No description available.

Fusion of cancer cells has been observed in tumors for more than a century and is thought to contribute to tumor development and drug resistance. The low frequency of cell fusion events and the instability of fused cells have hindered our ability to understand the molecular mechanisms that govern cell fusion. We have developed a patterned gel system that can isolate cell fusion events and we demonstrate that several breast cancer cell lines can fuse into multinucleated giant cells in vitro, and the initiation and longevity of fused cells can be regulated solely by biophysical factors. Dynamically tuning the adhesive area of the micropatterned substrates, reducing cytoskeletal tensions pharmacologically, altering matrix stiffness, and modulating pattern curvature all supported the spontaneous fusion and stability of these multinucleated giant cells. These observations highlight that the biomechanical microenvironment of cancer cells, including the matrix rigidity and interfacial curvature, can directly modulate their fusogenicity, an unexplored mechanism through which biophysical cues regulate tumor progression.

The cells from the inner cell mass (ICM) of an early embryo have the potential to differentiate into all the different cell types present in an adult organism. Cells from the ICM can be isolated and cultured in vitro, becoming embryonic stem cells (ESCs). ESCs have several properties that make them unique: they are unspecialized, can self-renew indefinitely in culture, and given the appropriate cues can differentiate into cells from all three germ layers (ecto-, meso-, and endoderm), including the germline, both in vivo and in vitro. Induced pluripotent stem cells (iPSCs) can be generated from adult, terminally differentiated somatic cells by transient exogenous expression of four transcription factors (Oct4, Sox2, Klf4, and cMyc; OSKM) present normally in ESCs. It has been shown that iPSCs are equivalent to ESCs in terms of morphology, gene expression, epigenetic signatures, in vitro proliferation capacity, and in vitro and in vivo differentiation potential. However, unlike ESCs, iPSCs can be obtained from a specific individual without the need for embryos. This makes them a promising source of pluripotent cells for regenerative medicine, tissue engineering, drug discovery, and disease modelling; additionally, in livestock species such as the bovine, they also have applications in genetic selection, production of transgenic animals for agricultural and biomedical purposes, and species conservancy. Nevertheless, ESC and iPSC lines that meet all pluripotency criteria have, to date, only been successfully produced in mice, rats, humans, and non-human primates. In the first part of this dissertation, we attempted reprogramming of three types of bovine somatic cells: fetal fibroblasts (bFFs), adult fibroblasts (bAFs), and bone marrow-derived mesenchymal stem cells (bMSCs), using six different culture conditions adapted from recent work in mice and humans. Using basic mouse reprogramming conditions, we did not succeed in inducing formation of ESC-like colonies in bovine somatic cells. The combination of 2i/LIF plus ALK5 inhibitor II and ascorbic acid, induced formation of colony-like structures with flat morphology, that occasionally produced trophoblast-like structures. These trophoblast-like vesicles did not appear when an inhibitor of Rho-associated, coiled-coil containing protein kinase 1 (ROCK) was included in the medium. We screened for expression of exogenous OSKM vector with RT-PCR and found upregulation of OSKM vector 24h after Dox was added to the medium; however, expression was sharply decreased on day 2 after Dox induction, and was not detectable after day 3. In a separate experiment, we induced reprogramming of bFF and bAFs using medium supplemented with 50% of medium conditioned by co-culture with the bovine trophoblast CT1 line. These cells expressed both OCT4 and the OSKM vector 24h after Dox induction. However, similar to our previous observations, both markers decreased expression until no signal was detected after day 3. In summary, we were unable to produce fully reprogrammed bovine iPSCs using mouse and human protocols, and the exact cause of our lack of success is unclear. It is possible that a different method of transgene expression could play a role in reprogramming. However, these ideas would be driven by a rather empirical reasoning, extrapolating findings from other species, and not contributing in our understanding of the particular differences of pluripotecy in ungulates. Our inability to produce bovine iPSCs, combined with the only partial reprogramming observed by others, justifies the need for in depth study of bovine pluripotency mechanisms, before meaningful attempts to reprogram bovine somatic cells to plutipotency are made. Therefore, we focused on getting a better understanding of bovine nuclear reprogramming. This would allow us to rationally target the specific requirements of potential bovine pluripotent cells. Cell fusion is a process that involves fusion of the membrane of two or more cells to form a multinucleated cell. Fusion of a somatic cell to an ESC is known to induce expression of pluripotency markers in the somatic nucleus. In the second part of this dissertation, we hypothesized that fusion of bFFs to mouse ESCs (mESCs) would induce expression of pluripotency markers in the bFF nucleus. We first optimized a cell fusion protocol based on the use of polyethylene glycol (PEG), and obtained up to 11.02% of multinucleated cells in bFFs. Next, we established a method to specifically select for multinucleated cells originated from the fusion of mESCs with bFFs (heterokaryons), using indirect immunofluorescence. With this in place, flow cytometry was used to select 200 heterokaryons which were further analyzed using RNA-seq. We found changes in bovine gene expression patterns between bFFs and heterokaryons obtained 24h after fusion. Focusing on the bovine transcriptome, heterokaryons presented upregulation of early pluripotency markers OCT4 and KLF4, as well as hypoxia response genes, contrasted with downregulation of cell cycle inhibitors such as SST. The cytokine IL6, known to increase survival of early embryos in vitro, was upregulated in heterokaryons, although its role and mechanism of action is still unclear. This indicates that the heterokaryon cell fusion model recapitulates several of the events of early reprogramming, and can therefore be used for further study of pluripotency in the bovine. The cell fusion model presented here can be used as a tool to characterize early changes in bovine somatic nuclear reprogramming, and to study the effect of different reprogramming conditions on the bovine transcriptome. / Ph. D. / The cells of an early embryo have the potential to give rise to any cell type found in the adult body. When these cells are transferred to a culture dish and kept under the right conditions, they become Embryonic Stem Cells (ESCs), and they retain the same developmental potential as the original embryonic cells they were derived from. In 2006, researchers in Japan found that it is possible to “reprogram” the cells of an adult individual (for example, fibroblast skin cells taken from a biopsy) to an embryonic state, by forcing the cells to express extra copies of genes that are normally active in embryos. These reprogrammed cells are called induced Pluripotent Stem Cells (iPSCs), and similarly to ESCs, they also have the potential to produce any cell type found in an adult organism. Lines of iPSCs from livestock species have possible applications in agriculture, species conservancy, biomedical industry, and veterinary and human health. Unfortunately, for reasons that are to date not fully understood, the technology to produce iPSCs has, so far, only worked in mice, rats, humans, and non-human primates. We first attempted to produce bovine iPSCs by adapting methods and conditions used to derive iPSCs in mice and humans. We observed partial reprogramming of bovine cells, but were ultimately not able to produce true bovine iPSCs. This suggests that the bovine requires alternative/additional factors to induce reprogramming in adult cells. However, not knowing exactly what conditions or reagents will induce the reprogramming process in the cow, we decided to take a different approach. We focused on trying to understand how nuclear reprogramming works in the bovine. This would allow us to rationally target the specific requirements of potential bovine pluripotent cells. It is known that the fusion (“merging”) of an adult cell with a stem cell, causes the adult cell to change its gene expression pattern to resemble a stem cell. We therefore fused mouse ESCs with bovine fibroblasts, and observed changes in bovine gene expression pattern as early as 24 hours after fusion. The gene expression changes observed resemble those found during early reprogramming of human and mouse iPSCs, and are accompanied by silencing of fibroblast specific genes. This suggests that our cell fusion model recreates the changes that happen during reprogramming, and can therefore be used as a tool to better understand pluripotency in the cow. The cell fusion method described in this dissertation can in theory be adapted to other species; by fusing somatic cells from other species to mouse ESCs, this model can be used to find species specific relevant pluripotency genes.

Cell fusion is an important technique that is used in the field of medicine and biomedical research. For instance, fusion can be used to create hybridomas and novel types of secretory hybrid cells. It may also be used to engineer cultured insulin-secreting pancreatic B-cell lines for the treatment of diabetes. Historically, the applications listed above have been accomplished by a number of methodologies including dielectrophoresis, centrifugation, polyethylene glycol (PEG) and viral fusion proteins. However, these approaches often fail to produce the desired results due to poor cell viability, lack of 1:1 fusion, and use of non-physiological environments. It is proposed that the application of an electrical field generated by corona charge (corona fields) and subsequent treatment with direct current (DC) pulse technology will overcome these deficiencies. Isolated and pre-labeled neuronally committed human teratocarcinoma (NT2) cells in monoculture or co-culture, were seeded in chambers, constructed in the laboratory, and allowed to adhere to the chamber bottom prior to corona treatment. A corona generator, also constructed in the laboratory, was used to expose cells to positive and negative electrical charges to induce cell-cell contact. The cells were then pulsed with DC voltage to induce fusion. During the experiments, cells were photographed sequentially to record cell movement/contact and fusion. The project was designed to identify optimal corona-based electrofusion parameters for viable, 1:1 cell fusion. Optimal results for cell-cell contact were obtained using a cell density of 2.35 times ten to the fourth power cells per microliter Dulbecco's Modified Eagle Medium (DMEM) in a grounded circular plate corona chamber following at least 3 minutes of settling time. Corona charges from (+) 6.1 kilivolt and (-) 5.5 kilivolt potentials were determined as being most favorable for cell movement and viability. Fusion was best achieved by first exposing either a circular or square ungrounded corona chamber configuration to 3 minutes (+) corona charge followed by 3 minutes (--) corona charge; disturbing the cells in the chamber with mechanical force; and then exposing them to 8-15 sequences of a 2,500 Volts per centimeter DC pulse at 100 microseconds.

Oncolytic measles virus is a promising cancer therapeutic in clinical trials which possesses multiple characteristics that are advantageous over traditional therapies. Currently, clinical oncolytic measles virus vectors are unmodified or express reporter transgenes that benefit its therapeutic efficacy. The next phase in its development will see genetically engineered vectors encoding transgenes that enhance its antineoplastic effects. To this end, preclinical research has focused on studying novel transgenes which favour viral replication, cytotoxicity, and the anti-cancer immune response. We sought to encode artificial micoRNAs targeting RIG-I as a strategy to interfere with innate immunity. Silencing RIG-I with multiple siRNAs yielded one which promotes measles virus syncytia formation through a mechanism that appears to be independent of RIG-I. The mechanism caused by the siRNA leads to enhanced measles virus cell-cell fusion and has peculiar characteristics which are not fully understood.

La thérapie cellulaire régénératrice offre des perspectives d'applications dans de nombreuses pathologies entraînant une perte cellulaire. Cependant, suite à un infarctus du myocarde et donc une diminution importante du nombre de cardiomyocytes, l'injection de cellules souches n'a permis de mettre en évidence qu'une amélioration légère et transitoire de la fonction cardiaque. Ces résultats suggèrent qu'il est nécessaire d'améliorer l'efficacité des protocoles de thérapie cellulaire cardiaque. Cette amélioration passe par une meilleure compréhension des mécanismes mis en jeu par les cellules souches dans la régénération myocardique. Parmi les hypothèses soulevées, la fusion entre les cellules souches et les cardiomyocytes a été décrite dans plusieurs études mais le rôle physiologique de ce phénomène reste inconnu. Mon travail de thèse a consisté à étudier ce mécanisme in vitro au sein de cocultures entres des cellules souches adultes humaines (cellules hMADS pour human multipotent adipose derived stem cells) et des cardiomyocytes murins adultes. Nous avons pu mettre en évidence un processus de fusion hétérologue entre ces deux types cellulaires, aboutissant à la reprogrammation du cardiomyocyte vers un stade de progéniteur. Les cellules hybrides résultant de cette fusion ont exprimé des marqueurs cardiomyogéniques précoces et de prolifération et ont été montrées comme ayant un génotype exclusivement murin. Ces cellules hybrides ou progéniteurs cardiaques se sont formés préférentiellement par un mécanisme de fusion partielle par l'intermédiaire de structures intercellulaires appelées nanotubes composés de f-actine et de microtubules. En outre, nous avons montré que le transfert de mitochondries des cellules souches vers les cardiomyocytes était indispensable pour la reprogrammation des cardiomyocytes. En conclusion, nos résultats apportent de nouveaux éléments dans la compréhension des mécanismes de régénération médiés par les cellules souches qui est un pré-requis pour optimiser les protocoles de thérapie cellulaire cardiaque / Regenerative cell therapy offers potential applications in many diseases involving cell loss. However, following myocardial infarction and the dramatic decrease in the number of cardiomyocytes, the injection of stem cells led to a poor and transient improvement of cardiac function. Therefore stem cell-based therapy to treat myocardial infarction requires a better understanding of the mechanisms brought into play by stem cells in heart regeneration. Among the different hypothesis raised, cell fusion between stem cells and cardiomyocytes has been described in several studies. However, the respective physiological impact of cell fusion remains unknown. During my thesis, I investigated this cell fusion mechanism in vitro in a coculture model between human multipotent adipose-derived stem cells (hMADS) and murine fully differentiated cardiomyocytes. We showed intercellular exchanges of cytoplasmic and nuclear material between both cell types, followed by a heterologous cell fusion process promoting cardiomyocyte reprogramming back to a progenitor-like state. The resulting hybrid cells expressed early cardiac commitment and proliferation markers and exhibited a mouse genotype. We provided evidence that cardiac hybrid cells were preferentially generated through partial cell fusion mediated by intercellular structures composed of f-actin and microtubule filaments. Furthermore, we showed that stem cell mitochondria were transferred into cardiomyocytes and were required for somatic cell reprogramming. In conclusion, by providing new insights into previously reported cell fusion processes, our results might contribute to a better understanding of stem cell-mediated regenerative mechanisms and thus, the development of more efficient stem cell-based heart therapies

Les macrophages sont une cible particulièrement importante de l’infection par le VIH-1 et jouent un rôle crucial dans la physiopathologie de l’infection. Lorsqu’ils sont infectés, leur capacité de survie dans les tissus leur permet de jouer un rôle essentiel dans la dissémination virale et l’établissement de réservoirs viraux au niveau des différents territoires tissulaires. In vitro, les étapes précoces et tardives du cycle de réplication virale dans les macrophages ont été analysées dans le cadre de l’infection par des virus libres. Cependant, les modalités d’infection des macrophages lors d’une transmission intercellulaire reste largement inexplorées. Les travaux présentés ici ont permis d’établir un modèle de transmission intercellulaire du VIH-1 de lymphocytes T infectés vers les macrophages. Nous avons montré que les lymphocytes T infectés sont capables d’interagir étroitement avec les macrophages, conduisant ainsi à la fusion cellulaire de ces deux cellules et permettant le transfert de matériel viral dans les macrophages cibles. Ce transfert viral par fusion cellulaire, rapide et efficace, est restreint aux virus utilisant le corécepteur CCR5 et dépend de l’interaction entre l’enveloppe virale et le récepteur CD4. Les virus transférés sont alors stockés au sein de compartiment cytoplasmique des cellules fusionnées mais nous observons également des évènements précoces d’assemblage et de bourgeonnement du VIH-1 à la membrane plasmique des cellules fusionnées résultant de la fusion des membranes des lymphocytes T infectés et des macrophages cibles. Ces cellules fusionnées acquièrent alors la capacité de fusionner avec les macrophages non infectés environnants permettant la dissémination du VIH-1. L’ensemble de ces résultats met en évidence un nouveau mécanisme de transmission intercellulaire entre lymphocytes T et macrophages via un mécanisme de double fusion cellulaire dépendant de l’enveloppe virale et des récepteurs CD4 et CCR5. Ces évènements successifs de fusion entre lymphocytes T et macrophages puis entre macrophages permettent la formation de cellules géantes multinucléés capables de produire de grande quantité de virus infectieux. Ces cellules multinculées pourraient correspondre aux macrophages multinuclées observés in vivo dans les organes lymphoïdes et le système nerveux central de patients infectés par le VIH-1 ou de singes infectés par le SIV. Ce mécanisme représente donc un modèle de transmission intercellulaire original permettant la dissémination virale et la formation de macrophages réservoirs durant l’infection par le VIH-1. / Macrophages are important targets of HIV-1 and play crucial roles in physiopathology of infection. Because of their long time survival capacity, infected macrophages participate in virus dissemination and establishment of persistent virus reservoirs in numerous tissues. In vitro, macrophages infection and analysis of the different steps of the virus cycle have been largely documented using cell-free virus infection. However, there is a paucity in knowledge of the mechanisms that control infection and dissemination to macrophages by cell-to-cell transfer. In the work presented here, we establish a model of HIV-1 cell-to-cell transfer from infected T cells to macrophages. We observed that infected T cells are able to interact with macrophages leading to cell fusion for transfer of viral material to macrophages targets. This cell-to-cell fusion transfer, very fast and efficient, is restricted to CCR5-tropic viruses, and mediated by viral envelope-receptor interactions. Transferred viruses can then accumulate in cytoplasmic compartments of newly lymphocyte/macrophages fused cells but we also observed early viral assembly and budding events at the plasma membrane of these fused cells, resulting from the merge of viral material between infected T cells and macrophages. These cells then acquire the ability to fuse with neighboring non-infected macrophages for virus dissemination. Together, these two-sequential envelope-dependent cell fusion process lead to the formation of highly virus-productive multinucleated giant cells reminiscent of the infected multinucleated giant macrophages detected in vivo in lymphoid organs and the central nervous system of HIV-1 infected patients and simian immunodeficiency virus-infected macaques. These mechanisms may represent an original mode of virus transmission for viral spreading and formation of macrophage virus reservoirs during HIV-1 infection.

No description available.

Le travail de thèse présenté dans ce manuscrit s’inscrit dans une dynamique d’intégration de matériaux non conventionnels en systèmes microfluidiques. Il vise à démontrer le potentiel du cPDMS, un matériau nanocomposite formé d’une matrice de polydiméthylsiloxane rendu conducteur par l’ajout de nanoparticules de carbone. Compatible avec les procédés technologiques habituels, le cPDMS peut être structuré dans une large gamme d’épaisseurs et de géométries mais présente surtout l’avantage de pouvoir être collé irréversiblement sur verre, PDMS et silicium. Son intégration est parfaitement étanche, rapide à mettre en oeuvre, et très économique. La première partie du manuscrit est consacrée à la caractérisation de ce matériau. Ses propriétés électriques et de surface, pouvant être critiques pour une utilisation en microfluidique, ont été particulièrement étudiées. Les champs électriques offrant de nombreuses possibilités pour réaliser des fonctions clés en microfluidique (détection, séparation, manipulation de fluides ou de particules), nous avons choisi d’évaluer l’intérêt d’électrodes de cPDMS dans deux types d’applications. Les aspects de détection ont d’abord été mis en évidence à l’aide de mesures électrochimiques. Cette méthode a permis à la fois de caractériser la surface du cPDMS tout en validant son utilisation potentielle pour des applications d’analyses électrochimiques. Dans la dernière partie du manuscrit, le matériau a été testé pour la manipulation de particules à travers l’observation de différents phénomènes électrocinétiques. Ceux-ci ont conduit à la mise au point de dispositifs microfluidiques (intégrant des lectrodes de cPDMS) dédiés à la lyse et à l’électrofusion de cellules. / The work presented in this thesis deals with the integration of non-conventional materials in microfluidic systems. It aims to demonstrate the potential of cPDMS, a conductive nanocomposite material made up of polydimethylsiloxane matrix mixed with carbon nanoparticles. Compatible with the usual technological processes such as soft lithography, cPDMS can be microstructured in a large range of thicknesses and geometries. Moreover, cPDMS can be quickly, irreversibly and perfectly sealed to glass, PDMS and silicon substrates, something that is not possible for conventional metallic electrodes. The first part of the manuscript is centered on the characterization of this material. Its electrical and surface properties that may turn out critical for microfluidic applications have been particularly studied. Electric fields present many opportunities to perform key functions in microfluidic (detection, separation, fluid or particles handling). We have chosen to assess the potential of cPDMS electrodes for two kinds of applications. Aspects of detection were first demonstrated using cyclic voltammetry measurements. This electrochemical method has enabled both to characterize the cPDMS surface while validating its potential as an electrochemical analysis tool. In the last part of this manuscript, cPDMS was tested for the electrokinetic manipulation of particles through thre study of different electrical fields with induced phenomena. This has led to the development of microfluidic devices (integrating cPDMS electrodes) designed for cell lysis and cells electrofusion.

La fusion des myoblastes est une étape cruciale pour une bonne formation musculaire pendant l'embryogenèse et après une blessure à l'âge adulte. Le système génétique simpliste des mouches a été largement utilisé dans le passé pour identifier les acteurs essentiels impliqués dans la fusion des myoblastes. Chez la drosophile, la protéine d'échafaudage Antisocial (Ants)/Rols7 joue un rôle essentiel dans la fusion des myoblastes en connectant les protéines de surface d'adhésion cellulaire au cytosquelette. Même si la plupart des voies moléculaires régissant la fusion des myoblastes sont évolutives conservées entre les mammifères et les mouches, les contributions relatives de Tanc1 et Tanc2, les orthologues mammifères de Ants/Rols7, dans la fusion de myoblastes n'ont pas été établies. Le premier objectif de la thèse était d'évaluer les contributions potentielles de Tanc1 et Tanc2 dans la fusion de myoblastes en utilisant la lignée cellulaire de myoblastes murins C2C12 comme modèle de différenciation et de fusion de myoblastes. Nous avons constaté que l'expression de Tanc1 et Tanc2 n'est pas modulée lors de la différenciation C2C12, mais que les deux échafaudages sont enrichis au niveau du cortex lors de la prolifération des myoblastes. De plus, le knockdown de Tanc1 ou Tanc2 a altéré la fusion des myoblastes sans affecter la différenciation des myoblastes. Notamment, l'expression du défaut de fusion humain entièrement restauré Tanc1 ou Tanc2 observé dans les cellules C2C12 épuisées pour Tanc1 ou Tanc2 suggérant qu'un niveau seuil de leur expression est critique pour une fusion efficace des myoblastes. De plus, ni Tanc1 ni Tanc2 n'ont pu se substituer à Ants/Rols7 lors de la fusion des myoblastes chez la drosophile, ce qui suggère que différents acteurs pourraient être impliqués dans la régulation de la fusion des myoblastes chez les mammifères. Le deuxième objectif de la thèse était de caractériser davantage le rôle de Tanc1 et Tanc2 dans la fusion de myoblastes en utilisant des modèles murins de souris. À cette fin, des souris knock-out Tanc1 totales (Tanc1 KO) et des souris knock-out Tanc2 conditionnelles (Tanc2 cKO) ont été générées. Bien que les souris Tanc2 KO aient été précédemment signalées comme étant mortelles sur le plan embryonnaire, nous rapportons ici que ces souris sont viables contrairement à ce qui a été rapporté. L'expression de Tanc1 et Tanc2 a été détectée dans les somites ainsi que dans les fibres musculaires primaires. L'analyse du phénotype musculaire au stade embryonnaire a révélé une différenciation normale des somites et la formation de fibres musculaires chez les souris Tanc1 KO et Tanc2 cKO. De plus, lors de l'analyse au stade adulte, aucune différence dans la section transversale des fibres musculaires entre les souris de type sauvage et les souris mutantes n'a été détectée. Cela pourrait-il impliquer une redondance potentielle entre Tanc1 et Tanc2 dans la régulation de la myogenèse ? Pour répondre à cette question, des souris double knockout Tanc1 et Tanc2 sont actuellement en cours de génération. En conclusion, nous avons identifié dans cette étude un nouveau rôle pour les protéines d'échafaudage Tanc1 et Tanc2 dans la fusion de myoblastes chez les mammifères. L'identification de nouveaux acteurs essentiels dans la fusion des myoblastes nous rapproche de sa compréhension et de son ciblage thérapeutique à long terme. / Myoblast fusion is a crucial step for proper muscle formation during embryogenesis and after in injury during adulthood. The simplistic genetic system of flies has been extensively used in the past to identify essential players involved in myoblast fusion. In Drosophila, the scaffold protein Antisocial (Ants)/Rols7 plays an essential role in myoblast fusion by connecting the cell adhesion surface proteins to the cytoskeleton. Even though most molecular pathways governing myoblast fusion are evolutionary conserved between mammals and flies, the relative contributions of Tanc1 and Tanc2, the mammalian orthologs of Ants/Rols7, in myoblast fusion have not been established. The first aim of the thesis was to assess the potential contributions of Tanc1 and Tanc2 in myoblast fusion by using the murine myoblast C2C12 cell line as a model for myoblasts differentiation and fusion. We found that Tanc1 and Tanc2 expression is not modulated during C2C12 differentiation, but that both scaffolds are enriched at the cortex during myoblast proliferation. Furthermore, the knockdown of either Tanc1 or Tanc2 impaired myoblast fusion without affecting myoblast differentiation. Notably, the expression of human Tanc1 or Tanc2 fully restored fusion defect observed in C2C12 cells depleted for Tanc1 or Tanc2 suggesting that a threshold level of their expression is critical for efficient myoblast fusion. Furthermore, neither Tanc1 nor Tanc2 could substitute for Ants/Rols7 during Drosophila myoblast fusion suggesting that different players might be involved in regulating myoblast fusion in mammals. The second aim of the thesis was to further characterize the role of Tanc1 and Tanc2 in myoblast fusion by using murine mice models. For this purpose, total Tanc1 knockout mice (Tanc1 KO) and conditional Tanc2 knockout mice (Tanc2 cKO) were generated. Although Tanc2 KO mice were previously reported to be embryonically lethal, we report here that those mice are viable contrary to what has been reported. Tanc1 and Tanc2 expression was detected in the somites as well as in the primary muscle fibers. Analysis of the muscle phenotype at the embryonic stage revealed normal somites differentiation and muscle fiber formation in both Tanc1 KO and Tanc2 cKO mice. Furthermore, when analyzed at the adult stage, no difference in the cross-sectional area of the muscle fibers between wild-type mice and mutant mice was detected. Could this imply a potential redundancy between Tanc1 and Tanc2 in regulating myogenesis? To answer this question, Tanc1 and Tanc2 double knockout mice are currently being generated. In conclusion, we identified in this study a novel role for the scaffold proteins Tanc1 and Tanc2 in myoblast fusion in mammals. Identifying new and essential players in myoblast fusion brings us a step closer to understanding it and on the long run target it therapeutically.