Biology subjects

Scher, N.

Publications and source records attributed to Scher, N..

7 recordsLinked to original sources

bioRxiv2026

PinCorr: A high-pressure freezing carrier with intrinsic landmarks for cryo-correlative light and electron microscopy

Cryo-correlative light and electron microscopy methods enable targeted structural analysis of fluorescently labelled features in vitrified specimens. However, correlative workflows on high-pressure frozen samples often remain challenging due to the lack of persistent landmarks for reliable sample tracking and image registration between different microscopes. Standard high-pressure freezing carriers provide little intrinsic reference information, as the exposed sample surface is often smooth and rotationally ambiguous, complicating localisation of regions of interest across imaging platforms. Here, we introduce PinCorr, a 3-mm high-pressure freezing carrier with an integrated coordinate system formed by four asymmetrically arranged pillars with distinct geometries. These built-in landmarks remain visible after freezing and provide a stable, sample-independent reference frame for orientation and correlation between cryo-fluorescence microscopy and electron microscopy. We show that PinCorr supports fluorescence-guided cryo-volume imaging, serial lift-out for cryo-electron tomography and freeze-substitution workflows followed by room-temperature on-section correlation. PinCorr thus provides a hardware-based approach to establishing a persistent spatial reference frame in HPF-based correlative imaging workflows for thick and multicellular specimens.

Molecular Biology↗

bioRxiv2026

Vesicular pseudopodia define the fusion site on large secretory vesicles of the Drosophila salivary glands

Large secretory vesicles (LSVs) pose a scaling problem for regulated exocytosis. Their micron-scale dimensions greatly increase the vesicular membrane surface area, making productive engagement between the vesicular and target membrane fusion machinery unlikely. Here, we show that vesicular pseudopodia define the fusion sites of LSVs in Drosophila larval salivary glands. Focused ion beam scanning electron microscopy revealed that most LSVs project polarized pseudopodia that interconnect neighboring vesicles and orient toward the apical membrane. Exposed pseudopodia were frequently observed at the apical surface and associated with narrow fusion pores, indicating that fusion occurs at these structures. Three-dimensional correlative light and electron microscopy showed that the I-BAR protein Missing in Metastasis (MIM) selectively localizes to exposed pseudopodia. Proteomic analysis based on a MIM pull-down assay identified exocyst components, including Sec15, which localizes to pseudopodia and persists at fusion sites throughout secretion. Finally, the tetraspanin Tsp42Ee marked complementary apical fusion domains and was required for efficient exocytosis. Our findings support a model in which prepatterned vesicular and apical membrane domains coordinate efficient exocytosis. SummaryRegulated exocytosis of large secretory vesicles is facilitated by vesicular pseudopodia and an apical fusion domain that spatially organizes membrane tethering and fusion during secretion.

cell biology↗

bioRxiv2026

Direct Membrane Penetration of Oligoarginines by Fluorescence and Cryo-electron Microscopy Combined with Molecular Simulations

Arginine-rich peptides are short amino acid chains capable of spontaneously crossing cellular membranes, with great potential for drug or other cargo delivery. Yet, the mechanisms underlying their cellular penetration are not fully understood. Here, we investigate the modes of action of nonaarginine (R9) across membranes of increasing compositional and biological complexity. We combine computational, fluorescence microscopy, and cryo-EM approaches to both visualize the membrane structural changes arising from peptide-lipid interactions and provide a molecular rationale for the observed effects. In large unilamellar vesicles, R9 binds preferentially to anionic and PE-rich membranes, induces lipid reorganization, and drives pronounced remodelling, including budding, bifurcations, and time-dependent formation of multilamellar stacks. In cell-derived extracellular vesicles, R9-induced remodelling is largely confined to bilamellar bifurcations. In live cells, fluorescent R9 forms surface puncta that precede cytosolic entry. Correlative cryo-fluorescence and electron tomography reveals that these puncta correspond to strongly folded, multilamellar membrane structures. We propose that these seemingly contrasting observations can be reconciled within a single R9 mechanism of action, involving membrane folding and stacking, where the different observed morphologies arise from the size of the accessible membrane reservoir.

biophysics↗

bioRxiv2025

Visualizing sub-organellar lipid distribution using correlative light and electron microscopy

Lipids and proteins compartmentalize biological membranes into nanoscale domains which are crucial for signaling, intracellular trafficking and many other cellular processes. Studying nanodomain function requires the ability to measure protein and lipid localization at the nanoscale. Current methods for visualizing lipid localization do not meet this requirement. Here, we introduce a correlative light and electron microscopy workflow to image lipids (Lipid-CLEM), combining near-native lipid probes and on-section labeling by click chemistry. This approach enables the quantification of relative lipid densities in membrane nanodomains. We find differential partitioning of sphingomyelin into intraluminal vesicles, recycling tubules, and the boundary membrane of the early endosome, representing a degree of nanoscale organization previously observed only for proteins. We anticipate that our Lipid-CLEM workflow will greatly facilitate the mechanistic analysis of lipid functions in cell biology, allowing for the simultaneous investigation of proteins and lipids during membrane nanodomain assembly and function.

cell biology↗

bioRxiv2023

High throughput screening identifies broad-spectrum Coronavirus entry inhibitors

The Covid-19 pandemic highlighted the pressing need for antiviral therapeutics capable of mitigating infection and spread of emerging coronaviruses (CoVs). A promising therapeutic strategy lies in inhibiting viral entry mediated by the Spike (S) glycoprotein. To identify small molecule inhibitors that block entry downstream of receptor binding, we established a high-throughput screening (HTS) platform based on pseudoviruses. We employed a three-step process to screen nearly 200,000 small molecules. First, we identified potential inhibitors by assessing their ability to inhibit pseudoviruses bearing the SARS-CoV-2 S glycoprotein. Subsequent counter-screening against pseudoviruses with the Vesicular Stomatitis Virus glycoprotein (VSV-G), yielding sixty-five SARS-CoV-2 S-specific inhibitors. These were further tested against pseudoviruses bearing the MERS-CoV S glycoprotein, which uses a different receptor. Out of these, five compounds including the known broad-spectrum inhibitor Nafamostat, were subjected to further validation and tested them against pseudoviruses bearing the S glycoprotein of the alpha, delta, and omicron variants as well as against bona fide SARS-CoV-2 in vitro. This rigorous approach revealed a novel inhibitor and its derivative as a potential broad-spectrum antiviral. These results validate the HTS platform and set the stage for lead optimization and future pre-clinical, in vivo studies.

microbiology↗

bioRxiv2023

Fusion pore dynamics of large secretory vesicles define a distinct mechanism of exocytosis

Exocrine cells utilize large secretory vesicles (LSVs) up to 10 m in diameter. LSVs fuse with the apical surface, often recruiting actomyosin to extrude their content through dynamic fusion pores. The molecular mechanism regulating pore dynamics remains largely uncharacterized. We observe that the fusion pore of LSVs in the Drosophila larval salivary glands expand, stabilize, and constrict. Arp2/3 is essential for pore expansion and stabilization, while myosin II is essential for pore constriction. We identify several Bin-Amphiphysin-Rvs (BAR) homology domain proteins that regulate fusion pore expansion and stabilization. We show that the I-BAR protein Missing-in-Metastasis (MIM) localizes to the fusion site and is essential for pore expansion and stabilization. The MIM I-BAR domain is essential but not sufficient for localization and function. We conclude that MIM acts in concert with actin, myosin II, and additional BAR-domain proteins to control fusion pore dynamics, mediating a distinct mode of exocytosis that facilitates actomyosin-dependent content release that maintains apical membrane homeostasis during secretion.

cell biology↗

bioRxiv2021

In-situ fiducial markers for 3D correlative cryo- fluorescence and FIB-SEM imaging

1.Imaging of cells and tissues has improved significantly over the last decade. Dual-beam instruments with a focused ion beam mounted on a scanning electron microscope (FIB-SEM), which offer high-resolution 3D imaging of large volumes and fields-of-view are becoming widely used in the life sciences. FIB-SEM has most recently been implemented on fully hydrated, cryo-immobilized, biological samples. However, correlative light and electron microscopy (CLEM) workflows combining cryo-fluorescence microscopy (cryo-FM) and FIB-SEM are not yet commonly available. Here, we demonstrate that fluorescently labeled lipid droplets can serve as in-situ fiducial markers for correlating cryo-FM and FIB-SEM datasets, and that this approach can be used to target the acquisition of large FIB-SEM stacks spanning tens of microns under cryogenic conditions. We also show that cryo-FIB-SEM imaging is particularly informative for questions related to organelle structure and inter-organellar contacts, nuclear organization and mineral deposits in cells.

cell biology↗