Biology subjects

Ghose, A.

Publications and source records attributed to Ghose, A..

16 recordsLinked to original sources

bioRxiv2026

Kaptin controls neuronal circuit assembly by limiting actin-driven axon collateral branching

Axon collateral branching is a fundamental determinant of neuronal connectivity, enabling individual neurons to innervate multiple targets and establish functional neural circuits. Although branch initiation requires local actin remodelling within the axon shaft, the mechanisms that restrict actin assembly to prevent excessive branching remain poorly understood. Here, we identify Kaptin (Kptn) as a conserved negative regulator of axon collateral formation that limits the maturation of axonal actin patches. Using primary neuronal cultures, quantitative live-cell imaging, and zebrafish genetics, we show that loss of Kptn enhances the conversion of actin patches into filopodial protrusions, leading to excessive collateral branching. Kptn-deficient zebrafish exhibit increased motor axon arborisation, elevated neuromuscular junction density and impaired motor behaviour. Mechanistically, Kptn antagonises the actin elongation factor Formin-2 (Fmn2) to regulate actin filament barbed-end dynamics, thereby controlling the threshold for productive branch initiation. Importantly, these branching defects occur independently of Kptns established role in mTORC1 signalling, revealing a distinct physiological function during neuronal development. Our findings identify Kptn as a key molecular brake that constrains axon collateral branching and establish negative regulation of actin patch maturation as a fundamental mechanism controlling neuronal circuit assembly. This work provides a mechanistic framework for understanding how KPTN mutations associated with intellectual disability and epilepsy disrupt neuronal connectivity.

neuroscience↗

bioRxiv2025

Initiation and maturation of the early axonal βII-spectrin membrane-associated periodic skeleton requires active cytoskeletal remodelling

The axonal membrane-associated periodic skeleton (MPS), consisting of F-actin rings crosslinked by spectrin heterotetramers, is ubiquitous and critical for neuronal function and homoeostasis. However, the initiation and early development of the axonal MPS are poorly understood. Using superresolution imaging, we show that {beta}II-spectrin is recruited early to the axonal cortex, followed by progressive establishment of long-range periodic order. Microtubule dynamics are essential for MPS formation in the early stages, but transition to a passive stabilising role in mature axons. We show that the early subplasmalemmal recruitment of {beta}II-spectrin is dependent on cortical actin but not on actomyosin contractility, and active nucleation of F-actin is required in early development but is dispensable for the mature MPS. Using a {beta}II-spectrin knockout model, we demonstrate that the actin-binding and lipid-interacting domains of {beta}II-spectrin are critical for its subplasmalemmal confinement and, subsequently, MPS maturation. These findings highlight stage-specific cytoskeletal remodelling underlying MPS development and advance our understanding of axonal subcellular architecture.

neuroscience↗

bioRxiv2023

The actin-associated protein Kaptin modulates F-actin barbed-end dynamics

Living cells require a dynamic and precisely regulated actin cytoskeleton to carry out normal cellular functions. In addition to well-established actin cytoskeleton regulators, such as nucleators, capping proteins, and bundlers, cells likely have uncharacterized modulators that regulate cytoskeleton dynamics, the detailed functions of which are not yet fully understood. In this study, we conducted biochemical exploration to identify the actin-regulatory activity of Kaptin (KPTN), a protein known to co-localize with actin-rich structures at the cells periphery. Using single-molecule assays, we demonstrated that KPTN inhibits actin nucleation. Our results revealed that KPTN possesses a novel barbed-end capping activity, which stabilizes and bundles actin filaments. Structural modeling, based on AlphaFold, suggests that KPTN is a member of the WD-repeat-containing protein family. Furthermore, we identified a crucial cationic residue in the putative N-terminal beta-propeller region of KPTN that plays a critical role in modulating actin dynamics. In summary, our data unveil the mechanistic underpinning functions of KPTN and establish its novel role as a regulator of the actin cytoskeleton.

cell biology↗

bioRxiv2021

Convergent energy state-dependent antagonistic signalling by CART and NPY modulates the plasticity of forebrain neurons to regulate feeding in zebrafish

Dynamic re-configuration of circuit function subserves the flexibility of innate behaviours tuned to physiological states. Internal energy stores adaptively regulate feeding-associated behaviours by integrating opposing hunger and satiety signals at the level of neural circuits. Across vertebrate lineages, the neuropeptides CART and NPY have potent anorexic and orexic functions, respectively, and show energy state-dependent expression in interoceptive neurons. However, how the antagonistic activities of these peptides modulate circuit plasticity remains unclear. Using behavioural, neuroanatomical and activity analysis in adult zebrafish, along with pharmacological interventions, we show that CART and NPY activities converge on a population of neurons in the dorsomedial telencephalon (Dm). While CART facilitates glutamatergic neurotransmission at the Dm, NPY dampens the response to glutamate. In energy-rich states, CART enhances NMDA receptor (NMDAR) function by PKA/PKC mediated phosphorylation of the NR1 subunit of the NMDAR complex. Conversely, starvation triggers NPY-mediated reduction in phosphorylated NR1 via calcineurin activation and inhibition of cAMP production leading to reduced responsiveness to glutamate. Our data identify convergent integration of CART and NPY inputs by the Dm neurons to generate nutritional state-dependent circuit plasticity that is correlated with the behavioural switch induced by the opposing actions of satiety and hunger signals.

neuroscience↗

bioRxiv2021

Development of motor neurons and motor activity in zebrafish requires F-actin nucleation by Fmn2b

BackgroundCytoskeletal remodelling plays a pivotal role in the establishment of neuronal connectivity during development and in plasticity in adults. Mutations in the cytoskeleton regulatory protein Formin-2 (Fmn2) are associated with neurodevelopmental disorders like intellectual disability, though its function in neuronal morphogenesis has not been characterised in vivo. ResultsHere we develop a loss-of-function model for fmn2b, the zebrafish orthologue of Fmn2, using CRISPR/Cas9-mediated gene editing. fmn2b mutants display motor deficits starting from the earliest motor responses in the embryo. We find that fmn2b is expressed in spinal motor neurons and its loss reduces motor neuron innervation of the axial muscles without affecting myotome integrity. The translocation of caudal primary (CaP) motor neuron outgrowth is compromised in fmn2b mutants, while rostral primary (RoP) motor neurons have missing soma or stall at the horizontal myoseptum. Strikingly, axon collateral branching of the motor neurons is severely compromised and results in reduced synaptic coverage of the myotome. Rescue experiments identify the requirement for Fmn2-mediated actin nucleation for motor neuron outgrowth and arborisation. ConclusionsThe zebrafish loss-of-function model of Fmn2 reveals the specific requirement of F-actin polymerisation by Fmn2 in neuromuscular development. It also underscores the role of Fmn2 in motor neuropathies, especially as a proportion of individuals harbouring mutations in Fmn2 present with hypotonia.

neuroscience↗

bioRxiv2020

Antagonistic activities of Fmn2 and ADF regulate axonal F-actin patch dynamics and the initiation of collateral branching

Interstitial collateral branching of axons is a critical component in the development of functional neural circuits. Axon collateral branches are established through a series of cellular processes initiated by the development of a specialized, focal F-actin network in axons. The formation, maintenance and remodelling of this F-actin patch is critical for the initiation of axonal protrusions that are subsequently consolidated to form a collateral branch. However, the mechanisms regulating F-actin patch dynamics are poorly understood. Fmn2 is a formin family member implicated in multiple neurodevelopmental disorders. We find that Fmn2 regulates the initiation of axon collateral protrusions. Fmn2 localises to the protrusion-initiating axonal F-actin patches and regulates the lifetime and size of these F-actin networks. The F-actin nucleation activity of Fmn2 is necessary for F-actin patch stability but not for initiating patch formation. We show that Fmn2 insulates the F-actin patches from disassembly by the actin-depolymerizing factor, ADF, and promotes long-lived, larger patches that are competent to initiate axonal protrusions. The regulation of axonal branching can contribute to the neurodevelopmental pathologies associated with Fmn2 and the dynamic antagonism between Fmn2 and ADF may represent a general mechanism of formin-dependent protection of Arp2/3-initiated F-actin networks from disassembly.

neuroscience↗

bioRxiv2020

Transient systemic inflammation in adult male mice results in underweight progeny

ProblemWhile the testes represent an immune privileged organ, there is evidence that systemic inflammation is accompanied by local inflammatory responses. We therefore examined if transient systemic inflammation caused any inflammatory and functional consequences in murine testes. Method of StudyUsing a single systemic administration of Toll-like receptor (TLR) agonists [lipopolysaccharide (LPS) or peptidoglycan (PG) or polyinosinic-polycytidylic acid (polyIC)] in young adult male mice, we assessed testicular immune-inflammatory landscape and reproductive functionality. ResultsOur findings demonstrated a significant induction of testicular TNF-, IL-1{beta} and IL-6 transcripts within 24 h of TLR agonist injection. By day 6 these cytokine levels returned to baseline. While there was no change in caudal sperm counts at early time points, eight weeks later, two-fold decrease of sperm count and reduced testicular testosterone levels was evident. When these mice were subjected to mating studies, no differences in mating efficiencies or litter sizes were observed compared to controls. Nonetheless, the neonatal weights of progeny from LPS/PG/polyIC treated sires were significantly lower than controls. Postnatal weight gain up to three weeks was also slower in the progeny of LPS/polyIC treated sires. Placental weights at 17.5 days post-coitum were significantly lower in females mated to LPS and polyIC treated males. Given this likelihood of an epigenetic effect, we found lower testicular levels of histone methyl-transferase enzyme, mixed-lineage leukemia-1, in mice given LPS/PG/polyIC eight weeks earlier. ConclusionExposure to transient systemic inflammation leads to transient local inflammation in the testes, with persistent sperm-mediated consequences for fetal development.

immunology↗

bioRxiv2020

The formin Fmn2 is required for the development of an excitatory interneuron module in the zebrafish acoustic startle circuit

The formin family member, Fmn2, is a neuronally enriched cytoskeletal remodelling protein conserved across vertebrates. Recent studies have implicated Fmn2 in neurodevelopmental disorders, including sensory processing dysfunction and intellectual disability in humans. Cellular characterization of Fmn2 in primary neuronal cultures has identified its function in the regulation of cell-substrate adhesion and consequently growth cone translocation. However, the role of Fmn2 in the development of neural circuits in vivo, and its impact on associated behaviours have not been tested. Using automated analysis of behaviour and systematic investigation of the associated circuitry, we uncover the role of Fmn2 in zebrafish neural circuit development. As reported in other vertebrates, the zebrafish ortholog of Fmn2 is also enriched in the developing zebrafish nervous system. We find that Fmn2 is required for the development of an excitatory interneuron pathway, the spiral fiber neuron, which is an essential circuit component in the regulation of the Mauthner cell-mediated acoustic startle response. Consistent with the loss of the spiral fiber neurons tracts, high-speed video recording revealed a reduction in the short latency escape events while responsiveness to the stimuli was unaffected. Taken together, this study provides evidence for a circuit-specific requirement of Fmn2 in eliciting an essential behaviour in zebrafish. Our findings underscore the importance of Fmn2 in neural development across vertebrate lineages and highlight zebrafish models in understanding neurodevelopmental disorders. SIGNIFICANCE STATEMENTFmn2 is a neuronally enriched cytoskeletal remodelling protein linked to neurodevelopment and cognitive disorders in humans. Recent reports have characterized its function in growth cone motility and chemotaxis in cultured primary neurons. However, the role of Fmn2 in the development of neural circuits in vivo and its implications in associated behaviours remain unexplored. This study shows that Fmn2 is required for the development of neuronal processes in the acoustic startle circuit to ensure robust escape responses to aversive stimuli in zebrafish. Our study underscores the crucial role of the non-diaphanous formin, Fmn2, in establishing neuronal connectivity and related behaviour in zebrafish.

neuroscience↗

bioRxiv2020

Fmn2 regulates growth cone motility by mediating a molecular clutch to generate traction forces

Growth cone - mediated axonal outgrowth and accurate synaptic targeting are central to brain morphogenesis. Translocation of the growth cone necessitates mechanochemical regulation of cell - extracellular matrix interactions and the generation of propulsive traction forces onto the growth environment. However, the molecular mechanisms subserving force generation by growth cones remain poorly characterized. The formin family member, Fmn2, has been identified earlier as a regulator of growth cone motility. Here, we explore the mechanisms underlying Fmn2 function in the growth cone. Evaluation of multiple components of the adhesion complexes suggests that Fmn2 regulates point contact stability. Analysis of F-actin retrograde flow reveals that Fmn2 functions as a clutch molecule and mediates the coupling of the actin cytoskeleton to the growth substrate, via point contact adhesion complexes. Using traction force microscopy, we show that the Fmn2-mediated clutch function is necessary for the generation of traction stresses by neurons. Our findings suggest that Fmn2, a protein associated with neurodevelopmental and neurodegenerative disorders, is a key regulator of a molecular clutch activity and consequently motility of neuronal growth cones.

neuroscience↗

bioRxiv2020

Coupling of dynamic microtubules to F-actin by Fmn2 regulates chemotaxis of neuronal growth cones

Dynamic co-regulation of the actin and microtubule subsystems enables the highly precise and adaptive remodeling of the cytoskeleton necessary for critical cellular processes, like axonal pathfinding. The modes and mediators of this interpolymer crosstalk, however, are inadequately understood. We identify Fmn2, a non-diaphanous related formin associated with cognitive disabilities, as a novel regulator of cooperative actin-microtubule remodeling in growth cones. We show that Fmn2 stabilizes microtubules in the growth cones of cultured spinal neurons and also in vivo. Superresolution imaging revealed that Fmn2 facilitates guidance of exploratory microtubules along actin bundles into the chemosensory filopodia. Using live imaging, biochemistry and single-molecule assays we show that a C-terminal domain in Fmn2 is necessary for the dynamic association between microtubules and actin filaments. In the absence of the cross-bridging function of Fmn2, filopodial capture of microtubules is compromised resulting in de-stabilized filopodial protrusions and deficits in growth cone chemotaxis. Our results uncover a critical function for Fmn2 in actin-microtubule crosstalk in neurons and demonstrate that modulating microtubule dynamics via associations with F-actin is central to directional motility. SIGNIFICANCE STATEMENTThe formin family member, Fmn2, is associated with cognitive impairment and neurodegenerative conditions though its function in neurons is poorly characterized. We report a novel actin-microtubule cross-bridging activity for Fmn2 that facilitates efficient targeting and capture of microtubules in growth cone filopodia. This activity is necessary for accurate pathfinding of axons and may contribute to Fmn2-associated neuropathologies. The precision and adaptability of cytoskeleton-driven processes are intimately dependent on the coupled activities of its component systems. Our study identifies a novel modality of co-regulated remodelling of the actin and microtubule cytoskeletons that facilitate critical cellular behaviour like neuronal chemotaxis.

cell biology↗

bioRxiv2019

Sensitivity of Olfactory Sensory Neurons to food cues is tuned to nutritional states by Neuropeptide Y signalling

BackgroundModulation of sensory perception by homeostatic feedback from physiological states is central to innate purposive behaviours. Olfaction is an important predictive modality for feeding-related behaviours and its modulation has been associated with hunger-satiety states. However, the mechanisms mapping internal states to chemosensory processing in order to modify behaviour are poorly understood.\n\nResultsIn the zebrafish olfactory epithelium, a subset of olfactory sensory neurons (OSNs) and the terminal nerve projections express neuropeptide Y (NPY). We find that NPY signalling in the peripheral olfactory system of zebrafish is correlated with its nutritional state and is both necessary and sufficient for the olfactory perception of food related odorants. NPY activity dynamically modulates the microvillar OSN activation thresholds and acts cooperatively with amino acid signalling resulting in a switch-like increase in OSN sensitivity in starved animals. We suggest that cooperative activation of phospholipase C by convergent signalling from NPY and amino acid receptors is central to this heightened sensitivity.\n\nConclusionsThis study provides ethologically relevant, physiological evidence for NPY signalling in peripheral modulation of OSN sensitivity to food-associated amino acid cues. We demonstrate sensory gating directly at the level of OSNs and identify a novel mechanistic framework for tuning olfactory sensitivity to prevailing energy states.

neuroscience↗

bioRxiv2019

The axonal actin-spectrin lattice acts as shock absorbers to protect neurons from stretch-induced damage

Axons are thin tubular extensions generated by neuronal cells to transmit signals across long distances. In the peripheral and the central nervous systems, axons experience large deformations during normal activity or as a result of injury. Yet, axon biomechanics, and its relation to the internal structure that allows axons to withstand such deformations, is poorly understood. Up to now, it has been generally assumed that microtubules and their associated proteins are the major load-bearing elements in axons. We revise this view point by combining mechanical measurements using a custom developed force apparatus with biochemical or genetic modifications to the axonal cytoskeleton, revealing an unexpected role played by the actin-spectrin skeleton. For this, we first demonstrate that axons exhibit a reversible strain-softening response, where its steady state elastic modulus decreases with increasing strain. We then explore the contributions from the various cytoskeletal components of the axon, and show that the recently discovered membrane-associated skeleton consisting of periodically spaced actin filaments interconnected by spectrin tetramers play a prominent mechanical role. Finally, using a theoretical model we argue that the actin-spectrin skeleton act as an axonal tension buffer by reversibly unfolding repeat domains of the spectrin tetramers to buffer excess mechanical stress.

biophysics↗

bioRxiv2018

The geography of malaria elimination in Bangladesh: combining data layers to estimate the spatial spread of parasites

Malaria control programs face difficult resource allocation decisions. Of particular concern for countries aiming for malaria elimination, the regular movement of individuals to and from endemic areas undermines local interventions by reintroducing infections and sustaining local transmission. Quantifying this movement of malaria parasites around a country has become a priority for national control programs, but remains methodologically challenging, particularly in areas with highly mobile populations. Here, we combined multiple data sources to measure the geographical spread of malaria parasites, including epidemiological surveillance data, travel surveys, parasite genetic data, and anonymized mobile phone data. We collected parasite genetic barcodes and travel surveys from 2,090 patients residing in 176 unions in southeast Bangladesh. We developed a genetic mixing index to quantify the likelihood of samples being local or imported. We then inferred the direction and intensity of parasite flow between locations using an epidemiological model, and estimated the proportion of imported cases assuming mobility patterns parameterized using the travel survey and mobile phone calling data. Our results show that each data source provided related but different information about the patterns of geographic spread of parasites. We identify a consistent north/south separation of the Chittagong Hill Tracts region in Bangladesh, and found that in addition to imported infections from forested regions, frequent mixing also occurs in low transmission but highly populated areas in the southwest. Thus, unlike risk maps generated from incidence alone, our maps provide evidence that elimination programs must address ongoing movement of parasites around the lower transmission areas in the southwest.

epidemiology↗

bioRxiv2017

Cytoskeletal mechanisms of axonal contractility

Mechanotransduction is likely to be an important mechanism of signalling in thin, elongated cells like neurons. Maintenance of pre-stress or rest tension may facilitate mechanotransduction in these cells. In recent years, functional roles for mechanical tension in neuronal development and physiology are beginning to emerge but the cellular mechanisms regulating neurite tension remain poorly understood. Active contraction of neurites is a potential mechanism of tension regulation. In this study, we have explored cytoskeletal mechanisms mediating active contractility of neuronal axons. We have developed a simple assay where we evaluate contraction of curved axons upon trypsin-mediated detachment. We show that curved axons undergo contraction and straighten upon de-adhesion. Axonal straightening was found to be actively driven by actomyosin contractility, while microtubules may subserve a secondary role. We find that while axons show a monotonous decrease in length upon contraction, subcellularly, the cytoskeleton shows a heterogeneous contractile response. Further, using an assay for spontaneous development of tension without trypsin-induced de-adhesion, we show that axons are intrinsically contractile. These experiments, using novel experimental approaches, implicate the axonal cytoskeleton in tension homeostasis. Our data suggest that while globally the axon behaves as a mechanical continuum, locally the cytoskeleton is remodelled heterogeneously.

biophysics↗

bioRxiv2016

CART neuropeptide modulates the extended amygdalar CeA-vBNST circuit to gate expression of innate fear

Innate fear is critical for the survival of animals and is under tight homeostatic control. Deregulation of innate fear processing is thought to underlie pathological phenotypes including, phobias and panic disorders. Although central processing of conditioned fear has been extensively studied, the circuitry and regulatory mechanisms subserving innate fear remain relatively poorly defined.\n\nIn this study, we identify cocaine- and amphetamine-regulated transcript (CART) neuropeptide signalling in the central amygdala (CeA) - ventral bed nucleus of stria terminalis (vBNST) axis as a key modulator of innate fear expression. TMT, a component of fox faeces, induces a freezing response whose intensity is regulated by the extent of CART-signalling in the CeA neurons. Abrogation of CART activity in the CeA attenuates the freezing response and reduces activation of vBNST neurons. Conversely, ectopically elevated CART signalling in the CeA potentiates the fear response concomitant with enhanced vBNST activation. We show that local levels of CART signaling modulate the activation of CeA neurons by NMDA receptor mediated glutamatergic inputs, in turn, regulating activity in the vBNST.\n\nThis study identifies the extended amygdalar CeA-vBNST circuit as a CART modulated axis encoding innate fear. CART signaling regulates the glutamatergic excitatory drive in the CeA-vBNST circuit, in turn, gating the expression of the freezing response to TMT.

neuroscience↗

bioRxiv2016

Distinct cAMP signaling modalities mediate behavioral flexibility and consolidation of social status in Drosophila aggression.

Social rituals, like male-male aggression in Drosophila, are often stereotyped and the component behavioral patterns modular. The likelihood of transition from one behavioral pattern to another is malleable by experience and confers flexibility to the behavioral repertoire. Experience-dependent modification of innate aggressive behavior in flies alters fighting strategies during fights and establishes dominant-subordinate relationships. Dominance hierarchies resulting from agonistic encounters are consolidated to longer lasting social status-dependent behavioral modifications resulting in a robust loser effect.\n\nWe show that cyclic adenosine monophosphate (cAMP) dynamics regulated by the calcium/calmodulin-dependent adenylyl cyclase, Rut and the cAMP phosphodiesterase, Dnc but not the Amn gene product, in specific neuronal groups of the mushroom body and central complex, mediate behavioral plasticity necessary to establish dominant- subordinate relationships. rut and dnc mutant flies are unable to alter fighting strategies and establish dominance relationships during agonistic interactions. This real-time flexibility during a fight is independent of changes in aggression levels. Longer-term consolidation of social status in the form of a loser effect, however, requires additional Amn-dependent inputs to cAMP signaling and involves a circuit-level association between the /{beta} and {gamma} neurons of the mushroom body.\n\nOur findings implicate cAMP signaling in mediating plasticity of behavioral patterns in aggressive behavior and in the generation of a temporally stable memory trace that manifests as a loser effect.\n\nSUMMARY STATEMENTPhasic recruitment of different cAMP signaling modalities in specific neuronal groups lead to the formation of temporally distinct components of learning and memory in fly aggression.

neuroscience↗