3-D Vision and Figure-Ground Separation by Visual Cortex

A neural network theory of :3-D vision, called FACADE Theory, is described. The theory proposes a solution of the classical figure-ground problem for biological vision. It does so by suggesting how boundary representations and surface representations are formed within a Boundary Contour System (BCS) and a Feature Contour System (FCS). The BCS and FCS interact reciprocally to form 3-D boundary and surface representations that arc mutually consistent. Their interactions generate 3-D percepts wherein occluding and occluded object completed, and grouped. The theory clarifies how preattentive processes of 3-D perception and figure-ground separation interact reciprocally with attentive processes of spatial localization, object recognition, and visual search. A new theory of stereopsis is proposed that predicts how cells sensitive to multiple spatial frequencies, disparities, and orientations are combined by context-sensitive filtering, competition, and cooperation to form coherent BCS boundary segmentations. Several factors contribute to figure-ground pop-out, including: boundary contrast between spatially contiguous boundaries, whether due to scenic differences in luminance, color, spatial frequency, or disparity; partially ordered interactions from larger spatial scales and disparities to smaller scales and disparities; and surface filling-in restricted to regions surrounded by a connected boundary. Phenomena such as 3-D pop-out from a 2-D picture, DaVinci stereopsis, a 3-D neon color spreading, completion of partially occluded objects, and figure-ground reversals are analysed. The BCS and FCS sub-systems model aspects of how the two parvocellular cortical processing streams that join the Lateral Geniculate Nucleus to prestriate cortical area V4 interact to generate a multiplexed representation of Form-And-Color-And-Depth, or FACADE, within area V4. Area V4 is suggested to support figure-ground separation and to interact. with cortical mechanisms of spatial attention, attentive objcect learning, and visual search. Adaptive Resonance Theory (ART) mechanisms model aspects of how prestriate visual cortex interacts reciprocally with a visual object recognition system in inferotemporal cortex (IT) for purposes of attentive object learning and categorization. Object attention mechanisms of the What cortical processing stream through IT cortex are distinguished from spatial attention mechanisms of the Where cortical processing stream through parietal cortex. Parvocellular BCS and FCS signals interact with the model What stream. Parvocellular FCS and magnocellular Motion BCS signals interact with the model Where stream. Reciprocal interactions between these visual, What, and Where mechanisms arc used to discuss data about visual search and saccadic eye movements, including fast search of conjunctive targets, search of 3-D surfaces, selective search of like-colored targets, attentive tracking of multi-element groupings, and recursive search of simultaneously presented targets.

Individuals with mutations in XPNPEP3, which encodes a mitochondrial protein, develop a nephronophthisis-like nephropathy.

The autosomal recessive kidney disease nephronophthisis (NPHP) constitutes the most frequent genetic cause of terminal renal failure in the first 3 decades of life. Ten causative genes (NPHP1-NPHP9 and NPHP11), whose products localize to the primary cilia-centrosome complex, support the unifying concept that cystic kidney diseases are "ciliopathies". Using genome-wide homozygosity mapping, we report here what we believe to be a new locus (NPHP-like 1 [NPHPL1]) for an NPHP-like nephropathy. In 2 families with an NPHP-like phenotype, we detected homozygous frameshift and splice-site mutations, respectively, in the X-prolyl aminopeptidase 3 (XPNPEP3) gene. In contrast to all known NPHP proteins, XPNPEP3 localizes to mitochondria of renal cells. However, in vivo analyses also revealed a likely cilia-related function; suppression of zebrafish xpnpep3 phenocopied the developmental phenotypes of ciliopathy morphants, and this effect was rescued by human XPNPEP3 that was devoid of a mitochondrial localization signal. Consistent with a role for XPNPEP3 in ciliary function, several ciliary cystogenic proteins were found to be XPNPEP3 substrates, for which resistance to N-terminal proline cleavage resulted in attenuated protein function in vivo in zebrafish. Our data highlight an emerging link between mitochondria and ciliary dysfunction, and suggest that further understanding the enzymatic activity and substrates of XPNPEP3 will illuminate novel cystogenic pathways.

Improved delineation of short cortical association fibers and gray/white matter boundary using whole-brain three-dimensional diffusion tensor imaging at submillimeter spatial resolution.

Recent emergence of human connectome imaging has led to a high demand on angular and spatial resolutions for diffusion magnetic resonance imaging (MRI). While there have been significant growths in high angular resolution diffusion imaging, the improvement in spatial resolution is still limited due to a number of technical challenges, such as the low signal-to-noise ratio and high motion artifacts. As a result, the benefit of a high spatial resolution in the whole-brain connectome imaging has not been fully evaluated in vivo. In this brief report, the impact of spatial resolution was assessed in a newly acquired whole-brain three-dimensional diffusion tensor imaging data set with an isotropic spatial resolution of 0.85 mm. It was found that the delineation of short cortical association fibers is drastically improved as well as the definition of fiber pathway endings into the gray/white matter boundary-both of which will help construct a more accurate structural map of the human brain connectome.

Tennyson and youth

This paper will examine the prominence of Alfred Tennyson's work in several textual accounts of youth penned between 1892 and the present day, by writers including T. S. Eliot, Virgina Woolf, Joseph Conrad, James Joyce, Kingsley Amis, J. M. Coetzee, William Faulkner and Andrew Motion. The young Woolf broke in her new pens by copying out Tennyson's 'Tithonus'; Eliot had a taste for Tennyson's 'martial and sanguinary poetry; as a young man. Kingsley Amis was singular among his contemporaries precisely because he admired the work of a poet considered outdated, and a reference for Modernist verse over that of Tennyson is seen as a sign of sophistication (however ironically presented) in the writings of people as diverse as Auden, Motion and Coetzee. [From the Author]

Isolation of retinal progenitor and stem cells from the porcine eye

Purpose: Retinal progenitor cells (RPCs) and retinal stem cells (RSCs) from rodents and humans have been isolated and characterized in vitro. Transplantation experiments have confirmed their potential as tools for cell replacement in retinal degenerative diseases. The pig represents an ideal pre-clinical animal model to study the impact of transplantation because of the similarity of its eye to the human eye. However, little is known about porcine RPCs and RSCs. We aimed to identify and characterize in vitro RPCs and RSCs from porcine ocular tissues. Methods: Cells from different subregions of embryonic, postnatal and adult porcine eyes were grown in suspension sphere culture in serum-free medium containing basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF). Growth curves and BrdU incorporation assays were performed to establish the proliferative capacity of isolated porcine retina-derived RPCs and ciliary epithelium (CE)-derived RSCs. Self-renewal potential was investigated by subsphere formation assays. Changes in gene expression were assayed by reverse transcription polymerase chain reaction (RT-PCR) at different passages in culture. Finally, differentiation was induced by addition of serum to the cultures and expression of markers for retinal cell types was detected by immunohistochemical staining with specific antibodies. Results: Dissociated cells from embryonic retina and CE at different postnatal ages generated primary nestin- and Pax6-immunoreactive neurosphere colonies in vitro in numbers that decreased with age. Embryonic and postnatal retina-derived RPCs and young CE-derived RSCs displayed self-renewal capacity, generating secondary neurosphere colonies. However, their self-renewal and proliferation capacity gradually decreased and they became more committed to differentiated states with subsequent passages. The expansion capacity of RPCs and RSCs was higher when they were maintained in monolayer culture. Porcine RPCs and RSCs could be induced to differentiate in vitro to express markers of retinal neurons and glia. Conclusions: Porcine retina and CE contain RPCs and RSCs which are undifferentiated, self-renewing and multipotent and which show characteristics similar to their human counterparts. Therefore, the pig could be a useful source of cells to further investigate the cell biology of RPCs and RSCs and it could be used as a non-primate large animal model for pre-clinical studies on stem cell-based approaches to regenerative medicine in the retina.

The role of a kinesin, KLP-20, on neural development and epidermal morphogenesis in Caenorhabditis elegans

The heterotrimeric kinesin-II motor in Caenorhabditis elegans consists of KLP-20, KLP-11, and KAP-1 subunits and broadly functions in cellular transport for the development of biological structures including cilia and axons. The results of this paper support the ubiquitous and necessary role kinesin-II motors have in development, particularly the KLP-20 microtubule-associating subunit. Mutations in klp-20 result in a variable abnormal (vab) phenotype characterized by observable epidermal defects, although the role of this gene in development and the mechanism by which the vab phenotype is produced is largely unknown. The vab phenotype is highly penetrant in the first larval stage (L1) of C. elegans, which supports that klp-20 functions in early development. Ciliated amphid sensory neurons can be stained with a fluorescent dye, DiI, to simultaneously test cilia structure and function, as well as the morphology of the amphid sensory organ. Reduced dye uptake in klp-20 mutant L1s suggests that the microtubule-based cilia are under-developed as a result of defective kinesin-II function. Consistent observations of the PLM mechanosensory neuron using the zdIs5 reporter suggest that klp-20 has an essential role in neuron development, as mutations to klp-20 result in under-developed PLM axons. Qualitative observations suggest there may be an interaction between the development of the overlying epidermis and the underlying nervous system, as a more severe vab phenotype is observed simultaneously with reduced dye uptake, and hence amphid sensory cilia under-development. Furthermore, a more severe vab phenotype manifested as large bumps on the posterior epidermis appears to be spatially correlated with PLM defects. The results presented and discussed in this paper suggest that KLP-20 has a necessary role in neurodevelopment and epidermal morphogenesis in C. elegans during embryogenesis.

Effect of osteoporosis on bone mineral density and fracture repair in a rat femoral fracture model

Osteoporosis (OP) is one of the most prevalent bone diseases worldwide with bone fracture the major clinical consequence. The effect of OP on fracture repair is disputed and although it might be expected for fracture repair to be delayed in osteoporotic individuals, a definitive answer to this question still eludes us. The aim of this study was to clarify the effect of osteoporosis in a rodent fracture model. OP was induced in 3-month-old rats (n = 53) by ovariectomy (OVX) followed by an externally fixated, mid-diaphyseal femoral osteotomy at 6 months (OVX group). A further 40 animals underwent a fracture at 6 months (control group). Animals were sacrificed at 1, 2, 4, 6, and 8 weeks postfracture with outcome measures of histology, biomechanical strength testing, pQCT, relative BMD, and motion detection. OVX animals had significantly lower BMD, slower fracture repair (histologically), reduced stiffness in the fractured femora (8 weeks) and strength in the contralateral femora (6 and 8 weeks), increased body weight, and decreased motion. This study has demonstrated that OVX is associated with decrease in BMD (particularly in trabecular bone) and a reduction in the mechanical properties of intact bone and healing fractures. The histological, biomechanical, and radiological measures of union suggest that OVX delayed fracture healing. (C) 2007 Orthopaedic Research Society. Published by Wiley Periodicals.

1-D constitutive model for evolution of stress-induced R-phase and localized Lüders-like stress-induced martensitic transformation of super-elastic NiTi wires

NiTi alloys have been widely used in the applications for micro-electro-mechanical-systems (MEMS), which often involve some precise and complex motion control. However, when using the NiTi alloys in MEMS application, the main problem to be considered is the degradation of functional property during cycling loading. This also stresses the importance of accurate prediction of the functional behavior of NiTi alloys. In the last two decades, a large number of constitutive models have been proposed to achieve the task. A portion of them focused on the deformation behavior of NiTi alloys under cyclic loading, which is a practical and non-negligible situation. Despite of the scale of modeling studies of the field in NiTi alloys, two experimental observations under uniaxial tension loading have not received proper attentions. First, a deviation from linearity well before the stress-induced martensitic transformation (SIMT) has not been modeled. Recent experiments confirmed that it is caused by the formation of stress-induced R phase. Second, the influence of the well-known localized Lüders-like SIMT on the macroscopic behavior of NiTi alloys, in particular the residual strain during cyclic loading, has not been addressed. In response, we develop a 1-D phenomenological constitutive model for NiTi alloys with two novel features: the formation of stress-induced R phase and the explicit modeling of the localized Lüders-like SIMT. The derived constitutive relations are simple and at the same time sufficient to describe the behavior of NiTi alloys. The accumulation of residual strain caused by R phase under different loading schemes is accurately described by the proposed model. Also, the residual strain caused by irreversible SIMT at different maximum loading strain under cyclic tension loading in individual samples can be explained by and fitted into a single equation in the proposed model. These results show that the proposed model successfully captures the behavior of R phase and the essence of localized SIMT.

Motion Management for Radical Radiotherapy in Non-small Cell Lung Cancer

Intrafraction tumour motion is an issue that is of increased interest in the era of image-guided radiotherapy. It is particularly relevant for non-small cell lung cancer, for which a number of recent developments are in use to aid with motion management in the delivery of radical radiotherapy. The ability to deliver hypofractionated ablative doses, such as in stereotactic radiotherapy, has been aided by improvements in the ability to analyse tumour motion and amend treatment delivery. In addition, accounting for tumour motion can enable dose escalation to occur by reducing the normal tissue being irradiated by virtue of a reduction in target volumes. Motion management for lung tumours incorporates five key components: imaging, breath-hold techniques, abdominal compression, respiratory tracking and respiratory gating. These will be described, together with the relevant benefits and associated complexities. Many studies have described improved dosimetric coverage and reduced normal tissue complication probability rates when using motion management techniques. Despite the widespread uptake of many of these techniques, there is a paucity of literature reporting improved outcome in overall survival and local control for patients whenever motion management techniques are used. This overview will review the extent of lung tumour motion, ways in which motion is detected and summarise the key methods used in motion management.

Laughter Type Recognition from Whole Body Motion

Despite the importance of laughter in social interactions it remains little studied in affective computing. Respiratory, auditory, and facial laughter signals have been investigated but laughter-related body movements have received almost no attention. The aim of this study is twofold: first an investigation into observers' perception of laughter states (hilarious, social, awkward, fake, and non-laughter) based on body movements alone, through their categorization of avatars animated with natural and acted motion capture data. Significant differences in torso and limb movements were found between animations perceived as containing laughter and those perceived as nonlaughter. Hilarious laughter also differed from social laughter in the amount of bending of the spine, the amount of shoulder rotation and the amount of hand movement. The body movement features indicative of laughter differed between sitting and standing avatar postures. Based on the positive findings in this perceptual study, the second aim is to investigate the possibility of automatically predicting the distributions of observer's ratings for the laughter states. The findings show that the automated laughter recognition rates approach human rating levels, with the Random Forest method yielding the best performance.

Evolution and biogenesis of microtubule-derived structures

Dissertação apresentada para obtenção do grau de Doutor em Biologia Celular pelo Instituto de Tecnologia Química e Biológica da Universidade Nova de Lisboa

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Primary ciliary dyskinesia (PCD) is an autosomal recessive disease with an incidence estimated between 1:2,000 and 1:40,000. Ciliated epithelia line the airways, nasal and sinus cavities, Eustachian tube and fallopian tubes. Congenital abnormalities of ciliary structure and function impair mucociliary clearance. As a consequence, patients present with chronic sinopulmonary infections, recurrent glue ear and female subfertility. Similarities in the ultrastructure of respiratory cilia, nodal cilia and sperm result in patients with PCD also presenting with male infertility, abnormalities of left-right asymmetry (most commonly situs inversus totalis) and congenital heart disease. Early diagnosis is essential to ensure specialist management of the respiratory and otological complications of PCD. Diagnostic tests focus on analysis of ciliary function and electron microscopy structure. Analysis is technically difficult and labour intensive. It requires expertise for interpretation, restricting diagnosis to specialist centres. Management is currently based on the consensus of experts, and there is a pressing need for randomised clinical trials to inform treatment.

Analyse fonctionnelle de la polycystine-1 et de son domaine intracellulaire dans le développement de la polykystose rénale autosomique dominante

La polykystose rénale autosomique dominante (PKRAD) est la maladie génétique rénale la plus commune touchant 1/500 personnes. Elle se caractérise principalement par la formation de kystes rénaux dans tous les segments du néphron, entraînant l’insuffisance rénale, et par des manifestations extrarénales kystiques (foie, pancréas, rate) et non-kystiques (anomalies cardiaques, vasculaires et cérébrales). Deux gènes, PKD1 et PKD2, sont responsables de 85 et 15% des cas respectivement. Ces gènes encodent les polycystine-1 (PC-1) et -2 (PC-2) qui forment un complexe à la membrane plasmique et ciliaire des cellules épithéliales rénales. PC-1 est une protéine transmembranaire de 4302 acides aminés possédant un court domaine intracellulaire incluant un motif coiled-coil impliqué dans l’interaction entre PC-1 et PC-2 in-vitro. L’importance du coiled-coil est démontrée par des mutations affectant spécifiquement ce motif chez des patients PKRAD. Le mécanisme pathogénétique responsable de la PKRAD est indéterminé. Chez la souris, la PKRAD se développe suite à l’ablation (Pkd1-/-) ou lors de la surexpression (SBPkd1TAG) de Pkd1, ce qui suggère un effet de dosage. Des anomalies ciliaires sont aussi souvent associées à PKRAD. Mon objectif était de déterminer in-vivo le mécanisme pathogénétique de la polycystine-1 dans le développement des symptômes PKRAD rénaux et extrarénaux et plus spécifiquement, le rôle du motif coiled-coil dans le mécanisme de kystogenèse. Pour ce faire, nous avons généré deux constructions, Pkd1 sauvage (Pkd1TAG) et Pkd1 tronquée de son motif coiled-coil (Pkd1ΔCoiled-coil), par recombinaison homologue à partir du BAC-Pkd1 sauvage comprenant la séquence murine entière de Pkd1. Trois lignées de souris Pkd1TAG générées par microinjection démontrent un niveau d’expression de Pkd1 qui corrèle avec le nombre de copie du transgène (2, 5 et 15 copies). Les souris Pkd1TAG reproduisent la PKRAD en développant des kystes rénaux dans toutes les parties du néphron et des cils primaires plus longs que les contrôles non transgéniques. Les analyses physiologiques supportent que les souris Pkd1TAG développent une insuffisance rénale et démontrent une augmentation du volume urinaire de même qu’une diminution de l’osmolalité, de la créatinine et des protéines urinaires. De plus, les souris Pkd1TAG développent des kystes hépatiques, des anomalies cardiaques associées à des dépôts de calcium et des anévrismes cérébraux. La sévérité du phénotype augmente avec l’expression de Pkd1 appuyant l’hypothèse d’un mécanisme de dosage. Nous avons aussi déterminé que l’expression du transgène Pkd1TAG complémente le phénotype létal-embryonnaire des souris Pkd1-/-. D’autre part, nous avons générés 4 lignées de souris Pkd1ΔCoiled-coil (2 et 15 copies du transgène) dont le nombre de copies corrèle avec le niveau d’expression du transgène. Ces souris Pkd1ΔCoiled-coil, contrairement aux Pkd1TAG de même âge, ne développent pas de kystes et possèdent des cils primaires de longueur normale. Afin d’évaluer le rôle du motif coiled-coil en absence de polycystine-1 endogène, nous avons croisé les souris Pkd1ΔCoiled-coil avec les souris Pkd1-/-. Contrairement aux souris Pkd1-/- qui meurent in-utéro, les souris Pkd1ΔCoiled-coil; Pkd1-/- survivent ~10 à 14 jours après la naissance. Elles démontrent des kystes rénaux et pancréatiques sévères, un retard de croissance et des anomalies pulmonaires. Tous les segments du néphron sont affectés. Mon projet démontre que la surexpression de Pkd1 est un mécanisme pathogénique de la PKRAD tant au niveau rénal qu’extrarénal. De plus, il démontre que le motif coiled-coil est un élément déterminant dans la kystogenèse/PKRAD in-vivo.

Genetic Landscape of Joubert syndrome in French Canadians

Le syndrome de Joubert est une maladie récessive caractérisée par une malformation congénitale distincte du tronc cérébral et du cervelet, associée à une anomalie des mouvements oculaires (apraxie oculomotrice), une respiration irrégulière, un retard de développement, et une ataxie à la démarche. Au cours de la dernière décennie, plus de 20 gènes responsables ont été identifiés, tous ayant un rôle important dans la structure et la fonction des cils primaires. Ainsi, le syndrome de Joubert est considéré une ciliopathie. Bien que le Syndrome de Joubert ait été décrit pour la première fois dans une famille canadienne-française en 1969, le(s) gène(s) causal demeurait inconnu dans presque tous les cas de syndrome de Joubert recensés en 2010 dans la population canadienne-française, soit début de mon projet doctoral. Nous avons identifié un total de 43 individus canadiens-français (35 familles) atteints du syndrome de Joubert. Il y avait un regroupement de familles dans la région du Bas-Saint-Laurent de la province de Québec, suggérant la présence d'un effet fondateur. L’objectif de ce projet était de caractériser la génétique du syndrome de Joubert dans la population canadienne-française. Notre hypothèse était qu’il existait un effet fondateur impliquant au moins un nouveau gène JBTS. Ainsi, dans un premier temps, nous avons utilisé une approche de cartographie par homozygotie. Cependant, nous n’avons pas identifié de région d’homozygotie partagée parmi les individus atteints, suggérant la présence d’une hétérogénéité génétique ou allélique. Nous avons donc utilisé le séquençage exomique chez nos patients, ce qui représente une approche plus puissante pour l’étude de conditions génétiquement hétérogènes. Nos travaux ont permis l’identification de deux nouveaux gènes responsables du syndrome de Joubert: C5orf42 et TMEM231. Bien que la localisation cellulaire et la fonction de C5orf42 soient inconnus au moment de cette découverte, nos résultats génétiques combinés avec des études ultérieures ont établi un rôle important de C5orf42 dans la structure et la fonction ciliaire, en particulier dans la zone de transition, qui est une zone de transition entre le cil et le reste de la cellule. TMEM231 avait déjà un rôle établi dans la zone de transition ciliaire et son interaction avec d’autres protéines impliquées dans le syndrome de Joubert était connu. Nos études ont également identifié des variants rares délétères chez un patient JBTS dans le gène ciliaire CEP104. Nous proposons donc CEP104 comme un gène candidat JBTS. Nous avons identifié des mutations causales dans 10 gènes, y compris des mutations dans CC2D2A dans 9 familles et NPHP1 dans 3 familles. Au total, nous avons identifié les mutations causales définitives chez 32 des 35 familles étudiées (91% des cas). Nous avons documenté un effet fondateur complexe dans la population canadienne-française avec de multiples mutations récurrentes dans quatre gènes différents (C5orf42, CC2D2A, TMEM231, NPHP1). Au début de ce projet de recherche, l’étiologie génétique était inconnue chez les 35 familles touchées du syndrome de Joubert. Maintenant, un diagnostique moléculaire définitif est identifié chez 32 familles, et probable chez les 3 autres. Nos travaux ont abouti à la caractérisation génétique du syndrome de Joubert dans la population canadienne-française grâce au séquençage exomique, et révèlent la présence d'un effet fondateur complexe avec une l'hétérogénéité allélique et intralocus importante. Ces découvertes ont éclairé la physiologie de cette maladie. Finalement, l’identification des gènes responsables ouvre de nouvelles perspectives diagnostiques ante-natales, et de conseils génétique, très précieuses pour les familles.

Études fonctionnelles de deux nouvelles protéines centrosomales, NPHP5 et Cep76, et leurs implications dans les maladies humaines

Les centrosomes sont de petits organites qui régulent divers processus cellulaires comme la polarité ou la mitose dans les cellules de mammifères. Ils sont composés de deux centrioles entourés par une matrice péricentriolaire. Ces centrosomes sont les principaux centres organisateurs de microtubules. De plus, ils favorisent la formation de cils, des protubérances sur la surface des cellules quiescentes qui sont critiques pour la transduction du signal. Une grande variété de maladies humaines telles que les cancers ou les ciliopathies sont liées à un mauvais fonctionnement des centrosomes et des cils. C’est pourquoi le but de mes projets de recherche est de comprendre les mécanismes nécessaires à la biogénèse et au fonctionnement des centrosomes et des cils. Tout d'abord, j’ai caractérisé une nouvelle protéine centrosomale nommée nephrocystine - 5 (NPHP5). Cette protéine est localisée dans les cellules en interphase au niveau de la région distale des centrioles. Sa déplétion inhibe la migration des centrosomes à la surface cellulaire lors de l’étape précoce de la formation des cils. NPHP5 interagit avec la protéine CEP290 via sa région C-terminale qui est essentielle pour la ciliogenèse. Elle interagit également avec la calmoduline ce qui empêche son auto-agrégation. J’ai démontré que les domaines de liaison de NHPH5 à CEP290 et à la calmoduline, ainsi que son domaine de localisation centrosomale sont séparables. De plus, j’ai démontré que les protéines NPHP5 présentant des mutations pathogènes ne peuvent plus interagir avec CEP290 et ne sont plus localisées aux centrosomes, rendant ainsi ces protéines non fonctionnelles. Enfin, en utilisant une approche pharmacologique pour moduler les événements en aval dans la voie ciliogénique, j’ai montré que la formation des cils peut être restaurée même en absence de NPHP5. D’autre part, j’ai étudié le rôle de NPHP5 dans l'assemblage et le trafic du complexe BBSome dans le cil. Le BBSome est composé de huit sous-unités différentes qui s’assemblent en un complexe fonctionnel dont on sait peu de chose sur la régulation spatiotemporelle de son processus d'assemblage. J’ai précédemment montré que NPHP5 favorisait la formation des cils et que son dysfonctionnement contribuait au développement de néphronophtise (NPHP). Bien que la NPHP et le syndrome de Bardet-Biedl (BBS) soient des ciliopathies qui partagent des caractéristiques cliniques communes, la base moléculaire de ces ressemblances phénotypiques n’est pas comprise. J’ai constaté que NPHP5, localisé à la base du cil, contient deux sites de liaison distincts pour le BBSome. De plus, j’ai démontré que NPHP5 et son partenaire CEP290 interagissent de façon dynamique avec le BBSome pendant la transition de la prolifération à la quiescence. La déplétion de NPHP5 ou CEP290 conduit à la dissociation d’au moins deux sous-unités du BBSome formant alors un sous-complexe dont la capacité de migration dans le cil n’est pas compromise. J’ai montré que le transport des cargos vers le compartiment ciliaire par ce sous-complexe n’est que partiellement altéré. Enfin, j’ai également concentré mes recherches sur une autre protéine centrosomale peu caractérisée. La protéine centrosomale de 76 kDa (Cep76) a été précédemment impliquée dans le maintien d’une duplication unique des centrioles par cycle cellulaire, et dans une interaction avec la kinase cycline-dépendante 2 (CDK2). Cep76 est préférentiellement phosphorylée par le complexe cycline A/CDK2 sur le site unique S83. Cet événement est essentiel pour supprimer l'amplification des centrioles en phase S. J’ai démontré que Cep76 inhibe cette amplification en bloquant la phosphorylation de Plk1 au niveau des centrosomes. D’autre part, Cep76 peut être acétylée au site K279 en phase G2, ce qui régule négativement son activité et sa phosphorylation sur le site S83. Ces études permettent d'améliorer notre compréhension de la biologie des centrosomes et des cils et pourraient conduire au développement de nouvelles applications diagnostiques et thérapeutiques.