La migration cellulaire concerne des cellules individuelles ou bien des groupes de cellules migrant de manière collective et coordonnée. De nombreux processus physiologiques, notamment au cours du développement embryonnaire, ainsi que pathologiques, notamment lors de maladies inflammatoires ou de la formation de métastases nécessitent des mouvements cellulaire collectifs. Au cours de l'ovogénèse chez la Drosophile, un groupe de cellules, appelés cellules de bordure, migrent entre les cellules nourricières, collectivement, au sein du follicule ovarien. Ces cellules de bordure constituent un modèle de choix pour étudier les mécanismes régulant la migration collective in vivo. La migration de ce groupe de cellules est divisée en deux phases. Lors de la première moitié de migration, du début de la migration à la moitié du parcours, les cellules de bordure adoptent un mouvement linéaire, au cours duquel chaque cellule maintient sa position au sein de l'entité, et une seule et même cellule conduit le groupe vers l'avant. Ensuite, à mi-chemin, ces groupes commencent à effectuer des mouvements de rotation sur eux-mêmes pour aller atteindre l'ovocyte, permettant à n'importe quelle cellule de pouvoir mener la migration. L'objectif de ma thèse a été d'élucider les mécanismes régulant le choix entre ces deux modes de migration (linéaire et rotationnel). Le cytosquelette d'acto-myosine est un des acteurs principaux régulant la contraction cellulaire nécessaire à la motilité des cellules. Au cours de ma thèse, nous avons mis en évidence le rôle de la myosine non musculaire de type II dans le contrôle du passage d'un mouvement linéaire à rotationnel. Nos travaux démontrent que l'apparition des mouvements de rotation effectués par les cohortes de cellules de bordure est corrélée à une augmentation de l'activité de la myosine non musculaire de type II. De plus, nous avons montré que l'activité de la myosine non musculaire de type II pouvait être régulée de manière antagoniste par les récepteurs de guidance. En conclusion, mes travaux de thèse nous ont permis de démontré le rôle clé de la myosine non musculaire de type II dans l'adaptation du mode de migration au cours de mouvements collectifs des cellules de bordure. De plus nous avons identifié les facteurs régulant l'activité de la myosine non musculaire de type II. En effet, cette dernière est régulée positivement par EGFR. / In many biological processes, cells can move individually or in a coordinated and collective manner. Collective migrations are necessary during several embryo developmental processes, and pathologies such as inflammatory diseases or metastasis formation. During Drosophila oogenesis, border cells, a group of 6-10 cells, migrate in between nurse cell until the oocyte, within the egg chamber and provide a good model to study collective cell migration in vivo. Border cell migration is divided in to two phases. From the anterior pole of the egg chamber to the half of migrated distance, border cell adopt a linear movement, in which each cell maintain its position within the cluster and one leader cell drive the migration. Midway of the migration path, border cell clusters rotate to reach the oocyte. During this second phase, any cell can take the lead of the migration. The aim of my PhD research works was to identify mechanisms regulating the choice between linear and rotational movements. Acto-myosin cytoskeleton is one of the main regulators of cell contraction necessary for cell motility. Through our research, we demonstrated that non-muscle myosin II (NMII) regulate the switch between linear and rotational behaviour. These results led us to identify mechanisms regulating NMII activity during border cell migration. Border cells express two guidance receptors: PVR (Platelet-derived growth factor receptor (PDGFR) and Vascular endothelial growth factor receptor (VEGFR) receptor Related) and EGFR (Epidermal Growth Factor Receptor). Recent studies shown that PVR play a crucial role in the first phase and EGFR predominantly regulate the second phase of migration. Our data shows that NMII is antagonistically regulated by PVR and EGFR. Indeed, the inhibition of NMII in border cell over expressing EGFR completely blocks the rotational movement To conclude, my PhD works allow us to demonstrate the key role of NMII for the regulation of border cell migration. Moreover, we found that EGFR positively regulates NMII activity.

Myofibrillogenesis is a complex process, which involves assembly of hundreds of structural proteins in a highly ordered manner to form the contractile structural unit of muscle, the sarcomere. Several myopathic conditions reported in humans are caused due to abnormal myofibrillogenesis owing to mutations in the genes coding for many of these structural proteins. These myopathies have highly variable clinical features and time of onset. Since their aetiology is poorly understood, it becomes imperative to have a model system to study the muscle defects. Present study proposes to employ the Indirect Flight Muscle (IFM) system in Drosophila melanogaster as a model to analyse the development/onset of some of these myopathies and resulting pathophysiology. We have carried out a systematic study on mutations in two major proteins of the sarcomere, actin and myosin, to understand the pathophysiology associated with the disease conditions and in turn gain insights into the process of myofibrillogenesis. To verify whether the human muscle phenotypes are observed in flies, we analysed the IFM for functional and structural defects categorised by the presence of aberrant sarcomeric structures. An important question that we have addressed is whether mutants of the Drosophila IFM recapitulate human conditions and whether it can serve as a good genetic model to study the developmental mechanisms of the human skeletal myopathies in vivo. Mutations of the human ACTA1 skeletal actin gene produce seven congenital myopathies – actin myopathy, nemaline rod myopathy, intranuclear rod myopathy, congenital fibre type disproportion, congenital myopathy with core-like areas, cap disease and zebra body myopathy. Four known mutations in Act88F—a Drosophila homologue of ACTA1—occur at the same actin residues mutated in ten ACTA1 nemaline mutations, A138D/P, R256H/L, G268C/D/R/S and R372C/S. These Act88F mutants were examined for muscle phenotypes with nemaline structures. Mutant homozygotes show phenotypes ranging from lack of myofibrils to almost normal sarcomeres at eclosion. Whereas, heterozygotes do allow myofibrillar assembly to certain extent; however, atypical structures are seen adjacent to normal sarcomeres. Aberrant Z disc-like structures and serial Z disc arrays, ‘zebra bodies’, are observed in homozygotes and heterozygotes of all the four Act88F mutants. The electron-dense structures observed in electron micrographs show homologies to human nemaline bodies/rods, but are much smaller than those typically found in the human myopathy. A possible mechanism for the ‘zebra bodies’ is proposed based on this study. Analysis of IFM at early developmental stages shows that in three of the mutants, there is an abnormal myofibril assembly leading to malformed sarcomeres mirrored in the adult stages. In one of the Act88F mutants, normal myofibrils are seen post-eclosion but the IFM show activity dependant progression of muscle degeneration. All the Act88F mutants produce dominant disruption of muscle structure and function which cannot be rescued even by three copies of the wild type Act88F gene implying that the mutants are strong antimorphs. Myosin myopathies are a group of human muscle diseases with heterogeneous clinical features and are caused by mutations in the skeletal muscle myosin heavy chain. We identified two chemical mutagen generated flightless mutants, Ifm(2)RU1 and ifm(2)RU2 that map closely to myosin heavy chain gene (Mhc) region. Since there are no structural proteins predicted in the mapped region, it was likely that these two are Mhc mutations. We show that Ifm(2)RU1 and ifm(2)RU2 are indeed Mhc mutations and the molecular aberrations affect amino acid residues present in the myosin rod region. Human muscle myosin heavy chain (MyHC) mutations that cause Laing early onset distal myopathy and myosin storage myopathy occur in this domain of the protein. Even though mutations lie in the same region of myosin rod, Ifm(2)RU1 is semidominant, whereas ifm(2)RU2 is recessive. Both the mutants show IFM defects and the presence of abnormal myofibrils. Mutant myofibrillar structures can be rescued with an additional wild type Mhc gene copy. However, the restored myofibrillar structure is incapable of rescuing the flight ability of mutants. The muscle phenotypes are due to defects in thick filament assembly which manifest from the early stages of sarcomere development. The MHC protein rod region is an α-helix that forms coiled-coils which further self assemble to form thick filaments or aggregates as observed in in vitro conditions. Biophysical and biochemical analyses reveal that the coiled-coil structure of mutant rods is not affected, however the thermodynamic stability is altered in ifm(2)RU2 mutation. Interestingly, rod aggregate size and stability are not affected in mutant rods. The Drosophila MHC mutant rods were studied along with four MHC mutant rods that harbour human rod mutations to compare the molecular consequences. The Drosophila mutations do not hamper the rod structure and assembly. Therefore, the defects may arise due to altered interactions with myosin rod binding proteins. Flightin is an extensively studied myosin rod binding protein. The amount and phosphorylation status of flightin are an extremely sensitive measure of thick filament assembly. Flightin phosphorylation is affected in the mutants suggesting a functional dependence on MHC and it also indicates MHC instability. In the light of the work done, we have assessed the mutations with respect to their structure-functional implications. The acto-myosin interactions responsible for the defects are also discussed. Formation of unusual myofibrillar structures are analysed with regards to the process of myofibrillogenesis. An understanding of this entire process with the information available from IFM is reviewed in detail. The work so far has helped in understanding the manifestation of myopathies at tissue/cellular levels with insights into the plausible mechanisms of origin of the disease phenotypes. Myopathic condition may arise due to developmental or functional defects. For therapeutic considerations, the fly provides a simple test to inspect the effects of adding extra copies of the wild type gene. We conclude that the Drosophila IFM provide a good model system for the study of human ACTA1 and MyHC myopathies.

The nervous system is the most complex system in an organism. Functioning of the nervous system requires proper formation of neural cells, as well as accurate connectivity and signaling among them. While the major events that occur during these processes are known, the finer details are yet to be understood. Hence, an attempt was made to look for novel genes that could be involved in them. The focus of the present study is on CG9650, a gene that was uncovered in a misexpression screen, as a possible player in neuronal development in Drosophila melanogaster. The first chapter of the thesis reviews existing knowledge about neuronal development and function. The first section of this chapter explains in brief the formation and specification of neural stem cells, and their differentiation to neurons and glia. Sections 2 and 3 describe neuronal connectivity and signaling with respect to axon growth, synapse formation, function and plasticity. A comparison of invertebrate and vertebrate neuronal development is provided in section 4 of this chapter. This part also explains the use of Drosophila as a model for neuronal development and function. Chapter 2 describes the expression pattern of CG9650, which was characterized to gain insights into the possible role it plays during Drosophila neurogenesis.CG9650 is expressed in multiple cell types in the nervous system at the embryonic stage. Some of the cell sub-types have been identified from their morphology and position. Expression was restricted to neurons in the larval stage (except in the optic lobe, where it was expressed in precursors also), and continued in the pupal stage. No expression was seen in adults (except in the optic lobe). CG9650 has a putative DNA binding region, which bears homology to the mouse proteins CTIP1 and CTIP2, implying that CG9650 is possibly a transcription factor. In order to understand the function of CG9650, the protein was knocked down panneuronally. The resultant animals showed locomotor defects at both larval and adult stages, which have been described in chapter 3. Knock down larvae showed reduced displacement and speed of movement. The number of peristaltic cycles was also reduced in these animals but the cycle period was normal. In adults, movement was uncoordinated and righting reflex was lost, resulting in inability to walk, climb or fly. These results imply a defect in neuronal signaling. Sensory perception was unaffected in these animals. Stage specific knockdown of CG9650 indicated that the requirement for this protein is primarily during the larval stage. All CG9650-expressing neurons in the ventral nerve cord were glutamatergic, implying that its role in controlling locomotor activity is likely through glutamatergic circuits. Following up on these observations, signaling at the neuromuscular junction was assessed in CG9650 knock down animals. Chapter 4 discusses the signaling defects seen on CG9650 knock down, and the possible role of this protein. Electrophysiological recordings from Dorsal Longitudinal Muscles showed reduced and irregular neuronal firing in the knock down animals. These animals also had reduced bouton and active zone numbers. Moreover, overexpression of BRP, an active zone protein, rescued the locomotor defects caused by knock down of CG9650. Chapter 5 reports the effect of over expression of CG9650. Pan-neural over expression of CG9650 resulted in embryos with severe axon scaffolding defects, as well as aberrant neuronal and glial pattern. However, the incorrectly positioned glial cells in these embryos did not express CG9650, indicating that their aberrant positioning was probably due to incorrect signaling from the neurons. In conclusion, this study reports the requirement for CG9650, a hitherto unknown protein, in locomotor activity and signaling, thus ascribing for it a role in neuronal development and function of Drosophila melanogaster.

L'intérieur des cellules eucaryotes est compartimenté en organites qui échangent des lipides et protéines entre eux et avec la membrane plasmique via le trafic vésiculaire. Dans les cellules polarisées comme les cellules épithéliales, dont la membrane plasmique est divisée en un pôle apical et un pôle basolatéral séparés par une ceinture de jonctions, le trafic vésiculaire est contrôlé par des systèmes de tri polarisé, permettant d'adresser les protéines appropriées au domaine membranaire approprié. Dans ces cellules épithéliales, le complexe adaptateur AP-1 contrôle l'adressage au pôle basolatéral et le trafic de la molécule d'adhésion E-Cadhérine, une protéine transmembranaire des jonctions d'adhérence. Il a de plus été démontré dans les cellules intestinales du nématode C. elegans et des mammifères qu'AP-1 est nécessaire au maintien de la polarité épithélial. J'ai étudié ces fonctions d'AP-1 chez l'organisme modèle Drosophila melanogaster. J'ai montré qu'AP-1 contrôle aussi le trafic de E-Cadhérine chez la Drosophile mais n'est pas requis pour la maintenance de la polarité de l'épithélium folliculaire, un épithélium entourant le cyste germinal femelle de 16 cellules au cours de l'ovogénèse chez la Drosophile. Ces expériences dans ce tissu m'ont amené à découvrir une nouvelle fonction de E-Cadhérine dans le cyste germinal. Les cellules de ce cyste sont connectées entre elles par des ponts cytoplasmiques stabilisés à l'issue de cytocinèses incomplètes. J'ai montré que les cellules du cyste mutantes pour AP-1 présentent un phénotype de multinucléation dû au décrochage des ponts cytoplasmiques. Ce phénotype corrèle avec un défaut d'adressage de E-Cadhérine dépendant d'AP-1 à la membrane plasmique entourant ces ponts, via les endosomes de recyclage. E-Cadhérine y est nécessaire pour leur ancrage à la membrane plasmique, un rôle qui avait été jusque-Là masqué par l'expression ectopique compensatoire de N-Cadhérine dans les mutants E-Cadhérine. Ce rôle d'E-Cadhérine passe par l'organisation de protrusions membranaires présentant l'aspect et contenant certains marqueurs protéiques des microvillosités observées au pôle apical des cellules épithéliales. / Eukaryotic cells are compartmentalized in organelles. Lipidic and proteic exchanges between organelles and the plasma membrane are controlled by vesicular trafficking. In polarised cells such as epithelial cells, whose plasma membrane is divided into an apical and a basolateral pole separated by a junctional belt, appropriate targeting of proteins to appropriate poles relies on polarised sorting mechanisms controlling vesicular trafficking. In these cells, the clathrin adaptor complex AP-1 controls basolateral targeting and trafficking of the adhesion molecule E-Cadherin, a transmembrane adherens junctions protein. AP-1 is furthermore necessary for epithelial polarity maintenance in intestinal epithelial cells in the nematode C. elegans and mammals. I studied AP-1 functions in the model organism Drosophila melanogaster. I showed AP-1 also controls E-Cadherin trafficking in Drosophila but is not required for polarity maintenance in follicular cells, an epithelium surrounding the female germline cyst during oogenesis. Experiments in this tissue led me to discover a new E-Cadherin function in the germline cyst. Germline cyst cells are interconnected by cytoplasmic bridges stabilised after incomplete cytokinesis. I showed AP-1 mutant cyst cells were multinucleated due to a detachment of cytoplasmic bridges from the plasma membrane. This phenotype correlated with an E-Cadherin AP-1-Dependent targeting defect from recycling endosomes to the plasma membrane surrounding these bridges. E-Cadherin is necessary for their anchoring to the plasma membrane, a role that was hidden by ectopic compensatory expression of N-Cadherin in E-Cadherin mutants. This new role is mediated by E-Cadherin-Dependent organisation of membrane protrusions similar in aspect with and containing proteins of microvillosities present at the apical pole of epithelial cells.

O cDNA da glicoproteína do vírus da raiva (GPV) foi clonado em vetores plasmidiais (indutíveis) contendo ou não o cDNA do sinal de secreção BiP e da resistência ao antibiótico higromicina B. Esses vetores foram transfectados em células S2 e foram obtidas populações e subpopulações. A população S2MTGPV-H apresentou níveis 5x maiores na expressão da GPV em análise por FACS (~ 50% das células) e por ELISA (~ 0,65 µg/107 células). A seleção de subpopulações permitiu um aumento de aproximadamente 10x na expressão da GPV, especialmente na população S2MTGPV*-H. O tratamento com NaBu resultou em uma redução de aproximadamente 20% no crescimento celular e um aumento de 50% na GPV expressa pela população S2MTGPV*-H (~ 8,3 µg/107 células). O meio de cultura SF900 II permitiu um maior crescimento das células S2MTGPV*-H e uma maior síntese de GPV comparado com outros meios de cultura. Nossos dados mostram que a expressão da GPV pôde ser otimizada através da construção de vetores de expressão/seleção, subpopulações, da exposição da cromatina e do meio de cultura utilizado. / The cDNA encoding the entire rabies virus glycoprotein (RVGP) gene was cloned in plasmids (inductive) with or without a cDNA coding for the secretion signal and coding for the selection hygromicin antibiotic. These vectors were transfected into S2 cells and we had obtain cells populations and subpopulations S2MTRVGP-H cell population were shown to express 5 times higher of RVGP as evaluated by FACS (~ 50 %) and ELISA (~ 0.65 mg/107 cells at day 7). Sub-population selection allowed a higher RVGP expression, especially for the S2MTRVGP*-H. NaBu treatment leading to lower cell growth and higher RVGP expression allowed an even higher RVGP synthesis by S2MTRVGP*-H (~ 8.3 mg/107 cells at day 7 after induction). SF900II medium leading to a higher S2MTRVGP*-H cell growth allowed a higher final RVGP synthesis in this cell culture. The data show that RVGP synthesis may be optimized by the expression/selection vectors design, cell sub-populations selection, chromatine exposure and culture medium employed.

O interesse em células de inseto para a produção de proteínas complexas se deve a sua maior facilidade de cultivo e ao padrão equivalente de glicosilação quando comparado aos sistemas com células de mamíferos. O objetivo deste trabalho foi identificar fatores que limitam ou inibem a produção da glicoproteína do vírus rábico (GPV) expressa na membrana citoplasmática de células de Drosophila melanogaster transfectadas, quando cultivadas em biorreator de bancada agitado e bubble-free, operado em modo descontínuo. Avaliaram-se as influências de oxigênio dissolvido (5 < pO2 <80%), da glicose (1 < GLC0 < 15g/L) e da glutamina (0.6 < GLN0 < 7g/L). Essas variáveis afetaram de forma diferenciada o crescimento celular (produção de células e velocidades específicas-µX), o metabolismo celular (fatores de conversão - YX/GLC, YX/GLN, YLAC/GLC, YALA/GLC, YNH4/GLN, YALA/GLN), assim como a expressão da proteína recombinante (concentração, teor celular e produtividade). O aumento do pO2 reduziu em 9 vezes o crescimento celular mas aumentou o teor celular de GPV em 1,4 vezes. Baixos valores de GLC0 e GLN0, claramente, limitaram o crescimento, de modo que incrementos na concentração desses substratos, até valores intermediários, aumentaram µX,MAX em 3 vezes e 2,5 vezes, respectivamente, e a produção de células em 11 vezes e 3 vezes, respectivamente. O teor celular de GPV máximo não foi afetado pela GLC, mas aumentou em 100% para valores de GLN0 igual ou superiores a 3,5 g/L. As concentrações de lactato produzidas foram consideradas baixas (inferiores a 0,8 g/L) para exercer qualquer efeito de inibição sobre o crescimento ou a expressão da proteína. Por sua vez, as concentrações de amônio parecem inibir tanto a produção de GPV (NH4+~50mg/L) quanto o crescimento celular (NH4+~80mg/L). A condição de cultivo com de 30% de pO2, 10 g/L de GLC0 e 3,5 g/L de GLN0 resultou nos maiores valores de produtividade (9,1 µg/L.h) e de concentração de GPV (1,2 mg/L). O metabolismo de GLC e GLN apresentou grande interdependência, com alterações em GLC0 afetando o metabolismo de GLN e vice-versa. Assim, em condições de excesso de GLC0, as células apresentaram um metabolismo mais ineficiente com reduções nos fatores YX/GLC (2,3 vezes) e YX/GLN (4,6 vezes) e maior geração de subprodutos, caracterizada por incrementos nos valores de YALA/GLC (51%), YLAC/GLC (11%) e YNH4/GLN (15%). O metabolismo da GLN apresentou resposta característica de substrato em excesso para toda a faixa de valores ensaiada, com redução de 25 vezes no valor de YX/GLN e inesperadamente também uma redução na geração de subprodutos de 7 vezes para YNH4/GLN e 12 vezes para YALA/GLN. O efeito sobre o metabolismo da GLC foi mais acentuado para valores mais elevados de GLN0, com redução de 3,6 vezes para YX/GLC e incrementos de 70% para YALA/GLC e para YLAC/GLC. Os resultados sugerem ainda que a célula utiliza duas vias para metabolizar a glutamina: glutaminólise, em condição de limitação em GLC; ou glutamato sintase - NADH-GOGAT, em condição de excesso em GLC. A célula demonstrou também capacidade de sintetizar GLN, a partir de amônio ou outros aminoácidos, quando atingiu concentrações abaixo de 50 mg/L. / The interest in using insect cells to produce complex proteins is due to its ease of cultivation and its glycosylation pattern equivalent to that of mammalian cells systems. The objective of this work was to identify the limiting or inhibiting factors for the production of a rabies virus glycoprotein (RVGP), expressed in the cytoplasmatic membrane of a transfected Drosophila melanogaster S2 cells, when cultivated in a bench stirred bubble-free bioreactor, in batch mode. The influence of dissolved oxygen (5 < pO2 < 80%), of initial glucose concentration (1 < GLC0 < 15 g/L) and of initial glutamine concentration (0.6 < GLN0 < 7 g/L) was evaluated. These variables affected in a different way cell growth (cell production and specific growth rate - µX), cell metabolism (yield factors - YX/GLC, YX/GLN, YLAC/GLC, YALA/GLC, YNH4/GLN and YALA/GLN), as well as the recombinant protein expression (RVGP concentration, RVGP cell content and RVGP productivity). pO2 increase reduced 9 times cell growth, but increased 1.4 times RVGP cell content. Low initial glucose and glutamine concentrations clearly limited the cell growth, in such a way that raising these substrates concentrations up to intermediate values, increased µX,MAX 3 times and 2.5 times, respectively, and increased cell production 11 times and 3 times, respectively. The maximum RVGP cell content was not affected by GLC0, but improved 100% when GLN0 was 3.5 g/L or higher. The concentrations of produced lactate were considered low (below 0.8 g/L) to cause any inhibition effect on growth or protein expression. On the other hand, ammonium concentrations seem to inhibit RVGP production (NH4+~50 mg/L), as well as cell growth (NH4+~80 mg/L). Maximum productivity values (9.1 µg/L.h) and RVGP concentration (1.2 mg/L) were attained for 30% pO2, 10 g/L of GLC0 and 3.5 g/L of GLN0 run. The metabolism of GLC and GLN showed a great interdependence, with GLC0 changes affecting the GLN metabolism, and viceversa. Thus, in glucose excess condition, cell metabolism was less efficient. This implied in reduction of yield factors - YX/GLC (2.3 times) e YX/GLN (4.6 times) - and in higher by-products generation, characterized by augmentation in YALA/GLC (51%), YLAC/GLC (11%) and YNH4/GLN (15%). The glutamine metabolism showed a substrate excess response pattern to the whole range of concentration studied, with reduction of YX/GLN (25 times) and, unexpectedly, a reduction of by-products liberation - YNH4/GLN (7 times) and YALA/GLN (12 times). The effect on glucose metabolism was more intense when the glutamine concentration was higher, showing a 3.6 times diminution YX/GLC and a 70% augmentation for YALA/GLC and YLAC/GLC. The results suggest that cells metabolize glutamine through two different pathways glutaminolysis, under glucose limitation, or glutamate synthase - NADH-GOGAT, under glucose excess. The cell, proved also to be able to synthesize glutamine from ammonium or other amino acids, when it reached concentrations below 50 mg/L.

L’utilisation de techniques de microscopie optique de plus en plus performantes a permis des avancées considérables en neurobiologie. Néanmoins, la population de neurones mise en jeu lors de la formation de la mémoire, ainsi que sa dynamique restent à ce jour très peu connues. L’objectif de la thèse est de développer puis d’utiliser deux types de microscopies originales couplées à des sondes fluorescentes de dernière génération (sondes calciques G-CaMP6f et sonde voltage ArcLight) pour l’étude in vivo des réseaux neuronaux impliqués dans la mémorisation chez la drosophile. Le choix du modèle Drosophila melanogaster pour cette étude neurobiologique est justifié par plusieurs atouts uniques : un cerveau peu volumineux, des capacités d’apprentissage remarquables, la possibilité d’analyser un réseau neuronal dans sa globalité avec une résolution cellulaire et la disponibilité d’outils génétiques très perfectionnés pour son étude. Le premier type de microscopie conçu est celui dite à illumination structurée de type HiLo permettant d'obtenir une coupe optique en profondeur. Nous avons alors étudié le rôle de divers récepteurs, tels que les récepteurs dopaminergiques et gabaergiques dans la transmission de l'information punitive jusqu'aux neurones des corps pédonculés. Nous avons également mis en évidence une non-homogénéité spatiale des neurones de type α/β des corps pédonculés en termes d’excitation et d’inhibition en réponse à une stimulation punitive pour une profondeur d’analyse d'environ 10 à 20 µm. Cette profondeur limite étant imposée par les aberrations, nous avons alors implémenté une boucle d’optique adaptative dans notre microscope. Cela a permis de réaliser des analyses morphologiques jusqu’à 50 µm de profondeur. Le second type de microscopie développé est la microscopie multiconfocale de type « spinning disk » dans le but d’imager l’ensemble des corps cellulaires des neurones des corps pédonculés. Le développement de ce projet n'est pas achevé, ce qui n’a pas encore permis de répondre à des questions biologiques d’intérêt. / Cellular and neural network dynamics involved in memory formation remain poorly known despite the progress brought by advanced optical microscopies to neurobiology. The use of Drosophila melanogaster as a model organism constitute one of the most promising approaches due to its unique features: a small brain size, outstanding learning capabilities, very powerful genetic tools and the possibility to analyze a whole neural network with a cellular resolution. To this aim, we implemented two types of optical fluorescence microscopes coupled to cutting-edge fluorescent biosensors, calcic G-CaMP6f and voltage ArcLight probes. We used HiLo structured illumination, a technique able to provide axial optical sectioning, deep in the brain, to study the role of dopaminergic and gabaergic molecular receptors in the transmission of aversive stimulus to mushroom bodies neurons. We also evidenced a non-uniform response of type α/β mushroom bodies neurons under electrical stimulation at 10 to 20 µm depth of analysis. To penetrate deeper in the brain, we added an adaptive optics feedback loop into our microscope in order to overcome aberrations issues. We were then able to rebuild optical sections down to 50 µm depth. The second type of microscopy we developed is a multiconfocal microscope using spinning disk. The aim was to image all the mushroom bodies neurons, at the level of their cell bodies, with a cellular resolution. Since this project is at its beginning, it did not allow us to answer to advanced biological questions yet.

The shape of a tissue or entire organ is important for its biological function. Tissue and organ shapes arise from molecular activities that control and execute cellular processes, such as oriented cell divisions, cell shape changes or cell rearrangements. However, how molecular activities control cellular processes during the shaping of organs is not well understood. This thesis spotlights two aspects of organ shaping based on Drosophila egg chambers as model tissue. One focus lies on three-dimensional imaging of cellular mechanics during development and the other aspect dissects the molecular function of the fat2 gene, that is crucial for tissue elongation in Drosophila egg chambers.:TABLE OF CONTENTS 1 SUMMARY ................................................................................................................... I 2 ZUSAMMENFASSUNG ...............................................................................................III 3 TABLE OF CONTENTS ................................................................................................V 4 LISTS ..........................................................................................................................10 5 INTRODUCTION ........................................................................................................16 6 AIMS OF THE THESIS ...............................................................................................40 7 MATERIALS AND METHODS .....................................................................................41 8 RESULTS ....................................................................................................................58 9 DISCUSSION .............................................................................................................92 10 ACKNOWLEDGEMENTS .......................................................................................103 11 REFERENCES ........................................................................................................105 12 APPENDIX ..............................................................................................................118 13 ERKLÄRUNG ..........................................................................................................123

Le but de ce travail a été de mieux comprendre les défenses mises en œuvre par l’hôte infecté par le champignon opportuniste humain Aspergillus fumigatus (Af). 1) Un modèle d’infection a été redéveloppé chez l’organisme modèle Drosophila melanogaster. Seules les mouches mutantes pour le gène MyD88 de la voie immunitaire Toll succombent à l’injection d’une poignée de conidies, sans toutefois qu’Af dissémine dans l’hôte. Ce travail a révélé que ce n’est pas la réponse immunitaire qui joue un rôle prépondérant dans la défense de l’hôte, mais sa capacité de résilience à l’exposition à des mycotoxines sécrétées par Af. 2) Un crible génétique d’envergure a été établi pour identifier des lignées transgéniques mutantes ARNi sensibles à l’infection par Af. 6.471 lignées ont été criblées et 241 gènes-candidats identifiés, dont peu fonctionnent dans la réponse immunitaire. Ainsi, ce travail a contribué à identifier de nombreux gènes impliqués dans la résilience de l’hôte à Af et ses mycotoxines. / The overarching goal of this work is to better understand host defenses against the human opportunistic fungus Aspergillus fumigatus (Af). 1) An infection model has been reestablished in the genetic model organism Drosophila melanogaster. Only flies mutant for the immune response Toll pathway gene MyD88 succumb to the injection of a handful of conidia even though Af is unable to disseminate throughout its host. This work revealed that it is not the immune response that plays a cardinal role in host defense but its resilience capacity to the exposure to some mycotoxins secreted by Af. 2) A large-scale genetic screen has been implemented to identify transgenic RNAi mutant lines susceptible to Af infection in survival experiments. 6,471 lines have been screened and 241 candidate genes identified, few of which are known to act in the immune response. Thus, this work has contributed to identifying numerous genes involved in host resilience to Af and to some of its mycotoxins.

Human Usher syndrome is a severe and congenital form of syndromic deafness that affects 1 person in 25,000 people in the world population. Normally the stereocilia, microvillar protrusions of the apical membrane of inner ear hair cells, are organized into coherent bundles. This precise organization is critical for mechanosensing, i.e. for hearing. Mutation in any of the five known Usher syndrome genes is sufficient to alter the precise organization of stereocilia, a condition that results in deafness. To date, however, the molecular mechanisms responsible for the splaying of stereocilia and genesis of the disease are not well understood. Here, I identified Drosophila melanogaster genes related to human Usher syndrome and characterized some of them (Cad99C, DSANS and crinkled) during Drosophila development, in the processes of microvilli morphogenesis in the follicular and wing imaginal disc epithelia. Cadherin Cad99C is a transmembrane protein with putative cell adhesion properties. Similar to its human ortholog Protocadherin 15, Drosophila Cad99C localizes to microvillar protrusions in the follicular epithelium. In this epithelium, Cad99C is required for the proper morphogenesis and organization of microvilli into bundles, similar to human Protocadherin 15. Further, overexpression of the full-length Cad99C or of a deleted version, devoid of the cytoplasmic region, promotes microvilli bundling. This finding suggests that Cad99C establishes adhesive interactions between microvilli via its extracellular region. Interestingly, morphological alteration of follicle cell microvilli associates with defective deposition of the vitelline membrane, an extracellular matrix that protects the embryo from osmotic stresses. These findings suggest that microvilli are normally required for the even deposition of the extracellular matrix. In order to test whether Cad99C is involved in microvilli morphogenesis and bundling in other tissues, I analyzed the function of Cad99C in a larval tissue, the wing imaginal disc. Cad99C overexpression, but not Cad99C removal, is sufficient to alter microvilli morphology and organization in the columnar epithelium of the wing imaginal disc. Likely, other molecules can compensate for Cad99C loss of function in this tissue. To possibly get some insights on the molecular function of other Usher syndrome proteins, I analyzed the function of Drosophila SANS and crinkled in the follicular epithelium, where both these genes are expressed. crinkled is the ortholog of myosinVIIa, that encodes a motor protein of the actin cytoskeleton. DSANS is related to human SANS and encodes a cytoplasmic protein of unknown function. It has been puzzling how removal of SANS, a cytoplasmic protein, could impair adhesion and bundling of stereocilia. To study the function of DSANS, I generated null mutant flies and observed that, in the absence of DSANS, delivery of Cad99C to microvilli is impaired. Cad99C localization is however unperturbed in crinkled mutant follicle cells. By immunostaining, DSANS immunoreactivity was detected diffusively in the cytoplasm and in dot-like structures, possibly corresponding to vesicles. In conclusion, DSANS is a cytoplasmic protein that is required for the efficient delivery of Cad99C to microvilli protrusions. Taken together, the analysis that I here performed of Drosophila Usher syndrome related genes indicates two novel molecular mechanisms of function for the corresponding human Usher syndrome proteins. First, human Protocadherin 15, like Drosophila Cad99C, could be involved in establishing adhesive interactions between microvilli protrusions of the inner ear (stereocilia). Removal of Protocadherin 15 would then cause splaying of stereocilia due to lack of inter-stereocilia adhesive links. Second, the analysis here performed suggests that SANS is involved in the efficient delivery of Protocadherin 15 to stereocilia. Mutations in SANS would then lead to splaying of stereocilia and deafness due to poor localization of Protocadherin 15 to stereocilia.