Les modifications post-traductionelles des histones contribuent à l’expression génique et à la stabilité du génome. La méthylation de la lysine 4 de l’histone H3 (H3K4me), une marque associée aux promoteurs de gènes transcrits, est déposé par les methyltransferases hautement conservées de la famille SET1, dans le contexte du complexe COMPASS. SET-2, l’homologue de SET1 chez Caenorhabditis elegans, est responsable de la déposition de H3K4me dans la lignée germinale, et son inactivation provoque une perte progressive de la fertilité. Le but de mon travail de thèse a été d’étudier comment SET-2 et la méthylation de H3K4 contribuent au maintien de la lignée germinale. J’ai montré que l’absence de SET-2 provoque une sensibilité accrue aux dommages à l’ADN. Cependant, les voies de signalisation et de réparation de ces dommages sont fonctionnelles dans le mutant set-2. Par séquençage de l’ADN, j’ai par ailleurs montré que la stérilité progressive observée en l’absence de set-2 n’est pas due à une capacité de réparation réduite. L’ensemble de mes résultats suggère que H3K4me pourrait agir en aval de la signalisation de dommages à l’ADN, en influençant l’organisation de la chromatine aux sites des cassures double brin. J’ai d’autre part mis en évidence une nouvelle fonction pour la méthylation de H3K4 dans l’organisation de la chromatine en montrant que set-2 interagit génétiquement avec le complexe Condensine II et la Topoisomérase II, facteurs clefs de l’organisation mitotique des chromosomes. Des expériences de microscopie par FLIM-FRET ont d’ailleurs validé une fonction de H3K4 méthylée dans l’organisation de la chromatine dans la lignée germinale. Enfin, j’ai montré par analyses transcriptomiques que la protéine CFP-1 du complexe COMPASS est impliquée dans la régulation du programme transcriptionnel de la lignée germinale et que cette fonction est indépendante de SET-2. L’ensemble de mes résultats montre comment la régulation chromatinienne impacte le maintien d’une lignée germinale fonctionnelle à plusieurs niveaux. / Post-translational modifications of histones contribute to gene expression and genome stability. Methylation of lysine 4 of histone H3 (H3K4me), a mark associated with actively transcribed genes, is deposited by the highly conserved SET1 family methyltransferases acting in COMPASS related complexes. SET-2, the SET1 homologue in Caenorhabditis elegans, is responsible for the deposition of H3K4me in the germ line, and its inactivation causes progressive loss of fertility. The purpose of my PhD work was to study how SET-2 and the methylation of H3K4 contribute to the maintenance of the germ line. I have shown that the absence of SET-2 causes increased sensitivity to DNA damage. However, the DNA damage-induced signaling and repair pathways are functional in the set-2 mutant. By DNA sequencing, I have also shown that the progressive sterility observed in the absence of set-2 is not due to a reduced repair capacity. Together, my results suggest that H3K4 methylation may act downstream of DNA damage signaling, potentially by influencing the organization of chromatin at the sites of double-strand breaks. I have also described a new function for H3K4 methylation in the organization of chromatin by showing that set-2 genetically interacts with the Condensitin II complex and Topoisomerase II, key factors in mitotic chromosome organization. Moreover, FLIM-FRET microscopy experiments have validated a role for H3K4 methylation in germline chromatin organization. Finally, using transcriptomic analyses, I have described a function for CFP-1, a component of the COMPASS complex, in the regulation of the germline transcriptional program independent of SET-2. Altogether, my results show how chromatin regulation affects the maintenance of a functional germline through multiple mechanisms.

Les microfaisceaux d’ions ont, au cours de ces dernières décennies, montré leur efficacité dansl’étude des effets des rayonnements ionisants sur le vivant notamment concernant les effets des faiblesdoses ou l’étude de l’effet de proximité. Le CENBG dispose depuis 2003 d’un dispositif permettant la micro-irradiation ciblée d’échantillons biologiques vivants. Les applications des microfaisceaux dans ce domainese sont récemment diversifiées et des études plus fines sur les mécanismes de réparation desdommages ADN radio-induits aux échelles cellulaire et multicellulaire sont devenues possibles via lesévolutions en imagerie par fluorescence et en biologie cellulaire. Ces approches ont nécessité une évolutionimportante de l'instrumentation de la ligne de micro-irradiation du CENBG qui a été entièrementredessinée et reconstruite dans un souci d’optimisation d’apport de nouvelles fonctionnalités. Les objectifsde mes travaux ont été i) la mise en service du dispositif, ii) la caractérisation des performances dusystème, iii) la mise en place de protocoles pour l’irradiation ciblée à dose contrôlée aux échelles cellulaireet multicellulaire, in vitro et in vivo, et le suivi en ligne des conséquences précoces de cette irradiation,iv) la modélisation des irradiations afin d’interpréter les observables biologiques au regard des donnéesphysiques calculées.Ces travaux ont permis i) de caractériser les performances du dispositif : une taille de faisceau d’environ2 μm sur cible et une précision de tir de ± 2 μm, de développer des systèmes de détection d’ions pour uncontrôle absolu de la dose délivrée, ii) d’induire des dommages ADN fortement localisés in vitro, et devisualiser en ligne le recrutement de protéines impliquées dans la réparation de ces dommages,iii) d’appliquer ces protocoles pour générer des dommages ADN in vivo au sein d’un organisme multicellulaireau stade embryonnaire, Caenorhabditis elegans.Ces résultats ouvrent la voie vers des expériences plus fines sur la ligne de micro-irradiation ciblée duCENBG pour étudier les effets de l’interaction des rayonnements ionisants avec le vivant, aux échellescellulaire et multicellulaire, in vitro et in vivo. / The main goal of radiobiology is to understand the effects of ionizing radiations on the living.These past decades, ion microbeams have shown to be important tools to study for example the effects oflow dose exposure, or the bystander effect. Since 2003, the CENBG has been equipped with a system toperform targeted micro-irradiation of living samples. Recently, microbeams applications on this subjecthave diversified and the study of DNA repair mechanisms at the cellular and multicellular scales, in vitroand in vivo, has become possible thanks to important evolutions of fluorescence imaging techniques andcellular biology. To take into account these new approaches, the CENBG micro-irradiation beamline hasbeen entirely redesigned and rebuilt to implement new features and to improve the existing ones. My PhDobjectives were i) commissioning the facility, ii) characterizing the system on track etch detectors, and onliving samples, iii) implementing protocols to perform targeted irradiations of living samples with a controlleddelivered dose, at the cellular and multicellular scales, and to visualize the early consequencesonline, iv) modelling these irradiations to explain the biological results using the calculated physical data.The work of these past years has allowed us i) to measure the performances of our system: a beam spotsize of about 2 μm and a targeting accuracy of ± 2 μm, and to develop ion detection systems for an absolutedelivered dose control, ii) to create highly localized radiation-induced DNA damages and to see onlinethe recruitment of DNA repair proteins, iii) to apply these protocols to generate radiation-induced DNAdamages in vivo inside a multicellular organism at the embryonic stage: Caenorhabditis elegans.These results have opened up many perspectives on the study of the interaction between ionizing radiationsand the living, at the cellular and multicellular scales, in vitro and in vivo.

No description available.

The insulin/IGF-1 signaling (IIS) was initially identified in C. elegansto control a developmental phenotype called dauer. Subsequently, it was realized that lifespan was extended by mutations in this pathway and became an intense focus of study. The IIS pathway regulates growth, metabolism and longevity across phylogeny and plays important roles in human disease such as cancer and diabetes. Given the large number of cellular processes that this pathway controls, understanding the regulatory mechanisms that modulate insulin/IGF-1 signaling is of paramount importance. IIS signaling is a very well-studied kinase cascade but few phosphatases in the pathway are known. Identification of these phosphatases, especially those that counteract the activity of the kinases, would provide a better insight into the regulation of this critical pathway. Study of serine/threonine phosphatases is hampered by the lack of appropriate reagents. In Chapter II, we discuss the design and results of an RNAi screen of serine/threonine phosphatases performed in C. elegans using dauer formation as a phenotypic output. We identified several strong regulators of dauer formation and in Chapter III, proceed to characterize one of the top candidates of our screen, pptr-1. We show that pptr-1 regulates the IIS and thereby affects lifespan, development and metabolism in C .elegans. pptr-1gene encodes a protein with high homology to the mammalian B56 family of PP2A regulatory subunits. PP2A is a ubiquitously expressed phosphatase that is involved in multiple cellular processes whose specificity determined by its association with distinct regulatory subunits. Our studies using C. elegans provides mechanistic insight into how the PP2A regulatory subunit PPTR-1 specifically modulates AKT-1 activity by regulating its phosphorylation status in the context of a whole organism. Furthermore, we show that this mechanism of regulation is conserved in mammals.

In a 4-cell C. elegans embryo the ventral blastomere EMS requires polarity signaling from its posterior sister cell, P2. This signaling event enables EMS to orient its division spindle along the anterior-posterior (A/P) axis and to specify the endoderm fate of its posterior daughter cell, E. Wnt pathway components have been implicated in mediating P2/EMS signaling. However, no single mutants or various mutant combinations of the Wnt pathway components disrupt EMS polarity completely. Here we describe the identification of a pathway that is defined by two tyrosine kinase related proteins, SRC-1 and MES-1, which function in parallel with Wnt signaling to specify endoderm and to orient the division axis of EMS. We show that SRC-1, a C. elegans homolog of c-Src, functions downstream of MES-1 to specifically enhance phosphotyrosine accumulation at the P2/EMS junction in order to control cell fate and mitotic spindle orientation in both the P2 and EMS cells. In the canonical Wnt pathway, GSK-3 is conserved across species and acts as a negative regulator. However, in C. elegans we find that GSK-3 functions in a positive manner and in parallel with other components in the Wnt pathway to specify endoderm during embryogenesis. In addition, we also show that GSK-3 regulates C. elegans germline development, a function of GSK-3 that is not associated with Wnt signaling. It is required for the differentiation of somatic gonadal cells as well as the regulation of meiotic cell cycle in germ cells. Our results indicate that GSK-3 modulates multiple signaling pathways to regulate both embryogenesis and germline development in C. elegans.

O estudo de fontes naturais pouco exploradas e que exibem interações ecológicas específicas no seu habitat tem sido enfatizado como estratégico para a descoberta de novas substâncias bioativas. Microrganismos endofíticos são fontes de produtos naturais relativamente pouco estudadas. Estes microrganismos vivem no interior de um vegetal sem causar danos aparentes ao hospedeiro. A interação ecológica específica entre os microrganismos endofíticos e sua planta hospedeira pode estimular a biossíntese de novos produtos naturais bioativos. Os fungos endofíticos \"Glomerella cingulata\" e \"Guignardia mangiferae\" foram isolados da folhas de \"Viguiera arenaria\". O fungo \"G. mangiferae\" foi cultivado em diferentes condições: meios líquidos Czapek, extrato de malte e caldo batata-dextrose e meio sólido de arroz. Extratos e frações obtidas com o cultivo de \"G. mangiferae\" foram avaliados em ensaios antimicrobianos, citotóxicos e enzimáticos. Foram realizados procedimentos cromatográficos com os extratos brutos, obtendo-se 13 substâncias puras, sendo cinco delas inéditas na literatura. Entre as novas substâncias, quatro são derivados tricicloalternarenos. O extrato bruto etanólico oriundo do cultivo em extrato de malte foi o mais promissor nos ensaios biológicos realizados. A partir desse extrato foi isolado a chaetoglobosina D, um composto já descrito na literatura como citotóxico em células cancerígenas. Os demais extratos, frações e substâncias ensaiadas apresentaram apenas atividade fraca ou moderada. O fungo \"G. cingulata\" foi investigado sobre a produção do metabólito secundário tirosol, previamente isolado de várias linhagens de fungos endofíticos. Devido à ampla ocorrência em fungos endofíticos, o tirosol pode estar correlacionado com uma função sinalizadora para a produção de outros metabólitos secundários. Para a determinação da quantidade de tirosol produzido por \"G. cingulata\", um método analítico quantitativo foi desenvolvido obedecendo-se padrões descritos pelo Guidance of Industry. Foi realizada a análise dos fluídos das culturas de \"G. cingulata\" em diferentes condições de cultivo em meio líquido Czapek. Observou-se que a melhor condição para produção do tirosol ocorre em pH 5,0, 120 rpm, 30 ºC, seis dias de incubação. O cultivo de \"G. cingulata\" com e sem adição de tirosol no meio líquido Czapek não permitiu resultados conclusivos sobre a possível função sinalizadora do tirosol na produção de metabólitos secundários em fungos endofíticos. Durante o período de estágio sanduíche no Departament of Molecular Biology do Massachusetts General Hospital (Harvard Medical School), sob a supervisão do Prof. Dr. Frederick M. Ausubel, foram avaliadas cerca de 170 amostras de origem natural do Brasil, sendo a maioria delas oriundas de fungos endofíticos, frente ao nematóide \"Caenorhabditis elegans\" infectado com linhagem patogênica de \"Enterococcus faecalis\". Cerca de 29% das substâncias puras e 2% dos extratos ensaiados apresentaram boa capacidade de recuperação do nematóide infectado. Os policetídeos chaetoviridinas foram os compostos mais ativos neste modelo de ensaio antibacteriano \"in vivo\". / The search for small bioactive molecules from under-explored natural sources that possess specific ecological interaction in their respective habitat has been emphasized as strategic for the discovery of bioactive compounds. Endophytic microorganisms are still relatively under-explored sources of natural products. These microorganisms live inside the host plant tissues without causing symptoms of disease to the host. The specific ecological interaction between the endophytes and their host plants may trigger the biosynthesis of new small bioactive molecules. The endophytic fungi \"Glomerella cingulata\" and \"Guignardia mangiferae\" were isolated from \"Viguiera arenaria\" leaves. G. mangiferae was cultured using different conditions: Czapek, malt extract and potato-dextrose broth liquid media and rice solid medium. Crude extracts and fractions obtained after \"G. mangiferae\" cultivation were evaluated in antimicrobial, cytotoxic and enzymatic assays. Chromatographic procedures were carried out with crude extracts and led to the isolation of 13 compounds, five of them new in the literature. From the novel compounds four are tricycloalternarene derivatives. The crude ethanolic extract obtained from malt extract cultivation was the most promising extract in the biological assays. Chaetoglobosin D, a cytotoxic compound against cancer cell lines previously described in the literature, was isolated from this bioactive extract. The other extracts, fractions and compounds assayed showed weak or moderate activity in the performed assays. The production of tyrosol by \"G. cingulata\" was investigated, since several endophytic fungal strains from Asteraceae species had already produced this compound. Tyrosol may act as a signaling molecule for the production of other metabolites in endophytic fungi. In order to quantify the production of tyrosol by \"G. cingulata\", an analytical method was validated under Guidance of Industry recommendations. Fluid culture analyses were performed after the cultivation of \"G. cingulata\" under different conditions using Czapek liquid medium. The best condition for tyrosol production occurred at pH 5.0, 120 rpm, 30 ºC, six days of incubation. Cultivation of \"G. cingulata\" with and without tyrosol addition in the Czapek liquid medium did not allow the conclusion that tyrosol act as a signaling molecule for metabolite production by endophytic fungi. During sandwich training at Department of Molecular Biology of Massachusetts General Hospital (Harvard Medical School), under Dr. Frederick M. Ausubel supervision, 170 samples from Brazil, the most part obtained from endophytic fungi, were assayed using the nematode \"Caenorhabditis elegans\" infected with the pathogen \"Enterococcus faecalis\". About 29% of pure compounds and 2% of extracts assayed were able to promote the survival of the infected nematode. The polyketides chaetoviridins were found to be the most active compounds in this \"in vivo\" antibacterial assay.

L‟épissage alternatif est un mécanisme de régulation de l‟expression des gènes ayant pris une importance croissante dans l‟étude du vivant. Si des méthodes existent pour déterminer les gènes qui y sont soumis, peu d‟outils sont disponibles pour suivre ces événements d‟épissage in vivo au cours du développement. Pourtant, la caractérisation des régulations sous-jacentes à ces évènements et la détermination des facteurs impliqués sont dépendantes de stratégies fiables pour les visualiser dans des conditions physiologiques.Nous avons développé un système adapté à l‟étude d‟événements d‟épissage basé sur un rapporteur fluorescent bicolore. Nous l‟avons appliqué à cinq gènes de l‟organisme modèle Caenorhabditis elegans et avons suivi leur épissage in vivo.Parmi les différents gènes suivis, deux d‟entre eux suivaient un modèle d‟épissage potentiellement stochastique, un autre une absence d‟épissage alternatif détectable. Les deux derniers gènes présentent un profil d‟épissage spécifique à certain types cellulaires mais ont un effet toxique sur l‟organisme lorsque nous les avons exprimés à partir de concatémères extrachromosomiques. Pour remédier à cela, nous avons choisi de mettre en place une méthode simplifiée d‟insertion en simple copie des rapporteurs utilisant le CRISPR-Cas.Nos résultats indiquent que le système rapporteur fonctionne avec succès. Cependant, il peut encore être amélioré pour se rapprocher des taux physiologiques de transcription grâce à une insertion en simple copie dans le génome de l‟organisme. Nous avons également révélé un événement sous le contrôle de régulations spatiales, temporelles et conditionnelles. De plus, nous avons créé une série de constructions capables de déterminer les éléments en cis impliqués dans la régulation du gène top-1. / Alternative splicing is a regulatory mechanism of gene expression which is increasingly studied in Life Science. Methods exist to study this mechanism but specific tools to follow each alternative splicing event in a spatio-temporal manner are lacking. Yet, the characterization of the regulation and the elements that determines them depends on valide strategies for visualising them in physiological conditions.We have developped a dual-fluorescent reporter-based system in order to follow alternative splicing event regulation in vivo. It has been applied to five different genes in the model organism Caenorhabditis elegans. Among the genes followed, two follow a potentially stochastic scheme, one show no visible sign of alternative splicing. The last display tissue specific splicing patterns but developed a toxic effect in the animal when expressed from a multicopy extrachromosomal array. To remediate this problem, we decided to develop a method that allows for simpler single copy insertion of fluorescent reporter using CRISPR-Cas.Our results indicates that the dual-fluorescent reporter works well. However, this system can be upgraded by getting close to physiological rates of transcription allowed by single-copy insertion in the genome of C.elegans. We also discovered an alternatiove splicing event which follows a spatial, temporal and conditionnal regulation. Moreover, we constructed a set of different reporter to unravel the regulation observed in the gene top-1.

Les infections par les nématodes gastro-intestinaux entrainent des baisses en productions animales et des pertes économiques majeures pour les éleveurs. Les lactones macrocycliques (LMs) sont parmi les antiparasitaires les plus utilisés dans la lutte contre les nématodes gastro-intestinaux en médecine vétérinaire. De part une utilisation intensive, des résistances aux LMs chez les parasites gastro-intestinaux se sont développées au sein des élevages du monde entier mettant en péril l'efficacité thérapeutique de ces molécules. Par ailleurs, le développement de nouveaux antiparasitaires est limité. Ainsi, un des enjeux pour assurer le contrôle de ces parasites est de ralentir les phénomènes de résistance aux LMs afin de prolonger leur efficacité. Le succès d'une telle stratégie repose sur les connaissances précises des mécanismes impliqués dans la résistance. Parmi eux, la modulation des systèmes de détoxification est décrite lors de phénomènes de résistance aux LMs. Au cours de ces travaux, nous avons étudiés la régulation des systèmes de détoxification, en réponse à l'ivermectine chez l'hôte. Nous avons montré, en comparaison à une administration unique, qu'une administration répétée d'ivermectine par voie orale chez la souris est responsable de l'induction de l'expression de certains gènes transporteurs ABC et cytochromes impliqués dans son métabolisme. Ceci entraîne, à la fois, une diminution de la concentration de la molécule parentale et une augmentation de la teneur de son métabolite principal dans le plasma et l'intestin. Ensuite, nous avons étudié l'implication des mécanismes de régulation des systèmes de détoxification, et notamment les récepteurs nucléaires, dans la tolérance à l'ivermectine chez le nématode C.elegans. Nous avons montré que le récepteur nucléaire nhr-a est important pour la tolérance et le développement de la résistance à l'ivermectine. Enfin, nous avons étudié l'impact d'inhibiteurs des transporteurs ABC sur l'efficacité de l'ivermectine. Nous avons mis en évidence la capacité de certains flavonoïdes et de l'ivermectine aglycone à potentialiser l'efficacité de l'ivermectine chez le nématode. Une exposition d'ivermectine induit la surexpression des systèmes de détoxification chez l'hôte. Ceci pourrait être la base des mécanismes moléculaires de la résistance chez le nématode. Cibler les systèmes de détoxification ou les mécanismes de résistance, par des inhibiteurs adaptés, représente une stratégie pertinente pour potentialiser l'efficacité de l'ivermectine. / Infections with gastrointestinal nematodes (GINs) in livestock leads to major losses in production and consequently impact economically farmers. Their intensive use has led to widespread anthelmintic resistance which is nowadays the main threat on the sustainable control of GINs in livestock. The development of new anthelmintic is limited due to the cost of such process. Then, the challenge remains in optimizing the use of existing molecules. Therefore, it is urgent to limit and control MLs resistance in order to extend their efficacy and to avoid therapeutic failure. Resistance mechanisms remain to be elucidated. In that context, we investigated regulatory mechanism of detoxification systems of ivermectin implicated in therapeutic efficacy in host and resistance development in nematode. Therapeutic combinations of ivermectin with flavonoïds have been evaluated to potentiate its efficacy in nematode. We showed that repeated oral administration of ivermectin induced gene expression encoding some ABC efflux transporters and cytochromes involved in its metabolism. Compared with single administration, repeated ivermectin administration lowered plasma, liver and intestine drug concentration, while increasing main metabolite content in plasma and intestine. We have also shown that nuclear receptor nhr-a was important for ivermectin tolerance and ivermectin development of resistance in C. elegans. Finally, we demonstrated the ability of the flavonoïd phloretin to potentiate ivermectin efficacy in the nematode C. elegans. Taken together, these data suggest that induction of detoxification systems impact on ivermectin distribution and targeting their regulation could be an appropriate strategy to potentiate ivermectin efficacy in host and to reverse resistance in nematode.

A stereoselective synthesis of (25S)-Δ1-, (25S)-Δ1,4-, (25S)-Δ1,7-, (25S)-Δ8(14)-, (25S)-Δ4,6,8(14)-dafachronic acid, methyl (25S)-Δ1,4-dafachronate and (25S)-5α-hydroxy-3,6-dioxocholest-7-en-26-oic acid is described. (25S)-Δ1,4-Dafachronic acid and its methyl ester are natural products isolated from corals and have been obtained by synthesis for the first time. (25S)-5α-Hydroxy-3,6-dioxocholest-7-en-26-oic acid represents a promising synthetic precursor for cytotoxic marine steroids. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

The mitotic spindle is a bipolar microtubule-based structure that mediates proper cell division by segregating the genetic material and by positioning the cytokinesis cleavage plane. Spindle assembly is a complex process, involving the modulation of microtubule dynamics, microtubule focusing at spindle poles and the formation of stable microtubule attachments to chromosomes. The cellular events leading to spindle formation are highly regulated, and mitotic kinases have been implicated in many aspects of this process. However, little is known about their counteracting phosphatases. A screen for genes required for early embryonic cell divisions in C. elegans identified rsa-1 (for regulator of spindle assembly 1), a putative Protein Phosphatase 2A (PP2A) regulatory subunit whose silencing causes defects in spindle formation. Upon rsa-1(RNAi), spindle poles collapse onto each other and microtubule amounts are strongly reduced. My thesis work demonstrates that RSA-1 indeed functions as a PP2A regulatory subunit. RSA-1 associates with the PP2A enzyme and recruits it to centrosomes. The centrosome binding of PP2A furthermore requires the new protein RSA-2 as well as the core centrosomal protein SPD-5 and is based on a hierarchical protein-protein interaction pathway. When PP2A is lacking at centrosomes after rsa-1(RNAi), the centrosomal amounts of two critical mitotic effectors, the microtubule destabilizer KLP-7 and the kinetochore microtubule stabilizer TPXL-1, are altered. KLP-7 is increased, which may account for the reduction of microtubule outgrowth from centrosomes in rsa-1(RNAi) embryos. TPXL-1 is lost from centrosomes, which may explain why spindle poles collapse in the absence of RSA-1. TPXL-1 physically associates with RSA-1 and RSA-2, suggesting that it is a direct target of PP2A. In summary, this work defines the role of a novel PP2A complex in mitotic spindle assembly and suggests a model for how different microtubule re-organization steps might be coordinated during spindle formation.