Dynamics of glutamatergic signaling in the mushroom body of young adult Drosophila

<p>Abstract</p> <p>Background</p> <p>The mushroom bodies (MBs) are paired brain centers located in the insect protocerebrum involved in olfactory learning and memory and other associative functions. Processes from the Kenyon cells (KCs), their intrinsic neurons, form the bulk of the MB's calyx, pedunculus and lobes. In young adult <it>Drosophila</it>, the last-born KCs extend their processes in the α/β lobes as a thin core (α/β cores) that is embedded in the surrounding matrix of other mature KC processes. A high level of L-glutamate (Glu) immunoreactivity is present in the α/β cores (α/βc) of recently eclosed adult flies. In a <it>Drosophila </it>model of fragile X syndrome, the main cause of inherited mental retardation, treatment with metabotropic Glu receptor (mGluR) antagonists can rescue memory deficits and MB structural defects.</p> <p>Results</p> <p>To address the role of Glu signaling in the development and maturation of the MB, we have compared the time course of Glu immunoreactivity with the expression of various glutamatergic markers at various times, that is, 1 hour, 1 day and 10 days after adult eclosion. We observed that last-born α/βc KCs in young adult as well as developing KCs in late larva and at various pupal stages transiently express high level of Glu immunoreactivity in <it>Drosophila</it>. One day after eclosion, the Glu level was already markedly reduced in the α/βc neurons. Glial cell processes expressing glutamine synthetase and the Glu transporter dEAAT1 were found to surround the Glu-expressing KCs in very young adults, subsequently enwrapping the α/β lobes to become distributed equally over the entire MB neuropil. The vesicular Glu transporter DVGluT was detected by immunostaining in processes that project within the MB lobes and pedunculus, but this transporter is apparently never expressed by the KCs themselves. The NMDA receptor subunit dNR1 is widely expressed in the MB neuropil just after eclosion, but was not detected in the α/βc neurons. In contrast, we provide evidence that DmGluRA, the only <it>Drosophila </it>mGluR, is specifically expressed in Glu-accumulating cells of the MB α/βc immediately and for a short time after eclosion.</p> <p>Conclusions</p> <p>The distribution and dynamics of glutamatergic markers indicate that newborn KCs transiently accumulate Glu at a high level in late pupal and young eclosed <it>Drosophila</it>, and may locally release this amino acid by a mechanism that would not involve DVGluT. At this stage, Glu can bind to intrinsic mGluRs abundant in the α/βc KCs, and to NMDA receptors in the rest of the MB neuropil, before being captured and metabolized in surrounding glial cells. This suggests that Glu acts as an autocrine or paracrine agent that contributes to the structural and functional maturation of the MB during the first hours of <it>Drosophila </it>adult life.</p

On perturbations of Dirac operators with variable magnetic field of constant direction

We carry out the spectral analysis of matrix valued perturbations of 3-dimensional Dirac operators with variable magnetic field of constant direction. Under suitable assumptions on the magnetic field and on the pertubations, we obtain a limiting absorption principle, we prove the absence of singular continuous spectrum in certain intervals and state properties of the point spectrum. Various situations, for example when the magnetic field is constant, periodic or diverging at infinity, are covered. The importance of an internal-type operator (a 2-dimensional Dirac operator) is also revealed in our study. The proofs rely on commutator methods.Comment: 12 page

A novel neuron-specific regulator of the V-ATPase in Drosophila

The V-ATPase is a highly conserved enzymatic complex that ensures appropriate levels of organelle acidification in virtually all eukaryotic cells. While the general mechanisms of this proton pump have been well studied, little is known about the specific regulations of neuronal V-ATPase. Here, we studied CG31030, a previously uncharacterized Drosophila protein predicted from its sequence homology to be part of the V-ATPase family. In contrast to its ortholog ATP6AP1/VhaAC45 which is ubiquitous, we observed that CG31030 expression is apparently restricted to all neurons, and using CRISPR/Cas9-mediated gene tagging, that it is mainly addressed to synaptic terminals. In addition, we observed that CG31030 is essential for fly survival and that this protein co-immunoprecipitates with identified V-ATPase subunits, and in particular ATP6AP2. Using a genetically-encoded pH probe (VMAT-pHluorin) and electrophysiological recordings at the larval neuromuscular junction, we show that CG31030 knock-down induces a major defect in synaptic vesicle acidification and a decrease in quantal size, which is the amplitude of the postsynaptic response to the release of a single synaptic vesicle. These defects were associated with severe locomotor impairments. Overall, our data indicate that CG31030, which we renamed VhaAC45-related protein (VhaAC45RP), is a specific regulator of neuronal V-ATPase in Drosophila that is required for proper synaptic vesicle acidification and neurotransmitter release

The serotonergic central nervous system of the Drosophila larva: anatomy and behavioral function.

The Drosophila larva has turned into a particularly simple model system for studying the neuronal basis of innate behaviors and higher brain functions. Neuronal networks involved in olfaction, gustation, vision and learning and memory have been described during the last decade, often up to the single-cell level. Thus, most of these sensory networks are substantially defined, from the sensory level up to third-order neurons. This is especially true for the olfactory system of the larva. Given the wealth of genetic tools in Drosophila it is now possible to address the question how modulatory systems interfere with sensory systems and affect learning and memory. Here we focus on the serotonergic system that was shown to be involved in mammalian and insect sensory perception as well as learning and memory. Larval studies suggested that the serotonergic system is involved in the modulation of olfaction, feeding, vision and heart rate regulation. In a dual anatomical and behavioral approach we describe the basic anatomy of the larval serotonergic system, down to the single-cell level. In parallel, by expressing apoptosis-inducing genes during embryonic and larval development, we ablate most of the serotonergic neurons within the larval central nervous system. When testing these animals for naïve odor, sugar, salt and light perception, no profound phenotype was detectable; even appetitive and aversive learning was normal. Our results provide the first comprehensive description of the neuronal network of the larval serotonergic system. Moreover, they suggest that serotonin per se is not necessary for any of the behaviors tested. However, our data do not exclude that this system may modulate or fine-tune a wide set of behaviors, similar to its reported function in other insect species or in mammals. Based on our observations and the availability of a wide variety of genetic tools, this issue can now be addressed

Contribution a la caracterisation biochimique du mecanisme de la liberation de l'acethylcholine, etudie sur les synaptosomes de l'organe electrique de la torpille et dans des systemes reconstitues

SIGLECNRS T 59793 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Mécanismes moléculaires et de signalisation induits par le stress oxydatif dans des modèles in vivo de la maladie de Parkinson chez la drosophile (intoxication au paraquat et expression de l'a-synucléine)

La maladie de Parkinson (MP) est une maladie neurodégénérative qui se caractérise par la perte progressive des neurones dopaminergiques (DA) de la substance noire, une structure sous-corticale des ganglions de la base. Si la majorité des cas sont sporadiques, l exposition à des facteurs environnementaux (composés organochlorés, pesticides) ou des mutations associées à une quinzaine de gènes (dardarine, -synucléine, ) sont connues pour être à l origine de formes de cette maladie. L -synucléine est également le composant majoritaire des corps de Lewy, inclusions cytoplasmiques présentes dans les neurones DA des patients. Pendant mon doctorat, je me suis attachée à comprendre les mécanismes de neurotoxicité induits par le paraquat (PQ), un générateur de stress oxydatif impliqué dans la MP. Ces recherches ont mis en évidence une implication de la signalisation DA dans la toxicité du PQ dans le système nerveux central par l activation aberrante d un récepteur DA de type D1, impliqué dans la mémoire chez la drosophile. L inactivation de ce récepteur dans les neurones glutamatergiques protège significativement les drosophiles contre les effets délétères du PQ. Je me suis également intéressée aux mécanismes de neurotoxicité de l -synucléine chez la drosophile et son rapport avec le stress oxydatif. Cette étude m a mené au développement d une technique de mise en culture du système nerveux central entier de drosophile permettant l étude des effets progressifs de l -synucléine sur la dynamique vésiculaire dans les axones DA par des expériences de FRAP. Ces travaux contribuent à mieux comprendre les rapports entre dopamine et stress oxydatif dans la pathogenèse de la MPParkinson s disease (PD) is well characterized as a neurodegenerative disease with progressive loss of dopaminergic neurons (DAn) from substantia nigra, a subcortical structure of the basal ganglia. Most of time, PD is sporadic but it is known that exposure to environmental toxins like pesticides or mutations of genes like -synuclein can cause PD. -syncuclein is the main component of Lewy s bodies, which are cytoplasmic inclusions present in DAn in PD. During my Ph.D., I focused first on the study of paraquat (PQ) neurotoxicity, a strong oxidative stress generator involved in PD. Our results show that PQ toxicity can be triggered by dopamine signaling trough a D1-like dopamine receptor known mainly for its involvement in memory processes in Drosophila. Inactivation of this receptor in glutamatergic neurons was found to be protective against PQ toxicity in Drosophila. Later, I focused on the study of a-synuclein neurotoxicity and its relationship with oxidative stress. This led to the development of a whole Drosophila central nervous system explants culture technique that allowed study of a-synuclein effects on vesicular dynamic along the axons of DAn through FRAP experiments. This study led to a better understanding of the relationships between DA and oxidative stress in the PD s pathogenesisPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Identification des transporteurs d'acides aminés excitateurs chez la Drosophile et analyse de leurs profils d'expression au cours du développement

AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

La chorée de Huntington chez la drosophile et chez la souris: vers de nouvelles pistes thérapeutiques?

La chorée de Huntington est une maladie neurodégénérative héréditaire dominante, caractérisée par l’apparition progressive d’une dyskinésie, de déficits cognitifs et de troubles émotionnels. Près d’une décennie après l’identification du gène et de la mutation responsable de cette maladie, celle-ci reste incurable. Néanmoins, le développement de modèles transgéniques a permis une avancée majeure dans la connaissance des mécanismes cellulaires et moléculaires précoces de la maladie. La mutation conduirait à un dérèglement de la transcription, à une altération de la dégradation des protéines défectueuses par les protéasomes, ainsi qu’à des processus excitotoxiques et à un dysfonctionnement des mitochondries. Cet article souligne les apports récents de l’utilisation de modèles transgéniques chez la souris et chez la drosophile dans la compréhension de la pathogénie et dans l’élaboration de nouvelles stratégies thérapeutiques.Huntington’s disease is an hereditary dominant neurodegenerative disorder clinically characterised by progressive dyskinesia, cognitive decline and psychiatric disturbances. One decade after the identification of the gene whose mutation is responsible for the disease, this pathology remains incurable. However, major insights into early cellular and molecular basis of Huntington’s disease have arisen from transgenic models. Transcriptional dysregulation, abnormal degradation of misfolded proteins as well as excitotoxic processes and mitochondrial dysfunction are involved in Huntington’s disease. The present review discusses the recent insights gained from mouse and Drosophila models towards the understanding of pathogenesis and the development of new therapeutic tools

Les astrocytes dans la chorée de Huntington

La chorée de Huntington est une maladie neurodégénérative héréditaire dominante caractérisée par l’apparition progressive de déficits moteurs, de troubles émotionnels et de l’humeur, ainsi que d’une détérioration des capacités intellectuelles. Elle aboutit irrémédiablement au décès des patients après environ 15-20 ans. Les études sur cette maladie ont pour la plupart avant tout cherché à identifier les mécanismes intrinsèques qui conduisent certaines populations de neurones à dysfonctionner, puis à dégénérer. Ce n’est que depuis les cinq dernières années que l’intérêt s’est aussi porté sur d’autres cellules du cerveau : les astrocytes. Cet article présente les arguments qui ont permis aujourd’hui d’admettre que le fonctionnement des astrocytes est également compromis dans la chorée de Huntington. Parmi les mécanismes possibles, la mutation responsable de cette maladie pourrait altérer la voie de signalisation du récepteur à l’EGF, qui régule en particulier la réponse des astrocytes à une atteinte des neurones

Régulation génétique de la différenciation des cellules dopaminergiques (contrôle transcriptionnel et post-transcriptionnel de l'expression de la tyrosine chez Drosophila melanogaster)

AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF