Project

medial limbic cortex; cortex; neuronal precursors; pyramidal; neuronal migration; cortex; Wnt signaling

Lead
Les couches corticales du cerveau sont générées par une coordination précise de la migration des cellules et le cerveau des mammifères est particulièrement vulnérable à des désordres touchant ces migrations. La compréhension des mécanismes contrôlant ces migrations est par conséquent cruciale pour comprendre comment leur dysfonctionnement peut engendrer des désordres du développement neural. Les voies de signalisation Wnt sont connues depuis longtemps pour leur rôle central dans de nombreux aspects de la corticogenèse, notamment la prolifération des précurseurs neuronaux et la différentiation des neurones. Cependant, le rôle direct de Wnt dans la régulation de la migration et le positionnement des cellules neuronales est encore inconnu.
Lay summary
Nous avons centré nos études sur le cortex limbique dorso-médial, comprenant le cortex cingulaire et le cortex rétro-splénial. Nous proposons de raffiner nos outils moléculaires ciblant la voie canonicale Wnt afin de tester plusieurs hypothèses concernant cette voie de signalisation. Ces hypothèses sont : (1) la polarisation à travers le cortex des progéniteurs multi-polaires ; (2) la locomotion médiée par la glie radiale ; (3) le positionnement des cellules au cours des étapes finales de la migration radiale. Nous créerons des constructions plasmidiques auto-inductibles par la doxycycline, pour reproduire des situations de « loss-of-function » ou « gain-of-function » dans la voie de signalisation Wnt/béta-caténine.  Nous étudierons ensuite les effets de ces manipulations sur le positionnement et la morphologie des cellules pyramidales à l’aide d’un microscope confocal. Afin de suivre la migration des neurones en temps réel, des « vidéos time-lapse » seront effectuées sur des préparations en coupe.  Le travail proposé ici devrait fournir des informations inédites sur le contrôle de la migration et du positionnement des cellules dans le cortex cérébral. De nombreux troubles du développement neural sont associés à des altérations de la migration des neurones. Ces troubles vont des malformations sévères avec retard mental et épilepsie jusqu’à des troubles comme l’autisme, la schizophrénie ou la dyslexie. Les voies de signalisation Wnt sont impliquées dans des troubles psychiatriques sévères comme la schizophrénie, eux-mêmes associés à des désordres du développement. Nos résultats devraient donc fournir des informations pour élucider les mécanismes impliquées dans ces troubles neurologiques.

Direct link to Lay Summary

Last update: 16.03.2017

Lead
Cortical layers are generated by precisely coordinated cell migration events and the mammalian cortex is particularly susceptible to disorders of migration. Understanding the mechanisms and regulation of migratory events is therefore crucial to understand how alterations in this process might contribute to neurodevelopmental disorders. It has long been known that Wnt signaling pathways play a central role in many aspects of corticogenesis, including neural progenitor proliferation and neuronal differentiation, but its direct role in regulating cell migration and positioning remained unknown.
Lay summary
We focuse our studies on the dorsomedial limbic cortex, comprising the cingulate and retrosplenial cortex. We propose to refine our molecular tools to target Wnt canonical signaling in order to test a series of specific hypotheses concerning the role of this signaling pathway in events including: 1) polarizing multipolar progenitors towards the cortex; 2) radial glia mediated locomotion and 3) cell positioning during the final stage of radial migration. We will engineer doxycycline inducible constructs to carry out loss-of-function or gain-of-function experiments. We plan to investigate the effects of manipulating Wnt/beta-catenin signaling on positioning and morphology of pyramidal cells using confocal microscopy. In order to monitor in real time the migration of neurons, video time-lapse imaging will be performed on slice preparations. The work proposed here will provide novel information on the control of cell migration and positioning in the cerebral cortex. Many human neurodevelopmental disorders are associated with alterations in neuronal migration, ranging from severe malformations with mental retardation and epilepsy to disorders such as autism, schizophrenia and dyslexia. Wnt signaling pathways have been implicated in major psychiatric pathologies such as schizophrenia that are supposed to be associated with developmental disturbances. The results of these investigations may help to gain insight into the mechanisms relevant to some of these disorders

Direct link to Lay Summary

Last update: 16.03.2017

Number	Title	Start	Funding scheme

Perinatal damaging insults are the most important cause of brain injury in the preterm infant. A critical feature of this pathology is that it impacts on the mechanisms that govern cortical network formation including neuronal precursor migration and positioning. Therefore, understanding the mechanisms and regulation of migratory events in the perinatal developmental context is crucial to understand how alterations in this process might contribute to neurodevelopmental disorders. Using focal in vivo administration of GFP coding lentiviral vectors, we discovered a pool of postmitotic neuronal precursors in the subventricular zone that migrate radially into the medial limbic cortex (cingulate and retrosplenial cortex) during the first 4 postnatal days. In the retrosplenial granular cortex, these progenitors give rise to layer 2 pyramidal neurons that form typical dendritic bundles. The model creates an opportunity to study the cellular mechanisms and molecular programs that regulate the postnatal migration of a defined cell population and allows to explore the plasticity of this system in response to damaging insults. The hypothesis we propose to test in this project is that Wnt signaling pathways through an autocrine or paracrine loop, may play a role in the sequential steps leading to the postnatal positioning of pyramidal neurons. This prediction is based on the expression pattern of Wnt signaling components in the medial cortex and the established role of Wnt signaling in cell migration in other contexts. To test this hypothesis, the main strategy will be employing lentiviral-mediated loss or gain of function manipulations in single cells in vivo. This will allow to study the impact of Wnt signaling pathways over long-term experiments in a physiological context.We propose to address three main questions: 1. Is Wnt signaling required for neuronal precursor positioning in vivo? To address this question we will use RNA interference to downregulate the phosphoprotein disheveled (Dvl), an important transducer of Wnt signaling. We propose to investigate the effects of Wnt signaling downregulation on positioning and morphology of pyramidal cells using confocal microscopy. 2. How does disruption of Wnt signaling pathways impact on cell behavior? To monitor in real time the migration of new neurons video time-lapse imaging will be performed on slice preparations.3. What are the possible Wnt ligands and receptors (Frizzled) involved in cell positioning and morphogenesis? We will address this issue by determine the expression pattern of Wnt signaling elements in migrating progenitors and in cells of the environment using immunocytochemistry and in situ hybridization. We will also investigate the effects of recombinant Wnt proteins on slice preparation and perform loss and gain of function experiments to study the role of specific ligands .Importance: The work proposed here could provide novel and fundamental information on the control of neuronal positioning in the cerebral cortex. This may open new possibilities to study the impact of perinatal damaging insults on cell migration and may be, to manipulate progenitor cells to target them to site of injuries.