Biology subjects

Spatz, J. P.

Publications and source records attributed to Spatz, J. P..

5 recordsLinked to original sources

bioRxiv2026

Giant Vesicle Platform for Synthetic Endoplasmic Reticulum Networks

The endoplasmic reticulum (ER) is a membrane-bound organelle found in all eukaryotic cells. This organelle has a fascinating morphology, which involves a network of membrane nanotubes and three-way junctions connecting three nanotubes. Previous reconstitution studies were based on proteo-liposomes with a size of 100 to 200 nanometers, using electron microscopy as the main method to image the resulting membrane morphologies. These studies revealed the importance of membrane GTPases, that is, membrane proteins that hydrolyse GTP. Here, we introduce an alternative platform for the formation of synthetic ER networks starting from giant unilamellar vesicles with a typical size of 10 mirometers and containing a single membrane GTPase such as atlastin from fruit flies or Sey1 from yeast. This giant vesicle approach makes the networks accessible to optical microscopy, by which one can elucidate both their structure and their dynamics. We first demonstrate that the membranes' propensity to form synthetic ER networks depends strongly on the lipid composition. More precisely, we show that this propensity varies non-monotonically with the mole fraction of cholesterol and that the frequency of three-way junctions has a maximum for an optimal mole fraction between 10 and 15 mol%. This optimal value is comparable to the mole fraction of cholesterol as estimated for ER membranes in vivo. We also demonstrate the formation of synthetic ER networks when the membranes contain only the membrane GTPase Sey1 but no other membrane protein, which implies that Sey1 is able on its own to generate a high membrane curvature. Based on the reconstitution approach introduced here, the synthetic ER networks can now be further investigated using the versatile toolbox that has been developed for giant vesicles.

synthetic biology↗

bioRxiv2026

Optogenetic cross-linking of the actin cytoskeleton using DARPins

Precise tools to control actin filament organization and dynamics are essential for studying how the actin cytoskeleton regulates fundamental cell processes, such as morphological changes, migration and intracellular transport. Here, we present an optogenetic system for the reversible, spatiotemporal manipulation of actin cross-linking in living cells. Our approach employs actin-binding Designed Ankyrin Repeat Proteins (DARPins) fused to the improved Light-Induced Dimer (iLID) system, enabling actin cross-linking upon light-triggered dimerization. Following validation of cross-linking of bifunctional DARPins in reconstituted networks, the iLID system was integrated to create light-controlled associations inside cells. Optogenetic DARPin dimerization is rapid, reversible, and locally inducible. Activation of the DARPin-based actin cross-linkers revealed significant inhibition of cell traction forces when triggered throughout the cell. Our findings establish a versatile tool for investigating cytoskeletal dynamics with high spatial and temporal precision, paving the way for controlled manipulation of cellular architecture and mechanics. Graphical Abstract/Table of Contents Figure O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=98 SRC="FIGDIR/small/726659v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@c27701org.highwire.dtl.DTLVardef@112e82borg.highwire.dtl.DTLVardef@4892e4org.highwire.dtl.DTLVardef@a3d5a7_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2021

pH-Triggered Assembly of Endomembrane Multicompartments in Synthetic Cells

Bottom-up synthetic biology thrives to reconstruct basic cellular processes into a minimalist cellular replica to foster their investigation in greater details with a reduced number of variables. Among these cellular features, the endomembrane system is an important aspect of cells which is at the origin of many of their functions. Still, the reconstruction of these inner compartments within a lipid-based vesicle remains challenging and poorly controlled. Herein, we report the use of pH as external trigger to self-assemble compartmentalized giant unilamellar vesicles (GUVs) by either bulk, or droplet-based microfluidics. By co-encapsulating pH sensitive small unilamellar vesicles (SUVs), negatively charged SUVs and/or proteins, we show that acidification of the droplets efficiently produces GUVs while sequestrating the co-encapsulated material with flexibility and robustness. The method enables the simultaneous reconstruction of more than a single cellular phenotype from the bottom-up, corresponding to an important advancement in the current status quo of bottom-up synthetic biology.

synthetic biology↗

bioRxiv2021

Integrin α5β1 nano-presentation regulates collective keratinocyte migration independent of substrate rigidity

Nanometer-scale properties of the extracellular matrix influence many biological processes, including cell motility. While much information is available for single cell migration, to date, no knowledge exists on how the nanoscale presentation of extracellular matrix receptors influences collective cell migration. In wound healing, basal keratinocytes collectively migrate on a fibronectin-rich provisional basement membrane to re-epithelialize the injured skin. Among other receptors, the fibronectin receptor integrin 5{beta}1 plays a pivotal role in this process. Using a highly specific integrin 5{beta}1 peptidomimetic combined with nanopatterned hydrogels, we show that keratinocyte sheets regulate their migration ability at an optimal integrin 5{beta}1 nanospacing. This efficiency relies on the effective propagation of stresses within the cell monolayer independent of substrate stiffness. For the first time, this work highlights the importance of extracellular matrix receptor nanoscale organization required for efficient tissue regeneration.

biophysics↗

bioRxiv2019

Protein-free division of giant unilamellar vesicles controlled by enzymatic activity

Cell division is one of the hallmarks of life. Success in the bottom-up assembly of synthetic cells will, no doubt, depend on strategies for the controlled autonomous division of protocellular compartments. Here, we describe the protein-free division of giant unilamellar lipid vesicles (GUVs) based on the combination of two physical principles - phase separation and osmosis. We visualize the division process with confocal fluorescence microscopy and derive a conceptual model based on the vesicle geometry. The model successfully predicts the shape transformations over time as well as the time point of the final pinching of the daughter vesicles. Remarkably, we show that two fundamentally distinct yet highly abundant processes - water evaporation and metabolic activity - can both regulate the autonomous division of GUVs. Our work may hint towards mechanisms that governed the division of protocells and adds to the strategic toolbox of bottom-up synthetic biology with its vision of bringing matter to life.

biophysics↗