Hippocampal Dendritic Spines Are Segregated Depending on Their Actin Polymerization

Dendritic spines are mushroom-shaped protrusions of the postsynaptic membrane. Spines receive the majority of glutamatergic synaptic inputs. Their morphology, dynamics, and density have been related to synaptic plasticity and learning. The main determinant of spine shape is filamentous actin. Using FRAP, we have reexamined the actin dynamics of individual spines from pyramidal hippocampal neurons, both in cultures and in hippocampal organotypic slices. Our results indicate that, in cultures, the actin mobile fraction is independently regulated at the individual spine level, and mobile fraction values do not correlate with either age or distance from the soma. The most significant factor regulating actin mobile fraction was the presence of astrocytes in the culture substrate. Spines from neurons growing in the virtual absence of astrocytes have a more stable actin cytoskeleton, while spines from neurons growing in close contact with astrocytes show a more dynamic cytoskeleton. According to their recovery time, spines were distributed into two populations with slower and faster recovery times, while spines from slice cultures were grouped into one population. Finally, employing fast lineal acquisition protocols, we confirmed the existence of loci with high polymerization rates within the spine

MAP1B Light Chain Modulates Synaptic Transmission via AMPA Receptor Intracellular Trapping.

The regulated transport of AMPA-type glutamate receptors (AMPARs) to the synaptic membrane is a key mechanism to determine the strength of excitatory synaptic transmission in the brain. In this work, we uncovered a new role for the microtubule-associated protein MAP1B in modulating access of AMPARs to the postsynaptic membrane. Using mice and rats of either sex, we show that MAP1B light chain (LC) accumulates in the somatodendritic compartment of hippocampal neurons, where it forms immobile complexes on microtubules that limit vesicular transport. These complexes restrict AMPAR dendritic mobility, leading to the intracellular trapping of receptors and impairing their access to the dendritic surface and spines. Accordingly, increasing MAP1B-LC expression depresses AMPAR-mediated synaptic transmission. This effect is specific for the GluA2 subunit of the AMPAR and requires glutamate receptor interacting protein 1 (GRIP1) interaction with MAP1B-LC. Therefore, MAP1B-LC represents an alternative link between GRIP1-AMPARs and microtubules that does not result in productive transport, but rather limits AMPAR availability for synaptic insertion, with a direct impact on synaptic transmission.pre-print7208 K

Hippocampal Dendritic Spines Are Segregated Depending on Their Actin Polymerization

Dendritic spines are mushroom-shaped protrusions of the postsynaptic membrane. Spines receive the majority of glutamatergic synaptic inputs. Their morphology, dynamics, and density have been related to synaptic plasticity and learning. The main determinant of spine shape is filamentous actin. Using FRAP, we have reexamined the actin dynamics of individual spines from pyramidal hippocampal neurons, both in cultures and in hippocampal organotypic slices. Our results indicate that, in cultures, the actin mobile fraction is independently regulated at the individual spine level, and mobile fraction values do not correlate with either age or distance from the soma. The most significant factor regulating actin mobile fraction was the presence of astrocytes in the culture substrate. Spines from neurons growing in the virtual absence of astrocytes have a more stable actin cytoskeleton, while spines from neurons growing in close contact with astrocytes show a more dynamic cytoskeleton. According to their recovery time, spines were distributed into two populations with slower and faster recovery times, while spines from slice cultures were grouped into one population. Finally, employing fast lineal acquisition protocols, we confirmed the existence of loci with high polymerization rates within the spine

Sustainable livelihoods to adaptive capabilities: a global learning journey in a small state, Zanzibar

This thesis takes global learning out of the formal setting of a Northern classroom to a rural community setting in the Global South as a social learning process. It begins with a critical reflection of a large EU project to develop a global learning programme as a Global North South initiative. The focus narrows to Zanzibar, a small island state, to critically reflect on the delivery of the programme. And then further to focus on the global social learning and change that occurred in a rural community setting in the north of the island. Through participatory action research, I investigate the relevance of global learning as a social learning process, how norms and rules are shaped within a community setting and how these enable social change towards sustainable livelihoods. The thesis splices the intersection between critical and social theories of learning and engagement, to include critical social theories of Habermas (1984) and Wals (2007); critical race theories of Giroux (1997) and Said (1994) and distributive justice and entitlements theories of Sen (1997) and Moser (1998). It demonstrates the importance of dissonance and a safe space for deliberative dialogue, to be able to consider the global pressures and forces on local realities as the precursor to social change towards sustainability. I conclude by relating the learning from this small island state to the wider world and the current discourse on quality of education in a community development context

Valeur prédictive de la spectroscopie par résonance magnétique sur le devenir neurodéveloppemental à l'âge de 2 ans chez une cohorte de nouveau-nés grands prématurés

Despite progress in the survival of preterm children, their neurocognitive development remains a concern. Prematurity itself has a minor influence on neurodevelopmental fate, while per-natal factors have a predominant role in predicting their outcome. These factors include intrinsic factors such as intra-uterine growth restriction, or extrinsic factors such as antenatal cortico-therapy. Thus, the early identification (corrected term) of infants at high risk of neurodevelopmental disorder will allow appropriate and early support. However, precise prognostic markers are currently lacking to assess this risk. Magnetic resonance spectroscopy (MRS) objectively measures brain biochemistry in vivo. MRS is an imaging technique studying cerebral metabolism and variations in the concentration of metabolites, which is already used to characterize various pathologies such as anoxoischemia encephalopathy. Therefore, we believe that tissue metabolites can serve as important early diagnostic and prognostic biomarkers. But few studies have explored SRM over time to predict the fate of the very premature. The EPIPAGE2-EPIRMEX project allowed us to study by brain SRM the brain metabolites of 69 preterm infants, as well as their neurodevelopment at 2 years oldMalgré les progrès dans la survie des enfants nés très prématurément, leur développement neurocognitif reste préoccupant. Mais la prématurité elle-même a une influence mineure sur le devenir neurodéveloppemental, alors que des facteurs per-nataux ont un rôle prédominant dans la prédiction de leur devenir. Ces facteurs incluent des facteurs intrinsèques comme la restriction de croissance intra-utérine, ou extrinsèques comme la corticothérapie anténatale. Ainsi, l’identification précoce (terme corrigé) des nourrissons à haut risque de trouble du neurodéveloppement permettra une prise en charge adaptée et précoce.Néanmoins, des marqueurs pronostiques précis manquent à l’heure actuelle pour apprécier ce risque. La spectroscopie par résonance magnétique (SRM) permet objectivement de mesurer la biochimie cérébrale in vivo. La SRM est une technique d’imagerie permettant une étude du métabolisme cérébral et des variations de concentration des métabolites qui est déjà utilisée pour caractériser différentes pathologies comme l’encéphalopathie anoxo ischémique. Par conséquent, nous pensons que les métabolites tissulaires peuvent servir en tant que biomarqueurs diagnostiques et pronostiques précoces importants. Mais peu d’études ont exploré la SRM à terme dans la prédiction du devenir du nouveau-né grand prématuré.Le projet EPIPAGE2-EPIRMEX nous a permis d’étudier par SRM les métabolites cérébraux de 69 nouveau-nés grands prématurés, ainsi que leur neurodéveloppement à 2 ans

Les Protéines de la famille striatine (un sujet épineux)

Mon travail de thèse a été réalisé dans l'équipe qui a identifié la famille striatine ,une nouvelle famille de protéines d'échafaudage principalement exprimée dans les neurones où elle est concentrée dans les épines dendritiques. Chez les mammifères, cette famille de protéines comprend trois membres, la striatine, la zinédine et SG2NA, qui partagent quatre domaines d'interaction protéine-protéine identiques (un domaine de fixation à la cavéoline, une structure coiled-coil, un domaine de fixation au complexe Ca2+ /calmoduline et un domaine de répétitions WD), agencés dans le même ordre, très conservés au cours de l'évolution, et considérés comme la signature des membres de la famille striatine. Ces trois protéines interagissent avec de nombreuses protéines de signalisation comme la calmoduline, PP2A, ER a... (voir Benoist et al., 2006). Alors que la répartition de SG2NA et de la striatine dans le système nerveux central avait été déterminée (Salin et al., 1998; Castets et al., 2000; Gaillard et al., 2006), celle de la zinédine restait inconnue. Au cours de ma thèse, j'ai montré que la zinédine, à l inverse de SG2NA et de la striatine qui présentent une expression caudale et centrale respectivement, a une expression principalement rostrale. Elle est exprimée majoritairement dans les neurones de l'hippocampe, du cortex cérébral et du bulbe olfactif. Comme les autres membres de la famille striatine, la zinédine a une distribution polarisée dans le compartiment somatodendritiquedes neurones et est enrichie dans les épines dendritiques (Benoist et al., 2008). Nous avons également étudié l adressage des protéines de la famille striatine aux épines dendritiques, et montré que l adressage de ces protéines nécessite leur oligomérisation par le domaine coiled-coil (Gaillard et al., 2006). Enfin, j'ai commencé à disséquer le rôle des protéines de la famille striatine dans le trafic vésiculaire. Dans ce but, j'ai développé un test d'endocytose, fondé sur l'infection des cellules N2a par le virus de la stomatite vésiculeuse. Dans ce modèle, la surexpression des membres de la famille striatine inhibe l'endocytose dépendante de la clathrine. Cette inhibition nécessite le domaine entre les acides aminés 185 et 194 de SG2NA, à proximité du domaine de fixation de la calmoduline. Dans les neurones d'hippocampe en culture, un test d endocytose de la transferrine m'a permis de montrer que SG2NA est un régulateur de l'endocytose dépendante de la clathrine comme dans les cellules N2a (Benoist et al., en préparation). En conclusion, les protéines de la famille striatine ont un rôle déterminant dansl'endocytose dépendante de la clathrine. Ainsi, ces protéines agissent probablement comme un lien entre les processus de signalisation et d'endocytose. Nos données mettent ces protéines au centre de la physiologie des épines dendritiques.AIX-MARSEILLE2-BU Méd/Odontol. (130552103) / SudocSudocFranceF

Hippocampal Dendritic Spines Are Segregated Depending on Their Actin Polymerization

Dendritic spines are mushroom-shaped protrusions of the postsynaptic membrane. Spines receive the majority of glutamatergic synaptic inputs. Their morphology, dynamics, and density have been related to synaptic plasticity and learning. The main determinant of spine shape is filamentous actin. Using FRAP, we have reexamined the actin dynamics of individual spines from pyramidal hippocampal neurons, both in cultures and in hippocampal organotypic slices. Our results indicate that, in cultures, the actin mobile fraction is independently regulated at the individual spine level, and mobile fraction values do not correlate with either age or distance from the soma. The most significant factor regulating actin mobile fraction was the presence of astrocytes in the culture substrate. Spines from neurons growing in the virtual absence of astrocytes have a more stable actin cytoskeleton, while spines from neurons growing in close contact with astrocytes show a more dynamic cytoskeleton. According to their recovery time, spines were distributed into two populations with slower and faster recovery times, while spines from slice cultures were grouped into one population. Finally, employing fast lineal acquisition protocols, we confirmed the existence of loci with high polymerization rates within the spine.Spanish Ministry of the Economy and Competitiveness: BFU 2010-1753Peer Reviewe

PTEN counteracts PIP3 upregulation in spines during NMDA-receptor-dependent long-term depression

© 2014. Phosphoinositide 3-kinase (PI3K) and PTEN have been shown to participate in synaptic plasticity during long-term potentiation (LTP) and long-term depression (LTD), respectively. Nevertheless, the dynamics of phosphatidylinositol-(3,4,5)-trisphosphate (PIP3) and the regulation of its synthesis and degradation at synaptic compartments is far from clear. Here, we have used fluorescence resonance energy transfer (FRET) imaging to monitor changes in PIP3 levels in dendritic spines from CA1 hippocampal neurons under basal conditions and upon induction of NMDA receptor (NMDAR)-dependent LTD and LTP. We found that PIP3 undergoes constant turnover in dendritic spines. Contrary to expectations, both LTD and LTP induction trigger an increase in PIP3 synthesis, which requires NMDARs and PI3K activity. Using biochemical methods, the upregulation of PIP3 levels during LTP was estimated to be twofold. However, in the case of LTD, PTEN activity counteracts the increase in PIP3 synthesis, resulting in no net change in PIP3 levels. Therefore, both LTP and LTD signaling converge towards PIP3 upregulation, but PTEN acts as an LTD-selective switch that determines the outcome of PIP3 accumulation.The Spanish Ministry [grant numbers CSD-2010-00045 and SAF-2011-24730]; and Fundación Ramón ArecesPeer Reviewe