Biology subjects

Robinson, C. G.

Publications and source records attributed to Robinson, C. G..

13 recordsLinked to original sources

bioRxiv2026

LRRC57/RABIN is a presynaptic inhibitor of Rab GTPases in glutamatergic neurons

Synaptic vesicle cycling, if not properly constrained, can result in excessive neurotransmitter release and subsequent neural pathology. Rab GTPases orchestrate synaptic vesicle trafficking through GTP-dependent interactions with effector proteins, but the restraining mechanism of these interactions is unknown. Here we identify LRRC57 (or RABIN for RAB INhibitor), a conserved brain-enriched protein in glutamatergic synapses that binds multiple GTP-loaded synaptic Rabs and competitively blocks access to their effectors. Loss of Rabin increased glutamate release, expanded vesicle pools, accelerated vesicle turnover, and produced circuit hyperexcitability with epileptiform activity, which was mitigated by an antiepileptic agent that targets presynaptic function. Conversely, overexpression of the Rabin gene suppressed neurotransmitter release and protected against induced seizures and persistent epileptiform discharges. Together, these findings define a noncanonical decoy-effector mechanism that constrains presynaptic Rab signaling to preserve excitatory circuit stability.

neuroscience↗

bioRxiv2026

Alternative organelle targeting of OPA1 mediates fatty acid release from lipid droplets

Mitochondria and lipid droplets (LDs) are functionally coupled to coordinate fatty acid utilization and storage. However, a comprehensive understanding of mitochondria-LD alliances remains elusive. We have identified a previously unrecognized role for optical atrophy 1 (OPA1), a mitochondrial fusion factor, in the regulation of fatty acid release from LDs. We demonstrated that OPA1s exon 4 adapts an amphipathic helix to target OPA1 to LDs. OPA1 localized to LDs promote fatty acid release by facilitating the recruitment of lipases to LDs. In addition, OPA1s residence on LDs competes with its mitochondrial entry, influencing mitochondria fusion and connectivity. Furthermore, the S158N polymorphism within OPA1s exon 4 exhibiting attenuated fatty acid release from LDs is associated with changes in metabolic traits in pediatric cancer survivors. Altogether, our findings reveal that OPA1 actively mediates fatty acid release from LDs and provide a mechanistic link between OPA1 and human metabolism.

cell biology↗

bioRxiv2026

APOE is a presynaptic protein that accumulates with age and modulates neurotransmitter release

The synaptic vesicle (SV) cycle is the fastest membrane trafficking and protein sorting process in biology. It underlies neuronal communication and cognition, yet synaptic function declines during normal aging, increasing vulnerability to neurologic disease. How the SV cycle is maintained across the lifespan of a complex organism remains unclear. Here, we used wild-type mice (C57BL/6J) to define the age- and sex-stratified molecular landscape of SVs and identified apolipoprotein E (APOE) as an abundant presynaptic protein further enriched in aged female samples. Super-resolution imaging, cell-type selective expression, and protease protection assays demonstrate that APOE originates from astroglia and associates with the cytosolic face of SVs. Using iGluSnFR and pHluorin optophysiology, we find that both decreased and increased APOE levels impair neurotransmission during stimulus trains. Together, these findings place APOE at the synapse and establish it as a cell-nonautonomous regulator of the SV cycle.

neuroscience↗

bioRxiv2026

Protein domain characterization reveals human MIC60 tolerates loss of helical bundle domain

The mitochondrial contact site and cristae organizing system (MICOS) is essential for cristae junction formation and inner mitochondrial membrane architecture. To define how MICOS integrity is established and maintained, we generated conditional deletion models of Immt (encoding MIC60), a core MICOS subunit, in tissue-specific settings and in cultured cells. Liver-specific deletion of Immt in mice induced profound defects in mitochondrial ultrastructure and function, establishing MIC60 as essential for mitochondrial integrity. Notably, despite the severity of the defects, we did not detect increased apoptosis in liver tissue or in cells. To directly link MIC60 structure to its function, we performed a systemic structure-function analysis of human MIC60 using domain-specific deletion mutants expressed in Immt-deleted cells. We identified that the transmembrane, coiled-coil, and mitofilin domains are required for MICOS assembly, mitochondrial morphology, and respiratory function. Unexpectedly, deletion of the predicted helical bundle (a region spanning 229 amino acids) substantially restored mitochondrial structure and function, nearly matching full-length MIC60. A mutation (K299E) associated with human disease within this domain similarly preserved most MIC60-dependent functions. Together, these results establish MIC60 as a non-redundant regulator of mitochondrial architecture while revealing that a large predicted structural domain is largely dispensable for MIC60s core functions, refining current models of MICOS organization and uncovering unexpected modularity within MIC60.

cell biology↗

bioRxiv2025

Carbohydrate adaptation drives liver-brain axis maturation

Mammalian postnatal life requires adaptation to a carbohydrate-rich diet, yet how metabolic programs are coordinated within and across organs is unclear. Using time-resolved transcriptomic and metabolomic analyses from the neonatal period through adulthood, we show that mouse liver rapidly acquires oxidative and detoxification capacity after weaning. This transition enables the brain to establish energy-sufficient, low-toxicity metabolic environment for neuronal development. This maturation process is marked by progressive activation of the hepatic electron transport chain (ETC), with the mitochondrial RNA endoribonuclease LACTB2 acting as a key regulator. LACTB2 prevents the accumulation of mitochondrial RNAs and sustains expression of mtDNA-encoded ETC subunits, thereby preserving mitochondrial competence for oxidative metabolism. LACTB2 is postnatally induced in hepatocytes, and its loss causes defective glucose utilization, systemic metabolic toxicity, and impaired brain metabolism and myelination, leading to prepubertal lethality, particularly in males. Restoring ETC function through liver-targeted expression of yeast NADH dehydrogenase NDI1, inhibiting the integrated stress response or ammonia scavenging improved survival. Our findings identify LACTB2-dependent hepatic mitochondrial maturation as a central mechanism that aligns carbohydrate adaptation with the liver-brain metabolic coordination to support early-life development.

developmental biology↗

bioRxiv2024

iTome Volumetric Serial Sectioning Apparatus for TEM

An automated ultra-microtome capable of sectioning thousands of ultrathin sections onto standard TEM slot grids was developed and used to section: a complete Drosophila melanogaster first-instar larva, three sections per grid, into 4,866 34-nm-thick sections with a cutting and pickup success rate of 99.74%; 30 microns of mouse cortex measuring roughly 400 um x 2000 um at 40 nm per slice; and a full adult Drosophila brain and ventral nerve column into 9,300 sections with a pickup success rate of 99.95%. The apparatus uses optical interferometers to monitor a reference distance between the cutting knife and multiple sample blocks. Cut sections are picked up from the knife-boat water surface while they are still anchored to the cutting knife. Blocks without embedded tissue are used to displace tissue-containing sections away from the knife edge so that the tissue regions end up in the grid slot instead of on the grid rim.

neuroscience↗

bioRxiv2024

Synaptic plasticity in human thalamocortical assembloids

Synaptic plasticities, such as long-term potentiation (LTP) and depression (LTD), tune synaptic efficacy and are essential for learning and memory. Current studies of synaptic plasticity in humans are limited by a lack of adequate human models. Here, we modeled the thalamocortical system by fusing human induced pluripotent stem cell-derived thalamic and cortical organoids. Single-nucleus RNA-sequencing revealed that most cells in mature thalamic organoids were glutamatergic neurons. When fused to form thalamocortical assembloids, thalamic and cortical organoids formed reciprocal long-range axonal projections and reciprocal synapses detectable by light and electron microscopy, respectively. Using whole-cell patch-clamp electrophysiology and two-photon imaging, we characterized glutamatergic synaptic transmission. Thalamocortical and corticothalamic synapses displayed short-term plasticity analogous to that in animal models. LTP and LTD were reliably induced at both synapses; however, their mechanisms differed from those previously described in rodents. Thus, thalamocortical assembloids provide a model system for exploring synaptic plasticity in human circuits. HighlightsO_LIHuman thalamic organoids consist of mostly glutamatergic projection neurons. C_LIO_LIThalamocortical assembloids form reciprocal glutamatergic synapses. C_LIO_LISynapses are functional and undergo short-term plasticity resembling animal models. C_LIO_LILong-term potentiation and depression reveal mechanisms distinct from rodents. C_LI eTOCHuman organoids are often used to model diseases with synaptic pathology; however, few studies have examined synaptic function via single-cell or single-synapse recordings. Patton et al. fused human thalamic and cortical organoids into assembloids to examine synaptic transmission and short- and long-term synaptic plasticity in human thalamocortical and corticothalamic circuits. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=199 HEIGHT=200 SRC="FIGDIR/small/578421v2_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@21546org.highwire.dtl.DTLVardef@c2ba28org.highwire.dtl.DTLVardef@4bc28aorg.highwire.dtl.DTLVardef@1d12a98_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2023

A fluorogenic complementation tool kit for interrogating lipid droplet-organelle interaction

Contact sites between lipid droplets and other organelles are essential for cellular lipid and energy homeostasis. Detection of these contact sites at nanometer scale over time in living cells is challenging. Here, we developed a tool kit for detecting contact sites based on Fluorogen- Activated Bimolecular complementation at CONtact sites, FABCON, using a reversible, low affinity split fluorescent protein, splitFAST. FABCON labels contact sites with minimal perturbation to organelle interaction. Via FABCON, we quantitatively demonstrated that endoplasmic reticulum (ER)- and mitochondria (mito)-lipid droplet contact sites are dynamic foci in distinct metabolic conditions, such as during lipid droplet biogenesis and consumption. An automated analysis pipeline further classified individual contact sites into distinct subgroups based on size, likely reflecting differential regulation and function. Moreover, FABCON is generalizable to visualize a repertoire of organelle contact sites including ER-mito. Altogether, FABCON reveals insights into the dynamic regulation of lipid droplet-organelle contact sites and generates new hypotheses for further mechanistical interrogation during metabolic switch.

cell biology↗

bioRxiv2023

Altered GM1 catabolism affects NMDAR-mediated Ca2+ signaling at ER-PM junctions and increases synaptic spineformation

Endoplasmic reticulum-plasma membrane (ER-PM) junctions mediate Ca2+ flux across neuronal membranes. The properties of these membrane contact sites are defined by their lipid content, but little attention has been given to glycosphingolipids (GSLs). Here, we show that GM1-ganglioside, an abundant GSL in neuronal membranes, is integral to ER-PM junctions; it interacts with synaptic proteins/receptors and regulates Ca2+ signaling. In a model of the neurodegenerative lysosomal storage disease, GM1-gangliosidosis, pathogenic accumulation of GM1 at ER-PM junctions due to {beta}-galactosidase deficiency drastically alters neuronal Ca2+ homeostasis. Mechanistically, we show that GM1 interacts with the phosphorylated NMDAR Ca2+ channel, thereby increasing Ca2+ flux, activating ERK signaling, and increasing the number of synaptic spines without increasing synaptic connectivity. Thus, GM1 clustering at ER-PM junctions alters synaptic plasticity and exacerbates the generalized neuronal cell death characteristic of GM1-gangliosidosis.

neuroscience↗

bioRxiv2022

PPIX-binding Proteins Reveal Porphyrin Synthesis and Ferroptosis Link

All aerobic organisms require the cofactor heme to survive, but its synthesis requires formation of a potentially toxic intermediate protoporphyrin IX (PPIX). Little is known about the extent of PPIXs cellular interactions. Here, we report the development of PPB, a biotin-conjugated, PPIX-probe that captures proteins capable of interacting with PPIX. Quantitative proteomics with PPB identified common proteins among a diverse panel of mammalian cell lineages. Pathway and quantitative difference analysis revealed PPB-bound proteins related to iron and heme metabolism and suggested that these processes might be altered by heme/porphyrin synthesis. We show that increased heme/porphyrin synthesis in cells promotes ferroptosis that is pharmacologically distinct from canonical ferroptosis driven by erastin, an inhibitor of the cystine/glutamate antiporter. Proteomic data derived from PPB revealed an interactor, PRDX3, a mitochondrial peroxidase, that modulated heme/porphyrin biosynthesis driven ferroptosis. Consistent with a role in porphyrin-induced ferroptotic death targeted gene knockdown of PRDX3, but not peroxidases, PRDX1 or 2, enhanced porphyrin-induced ferroptotic death. The relationship between increased heme/porphyrin synthesis and ferroptosis was also found in a ferrochelatase-deficient T-lymphoblastoid leukemia cell line, suggesting potential strategy for treating certain cancers. We demonstrate that when the PPB probe is coupled with unbiased proteomics a previously unreported relationship between heme/porphyrin synthesis, and ferroptosis was discovered.

biochemistry↗

bioRxiv2022

Morphogen Directed Coordination of GPCR Activity Promotes Primary Cilium Function for Downstream Signaling

Sonic Hedgehog (SHH) signaling is an essential driver of embryonic patterning that, when corrupted, leads to developmental disorders and cancers. SHH effector responses are organized through nonmotile primary cilia that grow and retract with the cell cycle and in response to distinct extracellular cues. Destabilization of primary cilium length corrupts SHH pathway regulation, which places significant pressure on SHH to maintain ciliary architecture. Herein, we investigate whether SHH signaling promotes ciliary length control. We reveal a signal crosstalk circuit induced by SHH activation of Phospholipase A2 (cPLA2) that drives ciliary EP4 signaling to stabilize primary cilium length. We demonstrate that chemical or genetic blockade of SHH-EP4 crosstalk leads to destabilized primary cilium cyclic AMP (cAMP) control, reduced ciliary length, and attenuated SHH pathway induction. Accordingly, we find that Ep -/- mice display shortened neuroepithelial primary cilia and altered SHH-dependent neuronal cell fate specification. Thus, SHH initiates a signaling crosstalk circuit that maintains primary cilium length for a robust downstream signaling response.

cell biology↗

bioRxiv2020

Myosin 10 and a Cytoneme-Localized Ligand Complex Promote Morphogen Transport

Morphogens function in concentration-dependent manners to instruct cell fate during tissue patterning. Molecular mechanisms by which these signaling gradients are established and reinforced remain enigmatic. The cytoneme transport model posits that specialized filopodia extend between morphogen-sending and responding cells to ensure that appropriate signal activation thresholds are achieved across developing tissues. How morphogens are transported along and deployed from cytonemes is not known. Herein we show that the actin motor Myosin 10 promotes cytoneme-based transport of Sonic Hedgehog (SHH) morphogen to filopodial tips, and that SHH movement within cytonemes occurs by vesicular transport. We demonstrate that cytoneme-mediated deposition of SHH onto receiving cells induces a rapid signal response, and that SHH cytonemes are promoted by a complex containing a ligand-specific deployment protein and associated co-receptor. One-Sentence summaryCytoneme-based delivery of the Sonic Hedgehog activation signal is promoted by Myosin 10 and BOC/CDON co-receptor function.

cell biology↗

bioRxiv2017

A Complete Electron Microscopy Volume Of The Brain Of Adult Drosophila melanogaster

Drosophila melanogaster has a rich repertoire of innate and learned behaviors. Its 100,000-neuron brain is a large but tractable target for comprehensive neural circuit mapping. Only electron microscopy (EM) enables complete, unbiased mapping of synaptic connectivity; however, the fly brain is too large for conventional EM. We developed a custom high-throughput EM platform and imaged the entire brain of an adult female fly. We validated the dataset by tracing brain-spanning circuitry involving the mushroom body (MB), intensively studied for its role in learning. Here we describe the complete set of olfactory inputs to the MB; find a new cell type providing driving input to Kenyon cells (the intrinsic MB neurons); identify neurons postsynaptic to Kenyon cell dendrites; and find that axonal arbors providing input to the MB calyx are more tightly clustered than previously indicated by light-level data. This freely available EM dataset will significantly accelerate Drosophila neuroscience.\n\nHIGHLIGHTS- A complete adult fruit fly brain was imaged, using electron microscopy (EM)\n- The EM volume enables brain-spanning mapping of neuronal circuits at the synaptic level\n- Olfactory projection neurons cluster more tightly in mushroom body calyx than expected from light-level data\n- The primary postsynaptic targets of Kenyon cells (KCs) in the MB are other KCs, as well as the anterior paired lateral (APL) neuron\n- A newly discovered cell type, MB-CP2, integrates input from several sensory modalities and provides microglomerular input to KCs in MB calyx\n- A software pipeline was created in which EM-traced skeletons can be searched for within existing large-scale light microscopy (LM) databases of neuronal morphology, facilitating cell type identification and discovery of relevant genetic driver lines

neuroscience↗