Biology subjects

Hart, M. P.

Publications and source records attributed to Hart, M. P..

11 recordsLinked to original sources

bioRxiv2026

Neurexin mediates neuropeptide release from cholinergic motor neurons through dense-core vesicle localization

Neurexins are critical synaptic cell adhesion molecules that play many roles in modulating neurotransmitter release and synaptic function, and are high-confidence risk genes for neurodevelopmental conditions such as autism. Understanding the function of the neurexin superfamily has been challenging in mammalian systems that have 3 genes (NRXN1-3) that encode 2-3 major isoforms, which undergo extensive alternative splicing and generate thousands of transcripts. In contrast to mammals, C. elegans has a single gene, nrx-1, encoding only long alpha and short gamma isoforms. Neurexins canonically regulate synapse morphology and function in a neuron- and context-specific manner, through mechanisms related to release of chemical neurotransmitters and receptors. Whether neurexins (nrx-1) impact other secretory molecules such as neuropeptides (NPs) and NP containing dense-core vesicles (DCVs) is not well understood. Here, we report that nrx-1 regulates the release of multiple NPs from cholinergic motor neurons in C. elegans. Using tissue specific expression and degradation of endogenous NRX-1, we find that nrx-1 functions in NP release in a cell-autonomous manner and that the short gamma-isoform is required to regulate NP secretion from the cholinergic neurons. We confirm that loss of nrx-1 gamma-isoform impacts cholinergic active-zone number, but also find it regulates the clustering, distribution, and expression of the DCV protein, IDA-1 (PTPRN), and the DCV secretion regulator, UNC-31 (CADPS). We find that nrx-1 functions to maintain separation and juxtaposition of neurotransmitter and NP release sites and DCV localization. Loss of cholinergic excitation (unc-17) or GABAergic inhibition (unc-25) did not impact cholinergic NP release, but that the increased NP release upon loss of nrx-1 is dependent on the calcium channel unc-2. We find that neurexins can regulate NP signaling, a novel mechanism to modify circuits and behaviors, and of potential importance for NRXN1 associated human conditions.

neuroscience↗

bioRxiv2026

Allele-specific rescue of neurexin behavioral phenotypes by monoamine-targeting compounds

Neurexins are synaptic adhesion molecules associated with neurologic changes in humans, including neurodevelopmental delay, autism, schizophrenia, Tourette syndrome, and seizures. The NRXN1 gene produces >100 protein isoforms through alternative promoters and extensive splicing, which are differentially impacted by NRXN1 variants found in patients. Yet pharmacologic targeting of NRXN1 isoforms or deletions has not been comprehensively studied. Here, we developed a behavioral screening approach in C. elegans to identify small molecule compounds that modify the decreased activity levels caused by isoform-specific deletions of neurexin(nrx-1). Screening 190 compounds, we discovered that monoamine-targeting compounds differentially improve behavioral phenotypes depending on which nrx-1 isoforms are disrupted. Broad modulation of monoamine signaling, or antagonism of specific serotonin receptors, are required to increase the activity of both alleles tested. The FDA-approved atypical antipsychotic olanzapine was the sole validated compound achieving Z-scores >2 in both screens, which notably also rescued behavioral phenotypes of C. elegans harboring a conserved autism-associated NRXN1 missense variant (L18Q/L16Q) identified in human patients. In Drosophila Nrx-1 mutants, olanzapine uniquely and significantly improved activity deficits and extended survival, demonstrating evolutionary conservation of our findings. Multi-behavior testing revealed pharmacological specificity: olanzapine improved both activity and social feeding phenotypes of nrx-1 alleles, while asenapine maleate improved activity, but worsened social feeding, indicating distinct impacts across behavioral domains. Our findings establish monoamine modulation as a conserved compensatory mechanism for neurexin loss, identify olanzapine as a lead compound for targeting neurexin loss, and demonstrate that allele stratification and pharmacogenomic approaches are needed for precision intervention in behavioral conditions. Neurexins are synaptic adhesion molecules implicated in autism, schizophrenia, and neurodevelopmental disorders. NRXN1 produces over 100 isoforms differentially affected by patient variants, yet pharmacologic targeting has not been systematically studied. We developed a C. elegans behavioral screen to identify compounds rescuing activity deficits caused by isoform-specific deletions. Screening 190 compounds, we discovered that monoamine-targeting drugs differentially improved behavioral phenotypes depending on which isoforms were disrupted. The FDA-approved antipsychotic olanzapine uniquely achieved robust rescue (Z-scores >2) across all genetic backgrounds tested, including a conserved autism-associated NRXN1 missense variant (L18Q/L16Q) identified in patients. Olanzapines efficacy was conserved in Drosophila Nrx-1 mutants, improving activity and extending survival. Multi-behavior testing revealed pharmacological specificity: olanzapine rescued both activity and social feeding phenotypes, while asenapine differentially affected behavioral domains. Our findings establish monoamine modulation as a compensatory mechanism for neurexin loss and identify olanzapine as a therapeutic lead for precision intervention in neurexin-associated disorders.

neuroscience↗

bioRxiv2025

Insertion of rare autism variants in synaptic genes induce novel behavioral phenotypes in C. elegans

Neurodevelopmental conditions and disorders, including autism, involve a complex interplay of genetic, environmental, and developmental factors. Despite this complexity, genetic studies have identified more than 150 candidate genes that increase risk for autism and related neurodevelopmental and neuropsychiatric conditions. Unsurprisingly, synaptic genes are a large proportion of these genes, likely due to their roles in the formation and maintenance of synaptic architecture, function, and the plasticity of neurons and circuits. The association of synaptic genes with autism and similar conditions is driven by all types of genetic variation, including inherited and de novo rare variants that have unknown impacts on the function of the gene. Here we insert 4 conserved rare variants in the C. elegans orthologs of NLGN4X, NRXN1, and SHANK3, and define their impact on gene function compared to known loss of function variants using behavioral assays. We find that the rare variants impact multiple foraging behaviors, with each gene and variant having a unique pattern of behavioral changes and functional impact. The NLGN4X(A283T) variant induced clear loss of function, while NLGN4X(G84R) induces a loss of function in one behavior, but a gain of function in another behavior. The NRXN1(L18Q) variant induced remarkable loss and gain of functions with distinct impacts across each behavior. The SHANK3(L143P) variant induced partial loss of function in a single behavior. We also identify for the first time that loss of function of shn-1/SHANK3 alters social feeding and food response behaviors. We uncover a remarkably complex impact of rare variants in synaptic genes, with differential impacts across behaviors, highlighting the importance of broad behavioral analysis and the nuanced effects of missense variants compared to loss of function alleles. Together, we define the complex functional impact of each variant on gene function, compare the impact of variants and genes across multiple behaviors, and provide further support for the use of C. elegans to define the impact of genetic variation derived from human neurodevelopmental and neuropsychiatric disorders.

genetics↗

bioRxiv2025

Functional comparison of control and 3' deletion human NRXN1 isoforms in C. elegans

Heterozygous deletions in NRXN1, encoding the presynaptic adhesion molecule Neurexin 1, are among the most frequently identified rare variants in schizophrenia and other neuropsychiatric disorders. Patient sequencing has revealed that 3 deletions within NRXN1 generate novel isoforms not produced from the intact locus, yet whether these isoforms are functional, passively non-functional, or actively pathogenic in vivo is still not clear. To address this, we expressed eight human NRXN1 isoforms in C. elegans neurons including four control isoforms and four 3 deletion variant isoforms identified in schizophrenia patient cell lines, and characterized their effects on protein localization and two independent behaviors: a food deprivation response and social feeding behaviors. Most human isoforms showed expression and localization within the nerve ring and neurons similar to the C. elegans ortholog, NRX-1; however, several isoforms, particularly among the 3 deletion variants, displayed aberrant accumulation in neuronal cell bodies or as puncta in neuropil. Functionally, isoforms fell into one of three categories: no effect on nrx-1 loss-of-function behavioral phenotypes, partial rescue, or gain of function, with multiple isoforms showing differences between the behaviors. Strikingly, two 3 deletion isoforms produced gain-of-function behavioral phenotypes more severe than the nrx-1 null mutant, demonstrating that these patient-derived variants can be actively pathogenic. These results establish C. elegans as a tractable in vivo platform for dissecting the isoform-specific functional consequences of NRXN1 variants and suggest that strategies for NRXN1-associated neuropsychiatric diseases must account for both loss-of-function and gain-of-function isoform mechanisms.

neuroscience↗

bioRxiv2025

Variation in social feeding behavior and interactions among Caenorhabditis nematodes

The ability to respond to complex stimuli and environmental cues is essential for organisms to survive and reproduce. Responding to a wide range of stimuli requires a neuronal network that can integrate cues and execute behavioral responses. Evolution of behaviors occurs ubiquitously in most established ecological niches, even among closely related species. To uncover the genetic and neuronal drivers of evolving behaviors, we have taken advantage of the large and relatively ancient divergence in the Caenorhabditis genus to ask how different Caenorhabditis nematodes respond to environmental stimuli and whether behavioral traits are shared or distinct. Here, we assayed foraging behaviors of twelve members of the Caenorhabditis clade, including members of both the elegans and japonica supergroup, and the basal taxon C. monodelphis. For each species, we analyzed social feeding and bordering behaviors, which are well characterized in C. elegans. These behaviors are the functional readout of complex sensory integration of multiple sensory cues including pheromones, touch, O2/CO2 concentration, and attractive and noxious stimuli. We hypothesized that the evolutionary divergence between species would correlate to divergence in these behaviors. We observed a wide variation in social aggregate feeding and bordering behaviors of hermaphrodite and female animals, but the variation did not correlate with evolutionary relatedness of the species. Addition of male animals with female or hermaphrodite animals of the same species increased aggregation behavior of subset of species, but not others. Combination of a second species with C. elegans significantly reduced aggregate feeding behavior of C. elegans, but not the other species. Intraspecies and interspecies interactions therefore modifies behavioral paradigms. Overall, we find that foraging and social feeding behaviors vary widely across Caenorhabditis species, likely due to species-specific responses and integration of environmental and context sensory cues. In general, the clade represents a compelling model to dissect evolution of behavior across diverse environments and a large timescale.

evolutionary biology↗

bioRxiv2025

Multiple autism genes influence GABA neuron remodeling via distinct developmental trajectories

Variation in over 100 genes are now associated with increased risk for autism and related neurodevelopmental condition, but how this variation results in distinct and overlapping behavioral changes is still not well understood. Recent efforts have focused on screening many autism genes at once for functional and phenotypic convergence, and identified subsets that are crucial for many early steps of neurodevelopment. Few studies have screened later steps of neurodevelopment, circuit function, circuit plasticity, or behaviors. We screened twenty conserved autism-associated genes for impact on experience-dependent neuron remodeling in C. elegans. Loss of unc-44/ANK2, set-4/KMT5B, daf-18/PTEN, gap-2/SYNGAP1, and chd-1/CHD8 increased, while CACNA2D3/unc-36 decreased, neurite outgrowth of the GABAergic DVB neuron in adults. Although daf-18/PTEN, set-4/KMD5B, and unc-44/ANK2 had convergent phenotypes, they arise from distinct temporal trajectories with differential impact on DVB pre-synaptic morphology. Screening for the DVB regulated spicule protraction behavior identified multiple autism genes involved, but only unc-44/ANK2 and CACNA2D3/unc-36 were shared between screens. Application of a metric geometry computational framework (CAJAL) to the DVB morphology dataset identified 5 additional genes that impact DVB morphology, including unc-2/CACNA1A and unc-10/RIMS1, which also significantly impacted behavior. This work defines new regulators and molecular mechanisms of experience-dependent neuron remodeling and circuit plasticity, and further links these processes with conserved autism genes. It also demonstrates the utility of using intact, behavior generating circuits in C. elegans, to screen for novel roles for conserved autism genes.

neuroscience↗

bioRxiv2024

Neurexin drives C. elegans avoidance behavior independently of its post-synaptic binding partner Neuroligin

Neurexins and their canonical binding partners, neuroligins, are localized to neuronal pre-, and post-synapses, respectively, but less is known about their role in driving behaviors. Here, we use the nematode C. elegans to show that neurexin, but not neuroligin, is required for avoiding specific chemorepellents. We find that adults with knockouts of the entire neurexin locus exhibit a strong avoidance deficit in response to glycerol and a weaker defect in response to copper. Notably, the C. elegans neurexin (nrx-1) locus, like its mammalian homologs, encodes multiple isoforms, and {gamma}. Using isoform-specific mutations, we find that the {gamma} isoform is selectively required for glycerol avoidance. Next, we used transgenic rescue experiments to show that this isoform functions at least partially in the nervous system. We also confirm that the transgenes are expressed in the neurons and observe protein accumulation in neurites. Furthermore, we tested whether these mutants affect the behavioral responses of juveniles. We find that juveniles (4th larval stages) of mutants knocking out the entire locus or the -isoforms, but not {gamma}-isoform, are defective in avoiding glycerol. These results suggest that the different neurexin isoforms affect chemosensory avoidance behavior in juveniles and adults, providing a general principle of how isoforms of this conserved gene affect behavior across species. Article SummaryThe conserved neurexin locus can encode multiple isoforms via alternate splicing, but very little is known about the function of individual isoforms. We show that the C. elegans neurexin {gamma} isoform is specifically required for glycerol, but not copper or quinine avoidance in adults. In contrast, we find that , but not {gamma}, isoforms are required for avoiding glycerol in juveniles. Collectively, we suggest that different neurexin isoforms are required in juveniles and adults to modify chemosensory behavior.

neuroscience↗

bioRxiv2023

Conserved autism-associated genes tune social feeding behavior in C. elegans

Animal foraging is an essential and evolutionarily conserved behavior that occurs in social and solitary contexts, but the underlying molecular pathways are not well defined. We discover that conserved autism-associated genes (NRXN1(nrx-1), NLGN3(nlg-1), GRIA1,2,3(glr-1), GRIA2(glr-2), and GLRA2,GABRA3(avr-15)) regulate aggregate feeding in C. elegans, a simple social behavior. NRX-1 functions in chemosensory neurons (ADL and ASH) independently of its postsynaptic partner NLG-1 to regulate social feeding. Glutamate from these neurons is also crucial for aggregate feeding, acting independently of NRX-1 and NLG-1. Compared to solitary counterparts, social animals show faster presynaptic release and more presynaptic release sites in ASH neurons, with only the latter requiring nrx-1. Disruption of these distinct signaling components additively converts behavior from social to solitary. Aggregation induced by circuit activation is also dependent on nrx-1. Collectively, we find that aggregate feeding is tuned by conserved autism-associated genes through complementary synaptic mechanisms, revealing molecular principles driving social feeding. TEASERConserved autism-associated genes mediate distinct molecular and circuit signaling components that cooperate to tune C. elegans social feeding behavior.

neuroscience↗

bioRxiv2023

Structural neuroplasticity after sleep loss modifies behavior and requires neurexin and neuroligin

Sleep is conserved across species, and alterations in sleep are associated with a multitude of neurologic conditions. Structural neuroplasticity, or changes in the size, strength, number, and targets of neuronal synaptic connections, can be modified by sleep and sleep disruption. However, the causal relationships between sleep loss and neuroplasticity, behavioral impacts, and genetic perturbations are poorly understood. The C. elegans GABAergic DVB neuron undergoes structural plasticity in adult males that rewires synaptic connections and alters behavior; the rewiring is dependent on the conserved autism-associated genes NRXN1/nrx-1 and NLGN3/nlg-1. Stress exposure during sexual maturation, which overlaps with a developmental sleep period, alters DVB structural plasticity in early adulthood. Here, we use four distinct methods to ask whether sleep deprivation results in altered structural and behavioral plasticity of the DVB neuron. Following sleep deprivation using the genetic mutants (aptf-1 and npr-1), vibration stimulus, or chemo-genetic silencing of a sleep-producing neuron, we find that DVB neurite outgrowth at day 1 of adulthood. Sleep deprivation also leads to an increase in the time to spicule protraction, the behavioral output of DVB function. We find that nrx-1 and nlg-1 both function to regulate sleep loss induced DVB structural and functional changes. Lastly, differences in DVB neurite outgrowth in sleep deprived animals at day 1 are transient, with DVB morphology being indistinguishable from controls by day 3. These results show that sleep loss modifies DVB structural plasticity and its behavioral consequences. Further, we show nrx-1 and nlg-1 mediate the effect of sleep deprivation on behavior at the level of DVB structural plasticity. These insights into sleep, neuroplasticity, behavior, and conserved autism genes have important implications for the role of sleep in neurologic disease. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=128 SRC="FIGDIR/small/545788v1_figu1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@2320c4org.highwire.dtl.DTLVardef@3c3b86org.highwire.dtl.DTLVardef@67dc96org.highwire.dtl.DTLVardef@c3033d_HPS_FORMAT_FIGEXP M_FIG Graphical AbstractGABAergic morphologic and behavioral plasticity induced by developmental sleep deprivation depends on the conserved autism genes, nrx-1 and nlg-1 A) Sleep depriving male C. elegans during all larval sleep periods in development (aptf-1 or npr-1) or selectively inhibiting sleep during L4-adult molt (vibration or RIS silencing) results in an increase in DVB outgrowth. B) Mutations in nrx-1 (and nlg-1 in npr-1 animals) prevent sleep deprivation induced morphologic plasticity changes. C) DVB neurite outgrowth results in a functional change in spicule protraction rate as a result of increased GABAergic inhibitory signaling, which also depends on nrx-1 and nlg-1. C_FIG

neuroscience↗

bioRxiv2022

A general framework for the combined morphometric, transcriptomic, and physiological analysis of cells using metric geometry

High-resolution imaging-based single-cell profiling has transformed the study of cells in their spatial context. However, the lack of quantitative methods that can summarize the great diversity of complex cell shapes found in tissues and infer associations with other single-cell data modalities limits current analyses. Here, we report a general computational framework for the multi-modal analysis and integration of single-cell morphological data. We build upon metric geometry to construct cell morphology latent spaces, where distances in these spaces indicate the amount of physical deformation needed to change the morphology of one cell into that of another. Using these spaces, we integrate morphological data across technologies and leverage associated single-cell RNA-seq data to infer relations between morphological and transcriptomic cellular processes. We apply this framework to imaging and multi-modal data of neurons and glia to uncover genes related to neuronal plasticity. Our approach represents a strategy for incorporating cell morphological data into single-cell omics analyses.

bioinformatics↗

bioRxiv2018

Stress-induced neuron remodeling reveals differential interplay between neurexin and environmental factors

Neurexins are neuronal adhesion molecules important for synapse maturation, function, and plasticity. Neurexins have been genetically associated with neurodevelopmental disorders including autism spectrum disorders (ASDs) and schizophrenia, but can have variable penetrance and phenotypic severity. Heritability studies indicate that a significant percentage of risk for ASD and schizophrenia includes environmental factors, highlighting the poorly understood interplay between genetic and environmental factors in pathogenesis of these disorders. The singular C. elegans ortholog of human neurexins, nrx-1, controls experience-dependent morphologic remodeling of a GABAergic neuron in adult males. Here I show that this GABAergic neurons morphology is altered in response to each of three environmental stressors (nutritional, heat, or genotoxic stress) applied during sexual maturation, but not during adulthood. Increased outgrowth of axon-like neurites following adolescent stress results from an altered morphologic plasticity that occurs upon entry into adulthood. Despite axonal remodeling being induced by each of the three stressors, only nutritional stress (starvation) impacts behavior and is dependent on neurexin/nrx-1. Heat or genotoxic stress during sexual maturation did not alter behavior despite inducing GABAergic neuron remodeling, and this remodeling was independent of neurexin/nrx-1. Remodeling induced by starvation stress was found be dependent on neuroligin/nlg-1, the canonical binding partner for neurexin/nrx-1, as well as the stress signaling transcription factors FOXO/daf-16 and HSF1/hsf-1, each of which was also found to have unique roles in remodeling induced by heat and UV stress. The differential molecular mechanisms underlying GABAergic neuron remodeling in response to different stressors, and the disparate effects of stressors on behavior, is a novel paradigm for understanding how genetics, environmental exposures, and plasticity may contribute to brain dysfunction in ASDs and schizophrenia.

neuroscience↗