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Claude-Agnès Reynaud

Publications and source records attributed to Claude-Agnès Reynaud.

18 recordsLinked to original sources
PubMed2005

Contribution of DNA polymerase eta to immunoglobulin gene hypermutation in the mouse.

The mutation pattern of immunoglobulin genes was studied in mice deficient for DNA polymerase eta, a translesional polymerase whose inactivation is responsible for the xeroderma pigmentosum variant (XP-V) syndrome in humans. Mutations show an 85% G/C biased pattern, similar to that reported for XP-V patients. Breeding these mice with animals harboring the stop codon mutation of the 129/Olain background in their DNA polymerase iota gene did not alter this pattern further. Although this G/C biased mutation profile resembles that of mice deficient in the MSH2 or MSH6 components of the mismatch repair complex, the residual A/T mutagenesis of pol eta-deficient mice differs markedly. This suggests that, in the absence of pol eta, the MSH2-MSH6 complex is able to recruit another DNA polymerase that is more accurate at copying A/T bases, possibly pol kappa, to assume its function in hypermutation.

Animals↗
PubMed2005

Do developing B cells need antigen?

Just as potentially useful T cells are positively selected by MHC-peptide complexes in the thymus, it has been proposed that self or commensal bacterial epitopes might select B cell populations with the capacity to recognize polysaccharide or protein structures on pathogens. Recent studies indicate that the repertoire of B cells entering the periphery is not shaped by specific stimuli, but that mature B cell subsets may be under different selective pressures.

Antibody Diversity↗
PubMed2005

Splenic marginal zone B cells in humans: where do they mutate their Ig receptor?

Human IgM+ IgD+ CD27+ B cells have mutated Ig genes and harbor a splenic marginal zone (MZ) phenotype. In this issue, the group of R. Küppers has studied the expression of the enzyme activation-induced cytidine deaminase (AID) in human spleen samples by immunocytochemistry and failed to detect a significant AID-expressing subset in the MZ region. The consequences on the possible origin of these cells are discussed.

Animals↗
PubMed2005

Normal immune system development in mice lacking the Deltex-1 RING finger domain.

The Notch signaling pathway controls several cell fate decisions during lymphocyte development, from T-cell lineage commitment to the peripheral differentiation of B and T lymphocytes. Deltex-1 is a RING finger ubiquitin ligase which is conserved from Drosophila to humans and has been proposed to be a regulator of Notch signaling. Its pattern of lymphoid expression as well as gain-of-function experiments suggest that Deltex-1 regulates both B-cell lineage and splenic marginal-zone B-cell commitment. Deltex-1 was also found to be highly expressed in germinal-center B cells. To investigate the physiological function of Deltex-1, we generated a mouse strain lacking the Deltex-1 RING finger domain, which is essential for its ubiquitin ligase activity. Deltex-1(Delta/Delta) mice were viable and fertile. A detailed histological analysis did not reveal any defects in major organs. T- and B-cell development was normal, as were humoral responses against T-dependent and T-independent antigens. These data indicate that the Deltex-1 ubiquitin ligase activity is dispensable for mouse development and immune function. Possible compensatory mechanisms, in particular those from a fourth Deltex gene identified during the course of this study, are also discussed.

Amino Acid Sequence↗
PubMed2004

Human blood IgM "memory" B cells are circulating splenic marginal zone B cells harboring a prediversified immunoglobulin repertoire.

The human peripheral B-cell compartment displays a large population of immunoglobulin M-positive, immunoglobulin D-positive CD27(+) (IgM(+)IgD(+)CD27(+)) "memory" B cells carrying a mutated immunoglobulin receptor. By means of phenotypic analysis, complementarity-determining region 3 (CDR3) spectratyping during a T-independent response, and gene-expression profiling of the different blood and splenic B-cell subsets, we show here that blood IgM(+)IgD(+)CD27(+) cells correspond to circulating splenic marginal zone B cells. Furthermore, analysis of this peripheral subset in healthy children younger than 2 years shows that these B cells develop and mutate their immunoglobulin receptor during ontogeny, prior to their differentiation into T-independent antigen-responsive cells. It is therefore proposed that these IgM(+)IgD(+)CD27(+) B cells provide the splenic marginal zone with a diversified and protective preimmune repertoire in charge of the responses against encapsulated bacteria.

Adolescent↗
PubMed2004

DNA polymerase eta is involved in hypermutation occurring during immunoglobulin class switch recombination.

Base substitutions, deletions, and duplications are observed at the immunoglobulin locus in DNA sequences involved in class switch recombination (CSR). These mutations are dependent upon activation-induced cytidine deaminase (AID) and present all the characteristics of the ones observed during V gene somatic hypermutation, implying that they could be generated by the same mutational complex. It has been proposed, based on the V gene mutation pattern of patients with the cancer-prone xeroderma pigmentosum variant (XP-V) syndrome who are deficient in DNA polymerase eta (pol eta), that this enzyme could be responsible for a large part of the mutations occurring on A/T bases. Here we show, by analyzing switched memory B cells from two XP-V patients, that pol eta is also an A/T mutator during CSR, in both the switch region of tandem repeats as well as upstream of it, thus suggesting that the same error-prone translesional polymerases are involved, together with AID, in both processes.

Adult↗
PubMed2004

A bird's eye view on human B cells.

We show in this review that there is a continuum between the chicken B-cell system classified as the first GALT model described and the human B-cell system. We propose that humans have conserved for one B-cell subpopulation, the marginal zone B-cell subset in charge of T-independent responses, the strategies of diversification used by GALT species to generate their pre-immune repertoire.

Animals↗
PubMed2003

Specific over-expression of deltex and a new Kelch-like protein in human germinal center B cells.

Ig gene hypermutation was originally described as the molecular process underlying B cell affinity maturation following a T-dependent immune response. Somatic hypermutation is also used in some species such as sheep, to generate diversity during formation of the primary antibody repertoire. In sheep, B cells mutate their Ig receptor during antigen-independent development in the lymphoid follicles of ileal Peyer's patches, but this process is arrested when these same B cells are cultured in vitro. We have used these differences between in vivo and in vitro B cell development to perform a cDNA subtraction between these two cell populations, in order to search for genes that might be involved in the hypermutation process. We describe in this paper the characterization of two genes, highly expressed in sheep ileal Peyer's patch B cells and also in centroblasts of human tonsils: deltex (Drosophila) homolog 1 (DTX1), which is related to the Notch pathway and a new Kelch-like protein, KLHL6. The putative role of these proteins, which are more likely involved in the germinal center B cell differentiation pathway than in the hypermutation mechanism per se, is discussed.

Amino Acid Sequence↗
PubMed2003

Immunoglobulin kappa light chain gene rearrangement is impaired in mice deficient for DNA polymerase mu.

DNA polymerase mu (pol mu) is a template-dependent polymerase closely related to the lymphoid-specific enzyme terminal deoxynucleotidyl transferase (TdT). We report here the phenotype of pol mu-deficient mice. Such animals display an abnormal B cell differentiation, with a specific alteration in the IgM- to IgM+ transition in bone marrow. In all mice, Ig light chain gene rearrangement is impaired at the level of the Vkappa-Jkappa and Vlambda-Jlambda junctions, which show extensive nibbling of both coding extremities. These alterations lead to a profound defect in the peripheral B cell compartment which, although variable between animals, results in an average 40% reduction in the splenic B cell fraction. Pol mu appears, therefore, as a key element contributing to the relative homogeneity in size of light chain CDR3 and taking part in Ig gene rearrangement at a stage where TdT is no longer expressed.

Animals↗
PubMed2003

What role for AID: mutator, or assembler of the immunoglobulin mutasome?

Activation-induced cytidine deaminase (AID) has been shown to trigger three mechanisms for diversifying immunoglobulin genes--somatic hypermutation, isotype switch recombination and gene conversion--most probably by initiating cytidine deamination at the immunoglobulin locus. Although this deamination process has been shown to be potentially mutagenic by itself, most of the mutations generated in the physiological hypermutation process seem to be created through the AID-mediated assembly of a mutasome complex involving specific repair activities and error-prone DNA polymerases.

Animals↗
PubMed2003

Hypermutation in human B cells in vivo and in vitro.

We develop our previous observation that a subpopulation of circulating memory IgM(+)IgD(+)CD27(+)B cells belongs to a separate pathway of differentiation in humans. This subpopulation, which represents 5-25% of peripheral B cells, is also present in spleen in the same proportion and displays a marginal-zone-like B cell phenotype. In addition, we describe a short-time in vitro induction model for somatic hypermutation by using the BL2 Burkitt's lymphoma cell line stimulated by a combination of antibodies directed against different surface receptors. This short-time assay allows us to show that mutations are stably introduced in one DNA strand of the BL2 VH gene in the G1 phase of the cell cycle.

B-Lymphocytes↗
PubMed2002

Induction of somatic hypermutation in immunoglobulin genes is dependent on DNA polymerase iota.

Somatic hypermutation of immunoglobulin genes is a unique, targeted, adaptive process. While B cells are engaged in germinal centres in T-dependent responses, single base substitutions are introduced in the expressed Vh/Vl genes to allow the selection of mutants with a higher affinity for the immunizing antigen. Almost every possible DNA transaction has been proposed to explain this process, but each of these models includes an error-prone DNA synthesis step that introduces the mutations. The Y family of DNA polymerases--pol eta, pol iota, pol kappa and rev1--are specialized for copying DNA lesions and have high rates of error when copying a normal DNA template. By performing gene inactivation in a Burkitt's lymphoma cell line inducible for hypermutation, we show here that somatic hypermutation is dependent on DNA polymerase iota.

Antibody Affinity↗
PubMed2002

AID-dependent somatic hypermutation occurs as a DNA single-strand event in the BL2 cell line.

Immunoglobulin (Ig) gene hypermutation can be induced in the BL2 Burkitt's lymphoma cell line by IgM cross-linking and coculture with normal or transformed T helper clones. We describe here a T cell#150;independent in vitro induction assay, by which hypermutation is induced in BL2 cells through simultaneous aggregation of three surface receptors: IgM, CD19 and CD21. The mutations arise as a post-transcriptional event within 90 min. They are stably introduced in the G1 phase of the cell cycle, occurring in one of the two variable gene DNA strands, and eventually become fixed by replication in one of the daughter cells. Inactivation of AID (activation-induced cytidine deaminase) by homologous recombination in BL2 cells completely inhibits the process, thus validating this induction procedure as a model for the in vivo mechanism.

Burkitt Lymphoma↗
PubMed2002

Cutting edge: DNA polymerases mu and lambda are dispensable for Ig gene hypermutation.

Mutations arising in Ig V genes during an immune response are most likely introduced by one or several error-prone DNA polymerases. Many of the recently described nonreplicative DNA polymerases have an intrinsic fidelity compatible with such an activity, the strongest candidates being polymerase (pol) eta, pol iota, pol zeta, and pol mu. We report in this work that mice inactivated for either of the two polymerases related to pol beta (i.e., pol mu and pol lambda) are viable and fertile and display a normal hypermutation pattern.

Animals↗