Biology subjects

Burden, J. J.

Publications and source records attributed to Burden, J. J..

13 recordsLinked to original sources

bioRxiv2026

Quantitative spatial connectomics of liver reveals a partially exposed sympathetic network that integrates multiple cell types across the portal tract

Peripheral tissues are innervated by sparse axonal networks that regulate homeostasis, regeneration and disease, yet their three-dimensional architecture and cellular targets remain largely unknown. Here, we present an EM workflow for quantitative 3D spatial connectomics to define these networks. We identify the mouse liver connectome as a meshwork, rather than a tree-like structure, of mainly sympathetic axons, in which partial Schwann cell coverage is associated with exposed varicosities along the length of individual axons with large regions of the network devoid of glial coverage. Axon tracing identified axonal terminals throughout the network, but the vast majority of cellular contacts involved exposed 'en passant' varicosities. While both terminals and varicosities innervated the vasculature, most synaptic-like contacts involved hepatocytes, fibroblasts, macrophages, and the stem-cell niche, with all individual axons contacting different cell types along their length, highlighting the network nature of liver innervation, the potential for co-ordinating tissue function and demonstrating the power of this approach for decoding connectivity in peripheral tissues.

neuroscience↗

bioRxiv2026

Reciprocal mechanochemical feedback couples neural crest migration and neurulation

Cephalic neurulation and neural crest migration are defining morphogenetic events of vertebrate head development. Although traditionally viewed as independent tissue-autonomous programs, their striking spatiotemporal overlap suggests functional coupling. Here, we show that these processes are linked by reciprocal mechanochemical feedback. We find that collective neural crest migration is essential for neural tube closure. As neural crest cells delaminate and invade the surrounding mesoderm, they remodel fibronectin at the neural crest-neural plate interface, creating a specialized extracellular matrix that both separates the two tissues and promotes neural tube morphogenesis by enabling radial intercalation and apical constriction of neural plate cells. This extracellular matrix remodeling requires neural crest-specific expression of the membrane-bound metalloproteinase MMP14. Conversely, neural tube morphogenesis drives neural crest migration. Mechanical compression generated during neural plate bending induces MMP14 expression in neural crest cells, triggering extracellular matrix remodeling that feeds back to facilitate neural tube closure. Together, our findings reveal that neurulation and neural crest migration are not independent morphogenetic programs but components of a self-reinforcing mechanochemical circuit that coordinates vertebrate head morphogenesis.

developmental biology↗

bioRxiv2022

A Dystroglycan-Laminin-Integrin axis controls cell basal geometry remodeling in the developing Drosophila retina

Cell shape remodeling is a principal driver of epithelial tissue morphogenesis. While progress continues to be made in our understanding of the pathways that control the apical (top) geometry of epithelial cells, we know comparatively little about those that control cell basal (bottom) geometry. To examine this issue, we used the fly ommatidium, which is the basic visual unit of the compound eye. The ommatidium is shaped as a hexagonal prism, and generating this three-dimensional structure requires ommatidial cells to adopt specific apical and basal polygonal geometries. Using this model system, we find that generating cell type-specific basal geometries starts with patterning of the basement membrane, whereby Laminin accumulates at discrete locations across the basal surface of the retina. We show that the Dystroglycan surface receptor promotes this localized Laminin accumulation. Moreover, our results reveal that localized accumulation of Laminin-Dystroglycan induces polarization of Integrin adhesion in ommatidial cells. This underpins cell basal geometry remodeling by anchoring the basal surface of cells to the basement membrane at specific, discrete locations. Altogether, our work shows that patterning of a basement membrane by generating discrete Laminin domains, can direct Integrin adhesion. In the retina, this pathway generates specific basal polygonal geometries to organize a complex multicellular structure in three-dimensions.

developmental biology↗

bioRxiv2022

Perivascular SPP1 Mediates Microglial Engulfment of Synapses in Alzheimers Disease Models

Microglia are phagocytes of the brain parenchyma, where they interact with neurons to engulf synapses in a context-dependent manner. Genetic studies in Alzheimers disease (AD) highlight dysfunctional phagocytic signaling in myeloid cells as disease-associated pathway. In AD models, there is a region-specific reactivation of microglia-synapse phagocytosis involving complement; however, what drives microglia-synapse engulfment remains unknown. Here, we show that SPP1 (Osteopontin), a glycoprotein associated with inflammation, is regionally upregulated and modulates microglial synaptic engulfment in AD mouse models. Ultrastructural examination revealed SPP1 expression predominantly by perivascular macrophages, a subtype of border-associated macrophages, in the hippocampus of mice and patient tissues. Cell-cell interaction networks of single-cell transcriptomics data suggested that perivascular SPP1 drives microglial functional states in the hippocampal microenvironment of AD mice. Absence of Spp1 expression resulted in failure of microglia to mediate synaptic phagocytosis. This study suggests a critical role for perivascular SPP1 in neuroimmune crosstalk in AD-relevant context.

neuroscience↗

bioRxiv2022

The Vaccinia virus chondroitin sulfate binding protein drives host membrane curvature to facilitate fusion

Virus binding serves to define virus tropism and species specificity1. Virus binding proteins are classically considered as facilitators of cell surface attachment prior to receptor engagement and virus internalization. For efficient entry vaccinia virus (VACV) - the prototypic poxvirus - relies on four binding proteins and an eleven-protein entry fusion complex (EFC)2. We recently demonstrated that VACV binding and fusion proteins are organized into distinct functional domains, with localization of EFC proteins to virion tips directly influencing membrane fusion activity3. However, the relationship between virus binding protein distribution, virion binding orientation and subsequent membrane fusion remain unexplored. Here, we show that virus binding proteins guide side-on virion binding and promote curvature of the host membrane towards EFC-containing virion tips to facilitate virus fusion. Using a cell-derived membrane-bleb model system together with super-resolution and electron microscopy we found that side-bound VACV virions induce membrane invagination in the presence of low pH. Repression or deletion of individual binding proteins revealed that three of four contribute to binding orientation, amongst which the chondroitin sulphate binding protein, D8, is required for host membrane bending. Consistent with low-pH dependent macropinocytic entry of vaccinia virus4,5, loss of D8 prevents virion-associated macropinosome membrane bending, disrupts fusion pore formation and infection kinetics. Our results extend the role of viral binding proteins from mere attachment factors to active participants in successful viral membrane fusion and further illustrate the influence of virus protein architecture on successful infection.

microbiology↗

bioRxiv2021

Structure modeling hints at a granular organization of the Vertebrate Golgi ribbon

Vertebrate cells display a specific Golgi apparatus architecture, known as the "ribbon", where the functional subunits, the mini-stacks, are linked into a tridimensional network. The importance of the ribbon architecture is underscored by evidence of its disruption in a host of diseases, but just how it relates to the biological Golgi functions remains unclear. Are all the connections between mini-stacks functionally equal? Is the local structure of the ribbon of functional importance? These are difficult questions to address, due to the lack of a secretory cargo providing a quantifiable readout of the functional output of ribbon-embedded mini-stacks. Endothelial cells produce rod-shaped secretory granules, the Weibel-Palade bodies (WPB), whose von Willebrand Factor (VWF) cargo is central to hemostasis. In these cells, the Golgi apparatus exerts a dual control on WPB size at both mini-stack and ribbon levels. Mini-stack dimensions delimit the size of VWF boluses" while the ribbon architecture allows their linear co-packaging at the trans-Golgi network generating WPBs of different lengths. This Golgi/WPB size relationship lends itself to mathematical analysis. Here, different ribbon structures were modeled and their predicted effects on WPB size distribution compared to the ground truth of experimental data. Strikingly, the best-fitting model describes a Golgi ribbon made by linked subunits corresponding to differentially functioning monomer and dimer ministacks. These results raise the intriguing possibility that the fine-grained structure of the Golgi ribbon is more complex than previously thought.

cell biology↗

bioRxiv2020

Poxviruses package viral redox proteins in lateral bodies and modulate the host oxidative response

All poxviruses contain a set of proteinaceous structures termed lateral bodies (LB) that deliver viral effector proteins into the host cytosol during virus entry. To date, the spatial proteotype of LBs remains unknown. Using the prototypic poxvirus, vaccinia virus (VACV), we employed a quantitative comparative mass spectrometry strategy to determine the poxvirus LB proteome. We identified a large population of cellular proteins, the majority being mitochondrial, and 15 viral LB proteins. Strikingly, one-third of these comprise the full set of VACV redox proteins whose LB residency could be confirmed using super-resolution microscopy. We further show that VACV infection exerts an anti-oxidative effect on host cells and that artificial induction of oxidative stress impacts early gene expression and virion production. In addition to defining the spatial proteotype of these enigmatic viral structures, these findings implicate poxvirus redox proteins as modulators of host oxidative anti-viral responses and provide a solid starting point for future investigations into the role of LB resident proteins in host immunomodulation.

microbiology↗

bioRxiv2020

The white matter is a pro-differentiative microenvironment for glioblastoma

Glioblastomas are hierarchically organised tumours driven by glioma stem cells that retain partial differentiation potential. Glioma stem cells are maintained in specialised microenvironments, but how they undergo lineage progression outside of these niches remains unclear. Here we identify the white matter as a differentiative niche for glioblastomas with oligodendrocyte lineage competency. Tumour cells in contact with white matter acquire pre-oligodendrocyte-like fate, resulting in decreased proliferation and invasion. Differentiation is a response to white matter injury, which is caused by tumour infiltration itself in a tumoursuppressive feedback loop. Mechanistically, tumour cell differentiation is driven by selective white matter upregulation of SOX10, a master regulator of normal oligodendrogenesis. SOX10 overexpression or treatment with myelination-promoting agents that upregulate endogenous SOX10, mimic this response, leading to white matter-independent pre-oligodendrocyte-like differentiation and tumour suppression in vivo. Thus, glioblastoma recapitulates an injury response and exploiting this latent programme may offer treatment opportunities for a subset of patients.

cancer biology↗

bioRxiv2020

Modulation of early host innate immune response by a Fowlpox virus (FWPV) lateral body protein

The avian pathogen, fowlpox virus (FWPV) has been successfully used as vaccine vector in poultry and humans but relatively little is known about its ability to modulate host antiviral immune responses in these hosts, which are replication permissive and non-permissive, respectively. FWPV is highly resistant to avian type I interferon (IFN) and able to completely block the host IFN-response. Microarray screening of host IFN-regulated gene expression in cells infected with 59 different, non-essential FWPV gene knock-out mutants revealed that FPV184 confers immunomodulatory capacity. We report that FPV184-knockout virus (FWPV{Delta}184) induces the cellular IFN response as early as 2 hours post-infection. The wild-type, uninduced phenotype can be rescued by transient expression of FPV184 in FWPV{Delta}184-infected cells. Ectopic expression of FPV184 inhibited polyI:C activation of the chicken IFN-{beta} promoter and IFN- activation of the chicken Mx promoter. Confocal and correlative super-resolution light and electron microscopy demonstrated that FPV184 has a functional nuclear localisation signal domain and is packaged in the lateral bodies of the virions. Taken together, these results provide a paradigm for a late poxvirus structural protein packaged in the lateral bodies and capable of supressing IFN induction early during the next round of infection.

microbiology↗

bioRxiv2020

ER-PM contacts regulate apical domain formation in hepatocytes

Apico-basal membrane polarity is fundamental for epithelial cell development and function. Polarity factors including the small GTPase Cdc42, the Par3/Par6/aPKC complex, and cytoskeletal proteins are recruited by the anionic lipids phosphatidylinositol 4,5-bisphosphate and phosphatidylserine. But how these lipids accumulate at polarised sites remains unclear. We have examined roles of contacts between the endoplasmic reticulum and plasma membrane (ER-PM contacts) in generating lipid gradients during apical domain formation. Comprehensive electron microscopy analyses in hepatocytes and epithelial spheroids revealed two distinct ER-PM contact architectures that are spatially linked to apical and baso-lateral domains. Moreover, apical domain formation was delayed in HepG2 cells upon modulating the ER-PM contact proteins E-Syt1 and ORP5. We propose ER-PM contacts regulate apico-basal polarity via the lipid transfer proteins E-Syt1 and ORP5. Importantly, our findings suggest that the spatial organisation of ER-PM contacts is a conserved feature of polarised epithelial cells.

cell biology↗

bioRxiv2019

Clathrin light chain diversity regulates lattice properties and efficiency of synaptic vesicle formation

Clathrin light chain (CLC) subunits in vertebrates are encoded by paralogous genes CLTA and CLTB and both gene products are alternatively spliced in neurons. To understand how this CLC diversity influences neuronal clathrin function, we characterised the biophysical properties of clathrin comprising individual CLC variants for correlation with neuronal phenotypes of mice lacking either CLC-encoding gene. CLC splice variants differentially influenced clathrin knee conformation within assemblies, and clathrin with neuronal CLC mixtures was more effective in membrane deformation than clathrin with single neuronal isoforms nCLCa or nCLCb. Correspondingly, electrophysiological recordings revealed that neurons from mice lacking nCLCa or nCLCb were both defective in synaptic vesicle replenishment. Mice with only nCLCb had a reduced synaptic vesicle pool and impaired neurotransmission compared to wild-type mice, while nCLCa-only mice had increased synaptic vesicle numbers, restoring normal neurotransmission. These findings highlight differences between the CLC isoforms and show that isoform mixing influences tissue-specific clathrin activity in neurons, which requires their functional balance. SIGNIFICANCE STATEMENTThis study reveals that diversity of clathrin light chain (CLC) subunits alters clathrin properties and demonstrates that the two neuronal CLC subunits work together for optimal clathrin function in synaptic vesicle formation. Our findings establish a role for CLC diversity in synaptic transmission and illustrate how CLC variability expands the complexity of clathrin to serve tissue-specific functions.

cell biology↗

bioRxiv2019

Dual role of Miro protein clusters in mitochondrial cristae organisation and ER-Mitochondria Contact Sites

Mitochondrial Rho (Miro) GTPases localize to the outer mitochondrial membrane and are essential machinery for the regulated trafficking of mitochondria to defined subcellular locations. However, their sub-mitochondrial localization and relationship with other critical mitochondrial complexes remains poorly understood. Here, using super-resolution fluorescence microscopy, we report that Miro proteins form nanometer-sized clusters along the mitochondrial outer membrane in association with the Mitochondrial Contact Site and Cristae Organizing System (MICOS). Using knockout mouse embryonic fibroblasts (MEF) we show that Miro1 and Miro2 are required for normal mitochondrial cristae architecture and endoplasmic reticulum-mitochondria contacts sites (ERMCS). Further, we show that Miro couples MICOS to TRAK motor protein adaptors to ensure the concerted transport of the two mitochondrial membranes and the correct distribution of cristae on the mitochondrial membrane. The Miro nanoscale organization, association with MICOS complex and regulation of ERMCS reveal new levels of control of the Miro GTPases on mitochondrial functionality.

cell biology↗

bioRxiv2019

Planar differential growth rates determine the position of folds in complex epithelia

Folding is a fundamental process shaping epithelial sheets into 3D architectures of organs. Initial positioning of folds is the foundation for the emergence of correct tissue morphology. Mechanisms forming individual folds have been studied, yet the precise positioning of the folds in complex, multi-folded epithelia is an open question. We present a model of morphogenesis, encompassing local differential growth, and tissue mechanics to investigate tissue fold positioning. We use Drosophila melanogaster wing imaginal disc as our model system, and show that there is spatial and temporal heterogeneity in its planar growth rates. This planar differential growth is the main driver for positioning the folds. Increased stiffness of the apical layer and confinement by the basement membrane drive fold formation. These influence fold positions to a lesser degree. The model successfully predicts the emergent morphology of wingless spade mutant in vivo, via perturbations solely on planar differential growth rates in silico.

biophysics↗