Med Sci.

Since our seminal study in 2003, much has been written about core planar cell polarity (core PCP) signaling and the inner ear. In just a few years, and using the inner ear as a model system, our understanding of the molecular basis of this signaling pathway and how it can influence the development of tissues in mammals has increased considerably. Recently, a number of studies using various animal models of development have uncovered original relationships between the cilia and PCP, and the study of the hair cells of the inner ear has helped elucidating one of these links. In this review, we highlight the differences of PCP signaling between mammals and invertebrates. In the light of recent results, we sum up our current knowledge about PCP signaling in the mammalian cochlear epithelium and we discuss the impact of recent data in the field. We focus our attention on the interrelationship between asymmetric polarity complexes and the position of the cilium, which is essential for the establishment of the overall tissue polarity

Front Aging Neurosci

Decline in episodic memory is one of the hallmarks of aging and represents one of the most important health problems facing western societies. A key structure in episodic memory is the hippocampal formation and the dentate gyrus in particular, as the continuous production of new dentate granule neurons in this brain region was found to play a crucial role in memory and in age-related decline in memory. As such, understanding the molecular processes that regulate the relationship between adult neurogenesis and aging of memory function holds great therapeutic potential. Recently, we found that Vang-gogh like 2 (Vangl2), a core component of the planar cell polarity signaling pathway, is enriched in the dentate gyrus of adult mice. In this context, we sought to evaluate the involvement of this effector of the Wnt/PCP pathway in both adult neurogenesis and memory abilities in adult and middle-aged mice. Using a heterozygous mouse model carrying a dominant negative mutation in Vangl2 gene, we show that alteration in Vangl2 expression decreases the survival of adult-born granule cells and advances the onset of decrease in cognitive flexibility. Inability of mutant mice to erase old irrelevant information to the benefit of new relevant ones highlights a key role of Vangl2 in interference-based forgetting. Taken together, our findings show for the first that Vangl2 activity may constitute an interesting target to prevent age-related decline in hippocampal plasticity and memory.Bordeaux Region Aquitaine Initiative for NeuroscienceNeurogénèse hippocampique: un nouveau substrat de la mémoir

Lhx3, a LIM domain transcription factor, is regulated by Pou4f3 in the auditory but not in the vestibular system

A dominant mutation of the gene encoding the POU4F3 transcription factor underlies human non-syndromic progressive hearing loss DFNA15. Using oligonucleotide microarrays to generate expression profiles of inner ears of Pou4f3 ddl/ ddl mutant and wild-type mice, we have identified and validated Lhx3, a LIM domain transcription factor, as an in vivo target gene regulated by Pou4f3. Lhx3 is a hair cell-specific gene expressed in all hair cells of the auditory and vestibular system as early as embryonic day 16. The level of Lhx3 mRNA is greatly reduced in the inner ears of embryonic Pou4f3 mutant mice. Our data also show that the expression of Lhx3 is regulated differently in auditory and vestibular hair cells. This is the first example of a hair cell-specific gene expressed both in auditory and in vestibular hair cells, with differential regulation of expression in these two closely related systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72019/1/j.1460-9568.2007.05332.x.pd

Ciliary proteins Bbs8 and Ift20 promote planar cell polarity in the cochlea

Primary cilia have been implicated in the generation of planar cell polarity (PCP). However, variations in the severity of polarity defects in different cilia mutants, coupled with recent demonstrations of non-cilia-related actions of some cilia genes, make it difficult to determine the basis of these polarity defects. To address this issue, we evaluated PCP defects in cochlea from a selection of mice with mutations in cilia-related genes. Results indicated notable PCP defects, including mis-oriented hair cell stereociliary bundles, in Bbs8 and Ift20 single mutants that are more severe than in other cilia gene knockouts. In addition, deletion of either Bbs8 or Ift20 results in disruptions in asymmetric accumulation of the core PCP molecule Vangl2 in cochlear cells, suggesting a role for Bbs8 and/or Ift20, possibly upstream of core PCP asymmetry. Consistent with this, co-immunoprecipitation experiments indicate direct interactions of Bbs8 and Ift20 with Vangl2. We observed localization of Bbs and Ift proteins to filamentous actin as well as microtubules. This could implicate these molecules in selective trafficking of membrane proteins upstream of cytoskeletal reorganization, and identifies new roles for cilia-related proteins in cochlear PCP

Gα_i Proteins are Indispensable for Hearing

Background/Aims: From invertebrates to mammals, Gαi proteins act together with their common binding partner Gpsm2 to govern cell polarization and planar organization in virtually any polarized cell. Recently, we demonstrated that Gαi3-deficiency in pre-hearing murine cochleae pointed to a role of Gαi3 for asymmetric migration of the kinocilium as well as the orientation and shape of the stereociliary (“hair”) bundle, a requirement for the progression of mature hearing. We found that the lack of Gαi3 impairs stereociliary elongation and hair bundle shape in high-frequency cochlear regions, linked to elevated hearing thresholds for high-frequency sound. How these morphological defects translate into hearing phenotypes is not clear. Methods: Here, we studied global and conditional Gnai3 and Gnai2 mouse mutants deficient for either one or both Gαi proteins. Comparative analyses of global versus Foxg1-driven conditional mutants that mainly delete in the inner ear and telencephalon in combination with functional tests were applied to dissect essential and redundant functions of different Gαi isoforms and to assign specific defects to outer or inner hair cells, the auditory nerve, satellite cells or central auditory neurons. Results: Here we report that lack of Gαi3 but not of the ubiquitously expressed Gαi2 elevates hearing threshold, accompanied by impaired hair bundle elongation and shape in high-frequency cochlear regions. During the crucial reprogramming of the immature inner hair cell (IHC) synapse into a functional sensory synapse of the mature IHC deficiency for Gαi2 or Gαi3 had no impact. In contrast, double-deficiency for Gαi2 and Gαi3 isoforms results in abnormalities along the entire tonotopic axis including profound deafness associated with stereocilia defects. In these mice, postnatal IHC synapse maturation is also impaired. In addition, the analysis of conditional versus global Gαi3-deficient mice revealed that the amplitude of ABR wave IV was disproportionally elevated in comparison to ABR wave I indicating that Gαi3 is selectively involved in generation of neural gain during auditory processing. Conclusion: We propose a so far unrecognized complexity of isoform-specific and overlapping Gαi protein functions particular during final differentiation processes

Polarité planaire chez les Mammifères : similitudes et divergences avec la Drosophile

Les gènes de la polarité planaire (PP) furent initialement découverts chez les Invertébrés (Drosophila Melanogaster) pour leur rôle dans l'orientation uniforme de structure (cils, groupes de cellules) dans le plan de l'épithélium. Au cours de ces cinq dernières années, de nombreux travaux ont montré que chez les Vertébrés, et en particulier les Mammifères, certains homologues de ces gènes sont importants dans des mécanismes développementaux aussi divers que la fermeture de la gouttière neurale, la maladie polykystique du rein, les fonctions de l'oreille interne (audition, équilibre) ou encore la maladie de Bardet- Biedl. Ces processus font appel à un groupe de gènes dont l'implication dans des mécanismes de PP est conservée au cours de l'évolution pour certains, ou uniquement présente chez les Mammifères pour d'autres. En 2003, l'identification de la cochlée comme modèle d'étude de la PP chez les Vertébrés a ouvert la voie à l'identification des gènes importants chez les Mammifères. Les protéines codées par ces gènes sont des protéines de surface et des protéines de la signalisation intracellulaire dont les mécanismes d'action restent encore énigmatiques. Il semble de plus en plus évident que notre compréhension des mécanismes de la PP chez les Mammifères passe par l'analyse de gènes homologues à ceux de la Drosophile, mais également par l'identification de gènes spécifiques aux Mammifères

Semin Cell Dev Biol.

Since the first implication of the core planar cell polarity (PCP) pathway in stereocilia orientation of sensory hair cells in the mammalian cochlea, much has been written about this subject, in terms of understanding how this pathway can shape the mammalian hair cells and using the inner ear as a model system to understand mammalian PCP signaling. However, many conflicting results have arisen, leading to puzzling questions regarding the actual mechanism and roles of core PCP signaling in mammals and invertebrates. In this review, we summarize our current knowledge on the establishment of PCP during inner ear development and revisit the contrast between wing epithelial cells in Drosophila melanogaster and sensory epithelia in the mammalian cochlea. Notably, we focus on similarities and differences in the asymmetric distribution of core PCP proteins in the context of cell autonomous versus non-autonomous role of PCP signaling in the two systems. Additionally, we address the relationship between the kinocil- ium position and PCP in cochlear hair cells and increasing results suggest an alternate cell autonomous pathway in regulating PCP in sensory hair cells.Caractérisation moléculaire et fonctionnelle de vangl2 et de ses partenaires chez le mammifèr

Régulation de la protéine centrale de la polarité planaire cellulaire Vangl2 dans l'organe de Corti

Outre leur polarité apico-basale, certaines cellules épithéliales développent une seconde polarité, appelée Polarité Planaire Cellulaire (PCP). L'axe de la PCP est orienté perpendiculairement à l'axe de polarité apico-basale et régit l'orientation uniforme de certaines structures, comme les poils ou cils, non seulement à l'échelle de la cellule mais également au sein du tissu. L'épithélium cochléaire est l'un des meilleurs modèles d'étude de PCP chez les mammifères. En effet, les cellules neuro-épitheliales qui le composent, soutenues par des cellules de soutien, présentent à leur apex, des touffes ciliaires dont l'orientation est parfaitement coordonnée par la voie de la polarité planaire. Les deux premiers gènes impliqués dans la PCP chez les mammifères, Vangl2 et Scrib1, ont été identifiés sur la base du phénotype de la cochlée chez les mutants. L'analyse de la localisation de Vangl2 dans l'organe de Corti a également révélé une localisation asymétrique proximo-distale et transitoire de la protéine, perpendiculaire à l'axe apico-basal classique. Cette asymétrie apparaît à la jonction entre deux types cellulaires : une cellule sensorielle ciliée et une cellule de soutien. J'ai pu montrer au cours de mes travaux de thèse que cette asymétrie était majoritairement due à une accumulation de Vangl2 du côté distal des cellules de soutien, et que dans une moindre mesure, Vangl2 pouvait ségréger du côté distal des cellules ciliées. Cette localisation subcellulaire très précise et limitée dans l'espace semble être indépendante de l'expression du gène Scrib1 dans les cellules ciliées. La délétion du gène Scrib1 dans les cellules ciliées m'a toutefois permis de mettre en évidence que ce gène avait un rôle autonome dans la régulation de la PCP, et que les cellules de soutien de l'organe de Corti pouvaient jouer un rôle prépondérant dans le contrôle de la PCP. Mes travaux ont également permis de mettre en évidence que GIPC1 avait un rôle dans la régulation de la PCP et le maintien de l'intégrité des touffes ciliaires des cellules sensorielles, et que le complexe GIPC1/Myosine VI pouvait réguler l'établissement de l'asymétrie de Vangl2 dans l'organe de Corti.Several epithelia exhibit a second polarity perpendicular to the apico-basal axis, called planar polarity and that governs the orientation of structures such as stereocilia and hear. Our laboratory studies planar polarity, using mammalian cochlear sensory epithelium and we focus our studies on Vangl2, that we identified as the first mammalian planar polarity gene. Vangl2 encodes a four-transmembrane protein that contains a PDZ binding domain in its C-terminus tail. Vangl2 is asymmetrically located at the junction between mechanosensory hair cells and supporting cells, and this asymmetry appears important for planar cell polarity. I have shown in my thesis, using STED microscopy, that Vangl2 asymmetry is mainly due to an accumulation of Vangl2 to the distal side of supporting cells. I sought to dissect the molecular role of Vangl2 by analysing its trafficking within the cochlear epithelium. Deletion analysis shows that the last 12 amino acids, unlike its N-terminus tail are essential for Vangl2 endoplasmic reticulum sorting, its plasma membrane targeting and its function. Conditional mutant mice analysis show that Scrib1, which we have previously shown, interacts with Vangl2 through the PDZ binding domain of its C-terminal tail, is not the protein mediating this asymmetry. My work also highlight that GIPC1 had a role in the regulation of PCP and maintaining the integrity of hair bundles of sensory cells, and that the complex GIPC1/Myosin VI could regulate Vangl2 asymmetry in the organ of Corti.BORDEAUX2-Bib. électronique (335229905) / SudocSudocFranceF