Biology subjects

Charrier, C.

Publications and source records attributed to Charrier, C..

5 recordsLinked to original sources

bioRxiv2026

The human-specific gene FRMPD2B couples postnatal experience to the expansion of cortical connectivity

The human neocortex is characterized by its uniquely prolonged postnatal developmental period during which experience sculpts neuronal circuits, a process essential to human cognitive abilities. Yet whether human-specific genetic innovations have shaped the activity-dependent mechanisms regulating circuit assembly remains unknown. Here, we identify the human-specific gene FRMPD2B as an activity- and experience-regulated modifier of cortical connectivity. FRMPD2B is primarily expressed in cortico-cortical projection neurons postnatally and throughout childhood. It promotes dendritic, axonal and synaptic development, and is required for proper morphogenesis in xenotransplanted human cortical neurons. FRMPD2B expression is bidirectionally regulated by neuronal activity and experience. This activity-responsiveness was gained after FRMPD2B arose through partial gene duplication, when a retrotransposon insertion remodeled its promoter. Our findings highlight how a series of genetic innovations have led to the emergence of a human-specific activity-regulated developmental program through which postnatal experience drives cortical connectivity expansion, linking genome evolution to human brain plasticity.

neuroscience↗

bioRxiv2024

Optical profiling of NMDA receptor molecular diversity at synaptic and extrasynaptic sites

Neurotransmitter receptors are the linchpin of neuronal communication. These receptors often form large multimeric complexes that differ in their subunit composition, distribution and signaling properties. Studying individual subtypes in native tissues with subunit stoichiometry resolution remains challenging. This is the case of NMDA receptors (NMDARs), a class of glutamate-gated ion channels playing essential roles in brain development and plasticity. These receptors co-exist as multiple subtypes, with GluN1/GluN2A (GluN2A diheteromers), GluN1/GluN2B (GluN2B diheteromers) and GluN1/GluN2A/GluN2B (GluN2A/GluN2B triheteromers) receptors prevailing in the adult forebrain. Despite numerous investigations, the relative abundance and subcellular distribution of these subtypes remain contentious. Here, we designed a photochemical tool (Opto2B) enabling specific and reversible modulation of GluN2B diheteromers, while leaving other receptor subtypes unaffected (in particular GluN2A/GluN2B tri-heteromers). Using Opto2B, we established the differential contribution of GluN2B diheteromers to synaptic and extrasynaptic NMDAR pools during development. In particular, we show that in adult hippocampal CA1 pyramidal cells, GluN2A-receptors predominate in both pools, with no preferential contribution of GluN2B diheteromers to extrasynaptic currents. Our study clarifies decades of controversial research on extrasynaptic NMDARs and paves the way for interrogating NMDAR signaling diversity with unprecedented molecular and spatio-temporal resolution. Significance StatementPharmacological and genetic approaches, the gold standards for investigating receptor diversity, cannot easily distinguish between receptor populations containing one or more copies of the same subunit. For NMDARs, discriminating GluN2A/GluN2B triheteromers (containing one copy of GluN2A and one copy of GluN2B) from their diheteromeric counterparts (containing two copies of GluN2A or GluN2B) remains difficult. Here, we designed the first tool (Opto2B) allowing selective modulation of GluN2B diheteromers, leaving GluN2A/GluN2B triheteromers unaffected. Using Opto2B, we show that GluN2B diheteromers form a minor population in both synaptic and extrasynaptic compartments of the adult CA1 hippocampus, refuting the common belief of an enrichment of GluN2B diheteromers at extrasynaptic sites. This study should inform future drug discovery programs and studies on NMDAR molecular physiology.

neuroscience↗

bioRxiv2023

Human synaptic neoteny requires species-specific balancing of SRGAP2-SYNGAP1 cross-inhibition

Human-specific (HS) genes are potential drivers of brain evolution, but their impact on human neuron development and disease remains unclear. Here we studied HS genes SRGAP2B/C in human cortical projection neurons (CPNs) in vivo, using xenotransplantation in the mouse cortex. Downregulation of SRGAP2B/C in human CPNs greatly accelerated synaptic development, indicating their requirement for human-specific synaptic neoteny. SRGAP2B/C acted by downregulating their ancestral paralog SRGAP2A, thereby upregulating postsynaptic levels of SYNGAP1, a major intellectual deficiency/autism spectrum disorder (ID/ASD) gene. Combinatorial genetic invalidation revealed that the tempo of synaptogenesis is set by a balance between SRGAP2A and SYNGAP1, which in human CPNs is tipped towards neoteny by SRGAP2B/C. Our results demonstrate that HS genes can modify the phenotypic expression of ID/ASD mutations through regulation of synaptic neoteny. One-Sentence SummaryHuman-specific genes SRGAP2B/C control human cortical neuron neoteny by regulating the function of neurodevelopmental disorder gene SYNGAP1

neuroscience↗

bioRxiv2022

CTNND2 moderates neuronal excitation and links human evolution to prolonged synaptic development in the neocortex

Human-specific genes are potential drivers of brain evolution. Among them, SRGAP2C has contributed to the emergence of features characterizing human cortical synapses, including their extended period of maturation. SRGAP2C inhibits its ancestral copy, the postsynaptic protein SRGAP2A; yet the synaptic molecular pathways differentially regulated in humans by SRGAP2 proteins remain largely unknown. Here, we identify CTNND2, a protein implicated in severe intellectual disability (ID) in the Cri-du-Chat syndrome, as an SRGAP2 effector. We demonstrate that CTNND2 slows down synaptic maturation and promotes neuronal homeostasis. During postnatal development, CTNND2 moderates neuronal excitation and excitability. In adults, it supports synapse maintenance. While CTNND2 deficiency is deleterious and results in the synaptic loss of SYNGAP1, another major ID-associated protein, the human-specific protein SRGAP2C enhances CTNND2 synaptic accumulation in human neurons. Our findings reveal that CTNND2 regulation by SRGAP2C contributes to synaptic neoteny in humans, and link human-specific and ID genes at the synapse.

neuroscience↗

bioRxiv2020

Morphologically constrained modeling of spinous inhibition in the somato-sensory cortex

Pyramidal neurons are covered by thousands of dendritic spines receiving excitatory synaptic inputs. The ultrastructure of dendritic spines shapes signal compartmentalization but ultrastructural diversity is rarely taken into account in computational models of synaptic integration. Here, we developed a 3D correlative light-electron microscopy (3D-CLEM) approach allowing the analysis of specific populations of synapses in genetically defined neuronal types in intact brain circuits. We used it to reconstruct segments of basal dendrites of layer 2/3 pyramidal neurons of adult mouse somatosensory cortex and quantify spine ultrastructural diversity. We found that 10% of spines were dually-innervated and 38% of inhibitory synapses localized to spines. Using our morphometric data to constrain a model of synaptic signal compartmentalization, we assessed the impact of spinous versus dendritic shaft inhibition. Our results indicate that spinous inhibition is locally more efficient than shaft inhibition and that it can decouple voltage and calcium signaling, potentially impacting synaptic plasticity.

neuroscience↗