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Research question What is the impact of radiation exposure on oocyte quality and female fertility? Design Prepubertal mice underwent whole-body irradiation with a single dose (0.02, 0.1, 0.5, 2, 8 Gy) of gamma- or X-rays. Oocytes were quantified in irradiated (n = 36) and sham-treated (n = 8) mice. After a single exposure to 2 Gy, formation of DNA double-strand breaks (n = 10), activation of checkpoint kinase (Chk2) (n = 10) and dynamics of follicular growth (n = 18) were analysed. Fertility assessment was performed in adult irradiated mice and controls from the number of pups per mouse (n = 28) and the fetal abortion rate (n = 24). Ploidy of mature oocytes (n = 20) was analysed after CREST immunostaining, and uterine sections were examined. Results Radiation exposure induced a massive loss of primordial follicles with LD50 below 50 mGy for both gamma and X-rays. Growing follicles survived doses up to 8 Gy. This difference in radiosensitivity was not due to a different amount of radio-induced DNA damage, and Chk2 was activated in all oocytes. Exposure to a 2 Gy dose abolished the long-term fertility of females due to depletion of the ovarian reserve. Detailed analysis indicates that surviving oocytes were able to complete folliculogenesis and could be fertilized. This transient fertility allowed irradiated females to produce a single litter albeit with a high rate of fetal abortion (23%, P = 0.0096), related to altered ploidy in the surviving oocytes (25.5%, P = 0.0035). Conclusions The effects of radiation on surviving oocyte quality question natural conception as a first-line approach in cancer survivors. Together, the data emphasize the need for fertility preservation before radiation exposure and call for reassessment of the use of cryopreserved oocytes.

Genetic instability is a hallmark of both cancer and aging. Homologous recombination (HR) is a prominent DNA repair pathway maintaining genomic integrity. Mutations in many HR genes lead to cancer predisposition. Paradoxically, the consequences of mutations in the pivotal HR player, RAD51, on cancer development remain puzzling. Moreover, in contrast with other HR genes, RAD51 mouse models are not available to experimentally address the role of RAD51 on aging and carcinogenesis, in vivo. Here, we engineered a mouse model with an inducible dominant negative form of RAD51 (SMRad51) that suppresses RAD51-mediated HR without stimulating alternative non-conservative repair pathways. We found that, in vivo expression of SMRad51 did not trigger tumorigenesis, but instead induced premature aging. We propose that these in vivo phenotypes result from the exhaustion of proliferating progenitors submitted to chronic endogenous replication stress resulting from RAD51-mediated HR suppression. Our data underline the importance of the RAD51 activity for progenitors homeostasis, preventing aging, and more generally for the balance between cancer and aging.

Creatine transporter deficiency prevents creatine uptake into the brain, leading to mental retardation. To better understand the pathophysiology, this study focuses on the identification of biomarkers related to cognitive improvement in a Slc6a8 knockout mouse model (Slc6a8/y) engineered to mimic the clinical features of CTD patients which have low brain creatine content. Shotgun proteomics analysis of 4,035 proteins in four different brain regions; the cerebellum, cortex, hippocampus (associated with cognitive functions) and brain stem, and muscle as a control, was performed in 24 mice. Comparisons of the protein abundance in the four brain regions between DCE-treated intranasally Slc6a8-/y mice and wild type and DCE-treated Slc6a8-/y and vehicle group identified 14 biomarkers, shedding light on the mechanism of action of DCE. Integrative bioinformatics and statistical modeling identified key proteins associated with CTD, including KIF1A and PLCB1. The abundance of these proteins in the four brain regions was significantly correlated with both the object recognition and the Y-maze tests. Functional analysis confirmed their key roles and associated molecules in CTD pathogenesis.

International audience; Many endocrine disruptors have been proven to impair the meiotic process which is required for the production of healthy gametes. Bisphenol A is emblematic of such disruptors, as it impairs meiotic prophase I and causes oocyte aneuploidy following in utero exposure. However, the mechanisms underlying these deleterious effects remain poorly understood. Furthermore, the increasing use of BPA alternatives raises concerns for public health. Here, we investigated the effects of foetal exposure to two BPA alternatives, bisphenol A Diglycidyl Ether (BADGE) and bisphenol AF (BPAF), on oogenesis in mice. These compounds delay meiosis initiation, increase the number of MLH1 foci per cell and induce oocyte aneuploidy. We further demonstrate that these defects are accompanied by changes in gene expression in foetal premeiotic germ cells and aberrant mRNA splicing of meiotic genes. We observed an increase in DNA oxidation after exposure to BPA alternatives. Specific induction of oxidative DNA damage during foetal germ cell differentiation causes similar defects during oogenesis, as observed in 8-oxoguanine DNA Glycosylase (OGG1)-deficient mice or after in utero exposure to potassium bromate (KBrO3), an inducer of oxidative DNA damage. The supplementation of BPA alternatives with N-acetylcysteine (NAC) counteracts the effects of bisphenols on meiosis. Together, our results propose oxidative DNA lesion as an event that negatively impacts female meiosis with major consequences on oocyte quality. This could be a common mechanism of action for numerous environmental pro-oxidant pollutants, and its discovery, could lead to reconsider the adverse effect of bisphenol mixtures that are simultaneously present in our environment.

International audience; In budding yeast, the MutL homolog heterodimer Mlh1-Mlh3 (MutLγ) plays a central role in the formation of meiotic crossovers. It is also involved in the repair of a subset of mismatches besides the main mismatch repair (MMR) endonuclease Mlh1-Pms1 (MutLα). The heterodimer interface and endonuclease sites of MutLγ and MutLα are located in their C-terminal domain (CTD). The molecular basis of MutLγ’s dual roles in MMR and meiosis is not known. To better understand the specificity of MutLγ, we characterized the crystal structure of Saccharomyces cerevisiae MutLγ(CTD). Although MutLγ(CTD) presents overall similarities with MutLα(CTD), it harbors some rearrangement of the surface surrounding the active site, which indicates altered substrate preference. The last amino acids of Mlh1 participate in the Mlh3 endonuclease site as previously reported for Pms1. We characterized mlh1 alleles and showed a critical role of this Mlh1 extreme C terminus both in MMR and in meiotic recombination. We showed that the MutLγ(CTD) preferentially binds Holliday junctions, contrary to MutLα(CTD). We characterized Mlh3 positions on the N-terminal domain (NTD) and CTD that could contribute to the positioning of the NTD close to the CTD in the context of the full-length MutLγ. Finally, crystal packing revealed an assembly of MutLγ(CTD) molecules in filament structures. Mutation at the corresponding interfaces reduced crossover formation, suggesting that these superstructures may contribute to the oligomer formation proposed for MutLγ. This study defines clear divergent features between the MutL homologs and identifies, at the molecular level, their specialization toward MMR or meiotic recombination functions.

Simple Summary Homologous recombination (HR) is a DNA repair pathway essential to genome stability and mutations in many HR genes are correlated with cancer predisposition. Transgenic mouse models are critical to establish HR factors as tumor suppressor genes. However, investigating the effects of suppressing HR genes in vivo is challenging because invalidation of most of them leads to embryonic lethality in mammals. To tackle this issue, elaborated alternative strategies have been developed. Here we review these alternative HR-defective mouse models and reveal the impact of HR defects on tumorigenesis. We highlight that the central HR factor, RAD51, has yet to be well characterized in vivo and, unlike most HR factors, its inactivation has not been associated with cancer predisposition, revealing what we call the “RAD51 paradox”. Finally, we discuss the use of mouse models to develop targeted cancer therapies as well as to understand the mechanisms of HR inactivation-driven tumorigenesis in vivo. Abstract Homologous recombination (HR) is a fundamental evolutionarily conserved process that plays prime role(s) in genome stability maintenance through DNA repair and through the protection and resumption of arrested replication forks. Many HR genes are deregulated in cancer cells. Notably, the breast cancer genes BRCA1 and BRCA2, two important HR players, are the most frequently mutated genes in familial breast and ovarian cancer. Transgenic mice constitute powerful tools to unravel the intricate mechanisms controlling tumorigenesis in vivo. However, the genes central to HR are essential in mammals, and their knockout leads to early embryonic lethality in mice. Elaborated strategies have been developed to overcome this difficulty, enabling one to analyze the consequences of HR disruption in vivo. In this review, we first briefly present the molecular mechanisms of HR in mammalian cells to introduce each factor in the HR process. Then, we present the different mouse models of HR invalidation and the consequences of HR inactivation on tumorigenesis. Finally, we discuss the use of mouse models for the development of targeted cancer therapies as well as perspectives on the future potential for understanding the mechanisms of HR inactivation-driven tumorigenesis in vivo.

SummaryMany endocrine disruptors have been proven to impair the meiotic process that is mandatory to produce healthy gametes. Bisphenol A is emblematic as it impairs meiotic prophase I and causes oocyte aneuploidy followingin uteroexposure. However, the mechanisms underlying these deleterious effects remain poorly understood. Furthermore, the increasing uses of BPA analogs raise concerns for public health. Here, we investigated the effect on oogenesis in mouse of fetal exposure to two BPA analogs, Bisphenol A Diglycidyl Ether (BADGE) or Bisphenol AF (BPAF). These analogs delay meiosis initiation, increase MLH1 focipercell and induce oocyte aneuploidy. We further demonstrate that these defects are accompanied by a deregulation of gene expression and aberrant mRNA splicing in fetal premeiotic germ cells. Interestingly, we observed an increase in DNA oxidation after exposure to BPA analogs. Specific induction of oxidative DNA damages during fetal germ cell differentiation causes similar defects during oogenesis, as observed in 8-Oxoguanine DNA Glycosylase (OGG1) deficient mice or afterin uteroexposure to potassium bromate (KBrO3), an inducer of oxidative DNA damages. Moreover, the supplementation of N-acetylcysteine (NAC) with BPA analogs counteracts the bisphenol-induced meiotic effect. Together our results position oxidative stress as a central event that negatively impacts the female meiosis with major consequences on oocyte quality. This could be a common mechanism of action for so called endocrine disruptors pollutants and it could lead to novel strategies for reprotoxic compounds.

During meiosis, programmed double-strand breaks are repaired by homologous recombination (HR) to form crossovers that are essential to homologous chromosome segregation. Single-stranded DNA (ssDNA) containing intermediates are key features of HR, which must be highly regulated. RPA, the ubiquitous ssDNA binding complex, was thought to play similar roles during mitotic and meiotic HR until the recent discovery of MEIOB and its partner, SPATA22, two essential meiosis-specific proteins. Here, we show that like MEIOB, SPATA22 resembles RPA subunits and binds ssDNA. We studied the physical and functional interactions existing between MEIOB, SPATA22, and RPA, and show that MEIOB and SPATA22 interact with the preformed RPA complex through their interacting domain and condense RPA-coated ssDNA in vitro. In meiotic cells, we show that MEIOB and SPATA22 modify the immunodetection of the two large subunits of RPA. Given these results, we propose that MEIOB-SPATA22 and RPA form a functional ssDNA-interacting complex to satisfy meiotic HR requirements by providing specific properties to the ssDNA.

Recombination is crucial for chromosome pairing and segregation during meiosis. SPATA22, along with its direct binding partner and functional collaborator, MEIOB, is essential for the proper repair of double-strand breaks (DSBs) during meiotic recombination. Here we describe a novel point-mutated allele (shani) of mouse Spata22 that we isolated in a forward genetic screen. shani mutant mice phenocopy Spata22-null and Meiob-null mice: mutant cells appear to form DSBs and initiate meiotic recombination, but are unable to complete DSB repair, leading to meiotic prophase arrest, apoptosis and sterility. shani mutants show precocious loss of DMC1 foci and improper accumulation of BLM-positive recombination foci, reinforcing the requirement of SPATA22-MEIOB for the proper progression of meiotic recombination events. The shani mutation lies within a Spata22 coding exon and molecular characterization shows that it leads to incorrect splicing of the Spata22 mRNA, ultimately resulting in no detectable SPATA22 protein. We propose that the shani mutation alters an exonic splicing enhancer element (ESE) within the Spata22 transcript. The affected DNA nucleotide is conserved in most tetrapods examined, suggesting that the splicing regulation we describe here may be a conserved feature of Spata22 regulation.

Background: Primary Ovarian Insufficiency (POI), a major cause of infertility, affects about 1–3% of women under forty years of age. Although there is a growing list of causal genetic alterations, POI remains mostly idiopathic. Methods: We performed exome sequencing (WES) of two sisters affected with POI, one unaffected sister and their mother from a consanguineous family. We assessed the impact of the identified MEIOB variant with a minigene assay and by sequencing illegitimate transcripts from the proband's leukocytes. We studied its functional impact on the interaction between MEIOB with its partner SPATA22 and their localization to DNA double-strand breaks (DSB). Findings: We identified a homozygous variant in the last base of exon 12 of MEIOB, which encodes a factor essential for meiotic recombination. This variant was predicted to strongly affect MEIOB pre-mRNA splicing. Consistently, a minigene assay showed that the variant induced exon 12 skipping, which was confirmed in vivo in the proband's leukocytes. Aberrant splicing leads to the production of a C-terminally truncated protein that cannot interact with SPATA22, abolishing their recruitment to DSBs. Interpretation: This truncating MEIOB variant is expected to provoke meiotic defects and a depleted follicular stock, as in Meiob−/− mice. This is the first molecular defect reported in a meiosis-specific single-stranded DNA-binding protein (SSB) responsible for POI. We hypothesise that alterations in other SSB proteins could explain cases of syndromic or isolated ovarian insufficiency. Fund: Université Paris Diderot, Fondation pour la Recherche Médicale, Fondation ARC contre le cancer, Commissariat à l'Energie Atomique and Institut Universitaire de France. Keywords: Exon skipping, Female infertility, MEIOB, Meiotic recombination, Primary ovarian insufficiency

Meiotic homologous recombination is a specialized process that involves homologous chromosome pairing and strand exchange to guarantee proper chromosome segregation and genetic diversity. The formation and repair of DNA double-strand breaks (DSBs) during meiotic recombination differs from those during mitotic recombination in that the homologous chromosome rather than the sister chromatid is the preferred repair template. The processing of single-stranded DNA (ssDNA) formed on intermediate recombination structures is central to driving the specific outcomes of DSB repair during meiosis. Replication protein A (RPA) is the main ssDNA-binding protein complex involved in DNA metabolism. However, the existence of RPA orthologs in plants and the recent discovery of meiosis specific with OB domains (MEIOB), a widely conserved meiosis-specific RPA1 paralog, strongly suggest that multiple RPA complexes evolved and specialized to subdivide their roles during DNA metabolism. Here we review ssDNA formation and maturation during mitotic and meiotic recombination underlying the meiotic specific features. We describe and discuss the existence and properties of MEIOB and multiple RPA subunits in plants and highlight how they can provide meiosis-specific fates to ssDNA processing during homologous recombination. Understanding the functions of these RPA homologs and how they interact with the canonical RPA subunits is of major interest in the fields of meiosis and DNA repair. Electronic supplementary material The online version of this article (doi:10.1007/s00412-015-0552-7) contains supplementary material, which is available to authorized users.

SummaryCrossovers produced by homologous recombination promote accurate chromosome segregation in meiosis and are controlled such that at least one forms per chromosome pair and multiple crossovers are widely spaced. Recombination initiates with an excess number of double-strand breaks made by Spo11 protein. Thus, crossover control involves a decision by which some breaks give crossovers while others follow a predominantly noncrossover pathway(s). To understand this decision, we examined recombination when breaks are reduced in yeast spo11 hypomorphs. We find that crossover levels tend to be maintained at the expense of noncrossovers and that genomic loci differ in expression of this “crossover homeostasis.” These findings define a previously unsuspected manifestation of crossover control, i.e., that the crossover/noncrossover ratio can change to maintain crossovers. Our results distinguish between existing models of crossover control and support the hypothesis that an obligate crossover is a genetically programmed event tied to crossover interference.

To investigate the role of the nucleosome during repair of DNA damage in yeast, we screened for histone H2B mutants that were sensitive to UV irradiation. We have isolated a new mutant, htb1-3, that shows preferential sensitivity to UV-C. There is no detectable difference in bulk chromatin structure or in the number of UV-induced cis-syn cyclobutane pyrimidine dimers (CPD) between HTB1 and htb1-3 strains. These results suggest a specific effect of this histone H2B mutation in UV-induced DNA repair processes rather than a global effect on chromatin structure. We analyzed the UV sensitivity of double mutants that contained the htb1-3 mutation and mutations in genes from each of the three epistasis groups of RAD genes. The htb1-3 mutation enhanced UV-induced cell killing in rad1Δ and rad52Δ mutants but not in rad6Δ or rad18Δ mutants, which are defective in postreplicational DNA repair (PRR). When combined with other mutations that affect PRR, the histone mutation increased the UV sensitivity of strains with defects in either the error-prone (rev1Δ) or error-free (rad30Δ) branches of PRR, but did not enhance the UV sensitivity of a strain with a rad5Δ mutation. When combined with a ubc13Δ mutation, which is also epistatic with rad5Δ, the htb1-3 mutation enhanced UV-induced cell killing. These results suggest that histone H2B acts in a novel RAD5-dependent branch of PRR.

Meiotic recombination is a mandatory process for sexual reproduction. We identified a protein specifically implicated in meiotic homologous recombination that we named: meiosis specific with OB domain (MEIOB). This protein is conserved among metazoan species and contains single-strand DNA binding sites similar to those of RPA1. Our studies in vitro revealed that both recombinant and endogenous MEIOB can be retained on single-strand DNA. Those in vivo demonstrated the specific expression of Meiob in early meiotic germ cells and the co-localization of MEIOB protein with RPA on chromosome axes. MEIOB localization in Dmc1 −/− spermatocytes indicated that it accumulates on resected DNA. Homologous Meiob deletion in mice caused infertility in both sexes, due to a meiotic arrest at a zygotene/pachytene-like stage. DNA double strand break repair and homologous chromosome synapsis were impaired in Meiob −/− meiocytes. Interestingly MEIOB appeared to be dispensable for the initial loading of recombinases but was required to maintain a proper number of RAD51 and DMC1 foci beyond the zygotene stage. In light of these findings, we propose that RPA and this new single-strand DNA binding protein MEIOB, are essential to ensure the proper stabilization of recombinases which is required for successful homology search and meiotic recombination., Author Summary Homologous recombination allows faithful repair of damaged DNA; in mitotic cells, it necessitates the formation of single strand DNA (ssDNA), which is first protected by RPA and then coated by the RAD51 recombinase to mediate homology search. Specific modifications are made to this mechanism during meiosis, a specialized division that allows halving the ploidy of the genome and the production of haploid gametes. Among others a specialized recombinase DMC1 is added to its somatic paralog RAD51 to perform homology search. We identified a new meiotic protein that we named meiosis specific with OB domains (MEIOB). Our findings indicate that MEIOB binds ssDNA, and we propose that MEIOB is a meiotic paralog of RPA, another OB-domain containing protein. Meiob mutant mice were infertile and unable to complete meiotic recombination, most likely due to destabilization of DMC1 and RAD51 in the absence of MEIOB. Meiosis appears thus to be a ‘game of two pairs’ using both the canonical players in homologous recombination (RPA and RAD51) and a second set of paralogs (MEIOB and DMC1). Identifying such new players should help clarify some genetic causes of infertility and shed new light on the interplay between the molecular actors involved in maintaining genome stability.

Fun30 and SMARCAD1 are identified as chromatin remodellers that promote DNA end resection during DNA repair and preserve genome stability in yeast and humans, respectively. For breakages in double-stranded DNA to be repaired, the 5′ terminal strand is resected to yield a 3′ terminal single-stranded tail. How resection occurs in the context of chromatin was unknown. The laboratories of Grzegorz Ira and Bertrand Llorente have identified the yeast Fun30 and human SMARCAD1 proteins as the chromatin re-modellers that facilitate resection. Fun30 is also required to overcome the inhibition of resection that occurs owing to binding of Rad9, a checkpoint adaptor protein, to the 5′ end of the break. Several homology-dependent pathways can repair potentially lethal DNA double-strand breaks (DSBs). The first step common to all homologous recombination reactions is the 5′–3′ degradation of DSB ends that yields the 3′ single-stranded DNA required for the loading of checkpoint and recombination proteins. In yeast, the Mre11–Rad50–Xrs2 complex (Xrs2 is known as NBN or NBS1 in humans) and Sae2 (known as RBBP8 or CTIP in humans) initiate end resection, whereas long-range resection depends on the exonuclease Exo1, or the helicase–topoisomerase complex Sgs1–Top3–Rmi1 together with the endonuclease Dna2 (refs 1–6). DSBs occur in the context of chromatin, but how the resection machinery navigates through nucleosomal DNA is a process that is not well understood7. Here we show that the yeast Saccharomyces cerevisiae Fun30 protein and its human counterpart SMARCAD1 (ref. 8), two poorly characterized ATP-dependent chromatin remodellers of the Snf2 ATPase family, are directly involved in the DSB response. Fun30 physically associates with DSB ends and directly promotes both Exo1- and Sgs1-dependent end resection through a mechanism involving its ATPase activity. The function of Fun30 in resection facilitates the repair of camptothecin-induced DNA lesions, although it becomes dispensable when Exo1 is ectopically overexpressed. Interestingly, SMARCAD1 is also recruited to DSBs, and the kinetics of recruitment is similar to that of EXO1. The loss of SMARCAD1 impairs end resection and recombinational DNA repair, and renders cells hypersensitive to DNA damage resulting from camptothecin or poly(ADP-ribose) polymerase inhibitor treatments. These findings unveil an evolutionarily conserved role for the Fun30 and SMARCAD1 chromatin remodellers in controlling end resection, homologous recombination and genome stability in the context of chromatin.

DNA repair occurs in a chromatin context, and nucleosome remodeling is now recognized as an important regulatory feature by allowing repair factors access to damaged sites. The yeast mating type locus (MAT) has emerged an excellent model to study the role of chromatin remodeling at a well-defined DNA double-strand break (DSB). We discuss methods to study nucleosome dynamics and DSB repair factor recruitment to the MAT locus after a DSB has been formed.

It has been known for some time that DNA double-strand breaks (DSBs) initiate homologous recombination during meiosis. Two recent studies show that the fate of a single DSB in yeast is strongly influenced by the presence of other breaks in the genome, hinting that cell-wide or chromosome-regional mechanisms control the outcome of DSB repair.

The subcellular distribution and posttranslational modification of human chromatin assembly factor 1 (CAF-1) have been investigated after UV irradiation of HeLa cells. In an asynchronous cell population only a subfraction of the two large CAF-1 subunits, p150 and p60, were found to exist in a chromatin-associated fraction. This fraction is most abundant during S phase in nonirradiated cells and is much reduced in G2 cells. After UV irradiation, the chromatin-associated form of CAF-1 dramatically increased in all cells irrespective of their position in the cell cycle. Such chromatin recruitment resembles that seen for PCNA, a DNA replication and repair factor. The chromatin-associated fraction of p60 was predominantly hypophosphorylated in nonirradiated G2 cells. UV irradiation resulted in the rapid recruitment to chromatin of phosphorylated forms of the p60 subunit. Furthermore, the amount of the p60 and p150 subunits of CAF-1 associated with chromatin was a function of the dose of UV irradiation. Consistent with these in vivo observations, we found that the amount of CAF-1 required to stimulate nucleosome assembly during the repair of UV photoproducts in vitro depended upon both the number of lesions and the phosphorylation state of CAF-1. The recruitment of CAF-1 to chromatin in response to UV irradiation of human cells described here supports a physiological role for CAF-1 in linking chromatin assembly to DNA repair.

Conserved among eukaryotes, homologous recombination is essential for the formation of cross-overs that are mandatory for pairing and chromosomes segregation during meiosis. Meiotic recombination is regulated by the combined action of ubiquitous and meiotic specific factors. SPATA22 and its meiotic-specific partner MEIOB are essential for the repair of DNA double strand breaks (DSB) during meiotic recombination. They interact with RPA, the major ubiquitous single-stranded DNA binding complex, in the progression and specialization of meiotic recombination. They are also expressed ectopically in some human cancers and are thus referred as Cancer Testis Antigens (CTA). First, we sought to specify the role of SPATA22 through the study of a novel point mutant (shani) of Spata22 in mice. shani mutant mice phenocopy Spata22-null and Meiob-null mice: unrepaired DSBs lead to meiotic prophase arrest, apoptosis and sterility. The shani mutation lies within a Spata22 coding exon and leads to incorrect splicing of Spata22 mRNA resulting in no detectable protein. We propose that the shani mutation alters an exonic splicing enhancer element (ESE) within the Spata22 transcript. To our knowledge, this is the first description of an ESE element in a meiotic murine gene.Then, we sought to determine the putative role of the ectopic expression of MEIOB and SPATA22 in some cancers. We analysed open access transcriptomic data and observed that MEIOB and SPATA22 are co-expressed in some tumors and cancer cell lines, suggesting a potential functionality of MEIOB-SPATA22. Our preliminary results suggest that MEIOB and SPATA22 modify cell proliferation when expressed transiently. We are developing stable inducible cell lines for the expression of MEIOB and SPATA22 in order to further study cell proliferation, DNA repair and genetic instability., Conservé chez les eucaryotes, la recombinaison homologue est essentielle à la formation des cross-overs indispensables à l’appariement et à la ségrégation des chromosomes au cours de la méiose. La recombinaison méiotique est régulée par l’action combinée de facteurs ubiquitaires et méiotiques spécifiques. SPATA22 et son partenaire MEIOB, tous deux méiotiques spécifiques, sont essentielles à la réparation des cassures doubles brins (CDB) de l’ADN au cours de la recombinaison méiotique. Ils interagissent avec RPA, le complexe ubiquitaire majeur de liaison à l’ADN simple brin, dans la progression et spécialisation de la recombinaison en méiose. Ils s’expriment aussi anormalement dans certains cancers chez l’Homme et sont ainsi désignés gènes Cancer Testis Antigens (CTA). D’une part, nous avons cherché à spécifier le rôle de SPATA22 à travers l’étude d’un nouveau mutant ponctuel (shani) de Spata22 chez la souris. Le mutant shani arbore un phénotype similaire aux souris nulles Spata22-/- ou Meiob-/- : la réparation incomplète des CDBs induit un arrêt des cellules germinales en prophase I induisant de l’apoptose et la stérilité. La mutation shani se situe sur un exon codant de Spata22 et aboutit à l’épissage incorrect du transcrit et une absence de détection protéique. Nous proposons que la mutation shani altère une séquence éxonique activatrice de l’épissage, un ESE (Exonic Splicing Enhancer), du transcrit de Spata22. A notre connaissance, il s’agit de la première description d’un élément ESE d’un gène méiotique murin. D’autre part, nous avons cherché à déterminer l’influence potentielle de l’expression ectopique de MEIOB et SPATA22 dans les cancers. A partir des données transcriptomiques en libre accès, nous avons pu observer que certaines tumeurs et lignées cellulaires expriment conjointement MEIOB et SPATA22 suggérant une possible fonctionnalité du complexe. Nos données préliminaires indiquent que MEIOB et SPATA22 semblent impacter la reprise de prolifération des cellules qui les expriment transitoirement. Des lignées cellulaires stables inductibles pour l’expression de MEIOB et SPATA22 sont en cours de réalisation afin d’étudier par la suite la survie/prolifération, la réparation de l’ADN et l’instabilité génétique en présence de MEIOB et SPATA22 dans ce contexte.