Jul 2026· Proceedings of the National Academy of Sciences of the United States of America· Vol 123 30, pp.
e2601488123
· 0 citations· 43 references
Medicine
TL;DR
Gephyrin is identified as the primary synaptic anchor for PX-RICS and the N-terminal gephyrin-binding region (GBR) engages gephyrin E-domain through conserved hydrophobic interactions, explaining the isoform-specific targeting of PX-RICS (but not RICS) to inhibitory synapses.
Abstract
Precise regulation of excitatory-inhibitory balance is critical for neural circuit function, and its disruption underlies neurodevelopmental disorders such as autism spectrum disorder (ASD) and epilepsy. PX-RICS, a major ARHGAP32 splice variant enriched at inhibitory synapses, has been linked to cognitive dysfunctions; however, the molecular basis of its synaptic targeting and function remains unknown. Here, we identify gephyrin as the primary synaptic anchor for PX-RICS and determine the 2.2 Å crystal structure of their complex. Our structural analysis reveals that the N-terminal gephyrin-binding region (GBR) engages gephyrin E-domain through conserved hydrophobic interactions, explaining the isoform-specific targeting of PX-RICS (but not RICS) to inhibitory synapses. This binding interface overlaps with the neurotransmitter receptor binding site on gephyrin, suggesting a competitive yet dynamic interaction landscape among these inhibitory synaptic proteins. Arhgap32ΔGBR mice exhibit key features of ARHGAP32-related disorders, including impaired social novelty recognition and increased seizure susceptibility, indicating that gephyrin-mediated anchoring is critical for PX-RICS to function in inhibitory synapses.
Precise control of membrane protein localization and turnover is essential for synaptic function and circuit stability. Disruption of these processes alters the surface expression of receptors and transporters, ultimately impacting the excitatory/inhibitory (E/I) balance. Leucine-rich repeat kinase 2 (LRRK2) is emerging as a key regulator of these membrane-associated processes, acting at the interface between intracellular trafficking and synaptic signaling. LRRK2 integrates kinase activity with scaffolding functions to coordinate Rab-dependent vesicular trafficking, endosomal recycling, cytoskeletal dynamics, and endolysosomal pathways. Through these mechanisms, it controls the surface expression and distribution of synaptic receptors and neurotransmitter transporters in both neuronal and glial compartments. Pathogenic LRRK2 variants associated with Parkinson’s disease (PD), converge on kinase hyperactivation and lead to sustained alterations in trafficking networks, resulting in selective mislocalization of membrane proteins. In this review, we examine how LRRK2-dependent trafficking mechanisms regulate key components of synaptic transmission, including glutamatergic and GABAergic receptors, as well as astrocytic transporters. We highlight how disruption of these processes affects neurotransmitter clearance, receptor activation, and ultimately E/I balance. Notably, accumulating evidence indicates that LRRK2 functions as an upstream coordinator of membrane organization at the crossroads of synaptic signaling and neurotransmitter homeostasis. Understanding how LRRK2 regulates trafficking pathways across cellular compartments provides mechanistic insight into circuit vulnerability in PD and highlights membrane-targeted strategies as potential approaches for restoring synaptic stability.
Graphical Abstract
LRRK2 in Synaptic Communication.
LRRK2 acts as a central regulator of membrane trafficking in neurons and astrocytes. Through control of vesicular pathways, cytoskeletal dynamics, and endolysosomal function, LRRK2 modulates synaptic receptors and neurotransmitter transporters, contributing to excitatory/inhibitory balance. Pathogenic variants disrupt these processes, promoting synaptic dysfunction and circuit instability
Angela Di Iacovo, Chiara D’Agostino, Giulia Casoli et al.· Cellular and molecular neuro...· 0 citations
The findings implicate disrupted SYTL4-RAB27A-dependent vesicle trafficking in ASD pathogenesis and identify SYTL4 and RAB27A as previously unrecognized contributors to autism-associated synaptic deficits and behavior.
Yang Liao, Shuju Zhang, Xiaolei Zhang et al.· Proceedings of the National...· 0 citations
Synapse formation and function are coordinated spatially and temporally by a host of synaptic proteins that regulate neuronal signaling, synapse specificity, and plasticity; many of which are implicated in neuropsychiatric disorders. Members of the C1q/TNF superfamily function as synaptic organizers, shaping synapse assembly and maintenance. Among them, C1QL3 plays a putative role in trans-synaptic adhesion and modulation of synaptic strength, but the lack of a reliable antibody to detect it has severely limited the ability to map its endogenous localization and study its biochemical properties. Here, we present a novel epitope-tagged knock-in mouse line (C1ql32HA), in which two hemagglutinin (HA) epitopes were inserted near the N-terminus of the endogenous C1QL3 protein. This model enables purification, detection, and subcellular localization of native C1QL3 protein (C1QL3-2HA) with high specificity, eliminating the need for overexpression or custom antibodies. We validated that C1ql32HA mice maintain normal mRNA expression, biochemical properties, and behavior. Using native PAGE, we determined the endogenous oligomeric state of C1QL3-2HA. Brain-wide light-sheet microscopy uncovered an expanded neuroanatomical map of C1QL3-2HA expression, including newly identified populations in cortical and subcortical regions as well as the retina. Dual immunohistochemistry confirmed cell type-specific expression patterns, and super-resolution STED microscopy localized C1QL3-2HA to hippocampal mossy fiber synapses, positioned between pre- and post-synaptic markers, supporting its hypothesized role in trans-synaptic complexes. This knock-in mouse line is a powerful tool for studying the anatomical, molecular, and synaptic biology of C1QL3 in all cellular/tissue contexts, enabling future studies into its potential roles in the nervous system and beyond.
William P. Armstrong, James M. Salvatore, Matthew J. Sticco et al.· bioRxiv· 0 citations
Results suggest that Adgrd1 plays a key role in maintaining hippocampal resilience and regulating motivational behaviors through integrated molecular and circuit-level mechanisms.
Inés Martínez-Soria, Pol Picón-Pagès, A. P. Pérez González et al.· bioRxiv· 0 citations
The RAC subfamily of Rho family small GTPases plays a crucial role in neurodevelopment by regulating cellular signaling pathways and the actin cytoskeleton. The activity of RAC is controlled by guanine nucleotide exchange factors (GEFs), which facilitate the transition from an inactive GDP-bound form to an active GTP-bound form. A novel de novo variant, NM_020820.4:c.572 A > G p.(Y191C), was identified in PREX1, which encodes a RAC-specific GEF, by whole-exome sequencing of a patient with epilepsy. Biochemical analysis using recombinant proteins demonstrated that the p.Y191C variant reduced the GDP/GTP exchange activity of PREX1 toward RAC1 and attenuated RAC1-PAK1 signaling compared with wild-type PREX1, suggesting that the p.Y191C variant is hypofunctional. To explore its neurodevelopmental consequences in vivo, we performed in utero electroporation-mediated RNA interference targeting PREX1 in cerebrocortical progenitor cells in mice at embryonic day 14 (E14). While no significant effects on radial migration or morphological development were observed at E17, PREX1-knockdown neurons were located more apically within layer II/III than controls at postnatal day 0 (P0). By P7, these neurons showed aberrant dendritic arborization with a significant increase in apical dendritic branching. Likewise, dendritic overgrowth was observed in granule cells of the hippocampal dentate gyrus following PREX1 knockdown at P0, with minimal effects on dendritic spine morphology. Functionally, PREX1 knockdown enhanced spontaneous Ca²⁺ activity in cultured hippocampal neurons and depolarization-evoked Ca²⁺ responses in layer II/III cortical neurons in acute brain slices. These findings indicate that reduced PREX1-RAC1 signaling leads to mislocalization, dendritic overgrowth, and neuronal hyperexcitability, which may underlie epilepsy in the human case.
Neurodevelopmental disorders are frequently caused by mutations in pleiotropic kinases, yet downstream effectors driving neuronal pathology remain undefined. Here, we identify the G3BP1-dependent stress granule pathway as the dominant effector of casein kinase 2 (CK2α) in developing neurons, implying that its dysregulation underlies the neurodevelopmental deficits of Okur-Chung neurodevelopmental syndrome (OCNDS). OCNDS-associated CK2α mutations reduce phosphorylation of G3BP1 at serine 149, promoting aberrant phase separation and persistent granules that sequester neuronal mRNAs and suppress local protein synthesis across axonal and dendritic compartments. These phenotypes produce allele-specific deficits in neuronal morphogenesis, synaptic abundance, and network excitability, which are conserved in a knock-in mouse model and in patient-derived iPSC neurons. G3bp1 knockdown rescues translational and morphological phenotypes across all OCNDS alleles, demonstrating that restoring granule homeostasis reverses neuronal pathology. Together, these findings establish OCNDS as a disorder of compartment-specific translational dysregulation driven by impaired CK2α–G3BP1 control of RNA granule homeostasis. Summary OCNDS mutations disrupt CK2α–G3BP1 signaling, causing persistent granules and defective neuronal translation and development.