Biology subjects

Schorb, M.

Publications and source records attributed to Schorb, M..

8 recordsLinked to original sources

bioRxiv2023

Targeted volume Correlative Light and Electron Microscopy of an environmental marine microorganism

Photosynthetic microalgae are responsible for an important fraction of CO2 fixation and O2 production on Earth. Three-dimensional ultrastructural characterization of these organisms in their natural environment can contribute to a deeper understanding of their cell biology. However, the low throughput of volume electron microscopy (vEM) methods, along with the complexity and heterogeneity of environmental samples, pose great technical challenges. In the present study, we used a workflow based on a specific EM sample preparation, compatible with both light and vEM imaging in order to target one cell among a complex natural community. This method revealed the 3D subcellular landscape of a photosynthetic dinoflagellate with quantitative characterization of multiple organelles. We could show that this cell contains a single convoluted chloroplast and the arrangement of the flagellar apparatus with its associated photosensitive elements. Moreover, we observed chromatin features that could shed light on how transcriptional activity takes place in organisms where chromosomes are permanently condensed. Together with providing insights in dinoflagellates biology, this proof-of-principle study illustrates an efficient tool for the targeted ultrastructural analysis of environmental microorganisms in heterogeneous mixes.

cell biology↗

bioRxiv2022

IFITM3 blocks viral entry by sorting lipids and stabilizing hemifusion

Interferon-induced transmembrane protein 3 (IFITM3) inhibits the entry of numerous viruses through undefined molecular mechanisms. IFITM3 localizes in the endosomal-lysosomal system and specifically impacts virus fusion with target cell membranes. We found that IFITM3 induces local lipid sorting, resulting in an increased concentration of lipids disfavoring viral fusion at the hemifusion site. This increases the energy barrier for fusion pore formation and the hemifusion dwell time, promoting viral degradation in lysosomes. In situ cryo-electron tomography captured IFITM3-mediated arrest of influenza A virus membrane fusion. Observation of hemifusion diaphragms between viral particles and late endosomal membranes confirmed hemifusion stabilization as a molecular mechanism of IFITM3. The presence of the influenza fusion protein hemagglutinin in post-fusion conformation close to hemifusion sites further indicated that IFITM3 does not interfere with the viral fusion machinery. Collectively, these findings show that IFITM3 induces lipid sorting to stabilize hemifusion and prevent virus entry into target cells.

molecular biology↗

bioRxiv2022

Bacterial cell widening alters periplasmic size and activates envelope stress responses

The Rcs signal transduction system is a phosphorelay responsible for sensing a wide variety of enterobacterial cell envelope stresses. In Escherichia coli, the Rcs system is required to survive A22 and mecillinam treatment, two drugs that perturb cell size. To test whether cell size changes might be correlated with envelope damage and thereby sensed by the Rcs system, we tuned E. coli cell size via drug inhibition with A22, point mutations to the cell-shape determinant MreB, and mechanically confined growth. In all conditions, cell width was strongly correlated with Rcs activation, with wider cells exhibiting more activation than wild-type. In all conditions, RcsF, the outer membrane-localized upstream component of the Rcs system, was essential for responding to cell width changes. Consistently, several envelope gene deletions known to induce the Rcs system via RcsF resulted in cells that were wider than wild-type. Cryo- electron microscopy revealed that the periplasm of a wide MreB mutant was on average [~]3 nm thinner than wild-type, thereby bringing RcsF closer to the downstream components of the signaling cascade in the inner membrane. Conversely, extending the flexible linker region of RcsF by [~]3 nm increased Rcs activity in wild-type cells. In summary, we propose that the Rcs system responds to changes in cell width because of altered periplasmic thickness.

microbiology↗

bioRxiv2022

MoBIE: A Fiji plugin for sharing and exploration of multi-modal cloud-hosted big image data

Facing the challenge of exploring and sharing multi-terabyte, multi-modal and multi-scale image data of heterogeneous dimensionality, we developed MoBIE, a Fiji plugin that provides rich visualization features to enable browsing data from numerous biomedical applications on a standard laptop computer. MoBIE also supports segmentations, associated measurements and annotations. Users can configure complex views of datasets, share them with collaborators, and use them for interactive figure panels. The MoBIE plugin also offers a convenient interface for converting data into compatible data formats; an additional Python library facilitates managing diverse MoBIE projects.

bioinformatics↗

bioRxiv2020

The 3D architecture and molecular foundations of de novo centriole assembly via bicentrioles

Abstract/SummaryCentrioles are structurally conserved organelles, composing both centrosomes and cilia. In animal cycling cells, centrioles often form through a highly characterized process termed canonical duplication. However, a large diversity of eukaryotes form centrioles de novo through uncharacterized pathways. This unexplored diversity is key to understanding centriole assembly mechanisms and how they evolved to assist specific cellular functions. Here, combining electron microscopy and tomography, we show that during spermatogenesis of the moss Physcomitrium patens, centrioles are born as a co-axially oriented centriole pair united by a cartwheel. We observe that microtubules emanate from those bicentrioles, which localize to the spindle poles during cell division. Thereafter, each bicentriole breaks apart, and the two resulting sister centrioles mature asymmetrically, elongating specific microtubule triplets and a naked cartwheel. Subsequently, two cilia are assembled which are capable of beating asynchronously. We further show that conserved cartwheel and centriole wall components, SAS6, BLD10 and POC1 are expressed during spermatogenesis and are required for this de novo biogenesis pathway. Our work supports a scenario where centriole biogenesis is more diverse than previously thought and that conserved molecular modules underlie diversification of this essential pathway.

cell biology↗

bioRxiv2018

Software tools for automated transmission electron microscopy

In the recent years, electron microscopy in the life sciences has witnessed increasing demand for high-throughput data collection in both structural and cellular biology. We present a combination of software tools that enable automated acquisition guided by image analysis for a wide variety of Transmission Electron Microscopy applications. Using these tools, we demonstrate dose-reduction in single particle cryo-EM experiments, fully automated acquisition of every single cell in a plastic section and automated targeting of features on serial sections for 3D volume imaging even across multiple grids.

cell biology↗

bioRxiv2017

Postmitotic Nuclear Pore Assembly Proceeds By Radial Dilation Of Small ER Membrane Openings

The nuclear envelope has to be reformed after mitosis to create viable daughter cells with closed nuclei. How membrane sealing of DNA and assembly of nuclear pore complexes (NPCs) are achieved and coordinated is poorly understood. Here, we reconstructed nuclear membrane topology and structure of assembling NPCs in a correlative three dimensional electron microscopy time-course of dividing human cells. Our quantitative ultrastructural analysis shows that nuclear membranes form from highly fenestrated ER sheets, whose shrinking holes are stabilized and then dilated into NPCs during inner ring complex assembly, forming thousands of transport channels within minutes. This mechanism is fundamentally different from interphase NPC assembly and explains how mitotic cells can rapidly establish a closed nuclear compartment while making it transport-competent at the same time.

cell biology↗

bioRxiv2016

Exosomes purified from a single cell type have diverse morphology and composition

Extracellular vesicles (EVs) are produced by all known organisms and have important roles in cell communication and physiology. Exosomes are known in the literature to be small round EVs (40 to 100 nm in diameter) and are commonly purified with a serial ultracentrifugation protocol followed by density gradient floatation. Great morphological diversity has been described before regarding EVs found in body fluids such as blood plasma, breast milk and ejaculate. However, a detailed morphological analysis has never been performed on exosomes purified from a single cell type.\n\nTherefore, the aim of this study was to analyze and quantify via multiple electron microscopy techniques the morphology of exosomes purified from the human mast cell line HMC-1. The results revealed a novel spectrum of diversity in exosomes, which suggests that subpopulations of exosomes with different and specific functions might also exist. Our findings therefore argue that a new and more efficient way of defining exosome subpopulations is necessary. A system was proposed where exosomes were classified into nine different categories according to their size and shape. Three additional morphological features could also be found in exosomes regardless of their classification.\n\nThese findings show that morphological diversity is found among exosomes purified from a single cell line, similarly to what was previously observed for EVs in body fluids. This knowledge can help improving the interpretation of experimental results and widening our general understanding of the biological functions of exosomes.

cell biology↗