Implications des cellules non sensorielles dans le développement de l'organe de l'audition murin

Chez les mammifères, la perception des sons est rendue possible grâce à un épithélium sensoriel localisé dans l’oreille interne : l’organe de Corti. Celui-ci est constitué par deux types de cellules mécanosensorielles ainsi que par quatre autres types de cellules de soutien organisées en une mosaïque hautement ordonnée s’étalant sur toute la longueur du canal cochléaire. L’audition joue un rôle fondamental dans la survie et la reproduction des mammifères. Chez l’humain, ce sens est primordial dans la communication entre individus, conditionnant à la fois l’apprentissage et l’utilisation des échanges vocaux et influençant les interactions sociales. Dès lors, une perte de l’audition induit inévitablement une baisse de qualité de vie. Lorsque cette perte auditive est provoquée par une dégénérescence des cellules sensorielles de l’organe de Corti, elle est alors incurable ; l’épithélium sensoriel ne pouvant pas se régénérer. Dans ce contexte, la compréhension des différents mécanismes impliqués dans le développement de l’organe de l’audition paraît essentielle dans l’élaboration de stratégies thérapeutiques visant un rétablissement de la fonction auditive. Grâce à de nouvelles méthodes d’investigation, de grands progrès ont été réalisés ces deux dernières décennies. Néanmoins, de nombreuses questions concernant le développement morphologique, cellulaire et moléculaire de l’organe de l’audition des mammifères restent en suspend. Dans le présent travail, nous avons étudié le développement de l’organe de Corti avec une attention particulière portée aux cellules de soutien. Nos observations montrent que durant la mise en place de l’organe de Corti, la première cellule qui se distingue n’est pas une cellule sensorielle mais une cellule pilier interne et qu’au sein de cette dernière, la voie de signalisation Notch ne semble pas activée, contrairement à ce qui est observé dans les autres cellules de soutien. Nous mettons également pour la première fois en évidence une transition épithélio-mésenchymateuse partielle ainsi que l’apparition de microtubules à 15 protofilaments au sein des cellules de soutien durant une étape clé du remodelage de l’organe de Corti. De plus, nous montrons que l’acétylation de ces microtubules n’est pas indispensable à leur structure à 15 protofilaments. L’ensemble de nos résultats indiquent l’important rôle que jouent les cellules de soutien durant la mise en place et le remodelage de l’organe de Corti

Laser-Excited Elastic Guided Waves Reveal the Complex Mechanics of Nanoporous Silicon

Nanoporosity in silicon leads to completely new functionalities of this mainstream semiconductor. A difficult to assess mechanics has however significantly limited its application in fields ranging from nanofluidics and biosensorics to drug delivery, energy storage and photonics. Here, we present a study on laser-excited elastic guided waves detected contactless and non-destructively in dry and liquid-infused single-crystalline porous silicon. These experiments reveal that the self-organised formation of 100 billions of parallel nanopores per square centimetre cross section results in a nearly isotropic elasticity perpendicular to the pore axes and an 80% effective stiffness reduction, altogether leading to significant deviations from the cubic anisotropy observed in bulk silicon. Our thorough assessment of the wafer-scale mechanics of nanoporous silicon provides the base for predictive applications in robust on-chip devices and evidences that recent breakthroughs in laser ultrasonics open up entirely new frontiers for in-situ, non-destructive mechanical characterisation of dry and liquid-functionalised porous materials.Comment: 12 pages, 8 figures, Supplementary information available as ancillary file, in pres

Cochlear connexin 30 homomeric and heteromeric channels exhibit distinct assembly mechanisms.

Many of the mutations in GJB2 and GJB6, which encode connexins 26 and 30 (Cx26 and Cx30), impair the formation of membrane channels and cause autosomal syndromic and non-syndromic hearing loss. In cochlear non-sensory supporting cells, Cx26 and Cx30 form two types of homomeric and heteromeric gap junctions. The biogenesis processes of these channels occurring in situ remain largely unknown. Here we show that Cx30 homomeric and Cx26/Cx30 heteromeric gap junctions exhibit distinct assembly mechanisms in the cochlea. When expressed as homomeric channels, Cx30 preferentially interacts with beta-actin in the peripheral non-junctional membrane region, called perinexus, and strongly relies on the actin network for gap junction plaque assembly. In contrast, we found that Cx26/Cx30 heteromeric gap junction plaques are devoid of perinexus and associated actin network, and resist to actin-depolymerizating drug. This supports that Cx26/Cx30 oligomers could be directly delivered from the interior of the cell to the junctional plaque. Altogether, our data provide a novel insight in homomeric and heteromeric gap junction plaque assembly in the cochlea

Experimental and Numerical analysis of a Solar Rotary Kiln for Continuous Treatment of Particle Material

Several energy intensive industrial processes, such as cement production, require particulate material to be treated at high temperatures. Renewable energy could be used to remove the reliance upon fossil fuels in such processes, and of the available technologies concentrated solar energy is perfectly adapted to provide a high temperature energy source. With this objective, the present study focuses on a solar reactor continuously transferring concentrated solar radiation to a bed of flowing particles. Rotary kilns are the chosen concept due to their technical maturity, easy control and simple design. The feasibility of a solar driven rotary kiln has already been proven at lab-scale, with the successful calcination of materials up to a scale of kg/h. The present work describes a large solar rotary kiln able to heat particles to over 1000 °C at flow rates of up to 20 kg/h. The thermal performance of the reactor was evaluated through an on-sun experimental campaign, performed in the high flux solar simulator at the DLR. During one test, 17 kg/h of particles were heated up to 990 °C, with a thermal efficiency of 45 %. An improvement of the efficiency can be obtained by optimizing the reactor. To do this, a numerical model was developed and its parameters fit to the measured data. Simulations were used to quantify the different heat loss mechanisms, and to explore ways of reducing them. The promising experimental results, together with the mprovements suggested by the model, provide the basis for an upcoming chemical campaign, where the calcination of CaCO3 and the effect of endothermic reactions on the temperature distribution will be investigated

Hypervulnerability to Sound Exposure through Impaired Adaptive Proliferation of Peroxisomes

A deficiency in pejvakin, a protein of unknown function, causes a strikingly heterogeneous form of human deafness. Pejvakin-deficient (Pjvk(-/-)) mice also exhibit variable auditory phenotypes. Correlation between their hearing thresholds and the number of pups per cage suggest a possible harmful effect of pup vocalizations. Direct sound or electrical stimulation show that the cochlear sensory hair cells and auditory pathway neurons of Pjvk(-/-) mice and patients are exceptionally vulnerable to sound. Subcellular analysis revealed that pejvakin is associated with peroxisomes and required for their oxidative-stress-induced proliferation. Pjvk(-/-) cochleas display features of marked oxidative stress and impaired antioxidant defenses, and peroxisomes in Pjvk(-/-) hair cells show structural abnormalities after the onset of hearing. Noise exposure rapidly upregulates Pjvk cochlear transcription in wild-type mice and triggers peroxisome proliferation in hair cells and primary auditory neurons. Our results reveal that the antioxidant activity of peroxisomes protects the auditory system against noise-induced damage

Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Our galaxy

As we learn more about the multi-scale interstellar medium (ISM) of our Galaxy, we develop a greater understanding for the complex relationships between the large-scale diffuse gas and dust in Giant Molecular Clouds (GMCs), how it moves, how it is affected by the nearby massive stars, and which portions of those GMCs eventually collapse into star forming regions. The complex interactions of those gas, dust and stellar populations form what has come to be known as the ecology of our Galaxy. Because we are deeply embedded in the plane of our Galaxy, it takes up a significant fraction of the sky, with complex dust lanes scattered throughout the optically recognizable bands of the Milky Way. These bands become bright at (sub-)millimetre wavelengths, where we can study dust thermal emission and the chemical and kinematic signatures of the gas. To properly study such large-scale environments, requires deep, large area surveys that are not possible with current facilities. Moreover, where stars form, so too do planetary systems, growing from the dust and gas in circumstellar discs, to planets and planetesimal belts. Understanding the evolution of these belts requires deep imaging capable of studying belts around young stellar objects to Kuiper belt analogues around the nearest stars. Here we present a plan for observing the Galactic Plane and circumstellar environments to quantify the physical structure, the magnetic fields, the dynamics, chemistry, star formation, and planetary system evolution of the galaxy in which we live with AtLAST; a concept for a new, 50m single-dish sub-mm telescope with a large field of view which is the only type of facility that will allow us to observe our Galaxy deeply and widely enough to make a leap forward in our understanding of our local ecology

DNA Labeling at Electron Microscopy

peer reviewedHere, we describe a method for locating DNA on ultrathin sections. This technique is compatible with all usual fixation and embedding procedures and can be combined with cytochemical methods. Ultrathin sections are incubated in a medium containing terminal deoxynucleotidyl transferase (TdT) and various non-isotopic nucleotide analogs. The labeled nucleotides bound to the surface of ultrathin sections are then visualized by an indirect immunogold labeling technique. This high-resolution method provides a powerful tool for pinpointing the precise location of DNA within biological material, even where DNA is present in very low amounts

Spatio-temporal localization of the glial fibrillary acidic protein (GFAP) in the spiral ganglion from the 16th embryonic day until the 25th postnatal day in rats

The spiral ganglion (SG) is responsible for the conduction of the information between the sensory epithelium of the auditory organ (the organ of Corti) and the central nervous system. The origin and nature of the SG glial cells in mammals are barely known, although glial cells are essential to the development and the working of the nervous system. Using confocal microscopy, we studied the spatio-temporal distribution of the GFAP in the rat SG from the 16th embryonic day (E16) until the 25th postnatal day (P25). We performed a double-labelling experiment targeting GFAP- and betaIIItubulin-positive cells. BetaIII-tubulin is used for the labelling of (pro)neural cells, according to a previous preliminary study from our team. Our first results show clearly that the GFAP is expressed in the SG from P0 until P25. A homogenous labelling is found in the cytoplasm of a few dispersed unidentified cells among the (pro)neurons, whereas a granular labelling appears among a group of cells neighbouring the bundle of fibers innervating the organ of Corti. The identity of the GFAP-positive cells will be further investigated by electron microscopy. The reason why the labelling of the GFAP adopts those two different aspects is still unknown. Moreover, it seems that, surprisingly, some cells of the ganglion are not labelled by either marker. The possibility that such cells correspond to fibroblasts will be tested thanks to the labelling of vimentin.Origine et caractérisation des cellules gliales du ganglion spiralé au cours du développement chez les mammifère

Spatio‑temporal dynamics of β‑tubulin isotypes during the development of the sensory auditory organ in rat

There are different β-tubulin isoforms in microtubules of vertebrate tissues. However, their functional significance is still largely unknown. In the present study, we investigated the localization of five β-tubulin isotypes (β1– 5) within the hearing organ during development in rat. By using confocal microscopy, we showed that with the exception of the β3-tubulin isoform that was specific to nerve fibres, all the different β-tubulin isoforms were mainly present in the supporting cells. Contrary to β1–4-tubulins, we also found that the β5-tubulin isoform appeared only at a key stage of the post-natal development in specific cell types (pillar cells and Deiters’ cells). By using transmission electron microscopy, we revealed further that this developmental stage coincided with the formation of two separate bundles of microtubules from a unique one in these supporting cells. Together, these results suggest that the β5-tubulin isoform might be involved in the generation of new microtubule bundles from a pre-existing one