Biology subjects

Humeau, Y.

Publications and source records attributed to Humeau, Y..

8 recordsLinked to original sources

bioRxiv2024

A minor impact of VGLUT1 expression level on quantal size revealed through the characterization of VGLUT1mEos2 knock-down new mouse model

Synaptic vesicles (SVs) are small organelles secreting neurotransmitters at synapses. By fusing a photoactivated fluorescent protein to VGLUT1, we generated a VGLUT1mEos2 knock-in mouse. VGLUT1mEos2 knock-in mice are viable and healthy, but exhibit a severe reduction in VGLUT1 expression levels. Using VGLUT1mEos2 expressing neurons, we established paradigms to trace individual SV mobility at the single-molecule level or via massive photoconversion. Hippocampal neurons with significantly diminished VGLUT1 expression maintain unaltered miniature glutamate release characteristics in terms of quantal size and frequency. We demonstrate that VGLUT1 expression level are not correlated in a linear fashion with the vesicular glutamate content. In conclusion, the VGLUT1mEos2 mouse line serves as a powerful tool for exploring SV mobility properties and elucidating the contributions of VGLUT1 to excitatory neurotransmission and cognitive processes.

neuroscience↗

bioRxiv2023

CA3 hippocampal synaptic plasticity supports ripple physiology during memory consolidation

Consolidation of recent memory depends on hippocampal activities during resting periods that immediately follows the memory encoding. There, Slow Save Sleep phases appear as privileged periods for memory consolidation as hosting the ripple activities, which are fast oscillations generated within the hippocampus whose inactivation leads to memory impairment. If a strong correlation exists between these replays of recent experience and the persistence of behavioural adaptations, the mobilisation, the localization and the importance of synaptic plasticity events in this process is largely unknown. To question this issue, we used cell-surface AMPAR immobilisation to block post-synaptic LTP within the hippocampal region at various steps of the memory process. 1- Our results show that hippocampal synaptic plasticity is engaged during the consolidation but is dispensable during the encoding or recall of a working memory based spatial memory task. 2- Blockade of plasticity during sleep leads to apparent forgetting of the encoded rule. 3- In vivo recordings of ripple activities during resting periods show a strong impact of AMPAR immobilization solely, prominent when a rule has been recently encoded. 4- In situ examination of the interplay between AMPAR mobility, hippocampal plasticity and spontaneous ripple activities pointed that post-synaptic plasticity at CA3-CA3 recurrent synapses support ripple generation. As crucial results were reproduced using another AMPARM blockade strategy, we propose that after rule encoding, post-synaptic AMPAR mobility at CA3 recurrent synapses support the generation of ripples necessary for rule consolidation.

neuroscience↗

bioRxiv2022

AUTS2 gene dosage affects synaptic AMPA receptors via a local dendritic spine AUTS2-TTC3-AKT-mTORC1 signaling dysfunction

The Human 1.2-Mb AUTS2 locus on chromosome 7q11.22 encodes a 1259-aa full-length protein, and a 711-aa C-terminal isoform. Functions of these AUTS2 proteins are only partly known. The major traits found in patients displaying AUTS2 locus mutations are Intellectual Disabilities, microcephaly attention deficit hyperactivity disorder (ADHD) (54%), and autistic traits. Furthermore, AUTS2 common variants were recently found associated to alcohol consumption and dyslexia using GWAS approaches. Auts2 localizes mainly in cell nuclei. We evidenced by super-resolution that Auts2 is present in dendritic spines. Auts2 interacts with Ttc3, the Akt2 E3 ligase, and negatively regulates Akt2 ubiquitination. Auts2 haploinsufficiency affects Akt/mTorc1 pathway with a decrease in AMPA and NMDA receptor subunits and in synaptic currents. Akt2 injection in postsynaptic neurons is sufficient to reverse changes in synaptic currents generated by Auts2 haploinsufficiency. Using chromosome engineering based on targeted meiotic recombination, we generated two mouse models with Auts2 locus deletion and duplication. Deleted Auts2 locus mice display stereotypies (rearing), perseveration and abnormal recognition memory. Duplicated Auts2 locus mice display similar perseveration and abnormal recognition memory but also a decrease in cued and contextual fear memory. Gene dosage induce changes in brain sub-region neuronal networks. In the thalamo-lateral amygdala pathway linked to cued fear memory, we found synaptic impairments linked to AMPA receptors, with a specific decrease in pAKT/total AKT ratio in duplicated Auts2 mice. Altogether, our study thereby provides a novel mechanistic and potentially therapeutic understanding of synaptic AKT/mTORC1 deregulated signaling and its related behavioral and cognitive phenotypes.

neuroscience↗

bioRxiv2021

High-resolution imaging and manipulation of endogenous AMPA receptor surface mobility during synaptic plasticity and learning

Regulation of synaptic neurotransmitter receptor content is a fundamental mechanism for tuning synaptic efficacy during experience-dependent plasticity and behavioral adaptation. However, experimental approaches to track and modify receptor movements in integrated experimental systems are limited. Exploiting AMPA-type glutamate receptors (AMPAR) as a model, we generated a knock-in mouse expressing the biotin acceptor peptide (AP) tag on the GluA2 extracellular N-terminus. Cell-specific introduction of biotin ligase allows the use of monovalent or tetravalent avidin variants to respectively monitor or manipulate the surface mobility of endogenous AMPAR containing biotinylated AP-GluA2 in neuronal subsets. AMPAR immobilization precluded the expression of long-term potentiation and formation of contextual fear memory, allowing for target-specific control of the expression of synaptic plasticity and animal behavior. The AP tag knock-in model offers unprecedented access to resolve and control the spatiotemporal dynamics of endogenous receptors, and opens new avenues to study the molecular mechanisms of synaptic plasticity and learning.

neuroscience↗

bioRxiv2020

Abnormal AMPAR-mediated synaptic plasticity, cognitive and autistic-like behaviors in a missense Fmr1 mutant mouse model of Fragile X syndrome

Fragile X syndrome (FXS) is the most frequent form of inherited intellectual disability and the best-described monogenic cause of autism. FXS is usually caused by a CGG-repeat expansion in the FMR1 gene leading to its silencing and the loss-of-expression of the Fragile X Mental Retardation Protein (FMRP). Missense mutations were also identified in FXS patients, including the recurrent FMRP-R138Q mutation. To investigate the mechanisms underlying FXS in these patients, we generated a knock-in mouse model (Fmr1R138Q) expressing the FMRP-R138Q protein. We demonstrate that the Fmr1R138Q hippocampus has an increased spine density associated with postsynaptic ultrastructural defects and increased AMPA receptor surface expression. Combining biochemical assays, high-resolution imaging and electrophysiological recordings, we also show that the mutation impairs the hippocampal long-term potentiation (LTP) and leads to socio-cognitive deficits in Fmr1R138Q mice. These findings reveal that the R138Q mutation impacts the synaptic functions of FMRP and highlight potential mechanisms causing FXS in FMRP-R138Q patients.

neuroscience↗

bioRxiv2019

Non-linear dendritic integration in frontal circuits shapes sensory discrimination in rodents

Survival depends on the ability of animals to select the appropriate behavior in response to threat and safety sensory cues. However, the synaptic and circuit mechanisms by which the brain learns to encode accurate predictors of threat and safety remain largely unexplored. Here, we show that frontal association cortex (FrA) pyramidal neurons integrate auditory cues and basolateral amygdala (BLA) inputs non-linearly in a NMDAR-dependent manner. We found that the response of FrA pyramidal neurons was more pronounced to Gaussian noise than to pure 8 kHz tone, and that the activation of BLA-to-FrA axons was the strongest during safe periods in between conditioning pairings. Blocking BLA-to-FrA signaling specifically at the time of presentation of Gaussian noise (but not 8 kHz tone) as a safety signal impaired the formation of auditory fear memories. Taken together, our data reveal a circuit mechanism that facilitates the formation of fear traces in the FrA, thus providing a new framework for probing discriminative learning and related disorders.

neuroscience↗

bioRxiv2018

Mammalian vesicular glutamate transporter VGLUT1 reduces synaptic vesicle superpool size and spontaneous release frequency.

Glutamate secretion at excitatory synapses is tightly regulated to allow for the precise tuning of synaptic strength. Vesicular Glutamate Transporters (VGLUT) accumulate glutamate into synaptic vesicles (SV) and thereby regulate quantal size. Further, the number of release sites and the release probability of SVs maybe regulated by the organization of active zone proteins and SV clusters. In the present work, we uncover a mechanism mediating an increased SV clustering through a tripartite interaction of VGLUT1, endophilinA1 and intersectin1. This strengthening of SV clusters results in a combined reduction of axonal SV super-pool size and miniature excitatory events frequency. Our findings support a model in which clustered vesicles are held together through multiple weak interactions between SH3 domains and proline rich sequences of synaptic proteins. In mammals, VGLUT1 gained a poly-proline sequence that recruits endophilinA1 and turns the transporter into a dual regulator of quantal release parameters at excitatory synapses.

neuroscience↗

bioRxiv2018

Pharmacological modulation of AMPA receptor surface diffusion restores hippocampal synaptic plasticity and memory in Huntington’s disease

Impaired hippocampal synaptic plasticity is increasingly considered to play an important role in cognitive impairment in Huntingtons disease (HD). However, the molecular basis of synaptic plasticity defects is not fully understood. Combining live-cell nanoparticle tracking and super-resolution imaging, we show that dysregulation of AMPA receptors (AMPARs) surface diffusion represents a molecular basis underlying the aberrant hippocampal synaptic plasticity during HD. AMPARs surface diffusion is increased in various HD neuronal models, which results in the failure of AMPARs surface stabilization after long-term potentiation (LTP) stimuli. This appears to result from a defective brain-derived neurotrophic factor (BDNF) - tyrosine receptor kinase B (TrkB) - Ca2+/calmodulin-dependent protein kinase II (CaMKII) signaling pathway that impacts the interaction between the AMPAR auxiliary subunit stargazin and postsynaptic density protein 95 (PSD-95). Notably, the disturbed AMPAR surface diffusion is rescued, via BDNF signaling pathway and by the antidepressant tianeptine. Tianeptine also restores the impaired LTP and hippocampus-dependent memory as well as anxiety/depression-like behavior in different HD mouse models. We thus unveil a mechanistic framework underlying hippocampal synaptic and memory dysfunction and propose a new perspective in HD treatment by targeting AMPAR surface diffusion.

neuroscience↗