As paredes celulares vegetais são estruturas essenciais para o crescimento e desenvolvimento das plantas. Além das suas diversas funções biológicas, os componentes polissacarídicos constituintes das paredes celulares (celulose, hemiceluloses e pectinas) são de vital importância como fonte natural de fibras para a nutrição humana e animal e são considerados os principais recursos renováveis do planeta, utilizados como matéria-prima para diversos processos industriais, por exemplo nos processos de produção de polpa celulósica. Todos esses fatores têm despertado grande interesse no estudo da composição e biossíntese das paredes celulares. A biossíntese dos seus polímeros se inicia no citoplasma das células, onde ocorre a formação dos precursores por uma rota metabólica complexa de biossíntese de açúcares-nucleotídeo. O entendimento da regulação dessa rota metabólica é fundamental para modular a dinâmica de biossíntese desses açúcares e assim tentar manipular as propriedades bioquímicas das paredes celulares. Nesse contexto, o presente projeto de pesquisa teve como objetivo avaliar o efeito da superexpressão do gene miox2 de Arabidopsis thaliana em plantas de Nicotiana tabacum. O produto desse gene é a enzima mio-inositol oxigenase (E.C. 1.13.99.1), cuja função é converter o mio-inositol em ácido D-glucurônico, composto central da rota de biossíntese de açúcares-nucleotídeo. Foram determinadas quatro isoformas tecido-específicas para o gene miox (miox1, miox2, miox4 e miox5) em Arabidopsis, sendo que a isoforma miox2 é a predominante em caules. Esse gene foi clonado em trabalhos anteriores realizados no laboratório e no presente trabalho, o cDNA do gene miox2 foi superexpresso em plantas de tabaco (Nicotiana tabacum) a fim de se avaliar o efeito da superexpressão na composição de carboidratos de parede celular secundária. As linhagens de plantas transgênicas obtidas, não mostraram diferenças visualmente perceptíveis em comparação aos controles, indicando ausência de alterações fisiológicas e morfológicas. Foram quantificados os monossacarídeos de paredes celulares secundárias (arabinose, ramnose, galactose, glicose, xilose, manose), os ácidos urônicos (ácido galacturônico e glucurônico) e as ligninas (solúvel e insolúvel), a partir de tecido xilemático e parênquima medular do caule. A ausência de modificações significativas nas proporções desses metabólitos, indica que as plantas exercem um estrito controle na regulação da biossíntese de paredes celulares secundárias de forma que a superexpressão do gene miox2 não provocou nenhuma alteração altamente significativa. Outros genes candidatos e os mecanismos envolvidos na sua regulação deverão ser testados quanto ao nível de transcrição, modificações pós-trancricionais e pós-traducionais a fim de entender a regulação do fluxo de carbono para a biossíntese de paredes celulares. / Cell-walls are essential structures for plant development and growth. Apart from its biological functions, the polyssacharides that make cell-walls (cellulose, hemicellulose and pectins) are the principal natural fibrous materials used for human and animal nutrition. They are also considered the most important renewable resource on earth and their use as industrial raw material is inevitable. An example is the use of wood in the production of pulp and paper. For all these reasons, the study of molecular composition and biosynthesis of plant cell-walls has been a matter of great interest for researchers over the past few years. Cell-wall polyssacharides biosynthesis begins at the cytoplasm, where a pool of UDP-glucose and other activated sugar nucleotide precursors are generated by multiple and complex interconvertion reactions. Understanding how cells control the metabolic pathways responsible for sugar nucleotide precursors synthesis, would be a primary requirement for manipulating them in an attempt to generate plants with improved properties for human use. In that context, tha aim of this research work was to analyze the effects of Arabidopsis thaliana miox2 gene overexpression in a plant model system (Nicotiana tabacum). The product of miox2 gene is myo-inositol oxygenase enzyme 2 (E.C.1.13.99.1) which converts D-glucuronic acid, an important sugar nucleotide precursor, from its substrate myo-inositol. Four isoforms of miox gene, with apparent tissue specific expression (miox1, miox2, miox4 and miox5) were already determined, but miox2 is the one primarily expressed in stems. Its cDNA was cloned from Arabidopsis thaliana in previous works and overexpressed in tobacco plants. Five normal transgenic lines were obtained, showing no phenotypically differences relative to the control line. This fact implied that miox2 overexpression did not alter any physiological nor morphological aspect of plant development. The cell-wall monossacharides (arabinose, rhamnose, galactose, glucose, xylose and mannose), uronic acids (galacturonic and glucuronic acid) and lignins (soluble and insoluble) from stem xylem and parenchymal tissue were quantified. The absence of major changes in any of the compounds measured for the transgenic lines indicated that they were able to adjust their level of carbohydrate composition. Plants seem to regulate the proportions of sugar nucleotide precursors through highly complex metabolic pathways that establish strong compensatory mechanisms. It will be necessary to study other candidate genes and some aspects of their regulation at transcriptional, postranscriptional and postransaltional level, as an attempt to understand the cell-wall carbohydrate flux.

Os compostos de origem microbiana tem readquirido interesse pela biodisponibilidade, especificidade de alvo e diversidade química, mas as vias biosintéticas permanecem crípticas em condições de cultura. Uma estratégia para expressa-las é a super-expressão de genes ativadores. O laboratório de Bio-Produtos no ICB na USP tem trabalhado com Streptomyces olindensis produtor da Cosmomicina D uma molécula com atividade antitumoral de interesse devido ao padrão de glicosilação. O genoma de S. olindensis foi sequenciado e submetido ao NCBI (JJOH00000000) e utilizando o software antiSMASH foram identificados 33 clusters envolvidos na produção de metabolitos secundários. Encontraram-se clusters gênicos para a produção de metabolitos como Melanina, Geosmina, entre outros. Além, foi realizada uma analise de genômica comparativa para caracterizar e anotar as 22 vias biossintéticas desconhecidas em S. olindensis. Finalmente, escolheram-se a via do aminociclitol e um Policetídeo Tipo I para a super-expressão de genes reguladores levando a detecção do composto sob condições de cultura. / Microbial metabolites regain interest due to its bioavailability, target specificity and chemical diversity, but the biosynthetic pathways remain silenced under culture conditions. A strategy to obtain them is the over expression of regulatory genes. Bio-products laboratory at USP has been working with Streptomyces olindensis, products of Cosmomycin D, an antitumoral molecule with a distinctive glycosylation pattern. S. olindensis genome was sequenced and submitted to NCBI (JJOH00000000) and employing antiSMASH server 33 secondary metabolite related clusters were identified. Known pathways were found such as genes for melanin production, Geosmin and others. Additionally, a comparative genomic approach was used to characterize the 22 biosynthetic unknown pathways described in S. olindensis. Subsequently, Aminocyclitol and Polyketide Type I were chosen to evaluated, over expressing the regulatory genes, leading to the compound detection in regular culture conditions.

Abstract Adenosine receptors are heterotrimeric guanine nucleotide-binding (G protein)-coupled receptors (GPCRs) that mediate the effects of the endogenous agonist adenosine. The adenosine A3 receptor (A3R) is the least explored among the four human adenosine receptor subtype members (A1, A2A, A2B and A3) and it is implicated in both neuroprotective and neurodegenerative effects. During the course of this work, the production of the recombinant human A3R in yeast and insect cells was evaluated and heteromerization between the human adenosine A2A receptor (A2AR) and the dopamine D2 receptor (D2R) was studied. A3R with carboxyl-terminal GFP tag was expressed in the yeast Saccharomyces cerevisiae upto 15 mg per litre of culture. Another yeast Pichia pastoris increased the expression up to 108 mg/L of the same receptor when grown in bioreactors. Despite the very high expression levels, purification of A3R from both yeasts was a daunting task, as the aggregation of the receptor could not be averted. In this study, insect cells have been found out to be more suitable host for A3R expression: 10µg of the monomeric A3R could be purified from one liter of insect cell culture. For successful crystallization thermostability of the A3R was to be improved. This work has demonstrated that insertion of T4L, a fusion protein, in the third intracellular loop of A3R increased the thermostability of the receptor by 10°C. As a next step, the combination of point mutations based on alanine-scanning mutagenesis and a fusion protein approach could be useful to stabilize and further crystallize the A3R. This work has demonstrated that the amounts of A3R expressed in insect cells and the final yield of the receptor isolated by affinity purifications, forms a good basis for the beginning of biochemical characterization Receptor heteromerization is a mechanism used by GPCRs to diversify their signaling properties and functions. The human A2AR and D2R heteromers exist in the GABAergic enkephalinergic neurons. The domains responsible for forming intermolecular contacts were purified from Escherichia coli (E. coli). Using biochemical/biophysical techniques such as native-PAGE and mass spectrometry, It was validated that purified carboxyl-terminus of the A2AR and the 3rd intracellular loop of D2R form heterodimers. The investigation of purified calmodulin protein binding to the 3rd intracellular loop of D2R showed that the protein-protein interactions are calcium dependent. / Tiivistelmä Adenosiinireseptorit kuuluvat G-proteiinikytkeiset reseptorit (GPCR:t) proteiiniperheeseen. Adenosiinireseptorit välittävät endogeenisen ligandinsa adenosiinin vaikutuksia solukalvolta solunsisäisiin signaalijärjestelmiin. Adenosiini A3 reseptori (A3R) on adenosiinireseptorien neljästä alatyypistä (A1, A2A, A2B ja A3) vähiten tutkittu. Aikaisempien tutkimusten perusteella A3 reseptori yhdistetään sekä hermosoluja suojaaviin että rappeuttaviin tapahtumiin. Tässä työssä arvioitiin sekä ihmisen rekombinantti-A3R:n tuottumista hiiva- ja hyönteissoluissa että tutkittiin ihmisen adenosiini A2A reseptorin (A2AR) ja dopamiini D2 reseptorin (D2R) heteromerisoitumista. Rekombinantti A3 reseptori- vihreä fluoresoiva proteiini (GFP) fuusioproteiinia tuotettiin Saccharomyces cerevisiae -hiivassa 15 mg litrassa kasvatusliuosta. Pichia pastoris -hiivakanta taas kasvatti saman reseptorin tuottumista aina 108 mg/l saakka, kun tuotto tehtiin bioreaktorissa. Hyvin korkeasta tuottotasosta huolimattaA3R:n puhdistus hiivasta oli ylitsepääsemätön tehtävä, sillä reseptorin saostumista ei voinut välttää. Työssä havaittiin, että hyönteissolut sopivat paremmin A3R:n tuottoon: noin 10 µg monomeerista A3R:a voitiin puhdistaa litran hyönteissoluviljelmästä. Reseptorin stabiilisuuden lisääminen helpottaa reseptorin biokemiallista ja biofysikaalista karakterisointia. Tässä työssä osoitettiin, että T4L-proteiinin lisääminen A3R:n kolmannen solunsisäisen silmukan paikalle lisää reseptorin lämpöstabiilisuutta 10 °C. Jatkotutkimuksissa voitaisiin käyttää alaniiniskannausmutageneesiin perustuvien pistemutaatioiden ja fuusioproteiinin yhdistelmää A3R:n lisästabilointiin ja kiteytykseen. Tämän työn perusteella määrät, joilla A3R tuottuu hyönteissoluissa ja jotka saadaan eristettyä affiniteettipuhdistuksilla, muodostavat hyvän perustan proteiinin biokemialliselle karakterisoinnille. Reseptorin heteromerisoituminen on GPCR:en käyttämä mekanismi signalointiominaisuuksien ja toimintojen monipuolistamiseksi. Ihmisessä A2AR ja D2R heteromeereja on GABAergisissä enkefalinergisissä hermosoluissa. Molekyylien välisiin kontakteihin osallistuvat domeenit puhdistettiin Escherichia coli (E. coli) -bakteerista. Biokemiallisia ja biofysikaalisia tekniikoita kuten natiivi-PAGE:a ja massaspektrometriaa käyttäen vahvistettiin, että puhdistettu A2AR:n karboksiterminaalinen osa ja D2R:n kolmas solunsisäinen silmukka muodostavat heterodimeereja. Myös tutkittaessa puhdistetun kalmoduliini-proteiinin sitoutumista D2R:n kolmanteen solunsisäiseen silmukkaan osoitettiin proteiini-proteiini -vuorovaikutuksen olevan kalsiumista riippuvainen.

Quelques régions stables ont été découvertes sur les gp d’env du VIH-1 contre lesquelles des patients produisent des anticorps neutralisants. Les épitopes les plus prometteurs se trouvent dans la MPER et sont probablement exposés durant la fusion. Alors que les peptides isolés à partir de cette région ne sont pas parvenus à induire une réaction immunogène neutralisante, des études antérieures suggèrent que la membrane lipidique joue un rôle dans la structuration des antigènes et dans la réponse immunogénique.C’est pourquoi nous étudions la structure de ces épitopes. Cela nécessite leur surexpression, leur purification et leur reconstitution dans des liposomes. Une étude de CD montre qu’ils pourraient changer de conformation, cela sera confirmé par RMN. En outre, leur immunogénicité sera vérifiée par vaccination des souris. En plus, nous trouvons que le cholestérol peut modifier l’orientation des peptides englobant le motif CRAC de la gp41. / A few stable regions have been discovered on the HIV-1 env gp against which some patients produce neutralizing antibodies. The most promising ones are located in the MPER and are probably exposed transiently during the fusion. Whereas the peptides isolated from this region failed to induce immunogenic response, previous studies suggest the lipid membrane plays a role in antigens structure and in the immunogenic response.That is why we investigate the structure of these épitopes in membrane models. This requires the production of these épitopes by bacterial overexpression, their purification and their reconstitution in liposomes. A CD study shows that they could undergo a conformational change; this will be confirmed by NMR. Also their immunogenicity will be checked by mice immunization. In addition, we find that cholesterol could change the orientation of peptides encompassing a gp41 CRAC motif.

Le VHS-1 est un modèle très utilisé pour l’étude du cycle viral et des interactions hôte-pathogène des Herpesvirdidae, en partie dû à sa capacité de se répliquer de façon rapide dans plusieurs types cellulaires. La transcription, réplication de l’ADN et la formation des capsides de ce virus se produisent dans le noyau cellulaire. Une fois les capsides formées, elles doivent sortir du noyau pour continuer le cycle. Cependant, les capsides sont trop grandes (125 nm) pour passer à travers les pores nucléaires, dont la taille d’exclusion est de 40 nm, et elles entament alors un processus d’enveloppement dé-enveloppement à travers les deux membranes nucléaires. Le complexe LINC (de l’anglais Linker of the Nucleoskeleton and Cytoskeleton) est un complexe qui se retrouve dans les membranes nucléaires et l’espace périnucléaire. Il sert de liaison entre le noyau et le cytoplasme et, parmi ses fonctions on retrouve le maintien d’un espace périnucléaire constant, le positionnement du noyau et la transmission de forces entre le noyau et le cytoplasme. Le complexe LINC est composé par les protéines de la famille SUN et par les protéines de la famille KASH, qui interagissent physiquement l'une avec l'autre. L'implication du complexe LINC dans la propagation du virus de la pseudo-rage (PrV) a déjà été démontrée. Étant donné que le PrV fait partie de la même famille de virus que le VHS-1, notre hypothèse est que le complexe LINC joue aussi un rôle dans la propagation du VHS-1. Mes travaux démontrent que la surexpression d'une forme négative dominante de SUN2 ou sa déplétion montre un effet proviral sur la propagation du VHS-1. Ce résultat diffère de ce qui a été précédemment constaté pour le PrV en ce sens que SUN2 est antiviral pour le PrV. Ceci confirme notre hypothèse, mais démontre un scénario plus complexe qu'anticipé. / HSV-1 is widely used to study viral cycles and host-pathogen interactions of Herpesvirdidae, because it replicates quickly and efficiently in many cells types. The transcription, replication and capsid assembly of HSV-1 take place in the nucleus of the infected cell. The assembled HSV-1 capsid must exit the nucleus to continue the viral cycle. The nuclear membranes constitute a barrier for the nuclear egress of nucleocapsids (125 nm) given the exclusion size of the nuclear pores is approximately 40 nm. The nucleocapsids therefore pass through the nuclear membranes by an envelopement-deenvelopement process. The capsids acquire an envelope from the inner nuclear membrane when they are released into the perinuclear space. This primary viral envelope then fuses with the outer nuclear membrane, enabling the capsid to reach the cytoplasm. Situated between the two nuclear membranes is the linker of the nucleoskeleton and cytoskeleton (LINC) complex. It is involved in the maintenance of the perinuclear space, nuclear positioning and force transmission between the nucleus and the cytoplasm. The LINC complex is composed of two families of proteins, SUN and KASH proteins. SUN proteins are found in the inner nuclear membrane, their N-terminal interacts with the nucleoskeleton and the C-terminal includes a conserved domain, the SUN domain, which interacts in the perinuclear space with the conserved domain of KASH proteins. The implication of the LINC complex in the propagation of the pseudorabies virus (PrV), a member of the alphaherpesviruses, has already been demonstrated. Since PrV is part of the same family as HSV-1, we hypothesized it may also play a role in HSV-1 propagation. My work shows that overexpression of a dominant negative form of SUN2 or its depletion shows a proviral effect on HSV-1 propagation. This result differs to what has been previously found for PrV, where SUN2 displays an antiviral phenotype. This work confirms our hypothesis but reveals a more complex scenario than anticipated.

Cyanobacteria are a model organism for photosynthesis and the Calvin cycle, and a promising chassis for 4th generation biofuel production. There are many ongoing efforts to improve the performance of cyanobacteria, in terms of CO2 fixation and production rate of biofuels. One straightforward way to improve CO2 fixation could be to overexpress the genes of limiting enzymes. In this project, we used a high-throughput method to test the overexpression of thousands of genes in cyanobacteria and measure the effect on growth rate. We created barcoded overexpression libraries, consisting of gene fragments from different cyanobacteria strains and transformed them into a model cyanobacterium, Synechocystis PCC 6803. We then cultivated the transformed cyanobacteria libraries and screened for effects of increased gene copy number on both maximum growth rate and robustness of growth under stress conditions. The cell populations were cultivated in a turbidostat, resulting in competitive growth between transformants. The relative abundance of each mutant was estimated using deep sequencing. Fitness scores, for each gene show how expression of that gene affects growth rate. This method, competitive growth and tracking of mutant populations with deep sequencing, is a high throughput method for screening a large proportion of genes from several organism at once, allowing the identification of trans-species effects as well as the effect of single genes on the metabolism of the host cell. / Cyanobakterier är en modellorganism för fotosyntes och Calvin-cykeln och ett lovande chassi för fjärde generationens biobränsleproduktion. Det finns många pågående ansträngningar för att förbättra cyanobakteriens prestanda med avseende på CO2-fixering och produktionshastighet för biobränslen. Ett enkelt sätt att förbättra CO2-fixering kan vara att överuttrycka generna för begränsande enzymer. I detta projekt använde vi en metod med hög kapacitet för att testa överuttryck av tusentals gener i cyanobakterier och mäta effekten på tillväxthastigheten. Vi skapade streckkodade överuttrycksbibliotek, bestående av genfragment från olika arter av cyanobakterier och transformerade in dem i en modellorganism för cyanobakterium, Synechocystis PCC 6803. Vi odlade sedan de transformerade biblioteken och screenade efter effekten av ökade antal genkopior på både maximal tillväxthastighet och robusthet hos tillväxt under stressförhållanden. Cellpopulationerna odlades i en Turbidostat, vilket resulterade i konkurrerande tillväxt mellan transformanter. Den relativa mängden av varje mutant uppskattades med användning av djup sekvensering. "Fitnesspoäng" för varje gen visar hur uttrycket av den genen påverkar tillväxthastigheten. Denna metod, konkurrerande tillväxt och spårning av mutantpopulationer med djup sekvensering, är en metod med hög genomströmning för att screena en stor andel gener från flera organismer samtidigt, vilket möjliggör identifiering av trans-art effekter såväl som effekten av enstaka gener på värdcellens metabolism.

Les cellules souches somatiques présentent habituellement un comportement très différent des cellules souches pluripotentes. Les bases moléculaires de l’auto-renouvellement des cellules souches embryonnaires ont été récemment déchiffrées grâce à la facilité avec laquelle nous pouvons maintenant les purifier et les maintenir en culture durant de longues périodes de temps. Par contre, il en va tout autrement pour les cellules souches hématopoïétiques. Dans le but d’en apprendre davantage sur le fonctionnement moléculaire de l’auto-renouvellement des cellules souches hématopoïétiques, j’ai d’abord conçu une nouvelle méthode de criblage gain-de-fonction qui répond aux caprices particuliers de ces cellules. Partant d’une liste de plus de 700 facteurs nucléaires et facteurs de division asymétrique candidats, j’ai identifié 24 nouveaux facteurs qui augmentent l’activité des cellules souches hématopoïétiques lorsqu’ils sont surexprimés. J’ai par la suite démontré que neuf de ces facteurs agissent de manière extrinsèque aux cellules souches hématopoïétiques, c’est-à-dire que l’effet provient des cellules nourricières modifiées en co-culture. J’ai également mis à jour un nouveau réseau de régulation de transcription qui implique cinq des facteurs identifiés, c’est-à-dire PRDM16, SPI1, KLF10, FOS et TFEC. Ce réseau ressemble étrangement à celui soutenant l’ostéoclastogénèse. Ces résultats soulèvent l’hypothèse selon laquelle les ostéoclastes pourraient aussi faire partie de la niche fonctionnelle des cellules souches hématopoïétiques dans la moelle osseuse. De plus, j’ai identifié un second réseau de régulation impliquant SOX4, SMARCC1 et plusieurs facteurs identifiés précédemment dans le laboratoire, c’est-à-dire BMI1, MSI2 et KDM5B. D’autre part, plusieurs indices accumulés tendent à démontrer qu’il existe des différences fondamentales entre le fonctionnement des cellules souches hématopoïétiques murines et humaines. / Somatic stem cells usually exhibit a very different behavior compared to pluripotent stem cells. The molecular basis of embryonic stem cell self-renewal was recently decrypted by the relative straightforwardness with which we can now purify and maintain these cells in culture for long periods of time. However, this is not the case with hematopoietic stem cells. In order to elucidate the molecular mechanisms of hematopoietic stem cell self-renewal, I developed a novel gain-of-function screening strategy, which bypasses some constraints found with these cells. Starting from a list of more than 700 candidate nuclear factors and asymmetric division factors, I have identified 24 new factors that increase hematopoietic stem cell activity when overexpressed. I have also found that nine of these factors act extrinsically to hematopoietic stem cells, i.e., the effect comes from the engineered feeder cells in co-culture. Moreover, I have revealed a new transcriptional regulatory network including five of the factors identified, i.e., PRDM16, SPI1, KLF10, FOS and TFEC. This network is particularly similar to that involved in osteoclastogenesis. These results raise the hypothesis that osteoclasts might also be part of the functional hematopoietic stem cell niche in the bone marrow. Furthermore, I have identified a second regulatory network involving SOX4, SMARCC1 and several factors previously identified in the laboratory, i.e., BMI1, MSI2 and KDM5B. Besides, several lines of evidence tend to show that there are fundamental differences between mouse and human hematopoietic stem cells.

A pesar de la abundancia de estudios realizados sobre el papel de las células acinares en las patologías exocrinas del páncreas (i.e. pancreatitis y cáncer), el estudio de las modificaciones producidas durante la diferenciación acinar en dichas patologías, se ha visto limitado por la escasez de modelos celulares no tumorales. Resultados previos de nuestro laboratorio, muestran que las células mES (células madre embrionarias de ratón )- pluripotentes y con la capacidad para generar tipos celulares especializados- pueden desarrollar un fenotipo acinar in vitro. Los objetivos de esta tesis han sido aumentar el contenido de enzimas digestivos así como las propiedades funcionales de las células generadas. Para ello se sobreexpresaron de forma estable p48, RBPJL y Mist1en células madre por transducción lentiviral de estos genes. Obtuvimos, gracias a una estrategia de infección en múltiples etapas, líneas celulares transgénicas mES que expresaban de forma constitutiva RBPJL y/o Mist1. La superimposición de la expresión de p48 por infección lentiviral en células en proceso de diferenciación dio lugar a una fuerte expresión de enzimas digestivos, con un patrón de regulación similar al que acontece in vivo durante el desarrollo pancreático. En esta inducción, tanto p48 como RPBJL son indispensables. Por otro lado, hemos mostrado un aumento elevado en la producción de varios componentes de la maquinaria secretota dependiente de Mist1. Además, hay que hacer notar ,que las células p48/RBPJL/Mist1 exhiben una regulada-secreción en respuesta a los secretagogos acinares y una mejor actividad de que la línea celular acinar 266-6. La expresión combinada de genes clave implicados en el desarrollo pancreático en células ES es un prometedor abordaje que nos llevará a una comprensión de los sutiles procesos del desarrollo exocrino pancreático. / Despite known involvement of acinar cells in pancreatic exocrine pathologies (i.e pancreatitis and pancreatic cancer), the lack of normal cell-based models has limited the study of the alterations that occur in the acinar differentiation program. Our previous data showed that mES (murine embryonic stem) cells, which are pluripotent and have the ability to generate specialized cell types, can acquire an acinar phenotype in vitro. The aim of this work was to increase the digestive enzyme content of the generated cells as well as their functional properties based on stable overexpression of p48, RBPJL and Mist1 by lentiviral gene transduction. Thus, we engineered transgenic mES cell lines constitutively expressing RBPJL and/or Mist1 using a multi-step infection strategy. The superimposition of p48 expression by lentiviral infection of differentiating cells resulted in a strong expression of digestive enzymes, with a pattern of regulation similar to what occurs in vivo during pancreatic development. In this induction, both p48 and RPBJL are indispensable. On the other hand, we showed a high increase in the production of several components of the secretory machinery which was dependent of Mist1. Importantly, p48/RBPJL/Mist1 cells exhibited a regulated-secretory in response to acinar secretagogues and a better secretion activity than the 266-6 acinar cell line. Combined expression of key genes involved in pancreatic development in ES cells may be a promising approach to better understand subtle steps of pancreatic exocrine development.

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Les cellules souches somatiques présentent habituellement un comportement très différent des cellules souches pluripotentes. Les bases moléculaires de l’auto-renouvellement des cellules souches embryonnaires ont été récemment déchiffrées grâce à la facilité avec laquelle nous pouvons maintenant les purifier et les maintenir en culture durant de longues périodes de temps. Par contre, il en va tout autrement pour les cellules souches hématopoïétiques. Dans le but d’en apprendre davantage sur le fonctionnement moléculaire de l’auto-renouvellement des cellules souches hématopoïétiques, j’ai d’abord conçu une nouvelle méthode de criblage gain-de-fonction qui répond aux caprices particuliers de ces cellules. Partant d’une liste de plus de 700 facteurs nucléaires et facteurs de division asymétrique candidats, j’ai identifié 24 nouveaux facteurs qui augmentent l’activité des cellules souches hématopoïétiques lorsqu’ils sont surexprimés. J’ai par la suite démontré que neuf de ces facteurs agissent de manière extrinsèque aux cellules souches hématopoïétiques, c’est-à-dire que l’effet provient des cellules nourricières modifiées en co-culture. J’ai également mis à jour un nouveau réseau de régulation de transcription qui implique cinq des facteurs identifiés, c’est-à-dire PRDM16, SPI1, KLF10, FOS et TFEC. Ce réseau ressemble étrangement à celui soutenant l’ostéoclastogénèse. Ces résultats soulèvent l’hypothèse selon laquelle les ostéoclastes pourraient aussi faire partie de la niche fonctionnelle des cellules souches hématopoïétiques dans la moelle osseuse. De plus, j’ai identifié un second réseau de régulation impliquant SOX4, SMARCC1 et plusieurs facteurs identifiés précédemment dans le laboratoire, c’est-à-dire BMI1, MSI2 et KDM5B. D’autre part, plusieurs indices accumulés tendent à démontrer qu’il existe des différences fondamentales entre le fonctionnement des cellules souches hématopoïétiques murines et humaines. / Somatic stem cells usually exhibit a very different behavior compared to pluripotent stem cells. The molecular basis of embryonic stem cell self-renewal was recently decrypted by the relative straightforwardness with which we can now purify and maintain these cells in culture for long periods of time. However, this is not the case with hematopoietic stem cells. In order to elucidate the molecular mechanisms of hematopoietic stem cell self-renewal, I developed a novel gain-of-function screening strategy, which bypasses some constraints found with these cells. Starting from a list of more than 700 candidate nuclear factors and asymmetric division factors, I have identified 24 new factors that increase hematopoietic stem cell activity when overexpressed. I have also found that nine of these factors act extrinsically to hematopoietic stem cells, i.e., the effect comes from the engineered feeder cells in co-culture. Moreover, I have revealed a new transcriptional regulatory network including five of the factors identified, i.e., PRDM16, SPI1, KLF10, FOS and TFEC. This network is particularly similar to that involved in osteoclastogenesis. These results raise the hypothesis that osteoclasts might also be part of the functional hematopoietic stem cell niche in the bone marrow. Furthermore, I have identified a second regulatory network involving SOX4, SMARCC1 and several factors previously identified in the laboratory, i.e., BMI1, MSI2 and KDM5B. Besides, several lines of evidence tend to show that there are fundamental differences between mouse and human hematopoietic stem cells.