Éditeur(s) : HAL CCSD BioMed Central
Résumé : International audience
BACKGROUND: Homologous recombination is the key process that generates genetic diversity and drives evolution. SPO11 protein triggers recombination by introducing DNA double stranded breaks at discreet areas of the genome called recombination hotspots. The hotspot locations are largely determined by the DNA binding specificity of the PRDM9 protein in human, mice and most other mammals. In budding yeast Saccharomyces cerevisae, which lacks a Prdm9 gene, meiotic breaks are formed opportunistically in the regions of accessible chromatin, primarily at gene promoters. The genome-wide distribution of hotspots in this organism can be altered by tethering Spo11 protein to Gal4 recognition sequences in the strain expressing Spo11 attached to the DNA binding domain of the Gal4 transcription factor. To establish whether similar re-targeting of meiotic breaks can be achieved in PRDM9-containing organisms we have generated a Gal4BD-Spo11 mouse that expresses SPO11 protein joined to the DNA binding domain of yeast Gal4. RESULTS: We have mapped the genome-wide distribution of the recombination initiation sites in the Gal4BD-Spo11 mice. More than two hundred of the hotspots in these mice were novel and were likely defined by Gal4BD, as the Gal4 consensus motif was clustered around the centers in these hotspots. Surprisingly, meiotic DNA breaks in the Gal4BD-Spo11 mice were significantly depleted near the ends of chromosomes. The effect is particularly striking at the pseudoautosomal region of the X and Y chromosomes -- normally the hottest region in the genome. CONCLUSIONS: Our data suggest that specific, yet-unidentified factors influence the initiation of meiotic recombination at subtelomeric chromosomal regions.
ISSN: 1471-2164

inserm-00849779
http://www.hal.inserm.fr/inserm-00849779
http://www.hal.inserm.fr/inserm-00849779/document
http://www.hal.inserm.fr/inserm-00849779/file/1471-2164-14-493.pdf
DOI : 10.1186/1471-2164-14-493

Éditeur(s) : HAL CCSD Cold Spring Harbor Laboratory Press
Résumé : International audience
Meiotic recombination is required for the segregation of homologous chromosomes and is essential for fertility. In most mammals, the DNA double-strand breaks (DSBs) that initiate meiotic recombination are directed to a subset of genomic loci (hot spots) by sequence-specific binding of the PRDM9 protein. Rapid evolution of the DNA-binding specificity of PRDM9 and gradual erosion of PRDM9-binding sites by gene conversion will alter the recombination landscape over time. To better understand the evolutionary turnover of recombination hot spots and its consequences, we mapped DSB hot spots in four major subspecies of Mus musculus with different Prdm9 alleles and in their F1 hybrids. We found that hot spot erosion governs the preferential usage of some Prdm9 alleles over others in hybrid mice and increases sequence diversity specifically at hot spots that become active in the hybrids. As crossovers are disfavored at such hot spots, we propose that sequence divergence generated by hot spot turnover may create an impediment for recombination in hybrids, potentially leading to reduced fertility and, eventually, speciation
ISSN: 0890-9369

hal-01281480
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01281480
DOI : 10.1101/gad.270009.115
PUBMED : 26833728

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Mitochondrial DNA integrity is ensured by several nuclear-encoded proteins in vertebrates, and a number of mtDNA alterations in human diseases, including deletions and duplications, have been suspected to result from errors in the mitochondrial recombination pathway. However, the presence of the latter system is still a matter of controversy as RecA proteins display various functions in vitro. In Escherichia coli, RecA plays a central role in homologous recombination by pairing and transferring a single strand to a homologous duplex DNA. To address indirectly the issue of a mitochondrial recombination pathway in vivo, we have constructed a chimeric gene containing an N terminal mitochondrial targeting sequence and the E. coli RecA gene. Cells were transfected by the recombinant plasmid, then tested for their mtDNA repair upon bleomycin treatment. We found an increased repair rate of the mitochondrial DNA in cells expressing RecA as compared to control cells. These results indicate that the transfected cells display an improved mtDNA repair replication pathway due to the exogenous RecA, likely in synergy with an endogenous rate-limiting mitochondrial recombination pathway.
ISSN: 0027-5107

hal-01680533
https://hal.univ-antilles.fr/hal-01680533
PUBMED : 11356332

Éditeur(s) : HAL CCSD
Résumé : The recent accumulation of genomic sequence data has shown that gene evolution is not strictly tree-Like. Many evolutionary processes, like exon shuffling, gene fusion or nonhomologous recombination remodel genes by creating composite structures that are made from parts with different evolutionary histories. The development of sequence similarity networks provides an analytical framework to study the impact of these processes on molecular evolution, by structuring the resemblance relationships between sequences and by formalizing, in terms of graph theory, the detection of composite genes (intransitive triplets) and gene families (clique minimal separators). The size of current data sets, typically several million sequences, has also required the development of new tools and methods: sequence comparison parallelization, large networks visualization with Louvain communities and large cycles identification. When applied to eukaryotic and viral genome data sets, these methods have shown that composite genes are found throughout cellular organisms and mobile genetic elements. Proportionally, composite genes are more numerous in eukaryotic genomes; in absolute number, they are more numerous in viruses. In the latter, composite genes functional distribution is biased (enrichment of genes families that are essential for the perpetuation of the viral cycle), and the various parts of composite genes sometimes even originate from the genetic material of different viral classes. More generally, the extent of combinatorial processes, by unravelling other evolutionary bonds than homology bonds in the strictest sense, legitimates a pluralistic study of similarity relationships between sequences.
L’accumulation récente de données de séquences génomiques a montré que l’évolution des gènes n’est pas strictement arborescente. De nombreux processus évolutifs, comme l’exon shuffling, la fusion de gènes ou la recombinaison illégitime remodèlent les gènes, créant des structures composites, formées de parties dont les histoires évolutives sont différentes. Le développement de réseaux de similarité de séquences fournit un cadre analytique permettant d’étudier l’impact de ces processus sur l’évolution moléculaire, en structurant les relations de ressemblance entre séquences et en formalisant en termes de graphes la détection de gènes (triplets intransitifs) et de familles de gènes (cliques minimales séparatrices) composites. La taille des jeux de données actuels, de l’ordre de plusieurs millions de séquences, a également requis le développement de nouveaux outils et méthodes : parallélisation des comparaisons de séquences, visualisation de très grands réseaux par simplification en communautés de Louvain et identification de grands cycles. Appliquées à des jeux de données de génomes eucaryotes et viraux, ces méthodes ont démontré la présence de gènes composites dans tout le vivant et les éléments génétiques mobiles. En proportion, les gènes composites sont plus nombreux dans les génomes eucaryotes ; en nombre absolu, ils sont plus nombreux à être portés par des virus. Chez ces derniers, la distribution fonctionnelle des gènes composites est biaisée (enrichissement dans les familles essentielles pour la perpétuation du cycle viral), et les éléments des gènes composites trouvent même parfois leurs origines dans le matériel génétique de classes virales différentes. Plus généralement, l’étendue des processus combinatoires, en révélant des liens évolutionnaires autres que les liens d’homologie au sens fort, justifie une étude pluraliste des relations de similarité entre séquences.
https://tel.archives-ouvertes.fr/tel-01127379

NNT : 2014PA066358
tel-01127379
https://tel.archives-ouvertes.fr/tel-01127379
https://tel.archives-ouvertes.fr/tel-01127379/document
https://tel.archives-ouvertes.fr/tel-01127379/file/2014PA066358.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene (B[a]P), are widely distributed environmental contaminants exerting toxic effects such as genotoxicity and carcinogenicity, mainly associated with aryl hydrocarbon receptor (AhR) activation and the subsequent induction of cytochromes P-450 (CYP) 1-metabolizing enzymes. We previously reported an up-regulation of AhR expression and activity in primary cultures of human T lymphocyte by a physiological activation. Despite the suggested link between exposure to PAHs and the risk of lymphoma, the potential of activated human T lymphocytes to metabolize AhR exogenous ligands such as B[a]P, and produce DNA damage has not been investigated. In the present study, we characterized the genotoxic response of primary activated T lymphocytes to B[a] P. We demonstrated that, following T lymphocyte activation, B[a]P treatment triggers a marked increase in CYP1 expression and activity generating, upon metabolic activation, DNA adducts and double-strand breaks (DSBs) after a 48-h treatment. At this time point, B[a]P also induces a DNA damage response with ataxia telangiectasia mutated kinase activation, thus producing a p53-dependent response and T lymphocyte survival. B[a]P activates DSB repair by mobilizing homologous recombination machinery but also induces gene mutations in activated human T lymphocytes which could consequently drive a cancer process. In conclusion, primary cultures of activated human T lymphocytes represent a good model for studying genotoxic effects of environmental contaminants such as PAHs, and predicting human health issues.
ISSN: 0006-2952

hal-01560145
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01560145
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01560145/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01560145/file/Liamin%20et%20al.%20-%20Benzo%5Ba%5Dpyrene-induced%20DNA%20damage%20associated%20with%20.pdf
DOI : 10.1016/j.bcp.2017.04.025