B lymphocytes, since lymphocyte populations enriched in surface-Ig-positive cells exhibited an increased proliferative response, and spleen cells from larvally thymectomized animals still responded to anti-IgM. Immunofluorescence analysis and gel electrophoresis of biosynthetically labeled Ig polypeptides revealed that lymphoblasts induced by anti-IgM differentiated into plasmablasts that synthesized and secreted mainly IgM and small amounts of IgY. The in vitro differentiation of B lymphocytes also occurred in spleen cells obtained from thymectomized animals. These findings are in contrast with those obtained in mammals and suggest that the differentiation of B lymphocytes in X. laevis is subject to different regulatory mechanisms.

Animals↗
PubMed1984

Mitogen-induced B-cell differentiation in Xenopus laevis.

Spleen cells from the South African clawed toad Xenopus laevis proliferate vigorously upon pokeweed mitogen (PWM) stimulation, as measured by 3H-thymidine uptake. The peak response is observed after 6-8 days of culture, and both light- and electron-microscopy examinations of stimulated cells reveal the presence of a large number of lymphoblasts. Beside proliferation, PWM induces the in vitro differentiation of a large proportion of lymphoblasts into immunoglobulin (Ig)-producing plasmablasts, as shown by direct immunofluorescence. On average, 25% of the lymphoblasts contain cytoplasmic high-molecular-weight Ig (IgM) at days 8-10, whereas less than 1% of the lymphoblasts have cytoplasmic low-molecular-weight Ig (IgY). Ig's of mitogen-stimulated cells were labeled biosynthetically and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS/PAGE). The results confirm that Xenopus lymphoblasts induced in vitro synthesize Ig polypeptide chains. These are assembled into monomers of H2L2 units or polymerized hexameric forms. Both the monomer and hexamer forms are secreted. Two Ig heavy chains with apparent molecular weights (MW) of 74 and 81 daltons (kd) are detected in the cell lysates. The secreted chains have respectively an MW which is 3 kd and 5 kd greater than the intracellular forms. The two-dimensional gel electrophoretic pattern of PWM-induced Ig's is as heterogeneous as that of serum IgM. We conclude that PWM induces the in vitro proliferation and polyclonal differentiation of a large proportion of splenic B lymphocytes into plasmablasts.

Animals↗
PubMed1982

Biochemical studies of Xenopus laevis lymphocytes surface immunoglobulins.

Cell surface immunoglobulins of adult Xenopus laevis splenic small lymphocytes were analysed utilizing direct immunofluorescent staining and lactoperoxidase-catalysed radioiodination followed by immunoprecipitation of Ig molecules and characterization on SDS-PAGE. Nearly 30% of splenic lymphocytes are surface Ig positive. The HMW and LMW Ig classes are present on the surface of 23% and less than 5% of the cells, respectively. The mu chains of membrane HMW Ig have an apparent m.w. of 84,000 versus 73,000 for the mu chains of serum HMW Ig. Using immunofluorescent technique, we previously reported the absence of Ig molecules on the surface of larval Xenopus thymocytes. When the lactoperoxidase radioiodination technique was used, no cell surface Ig molecules could be isolated from Xenopus thymocytes.

Animals↗
PubMed1980

A theoretical models of oncolysis by Clostridium oncolyticum M 55 ATCC 13,732.

Based on experimental data obtained by own experiments and investigations of other authors the first time it is tried to develop a new theoretical model of oncolysis by Clostridium oncolyticum M 55. The correlations between tumour, clostridial cells, the tumour kinin system and the immune system of the host are represented in their influence on oncolysis. The consequences for a therapeutic application of the tumour clostridia phenomenon are discussed.

Animals↗
PubMed1978

[The use of clostridial antigens for a serological and autoradiographical early diagnosis of tumours (author's transl)].

In continuation of the examinations on the usefulness of Cl. oncolyticum M 55 spores reported by Möse new experiments with an auto-radiographical method are plannes. After the isolation, chemical characterization of the cell wall antigens and the exo-antigens and the formation of antibodies, these antibodies should be at first labelled with 125 J and henceforth with 131 J. The iodine-labelled antibodies should allow the diagnosis and localization of the tumours.

Animals↗