Biology subjects

Nandi, A.

Publications and source records attributed to Nandi, A..

At least 19 recordsLinked to original sources

bioRxiv2026

Triazole Stress Induces Accelerated Degradation of Aspergillus fumigatus Hmg1

Triazole antifungals inhibit the lanosterol C14-demethylase Cyp51A/B and are the first-line treatment for invasive aspergillosis caused by Aspergillus fumigatus. We previously proposed that triazoles impose a secondary constraint on ergosterol biosynthesis through negative feedback regulation of HMG-CoA reductase (Hmg1) through its sterol sensing domain (SSD), and SSD mutations compromise this regulation to produce resistance. The molecular mechanism underpinning this feedback remained unknown. In this study, we show that voriconazole drives accelerated protein degradation of Hmg1 and that SSD mutation abolishes this regulated degradation. Triazole-induced Hmg1 degradation is proteasome-dependent and partially requires the ERAD E3 ubiquitin ligase, HrdA, and INSIG ortholog, InsA, both conserved regulators of HMG-CoA Reductase abundance. We provide genetic evidence that the initiating negative feedback signal is not triazole acting directly on Hmg1 but lanosterol accumulation resulting from Cyp51A/B inhibition. To test whether depleting Hmg1 protein could re-sensitize resistant strains, we utilized a GFP-targeted degradation system designed to target Hmg1 for degradation without engaging its SSD. Combining this system with voriconazole treatment reduced the MIC at least four-fold in both conidia and established hyphae in susceptible and resistant strains. Together, our findings support a model wherein triazole-induced lanosterol accumulation drives HrdA/InsA-dependent accelerated degradation of Hmg1 and establish that pharmacologically inducing this secondary mechanism can enhance triazole activity in both susceptible and resistant isolates.

microbiology↗

bioRxiv2026

Biotinylation-dependent near-neighbor analysis for identification of septation regulators in Aspergillus fumigatus

Recent work has established septation as a critical process for virulence in A. fumigatus, as strains lacking septa are avirulent. While our work has focused on the well-studied Septation Initiation Network (SIN), understanding of septation machinery upstream and downstream of SIN remains limited in filamentous fungi. Proximity labeling techniques are powerful tools to study pathway interactions, especially those that are transient. Recent advances have seen TurboID used to study pathways and processes important for fungal pathogenesis. In this study, we adapt TurboID for use in Aspergillus fumigatus and use overlapping datasets of two SIN components, the terminal NDR kinase SidB and its binding partner MobA, to identify putative septation effectors. Many known septation effectors, including septins and cell wall synthesis proteins, were enriched in our datasets, validating the approach. Phenotypic characterization of hits identified by LC-MS/MS revealed several previously uncharacterized gene products involved in septum formation and cell wall stress tolerance. These included the PP2A regulatory subunit PabA and IQGAP SepG, which have been shown to regulate septation in Aspergillus nidulans. Thus, TurboID is a useful tool to study fungal signaling and physiology in A. fumigatus and may be used to improve understanding of pathogenic processes.

microbiology↗

bioRxiv2026

Dynamic microtubules drive yolk-cytoplasm segregation in the syncytial Drosophila embryo

Yolk-cytoplasm segregation is among the earliest spatial organization events in the developing embryo of many oviparous animals. The segregation process is intimately linked to early embryonic cleavage and pattern formation, and exhibits a wide range of spatial and temporal diversity. However, the underlying cytoskeletal mechanism remains largely unknown, except for a small number of species. Using quantitative live imaging, we investigated yolk segregation in the Drosophila embryo during the syncytial nuclear cycles 11-14. We find that the yolk vesicles move progressively inward in spatial and temporal coordination with the inward expanding microtubule networks that are nucleated from centrosomes positioned at the cortex, whereas cortical actin meshwork remains spatially restricted. Using the gnu RNAi embryo to decouple nuclear migration and division from cytoskeletal dynamics, we establish causality with targeted pharmacological disruption and find that microtubule dynamics is required for yolk segregation, while depolymerization of actin has no discernible effect. In support of a mechanism of growth-propelled passive displacement, microtubule plus end comets come in apparent contact with yolk vesicles, and injected, inert microbeads are displaced towards the embryo center presumably by the same pushing force. These findings identify microtubule polymerization as a predominant driver of yolk-cytoplasm segregation in Drosophila and suggest that diverse cytoskeletal mechanisms evolved to accomplish this crucial reorganization process

developmental biology↗

bioRxiv2025

Scaling of the Bicoid morphogen gradient: the effect of state dependent diffusion

The mechanisms underlying the scaling of the Bicoid morphogen gradient in Drosophila with the embryo size is not clearly understood. We propose a model with a spatially varying diffusion coefficient along the anterior-posterior axis, that is proportional to the nearly periodic spatial distribution of the nucleo-cytoplasmic domains and alternating between regions of fast and slow diffusion. We postulate that for specific interpretation of the heterogeneous environment, where the space available for free diffusion within an energid is assumed to be proportional to the embryo size, a change in the embryo size can lead to a size-dependent scaling of the gradient lengthscale. We further study a two component model with slow and fast diffusing Bicoid, and identify this model to be equivalent to the heterogeneous diffusion model further postulating that the fast-state occupancy which is a measure of the fraction of time spent in the fast diffusing state, should also scale with the embryo size via the energid size. Finally, we incorporate nuclear shuttling into our model to understand the effect of shuttling on the gradient lengthscale and scaling with embryo size. We argue that for the particular case where the degradation within the nucleus is low, nuclear shuttling does not perturb the Bicoid gradient. Our study suggests that scaling of the gradient length scale is possible due to spatial heterogeneity and does not depend on nuclear trapping as suggested previously.

developmental biology↗

bioRxiv2025

Microbial Scl1 Activates TGFBR1 receptor kinase signalling to Drive Fibrosis-Inflammation Axis in Alcohol-Associated Liver Disease

Background and AimsAlcohol consumption alters gut microbiota, which can affect metabolism, immune regulation, and signalling pathways and lead to alcohol-associated liver disease (ALD). We investigated how alcohol-associated gut microbiota (AGMs) modulate liver kinome signalling to drive inflammation and fibrosis in ALD. MethodLiver kinome and metaproteome changes were studied in rats (n=6/group) colonized with stool of severe alcohol-related hepatitis (SAH) patients (SAH[->]healthy-rats) or healthy human donors (HD[->]ALD-rats). AGM-associated liver kinome changes were cross-correlated with bacterial genera. A bacterial protein; Streptococcal collagen-like protein 1 (Scl1) was identified with affinity for TGF{beta}R1. This was validated by molecular docking and immunoprecipitation-LCMS assay. Expression of Streptococcus pneumonia and pyogenes was done in stool of SAH patients (n=10). Also, Scl1 was quantified in patient stool (n=24) and liver tissue (n=19) samples. Validation was performed by assessing Scl1 level in plasma and Streptococcus level in stool samples before and after fecal microbiota transplantation (FMT) in SAH patients. ResultsStool metaproteomics showed significant increase in 10 bacterial genera (Streptococcus, Staphylococcus, and Clostridium) in SAH[->]Healthy-rats, mirroring changes seen in ALD-rats (FC>1.5, p<0.05). Clusters of Orthologous Groups analysis indicated increased post-translational modifications (PTMs) and decreased lipid metabolism in ALD-rats and SAH[->]Healthy-rats. Liver kinome profiling showed 85 upregulated kinases in SAH[->]Healthy-rats, with 34 overlapping with ALD-rats, associated with inflammation (Mapk14, Map3k10 and others), fibrosis (Tgfbr1, Igf1r, and others), lipid metabolism (Cdk14, Cdk18) and regeneration (Met, Bmpr1a and others). FMT from healthy human-donors to ALD-rats reversed the expression of Streptococcus (10-fold), Staphylococcus (3-fold), and Clostridium (5-fold), along with 18 kinases associated with inflammation (Btk, Camk4, Nuak1) and fibrosis (Tgfbr1, Col4a1, Fgfr2 and others). Strong association (r{superscript 2}>0.9, p<0.05) was seen between Streptococcus abundance and fibrosis and inflammation-related kinases. Level of Scl1 was significantly high in SAH and ALD-rat stool samples (FC>2, p<0.05). It showed strong affinity for TGF{beta}R1, as validated by molecular docking (>86%confidence) and immunoprecipitation assays (>100FC,p<0.05), indicating it as a potential ligand for TGF{beta}R1. Concordantly, expression of Scl1 was highest amongst all the known ligands for TGF{beta}R1 (p<0.05) suggesting Scl1 is a major contributor for TGF{beta}R1 activation and its downstream signalling in these patients. Following fecal microbiota transplantation, expression of Scl1 in plasma and Streptococcus levels in stool were significantly reduced by 2.1-folds and 1.9 folds respectively in SAH patients. Further, Scl1 levels SAH plasma is capable of predicting poor therapeutic response and 30-day mortality with high accuracy (AUC=0.92, cutoff >70 normalized abundance). ConclusionAlcohol induced gut dysbiosis alters the liver kinome, promoting inflammation, fibrosis, and lipid dysregulation. Streptococcal Scl1 is identified as a bacterial protein mimicking human collagen and capable of activating fibrotic signalling pathway through TGF{beta}R1in liver and is capable of predicting poor response in SAH. FMT from healthy donor restores microbial imbalance and harmful microbial-host interactions.

microbiology↗

bioRxiv2025

Explainable AI Based Coronary Heart Disease Prediction: Enhancing Model Transparency in Clinical Decision Making

Introduction: Coronary heart disease (CHD) is still a major cause of death globally, and hence early detection and risk stratification are necessary to avoid major cardiovascular events. The present study uses clinical and demographic characteristics to compare the predictive accuracy of eight machine learning models for CHD diagnosis. It also investigates the contribution and direction of influence of the most important features in the models to improve interpretability. MethodsWe contrasted the predictive accuracy of eight different machine learning models for CHD classification. The work identifies the most important features from the top-performing models and applies SHapley Additive exPlanations (SHAP) and Local Interpretable Model-Agnostic Explanations (LIME) to gain insight into how every feature affects the models prediction. These interpretive methods assist in displaying the direction and amount of feature contributions to allow transparency in AI-based CHD risk prediction. ResultsXGboost and Random Forest achieved the highest testing accuracies 0.839 and 0.805, with training accuracies of 0.901 and 0.957 respectively showing ideal model of XGboost and significant overfitting for random forest model. ECG-associated features, such as resting ECG and old peak (ST depression through workout), also place favorably, supporting the significance of cardiac electrical activity in diagnosis. ST slope has the highest impact, followed by Chest pain type and old peak, which increase the likelihood of heart disease with their high values contributing positively to the prediction. Resting bps, sex, and fasting blood sugar have lower impacts on the models predictions. ConclusionsIn conclusion, machine learning models, particularly XGboost and random forest, show substantial predictive accuracy for coronary heart disease, with testing AUROCs of 0.885. Feature importance, SHAP and LIME analysis highlight the critical role of ECG-derived metrics like ST slope, chest pain type, and resting ecp while traditional risk factors such as cholesterol, resting bps, and fasting blood sugar have less influence.

bioengineering↗

bioRxiv2025

Fusobacterium nucleatum is enriched in invasive biofilms in colorectal cancer

Fusobacterium nucleatum is an oral bacterium known to colonize colorectal tumors, where it is thought to play an important role in cancer progression. Recent advances in sequencing and phenotyping of F. nucleatum have revealed important differences at the subspecies level, but whether these differences impact the overall tumor ecology, and tumorigenesis itself, remain poorly understood. In this study, we sought to characterize Fusobacteria in the tumor microbiome of a cohort of individuals with CRC through a combination of molecular, spatial, and microbiologic analyses. We assessed for relative abundance of F. nucleatum in tumors compared to paired normal tissue, and correlated abundance with clinical and pathological features. We demonstrate striking enrichment of F. nucleatum and the recently discovered subspecies animalis clade 2 (Fna C2) specifically in colon tumors that have biofilms, highlighting the importance of complex community partnerships in the pathogenesis of this important organism.

microbiology↗

bioRxiv2024

Syntaxin-2 inhibits phagocytic uptake but promotes phagolysosome formation in macrophages

Phagocytosis engulfs receptor-bound particles by structuring phagocytic cups that expand to form phagosome vesicles. Phagosomes fuse with endosomes and lysosomes to gradually mature into acidic, hydrolase-enriched phagolysosomes for content degradation. While an essential cellular process for eliminating unwanted substances to secure host defense and organismal homeostasis, defective or uncontrolled phagocytosis can be detrimental. Here, we report syntaxin-2 (Stx2), a poorly characterized SNARE in phagocytes, defines the course of macrophage phagocytosis by coordinating cell surface receptor density, phagocytic cup expansion, and phagosome maturation. Stx2 is expressed on the plasma membrane, phagosomes, early endosomes, and to some extent on recycling endosomes, late endosomes and VAMP4-positive compartments. Stx2 knockdown (Stx2-KD) augments engagement and uptake of IgG-opsonized particles by enhanced surface expression of Fc receptors (FcR) and efficient expansion of phagocytic cups. These events are driven by increased recycling of FcR, and enhanced delivery of early endosomes and VAMP4-positive post-Golgi compartments to phagocytic cups. Interestingly, Stx2-KD macrophages exhibit reduced secretion of pro-cathepsins with concomitant increase in lysosome content. However, Stx2 depletion prevents phagosome coalescence with late endosomes and lysosomes to impair maturation by depleted acquisition of cathepsins and reduced acidification. Consequently, macrophages depleted of Stx2 manifest uncontrolled uptake of IgG-opsonized Escherichia coli and impaired digestion resulting in increased bacterial load. Collectively, we uncovered a previously unknown role of Stx2 as a critical balancer of phagocytic uptake and phagolysosomal clearance in macrophages, suggesting that it could be an attractive target for modulation of phagocytosis plasticity and to control aberrant phagocytosis.

cell biology↗

bioRxiv2023

Enhancing Luciferase Activity and Stability through Generative Modeling of Natural Enzyme Sequences

The availability of natural protein sequences synergized with generative artificial intelligence (AI) provides new paradigms to create enzymes. Although active enzyme variants with numerous mutations have been produced using generative models, their performance often falls short compared to their wild-type counterparts. Additionally, in practical applications, choosing fewer mutations that can rival the efficacy of extensive sequence alterations is usually more advantageous. Pinpointing beneficial single mutations continues to be a formidable task. In this study, using the generative maximum entropy model to analyze Renilla luciferase homologs, and in conjunction with biochemistry experiments, we demonstrated that natural evolutionary information could be used to predictively improve enzyme activity and stability by engineering the active center and protein scaffold, respectively. The success rate of designed single mutants is [~]50% to improve either luciferase activity or stability. These finding highlights natures ingenious approach to evolving proficient enzymes, wherein diverse evolutionary pressures are preferentially applied to distinct regions of the enzyme, ultimately culminating in an overall high performance. We also reveal an evolutionary preference in Renilla luciferase towards emitting blue light that holds advantages in terms of water penetration compared to other light spectrum. Taken together, our approach facilitates navigation through enzyme sequence space and offers effective strategies for computer-aided rational enzyme engineering.

bioinformatics↗

bioRxiv2023

F-box protein FBXB-65 regulates anterograde transport of UNC-104 through modification near the PH domain

Axonal transport is essential for cargo movement between the neuronal cell body and synapses. UNC-104/KIF1A, a Kinesin-3 motor in C. elegans that anterogradely transports precursors of synaptic vesicles (pre-SVs), is known to be degraded at synapses through the ubiquitin pathway. Knockdown of the E1 ubiquitin-activating enzyme, uba-1, leads to increased accumulation of UNC-104 at neuronal ends and at synapses of touch receptor neurons (TRNs). Loss of the F-box protein FBXB-65, a putative E3 ligase, leads to UNC-104 accumulation at distal ends of neurons, alters net anterograde movement of UNC-104, and the intensity of moving UNC-104 puncta likely bound to cargo without changes in synaptic UNC-104 levels. Using a theoretical model, we analyze the steady state distribution of the anterogradely moving UNC-104 motor. A good agreement between the model and the experimental distributions leads to a crucial hypothesis that UNC-104 may exhibit cooperative binding with moving motor puncta likely associated with cargo, which is regulated by fbxb-65. FBXB-65 regulates the modification of UNC-104 motor in a region besides the cargo binding PH-domain. Both fbxb-65 and UNC-104 motor independent of FBXB-65 regulate the extent of cargo transport in the axon and transport behaviour of cargo at branch points. Our study shows that modification of UNC-104 near its cargo-binding domain may regulate number of motors on the cargo surface and this regulation can fine-tune cargo transport to its destination, the synapse.

cell biology↗

bioRxiv2023

Pathogenic aggregates alter actin organization and cellular viscosity resulting in stalled clathrin mediated endocytosis

Protein aggregation is a common underlying feature of neurodegenerative disorders. Cells expressing neurodegeneration-associated mutant proteins show altered uptake of ligands, suggestive of impaired endocytosis, in a manner as yet unknown. Using live cell imaging, we show that clathrin-mediated endocytosis (CME) is affected due to altered actin cytoskeletal organization in the presence of Huntingtin aggregates. Additionally, we find that cells containing Huntingtin aggregates are stiffer and less viscous than their wild-type counterparts due to altered actin conformation, and not merely due to the physical presence of aggregate(s). We further demonstrate that CME and cellular viscosity can be rescued by overexpressing Hip1, Arp2/3 or transient LatrunculinA treatment. Examination of other pathogenic aggregates revealed that only a subset of these display defective CME, along with altered actin organization and increased stiffness. Together, our results point to an intimate connection between functional CME, actin organization and cellular stiffness in the context of neurodegeneration.

cell biology↗

bioRxiv2023

SRF-deficient astrocytes provide neuroprotection in mouse models of excitotoxicity and neurodegeneration

Reactive astrogliosis is a common pathological hallmark of central nervous system (CNS) injury, infection, and neurodegeneration, where reactive astrocytes can be protective or detrimental to normal brain functions. Currently, the mechanisms regulating neuroprotective astrocytes and the extent of neuroprotection are poorly understood. Here, we report that conditional deletion of serum response factor (SRF) in adult astrocytes causes reactive-like hypertrophic astrocytes throughout the mouse brain. These SrfGFAP-ERCKO astrocytes do not affect neuron survival, synapse numbers, synaptic plasticity or learning and memory. However, the brains of Srf knockout mice exhibited neuroprotection against kainic-acid induced excitotoxic cell death. Relevant to human neurodegenerative diseases, SrfGFAP-ERCKO astrocytes abrogate nigral dopaminergic neuron death and reduce {beta}-amyloid plaques in mouse models of Parkinsons and Alzheimers disease, respectively. Taken together, these findings establish SRF as a key molecular switch for the generation of reactive astrocytes with neuroprotective functions that attenuate neuronal injury in the setting of neurodegenerative diseases.

neuroscience↗

bioRxiv2023

Associations between in vitro, in vivo and in silico cell classes in mouse primary visual cortex

The brain consists of many cell classes yet in vivo electrophysiology recordings are typically unable to identify and monitor their activity in the behaving animal. Here, we employed a systematic approach to link cellular, multi-modal in vitro properties from experiments with in vivo recorded units via computational modeling and optotagging experiments. We found two one-channel and six multi-channel clusters in mouse visual cortex with distinct in vivo properties in terms of activity, cortical depth, and behavior. We used biophysical models to map the two one- and the six multi-channel clusters to specific in vitro classes with unique morphology, excitability and conductance properties that explain their distinct extracellular signatures and functional characteristics. These concepts were tested in ground-truth optotagging experiments with two inhibitory classes unveiling distinct in vivo properties. This multi-modal approach presents a powerful way to separate in vivo clusters and infer their cellular properties from first principles.

neuroscience↗

bioRxiv2021

Hippocampal astroglial hypertrophy in mice subjected to early life maternal deprivation

Early-life stress (ELS), including chronic deprivation of maternal care, exerts persistent life-long effects on animal physiology and behavior, and is associated with several neurodevelopmental disorders. Long-lasting changes in neuronal plasticity and electrophysiology are documented extensively in the animal models of ELS. However, the role of astroglia in the lasting effects of ELS remains elusive. Astrocytes are intricately involved in the regulation of synaptic physiology and behavior. Moreover, astrocytes play a major role in the innate and adaptive immune responses in the central nervous system (CNS). The role of immune responses and neuroinflammation in the altered brain development and persistent adverse effects of ELS are beginning to be explored. Innate immune response in the CNS is characterized by a phenomenon called astrogliosis, a process in which astrocytes undergo hypertrophy, along with changes in gene expression and function. While the immune activation and neuroinflammatory changes concomitant with ELS, or in juveniles and young adults have been reported, it is unclear whether mice subjected to ELS exhibit astrogliosis-like alterations well into late-adulthood. Here, we subjected mice to maternal separation from postnatal day 2 to day 22 and performed comprehensive morphometric analysis of hippocampal astrocytes during late-adulthood. We found that the astrocytes in the stratum radiatum region of the CA1 hippocampal subfield from maternally separated mice exhibit significant hypertrophy as late as 8 months of age, revealing the crucial changes in astrocytes that manifest long after the cessation of ELS. This study highlights the persistence of neuroinflammatory changes in mice exposed to ELS.

neuroscience↗

bioRxiv2020

Multi-modal characterization and simulation of human epileptic circuitry

Temporal lobe epilepsy is the fourth most common neurological disorder with about 40% of patients not responding to pharmacological treatment. Increased cellular loss in the hippocampus is linked to disease severity and pathological phenotypes such as heightened seizure propensity. While the hippocampus is the target of therapeutic interventions such as temporal lobe resection, the impact of the disease at the cellular level remains unclear in humans. Here we show that properties of hippocampal granule cells change with disease progression as measured in living, resected hippocampal tissue excised from epilepsy patients. We show that granule cells increase excitability and shorten response latency while also enlarging in cellular volume, surface area and spine density. Single-cell RNA sequencing combined with simulations ascribe the observed electrophysiological changes to gradual modification in three key ion channel conductances: BK, Cav2.2 and Kir2.1. In a bio-realistic computational network model, we show that the changes related to disease progression bring the circuit into a more excitable state. In turn, we observe that by reversing these changes in the three key conductances produces a less excitable, "early disease-like" state. These results provide mechanistic understanding of epilepsy in humans and will inform future therapies such as viral gene delivery to reverse the course of the disorder.

neuroscience↗

bioRxiv2020

Single-neuron models linking electrophysiology, morphology and transcriptomics across cortical cell types

Identifying the cell types constituting brain circuits is a fundamental question in neuroscience and motivates the generation of taxonomies based on electrophysiological, morphological and molecular single cell properties. Establishing the correspondence across data modalities and understanding the underlying principles has proven challenging. Bio-realistic computational models offer the ability to probe cause-and-effect and have historically been used to explore phenomena at the single-neuron level. Here we introduce a computational optimization workflow used for the generation and evaluation of more than 130 million single neuron models with active conductances. These models were based on 230 in vitro electrophysiological experiments followed by morphological reconstruction from the mouse visual cortex. We show that distinct ion channel conductance vectors exist that distinguish between major cortical classes with passive and h-channel conductances emerging as particularly important for classification. Next, using models of genetically defined classes, we show that differences in specific conductances predicted from the models reflect differences in gene expression in excitatory and inhibitory cell types as experimentally validated by single-cell RNA-sequencing. The differences in these conductances, in turn, explain many of the electrophysiological differences observed between cell types. Finally, we show the robustness of the herein generated single-cell models as representations and realizations of specific cell types in face of biological variability and optimization complexity. Our computational effort generated models that reconcile major single-cell data modalities that define cell types allowing for causal relationships to be examined. HighlightsO_LIGeneration and evaluation of more than 130 million single-cell models with active conductances along the reconstructed morphology faithfully recapitulate the electrophysiology of 230 in vitro experiments. C_LIO_LIOptimized ion channel conductances along the cellular morphology ( all-active) are characteristic of model complexity and offer enhanced biophysical realism. C_LIO_LIIon channel conductance vectors of all-active models classify transcriptomically defined cell-types. C_LIO_LICell type differences in ion channel conductances predicted by the models correlate with experimentally measured single-cell gene expression differences in inhibitory (Pvalb, Sst, Htr3a) and excitatory (Nr5a1, Rbp4) classes. C_LIO_LIA set of ion channel conductances identified by comparing between cell type model populations explain electrophysiology differences between these types in simulations and brain slice experiments. C_LIO_LIAll-active models recapitulate multimodal properties of excitatory and inhibitory cell types offering a systematic and causal way of linking differences between them. C_LI

neuroscience↗

bioRxiv2020

Chandelier cell anatomy and function reveal a variably distributed but common signal

The activity and connectivity of inhibitory cells has a profound impact on the operation of neuronal networks. While the average connectivity of many inhibitory cell types has been characterized, we still lack an understanding of how individual interneurons distribute their synapses onto their targets and how heterogeneous the inhibition is onto different individual excitatory neurons. Here, we use large-scale volumetric electron microscopy (EM) and functional imaging to address this question for chandelier cells in layer 2/3 of mouse visual cortex. Using dense morphological reconstructions from EM, we mapped the complete chandelier input onto 153 pyramidal neurons. We find that the number of input synapses is highly variable across the population, but the variability is correlated with structural features of the target neuron: soma depth, soma size, and the number of perisomatic synapses received. Functionally, we found that chandelier cell activity in vivo was highly correlated and tracks pupil diameter, a proxy for arousal state. We propose that chandelier cells provide a global signal whose strength is individually adjusted for each target neuron. This approach, combining comprehensive structural analysis with functional recordings of identified cell types, will be a powerful tool to uncover the wiring rules across the diversity of cortical cell types.

neuroscience↗

bioRxiv2020

Subfield-specific Effects of Chronic Mild Unpredictable Stress on Hippocampal Astrocytes

Major Depressive Disorder (MDD) is a debilitating neuropsychiatric illness affecting over 20% of the population worldwide. Despite its prevalence, our understanding of its pathophysiology is severely limited, thus hampering the development of novel therapeutic strategies. Recent advances have clearly established astrocytes as major players in the pathophysiology, and plausibly pathogenesis, of major depression. In particular, astrocyte density in the hippocampus is severely diminished in MDD patients and correlates strongly with the disease outcome. Moreover, astrocyte densities from different subfields of the hippocampus show varying trends in terms of their correlation to the disease outcome. Given the central role that hippocampus plays in the pathophysiology of depression and in the action of antidepressant drugs, changes in hippocampal astrocyte density and physiology may have a significant effect on behavioral symptoms of MDD. In this study, we used Chronic Mild Unpredictable Stress (CMUS) in mice, which induces a depressive-like state, and examined its effects on astrocytes from different subfields of the hippocampus. We used S100{beta} immunostaining to estimate the number of astrocytes per mm2 from various hippocampal subfields. Furthermore, using confocal images of fluorescently labeled GFAP-immunopositive hippocampal astrocytes, we quantified various morphology-related parameters and performed Sholl analysis. We found that CMUS exerts differential effects on astrocyte cell density, ramification, cell radius, surface area, and process width of hippocampal astrocytes from different hippocampal subfields. Taken together, our study reveals that chronic stress doesnt uniformly affect all hippocampal astrocytes; but exerts its effects differentially on different astrocytic subpopulations within the hippocampus.

neuroscience↗