CpG methylated minichromosomes become inaccessible for V(D)J recombination after undergoing replication.

Hsieh, Chih‐Lin; Lieber, Michael R.

doi:10.1002/j.1460-2075.1992.tb05054.x

Cited by 157 publications

(90 citation statements)

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“…Methylation also may serve a negative role by repressing the basal level of recombination throughout the loci and cryptic genomic sites. Previous studies have demonstrated that methylated recombination substrates are less recombinationally active (15)(16)(17). Further studies are required to isolate the factors that confer specificity to the recombination process and to determine the mechanism by which they alter the accessibility of loci for recombination.…”

Section: Discussionmentioning

confidence: 99%

“…Regulated demethylation could control the specificity of the V(D)J recombinase. Consistent with such a concept, exogenously introduced hypermethylated recombination substrates including both episomes and transgenes are refractory to V(D)J recombination compared with their unmethylated counterparts (15)(16)(17). At a minimum, this suggests that methylation of target sites bound by ubiquitous trans-acting factors inhibits recombination so that demethylation of these loci should be required for the initiation of recombination.…”

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confidence: 84%

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V(D)J recombination is not activated by demethylation of the kappa locus

Cherry

Beard

Jaenisch

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

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V(D)J recombination is thought to be regulated by changes in the accessibility of target sites, such as modulation of methylation. To test whether demethylation of the kappa locus can activate recombination, we generated two recombinationally active B cell lines in which the gene for maintenance of genomic DNA methylation, Dnmt1, was flanked with loxP sites. Transduction with a retrovirus expressing both the cre recombinase and green fluorescent protein allowed us to purify recombinationally active cells devoid of methylation. Loss of methylation of the kappa locus was not sufficient to activate recombination, although transcription was activated in one line. It appears that demethylation of the kappa locus is not the rate-limiting step for altering accessibility and thus regulated demethylation does not generate specificity of recombination.T he V(D)J recombination machinery assembles antigen receptor genes during lymphoid development from gene segments flanked by recombination signal sequences (1). This nonhomologous site-specific recombination process is precisely controlled by a number of different regulatory mechanisms. For one thing, the coexpression of the lymphoid-specific Rag-1 and Rag-2 genes occurs restrictively in developing B and T cells, ensuring that only the appropriate cell types are recombinationally active (2). A second level of regulation also controls lineage specificity: complete Ig gene rearrangement occurs only in B cells, whereas T cell receptor genes rearrange exclusively in T cells (3). Moreover, within developing B and T cells there are temporal controls over specific gene segment usage (4, 5). Additionally, allelic exclusion ensures that each B or T cell generates only one functional antigen receptor even though two alleles exist at each locus (6).This remarkable ability of the recombination machinery to target only a very small subset of substrates within a given cell together with the fact that a single recombinase is required for this process has led to the hypothesis that the accessibility of DNA targets to the recombination machinery is tightly controlled (7-9). Recombination loci are thought to be inaccessible until they are modified to allow the recombination machinery access to target sites. Changes in chromatin structure, transcriptional activity, or DNA methylation at each locus have been identified that correlate with recombinational activity. Many studies have attempted to define the cis-acting sequences and trans-acting factors required to regulate this process. Distinct enhancer sequences present within individual loci must be controlled by different trans-acting proteins to allow developmentally regulated changes in the accessibility of each locus to occur.DNA methylation has been shown to regulate chromatin structure, leading to changes of gene expression (10). Additionally, methylation has been correlated with Ig gene regulation: both the heavy chain and light chain are hypermethylated in cells in which they are not recombined (11,12). Concomitant with V(D)J rearrang...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 84%

V(D)J recombination is not activated by demethylation of the kappa locus

Cherry

Beard

Jaenisch

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

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“…The most direct evidence that DNA methylation suppresses homologous recombination has come from the work in Ascobolus, but several studies support a similar role in mammalian cells. For example, V(D)J recombination is reduced more than 100-fold when the recombination substrate is methylated (Hsieh and Lieber, 1992). In addition, Dnmt1 knockout ES cells exhibit a 10-fold increased mutation rate involving gene rearrangements (Chen et al, 1998), and individuals with ICF syndrome or cultured cells treated with 5-azaCdR show increased numbers of chromosomal translocations (Ji et al, 1997;Miniou et al, 1994).…”

Section: Dna Hypomethylation ± Roles In Cancer and Genome Stabilitymentioning

confidence: 99%

DNA methylation, methyltransferases, and cancer

2001

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The ®eld of epigenetics has recently moved to the forefront of studies relating to diverse processes such as transcriptional regulation, chromatin structure, genome integrity, and tumorigenesis. Recent work has revealed how DNA methylation and chromatin structure are linked at the molecular level and how methylation anomalies play a direct causal role in tumorigenesis and genetic disease. Much new information has also come to light regarding the cellular methylation machinery, known as the DNA methyltransferases, in terms of their roles in mammalian development and the types of proteins they are known to interact with. This information has forced a new view for the role of DNA methyltransferases. Rather than enzymes that act in isolation to copy methylation patterns after replication, the types of interactions discovered thus far indicate that DNA methyltransferases may be components of larger complexes actively involved in transcriptional control and chromatin structure modulation. These new ®ndings will likely enhance our understanding of the myriad roles of DNA methylation in disease as well as point the way to novel therapies to prevent or repair these defects. Oncogene (2001) 20, 3139 ± 3155.

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“…Recombination of these inappropriately broken ends might be responsible for the chromosomal translocations common to lymphoid leukemias and lymphomas (Korsmeyer 1992;Gauss and Lieber 1993) We infer that mechanisms, in addition to heptamer-nonamer recognition, must exist to limit the error rate of the V(D)J recombinase. Some data suggest that one such mechanism involves DNA methylation (Hsieh and Lieber 1992). Another mechanism might involve transcription activity.…”

Section: The Structure Of Broken-ended Rss Dna a Probable V{d)j Recomentioning

confidence: 99%

Double-strand signal sequence breaks in V(D)J recombination are blunt, 5'-phosphorylated, RAG-dependent, and cell cycle regulated.

Schlissel

Constantinescu²,

Morrow³

et al. 1993

Genes & Development

360

344

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Immunoglobulin and T-cell receptor genes are assembled during lymphocyte development by a novel, highly regulated series of gene rearrangement reactions known as V(D)I recombination. All rearranging loci are flanked by conserved heptamer-nonamer recombination signal sequences. Gene rearrangement results in the imprecise fusion of coding sequences and the precise fusion of signal sequences. DNA molecules with double-stranded breaks near signal sequences have been detected in cells undergoing V(D)I recombination of the TCR8 locus. We have devised a ligation-mediated PCR assay that detects broken-ended molecules in purified genomic DNA. Using this assay we found that DNA breaks occurring precisely at the signal sequence-coding sequence junction are a general feature of V(D)I recombination, appearing in association with each type of rearranging immunoglobulin gene segment. We show that a significant fraction of these broken ends are blunt and 5'-phosphorylated. In addition, detection of these broken-ended signal sequences is dependent on the activity of RAG-1 and RAG-2, and is restricted to the Go/G1 phase of the cell cycle

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CpG methylated minichromosomes become inaccessible for V(D)J recombination after undergoing replication.

Cited by 157 publications

References 50 publications

V(D)J recombination is not activated by demethylation of the kappa locus

V(D)J recombination is not activated by demethylation of the kappa locus

DNA methylation, methyltransferases, and cancer

Double-strand signal sequence breaks in V(D)J recombination are blunt, 5'-phosphorylated, RAG-dependent, and cell cycle regulated.

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