Biology subjects

Alexander, J.

Publications and source records attributed to Alexander, J..

At least 19 recordsLinked to original sources

bioRxiv2026

The Estuary Effect: Variations in Temperature and Salinity Alter msh Promoter Activity in Vibrio cholerae

Vibrio cholerae, the facultative pathogen underlying cholera, naturally inhabits warm aquatic estuaries. Environmental persistence is enhanced by the ability of V. cholerae to colonize host reservoirs and form multicellular biofilms, causing seasonally endemic outbreaks in many tropical regions. Most toxigenic strains utilize the type IVa mannose-sensitive hemagglutinin (MSHA) pilus for host reservoir colonization and biofilm formation. Temperature and salinity can alter V. cholerae biofilm formation, yet their impact on MSHA production specifically remains largely unknown. Here, we utilized transcriptional reporters of predicted msh promoters (msh-P1/msh-P2/msh-P3) and functional assays, to determine temperature and salinity impacts on msh expression and pilus biogenesis. Under standard laboratory conditions (30{degrees}C, 1% NaCl) only msh-P1/P2 are active and inversely-coordinated with one another. Both msh-P1/P2 activity were elevated by high temperature (37{degrees}C) and low salinity (0.25%/0.5% NaCl), and reduced by low temperature (20{degrees}C/25{degrees}C) and high salinity (2%/3% NaCl). Temperature-mediated alterations in promoter activity were not immediately reflected in changes to cell-surface MSHA levels, whereas high salinity led to decreased MSHA production. Combining high temperature (37{degrees}C) and high salinity (2%/3% NaCl), attenuated the salinity-mediated reduction of msh-P1/P2 activity. Biofilm biomass levels were only substantially heightened at 25{degrees}C and 20{degrees}C, likely a result of no temperature-dependent changes in cell-surface MSHA, and additional temperature-controlled biofilm regulation previously described. We also found msh-P1/P2 promoter activity and MSHA production varies widely across toxigenic O1 and O139 serogroups despite complete sequence homology. These results shed new light on how key signals regulate MSHA pilus production to support V. cholerae persistence in aquatic environments.

microbiology↗

bioRxiv2026

Host cohort has a larger impact on the gut microbiomes of mealworms and superworms than does the ingestion of polyethylene or polystyrene

Beetles (order Coleoptera) are a diverse insect group whose associated microbial communities remain understudied despite their ecological, commercial, and biotechnological importance. Larvae of the darkling beetle species Tenebrio molitor (mealworms) and Zophobas atratus (superworms) have gained attention for their reported ability to ingest and possibly degrade plastics such as polyethylene and polystyrene. This degradation is believed to be mediated by enzymes from their gut microbiota, yet the underlying microbial mechanisms remain unclear. Using deep shotgun metagenomics, we generated comprehensive gut metagenomes for mealworms and superworms, recovering 53 and 100 high-quality metagenome-assembled genomes (MAGs), respectively. We found that the gut microbiomes of both insect species are dominated by bacteria from the phyla Bacillota and Pseudomonadota, with superworms trending towards greater bacterial diversity than mealworms. Comparing gut bacterial communities of insects fed polyethylene or polystyrene versus controls revealed no clear plastic ingestion effects beyond those attributable to starvation. On the other hand, insect cohort contributed substantially to variation in bacterial community composition, explaining 23% and 33% of the total variation in mealworms and superworms, respectively. Finally, we computationally identified numerous secreted proteins with sequence similarity to enzymes previously implicated in polyethylene and polystyrene degradation, and we provide support for dye decolorizing peroxidase (DyP)-type peroxidases as being the enzyme class mostly likely to initiate plastic oxidation in the digestive tracts of mealworms and superworms. Overall, this study provides high-quality metagenomes and MAGs for mealworms and superworms, revealing substantial under-explored microbial biodiversity, and highlighting DyP-type peroxidases as promising targets for future plastic biodegradation studies.

microbiology↗

bioRxiv2026

SMAD4 loss drives chromosomal instability during tumourigenesis via translational reprogramming

Chromosomal instability (CIN), arising from errors in chromosome segregation during cell division, is a hallmark of cancer. Whilst CIN can result from several mitotic defects, the mechanisms that initiate CIN to drive tumourigenesis remain incompletely understood. Here, we show that loss of SMAD4 reprograms translation to induce CIN, resulting in tumour formation. Multi-omics analysis of tumourigenesis models driven by loss of SMAD4 complemented by functional studies demonstrate that loss of SMAD4 in pre-neoplastic cells leads to dysfunctional mitosis and an altered global translation landscape. We show that CDK11B is translationally downregulated in SMAD4-\- cells, and re-expression of the mitosis-specific isoform of this protein (CDK11B-p58) rescues the mitotic defects. Analysis of patient tumours reveals a strong correlation between markers of CIN and SMAD4 status, indicating the clinical relevance of this phenotype. Collectively, we reveal a previously unrecognised role for SMAD4 as a gatekeeper for CIN-mediated tumourigenesis via regulation of translation.

cancer biology↗

bioRxiv2026

Biotic modulators of global change effects on plant communities

Understanding and predicting future plant biodiversity and productivity is critical for prioritizing global change mitigation, conservation, and restoration efforts. One major challenge is that we know remarkably little of how interspecific interactions may modulate the effects of global change factors on diversity and productivity. Here, we develop and test a synthetic conceptual framework about how different biotic modulators (herbivory, plant-plant interactions, pathogens, mycorrhiza) can either amplify or mitigate the effects of global change drivers (nutrient and CO2 enrichment, changes in rainfall and temperature) on plant community biomass and diversity. We report that herbivores mitigated both biomass increment and diversity decline caused by different global change drivers, while plant competition did not significantly alter global change impacts due to mixed effects (both amplification and mitigation). Pathogens tended to function similarly to herbivores, while mycorrhiza both amplified and mitigated community responses. Our conceptual framework further identifies mechanisms by which species interactions can modify global change effects, provides new testable hypotheses, and identifies research gaps and future research directions. We conclude that plant consumers can be important agents stabilizing plant productivity and safeguarding plant biodiversity in the Anthropocene, while more research is urgently needed to understand the role of other biotic modulators.

ecology↗

bioRxiv2025

Non-transcriptional gibberellin DELLA signalling for microtubule dynamics

Plant cell growth is associated with changes in the dynamics and orientation of the microtubule (MT) cytoskeleton. The plant hormone Gibberellic acid (GA), a central regulator of growth also has an impact on MT arrangements, however the causal relationship between these processes and underlying molecular mechanism remain unclear. Here, examining the Arabidopsis thaliana root elongation zone, we show that MT reorientation occurs as a consequence of GA-induced cell elongation and that GA has also a direct effect on the rate of MT polymerization via a non-transcriptional mechanism. Preventing cell elongation blocked GA-induced MT reorganization, whereas GA still promoted elongation in the absence of intact MTs. On the other hand, GA promoted MT dynamics as revealed by the recovery of MTs following depolymerization or photobleaching. Live imaging revealed that GA directly promotes MT polymerization at their plus ends. This GA effect persists even when transcription or translation are inhibited, but still requires the DELLA canonical components of GA signalling and their interactors, the prefoldins (PFDs). Our results support a model where GA-induced DELLA degradation releases in nucleus sequestrated PFDs, enhancing their cytoplasmic function to promote MT polymerization. Hence, GA signalling branches into two mechanistically distinct modules: (i) canonical transcriptional pathway that promotes growth and indirectly drives MT reorientation; and (ii) the non-transcriptional DELLA-PFD axis that directly promotes MT polymerization. Such a dual mechanism enables plants to synchronize growth with cytoskeletal remodelling by coupling rapid, cytoplasmic responses to slower transcriptional programs.

cell biology↗

bioRxiv2025

Rapid adaptation and extinction across climates in synchronized outdoor evolution experiments of Arabidopsis thaliana

Climate change is threatening species with extinction, and rapid evolutionary adaptation may be their only option for population rescue over short ecological timescales. However, direct observations of rapid genetic adaptation and population dynamics across climates are rare across species. To fill this gap, we conducted a replicated, globally synchronized evolution experiment with the plant Arabidopsis thaliana for 5 years in over 30 outdoor experimental gardens with distinct climates across Europe, the Levant, and North America. We performed whole-genome sequencing on [~]70,000 surviving reproductive individuals and directly observed rapid and repeatable adaptation across climates. Allele frequency changes over time were parallel in experimental evolution replicates within the same climates, while they diverged across contrasting climates--with some allele frequency shifts best explained by strong selection between -46% to +60%. Screening the genome for signals of rapid climate adaptation identified a polygenic architecture with both known and novel adaptive genetic variants connected to important ecological phenotypes including environmental stress responses, CAM5 and HEAT SHOCK FACTORs, and germination and spring flowering timing, CYTOCHROME P450s and TSF. We found evolutionary adaptation trends were often predictable, but variable across environments. In warm climates, high evolutionary predictability was associated with population survival up to 5 years, while erratic trends were an early warning for population extinction. Together, these results show rapid climate adaptation may be possible, but understanding its limits across species will be key for biodiversity forecasting.

evolutionary biology↗

bioRxiv2025

Tomosyn-2 Regulates Postnatal β-Cell Expansion and Insulin Secretion to Maintain Glucose Homeostasis.

The transition from proliferative to functionally mature {beta}-cells is a critical developmental process, yet the molecular mechanisms that coordinate this shift remain poorly understood. Here, we identify Tomosyn-2 as a key regulator of {beta}-cell maturation. Tomosyn-2 expression declines with age in mouse islets, coinciding with enhanced biphasic glucose-stimulated insulin secretion (GSIS) and reduced {beta}-cell proliferation. Genetic deletion of Tomosyn-2 improves glucose tolerance, elevates plasma insulin levels, and augments islet insulin secretion, without altering systemic insulin sensitivity. Mechanistically, Tomosyn-2 interacts with syntaxin-1A (Stx1A) to inhibit insulin granule exocytosis by limiting SNARE complex formation. Transcriptomic and network analyses reveal that Tomosyn-2 loss reprograms gene expression to strengthen the coupling between insulin secretion and proliferative pathways. Its deletion also reduces {beta}-cell proliferation and mass expansion, suppresses cell cycle and Akt1 signaling, and promotes {beta}-cell identity, maturation, and altered islet architecture. These findings identify Tomosyn-2 as a crucial molecular switch that orchestrates the balance between proliferation and functional maturation during postnatal {beta}-cell development.

cell biology↗

bioRxiv2025

Independent Validation of Transgenerational Inheritance of Learned Pathogen Avoidance in Caenorhabditis elegans

Transgenerational inheritance of learned behaviors remains a controversial topic in biology. The Murphy lab previously demonstrated that C. elegans exposed to pathogenic Pseudomonas aeruginosa (PA14) not only learn to avoid this bacterium but also transmit this avoidance behavior to untrained offspring. A recent study has challenged these findings, questioning the robustness of this phenomenon. Here, we independently validate the transgenerational inheritance of PA14 avoidance in C. elegans. Adapting the protocol described by the Murphy lab, we show that worms trained on PA14 develop significant avoidance that persists in F1 and F2 generations, though with decreased strength after P0. Our results provide independent confirmation of transgenerational inheritance of PA14 avoidance through the F2 generation, in agreement with previous findings from the Murphy lab and in contrast to a recent study by the Hunter group that failed to detect this phenomenon beyond the F1 generation.

genetics↗

bioRxiv2025

Secreted small RNAs of Naegleria fowleri as biomarkers for diagnosis of primary amoebic meningoencephalitis

Rapid and accurate diagnostics are needed to effectively detect and treat primary amoebic meningoencephalitis (PAM) caused by the free-living amoeba, Naegleria fowleri. Delayed diagnosis and similarities to other causes of meningitis contribute to a case mortality rate of >97%, and current testing requires a spinal tap to obtain cerebrospinal fluid (CSF). Thus, there is an unmet medical need for a non-invasive liquid biopsy diagnostic method. We sequenced N. fowleri extracellular vesicles (EVs) and identified microRNAs, tRNAs and other small RNAs in N. fowleri-EVs. From these data we selected two prevalent small RNAs as biomarker candidates. We developed an RT-qPCR assay and both small RNAs were detected in N. fowleri-EVs and amoeba-conditioned media. In the mouse model of PAM, both small RNA biomarkers were detected in 100% of mouse plasma samples at the end-stage of infection. Notably, smallRNA-1 was detected in the urine of infected mice at timepoints as early as 24h post infection (18/23 mice) and in the plasma as early as 60h post infection (8/8 mice). Additionally, smallRNA-1 was detected in 100% (n=6) of CSF samples from human PAM cases, and in whole blood samples, but not in human plasma from PAM cases. In this study, we discovered small RNAs as biomarkers of N. fowleri infection--one which can be detected reliably in CSF, urine, and whole blood. The RT-qPCR assay is a highly sensitive diagnostic assay that can be conducted in [~]3h after receipt of liquid biopsy. The data suggest detection of smallRNA-1 biomarker could provide earlier diagnosis of PAM and be used to monitor biomass of amoebae during treatment. One Sentence SummarySmall RNAs of Naegleria fowleri can be detected in liquid biopsies and serve as early diagnostic biomarkers of primary amoebic meningoencephalitis.

microbiology↗

bioRxiv2024

MerQuaCo: a computational tool for quality control in image-based spatial transcriptomics

Image-based spatial transcriptomics platforms are powerful tools often used to identify cell populations and describe gene expression in intact tissue. Spatial experiments return large, high-dimensional datasets and several open-source software packages are available to facilitate analysis and visualization. The outputs of spatial transcriptomics platforms are typically imperfect. For example, local variations in transcript detection probability are common. Software tools to characterize imperfections and their impact on downstream analyses are lacking so the data quality is assessed manually, a laborious and often a subjective process. Here we describe imperfections in a dataset of 641 fresh-frozen adult mouse brain sections collected using the Vizgen MERSCOPE. Common imperfections included the local loss of tissue from the section, tissue outside the imaging volume due to detachment from the coverslip, transcripts missing due to dropped images, varying detection probability through space, and differences in transcript detection probability between experiments. We describe the incidence of each imperfection and the likely impact on the accuracy of cell type labels. We develop MerQuaCo, open-source code that detects and quantifies imperfections without user input, facilitating the selection of sections for further analysis with existing packages. Together, our results and MerQuaCo facilitate rigorous, objective assessment of the quality of spatial transcriptomics results.

bioinformatics↗

bioRxiv2024

Mountain roads across the globe significantly alter local soil microclimates

Mountain roads have repeatedly shown to host significantly different plant species communities compared to the adjacent natural vegetation. Besides the effect of propagule pressure, altered disturbance regime and soil processes, one of the reasons given for the strong influence of mountain roads on species distributions is a significantly altered microclimate in the roadside compared to the adjacent vegetation, a direct consequence of the altered disturbance regime. However, the microclimatic differences between roadside and natural vegetation have rarely been quantified, particularly lacking global analyses, hampering a better understanding of their importance for mountain biodiversity. In this study, we analysed in-situ measured soil temperatures along mountain roads in seven mountain regions across the globe, in order to assess the impact of mountain roads on a range of bioclimatic variables across the elevational gradient. Our results undeniably show the importance of roadsides as unique microhabitats, even in heterogeneous mountain environments. In most regions, roadside soils had warmer maxima (3.95 {+/-} 2.35{degrees}C warmer) and colder minima (0.85 {+/-} 1.11 {degrees}C colder) than the soil in the adjacent vegetation, with higher frost risks in winter. Therefore, we recommend future research to incorporate the notion that the local microclimates created by mountain roads could play a critical role in species redistributions in space and time.

ecology↗

bioRxiv2024

What are the best practices for curating eDNA custom barcode reference libraries? A case study using Australian subterranean fauna.

Identification of species for environmental assessment and monitoring is essential for understanding anthropogenic impacts on biodiversity, but for subterranean fauna this task is frequently difficult and time consuming. The implementation of environmental DNA (eDNA) metabarcoding for biodiversity discovery and assessment offers considerable promise for improving the rate, accuracy and efficiency of species detection in ecosystems both above and below the ground. Importantly, for a better understanding of the biodiversity and ecology of organisms detected using eDNA, a custom library of known reference sequences with associated correct taxonomic metadata--i.e., a barcode reference library (BRL)--is required. Yet, minimal guidance is currently available on how an effective (i.e. shareable, multi-sequence, that permits metadata and has a unified nomenclature) and accurate (i.e. verified) custom BRL can be achieved. Here, we present a detailed roadmap for curation of a BRL for subterranean fauna. To do this, we (1) curated a custom sequence database of subterranean fauna at an environmentally sensitive location, Bungaroo Creek in the Pilbara region of Western Australia, for four gene loci useful for eDNA metabarcoding (COI, 18S rRNA, 12S rRNA and 16S rRNA); (2) addressed major gaps in taxonomy and disparate nomenclature of subterranean fauna by estimating 17-29 putative new species with standard delimitation methods, including 34 Barcode Index Numbers (BINs) in BOLD, and (3) summarised a best practice workflow for curation of a custom BRL that has broad applicability and can be applied to any taxa. Scientific Significance StatementIn threatened ecosystems, environmental DNA (eDNA) metabarcoding for biodiversity discovery and assessment offers considerable promise for improvement in the rate, efficiency and accuracy of species detection. For a better understanding of the biodiversity and ecology of organisms detected using eDNA, a custom library of known reference sequences with associated correct taxonomic metadata is required. Minimal guidance is currently available on how an effective (i.e. shareable, multi-sequence, permits metadata and provides a unified nomenclature) custom barcode reference library (BRL) can be achieved for subterranean fauna. Here, we present a road map for sound and reliable curation of a BRL using subterranean fauna from Australia as a case study.

evolutionary biology↗

bioRxiv2024

Early signs of plant community responses to climate warming along mountain roads in Switzerland

O_LIGlobal warming is pushing species to shift their ranges towards higher latitudes and elevations, causing a reassembly of plant communities potentially accompanied by community thermophilization (i.e., an increasing number or cover of thermophilic species, sometimes at the expense of mesic or cold-adapted species). Given the large variation typically observed in the magnitude and direction of range shifts, quantifying community thermophilization might provide a sensitive method to detect range shifts within short time periods and across limited spatial extents. Assessing changes in plant community composition as a whole might integrate early signs of range shifts across co-occurring species while accounting for changes in both occurrence and abundance. C_LIO_LIHere, we combine an assessment of (i) species-level range shifts, (ii) changes in species richness and (iii) changes in community-inferred temperatures along three mountain roads in Switzerland to ask whether plant communities have responded to warming climate over a 10 year period, and whether community thermophilization is an appropriate metric for early detection of these changes. C_LIO_LIWe found a community thermophilization signal of +0.13{degrees}C over the 10-year study period based on presence-absence data only. Despite significant upward shifts of species upper range limits in the lower part of the studied elevational gradient and a decrease in species richness at high elevations, significant thermophilization was not detectable if community- inferred temperatures were weighted by species covers. Low cover values of species that were gained or lost over the study period and their similar species-specific temperatures to resident species explained the discrepancy between the thermophilization detected in either cover-weighted or unweighted models. C_LIO_LISynthesis. Our work shows that plant species are shifting to higher elevations along roadsides in the western Swiss Alps and that this translates into a detectable warming signal of plant communities within 10 years. However, the species-level range shifts and the community-level warming effect are mostly based on low cover values of gained/lost species, preventing the detection of community thermophilization signals when incorporating cover changes. We therefore recommend using unweighted approaches for early detection of community-level responses to changing climate, ideally set into context by also assessing species-level range shifts. C_LI

ecology↗

bioRxiv2024

Adaptation across a precipitation gradient from niche center to niche edge

Evaluating the potential for species to adapt to changing climate relies on an appreciation of current patterns of adaptive variation and selection, which might vary in intensity across a species niche, affecting our inference of where adaptation might be most important in the future. Here we investigate the genetic basis of adaptation in Lactuca serriola, the wild relative of the common lettuce, growing along a steep precipitation gradient in Israel approaching the species arid niche limit, and used candidate loci to inform predictions of its past and future adaptive evolution. Environmental association analyses combined with generalized dissimilarity models revealed 98 candidate genes showing non-linear shifts in allele frequencies across the gradient, with a large proportion under strong directional selection near the dry niche edge. Selection acts on genes with separate suites of biological functions, specifically related to osmotic stress and phenological adjustments at the dry edge, and related to biotic interactions at the niche center. The adaptive genetic composition of populations, as inferred through polygenic risk scores, indicates that intensified selection may be the key determinant of the dry niche edge. However, inference of past and future evolutionary change suggests larger adaptive shifts in the mesic part of the range, which is most affected by climate change. Our study highlights that non-linear spatial variation in selection has implications for predicting past and future responses to climate change.

genomics↗

bioRxiv2023

High-throughput single-nucleus hybrid sequencing reveals genome-transcriptome correlations in cancer

To deepen our understanding of cancer heterogeneity and uncover the dynamic interactions of tumor and host cells, we introduce hybrid BAG-seq: a high-throughput, multi-omic method that simultaneously captures DNA and RNA from tens of thousands of individual single nuclei. This method provides dual molecular layer information: DNA to distinguish tumor from stroma, identify tumor subclones, and detect mutant stromal sub-populations; and RNA to characterize distinct cell types, cell states, and signatures of aberrant expression. Additionally, we developed a suite of analysis tools to illuminate cluster phylogeny and connections between DNA identity and RNA expression. We applied this hybrid protocol to 65,499 single nuclei from samples of five uterine cancer patients, and validated the clustering using RNA-only and DNA-only protocols on 34,651 and 21,432 nuclei, respectively, from the same tissues. Multiple tumor genome or expression clusters were often present within a patient, with different tumor clones projecting into distinct or shared expression states, demonstrating nearly all possible genome-transcriptome correlations across the cohort. While tumor expression profiles were highly unique to each patient, the stromal cell types generally recurred across samples, but certain patients and tissues exhibited unique stromal sub-types characterized by aberrant expression. Moreover, we identified mutant stroma in various cell types from several patients with a significant loss of the X-chromosome. This study reveals the complex landscape of genome and transcriptome interactions at the resolution of single nuclei, providing new insights into mutant stroma and tumor heterogeneity.

genomics↗

bioRxiv2023

Connecting higher order interactions with ecological stability in experimental aquatic food webs

Community ecology is built on theories that represent the strength of interactions between species as pairwise links. Higher order interactions occur when the presence of a third (or more) species changes the pairwise interaction between a focal pair. Recent theoretical work has highlighted the stabilizing role of higher order interactions for large, simulated communities, yet it remains unclear how important higher order effects are in real communities. Here we used experimental communities of aquatic protists to examine the relationship between higher-order interactions and community stability (as measured by the persistence of species in a community). We cultured a focal pair of consumers in the presence of additional competitors and a predator and collected time series data of their abundances. We then fitted competition models with and without HOIs to measure interaction strength between the focal pair across different community compositions. We used survival analysis to measure the persistence of individual species. We found evidence that additional species positively affected persistence of the focal species and that HOIs were present in most of our communities. However, persistence was only linked to HOIs for one of the focal species. Our results vindicate community ecology theory positing that species interactions may deviate from assumptions of pairwise interactions, opening avenues to consider possible consequences for coexistence and community stability.

ecology↗

bioRxiv2023

Risk and loss aversion and attitude to COVID and vaccines in anxious individuals

Anxious individuals are known to show impaired decision-making in economic gambling task and in everyday life decisions. This impairment can be due to aversion to uncertainty about outcomes (risk aversion) and/or aversion to negative outcomes (loss aversion). We investigate how non-clinical individuals with high levels of Generalised Anxiety Disorder (GAD) (N = 54) behave compared to less anxious subjects (N = 61) in a gambling decision-making task delivered online and designed to separate the distinct influences of risk and loss aversion on decision-making. By modelling subjects choices using computational models derived from Prospect Theory and fitted using Hierarchical Bayesian methods, we estimate individual levels of risk and loss aversion. Moreover we analyse the reaction times and choice data using Hierarchical Drift Diffusion Models (HDDMs). We also link estimates of these parameters to individual propensity to risk averse behaviours during the COVID pandemic, like wearing safer types of face masks, or completing a COVID vaccination course. We report increased loss aversion in individuals with increased level of GAD compared to less anxious individuals and no differences in risk aversion. The HDDM analysis suggests that high anxiety subjects have a reduced bias towards gambling in trials where there is a risk to loose points, also consistent with them being loss averse. We also report no links between risk and loss aversion and attitudes towards COVID and vaccines. These results shed new light on the interplay of anxiety and risk and loss aversion and they can provide useful directions for clinical intervention.

pathology↗

bioRxiv2022

Synaptotagmin-9 and Tomosyn-1 molecular complex regulates Stx1A SNAREs to inhibit insulin secretion from pancreatic beta-cells

Stimulus-coupled insulin secretion from {beta}-cells involves the fusion of insulin granules to the plasma membrane (PM) via SNARE complex formation--a cellular process key for maintaining whole-body glucose homeostasis. Optimal insulin secretion depends on how the clamping of SNAREs is released, rendering granules fusogenic. We show that an insulin granule protein synaptotagmin-9 (Syt9) deletion in lean mice increased glucose clearance, random-fed plasma insulin levels, and insulin secretion (in vivo and ex vivo islets) without affecting insulin sensitivity. These outcomes demonstrate that Syt9 has an inhibitory function in insulin secretion. Moreover, Syt9 interacts with PM-Stx1A and soluble Tomosyn-1 proteins to form non-fusogenic complexes between PM and insulin granules, preventing Stx1A-SNARE formation and insulin secretion. Furthermore, Syt9 inhibits SNARE-complex formation by posttranscriptional regulation of Tomosyn-1. We conclude that Syt9 and Tomosyn-1 are endogenous inhibitors that modulate Stx1A availability to determine {beta}-cell secretory capacity. HighlightsO_LISynaptotagmin-9 inhibits biphasic insulin secretion from {beta}-cells. C_LIO_LISynaptotagmin-9, syntaxin-1A, and Tomosyn-1 forms a molecular complex that decreases the availability of syntaxin-1A to form SNARE complexes in insulin secretion. C_LIO_LISynaptotagmin-9-mediated inhibition of insulin secretion occurs through post-transcriptional regulation of Tomosyn-1. C_LI

cell biology↗