Claude-Agnès Reynaud

Rearrangement/hypermutation/gene conversion: when, where and why?

Diversification strategies for immunoglobulins vary widely in different species. Here, Jean-Claude Weill and Claude-Agnès Reynaud argue that V(D)J recombination arose as a means for achieving allelic exclusion rather than diversity, and postulate that the choice of a diversification strategy is selected along with a specific site of B-cell differentiation. They propose that somatic mutation and gene conversion represent analogous molecular strategies occurring in specific chromatin accessibility contexts.

Rearrangement-Enhancing Element Upstream of the Mouse Immunoglobulin Kappa Chain J Cluster

Transcriptional regulatory elements have been shown to be necessary but not sufficient for the developmental regulation of immunoglobulin gene rearrangement in mouse precursor B cells. In the chicken λ light chain locus, additional elements in the V-J intervening sequence are involved in negative and positive regulation of rearrangement. Here, mutation of the mouse homolog of a chicken element, located in the Vκ-Jκ intervening sequence upstream of the Jκ cluster, was shown to significantly decrease rearrangement. This cis-acting recombination-enhancing element affects the rearrangement process without being involved in regulating transcription.

Mismatch repair and immunoglobulin gene hypermutation: did we learn something?

Abstract Recently, several reports have described the consequences of mismatch repair deficiency on the process of hypermutation of immunoglobulin genes. Some of these results appear contradictory and interpretations differ. More surprisingly, the gene-targeted knockout models for the separate mismatch repair proteins present radically different phenotypes, despite their involvement in a common repair process. This article, through a direct comparison of mutation patterns in different mismatch-repair-deficient contexts, will emphasize the conflicting issues and the questions that remain to be addressed.

The size of the transcriptional units of the avian globin genes defined at the pre-messenger RNA level

Abstract The steady-state distribution of globin gene-specific transcripts was analysed in avian erythroblast nuclear RNA with the aim of determining the maximal extent of the corresponding transcriptional units. The experimental approach included gel electrophoresis in pure formamide at high temperature, which allows absolute molecular weight determinations excluding secondary structure effects and intermolecular aggregation. The fraction of molecules in the 2 × 106 to 5 × 106 Mr range, which includes the rapidly turning over bulk primary transcripts, was re-isolated after electrophoresis and shown by Cr0t ‡ analysis with a globin gene-specific probe to contain both α and β globin messenger RNA sequences at a Cr 0 t 1 2 value of 10.2; a heterologeous mRNA added as an internal control was totally absent from this fraction. Quantitative evaluations show that as little as one molecule per cell is present in the Mr range of 3 × 106 to 5 × 106 and about ten molecules per cell with 2 × 106 to 3 × 106 Mr. These numbers, which correlate well with synthesis time and turnover rates of RNA in this molecular weight range, demonstrate the difficulty of detecting these full transcripts by less sensitive techniques. Determination of the steady-state pattern of globin pre-mRNA shows that, in addition to the rare full transcripts, globin pre-mRNA molecules are found with 1 × 106 to 2 × 106 (“28 S”) and 0.2 × 106 to 0.8 × 106 Mr (“15 S”); the latter represent the most abundant class of globin pre-mRNA (about 1000 molecules/cell). We conclude that the transcriptional units for the α and β globin genes may include up to 15,000 base-pairs rather than only the 1600 or so base-pairs corresponding to the 15 S pre-mRNA, the substrate for the final splicing event. The question remains open as to whether the full transcripts we observe are the compulsory primary pre-mRNA, or only facultative transcripts of the globin genes.

Generation of diversity by post-rearrangement diversification mechanisms: The chicken and the sheep antibody repertoires

Publisher Summary There are different cellular and molecular strategies operating to generate an antibody repertoire. The major goal is the production of a large number of different antibody molecules carrying different antigen-recognizing domains. This chapter describes two different molecular mechanisms used by two different species to generate their pre-immune repertoire: gene conversion used by chickens and hypermutation used by sheep. Activation of hypermutation during early B-cell development in the sheep represents a new function for this mechanism, which is responsible for affinity maturation during T-dependent immune responses. The molecular strategies have evolved with the structure of the primary B cell organs. Ongoing rearrangement takes place in bone marrow and involves a few cellular divisions corresponding to the B-cell lifetime in the organ. However, certain species use gut-associated lymphoid tissue (GALT) or bone marrow to generate their primary B-cell repertoire. Certain differences also exist in the physiology of the B-cell system when comparing species using GALT instead of bone marrow. Therefore, it becomes necessary to postulate the existence of a post-GALT stem cell in the periphery to self-maintain the naive B-cell population.

Generation of Diversity during B Cell Ontogeny in the Chicken

The organization of the chicken Ig loci is described in this review. It is further shown that light chain diversity is generated by precise recombination events between a pool of pseudogenes and an already rearranged single Vk gene. This unexpected way to create an immune repertoire is associated in this species with a particular ontogenic pathway for the B lymphoid lineage.