The Experts below are selected from a list of 1380 Experts worldwide ranked by ideXlab platform

Abdellah Belmaaza - One of the best experts on this subject based on the ideXlab platform.

  • brca1 regulates rad51 function in response to dna damage and suppresses spontaneous sister chromatid Replication Slippage implications for sister chromatid cohesion genome stability and carcinogenesis
    Cancer Research, 2005
    Co-Authors: Isabelle Cousineau, Christine Abaji, Abdellah Belmaaza
    Abstract:

    The breast/ovarian cancer susceptibility proteins BRCA1 and BRCA2 maintain genome stability, at least in part, through a functional role in DNA damage repair. They both colocalize with RAD51 at sites of DNA damage/Replication and activate RAD51-mediated homologous recombination repair of DNA double-strand breaks (DSB). Whereas BRCA2 interacts directly with and regulates RAD51, the role of BRCA1 in this process is unclear. However, BRCA1 may regulate RAD51 in response to DNA damage or through its ability to interact with and regulate MRE11/RAD50/NBS1 (MRN) during the processing of DSBs into single-strand DNA (ssDNA) ends, prerequisite substrates for RAD51, or both. To test these hypotheses, we measured the effect of BRCA1 on the competition between RAD51-mediated homologous recombination (gene conversion and crossover) versus RAD51-independent homologous recombination [single-strand annealing (SSA)] for ssDNA at a site-specific chromosomal DSB within a DNA repeat, a substrate for both homologous recombination pathways. Expression of wild-type BRCA1 in BRCA1-deficient human recombination reporter cell lines promoted both gene conversion and SSA but greatly enhanced gene conversion. In addition, BRCA1 also suppressed both spontaneous gene conversion and deletion events, which can arise from either crossover or sister chromatid Replication Slippage (SCRS), a RAD51-independent process. BRCA1 does not seem to block crossover. From these results, we conclude that (a) BRCA1 regulates RAD51 function in response to the type of DNA damage and (b) BRCA1 suppresses SCRS, suggesting a role for this protein in sister chromatid cohesion/alignment. Loss of such control in response to estrogen-induced DNA damage after BRCA1 inactivation may be a key initial event that triggers genome instability and carcinogenesis.

  • brca1 regulates rad51 function in response to dna damage and suppresses spontaneous sister chromatid Replication Slippage implications for sister chromatid cohesion genome stability and carcinogenesis
    Cancer Research, 2005
    Co-Authors: Isabelle Cousineau, Christine Abaji, Abdellah Belmaaza
    Abstract:

    The breast/ovarian cancer susceptibility proteins BRCA1 and BRCA2 maintain genome stability, at least in part, through a functional role in DNA damage repair. They both colocalize with RAD51 at sites of DNA damage/Replication and activate RAD51-mediated homologous recombination repair of DNA double-strand breaks (DSB). Whereas BRCA2 interacts directly with and regulates RAD51, the role of BRCA1 in this process is unclear. However, BRCA1 may regulate RAD51 in response to DNA damage or through its ability to interact with and regulate MRE11/RAD50/NBS1 (MRN) during the processing of DSBs into single-strand DNA (ssDNA) ends, prerequisite substrates for RAD51, or both. To test these hypotheses, we measured the effect of BRCA1 on the competition between RAD51-mediated homologous recombination (gene conversion and crossover) versus RAD51-independent homologous recombination [single-strand annealing (SSA)] for ssDNA at a site-specific chromosomal DSB within a DNA repeat, a substrate for both homologous recombination pathways. Expression of wild-type BRCA1 in BRCA1-deficient human recombination reporter cell lines promoted both gene conversion and SSA but greatly enhanced gene conversion. In addition, BRCA1 also suppressed both spontaneous gene conversion and deletion events, which can arise from either crossover or sister chromatid Replication Slippage (SCRS), a RAD51-independent process. BRCA1 does not seem to block crossover. From these results, we conclude that (a) BRCA1 regulates RAD51 function in response to the type of DNA damage and (b) BRCA1 suppresses SCRS, suggesting a role for this protein in sister chromatid cohesion/alignment. Loss of such control in response to estrogen-induced DNA damage after BRCA1 inactivation may be a key initial event that triggers genome instability and carcinogenesis. (Cancer Res 2005; 65(24): 11384-91)

  • brca2 regulates homologous recombination in response to dna damage implications for genome stability and carcinogenesis
    Cancer Research, 2005
    Co-Authors: Christine Abaji, Isabelle Cousineau, Abdellah Belmaaza
    Abstract:

    BRCA2 has been implicated in the maintenance of genome stability and RAD51-mediated homologous recombination repair of chromosomal double-strand breaks (DSBs), but its role in these processes is unclear. To gain more insight into its role in homologous recombination, we expressed wild-type BRCA2 in the well-characterized BRCA2-deficient human cell line CAPAN-1 containing, as homologous recombination substrates, either direct or inverted repeats of two inactive marker genes. Whereas direct repeats monitor a mixture of RAD51-dependent and RAD51-independent homologous recombination events, inverted repeats distinguish between these events by reporting RAD51-dependent homologous recombination, gene conversion, and crossover events only. At either repeats, BRCA2 decreases the rate and frequency of spontaneous homologous recombination, but following chromosomal DSBs, BRCA2 increases the frequency of homologous recombination. At direct repeats, BRCA2 suppresses both spontaneous gene conversion and deletions, which can arise either from crossover or RAD51-independent sister chromatid Replication Slippage (SCRS), but following chromosomal DSBs, BRCA2 highly promotes gene conversion with little effect on deletions. At inverted repeats, spontaneous or DSB-induced crossover events were scarce and BRCA2 does not suppress their formation. From these results, we conclude that (i) BRCA2 regulates RAD51 recombination in response to the type of DNA damage and (ii) BRCA2 suppresses SCRS, suggesting a role for BRCA2 in sister chromatids cohesion and/or alignment. Loss of such control in response to estrogen-induced DNA damage after BRCA2 inactivation may be a key initial event triggering genome instability and carcinogenesis.

David Neil Cooper - One of the best experts on this subject based on the ideXlab platform.

  • transient hypermutability chromothripsis and Replication based mechanisms in the generation of concurrent clustered mutations
    Mutation Research-reviews in Mutation Research, 2012
    Co-Authors: Jianmin Chen, Claude Ferec, David Neil Cooper
    Abstract:

    Clustered mutations may be broadly defined as the presence of two or more mutations within a spatially localized genomic region on a single chromosome. Known instances vary in terms of both the number and type of the component mutations, ranging from two closely spaced point mutations to tens or even hundreds of genomic rearrangements. Although clustered mutations can represent the observable net result of independent lesions sequentially acquired over multiple cell cycles, they can also be generated in a simultaneous or quasi-simultaneous manner within a single cell cycle. This review focuses on those mechanisms known to underlie the latter type. Both gene conversion and transient hypermutability are capable of generating closely spaced multiple mutations. However, a recently described phenomenon in human cancer cells, known as 'chromothripsis', has provided convincing evidence that tens to hundreds of genomic rearrangements can sometimes be generated simultaneously via a single catastrophic event. The distinctive genomic features observed in the derivative chromosomes, together with the highly characteristic junction sequences, point to non-homologous end joining (NHEJ) as being the likely underlying mutational mechanism. By contrast, Replication-based mechanisms such as microhomology-mediated break-induced Replication (MMBIR) which involves serial Replication Slippage or serial template switching probably account for those complex genomic rearrangements that comprise multiple duplications and/or triplications.

  • elucidation of the complex structure and origin of the human trypsinogen locus triplication
    Human Molecular Genetics, 2009
    Co-Authors: Angelique Chauvin, David Neil Cooper, Jianmin Chen, Sylvia Quemener, Emmanuelle Masson, Hildegard Kehrersawatzki, Barbara Ohmle, Cedric Le Marechal, Claude Ferec
    Abstract:

    One of the causes of chronic pancreatitis is the duplication and triplication of a ∼605 kb segment containing the trypsinogen locus. Employing array-comparative genomic hybridization, we fully characterized the triplication copy number mutation (CNM) and found it to be part of a complex rearrangement that also contains a triplicated ∼137 kb segment and 21 bp sequence tract. This triplication allele therefore constitutes a gain of two tandemly arranged composite duplication blocks, each comprising a copy of the ∼605 kb segment, a copy of the inverted ∼137 kb segment and a copy of the inverted 21 bp sequence tract. As such, it represents the first characterization of a human complex triplication CNM at the DNA sequence level. All triplications and duplications identified were found to arise from a common founder chromosome. A two-step process is proposed for the generation of this highly unusual triplication CNM. Thus, the first composite duplication block is envisaged to have been generated by break-induced serial Replication Slippage during mitosis. This duplication would have provided the sequence homology required to promote non-allelic homologous recombination (NAHR) during meiosis which would then, in a second step, have generated the complex triplication allele. Our data provide support for the view that many human germline copy number variants arise through Replication-based mechanisms during the premeiotic mitotic divisions of germ cells. The low copy repeats thereby generated could then serve to promote NAHR during meiosis, giving rise to amplified DNA sequences which would themselves predispose to further recombinational events during both mitosis and meiosis.

  • intrachromosomal serial Replication Slippage in trans gives rise to diverse genomic rearrangements involving inversions
    Human Mutation, 2005
    Co-Authors: Jianmin Chen, Nadia Chuzhanova, Peter D Stenson, Claude Ferec, David Neil Cooper
    Abstract:

    Serial Replication Slippage in cis (SRScis) provides a plausible explanation for many complex genomic rearrangements that underlie human genetic disease. This concept, taken together with the intra- and intermolecular strand switch models that account for mutations that arise via quasipalindrome correction, suggest that intrachromosomal SRS in trans (SRStrans) mediated by short inverted repeats may also give rise to a diverse series of complex genomic rearrangements. If this were to be so, such rearrangements would invariably generate inversions. To test this idea, we collated all informative mutations involving inversions of >or=5 bp but <1 kb by screening the Human Gene Mutation Database (HGMD; www.hgmd.org) and conducting an extensive literature search. Of the 21 resulting mutations, only two (both of which coincidentally contain untemplated additions) were found to be incompatible with the SRStrans model. Eighteen (one simple inversion, six inversions involving sequence replacement by upstream or downstream sequence, five inversions involving the partial reinsertion of removed sequence, and six inversions that occurred in a more complicated context) of the remaining 19 mutations were found to be consistent with either two steps of intrachromosomal SRStrans or a combination of Replication Slippage in cis plus intrachromosomal SRStrans. The remaining lesion, a 31-kb segmental duplication associated with a small inversion in the SLC3A1 gene, is explicable in terms of a modified SRS model that integrates the concept of "break-induced Replication." This study therefore lends broad support to our postulate that intrachromosomal SRStrans can account for a variety of complex gene rearrangements that involve inversions. (c) 2005 Wiley-Liss, Inc.

  • complex gene rearrangements caused by serial Replication Slippage
    Human Mutation, 2005
    Co-Authors: Jianmin Chen, Nadia Chuzhanova, Peter D Stenson, Claude Ferec, David Neil Cooper
    Abstract:

    The now-classical model of Replication Slippage can in principle account for both simple deletions and tandem duplications associated with short direct repeats. Invariably, a single Replication Slippage event is invoked, irrespective of whether simple deletions or tandem duplications are involved. However, we recently identified three complex duplicational insertions that could also be accounted for by a model of serial Replication Slippage. We postulate that a sizeable proportion of hitherto inexplicable complex gene rearrangements may be explained by such a model. To test this idea, and to assess the generality of our initial findings, a number of complex gene rearrangements were selected from the Human Gene Mutation Database (HGMD). Some 95% (20/21) of these mutations were found to be explicable by twin or multiple rounds of Replication Slippage, the sole exception being a double deletion in the F9 gene that is associated with DNA sequences that appear capable of adopting non-B conformations. Of the 20 complex gene rearrangements, 19 (seven simple double deletions, one triple deletion, two double mutational events comprising a simple deletion and a simple insertion, six simple indels that may constitute a novel and non-canonical class of gene conversion, and three complex indels) were compatible with the model of serial Replication Slippage in cis; the remaining indel in the MECP2 gene, however, appears to have arisen via interchromosomal Replication Slippage in trans. Our postulate that serial Replication Slippage may account for a variety of complex gene rearrangements has therefore received broad support from the study of the above diverse series of mutations. (c) 2005 Wiley-Liss, Inc.

  • complex gene rearrangements caused by serial Replication Slippage
    Human Mutation, 2005
    Co-Authors: Jianmin Chen, Nadia Chuzhanova, Peter D Stenson, Claude Ferec, David Neil Cooper
    Abstract:

    The now-classical model of Replication Slippage can in principle account for both simple deletions and tandem duplications associated with short direct repeats. Invariably, a single Replication Slippage event is invoked, irrespective of whether simple deletions or tandem duplications are involved. However, we recently identified three complex duplicational insertions that could also be accounted for by a model of serial Replication Slippage. We postulate that a sizeable proportion of hitherto inexplicable complex gene rearrangements may be explained by such a model. To test this idea, and to assess the generality of our initial findings, a number of complex gene rearrangements were selected from the Human Gene Mutation Database (HGMD). Some 95% (20/21) of these mutations were found to be explicable by twin or multiple rounds of Replication Slippage, the sole exception being a double deletion in the F9 gene that is associated with DNA sequences that appear capable of adopting non-B conformations. Of the 20 complex gene rearrangements, 19 (seven simple double deletions, one triple deletion, two double mutational events comprising a simple deletion and a simple insertion, six simple indels that may constitute a novel and non-canonical class of gene conversion, and three complex indels) were compatible with the model of serial Replication Slippage in cis; the remaining indel in the MECP2 gene, however, appears to have arisen via interchromosomal Replication Slippage in trans. Our postulate that serial Replication Slippage may account for a variety of complex gene rearrangements has therefore received broad support from the study of the above diverse series of mutations.

Jianmin Chen - One of the best experts on this subject based on the ideXlab platform.

  • transient hypermutability chromothripsis and Replication based mechanisms in the generation of concurrent clustered mutations
    Mutation Research-reviews in Mutation Research, 2012
    Co-Authors: Jianmin Chen, Claude Ferec, David Neil Cooper
    Abstract:

    Clustered mutations may be broadly defined as the presence of two or more mutations within a spatially localized genomic region on a single chromosome. Known instances vary in terms of both the number and type of the component mutations, ranging from two closely spaced point mutations to tens or even hundreds of genomic rearrangements. Although clustered mutations can represent the observable net result of independent lesions sequentially acquired over multiple cell cycles, they can also be generated in a simultaneous or quasi-simultaneous manner within a single cell cycle. This review focuses on those mechanisms known to underlie the latter type. Both gene conversion and transient hypermutability are capable of generating closely spaced multiple mutations. However, a recently described phenomenon in human cancer cells, known as 'chromothripsis', has provided convincing evidence that tens to hundreds of genomic rearrangements can sometimes be generated simultaneously via a single catastrophic event. The distinctive genomic features observed in the derivative chromosomes, together with the highly characteristic junction sequences, point to non-homologous end joining (NHEJ) as being the likely underlying mutational mechanism. By contrast, Replication-based mechanisms such as microhomology-mediated break-induced Replication (MMBIR) which involves serial Replication Slippage or serial template switching probably account for those complex genomic rearrangements that comprise multiple duplications and/or triplications.

  • elucidation of the complex structure and origin of the human trypsinogen locus triplication
    Human Molecular Genetics, 2009
    Co-Authors: Angelique Chauvin, David Neil Cooper, Jianmin Chen, Sylvia Quemener, Emmanuelle Masson, Hildegard Kehrersawatzki, Barbara Ohmle, Cedric Le Marechal, Claude Ferec
    Abstract:

    One of the causes of chronic pancreatitis is the duplication and triplication of a ∼605 kb segment containing the trypsinogen locus. Employing array-comparative genomic hybridization, we fully characterized the triplication copy number mutation (CNM) and found it to be part of a complex rearrangement that also contains a triplicated ∼137 kb segment and 21 bp sequence tract. This triplication allele therefore constitutes a gain of two tandemly arranged composite duplication blocks, each comprising a copy of the ∼605 kb segment, a copy of the inverted ∼137 kb segment and a copy of the inverted 21 bp sequence tract. As such, it represents the first characterization of a human complex triplication CNM at the DNA sequence level. All triplications and duplications identified were found to arise from a common founder chromosome. A two-step process is proposed for the generation of this highly unusual triplication CNM. Thus, the first composite duplication block is envisaged to have been generated by break-induced serial Replication Slippage during mitosis. This duplication would have provided the sequence homology required to promote non-allelic homologous recombination (NAHR) during meiosis which would then, in a second step, have generated the complex triplication allele. Our data provide support for the view that many human germline copy number variants arise through Replication-based mechanisms during the premeiotic mitotic divisions of germ cells. The low copy repeats thereby generated could then serve to promote NAHR during meiosis, giving rise to amplified DNA sequences which would themselves predispose to further recombinational events during both mitosis and meiosis.

  • intrachromosomal serial Replication Slippage in trans gives rise to diverse genomic rearrangements involving inversions
    Human Mutation, 2005
    Co-Authors: Jianmin Chen, Nadia Chuzhanova, Peter D Stenson, Claude Ferec, David Neil Cooper
    Abstract:

    Serial Replication Slippage in cis (SRScis) provides a plausible explanation for many complex genomic rearrangements that underlie human genetic disease. This concept, taken together with the intra- and intermolecular strand switch models that account for mutations that arise via quasipalindrome correction, suggest that intrachromosomal SRS in trans (SRStrans) mediated by short inverted repeats may also give rise to a diverse series of complex genomic rearrangements. If this were to be so, such rearrangements would invariably generate inversions. To test this idea, we collated all informative mutations involving inversions of >or=5 bp but <1 kb by screening the Human Gene Mutation Database (HGMD; www.hgmd.org) and conducting an extensive literature search. Of the 21 resulting mutations, only two (both of which coincidentally contain untemplated additions) were found to be incompatible with the SRStrans model. Eighteen (one simple inversion, six inversions involving sequence replacement by upstream or downstream sequence, five inversions involving the partial reinsertion of removed sequence, and six inversions that occurred in a more complicated context) of the remaining 19 mutations were found to be consistent with either two steps of intrachromosomal SRStrans or a combination of Replication Slippage in cis plus intrachromosomal SRStrans. The remaining lesion, a 31-kb segmental duplication associated with a small inversion in the SLC3A1 gene, is explicable in terms of a modified SRS model that integrates the concept of "break-induced Replication." This study therefore lends broad support to our postulate that intrachromosomal SRStrans can account for a variety of complex gene rearrangements that involve inversions. (c) 2005 Wiley-Liss, Inc.

  • complex gene rearrangements caused by serial Replication Slippage
    Human Mutation, 2005
    Co-Authors: Jianmin Chen, Nadia Chuzhanova, Peter D Stenson, Claude Ferec, David Neil Cooper
    Abstract:

    The now-classical model of Replication Slippage can in principle account for both simple deletions and tandem duplications associated with short direct repeats. Invariably, a single Replication Slippage event is invoked, irrespective of whether simple deletions or tandem duplications are involved. However, we recently identified three complex duplicational insertions that could also be accounted for by a model of serial Replication Slippage. We postulate that a sizeable proportion of hitherto inexplicable complex gene rearrangements may be explained by such a model. To test this idea, and to assess the generality of our initial findings, a number of complex gene rearrangements were selected from the Human Gene Mutation Database (HGMD). Some 95% (20/21) of these mutations were found to be explicable by twin or multiple rounds of Replication Slippage, the sole exception being a double deletion in the F9 gene that is associated with DNA sequences that appear capable of adopting non-B conformations. Of the 20 complex gene rearrangements, 19 (seven simple double deletions, one triple deletion, two double mutational events comprising a simple deletion and a simple insertion, six simple indels that may constitute a novel and non-canonical class of gene conversion, and three complex indels) were compatible with the model of serial Replication Slippage in cis; the remaining indel in the MECP2 gene, however, appears to have arisen via interchromosomal Replication Slippage in trans. Our postulate that serial Replication Slippage may account for a variety of complex gene rearrangements has therefore received broad support from the study of the above diverse series of mutations. (c) 2005 Wiley-Liss, Inc.

  • complex gene rearrangements caused by serial Replication Slippage
    Human Mutation, 2005
    Co-Authors: Jianmin Chen, Nadia Chuzhanova, Peter D Stenson, Claude Ferec, David Neil Cooper
    Abstract:

    The now-classical model of Replication Slippage can in principle account for both simple deletions and tandem duplications associated with short direct repeats. Invariably, a single Replication Slippage event is invoked, irrespective of whether simple deletions or tandem duplications are involved. However, we recently identified three complex duplicational insertions that could also be accounted for by a model of serial Replication Slippage. We postulate that a sizeable proportion of hitherto inexplicable complex gene rearrangements may be explained by such a model. To test this idea, and to assess the generality of our initial findings, a number of complex gene rearrangements were selected from the Human Gene Mutation Database (HGMD). Some 95% (20/21) of these mutations were found to be explicable by twin or multiple rounds of Replication Slippage, the sole exception being a double deletion in the F9 gene that is associated with DNA sequences that appear capable of adopting non-B conformations. Of the 20 complex gene rearrangements, 19 (seven simple double deletions, one triple deletion, two double mutational events comprising a simple deletion and a simple insertion, six simple indels that may constitute a novel and non-canonical class of gene conversion, and three complex indels) were compatible with the model of serial Replication Slippage in cis; the remaining indel in the MECP2 gene, however, appears to have arisen via interchromosomal Replication Slippage in trans. Our postulate that serial Replication Slippage may account for a variety of complex gene rearrangements has therefore received broad support from the study of the above diverse series of mutations.

Isabelle Cousineau - One of the best experts on this subject based on the ideXlab platform.

  • brca1 regulates rad51 function in response to dna damage and suppresses spontaneous sister chromatid Replication Slippage implications for sister chromatid cohesion genome stability and carcinogenesis
    Cancer Research, 2005
    Co-Authors: Isabelle Cousineau, Christine Abaji, Abdellah Belmaaza
    Abstract:

    The breast/ovarian cancer susceptibility proteins BRCA1 and BRCA2 maintain genome stability, at least in part, through a functional role in DNA damage repair. They both colocalize with RAD51 at sites of DNA damage/Replication and activate RAD51-mediated homologous recombination repair of DNA double-strand breaks (DSB). Whereas BRCA2 interacts directly with and regulates RAD51, the role of BRCA1 in this process is unclear. However, BRCA1 may regulate RAD51 in response to DNA damage or through its ability to interact with and regulate MRE11/RAD50/NBS1 (MRN) during the processing of DSBs into single-strand DNA (ssDNA) ends, prerequisite substrates for RAD51, or both. To test these hypotheses, we measured the effect of BRCA1 on the competition between RAD51-mediated homologous recombination (gene conversion and crossover) versus RAD51-independent homologous recombination [single-strand annealing (SSA)] for ssDNA at a site-specific chromosomal DSB within a DNA repeat, a substrate for both homologous recombination pathways. Expression of wild-type BRCA1 in BRCA1-deficient human recombination reporter cell lines promoted both gene conversion and SSA but greatly enhanced gene conversion. In addition, BRCA1 also suppressed both spontaneous gene conversion and deletion events, which can arise from either crossover or sister chromatid Replication Slippage (SCRS), a RAD51-independent process. BRCA1 does not seem to block crossover. From these results, we conclude that (a) BRCA1 regulates RAD51 function in response to the type of DNA damage and (b) BRCA1 suppresses SCRS, suggesting a role for this protein in sister chromatid cohesion/alignment. Loss of such control in response to estrogen-induced DNA damage after BRCA1 inactivation may be a key initial event that triggers genome instability and carcinogenesis.

  • brca1 regulates rad51 function in response to dna damage and suppresses spontaneous sister chromatid Replication Slippage implications for sister chromatid cohesion genome stability and carcinogenesis
    Cancer Research, 2005
    Co-Authors: Isabelle Cousineau, Christine Abaji, Abdellah Belmaaza
    Abstract:

    The breast/ovarian cancer susceptibility proteins BRCA1 and BRCA2 maintain genome stability, at least in part, through a functional role in DNA damage repair. They both colocalize with RAD51 at sites of DNA damage/Replication and activate RAD51-mediated homologous recombination repair of DNA double-strand breaks (DSB). Whereas BRCA2 interacts directly with and regulates RAD51, the role of BRCA1 in this process is unclear. However, BRCA1 may regulate RAD51 in response to DNA damage or through its ability to interact with and regulate MRE11/RAD50/NBS1 (MRN) during the processing of DSBs into single-strand DNA (ssDNA) ends, prerequisite substrates for RAD51, or both. To test these hypotheses, we measured the effect of BRCA1 on the competition between RAD51-mediated homologous recombination (gene conversion and crossover) versus RAD51-independent homologous recombination [single-strand annealing (SSA)] for ssDNA at a site-specific chromosomal DSB within a DNA repeat, a substrate for both homologous recombination pathways. Expression of wild-type BRCA1 in BRCA1-deficient human recombination reporter cell lines promoted both gene conversion and SSA but greatly enhanced gene conversion. In addition, BRCA1 also suppressed both spontaneous gene conversion and deletion events, which can arise from either crossover or sister chromatid Replication Slippage (SCRS), a RAD51-independent process. BRCA1 does not seem to block crossover. From these results, we conclude that (a) BRCA1 regulates RAD51 function in response to the type of DNA damage and (b) BRCA1 suppresses SCRS, suggesting a role for this protein in sister chromatid cohesion/alignment. Loss of such control in response to estrogen-induced DNA damage after BRCA1 inactivation may be a key initial event that triggers genome instability and carcinogenesis. (Cancer Res 2005; 65(24): 11384-91)

  • brca2 regulates homologous recombination in response to dna damage implications for genome stability and carcinogenesis
    Cancer Research, 2005
    Co-Authors: Christine Abaji, Isabelle Cousineau, Abdellah Belmaaza
    Abstract:

    BRCA2 has been implicated in the maintenance of genome stability and RAD51-mediated homologous recombination repair of chromosomal double-strand breaks (DSBs), but its role in these processes is unclear. To gain more insight into its role in homologous recombination, we expressed wild-type BRCA2 in the well-characterized BRCA2-deficient human cell line CAPAN-1 containing, as homologous recombination substrates, either direct or inverted repeats of two inactive marker genes. Whereas direct repeats monitor a mixture of RAD51-dependent and RAD51-independent homologous recombination events, inverted repeats distinguish between these events by reporting RAD51-dependent homologous recombination, gene conversion, and crossover events only. At either repeats, BRCA2 decreases the rate and frequency of spontaneous homologous recombination, but following chromosomal DSBs, BRCA2 increases the frequency of homologous recombination. At direct repeats, BRCA2 suppresses both spontaneous gene conversion and deletions, which can arise either from crossover or RAD51-independent sister chromatid Replication Slippage (SCRS), but following chromosomal DSBs, BRCA2 highly promotes gene conversion with little effect on deletions. At inverted repeats, spontaneous or DSB-induced crossover events were scarce and BRCA2 does not suppress their formation. From these results, we conclude that (i) BRCA2 regulates RAD51 recombination in response to the type of DNA damage and (ii) BRCA2 suppresses SCRS, suggesting a role for BRCA2 in sister chromatids cohesion and/or alignment. Loss of such control in response to estrogen-induced DNA damage after BRCA2 inactivation may be a key initial event triggering genome instability and carcinogenesis.

Enrique Viguera - One of the best experts on this subject based on the ideXlab platform.

  • Replication Slippage of the thermophilic dna polymerases b and d from the euryarchaeota pyrococcus abyssi
    Frontiers in Microbiology, 2014
    Co-Authors: Melissa G Castillolizardo, Ghislaine Henneke, Enrique Viguera
    Abstract:

    Replication Slippage or slipped-strand mispairing involves the misalignment of DNA strands during the Replication of repeated DNA sequences, and can lead to genetic rearrangements such as microsatellite instability. Here, we show that PolB and PolD replicative DNA polymerases from the archaeal model Pyrococcus abyssi (Pab) slip in vitro during Replication of a single-stranded DNA template carrying a hairpin structure and short direct repeats. We find that this occurs in both their wild-type (exo+) and exonuclease deficient (exo-) forms. The Slippage behavior of PabPolB and PabPolD, probably due to limited strand displacement activity, resembles that observed for the high fidelity P. furiosus (Pfu) DNA polymerase. The presence of PabPCNA inhibited PabPolB and PabPolD Slippage. We propose a model whereby PabPCNA stimulates strand displacement activity and polymerase progression through the hairpin, thus permitting the error-free Replication of repetitive sequences.

  • In vitro Replication Slippage by DNA polymerases from thermophilic organisms.
    Journal of molecular biology, 2001
    Co-Authors: Enrique Viguera, Danielle Canceill, S D Ehrlich
    Abstract:

    Replication Slippage of DNA polymerases is a potential source of spontaneous genetic rearrangements in prokaryotic and eukaryotic cells. Here we show that different thermostable DNA polymerases undergo Replication Slippage in vitro, during single-round Replication of a single-stranded DNA template carrying a hairpin structure. Low-fidelity polymerases, such as Thermus aquaticus (Taq), high-fidelity polymerases, such as Pyrococcus furiosus (Pfu) and a highly thermostable polymerase from Pyrococcus abyssi (Pyra™ exo−) undergo Slippage. Thermococcus litoralis DNA polymerase (Vent®) is also able to slip; however, Slippage can be inhibited when its strand-displacement activity is induced. Moreover, DNA polymerases that have a constitutive strand-displacement activity, such as Bacillus stearothermophilus DNA polymerase (Bst), do not slip. Polymerases that slip during single-round Replication generate hairpin deletions during PCR amplification, with the exception of Vent® polymerase because its strand-displacement activity is induced under these conditions. We show that these hairpin deletions occurring during PCR are due to Replication Slippage, and not to a previously proposed process involving polymerization across the hairpin base.

  • Replication Slippage involves DNA polymerase pausing and dissociation
    EMBO Journal, 2001
    Co-Authors: Enrique Viguera, Danielle Canceill, S D Ehrlich
    Abstract:

    Genome rearrangements can take place by a process known as Replication Slippage or copy-choice recombination. The Slippage occurs between repeated sequences in both prokaryotes and eukaryotes, and is invoked to explain microsatellite instability, which is related to several human diseases. We analysed the molecular mechanism of Slippage between short direct repeats, using in vitro Replication of a single-stranded DNA template that mimics the lagging strand synthesis. We show that Slippage involves DNA polymerase pausing, which must take place within the direct repeat, and that the pausing polymerase dissociates from the DNA. We also present evidence that, upon polymerase dissociation, only the terminal portion of the newly synthesized strand separates from the template and anneals to another direct repeat. Resumption of DNA Replication then completes the Slippage process.

  • Replication Slippage of different DNA polymerases is inversely related to their strand displacement efficiency
    Journal of Biological Chemistry, 1999
    Co-Authors: Danielle Canceill, Enrique Viguera, S D Ehrlich
    Abstract:

    Replication Slippage is a particular type of error caused by DNA polymerases believed to occur both in bacterial and eukaryotic cells. Previous studies have shown that deletion events can occur in Escherichia coli by Replication Slippage between short duplications and that the main E. coli polymerase, DNA polymerase III holoenzyme is prone to such Slippage. In this work, we present evidence that the two other DNA polymerases of E. coli, DNA polymerase I and DNA polymerase II, as well as polymerases of two phages, T4 (T4 pol) and T7 (T7 pol), undergo Slippage in vitro, whereas DNA polymerase from another phage, Phi29, does not. Furthermore, we have measured the strand displacement activity of the different polymerases tested for Slippage in the absence and in the presence of the E. coli single-stranded DNA-binding protein (SSB), and we show that: (i) polymerases having a strong strand displacement activity cannot slip (DNA polymerase from Phi29); (ii) polymerases devoid of any strand displacement activity slip very efficiently (DNA polymerase II and T4 pol); and (iii) stimulation of the strand displacement activity by E. coli SSB (DNA polymerase I and T7 pol), by phagic SSB (T4 pol), or by a mutation that affects the 3' --> 5' exonuclease domain (DNA polymerase II exo(-) and T7 pol exo(-)) is correlated with the inhibition of Slippage. We propose that these observations can be interpreted in terms of a model, for which we have shown that high strand displacement activity of a polymerase diminishes its propensity to slip.