This thesis describes the work that I have carried out in the Laboratory of Neurophysiolgy at the Université Libre de Bruxelles, under the supervision of Prof. Serge Schiffmann, in collaboration with Prof. Stéphane Schurmans of Université of Liège.The work is divided in two distinct but related projects and the results section is thus divided into two main chapters. The results described are presented in the form of two manuscripts, the first chapter is named “Ciliary phosphoinositides regulation by INPP5E controls Shh signaling by allowing trafficking of Gpr161 in neural stem cells primary cilium”.The second is named “Regulation of phosphoinositides ciliary levels controls trafficking and ciliogenesis in ependymal cells”.Since both manuscripts are comprehensive regarding the results, and methods, these are inserted as such into the thesis.An expanded introduction to the field, placing the results into context, precedes these two chapters. An extended discussion section follows each chapter; it presents some elements of discussion not included in the manuscripts, the implications of the results and the scope for further research. / Doctorat en Sciences biomédicales et pharmaceutiques / info:eu-repo/semantics/nonPublished

The discovery of neural stem cells within the adult CNS has indicated an enormous potential in facilitating neuronal regeneration after injury. Studies from our laboratory have suggested that manipulation of the Rb/E2f pathway can directly impact embryonic and adult neurogenesis, thereby having tremendous potential for neuronal regeneration therapies. Recently, two new members of the Rb/E2f pathway have been discovered, the atypical E2fs: E2f7 and E2f8. Initial studies have suggested that atypical E2fs regulate diverse processes such as cell proliferation, DNA-stress response, apoptosis, however, their importance in the brain are unknown. To analyze their function during brain development, we crossed Nestin-Cre mice with mice bearing a conditional E2f7/E2f8 allele to delete both E2f7 and E2f8 in neural precursor cells. Whereas cortical development was largely unaffected by E2f7/E2f8 deficiency, we observed an enlargement of the lateral ventricles occurring postnatally, a brain condition named ventriculomegaly. We then looked at the ependymal cells, which are the cells lining the wall of the lateral ventricles, to determine if these cells were affected by the absence of atypical E2fs. We found progressive denaturation of the ependymal cell layer, distortion of the ependymal motile cilia and reactive astrocytes within the layer. We identified Gli3, a component of the Sonic hedgehog pathway (Shh), as a target for E2fs, including atypical E2fs. We unravelled a novel mechanism by which atypical E2fs regulate the expression of Gli3, leading to up-regulation of Numb/NumbL, which in consequence destabilizes cadherins organization within the ependymal cell layer. In conclusion, our work suggests that E2f7 and E2f8 transcription factors play an essential role in maintaining the ependymal cell barrier.

No description available.

Ischaemic stroke is a major cause of mortality and chronic disability for which there is no effective treatment. The subventricular zone (SVZ) is an adult neurogenic niche which mediates limited endogenous repair following stroke. To harness this phenomenon for therapy, it is important to understand how the SVZ niche is altered in stroke, and the processes that recruit neural precursors to the site of injury, which becomes a de facto neurogenic niche. Galectin-3 (Gal-3) is a β-galactoside binding protein involved in cellular adhesion, inflammation and tumour metastasis. Gal-3 is specifically expressed in the SVZ and maintains neuroblast migration to the olfactory bulb, although its role in post-stroke neurogenesis is not well-understood. Therefore, this project aimed to (1) characterise the cytoarchitecture of the SVZ in response to stroke, and (2) examine the role of Gal-3 in stroke outcome and tissue remodelling, and test the hypothesis that Gal-3 is required for neuroblast ectopic migration into the ischaemic striatum. Using the intraluminal filament model of middle cerebral artery occlusion (MCAO) in mice, and whole mounts of the lateral ventricular wall, significant SVZ reactive astrocytosis and increased vascular branching were observed, thereby disrupting the neuroblast migratory scaffold. Stroke increased SVZ cell proliferation without increase in cell death. Post-stroke ependymal cells were enlarged and non-proliferative, and assumed a reactive astroglial phenotype, expressing de novo high levels of glial fibrillary acidic protein. This was associated with focal planar cell polarity misalignment, and turbulent and decreased rate of cerebrospinal fluid flow. These findings demonstrate significant changes in multiple SVZ cell types which are positioned to influence post-stroke neurogenesis and regulation of the neural stem cell niche Gal-3 was up-regulated in the ischaemic brain and ipsilateral SVZ. To elucidate the role of Gal-3 after stroke, MCAO was performed in wildtype and Gal-3 null (Gal-3^-/-) mice, and parameters of stroke outcome and post-stroke neurogenesis compared. The deletion of Gal-3 did not affect infarct volumes or neurological outcomes, although neuroblast migration into the ischaemic striatum was increased in Gal-3^-/- brains. Gal-3^-/- mice failed to mount an angiogenic response in the ischaemic striatum, and this was associated with lower levels of vascular endothelial growth factor (VEGF) and increased anti-angiogenic protein levels. Loss of Gal-3 further disrupted the pro-proliferative neural-vascular interaction at the basement membrane. The current data indicate that Gal-3 is a pleiotropic molecule which has distinct roles in both the SVZ and the post-stroke striatum as niches of adult neurogenesis.

Les cellules épendymaires sont des cellules multiciliées qui tapissent les parois de toutes les cavités du cerveau. Une fois différenciées, ces cellules ne se divisent plus au cours de la vie. Le battement de ces multiples cils motiles joue un rôle important pour maintenir un flux constant de liquide cérébrospinal à travers toutes les cavités cérébrales. Les cellules épendymaires assurent également des fonctions critiques d’échanges moléculaires avec le liquide cérébrospinal. Dans son ensemble, l’implication des cellules épendymaires et de leurs cils motiles s’avère d’une importance majeure dans le maintien des circuits neuraux ainsi que dans le fonctionnement plus global du cerveau. Récemment, une nouvelle caractéristique des cellules épendymaires a été identifiée ; elles font partie d’un microenvironnement appelé une « niche » centrée autour de cellules souches neurales dans le cerveau du rongeur adulte. Ces cellules souches neurales adultes sont capables de produire de nouveaux neurones qui migreront vers le bulbe olfactif des rongeurs adultes. Concernant leur origine, il a été montré que les cellules épendymaires multiciliées dérivent des cellules souches neurales durant les stades tardifs embryonnaires. Ces mêmes cellules souches peuvent d’ailleurs donner naissance à la plupart des différents types de cellules du cerveau. Cependant, les mécanismes par lesquels les cellules souches décident de leur destin cellulaire restent largement méconnus. Dans ce projet, nous étudions quel type de division donne naissance à des cellules épendymaires et nous nous intéressons également au lignage épendymaire. Nos données suggèrent que les cellules épendymaires ne migrent pas après leur dernière division et qu’elles restent à proximité de l’endroit où elles ont été produites. Chose particulièrement intéressante, nous montrons que les cellules épendymaires peuvent être générées par division symétrique ou asymétrique. Nos résultats révèlent aussi que les cellules souches neurales embryonnaires se divisent de manière asymétrique pour donner naissance à la fois à une celluleépendymaire et à une cellule souche neurale adulte. Ces données viennent s’ajouter à la connaissance actuelle que nous avons du développement du cerveau. De plus, elles pourraient contribuer à ouvrir de nouvelles perspectives et stratégies thérapeutiques pour soigner les maladies neurodégénératives à beaucoup plus long terme. / Ependymal cells are multiciliated cells lining the walls of all brain cavities. Once they are mature, they do not divide during life. Their motile ciliary beating endorses a crucial role in maintaining a proper flow of cerebrospinal fluid throughout all brain cavities. Ependymal cells also ensure critical molecular exchanges of the cerebrospinal fluid. On the whole, the involvement of ependymal cells and their multiple motile cilia in the maintenance of the neural circuits and more globally in the well-functioning of the entire brain have proven paramount. More recently, a new characteristic of ependymal cells has been brought to light. Namely, they are part of a microenvironment so called a “niche” surrounding adult neural stem cells in the adult rodent brain. Noteworthy, these adult neuralstem cells are capable of producing new neurons that will migrate to the olfactory bulb of rodents. In terms of their origin, it was shown that multiciliated ependymal cells derive from neural stem cells during late embryonic stages. Besides, the same stem cells can give rise to most cell types of the brain. However, little is known about how fate-decision is made in neural stem cells. In this project, we tackle more particularly how multiciliated ependymal cells arise from the neural stem cells. Most specifically, we address the type of celldivision and the ependymal cell lineage. We find that ependymal cells are not migrating subsequent to their last division, but rather stay where they were first produced. Most interestingly, they can be generated through both symmetric and asymmetric cell division. We also show that embryonic neural stem cells divide asymmetrically to give rise to both an ependymal cell and an adult stem cell. We are confident that these data bring major new insights in the current understanding of neural development. Additionally, these findingscould contribute in opening new therapeutic perspectives and strategies to cure neurodegenerative diseases in a much longer term.

No description available.

<p dir="ltr">Though mammalian spinal cord injury (SCI) has long been a topic of study, effective therapies that promote functional recovery are not yet available. The axolotl, <i>Ambystoma mexicanum</i>, is a valuable animal model in the investigation of spinal cord regeneration, as this urodele is able to achieve functional recovery even after complete spinal cord transection. Understanding the similarities and differences between the mammalian SCI response and that of the axolotl provides insight into the process of successful regeneration, and bolsters the fundamental knowledge used in the development of future mammalian SCI treatments. This thesis provides a detailed analysis of the ultrastructure of the axolotl meninges, as this has not yet been presented in existing literature, and reveals that the axolotl meninges consist of 3 distinct layers as does mammalian meninges; the dura mater, arachnoid mater, and pia mater. The role of reactive meningeal and ependymal cells is also investigated in regard to the deposition and remodeling of the fibrotic ECM, which is found to be similar in composition to hydrogel scaffolds being studied in mammalian SCI. It is shown that meningeal fibroblasts are the primary source of the extensive fibrillar collagen deposition that fills the entire spinal canal, peaking at approximately 3 weeks post transection and remaining until approximately 5 weeks post transection, and that there is no deposition of type IV collagen within the lesion site. Mesenchymal ependymal cells are shown to contribute to the ECM deposition through the production of glycosaminoglycans that are used in sidechains of both unsulfated and sulfated proteoglycans, while simultaneously remodeling the ECM through the production of MMPs and phagocytosis of cellular debris. Further, this study shows that mesenchymal ependymal cells and a population of foamy macrophages contribute to the degradation of the fibrin clot that forms in the acute phase of injury, and that this fibrin clot provides a necessary and permissive substrate for early mesenchymal outgrowth.</p>