Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

The most common quorum sensing (QS) system in Gram-negative bacteria occurs via N-acyl homoserine lactone (AHLs) signals. An archetypical system consists of a LuxI-family protein synthesizing the AHL signal which binds at quorum concentrations to the cognate LuxR-family transcription factors which then control gene expression by binding to specific sequences in target gene promoters. QS LuxR-family proteins are approximately 250 amino acids long and made up of two domains; at the N-terminus there is an autoinducer-binding domain whereas the C-terminus contains a DNA-binding helix-turn-helix (HTH) domain. QS LuxRs display surprisingly low similarities (18-25%) even if they respond to structurally similar AHLs. 95% of LuxRs share 9 highly conserved amino acid residues; six of these are hydrophobic or aromatic and form the cavity of the AHL-binding domain and the remaining three are in the HTH domain. With only very few exceptions, the luxI/R cognate genes of AHL QS systems are located adjacent to each other. The sequencing of many bacterial genomes has revealed that many proteobacteria also possess LuxRs that do not have a cognate LuxI protein associated with them. These LuxRs have been called orphans and more recently solos. LuxR solos are widespread in proteobacterial species that possess a canonical complete AHL QS system as well as in species that do not. In many cases more than one LuxR solo is present in a bacterial genome. Scientists are beginning to investigate these solos. Are solos responding to AHL signals? If present in a bacterium which possesses a canonical AHL QS system are solos an integral part of the regulatory circuit? Are LuxR solos eavesdropping on AHLs produced by neighboring bacteria? Have they evolved to respond to different signals instead of AHLs, and are these signals endogenously produced or exogenously provided? Are they involved in interkingdom signaling by responding to eukaryotic signals? Recent studies have revealed that LuxR solos are involved in several mechanisms of cell-cell communication in bacteria implicating them in bacterial intraspecies and interspecies communication as well as in interkingdom signaling by responding to molecules produced by eukaryotes. LuxR solos are likely to become major players in signaling since they are widespread among proteobacterial genomes and because initial studies highlight their different roles in bacterial communication. This Research Topic allows scientists studying or interested in LuxR solos to report their data and/or express their hypotheses and thoughts on this important and currently understudied family of signaling proteins.

LuxR solos --- Quorum Sensing --- signaling --- AHL --- Bacteria

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Outre un cytosquelette cortical bien structuré et fortement ancré à la membrane, le globule rouge (GR) jouit d’une concentration en calcium intracellulaire ([Ca2+]i) finement contrôlée , impliquée dans sa déformation et sa destruction et dérégulée dans plusieurs formes d’anémies héréditaires. Grâce à l’imagerie confocale vitale de GRs, le laboratoire d’accueil a découvert que plusieurs classes de lipides du feuillet externe de la membrane plasmique (phosphatidylcholine [PC], sphingomyéline [SM], ganglioside GM1 et cholestérol) s’organisent en domaines submicrométriques partiellement reliés spatialement. Cette démonstration a été permise grâce (i) à l’insertion d’analogues lipidiques fluorescents (BODIPY-PC, -SM et - GM1) à la membrane plasmique, ou (ii) au marquage direct de lipides endogènes (SM et cholestérol) avec des fragments non toxiques de toxines spécifiques (lysénine et theta, respectivement). Mon projet s’intéresse à l’importance des domaines lipidiques pour la déformation des GRs, via le recrutement et/ou l’activation de protéines impliquées dans les échanges de Ca2+. Le premier objectif de mon mémoire a consisté à évaluer l’importance du Ca2+ pour l’organisation de la membrane des GRs en domaines lipidiques. J’ai tout d’abord déterminé en microscopie vitale à fluorescence l’abondance des domaines enrichis en SM (mis en évidence par le BODIPY-SM ou la lysénine) après stimulation de l’influx (par un ionophore, le A23187) ou de l’efflux de Ca2+ (par incubation dans un milieu dépourvu de Ca2+ par l’EGTA augmente d’un facteur trois l’abondance des domaines enrichis en SM. Cet effet est spécifique de certains domaines lipidiques puisque seuls les domaines enrichis en SM ou en ganglioside GM1 sont augmentés, mais pas ceux enrichis en cholestérol ou en PC. La suite de mon mémoire s’est donc focalisée sur les domaines enrichis en SM. J’ai ensuite étudié l’importance des domaines enrichis en SM pour les échanges de Ca2+. Dans ce but, j’ai tiré profit de l’observation que ces domaines (i) disparaissent suite au traitement à la sphingomyélinase ou à la métyl-B-cyclodextrine, des agents qui déplètent respectivement le contenu membranaire en SM et en cholestérol ; et à l’inverse (ii) augmentent en nombre suite au découplage de la membrane de son cytosquelette sous-jacent par activation de la PKC. J’ai ainsi pu montrer que la disparition des domines suite au traitement de la sphingolmyélinase ou à la cyclodextrine induit une augmentation de la [Ca2+]i. J’ai également observé que l’augmentation du nombre de domaines suite au découplage de la membrane de son cytosquelette sous-jacent s’accompagne d’une diminution de la [Ca2+]i. L’ensemble des résultats de ces deux premières parties montre qu’il existe une relation inverse entre l’abondance des domaines enrichis en SM et la [Ca2+]i. Pour ensuite tenter d’établir s’il existe une relation entre les domaines lipidiques, la [Ca2+]i et la déformabilité des GRs, j’ai travaillé sur des GRs de patients atteints d’elliptocytose et de sphérocytose héréditaires, deux maladies de fragilité membranaire des GRs. Alors que la régulation des échanges de Ca2+ est affectée chez les GRs elliptocytotiques, le nombre de domaines n’est pas significativement modifié. Chez les GRs sphérocytotiques, le nombre de domaines et les échanges de Ca2+ sont affectés de manière inversement proportionnelle, suggérant que l’organisation de la membrane en domaines enrichis en SM et la [Ca2+]i pourraient jouer un rôle dans la déformabilité des GRs. J’ai enfin commencé à rechercher par quel mécanisme Ca2+ pourrait moduler les domaines enrichis en SM. Avec l’aide des doctorants du groupe, j’ai notamment évalué si une modification de la [Ca2+]i pouvait avoir des conséquences sur (i) l’asymétrie membranaire (translocation de la phosphatidylsérine au feuillet externe mis en évidence par marquage à l’Annexine V fluorescente), ou (ii) la fluidité membranaire (mesurée par insertion du laurdan à la membrane plasmique du GR). En conclusion, les données obtenues au cours de ce mémoire ont permis de montrer la relation entre [Ca2+]i et l’organisation de la membrane en certains domaines lipidiques, ceux enrichis en SM et en ganglioside GM1. D’autre part, mes résultats suggèrent une relation entre les domaines, les échanges de Ca2+ et la déformabilité du GR. Cette étude ouvre de nombreuses perspectives en biophysique. Besides a well-structured cytoskeleton strongly anchored to the membrane, the red blood cell (RBC) exhibits an intracellular calcium concentration [Ca 2+]i finely controlled, involved in RBC deformation and destruction and deregulated in several forms of hereditary anemias. Using vital confocal imaging of RBCs, the host laboratory discovered that several types of lipids (phosphatidylcholine (PC), sphingomyelin (SM), ganglioside GM1 and cholesterol) are organized into spatially connected submicrometric domains at the outer plasma membrane leaflet. This discovery was made possible thanks to (i) incorporation at the plasma membrane of fluorescent lipid analogs (BODIPY-PC, -SM and –GM1), or (ii) direct labeling of endogenous lipids (SM and cholesterol) with non-toxic fragments of specific toxins (lysenin and theta, respectively). My project focuses on the importance of lipid domains for RBC plasticity, through the recruitment and/or activation of proteins involved in the exchange of Ca2+.The first aim of my master thesis was to assess the importance of Ca2+ in the organization of RBC membrane lipids into domains. I first determined by vital fluorescence microcopy the abundance of domains enriched in SM (highlighted by plasma membrane insertion of BODIPY-SM or decoration of endogenous SM by lysenin) after stimulation of the Ca2+ influx (by the ionopohore A23187) or efflux (by incubation in medium lacking Ca2+, in combination or not with a chelation by EGTA). Thanks to those agents, I showed that a stimulation of Ca2+ efflux by EGTA strongly increases the number of SM-enriched domains. This effect is specific to some lipid domains since only the ones enriched in SM or GM1 are increased, whereas those enriched in cholesterol or PC are not affected. The rest of my master thesis thereby focused on the domains enriched in SM. I subsequently studied the importance of SM-enriched domains for the exchanges of Ca2 To this end, I took advantage of the observation that these domains disappear upon treatment with sphingomyelinase or methyl-13-cyclodextrin, two agents that respectively deplete the membrane content in SM and cholesterol. I was able to show that the disappearance of SM­ enriched domains due to these treatments induces an increase in [Ca2+]i. 1 also showed that the increased domain abundance by plasma membrane: cytoskeleton uncoupling at 4.lR complexes is linked to a decrease in [Ca2+li· All these results show thatthere is an inverse relationship between the abundance of SM-enriched domains and [Ca2+]i. To next establish whether there is a relationship between lipid domains, [Ca2+]i and RBC deformability, 1 worked on RBCs of patients suffering from hereditary spherocytosis and elliptocytosis, two RBC membrane fragility diseases. ln elliptocytosis, whereas Ca2+ exchanges are modified, the number of domains is not significantly altered. ln contrast, in spherocytotic RBCs,ca2+ exchanges are favored and the abundance of domains is increased as compared to control RBCs, suggesting that membrane organization in SM-enriched domains and Ca 2+ exchanges could play a role in RBC deformability. I finally started to examine by which mechanism Ca2+ could modulate SM-enriched domains. With the help of PhD students in the group, 1 evaluated whether a modification of [Ca2+L could affect (i) membrane asymmetry (by probing the translocation of phosphatidylserine to the outer leaflet by labeling with fluorescent Annexin V); or (ii) membrane fluidity (by laurdan insertion at the RBC plasma membrane).ln conclusion, the data obtained in this master thesis have shown the relation between [Ca2+]i and the organization of the plasma membrane in domains enriched in SM (and ganglioside GM1). Moreover, my results suggest a relationship between domains, Ca2+ efflux and RBC plasticity. This study opens up many prospects in biophysics.

Lipid-Linked Proteins --- Calcium-Binding Proteins --- Calcium Signaling

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Activity within neural circuits shapes the synaptic properties of component neurons in a manner that maintains stable excitatory drive, a process referred to as homeostatic plasticity. These potent and adaptive mechanisms have been demonstrated to modulate activity at the level of an individual neuron, synapse, circuit, or entire network, and dysregulation at some or all of these levels may contribute to neuropsychiatric disorders, intellectual disability, and epilepsy. Greater mechanistic understanding of homeostatic plasticity will provide key insights into the etiology of these disorders, which may result from network instability and synaptic dysfunction. Over the past 15 years, the molecular mechanisms of this form of plasticity have been intensely studied in various model organisms, including invertebrates and vertebrates. Though once thought to have a predominantly postsynaptic basis, emerging evidence suggests that homeostatic mechanisms act on both sides of the synapse through mechanisms such as retrograde signaling, to orchestrate compensatory adaptations that maintain stable network function. These trans-synaptic signaling systems ultimately alter neurotransmitter release probability by a variety of mechanisms including changes in vesicle pool size and calcium influx. These adaptations are not expected to occur homogenously at all terminals of a pre-synaptic neuron, as they might synapse with neurons in non-overlapping circuits. However, the factors that govern the homeostatic control of synapse-specific plasticity are only beginning to be understood. In addition to our limited molecular understanding of pre-synaptic homeostatic plasticity, very little is known about its prevalence in vivo or its physiological and disease relevance. In this research topic, we aim to fill the aforementioned void by covering a broad range of topics that include: - Identification of signaling pathways and mechanisms that operate globally or locally to induce specific pre-synaptic adaptations - The nature of pre-synaptic ion channels relevant to this form of plasticity and their synapse-specific modulation and trafficking - Development and utilization of new tools or methods to study homeostatic plasticity in axons and pre-synaptic terminals - Novel mechanisms of homeostatic adaptations in pre-synaptic neurons - Postsynaptic sensors of activity and retrograde synaptic signaling systems - A comprehensive analysis of the kinds of pre-synaptic adaptations in diverse neural circuits and cell types - Identification of physiological or developmental conditions that promote pre-synaptic homeostatic adaptations - How activity-dependent (Hebbian) and homeostatic synaptic changes are integrated to both permit sufficient flexibility and maintain stable activity - Relevance of pre-synaptic homeostatic plasticity to the etiology of neuropsychiatric disorders - Computational modeling of pre-synaptic homeostatic plasticity and network stability.

homeostatic plasticity --- retrograde signaling --- Neurological Disease --- Presynaptic adaptation --- neurotransmitter release

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

The Centers for Disease Control and Prevention estimate that 1 in 68 children in the United states is afflicted with autism spectrum disorders (ASD), yet at this time, there is no cure for the disease. Autism is characterized by delays in the development of many basic skills, most notably the ability to socialize and adapt to novelty. The condition is typically identified in children around 3 years of age, however the high heritability of autism suggests that the disease process begins at conception. The identification of over 500 ASD risk genes, has enabled the molecular genetic dissection of the pathogenesis of the disease in model organisms such as mice. Despite the genetic heterogeneity of ASD etiology, converging evidence suggests that these disparate genetic lesions may result in the disruption of a limited number of key biochemical pathways or circuits. Classification of patients into groups by pathogenic rather than etiological categories, will likely aid future therapeutic development and clinical trials. In this set of papers, we explore the existing evidence supporting this view. Specifically, we focus on biochemical cascades such as mTOR and ERK signaling, the mRNA network bound by FMRP and UBE3A, dorsal and ventral striatal circuits, cerebellar circuits, hypothalamic projections, as well as prefrontal and anterior cingulate cortical circuits. Special attention will be given to studies that demonstrate the necessity and/or sufficiency of genetic disruptions (e.g. by molecular deletion and/or replacement) in these pathways and circuits for producing characteristic behavioral features of autism. Necessarily these papers will be heavily weighted towards basic mechanisms elucidated in animal models, but may also include investigations in patients.

Cerebellum --- Striatum --- Oxytocin --- mTOR --- Hypothalamus --- Neurodevelopmental disorders --- Cell signaling

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

In response to environmental stresses, or during development, plant cells will produce lipids that will act as intracellular or intercellular mediators. Glycerophospholipid and/or sphingolipid second messengers resulting from the action of lipid metabolizing enzymes (e.g. lipid-kinases or lipases) are commonly found within cells. The importance of such mediating lipids in plants has become increasingly apparent. Responses to biotic and abiotic stresses, and to plant hormones, all appear to involve and require lipid signals. Likewise, developmental processes, in particular polarized growth, seem also to involve signalling lipids. Amongst these lipids, phosphatidic acid (PA) has received the most attention. It can be produced by phospholipases D, but also by diacylglycerol kinases coupled to phospholipases C. Proteins that bind phosphatidic acid, and for which the activity is altered upon binding, have been identified. Furthermore, other lipids are also important in signalling processes. PA can be phosphorylated into diacylglycerol-pyrophosphate, and plants are one of the first biological models where the production of this lipid has been reported, and its implication in signal transduction have been demonstrated. PA can also be deacylated into lyso- phosphatidic acid. The phosphorylated phosphatidylinositols, i.e. the phosphoinositides, can act as substrate of phospholipases C, but are also mediating lipids per se, since proteins that bind them have been identified. Other important lipid mediators belong to the sphingolipid family such the phosphorylated phytosphingosine, or long-chain bases. Many questions remain unanswered concerning lipid signalling in plants. Understanding and discussing current knowledge on these mechanisms will provide insights into plant mechanisms in response to constraints, either developmental or environmental.

lipid-kinases --- Inositolphosphates --- diacylglycerolpyrophosphate --- Phospholipases --- phosphatidic acid --- lipid signaling --- phosphoinositides