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Biomedical subjects

S Cory

Publications and source records attributed to S Cory.

At least 109 records · Page 6Linked to original sources
PubMed1984

Immunoglobulin variable region genes.

The picture that emerges of a V gene locus, albeit still sketchy, is one of a continuously evolving region, subject on occasion to quite dramatic flux due to the operation of gene conversion, transposing elements, recombination and unequal crossing over. The V genes are separated by surprisingly large tracts of DNA of unknown function which are 'littered' by a number of simple-sequence and moderately repetitive elements. The diversity of immunoglobulins is in part accounted for by selection operating on multiple germline genes: 100-300 for mouse VK and VH, but probably less for human VK and VH. Somatic recombinational and mutational mechanisms play a substantial role in increasing the diversity still further.

Animals↗
PubMed1983

Fusion of DNA region to murine immunoglobulin heavy chain locus corresponds to plasmacytoma-associated chromosome translocation.

Murine plasmacytomas frequently exhibit a translocation of the distal region of chromosome 15 to the end of chromosome 12, where the immunoglobulin heavy chain locus resides. A candidate for the DNA across the chromosome fusion point is a cloned region of non-immunoglobulin DNA which in most plasmacytomas has recombined near the alpha heavy chain constant region gene. That the incoming DNA, provisionally designated LyR (lymphoid rearranging) DNA, does derive from chromosome 15 is shown here by blot analysis of DNA from two panels of somatic cell hybrids: hybridomas between an AKR T-lymphoma (Tikaut) and CBA mouse cells with a cytogenetically distinctive chromosome 15, and between mouse and Chinese hamster cells. LyR DNA segregated with chromosome 15 in all lines and the results assign LyR to the distal two thirds of that chromosome. This assignment, together with the previously reported high frequency of recombination between LyR and C(alpha) in plasmacytomas and associated alteration of LyR transcription suggests that translocation activates a LyR gene involved in plasmacytoma oncogenesis. Moreover, LyR rearrangement in certain T-lymphomas, such as the Tikaut line examined here, also implicate that gene in oncogenesis of some T-lymphomas.

Animals↗
PubMed1983

Interchromosomal recombination of the cellular oncogene c-myc with the immunoglobulin heavy chain locus in murine plasmacytomas is a reciprocal exchange.

The 15:12 chromosome translocations found in most murine plasmacytomas involve the cellular gene (c-myc) homologous to the oncogene (v-myc) of avian retrovirus MC29, Translocation links the c-myc gene of chromosome 15 to the immunoglobulin heavy (H) chain locus of chromosome 12, often within the switch recombination (S) region 5' to the alpha constant region (C alpha) gene. We have investigated c-myc rearrangements in 21 BALB/c plasmacytomas and three B lymphomas by Southern blot analysis. We show that the t(15;12) is a reciprocal chromosome exchange since most tumours contain not only a c-myc gene linked to the S alpha C alpha region but also a separate structure with S mu or S alpha linked to the c-myc 5'-flanking region. Analysis of the two rearrangement products cloned from plasmacytoma J558 suggests that one type of H locus target for translocation is an S alpha region recombined with S mu; two other targets appear to be other switched heavy chain genes and an unrearranged C alpha gene. Nearly all the chromosome 15 breakpoints fall within a 1.1-kb region spanning a 5' c-myc exon; hence scission of the transcriptional unit by translocation can account for the altered c-myc transcription in plasmacytomas. The c-myc breakpoint region lacks substantial homology with S mu or S alpha, arguing against homologous recombination as the translocation mechanism.

Animals↗
PubMed1983

Sequence of the murine and human cellular myc oncogenes and two modes of myc transcription resulting from chromosome translocation in B lymphoid tumours.

The 15;12 chromosome translocation in murine plasmacytomas and the 8;14 in human Burkitt lymphomas often link the cellular myc oncogene to the locus for constant regions of immunoglobulin heavy chains (CH locus). To clarify how and why c-myc translocation occurs, we have sequenced the mouse and human c-myc genes and correlated c-myc transcription with c-myc rearrangement. Both genes comprise three exons; the second and third encode the myc polypeptide, which is conserved between mammals and birds, particularly in its more basic C-terminal half. Southern blots showed that four of 12 Burkitt lines have c-myc linked near CH switch regions and two near the joining region (JH) locus. Hence, immunoglobulin recombination machinery may participate in translocation, although the common myc breakpoint region around exon 1 does not resemble a switch region. Tumours with breakpoints just 5' to exon 1, or distant from c-myc, had normal c-myc mRNAs of 2.25 and 2.4 kb, which differ at their 5' ends, while tumours with breakpoints within exon 1 or intron 1 had altered c-myc mRNAs (2.1-2.7 kb in Burkitt lines), initiated within intron 1. Both types of mRNAs probably yield the same polypeptide. Since the untranslocated c-myc allele was generally silent, translocation to the CH locus must induce constitutive c-myc expression. The presence of c-myc mRNA in immortal but non-tumorigenic lymphoblastoid cell lines may implicate c-myc in an immortalization step.

Amino Acid Sequence↗
PubMed1983

Cellular myc oncogene is altered by chromosome translocation to an immunoglobulin locus in murine plasmacytomas and is rearranged similarly in human Burkitt lymphomas.

Molecular cloning has recently established that the 15;12 chromosome translocations in murine plasmacytomas fuse DNA from chromosome 15 to the immunoglobulin heavy (H) chain locus, usually within the switch recombination region near the alpha constant region gene. We show here that the incoming DNA bears the cellular gene (c-myc) homologous to the oncogene (v-myc) of avian retrovirus MC29. In human Burkitt lymphomas bearing an 8;14 translocation, c-myc was also rearranged, apparently (in at least two cases) to an H chain switch recombination region (mu or alpha), and both products of a reciprocal chromosome exchange were detectable. Both the murine and human c-myc genes contain two exons homologous to v-myc, and additional 5' and 3' murine genomic segments (apparent exons) were defined by hybridization to c-myc mRNAs. In plasmacytomas, chromosome breakpoints fall near or within the 5' exon and apparently disrupt the normal c-myc transcriptional unit, because plasmacytoma c-myc mRNAs differ from the mRNA in lines without c-myc rearrangement. The translocated gene presumably has lost its normal 5' regulatory sequences and may well encode an altered myc polypeptide. We propose that altered expression of the c-myc gene, induced by translocation to an immunoglobulin locus, is a critical oncogenic event for these B lymphoid tumors. Two events may be required, because the plasmacytoma oncogene capable of transforming fibroblasts is not c-myc.

Animals↗
PubMed1982

Transcriptionally active DNA region that rearranges frequently in murine lymphoid tumors.

A DNA region not associated with conventional immunoglobulin gene rearrangement is rearranged in many lymphoid tumors. This region, designated here as lymphoid rearranging (LyR) DNA, was cloned from plasmacytoma J558 in which it had recombined 5' to a constant (C) region of the alpha heavy (H) chain gene, C alpha, within a switch (S) region, S alpha, involved in the switching of CH genes. Sequence determination established that LyR DNA had recombined within a S alpha recombination unit. LyR DNA does not originate from the H chain locus, and discordance between LyR DNA and CH copy number in certain lines suggests that LyR DNA probably derives from another chromosome. LyR DNA rearrangement is a characteristic of tumors of mature B cells; it was detected in 24 of 28 plasmacytomas and B-cell lymphomas, usually as LyR-S alpha, but not in 11 Abelson retrovirus-induced lymphomas of B-cell precursors nor detectably in normal B cells. In contrast, rearrangement was observed in only 3 of 18 T-cell lymphomas, and none of seven nonlymphoid lines. Most tumor lines (49 of 52), whether lymphoid or not, contained a low level of polyadenylylated LyR transcript(s), but several new RNA species with differences in their 5' regions appeared in B-cell lines in which LyR DNA was rearranged, suggesting that rearrangement may activate a new promoter or mode of splicing. The results suggest that the LyR-S alpha rearrangement represents a translocation to chromosome 12 that alters expression of LyR-encoded genes; hence, it may have participated in lymphoid tumor oncogenesis.

Animals↗
PubMed1981

Recombination events near the immunoglobulin Cmu gene join variable and constant region genes, switch heavy-chain expression, or inactivate the locus.

Immunoglobulin heavy-chain expression is initiated by recombination between a variable region (VH) gene and one of several joining region (JH) genes located near the mu constant region (Cmu) gene, and the active VH gene can subsequently switch to another CH gene. That the general mechanism for CH switching involves recombination between sites within the JH-Cmu intervening sequence and the 5' flanking region of another CH gene is supported here by Southern blot hybridization analysis of eight IgG- and IgA-secreting plasmacytomas. An alternative model requiring successive VH linkage to similar JH clusters near each CH gene is shown to be very unlikely since the mouse genome appears to contain only one complement of the JH locus and no JH gene was detectable within large cloned sequences flanking germline C gamma 3 and C gamma 1 genes. Thus, VH-JH joining and CH switching are mediated by separate regions of "the joining-switch" or J-S element. In each plasmacytoma examined, the J-S element had undergone recombination within both the JH locus and the switch region and was shown to be linked to the functional CH gene in an IgG3, and IgG1, and three IgA secretors. Both JH joining and CH switching occurred by deletion of DNA. Switch recombination occurred at more than one site within the J-S element in different lines, even for recombination with the same CH gene. Significantly, although heavy-chain expression is restricted to one allele ("allelic exclusion"), all rearranged in each plasmacytoma. Some rearrangements were aberrant, involving, for example, deletion of all JH genes from the allele. Hence, an error-prone recombination machinery may account for allelic exclusion in many plasmacytomas.

Animals↗
PubMed1981

Sets of immunoglobulin V kappa genes homologous to ten cloned V kappa sequences: implications for the number of germline V kappa genes.

To count V kappa genes homologous to particular V kappa nucleotide sequences, thereby permitting estimates for the total V kappa repertoire, we hybridized 10 cloned V kappa cDNA sequences to restriction fragments of mouse embryo DNA (Southern blots). Particular probes labeled up to 17 fragments, of which up to 8 were strongly labeled. This indicates that the germline contains sets of related V kappa genes. Only 4 nonoverlapping gene sets of 16-22 genes each were found. Assuming that the probes used are a random sample of the V kappa pool, the pattern repetitions suggest that the germline contains a total of about 5 distinct V kappa gene sets and about 90 V kappa genes. Correlating sets of strongly labeled genes with V kappa groups having similar N-terminal sequences led to an estimate of about 300 germline V kappa genes, while extrapolation from the number of genes in the VK-21 group gave an estimate of 90-140 genes. Since the three independent estimates fell between 90 and 320 genes, the germline V kappa repertoire, at least as expressed in myelomas, probably lies in that range. The V kappa fragment patterns given by three probes did not differ detectably between BALB/c, NZB, and A/J DNA but all three patterns differed in AKR DNA, indicating that there is limited polymorphism within the mouse V kappa locus. Somatic mutation must expand the number of expressed V kappa sequences, since the 8-12 VK-21 genes estimated for BALB/c and for NZB is significantly less than the 22 known NZB VK-21 polypeptides.

Animals↗
PubMed1981

Organization of genes and spacers within the mouse immunoglobulin VH locus.

The germline organization of mouse immunoglobulin VH genes has been investigated using cloned VH sequences. Hybridization studies with VH probes from plasmacytomas HPC76 (H76), S107, HOPC1 (H1), and lymphoma ABLS-8 (A8) demonstrated that the VH locus contains at least three distinct VH gene families. Comparison with other results suggests a total of about 10 such families, and of the order of 160 germline VH genes. Nucleotide sequencing revealed that the H76 family includes anti-inulin VH sequences, and the S107 family is known to encode antiphosphorylcholine sequences. The three VH gene families studied were mapped in the order H76-S107-A8/H1-CH by determining which VH genes had been deleted from several plasmacytomas by VH rearrangement events. Nine genomic clones from athe H76 family, and one each from the S107 and A8/H1 families, were characterized; collectively they span 103 kilobases (kb). Two clones from the H76 family and one from the S107 family each bore a pair of VH genes separated by approximately 14 kb, suggesting that related VH genes in these families are clustered with a typical spacing of approximately 14 kb. No other VH genes were detected within the spacers, arguing against intermingling of different families. Within the VH76 family cluster, however, two closely homologous VH genes were shown not to be adjacent. While spacer sequences were strongly conserved in the A8/H1 family, the H76 family had minimal conservation and that was restricted to regions immediately surrounding the genes. Hence conservation of spacer sequences cannot be essential for VH gene function, nor for maintenance of a VN family. Spacers in both the H76 and S108 family contained small repeat elements, some of which behaved like mobile DNA sequences.

Animals↗
PubMed1980

Cloned embryonic DNA sequences flanking the mouse immunoglobulin C gamma 3 and C gamma 1 genes.

To investigate the DNA surrounding genes for immunoglobulin heavy chain constant (CH) regions, we have isolated two clones bearing a C gamma 3 gene and two bearing a C gamma 1 gene from a library of mouse embryo DNA fragments. The C gamma 3 clones span 8.6 kilobase pairs (kb) on the 5' side of the gene and 6.7 kb on its 3' side, while the C gamma 1 clones together span 13 kb of 5' flanking sequence and 2.5 kb of 3' flanking sequence. Restriction mapping of the C gamma 3 gene indicates that intervening sequences divide the gene into segments of domain size, as in other CH genes. Hybridization of clone fragments to restriction digests of mouse DNA indicates that both the C gamma 1 and C gamma 3 genes probably occur as single copies in the genome. Moreover, the entire cloned sequences on the 5' side of both genes appear to be unique in the genome, indicating that no large common sequences flank CH genes. Restriction data suggest that the C gamma 3 gene is 37-40 kb 5' to the C gamma 1 gene.

Animals↗
PubMed1980

Deletions are associated with somatic rearrangement of immunoglobulin heavy chain genes.

The organization of mouse immunoglobulin heavy chain genes has been investigated by hybridization with cloned mu and alpha cDNA probes. Restriction endonuclease fragments bearing mu and alpha constant region genes and two types of variable region (VH) genes were compared in BALB/c embryos, liver and nine plasmacytomas synthesizing IgM, IgA, IgG1, IgG2a, IgG2b and IgG3. Embryo DNA was found to contain a single copy of the C mu gene per haploid genome. In contrast, one VH probe (HPC 76) detected at least six related VH genes, while the other (S107) detected a separate set of at least four genes, indicating that the germline contains distinct sets of multiple related VH genes. Most VH genes within the two subsets remained in germline context in different plasmacytomas, providing no evidence for somatic reassortment of VH genes. One plasmacytoma was devoid of specific VH genes, including some related to the expressed VH sequence. This may mean that the translocation event creating an active heavy chain gene involves deletion of the DNA between the expressed VH and CH sequences. The context of C mu sequences in DNA from a plasmacytoma secreting IgM differed from that in embryo DNA, as did C alpha sequences in two IgA- and several IgG-secreting plasmacytomas. Unlike heavy chain expression, rearrangement was not confined to one allele and often took different forms within a single cell line, presumably varying on different homologous chromosomes. Each rearrangement, whether resulting in an active C gene or not, appeared to change sequences upstream but not downstream from the CH gene. Significantly, the eight IgG and IgA plasmacytomas examined had undergone deletions of at least half and often all C mu sequences while retaining the embryo level of C alpha sequences. Hence a deletion mechanism may be responsible for the switch in expression from one CH gene to another which occurs during differentiation of a lymphocyte clone.

Alleles↗
PubMed1980

Intervening sequences divide the gene for the constant region of mouse immunoglobulin mu chains into segments, each encoding a domain.

To elucidate the structure of the gene for the constant region of immunoglobulin mu chains, we have cloned a 9.9-kilobase-pair fragment of mouse DNA bearing a gene for the constant region of the mu chain (C mu gene) from an IgM-secreting mouse plasmacytoma. The sequence around this gene has apparently undergone somatic rearrangement; the gene occurs in an EcoRI restriction endonuclease fragment of a different size from that in embryo or liver DNA and no C mu-bearing fragment of embryo size remains in the plasmacytoma. The cloned sequence lacks a variable region gene; hence, if this C mu gene is active, its position within the clone indicates that the gene for the variable region of a heavy chain (VH gene) must be more than 3.7 kilobase pairs away. The C mu gene is divided by three intervening sequences into four coding segments, each of which encodes one of the domains (homology units) of the polypeptide. The nucleotide sequence coding for amino acids near the V-C junction is not present within the C mu clone or clones bearing homologous embryonic VH genes. This suggests that an immunoglobulin heavy chain, in common with light chains, is encoded not only by a V and C gene, but also by an independent joining region (JH) gene.

Animals↗
PubMed1980

Expression of the immunoglobulin C mu gene in mouse T and B lymphoid and myeloid cell lines.

We have used cloned nucleotide sequences as probes to search for immunoglobulin RNA in T and B lymphoid and nonlymphoid tumor cell lines. Polyadenylated RNA from the cells was fractionated electrophoretically by size and fixed to diazobenzyloxymethyl-paper, and then immunoglobulin RNA species were revealed by hybridization with 32P-labeled cloned sequences for mu heavy chain and kappa light chain. kappa mRNA was detected only in B lymphoid lines known to synthesize kappa chains. No mu RNA was detectable in erythroleukemia, mastocytoma, or sarcoma cells. RNA bearing mu constant region (C mu) sequences, however, was detected in four of nine T lymphoma and four of five myeloid tumor cell lines tested, as well as in B lymphoma and "pre-B" Abelson lymphoma cells. In contrast to the single mu RNA species of 2.6 kilobases (kb) in a plasmacytoma, individual T lymphoma and myeloid lines yielded up to three discrete mu RNA species of apparent size 1.9, 2.2, and 3.0 kb, each different from the two mu RNA species in a B lymphoma line (2.4 and 2.7 kb) or the single species in "pre-B" lymphoma cells (2.9 kb). Both chromosomal complements of the C mu gene in STRij-4 T cells were found to be rearranged from their embryonic (germ line) context. The results suggest that the C mu gene functions not only in T cells, wherein the ability to recognize antigen is long established, but also in myeloid cells.

Animals↗
PubMed1980

Somatic rearrangements forming active immunoglobulin mu genes in B and T lymphoid cell lines.

We have cloned an active gene for an immunoglobulin mu heavy (H) chain, bearing the variable (VH), joining (JH), and constant (C mu) sequences expressed in the IgM-secreting mouse plasmacytoma HPC-76. The mu gene was formed by somatic recombination between a VH gene and one of several JH genes, which are located about 7.7 kilobase pairs from the C mu gene in embryo DNA. The JH-C mu intervening sequence has suffered a deletion of about 2.7 kilobase pairs in HPC-76. Because the delection encompasses sequences required to switch an expressed VH-JH gene from C mu to another CH gene, it may represent a mechanism for "freezing" a lymphocyte clone at the stage of IgM expression. For the second (inactive) C mu allele in HPC-76, the entire joining and switch regions have been deleted; functional inactivation of one allele may thus represent one mechanism by which a lymphocyte clone restricts expression to a single allele (allelic exclusion). Probes generated from the cloned mu gene allowed examination of the JH locus in B, Abelson "pre-B," and T lymphoma cell lines and a myeloid line, all of which cotain RNA species bearing C mu sequences. The B and pre-B lines exhibited recombination within both alleles of the JH locus, suggesting that both alleles may be expressed in some cells. The absence of the JH gene 5' to the recombination sites favors a deletion mechanism for VH-JH joining. Recombination within the JH locus was also detected in two out of four T lymphoma lines, but not in the myeloid line. This indicates that the mechanism by which B cells generate immunoglobulin diversity is operational in some T cells. Lines that synthesize mu RNA without JH rearrangement may have activated the C mu gene directly or have undergone recombination at a more distant locus.

Animals↗