Candida albicans est un organisme commensal présent dans le microbiote, qui peut cependant provoquer des infections superficielles mais aussi systémiques, engageant alors le pronostic vital chez les patients immunodéprimés. La transition entre forme bourgeonnante et forme filamenteuse hyphale hautement polarisée, ce qui nécessite une réorganisation du cytosquelette et un trafic membranaire soutenu, est associée à la virulence. Chez les eucaryotes, les GTPases de la famille Rab (Ras related protein in the brain) et leurs régulateurs jouent un rôle central dans le trafic membranaire. L'objectif de ce travail est de comprendre le rôle de ces protéines, en particulier de Ypt6, l'homologue de Rab6 humain, dans la transition morphologique et la virulence de C. albicans. Dans ce but, j'ai construit des mutants « perte de fonction » et déterminé que YPT6 n'est pas essentiel à la viabilité, mais est critique pour l'intégrité de la paroi cellulaire et la croissance hyphale invasive ; les hyphes du mutant ypt6 sont plus courtes que celles de la souche sauvage. En outre, YPT6 est critique pour la virulence dans deux modèles murins de candidose. Lors de la croissance hyphale, Ypt6 est co-localisé avec Arl1, une GTPase de la famille Arf (ADP Ribosylation Factor), également nécessaire pour la croissance hyphale et la virulence de C. albicans. De plus, la surexpression de YPT6 compense spécifiquement le défaut de croissance hyphale du mutant de délétion arl1, mais pas l'inverse. La délétion de YPT6 résulte également en une augmentation du nombre de citernes Golgiennes, suggérant que l'intégrité du Golgi est altérée dans ce mutant. Utilisant de l'imagerie sur cellules vivantes, j'ai montré que la distribution d’Abp1 (Actin binding protein 1), qui est un rapporteur des sites d’endocytose, est aussi altérée dans le mutant ypt6, en ceci qu’elle n’est plus restreinte à l’apex de l’hyphe, comme observé dans les cellules sauvages. Ces données suggèrent que le défaut de maintien de la croissance hyphale du mutant ypt6 est au moins en partie associé à une altération de la distribution des sites d’endocytose. En résumé, j’ai identifié le rôle de Ypt6 dans la croissance hyphale invasive et la virulence du pathogène fongique opportuniste de l’homme C. albicans, et mis en évidence une interaction entre deux GTPases, Ypt6 et Arl1, lors du processus de croissance hyphale. / Candida albicans is a harmless constituent of the human microbiota that causes superficial infections as well as life threatening infections in immune compromised individuals. The transition from a budding form to the highly polarized hyphal form is associated with virulence and requires cytoskeleton reorganization and sustained membrane trafficking. In a range of eukaryotes, Ras related protein in the brain (Rab) G proteins and their regulators have been shown to play a central role in membrane traffic. The objective of this work is to understand the role of Rab proteins, in particular Ypt6, the homolog of Human Rab6, in the morphological transition and virulence of C. albicans. To this aim, I generated loss of function mutants and found that YPT6 is not essential for viability, yet was critical for cell wall integrity and invasive hyphal growth, with ypt6 hyphal filaments shorter compared to that of the wild type (WT). Furthermore, YPT6 was important for virulence in two murine candidiasis models. I determined that Ypt6 was localized at the late Golgi compartment during hyphal growth, where it co-localized with Arl1, a small GTPase of the Arf (ADP Ribosylation Factor) family, also required for hyphal growth and virulence. Interestingly, overexpression of YPT6 specifically rescued the hyphal growth defect of the arl1 mutant, but not the converse. Further characterization of the ypt6 deletion mutant showed that the number of Golgi cisternae is increased in this mutant compared to that of WT strain, suggesting an alteration of Golgi integrity. In addition, using live cell imaging I showed that the distribution of Actin binding protein 1 (Abp1), which is a reporter for actin patches, was altered in the ypt6 mutant, in that it was no longer restricted to the tip of the filament, as is observed in WT cells. These data suggest that the defect in hyphal growth maintenance of the ypt6 deletion mutant is at least partly associated with an alteration of the distribution of endocytic sites. Thus, I identified a critical role of Ypt6 during invasive hyphal growth and virulence in the human fungal opportunistic pathogen C. albicans and revealed an interaction between Ypt6 and Arl1 in the hyphal growth process.

Tube formation, or tubulogenesis, is an elaborate form of epithelial morphogenesis that includes processes such as cell migration and cell shape changes. The embryonic Drosophila heart, or dorsal vessel, is an excellent model of tubulogenesis and more specifically the signaling mechanisms required for cell migration and lumen formation. Similar to vertebrate heart formation, Drosophila heart tubulogenesis begins with the collective migration of cardioblasts that meet at the midline and adhere at specialised junctions, enclosing a lumen between them. Roundabout, and its ligand Slit, are required to restrict cell-to-cell adhesions to the junctional domains of contralateral cardioblasts, as well as maintain the integrity of the lumen. The localisation patterns of Robo, and other luminal cell surface receptors important for lumen formation are significantly modified throughout heart formation. Initial receptor expression is broadly distributed over the cardioblast surface. Receptors are then relocalised to specific cell surface domains by late embryonic development. The mechanisms by which Robo and other cell surface receptors are localised have yet to be determined. Endocytosis is a promising mechanism by which cell surface receptors are targeted and trafficked to cell surface domains. Specifically, vesicular trafficking proteins, such as Rab GTPases, are molecular switches that regulate endocytic events. Here, we investigated the roles of Rab5, Rab11, and Sec6 during heart formation. Of these, only Rab5, a regulator of the early endosome, was required for lumen formation. Particularly, gain of function, loss of function, and overexpression of rab5 resulted in reduced lumen phenotype, characterised by lumen pockets rather than a continuous lumen along the anterior-posterior axis. Perturbed Rab5 function also resulted in the mislocalisation of Robo at the basal domain. Live imaging showed that expression of rab5 dominant negative, constitutively active, and overexpression constructs did not perturb apical membrane motility of migrating cardioblasts in the developing heart. / Thesis / Master of Science (MSc)

Introdução: In vivo ou in vitro a exposição de fibroblastos a alta concentração de glicose promove um aumento do estresse oxidativo e consequentemente prejudica a migração celular, assim como a maturação da adesão. Além disso, a elevada concentração de glicose reduz a expressão de diferentes integrinas na superfície celular devido alterações na síntese do receptor e sua reciclagem. Objetivo: Avaliar os efeitos da elevada concentração de glicose no tráfego de vesículas contendo EEA1 (endossomos primários), Rab4 (via rápida da reciclagem), Rab11 (via lenta de reciclagem) e Rab7 (endossomos de degradação) em fibroblastos NIH3T3. Métodos: células foram cultivadas em meio contendo baixa concentração de glicose (LG, 5 mM) ou em alta concentração (HG 25 mM) durante 21 dias antes de realizar os experimentos. EEA1, Rab4, Rab11 e Rab7 expressão e distribuição foram avaliados por western blotting e imunofluorescência, respectivamente. Resultados: Células expostas à alta concentração não apresentaram diferenças na expressão e distribuição das proteínas EEA1 e Rab7, enquanto a expressão de Rab11 foi reduzida em 30%. Conclusão: a alta concentração de glicose altera a via lenta da reciclagem contendo Rab11, afetando potencialmente a reciclagem de integrinas e outros receptores e a sua expressão na superfície celular. / Background: In vivo or in vitro exposure of fibroblasts to high glucose concentrations (HG) promotes oxidative stress and consequently impairs cell migration, also inhibiting adhesion maturation. Additionally, HG reduces the expression of different integrins on the cell surface, potentially due to altered receptor synthesis and recycling. Aim: to evaluate the effects of HG on the trafficking vesicles containing EEA1 (early endosomes), Rab4 (fast recycling pathway) and Rab7 (endocytic degradation pathway) on NIH3T3 fibroblasts. Methods: cells were cultured under low glucose (LG, 5 mM) or HG (25 mM) concentrations during 21 days before the assays. EEA1, Rab4 and Rab7 expression and distribution were evaluated by western blotting and immunofluorescence, respectively. Results: HG did not affect proteins EEA1 and Rab7 expression and distribution, whereas Rab11 expression was reduced by 30%. The number of vesicles containing Rab11 was also significantly reduced in HG cells. Conclusion: high glucose alters the slow recycling endocytic pathway via Rab11, potentially affecting integrins and other receptors synthesis and expression on the cell surface.

Introdução: In vivo ou in vitro a exposição de fibroblastos a alta concentração de glicose promove um aumento do estresse oxidativo e consequentemente prejudica a migração celular, assim como a maturação da adesão. Além disso, a elevada concentração de glicose reduz a expressão de diferentes integrinas na superfície celular devido alterações na síntese do receptor e sua reciclagem. Objetivo: Avaliar os efeitos da elevada concentração de glicose no tráfego de vesículas contendo EEA1 (endossomos primários), Rab4 (via rápida da reciclagem), Rab11 (via lenta de reciclagem) e Rab7 (endossomos de degradação) em fibroblastos NIH3T3. Métodos: células foram cultivadas em meio contendo baixa concentração de glicose (LG, 5 mM) ou em alta concentração (HG 25 mM) durante 21 dias antes de realizar os experimentos. EEA1, Rab4, Rab11 e Rab7 expressão e distribuição foram avaliados por western blotting e imunofluorescência, respectivamente. Resultados: Células expostas à alta concentração não apresentaram diferenças na expressão e distribuição das proteínas EEA1 e Rab7, enquanto a expressão de Rab11 foi reduzida em 30%. Conclusão: a alta concentração de glicose altera a via lenta da reciclagem contendo Rab11, afetando potencialmente a reciclagem de integrinas e outros receptores e a sua expressão na superfície celular. / Background: In vivo or in vitro exposure of fibroblasts to high glucose concentrations (HG) promotes oxidative stress and consequently impairs cell migration, also inhibiting adhesion maturation. Additionally, HG reduces the expression of different integrins on the cell surface, potentially due to altered receptor synthesis and recycling. Aim: to evaluate the effects of HG on the trafficking vesicles containing EEA1 (early endosomes), Rab4 (fast recycling pathway) and Rab7 (endocytic degradation pathway) on NIH3T3 fibroblasts. Methods: cells were cultured under low glucose (LG, 5 mM) or HG (25 mM) concentrations during 21 days before the assays. EEA1, Rab4 and Rab7 expression and distribution were evaluated by western blotting and immunofluorescence, respectively. Results: HG did not affect proteins EEA1 and Rab7 expression and distribution, whereas Rab11 expression was reduced by 30%. The number of vesicles containing Rab11 was also significantly reduced in HG cells. Conclusion: high glucose alters the slow recycling endocytic pathway via Rab11, potentially affecting integrins and other receptors synthesis and expression on the cell surface.

Eukaryotic cells are populated by membrane-enclosed organelles possessing discrete molecular and biochemical properties. Communication between organelles is established by shuttling vesicles that transport proteins and other molecules. Vesicles bud from a donor organelle, travel in the cytosol, and are delivered to a target organelle. All these steps are regulated to ensure that cargoes are transported in a specific and directed manner. The focus of this thesis is on the last part of the journey of a vesicle: the process of vesicle targeting. Two phases can be distinguished in this process: vesicle tethering, defined as the first interaction between the shuttling vesicle and the target membrane, and membrane fusion, which is the mixing of the lipid bilayers and of lumen content. Both phases are mediated by a minimal set of molecular components that include one member of the family of Rab GTPases, a vesicle tethering factor, a phosphoinositide lipid, and four SNAREs together with their regulatory proteins. While many studies have investigated the molecular details of how SNAREs mediate membrane fusion, the process of vesicle tethering is less well understood. The overall scope of my study is to describe the molecular details of vesicle tethering and how they can contribute to the general process of vesicle targeting. To address this question I developed an in vitro assay where I reconstitute in vitro the process of vesicle tethering. This bottom-up approach allows the molecular dissection of cellular processes outside of the complex context of the cell. With this assay I have characterized the vesicle tethering abilities of individual proteins involved in vesicle tethering on early endosomes. I show that a minimal vesicle tethering machinery can be formed by the concomitant interaction between one vesicle tethering factor and a phosphoinositide on the membrane of one vesicle, and by a vesicle tethering factor and a Rab GTPase on the membrane of another vesicle. These results provide an explanation for how vesicle tethering contributes to the specificity of vesicle targeting and to the directionality of cargo transport. In particular, specificity of vesicle targeting can arise from the specific interaction between a Rab and a vesicle tethering factor that is an effector of the Rab. I show that the asymmetric distribution of binding sites in the structure of a vesicle tethering factor can generate a heterotypic vesicle tethering reaction that can account for the directionality of cargo transport. The outcome of this thesis emphasizes the role that vesicle tethering factors have in the self-organized system of vesicle trafficking of eukaryotic cells. To identify novel Rab5 effectors implicated in vesicle tethering, I carried out a Rab5-chromatography on mouse liver. Amongst other novel Rab5 effectors, I identify a multi-subunit vesicle tethering complex that was not previously characterized in mammalian cells. The complex, named CORVET, is conserved from yeast to humans and plays a major role in cell physiology since its removal causes embryonic death in mice. I define its subunits composition, determine its subcellular localization, and elucidate its role in cargo transport. This finding reconciles a disharmony between findings in mammals and yeast regarding the molecular machinery responsible for the conversion from early to late endosomes. I also show that the newly identified subunit of the mammalian CORVET complex is the only Rab5 effector to localize to autophagosomes. I hypothesise that it is through the CORVET complex that Rab5 is involved in the formation and maturation of autophagosomes.

The Rab family of small GTPases orchestrates intracellular endomembrane transport through the recruitment of diverse effector proteins. Since its first discovery in 1987, almost 70 Rab proteins have been identified in humans to date and their perturbed function is implicated in several hereditary and acquired diseases. In this Ph.D. thesis, I systematically characterize cell type expression and subcellular localization of all Rab proteins present in Drosophila melanogaster utilizing a genetic resource that represents a major advance for studying membrane trafficking in vivo: the ’Drosophila YRab library’. This collection comprises 27 different D. melanogaster knock-in lines that harbor YFPMyc fusions to each Rab protein, referred to as YRab. For each YRab, I present a comprehensive data set of quantitative and qualitative expression profiles across six larval and adult tissues that include 23 annotated cell types. The whole image data set, along with its annotations, is publicly accessible through the FLYtRAB database that links to CATMAID for online browsing of tissues. I exploit this data set to address basic cell biological questions. i) How do differentiating cells reorganize their transport machinery to perform cell type-specific functions? My data indicates that qualitative and quantitative changes in YRab protein expression facilitate the functional specialization of differentiated cells. I show that about half of the YRab complement is ubiquitously expressed across D. melanogaster tissues, while others are missing from some cell types or reflect strongly restricted cell type expression, e.g. in the nervous system. I also depict that relative YRab expression levels change as cells differentiate. ii) Are specific Rab proteins dedicated to apical or basolateral protein transport in all epithelia? My data suggests that the endomembrane architecture reflects specific tasks performed by particular epithelial tissues, rather than a generalized apicobasal organization. I demonstrate that there is no single YRab that is similarly polarized in all epithelia. Rather, different epithelial tissues dynamically polarize the subcellular localization of many YRab compartments, producing membrane trafficking architectures that are tissue- and stage-specific. I further discuss YRab cell type expression and subcellular localization in the context of Rab family evolution. I report that the conservation of YRab protein expression across D. melanogaster cell types reflects their evolutionary conservation in eukaryotes. In addition, my data supports the assumption that the flexible deployment of an expanded Rab family triggered cell differentiation in metazoans. The FLYtRAB database and the ’Drosophila Rab Library’ are complementary resources that facilitate functional predictions based on YRab cell type expression and subcellular localization, and to subsequently test them by genetic loss-of-function experiments. I demonstrate the power of this approach by revealing new and redundant functions for Rab23 and Rab35 in wing vein patterning. My data collectively highlight that in vivo studies of endomembrane transport pathways in different D. melanogaster cell types is a valuable approach to elucidate functions of Rab family proteins and their potential implications for human disease.

Les RAB GTPases sont des régulateurs majeurs du trafic vésiculaire et sont localisées sur des compartiments spécifiques. L'identification des processus moléculaires régulant la localisation des RAB est donc cruciale afin de comprendre les mécanismes de transport intracellulaire. Nous sommes parvenus, pour la première fois, à incorporer des protéines RAB purifiées et prénylées dans des membranes artificielles. Nous avons tout d'abord observé que RAB6 est capable de promouvoir une agrégation de vésicules, phénomène qui n'est pas observé avec RAB1 et RAB5. Nous suggérons un modèle dans lequel RAB6 interagit en trans avec lui-même et par conséquent induit un accolement de membranes. La partie principale de cette étude consistait à identifier les propriétés physicochimiques des membranes requises pour le recrutement des protéines RAB. Nous avons observé que RAB1, RAB5 et RAB6 se lient préférentiellement à des membranes désordonnées et courbées, phénomène qui s'explique par l'insertion du groupement prenyl hydrophobe au niveau de défauts d'agencement de lipides. En revanche, le recrutement de RAB35 requiert la présence de lipides chargés négativement et peut être modulé, dans une moindre mesure, par les défauts d'agencement lipidique. Bien que RAB4 et RAB11 soient recrutées sur des fractions de Golgi purifiées, les charges membranaires et les défauts d'agencement lipidique ne sont pas suffisants pour permettre leur recrutement sur des vésicules synthétiques. Cela suggère que le recrutement de RAB4 et RAB11 nécessite des propriétés membranaires plus complexes. Nos travaux démontrent que les propriétés membranaires sont cruciales pour la localisation spécifique des protéines RAB. / RAB GTPases are major regulators of vesicular trafficking and localize to specific compartments. Deciphering the molecular mechanisms governing RAB localization is thus critical to understand intracellular transport processes. We have managed, for the first time, to incorporate purified and prenylated RABs into artificial membranes. By doing so, we observed that RAB6, but not RAB1 or RAB5, is able to promote by itself vesicle tethering. We believe that RAB6 is able to interact in trans with itself and to consequently drive homotypic membrane tethering. In the main part of this study, we investigated the physicochemical membrane requirements necessary for RAB recruitment. RAB1, RAB5 and RAB6 were all found to only localize to disordered membrane domains and to preferentially bind to curved membranes. We demonstrated that this specific recruitment of RAB1, RAB5 and RAB6 is primarily dependent on the hydrophobic insertion of their prenyl group into lipid packing defects. In contrast, RAB35 recruitment was primarily dependent on the presence of negatively charged lipids and was found to be modulated, to a lesser extent, by lipid packing defects. Although RAB4 and RAB11 were effectively recruited to purified Golgi fractions, in an effector-independent manner, membrane charges and lipid packing defects were not sufficient to promote their recruitment to synthetic vesicles; suggesting that RAB4 and RAB11 require more demanding membrane physicochemical properties. Our work demonstrates that the properties of membranes are critical for the regulation of RAB specific membrane targeting.

Lysosomes are acidic, hydrolase-rich vesicles capable of degrading most biological macromolecules. During the past several decades, much has been learned about different aspects of lysosome biogenesis. The selective phosphorylation of mannose residues on lysosomal enzymes, in conjunction with specific receptors for the mannose-6-phosphate recognition marker, has been found to be largely responsible for the targeting of newly synthesized lysosomal enzymes to lyzosomes. It is known that lysosomes receive input from both the endocytotic and biosynthetic pathways. Nevertheless the exact molecular mechanisms responsible for sorting of the biosynthetic imput involved in the lysosome biogenesis is still a matter of debate. Because osteoclast precursors do not secrete their lysosomal enzymes and osteoclasts do, the observation of modifications occuring during osteoclastogenesis is a good model to observe mechanisms responsible for lysosomal enzymes traffic. Osteoclasts are bone-degrading cells. To perform this specific task they have to reorganise the sorting of their lysosomal enzymes to be able to target them toward the bone surface in mature cells. Since few years, the differentiation of osteoclasts in vitro did help to study these cells. Osteoclast morphology has been therefore already well studied, and the nature of their specific membrane domains is now established. Sensing the proximity of a bone-like surface the cell reorganises its cytoskeleton, and creates specific membrane domains: an actin-rich ring-like zone (named actin ring) surrounded by highly ruffled membrane (named the ruffled border) where enzymes are secreted, while subsequent bone degradation products are endocytosed. Endocytosed material is then transported through the cell inside transcytotic vesicles and released at the top of the cell in an area named the functional secretory domain. Several molecular machineries are thought to control these different phenomena. The main purpose of this thesis was to identify the major regulators of lysosomal enzymes secretion and therefore to identify the molecular switches responsible for such a membrane traffic re-organisation.

Lysosomes are acidic, hydrolase-rich vesicles capable of degrading most biological macromolecules. During the past several decades, much has been learned about different aspects of lysosome biogenesis. The selective phosphorylation of mannose residues on lysosomal enzymes, in conjunction with specific receptors for the mannose-6-phosphate recognition marker, has been found to be largely responsible for the targeting of newly synthesized lysosomal enzymes to lyzosomes. It is known that lysosomes receive input from both the endocytotic and biosynthetic pathways. Nevertheless the exact molecular mechanisms responsible for sorting of the biosynthetic imput involved in the lysosome biogenesis is still a matter of debate. Because osteoclast precursors do not secrete their lysosomal enzymes and osteoclasts do, the observation of modifications occuring during osteoclastogenesis is a good model to observe mechanisms responsible for lysosomal enzymes traffic. Osteoclasts are bone-degrading cells. To perform this specific task they have to reorganise the sorting of their lysosomal enzymes to be able to target them toward the bone surface in mature cells. Since few years, the differentiation of osteoclasts in vitro did help to study these cells. Osteoclast morphology has been therefore already well studied, and the nature of their specific membrane domains is now established. Sensing the proximity of a bone-like surface the cell reorganises its cytoskeleton, and creates specific membrane domains: an actin-rich ring-like zone (named actin ring) surrounded by highly ruffled membrane (named the ruffled border) where enzymes are secreted, while subsequent bone degradation products are endocytosed. Endocytosed material is then transported through the cell inside transcytotic vesicles and released at the top of the cell in an area named the functional secretory domain. Several molecular machineries are thought to control these different phenomena. The main purpose of this thesis was to identify the major regulators of lysosomal enzymes secretion and therefore to identify the molecular switches responsible for such a membrane traffic re-organisation.

Résumé : Calnuc est une protéine ubiquitaire qui lie le calcium et qui est présente au réseau trans-golgien (TGN) ainsi qu'aux endosomes. Notre groupe a précédemment mis en évidence le rôle de Calnuc dans le transport de Low density lipoprotein receptor-related protein 9 (LRP9), un récepteur aux lipoprotéines de faible densité qui cycle entre le TGN et les endosomes. Les récepteurs lysosomiaux au mannose-6-phosphate (MPR) et Sortiline sont bien caractérisés et empruntent également cette voie. À l'image de LRP9, nous avons montré que Calnuc prévient leur dégradation aux lysosomes en participant à leur recyclage à partir des endosomes vers le TGN. En fait, Calnuc est importante pour l'activation et l'association membranaire de Rab7, une petite protéine G qui recrute ensuite le complexe Rétromère responsable du transport rétrograde des récepteurs. La glycoprotéine lysosomiale Ceroid lipofuscinosis neuronal 5 (CLN5) est également impliquée dans ce processus. La structure et la fonction de cette dernière n'étant pas clairement définies, nous avons établi qu'elle est synthétisée sous forme d’une glycoprotéine transmembranaire de type II, mais son domaine N-terminal cytoplasmique et son segment transmembranaire sont rapidement éliminés suivant le clivage du peptide signal de manière à former une protéine CLN5 mature fortement associée à la membrane par une hélice amphipathique (AH). La compréhension des propriétés de base de CLN5 est particulièrement pertinente puisque la protéine est impliquée dans certaines variantes de céroïdes-lipofuscinoses neuronales (NCL), une maladie neurodégénérative rare causée par une surcharge des lysosomes. D'ailleurs, nos données indiquent que les mutants pathologiques de CLN5 dépourvus de cette AH perdent leur association membranaire, sont retenus au réticulum endoplasmique et sont rapidement dégradés. En raison de la similitude des fonctions de Calnuc et de CLN5 au niveau du triage endosomial, nous avons exploré le lien entre les deux protéines. Calnuc cytosolique et CLN5 luminale semblent former un complexe, par l'intermédiaire de la protéine transmembranaire CLN3, de façon à influencer l'activité de Rab7. CLN3 étant aussi associée aux NCL, nous avons finalement exploré la potentielle implication de Calnuc dans la maladie. L'absence de Calnuc entraîne des phénotypes cellulaires typiques des NCL comme un engorgement des lysosomes, une accumulation de matériel autofluorescent et une augmentation de l'autophagie. Les niveaux protéiques de Calnuc sont diminués dans toutes les lignées de fibroblastes de patients atteints de NCL disponibles ce qui indique que Calnuc pourrait être impliquée dans certains types de NCL. La présente thèse couvre donc la découverte de la fonction de Calnuc dans le transport intracellulaire, jusqu'à son implication potentielle dans les NCL, de même qu'une étude topologique de CLN5. / Abstract : Calnuc is a ubiquitous Ca2+-binding protein present on the trans-Golgi network (TGN) and endosomes. We previously highlighted the role of Calnuc in the transport of Low density lipoprotein receptor-related protein 9 (LRP9), a low density lipoprotein (LDL) receptor that cycles between the TGN and endosomes. Lysosomal receptors mannose-6-phosphate receptor (MPR) and Sortilin are well-characterized and also use the TGN-to-endosome trafficking pathway. Similarly to LPR9, we showed that Calnuc prevent their degradation in lysosomes by acting in their recycling from endosomes to the TGN. In fact, Calnuc is a important for the activation and the membrane association of Rab7, a small G protein which then recruit the Retromer complex known to be responsible for the retrograde transport of receptors. Lysosomal glycoprotein Ceroid lipofuscinosis neuronal 5 (CLN5) is also involved in this process. Because its structure and function have not yet been clearly defined, we established that it is synthesized as a type II transmembrane (TM) glycoprotein, but its cytoplasmic N-terminus and TM segment are rapidly removed following signal-peptide cleavage to generate mature CLN5 which is tightly associated to membrane through an amphipathic helix (AH). The understanding of the basic properties of CLN5 is particularly important given that CLN5 is involved in some variants of neuronal ceroid lipofuscinosis (NCL), a rare neurodegenerative disease caused by lysosomal overload. Moreover, our data indicate that CLN5 pathological mutants deprived of AH lose their membrane association, are retained in the endoplasmic reticulum, and are rapidly degraded. Based on the similarity featured by Calnuc and CLN5 in endosomal sorting, we explored the link between these two proteins. Cytosolic Calnuc and luminal CLN5 seem to form a complex, through the transmembrane protein CLN3, in order to influence the activity of Rab7. As CLN3 is also associated with NCL, we finally explored the potential involvement of Calnuc in this disease. Canuc depletion leads to typical NCL phenotypes such as lysosome enlargement, accumulation of autofluorescent material and of an increased of autophagy induction. Canuc's levels are decreased in all fibroblasts cell lines of NCL patients available indicating that Calnuc could be involved in some types of NCL. This thesis thus covers the discovery of the function of Calnuc in intracellular transport up to its potential involvement in the NCL, as well as a topological study CLN5.