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Abstract Propagation of membrane tension mediates mechanical signal transduction along surfaces of live cells and sets the time scale of mechanical equilibration of cell membranes. Recent studies in several cell types and under different conditions revealed a strikingly wide variation range of the tension propagation speeds including extremely low ones. The latter suggests a possibility of long-living inhomogeneities of membrane tension crucially affecting mechano-sensitive membrane processes. Here, we propose, analyze theoretically, and support experimentally a mechanism of tension propagation in membranes crumpled by the contractile cortical cytoskeleton. The tension spreading is mediated by the membrane flow between the crumples. We predict the pace of the tension propagation to be controlled by the intra-cellular pressure and the degree of the membrane crumpling. We provide experimental support for the suggested mechanism by monitoring the rate of tension propagation in cells exposed to external media of different osmolarities.

Using the Raviv model, the feasibility of introducing photovoltaic cells on a very large scale across southwestern states of the United States, to reduce consumtion of fossil fuels, is studied.

Tetraspanin 4, a protein with four transmembrane helices and three connecting loops, senses membrane curvature and localizes to membrane tubes. This enrichment in tubular membranes enhances its diverse interactions. While the transmembrane part of the protein likely contributes to curvature sensitivity, the possible roles of the ectodomains in curvature sensitivity of tetraspanin 4 are still unknown. Here, using micropipette aspiration combined with confocal microscopy and optical tweezers, we show that the extracellular loop 2 contributes to the curvature sensitivity and curvature-induced interactions of tetraspanin 4. To this end, we created truncated tetraspanin 4 mutants by deleting each of the connecting loops. Subsequently, we pulled membrane tubes from giant plasma membrane vesicles containing tetraspanin 4-GFP or its mutants while maintaining controllable membrane tension and curvature. Among the mutations tested, the removal of the extracellular loop 2 had the most significant impact on both the curvature sensitivity and interactions of tetraspanin 4. Based on the results, we suggest that the extracellular loop 2 regulates the affinity of tetraspanin 4 towards curved membranes and affects its lateral interactions.

Migrasomes are signaling organelles that form in retraction fibers of migrating cells. Here authors show that migrasomes form by a two-stage process: an initial local membrane swelling matures and is stabilized by recruited tetraspanin proteins.