There is a basic rule to mammalian neocortical expansion: as it expands, so does it fold. The degree to which it folds, however, cannot strictly be attributed to its expansion. Across species, cortical volume does not keep pace with cortical surface area, but rather folds appear more rapidly than expected. As a result, larger brains quickly become disproportionately more convoluted than smaller brains. Both the absence (lissencephaly) and presence (gyrencephaly) of cortical folds is observed in all mammalian orders and, while there is likely some phylogenetic signature to the evolutionary appearance of gyri and sulci, there are undoubtedly universal trends to the acquisition of folds in an expanding neocortex. Whether these trends are governed by conical expansion of neocortical germinal zones, the distribution of cortical connectivity, or a combination of growth- and connectivity-driven forces remains an open question. But the importance of cortical folding for evolution of the uniquely mammalian neocortex, as well as for the incidence of neuropathologies in humans, is undisputed. In this hypothesis and theory article, we will summarize the development of cortical folds in the neocortex, consider the relative influence of growth- vs. connectivity-driven forces for the acquisition of cortical folds between and within species, assess the genetic, cell-biological, and mechanistic implications for neocortical expansion, and discuss the significance of these implications for human evolution, development, and disease. We will argue that evolutionary increases in the density of neuron production, achieved via maintenance of a basal proliferative niche in the neocortical germinal zones, drive the conical migration of neurons toward the cortical surface and ultimately lead to the establishment of cortical folds in large-brained mammal species.

Mast cells stem from the bone marrow and migrate via the blood as mast cell progenitors. Upon arrival in peripheral tissues, they develop into mast cells. These rare immune cells have numerous granules that contain large amounts of pro-inflammatory mediators. Mast cells accumulate at certain sites in the asthmatic lung, and once activated they release mediators that are thought to induce symptoms. In mouse models of allergic airway inflammation, the increase in lung mast cells in asthma can be mimicked and is mainly caused by the recruitment of mast cell progenitors to the lung. However, whether other types of lung inflammation stimulate the recruitment of mast cell progenitors to the lung was unknown until now. Here, using a murine model of influenza A virus infection, this type of virus was demonstrated to trigger an extensive recruitment of mast cell progenitors to the lung, most likely through the induction of VCAM-1 expression in the lung endothelium. Thereafter, some influenza-induced mast cell progenitors developed into an intermediate mast cell stage before they matured into mast cells. However, upon the resolution of inflammation, the mast cells that accumulated in the lung upon influenza infection were gradually lost. Because the recruitment of mast cell progenitors started early after influenza infection, the role of innate immune signals in inducing the recruitment of mast cell progenitors was addressed. The intranasal administration of either Poly I:C or IL-33 was sufficient to induce an increase in lung mast cell progenitors in a TLR3- or ST2-dependent fashion. However, the influenza-induced recruitment of mast cell progenitors to the lung occurred independently of TLR3 and ST2. VAAT/SLC10A4 is a member of the solute carrier family of proteins that is expressed in nerve cells and mast cells. In this study, murine VAAT was localized to mast cell granules and regulated the IgE/antigen-mediated release of granule-associated mediators and ATP. However, the absence of VAAT did not affect IgE/antigen-mediated de novo synthesis of cytokines and lipid mediators. Additionally, mice lacking VAAT had attenuated passive cutaneous anaphylaxis reactions and scratched less frequently in response to compound 48/80 injections, suggesting that VAAT regulates reactions for which mast cells are implicated in vivo.

L’insuffisance cardiaque (IC) est un problème majeur de santé publique. La pénurie des greffons cardiaques et la résistance de nombreux patients aux traitements conventionnels ont poussé les chercheurs à développer de nouvelles thérapeutiques dont la thérapie cellulaire. Bien que l’idée initiale de la thérapie cellulaire ait été de repeupler la partie nécrosée du cœur par l’administration de cellules viables et fonctionnelles, leur disparition rapide alors que les bénéfices perdurent dans le temps a conduit à l’hypothèse que les cellules agiraient via un mécanisme paracrine. Les vésicules extracellulaires (VE), incluant les exosomes et les microparticules, seraient principalement impliquées dans ce processus. Elles agiraient ainsi comme de véritables navettes transportant des biomolécules actives permettant d’activer des voies de réparation endogènes dans le tissu traité. Ce projet de thèse a pu mettre en évidence : 1) La non-infériorité des VE issues de progéniteurs cardiovasculaires (Pg) dérivés de cellules souches embryonnaires humaines par rapport à leurs cellules d’origine dans un modèle murin d’IC chronique (ICC). Ces VE activeraient des voies de signalisation endogènes impliquées dans la stimulation de la prolifération cellulaire, la survie cellulaire, la réparation de l’ADN et la diminution de la fibrose. Leur contenu moléculaire spécifique, et notamment les microARN, pourrait être impliqué dans ces phénomènes. 2) L’importance du choix du type cellulaire dans la production de VE efficaces sur le plan thérapeutique puisque ni les VE dérivées de cardiomyocytes matures ni celles de cellules souches mésenchymateuses n’ont eu d’effets bénéfiques sur la fonction cardiaque de souris en ICC. 3) L’implication des VE dans l’effet paracrine des cellules, confirmée par l’amélioration de la fonction cardiaque chez des souris présentant une ICC traitées avec des VE issues de Pg dérivés d’iPS. Des tests fonctionnels in vitro ont montré que les VE auraient un rôle pro-angiogénique, pro-prolifératif et amélioreraient la survie des cellules. Une thérapie a-cellulaire aurait une réelle pertinence clinique en réglant une partie des problèmes techniques, immunologiques et sécuritaires associés aux greffes de cellules. Si cette hypothèse est confirmée, il pourrait en résulter une simplification des problèmes réglementaires, une diminution des coûts de production et de ce fait une plus grande diffusion clinique de la méthode. / Heart failure (HF) is a major public health concern. The lack of donor hearts and the resistance of numerous patients to conventional treatments has led scientists to develop new therapies such as cell therapy. The initial goal of cell therapy was to repopulate the infarcted heart by directly injecting viable and functional cells. However, the rapid disappearance of the transplanted cells contrasts with their long term, ongoing functional benefits, suggesting that cells may act through a paracrine mechanism. Extracellular vesicles (EV), including exosomes and microparticles, may be key to this process, acting as shuttles to transport bioactive macromolecules that stimulate endogenous repair pathways in the host tissue. This PhD project demonstrates: 1) The non-inferiority of EV secreted by cardiovascular progenitors (Pg) derived from human embryonic stem cells as compared to their parent cells in a mouse model of chronic HF (CHF). These EV could act by the activation of endogenous signaling pathways implicated in cell proliferation, survival, DNA repair and decreased fibrosis. Their specific content, such as miRNA, could be involved in these benefits. 2) The importance of the cell type in the production of therapeutically effective EV, since EV derived from mature cardiomyocytes and mesenchymal stem cells did not improve cardiac function in mice with CHF. 3) The importance of EV in paracrine effects of cells, confirmed by the improvement of cardiac function in mice with CHF treated with EV secreted by Pg derived from iPS cells. In vitro data shows that EV might have pro-angiogenic, pro-proliferative and pro-survival effects. An acellular therapy should be clinically relevant by reducing technical, immunological and safety problems associated with cell transplantation. If this hypothesis is confirmed, regulatory concerns would be simplified and production costs reduced, facilitating large-scale production.

Les cellules souches neurales adultes (aNSCs) sont définies par des fonctions d’auto-Renouvellement et de multipotence qui leur permettent de générer dans le cerveau adulte tant des neurones que des cellules gliales. Contrairement aux mammifères, le cerveau de poisson zèbre présente de nombreuses zones de neurogenèse adulte dont la plus caractérisée est la zone ventriculaire du pallium. Elle est composée de cellules de glies radiaires qui font office de aNSCs dans cette partie du cerveau. Quels progéniteurs neuraux embryonnaires sont sélectionnés pour être à l’origine de ces aNSCs reste mal connu. Ce travail a pour objectif de déterminer la contribution relative de deux populations de progéniteurs neuraux embryonnaires, les “clusters proneuraux” (impliqués dans la neurogenèse embryonnaire) et les “pools de progéniteurs” (caractérisés par une neurogenèse tardive), dans la formation des aNSCs du pallium de poisson zèbre. Dans un premier temps, à l’aide de techniques génétiques de lignage cellulaire, nous avons pu identifier la population de progéniteurs neuraux embryonnaires à l’origine d’une sous-Population des aNSCs située dans la partie dorso-Médiane du pallium. Des expériences de lignage utilisant la lignée de poisson zèbre her4:ERT2CreERT2 combinées à des traitements inhibiteurs de la voie de signalisation Notch nous ont permis de déterminer que les progéniteurs neuraux donnant naissance aux aNSCs du pallium dorso-Médian expriment le gène « Enhancer of split » her4, qui caractérise les “clusters proneuraux”, ce dès des stades très précoces du développement. Dans un second temps, des analyses clonales ainsi que des recombinaisons spatialement contrôlées par laser nous ont permis de mettre en évidence que les aNSCs de la partie latérale du pallium de poisson zèbre ne proviennent pas de progéniteurs embryonnaires exprimant her4 et maintenus par la voie Notch, mais d’une population restreinte de cellules neuroépitheliales situées dans la plaque du toit du télencéphale embryonnaire. Ces cellules présentent des caractéristiques spécifiques des “pool de progéniteurs”, à savoir l’expression de gènes her non-Canoniques (dont l’expression n’est pas dépendante de la voie de signalisation Notch) tels que her6 et her9, l’expression de ligands de voies de signalisation telles que Wnt, BMP et FGF, et une neurogenèse tardive. Elles génèrent progressivement, à partir du stade juvénile, une grande partie des aNSCs du pallium latéral. De plus, une partie de ces cellules neuroépitheliales persistent dans le pallium latéral postérieur chez l’adulte et continuent de former de novo des aNSCs dans cette région du cerveau. Outre la vision globale que cette étude nous a permis d’avoir sur l’origine embryonnaire de la totalité des aNSCs du pallium de poisson zèbre, elle a aussi délivré des informations sur les étapes de maturation progressive des progéniteurs embryonnaires pour former les aNSCs, et les similitudes et divergences qui existent entre la population dorso-Médiane et latérale à ce sujet. Enfin, en traçant les neurones issus des cellules souches à différents stades, cette étude a pour la première fois mis en évidence la formation progressive des compartiments neuronaux du pallium de poisson zèbre, et ainsi permis d’apprécier les homologies de ces compartiments avec les régions du pallium de souris. / Adult neural stem cells (aNSCs) are defined by their self-Renewal and multipotency, which allow them to generate both neurons and glial cells in the adult brain. Contrary to mammals, the zebrafish brain maintains numerous neurogenic zones in the adult, among which the most characterized is the pallial ventricular zone. It is composed of radial glial cells serving as aNSCs. Which embryonic neural progenitors are at the origin of these aNSCs is still unknown. This work aims to determine the relative contributions of two embryonic neural progenitor populations, the «proneural clusters» (involved in embryonic neurogenesis) and the « progenitor pools » (characterized by a delayed neurogenesis), to the formation of aNSCs in the zebrafish pallium. First, using genetic lineage tracing techniques, we were able to identify the embryonic neural progenitor population at the origin of a subpopulation of aNSCs located in the dorso-Medial part of the pallium. The her4:ERT2CreERT2 transgenic driver line, combined with pharmacological treatments inhibiting the Notch signalling pathway, allowed showing that neural progenitors giving rise to dorso-Medial pallial aNSCs express the « Enhancer of split » her4 gene, specifically expressed in « proneural clusters » from very early stages of development. As a second step, clonal analyses as well as spatially controlled recombinations by laser highlighted that aNSCs of the zebrafish lateral pallium do not derive from her4-Positive embryonic progenitors maintained by the Notch pathway, but from a restricted population of neuroepithelial cells located in the embryonic telencephalic roof plate. These cells display « progenitor pool » specific features, as for instance the expression of non-Canonical her genes (independent of Notch signalling) such as her6 and her9, the expression of components of signalling pathways such as Wnt, BMP, FGF, and a late neurogenesis onset. These progenitors progressively generate, from juvenile stages, the vast majority of the aNSCs of the lateral pallium. Most interestingly, a small population of these neuroepithelial cells persists in the postero-Lateral pallium at adult stage and keeps generating de novo aNSCs of this brain region. In addition to identifying the origin of pallial aNSCs in the zebrafish, this study also delivers information on the progressive maturation steps that embryonic progenitors undergo to generate aNSCs, and highlights similarities and differencies existing between the dorso-Medial and lateral progenitors. Finally, this work also permits tracing the neurons generated by stem cells at different stages. This reveals for the first time the progressive formation of the different zebrafish pallial compartements, and allows appreciating their homologies with the mouse pallial regions.

Le cytosquelette d'actine est une structure dynamique capitale pour la cellule, qui intervient dans les processus de signalisation et génère des forces mécaniques pour compléter des fonctions aussi diverses que l'adhésion, la migration, la division ou la différenciation. Les protéines qui régulent cette structure sont capables de moduler ces fonctions. J'ai identifié une nouvelle famille de protéines régulatrices de l'actine, les protéines Refilines (RefilineA et RefilineB), dont l'expression est corrélée avec l'engagement des cellules dans des programmes de différenciation. La RefilineA est induite lors de la différenciation des cellules précurseurs neurales multipotentes en cellules progénitrices gliales. La RefilineB est stabilisée dans les cellules épithéliales lors de la transition épithélio-mésenchymateuse (TEM) induite par le TGF-β. Dans ces cellules, les Refilines agissent en se complexant à la FilamineA, une protéine qui se lie aux filaments d'actine et forme le maillage. Des syndromes génétiques de mutations sur le gène de la FilamineA entrainent d'importants défauts développementaux, cependant la fonction précise de la protéine reste à ce jour obscure. Le complexe Refiline/FilamineA induit la formation de câbles d'actine et génère également une nouvelle structure d'actine périnucléaire appelée coiffe d'actine (« actin cap ») ou « ligne TAN» qui s'ancre à l'enveloppe nucléaire pour réguler les mouvements et la morphologie du noyau. Les Refilines sont les seules protéines identifiées à ce jour capables de catalyser la formation de structures périnucléaires d'actine. Ces résultats ouvrent donc de nouvelles perspectives pour appréhender les fonctions de la FilamineA ainsi que la biologie et les fonctions des structures périnucléaires d'actine. / The actin cytoskeleton is a highly dynamic structure involved in cell signaling and that creates mechanical force for the completion of diverse functions such as adhesion, migration, division or differentiation. Proteins that regulate this structure can modulate its function. We identified a new protein family that regulates the actin cytoskeleton, Refilin proteins (RefilinA and RefilinB), and whose expression correlates with differentiation switches. RefilinA is induced during differentiation of neural multipotent precursors into glial progenitors, while RefilinB is stabilized in epithelial cells during epithelial-mesenchymal transition (EMT) induced by TGF-β. In cells, Refilins interact with FilaminA, a protein that binds actin filaments to organize them into a network. Genetic syndromes where the FilaminA gene is mutated lead to important developmental defects, The Refilin/FilaminA complex generates actin cables as well as a new perinuclear structure called « actin cap » or «TAN line» that interacts with the nuclear envelope to regulate nuclear movement and shape. Refilin proteins are the only proteins identified so far that induce the formation of perinuclear actin structures. These results open up new perspective for the understanding of FilaminA's function as well as for the biology and functions of perinuclear actin structures.

Mesenchymal-epithelial interactions are pivotal for proper pancreatic growth and development. The pancreatic progenitor cells present in the early pancreatic anlagen proliferate and eventually give rise to all pancreatic cell types. The Fibroblast Growth Factor 2b (FGFR2b) high-affinity ligand Fibroblast Growth Factor 10 (FGF10) has been linked to pancreatic epithelial cell proliferation and we have previously shown that Notch signalling controls pancreatic cell differentiation via lateral inhibition. By overexpressing FGF10 under the control of the Ipf1/Pdx1 promoter in mice, we have shown that persistent FGF10 activation in the embryonic pancreas of transgenic mice perturbs pancreatic epithelial cell proliferation and also inhibits pancreatic cell differentiation by maintaining Notch activation. In the Ipf1/Fgf10 transgenic mice, the pancreatic epithelial cells are ‘locked’ in an undifferentiated progenitor-like state with sustained proliferative capacity. Collectively, our data suggest a key role for FGFR2b/FGF10 signalling in the regulation of pancreatic growth and differentiation and that FGFR2b/FGF10 signalling interact with the Notch signalling pathway. Glucose homeostasis in mammals is critically dependent on co-ordinated glucose uptake, oxidative metabolism and insulin secretion in β-cells. Although, several key genes controlling various aspects of glucose sensing, glucose metabolism, insulin expression and secretion have been identified, we know relatively little about the molecular mechanisms that induce and maintain the expression of genes required for glucose-stimulated insulin secretion (GSIS) in β-cells. Attenuation of FGFR1c signalling leads to diabetes in mice. Overexpression of FGF2, a high-affinity FGFR1c ligand, under the control of the Ipf1/Pdx1 promoter also leads to diabetes in mice. The Ipf1/Fgf2 mice present with normal endocrine and exocrine differentiation but display impaired glucose-stimulated insulin secretion (GSIS), perturbed expression of genes required for glucose sensing uptake together with oxidative metabolism and increased expression of the FGF-signalling inhibitors Spry-2 and Pyst1/MKP3 in β-cells. Thus, stringent control of FGF signalling activation appears crucial for the maintenance of the regulatory circuit that ensures proper GSIS in pancreatic β-cells and hence normoglycaemia. The Wnt family of ligands via their receptors Frizzled (Frz) have been shown to mediate mesenchymal-epithelial interactions and cell proliferation in a variety of different systems. Expression of a plethora of Wnt ligands and Frz receptors has been previously reported in the pancreas and mice missexpressing Wnt1 and Wnt5a under the Ipf1/Pdx1 promoter display severely perturbed development. Here, we show the temporal and spatial expression of Wnt4, Wnt7b and Frz3 at different stages of pancreas development. To elucidate the role of Wnt signalling in the pancreas, we overexpressed a dominant negative form of mouse Frz8 under the Ipf1/Pdx1 promoter in mice. The Ipf1/Frz8CRD mice display severe pancreatic hypoplasia demonstrating that attenuation of Wnt signalling in the pancreas leads to perturbed pancreatic growth. Nevertheless, the transgenic mice present with normal endocrine and exocrine differentiation and remain normoglycaemic. The maintenance of normoglycaemia in these mice appears to be the consequence of a relative increase in endocrine cell number per pancreatic area combined with enhanced insulin biosynthesis and insulin secretion. Collectively our data provide evidence that Wnt signalling is required pancreatic growth but not adult β-cell function.

<p>Despite its lack of septation, the tissue patterning of the arterial pole of the zebrafish is remarkably similar to the patterning of pulmonary and aortic arterial poles observed in mouse and chick. The secondary heart field (SHF) is a conserved developmental domain in avian and mammalian embryos that contributes myocardium and smooth muscle to the cardiac arterial pole. This field is part of the overall heart field, and its myocardial component has been fate mapped from the mesoderm to the heart in both mammals and birds. In this study I demonstrate that the population that gives rise to the arterial pole of the zebrafish can be traced from the epiblast, is a discrete part of the mesodermal heart field. This zebrafish SHF contributes myocardium after initial heart tube formation, giving rise to both smooth muscle and myocardium. I show that this field expresses Isl1, a transcription factor associated with the SHF in other species. I further show that differentiation, induced by Bmp signaling, occurs in this progenitor population as cells are added to the heart tube. Some molecular pathways required for SHF development in birds and mammals are conserved in teleosts, as Nkx2.5 and Nkx2.7 as well as Fgf8 regulate Bmp signaling in the zebrafish heart fields. Additionally, the transcription factor Tbx1 and the Sonic hedgehog pathway are necessary for normal development of the zebrafish arterial pole.</p> / Dissertation

No description available.

Basotho family odes (diboko) form part of oral literature, and refer to names of families, clans or totems. They constitute poetic compositions conveying information about clans' historical origin, philosophy and ancestors. The performance of this oral art form makes use of formulaic techniques such as linking, parallelism, alliteration, etc., which are commonly used in praise poetry. As basis to the content of these oral art forms, the genealogies of the various Basotho clans are discussed to show the reflection of the progenitor names in the clan praises. The functions of family odes are of educational, social and religious nature. Other functions include their use in compositions of other genres, such as, praise poems, mine workers' chants, traditional doctors' falls (mawa) and songs. The recitation of this oral art form is characterised by the instability of the texts, which takes the form of extensions, additions, truncations, improvisations and genre transitions. / African Languages / M.A. (African Languages)

Despite being the leading cause of neurodegeneration and dementia in the aging brain, the cause of Alzheimer's disease (AD) remains unknown in most patients. The terminal pathological hallmarks of abnormal protein aggregation and neuronal cell death are well-known from the post-mortem brain tissue of Alzheimer's disease patients, but research into the earliest stages of disease development is hindered by limited model systems. In this thesis, an in vitro human neuronal system was derived from induced pluripotent stem (iPS) cell lines reprogrammed from dermal fibroblasts of AD patients and age-matched controls. This allows us to investigate the cellular mechanisms of AD neurodegeneration in the human neurons of sporadic AD (SAD) patients, whose development of the disease cannot be explained by our current understanding of AD. We show that neural progenitors and neurons derived from SAD patients show an unexpected expression profile of enhanced neuronal gene expression resulting in premature differentiation in the SAD neuronal cells. This difference is accompanied by the decreased binding of the repressor element 1-silencing transcription/neuron-restrictive silencer factor (REST/NRSF) transcriptional inhibitor of neuronal differentiation in the SAD neuronal cells. The SAD neuronal cells also have increased production of \(amyloid-\beta\) and higher levels of tau protein, the main components of the plaques and tangles in the AD brain.