Biology subjects

Sigrist, S. J.

Publications and source records attributed to Sigrist, S. J..

18 recordsLinked to original sources

bioRxiv2025

Autophagy-driven Presynaptic Reorganization as a Molecular Signature of Brain Resilience.

Neural circuits must remain functionally stable while responding flexibly to changing demands, stressors, and aging-related decline. While this balance is thought to be maintained through plasticity programs that integrate molecular, metabolic, and activity-dependent signals to reconfigure synapses structurally and functionally, direct mechanistic models of how such adaptations are orchestrated remain scarce. Here, we show that targeted impairment of autophagy in the Drosophila mushroom body (MB), a key sleep-regulatory and integrative center in the fly brain, triggers a brain-wide remodeling at presynaptic active zones (AZ). Quantitative proteomics revealed a specific upregulation of AZ scaffold proteins (including BRP, RIM, and Unc13A), accompanied by reduced levels of calcium channel subunits and increased Shaker-type potassium channels. These changes occurred largely independent of transcription and highlight a coordinated, excitability-tuning response centered on the AZ. Behaviorally, MB-specific autophagy impairment increased sleep and modestly extended lifespan. These adaptations resembled a previously described resilience program termed PreScale, which promotes restorative sleep homeostasis in response to sleep deprivation and early, still reversible brain aging. Conversely, overexpression of Atg5 in the MB delayed the onset of PreScale. Notably, autophagic disruption confined to MB neurons also caused widespread, non-cell autonomous accumulation of Ref(2)P and ATG8a-positive aggregates across the brain, revealing systemic propagation of proteostatic stress. Together, our findings identify MB autophagy as a key regulator of synaptic architecture and sleep-associated resilience. Such early acting programs may actively preserve circuit function and behavioral output by regulating synaptic plasticity, and define a genetically tractable model for how local stress signals can orchestrate brain-wide adaptation via post-transcriptional synaptic reprogramming.

neuroscience↗

bioRxiv2025

An active Unc13A is Reboundless in sleep homeostasis

One of the major characteristics of sleep is homeostatic sleep rebound following sleep loss. While the molecular mechanisms of baseline sleep regulation have been intensively studied, a specific molecular understanding of sleep rebound remains elusive. Here, we show that a constitutively active form of the Munc13-family presynaptic release factor Unc13A, which lacks the inhibitory Ca2+/calmodulin interaction domain (Unc13AWRWR), dominantly suppressed sleep rebound upon acute sleep deprivation, leading to a nearly complete elimination of recovery sleep ("reboundless"). In contrast, baseline sleep remained largely normal. Through a genetic modifier screen, we found that this dominant "reboundless" phenotype of Unc13AWRWR was rescued by a partial loss of Snap, a cofactor of NSF required for disassembly and recycling of post-fusion cis-SNARE complex. Given that Unc13A promotes fusion-competent trans-SNARE complex formation, these findings suggest that sleep rebound may depend on a delicate balance between SNARE complex assembly and recycling. Additionally, we found that expression of a human disease-associated active Unc13A (Unc13APL) variant attenuated baseline and rebound sleep. Since both Unc13AWRWR and Unc13APL were shown to promote presynaptic release probability (Pr), we speculate that Unc13A suppresses recovery sleep likely by increasing Pr and subsequently enhancing synaptic transmission, probably through elevated trans-SNARE formation and efficient cis-SNARE recycling. Taken together, our data demonstrate a fundamental role of Unc13A and SNARE dynamics in sleep homeostasis.

neuroscience↗

bioRxiv2025

Non-cell autonomous control of presynaptic remodeling by the hypothalamic autophagy/NPY axis

Macroautophagy/autophagy, a critical cellular degradation pathway essential for maintaining neuronal proteostasis, declines with age and has been increasingly implicated in the regulation of synaptic integrity and circuit resilience. Neuropeptide Y (NPY), the most abundantly expressed neuropeptide in the mammalian brain, has emerged as a key modulator of both autophagy and aging-related processes. In Drosophila, the NPY-family peptide short Neuropeptide F (sNPF) has been shown to causally influence aging-associated changes in synaptic architecture and function, particularly at the presynaptic active zone (AZ), via non-cell autonomous mechanisms. Extending this concept to mammals, we investigated whether NPY and autophagy interact within NPY-secreting neurons to regulate age-related AZ remodeling. Our results indicate that hypothalamic NPY/AgRP neurons may exert geroprotective effects through the release of NPY and potentially other signaling molecules, thereby influencing both metabolic homeostasis and brain-wide synaptic function. These data suggest a conserved role for autophagy in maintaining presynaptic organization and resilience during aging.

neuroscience↗

bioRxiv2025

A model investigation of short-term synaptic plasticity tuned via Unc13 isoforms.

Short-term synaptic plasticity (STP) is a fundamental mechanism of neural computation supporting a variety of nervous system functions from sensory adaptation and gain control to working memory and decision making. At the presynaptic release site, an interplay between distinct (M)Unc13 protein isoforms is suggested to orchestrate depressing and facilitating components of STP. In this study, we introduce a modification of the well-established TsodyksMarkram Model (TMM) for STP. We constrain our model by in vivo intracellular recordings in the olfactory system of the fruit fly, where previous work suggested Unc13A to provide a phasic, depressing and Unc13B a tonic, facilitating release component. A combination of a facilitating and a depressing model component indeed allowed for accurate model fits. Differential knock-down experiments of the Unc13A and Unc13B gene variants provide biological model interpretation, linking the protein-specific molecular mechanisms to synaptic function and STP. Our mathematical formulation of protein-dependent STP can be readily and efficiently used to design biologically realistic spiking neural network models that feature different genetically defined synapse types.

neuroscience↗

bioRxiv2025

Monoamine-induced diacylglycerol signaling rapidly accumulates Unc13 in nanoclusters for fast presynaptic potentiation

Neuromodulators control mood, arousal, and behavior by inducing synaptic plasticity via G-protein coupled receptors. Long-term potentiation of presynaptic neurotransmitter release requires structural changes, but how fast potentiation is achieved within minutes remains enigmatic. Using the Drosophila melanogaster neuromuscular junction, we show that on the timescale of one minute, octopamine, the invertebrate analog of nor-epinephrine, rapidly potentiates evoked neurotransmitter release by a G protein coupled pathway involving presynaptic OAMB receptors and phospholipase C. No changes of presynaptic calcium influx were seen, but confocal signals of the release factor Unc13A and the scaffolding protein Bruchpilot increased within one minute of octopamine treatment. On the same timescale, live, single-molecule imaging of endogenously tagged Unc13 revealed its instantly reduced motility and its increased concentration in synaptic nanoclusters with potentiation. Presynaptic knockdown of Unc13A fully blocked fast potentiation and removal of its N-terminal localization sequence delocalized the protein fragment to the cytosol, but it was rapidly recruited to the plasma membrane by DAG analog phorbol esters and octopamine, pointing to a role in C-terminal domains. Point mutation of endogenous Unc13 disrupting diacylglycerol-binding to its C1 domain blocked plasticity-induced nanoscopic enrichment and synaptic potentiation. The mutation increased basal neurotransmission but reduced Unc13 levels, revealing a gain of function and potential homeostatic compensation. The mutation also blocked phorbol ester-induced potentiation, decreased the calcium-sensitivity of neurotransmission and caused short-term synaptic depression. At the organismal level, the mutation reduced locomotion and survival while enhancing reproduction. Thus, the Unc13 C1 domain mediates acute subsynaptic compaction of Unc13 under monoamine-induced potentiation and influences short-term plasticity, locomotion, reproduction, and survival.

neuroscience↗

bioRxiv2024

Cognitive hyperplasticity drives insomnia

Sleep is vital for maintenance of cognitive functions and lifespan across the animal kingdom. Here, we report our surprising findings that insomniac (inc) Drosophila short sleep mutants, which lack a crucial adaptor protein for the autism-associated Cullin-3 ubiquitin ligase, exhibited excessive olfactory memory. Through a genetic modifier screen, we find that a mild attenuation of Protein Kinase A (PKA) signaling specifically rescued the sleep and longevity phenotypes of inc mutants. Surprisingly, this mild PKA signaling reduction further boosted the excessive memory in inc mutants, coupled with further exaggerated mushroom body overgrowth phenotypes. We propose that an intrinsic hyperplasticity scenario genuine to inc mutants enhances cognitive functions. Elevating PKA signaling seems to serve as a checkpoint which allows to constrain the excessive memory and mushroom body overgrowth in these animals, albeit at the sacrifice of sleep and longevity. Our data offer a mechanistic explanation for the sleep deficits of inc mutants, which challenges traditional views on the relation between sleep and memory, and suggest that behavioral hyperplasticity, e.g., prominent in autistic patients, can provoke sleep deficits.

neuroscience↗

bioRxiv2024

Identification and characterization of a synaptic active zone assembly protein

At presynaptic active zones (AZs), scaffold proteins play a crucial role in coordinating synaptic vesicle (SV) release and forming intricate nanoarchitectures essential for synaptic function. Despite their suspected importance, factors governing the assembly of nanoscale AZ scaffolds have remained elusive. Here, we identify "Blobby" as a novel regulator of AZ nanopatterning, localized within the AZ scaffold. Genetic loss of the extended Blobby protein led to aberrant accumulation of AZ scaffold proteins ("blobs") and disrupted the nanoscale architecture of the AZ scaffold, resulting in a significant reduction in the packing density of voltage-gated Ca2+ channels at AZs, as observed through intravital single-molecule imaging. This disruption correlated with decreased evoked synaptic currents and SV release probability. Our findings suggest that Blobby plays a crucial role in switching the AZ scaffold into a state which allows to fine-tune the dynamic nanopatterning of Ca2+ channels to maintain proper release.

neuroscience↗

bioRxiv2023

An antagonism between Spinophilin and Syd-1 operates upstream of memory promoting presynaptic long-term plasticity

We still face fundamental gaps in understanding how molecular plastic changes of synapses intersect with circuit operation to define behavioral states. Here we show that an antagonism between two conserved regulatory proteins, Spinophilin (Spn) and Syd-1, controls presynaptic long-term plasticity and the maintenance of olfactory memories in Drosophila. While Spn mutants could not trigger nanoscopic active zone remodeling under homeostatic challenge and failed to stably potentiate neurotransmitter release, concomitant reduction of Syd-1 rescued all these deficits. The Spn/Syd-1 antagonism converged on active zone close F-actin, and genetic or acute pharmacological depolymerization of F-actin rescued the Spn deficits by allowing access to synaptic vesicle release sites. Within the intrinsic mushroom body neurons, the Spn/Syd-1 antagonism specifically controlled olfactory memory stabilization but not initial learning. Thus, this evolutionarily conserved protein complex controls behaviorally relevant presynaptic long-term plasticity, also observed in the mammalian brain but still enigmatic concerning its molecular mechanisms and behavioral relevance.

neuroscience↗

bioRxiv2022

A brain-wide form of presynaptic active zone plasticity orchestrates resilience to brain aging in Drosophila

The brain as a central regulator of stress integration determines what is threatening, stores memories and regulates physiological adaptations across the aging trajectory. While sleep homeostasis is linked to brain resilience, how age-associated changes intersect to adapt brain resilience remains enigmatic. We here provide evidence that a brain-wide form of presynaptic active zone plasticity ("PreScale") promotes resilience by coupling sleep, longevity and memory during aging. PreScale increased until mid-age and contributed to the age-adaption of sleep patterns, in effect promoting longevity but not memory of aging flies. Mechanistically, imaging and electrophysiology suggest that genetically-encoded PreScale reprograms neuronal activity, membrane firing patterns and excitability of the sleep-promoting dorsal fan-shaped body neurons, qualitatively similar to aging. Flies metabolically reprogrammed by spermidine towards extended longevity and preserved memory skipped PreScale and subsequently age-associated sleep pattern changes. Acute deep sleep induction in mid-age flies reset PreScale back to juvenile levels and restored memory. Taken together, early along aging trajectory, PreScale seems to steer trade-offs between longevity and memory, illustrating how life strategy manifests on circuit and synaptic plasticity levels. GRAPHIC ABSTRACT Presynaptic plasticity at the active zone (AZ) during early aging triggers sleep pattern changes, and subsequently steers trade-offs between memory formation and longevity. Interventions like spermidine (Spd) and Gaboxadol (THIP) supplementation suppress PreScale and allow for new memory formation and lifespan extension. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=127 SRC="FIGDIR/small/498204v1_ufig1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@fa9a69org.highwire.dtl.DTLVardef@af6a27org.highwire.dtl.DTLVardef@62331aorg.highwire.dtl.DTLVardef@109029f_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2021

Homeostatic active zone remodeling consolidates memories in the Drosophila mushroom body

Establishing a detailed understanding of how the distinct forms of synaptic plasticity spatio-temporally engage into the initial storage and subsequent consolidation of memories remains a fundamental challenge of neuroscience. In addition to the better understood postsynaptic plasticity, different forms of presynaptic plasticity are widely expressed in mammalian brains and apparently operate along Hebbian or homeostatic rules. Their behavioral relevance remains enigmatic, however. Lately, acute upregulation of active zone (AZ) scaffold protein BRP and release factor Unc13A via specific axonal transport factors were shown to mediate stable expression of presynaptic homeostatic plasticity (PHP) at Drosophila neuromuscular junctions (NMJs). We here demonstrate that AZ scaling processes are specifically needed for stable expression of both, NMJ PHP as well as aversive olfactory mid-term memory within intrinsic neurons of the Drosophila mushroom body (MB). We first demonstrate that AZ upscaling via BRP is specifically needed for expression but not induction of NMJ homeostatic plasticity, thus establishing a direct temporal plasticity sequence of molecularly distinct AZ remodeling steps. Notably, when we reduced BRP and associated transport factors in MB intrinsic neurons, short-term memory persisted but robust deficits in stable memory expression for a few hours after conditioning were observed. In contrast, AZ release site protein RIM-BP affecting PHP induction was additionally needed for successful formation of short-term memory. Taken together, our data establish a specific role of homeostatic presynaptic long-term plasticity for memory consolidation. Such homeostatic refinement processes might well be needed to successfully integrate and display synaptic engrams constituting intermediary term memories.

neuroscience↗

bioRxiv2021

Spermidine reduces neuroinflammation and soluble amyloid beta in an Alzheimer's disease mouse model

Deposition of amyloid beta (A{beta}) along with glia cell-mediated neuroinflammation are prominent pathogenic hallmarks of Alzheimers disease (AD). In recent years, impairment of autophagy has been found to be another important feature, contributing to AD progression and aging. Therefore, we assessed the effect of the autophagy activator Spermidine, a small body-endogenous polyamine often used as dietary supplement and known to promote longevity, on glia cell-mediated neuroinflammation. Spermidine reduced TLR3- and TLR4- mediated inflammatory processes in microglia and astrocytes by decreasing cytotoxicity, inflammasome activity and NF-{kappa}B signaling. In line with these anti-inflammatory effects, oral treatment of the amyloid prone AD-like APPPS1 mice with Spermidine reduced neuroinflammation and neurotoxic soluble A{beta}. Mechanistically, single nuclei sequencing revealed microglia as one of the main targets of Spermidine treatment, with increased expression of genes implicated in cell motility and phagocytosis. Thus, Spermidine provides a promising therapeutic potential to target glia cells in AD progression.

neuroscience↗

bioRxiv2020

The autophagy activator Spermidine ameliorates Alzheimer's disease pathology and neuroinflammation in mice

Deposition of amyloid beta (A{beta}) and phosphorylated Tau along with microglia- and astrocyte-mediated neuroinflammation are prominent pathogeneic features of Alzheimers Disease (AD). In recent years, impairment of autophagy has also been shown to contribute to AD progression. Here, we provide evidence that oral treatment of amyloid-prone AD-like APPPS1 mice with the autophagy activator Spermidine, a small body-endogenous polyamine often used as dietary supplement, decreased neuroinflammation and reduced neurotoxic soluble A{beta} at both early and late stages of AD. Mechanistically, Spermidine induced autophagy in microglia as well as in astrocytes, which subsequently impacted TLR3- and TLR4-mediated inflammatory processes by decreasing cytotoxicity, inflammasome activity and NF-{kappa}B signalling. Our data highlight that autophagy targets the inflammatory response of glial cells and emphasize the potential of orally administered autophagy-activating drugs such as Spermidine to interfere with AD progression.

neuroscience↗

bioRxiv2020

Increased and synchronous recruitment of release sites underlies hippocampal mossy fiber presynaptic potentiation

Synaptic plasticity is a cellular model for learning and memory. However, the expression mechanisms underlying presynaptic forms of plasticity are not well understood. Here, we investigate functional and structural correlates of long-term potentiation at large hippocampal mossy fiber boutons induced by the adenylyl cyclase activator forskolin. We performed two-photon imaging of the genetically encoded glutamate sensor iGluu that revealed an increase in the surface area used for glutamate release at potentiated terminals. Moreover, time-gated stimulated emission depletion microscopy revealed no change in the coupling distance between immunofluorescence signals from calcium channels and release sites. Finally, by high-pressure freezing and transmission electron microscopy analysis, we found a fast remodeling of synaptic ultrastructure at potentiated boutons: synaptic vesicles dispersed in the terminal and accumulated at the active zones, while active zone density and synaptic complexity increased. We suggest that these rapid and early structural rearrangements likely enable long-term increase in synaptic strength.

neuroscience↗

bioRxiv2020

Presynaptic precursor vesicles originate from the trans-Golgi network, promoted by the small GTPase RAB2

Reliable delivery of presynaptic material, including active zone and synaptic vesicle proteins from neuronal somata to synaptic terminals is prerequisite for faithful synaptogenesis and neurotransmission. However, molecular mechanisms controlling the somatic assembly of presynaptic precursors remain insufficiently understood. Here we show that in mutants of the small GTPase RAB2 active zone and synaptic vesicle proteins accumulated in the neuronal somata at the trans-Golgi network and were consequently depleted at synaptic terminals, provoking neurotransmission deficits. The ectopic presynaptic material accumulations consisted of heterogeneous vesicles and short tubules of 40x60 nm and segregated in subfractions either positive for active zone proteins or co-positive for synaptic vesicle proteins and LAMP1, a lysosomal membrane protein. Genetically, rab2 behaved epistatic over arl8, a lysosomal adaptor controlling axonal export of precursors. Collectively, we here identified a Golgi-associated assembly sequence in presynaptic precursor vesicle biogenesis controlled by RAB2 dependent membrane remodelling and protein sorting at the trans-Golgi.

neuroscience↗

bioRxiv2019

Network-specific synchronization of electrical slow-wave oscillations regulates sleep in Drosophila

Slow-wave rhythms characteristic of deep sleep oscillate in the delta band (0.5-4 Hz) and can be found across various brain regions in vertebrates. Across systems it is however unclear how oscillations arise and whether they are the causal functional unit steering behavior. Here, for the first time in any invertebrate, we discover sleep-relevant delta oscillations in Drosophila. We find that slow-wave oscillations in the sleep-regulating R2 network increase with sleep need. Optical multi-unit voltage recordings reveal that single R2 neurons get synchronized by sensory and circadian input pathways. We show that this synchronization depends on NMDA receptor (NMDARs) coincidence detector function and on an interplay of cholinergic and glutamatergic inputs setting a resonance frequency. Genetically targeting the coincidence detector function of NMDARs in R2, and thus the uncovered mechanism underlying synchronization, abolished network-specific slow-wave oscillations. It also disrupted sleep and facilitated light-induced wakening, directly establishing a causal role for slow-wave oscillations in regulating sleep and sensory gating. We therefore propose that the synchronization-based increase in oscillatory power likely represents an evolutionarily conserved, potentially optimal, strategy for constructing sleep-regulating sensory gates.

neuroscience↗

bioRxiv2018

Rapid active zone remodeling consolidates presynaptic potentiation

Synaptic transmission is mediated by neurotransmitter release at presynaptic active zones (AZs) followed by postsynaptic neurotransmitter detection. Plastic changes in transmission maintain functionality during perturbations and enable memory formation. Postsynaptic plasticity targets neurotransmitter receptors, but presynaptic plasticity mechanisms directly regulating the neurotransmitter release apparatus remain largely enigmatic. Here we describe that AZs consist of nano-modular release site units and identify a molecular sequence adding more modules within minutes of plasticity induction. This requires cognate transport machinery and a discrete subset of AZ scaffold proteins. Structural remodeling is not required for the immediate potentiation of neurotransmitter release, but rather necessary to sustain this potentiation over longer timescales. Finally, mutations in Unc13 that disrupt homeostatic plasticity at the neuromuscular junction also impair shot-term memory when central neurons are targeted, suggesting that both forms of plasticity operate via Unc13. Together, while immediate synaptic potentiation capitalizes on available material, it triggers the coincident incorporation of modular release sites to consolidate stable synapse function.

neuroscience↗

bioRxiv2018

RIM-BP2 primes synaptic vesicles via recruitment of Munc13-1 at hippocampal mossy fiber synapses

All synapses require fusion-competent vesicles and coordinated Ca2+-secretion coupling for neurotransmission, yet functional and anatomical properties show a high diversity across different synapse types. We show here that the presynaptic protein RIM-BP2 has diversified functions in neurotransmitter release at different central mammalian synapses and thus contributes to synaptic diversity. At hippocampal pyramidal CA3-CA1 synapses, RIM-BP2 loss has a mild effect on neurotransmitter release, by only regulating Ca2+-secretion coupling. However, at hippocampal mossy fiber synapses RIM-BP2 has a strong impact on neurotransmitter release by promoting vesicle docking/priming via recruitment of Munc13-1. In wild type mossy fiber synapses, the distance between RIM-BP2 clusters and Munc13-1 clusters is larger than in hippocampal pyramidal CA3-CA1 synapses, suggesting that spatial organization may dictate the role a protein plays in synaptic transmission and that differences in active zone architecture is a major determinant factor in the functional diversity of synapses.

neuroscience↗

bioRxiv2017

A lineage-related reciprocal inhibition circuitry for sensory-motor action selection

The insect central complex and vertebrate basal ganglia are forebrain centres involved in selection and maintenance of behavioural actions. However, little is known about the formation of the underlying circuits, or how they integrate sensory information for motor actions. Here, we show that paired embryonic neuroblasts generate central complex ring neurons that mediate sensory-motor transformation and action selection in Drosophila. Lineage analysis resolves four ring neuron subtypes, R1-R4, that form GABAergic inhibition circuitry among inhibitory sister cells. Genetic manipulations, together with functional imaging, demonstrate subtype-specific R neurons mediate the selection and maintenance of behavioural activity. A computational model substantiates genetic and behavioural observations suggesting that R neuron circuitry functions as salience detector using competitive inhibition to amplify, maintain or switch between activity states. The resultant gating mechanism translates facilitation, inhibition and disinhibition of behavioural activity as R neuron functions into selection of motor actions and their organisation into action sequences.

neuroscience↗