Biology subjects

Ghisleni, A.

Publications and source records attributed to Ghisleni, A..

5 recordsLinked to original sources

bioRxiv2024

Dynamic mechanisms for membrane skeleton transitions

The plasma membrane and the underlying skeleton form a protective barrier for eukaryotic cells. The molecules forming this complex composite material constantly rearrange under mechanical stress to confer this protective capacity. One of those molecules, spectrin, is ubiquitous in the membrane skeleton and primarily located proximal to the inner leaflet of the plasma membrane and engages in protein-lipid interactions via a set of membrane-anchoring domains. Spectrin is linked by short actin filaments and its conformation varies in different types of cells. In this work, we developed a generalized network model for the membrane skeleton integrated with myosin contractility and membrane mechanics to investigate the response of the spectrin meshwork to mechanical loading. We observed that the force generated by membrane bending is important to maintain a smooth skeletal structure. This suggests that the membrane is not just supported by the skeleton, but has an active contribution to the stability of the cell structure. We found that spectrin and myosin turnover are necessary for the transition between stress and rest states in the skeleton. Our model reveals that the actin-spectrin meshwork dynamics are balanced by the membrane forces with area constraint and volume restriction promoting the stability of the membrane skeleton. Furthermore, we showed that cell attachment to the substrate promotes shape stabilization. Thus, our proposed model gives insight into the shared mechanisms of the membrane skeleton associated with myosin and membrane that can be tested in different types of cells. Significance StatementSpectrin was first observed in red blood cells, as a result of which, many theoretical models focused on understanding its function in this cell type. However, recently, experiments have shown that spectrin is an important skeletal component for many different cell types and that it can form different configurations with actin. In this work, we proposed a model to study the shared mechanisms behind the function of the actin-spectrin meshwork in different types of cells. We found that membrane dynamics in addition to spectrin and myosin turnover are necessary to achieve conformational changes when stresses are applied and to guarantee shape stability when the stresses are removed. We observed that membrane bending is important to support skeletal structure. Furthermore, our model gives insight into how cell shape is maintained despite constant spectrin turnover and myosin contraction.

biophysics↗

bioRxiv2023

Mechanically induced topological transition of spectrin regulates its distribution in the mammalian cortex

The cell cortex is a dynamic assembly that ensures cell integrity during passive deformation or active response by adapting cytoskeleton topologies with poorly understood mechanisms. The spectrin meshwork ensures such adaptation in erythrocytes and neurons. Erythrocytes rely on triangular-like lattices of spectrin tetramers, which in neurons are organized in periodic arrays. We exploited Expansion Microscopy to discover that these two distinct topologies can co-exist in other mammalian cells such as fibroblasts. We show through biophysical measurements and computational modeling that spectrin provides coverage of the cortex and, with the intervention of actomyosin, erythroid-like lattices can dynamically transition into condensates resembling neuron-like periodic arrays fenced by actin stress fibers. Spectrin condensates experience lower mechanical stress and turnover despite displaying an extension close to the contour length of the tetramer. Our study sheds light on the adaptive properties of spectrin, which ensures protection of the cortex by undergoing mechanically induced topological transitions.

cell biology↗

bioRxiv2022

PIP4K2B is a mechanosensor and induces heterochromatin-driven nuclear softening through UHRF1.

Phosphatidylinositol-5-phosphate (PtdIns5P)-4-kinases (PIP4Ks) are stress-regulated phosphoinositide kinases able to phosphorylate PtdIns5P to PtdIns(4, 5)P2. In cancer patients their expression is typically associated with bad prognosis. Among the three PIP4K isoforms expressed in mammalian cells, PIP4K2B is the one with more prominent nuclear localization. Here, we unveil the role for PIP4K2B as mechanosensor. PIP4K2B protein level, indeed, strongly decreases in cells growing on soft substrates. Its direct silencing or pharmacological inhibition, mimicking cell response to soft, triggers a concomitant reduction of the epigenetic regulator UHRF1 and induces changes in nuclear polarity, nuclear envelope tension and chromatin compaction. This substantial rewiring of the nucleus mechanical state drives YAP cytoplasmic retention and impairment of its activity as transcriptional regulator, finally leading to defects in cell spreading and motility. Since YAP signalling is essential for initiation and growth of human malignancies, our data suggest that potential therapeutic approaches targeting PIP4K2B could be beneficial in the control of the altered mechanical properties of cancer cells.

cell biology↗

bioRxiv2020

Adaptive mechanoproperties characterize glioblastoma fitness for invasion

Glioblastoma are heterogeneous tumors composed of highly invasive and highly proliferative clones. Heterogeneity in invasiveness could emerge from discrete biophysical properties linked to specific molecular expression. We identified clones of patient-derived glioma propagating cells that were either highly proliferative or highly invasive and compared their cellular architecture, migratory and biophysical properties. We discovered that invasiveness was linked to cellular fitness. The most invasive cells were stiffer, developed higher mechanical forces on the substrate and moved stochastically. The mechanochemical-induced expression of the formin FMN1 conferred invasive strength that was confirmed in patient samples. Moreover, FMN1 ectopic expression in less invasive clones increased fitness parameters. Mechanistically, FMN1 acts from the microtubule lattice, counteracting microtubule bundling and promoting a robust cell-body cohesion leading to highly invasive hurdling motility. One Sentence SummaryFMN1 increases cell mechanics and invasiveness.

cell biology↗

bioRxiv2019

Mesoscale Dynamics of Spectrin and Acto-Myosin shape Membrane Territories during Mechanoresponse

The spectrin cytoskeleton is a major component of the cell cortex. While ubiquitously expressed, its dynamic interaction with the other cortex components, including the plasma membrane or the acto-myosin cytoskeleton, is poorly understood. Here, we investigated how the spectrin cytoskeleton re-organizes spatially and dynamically under the membrane during changes in cell mechanics. We found spectrin and acto-myosin cytoskeletons to be spatially distinct but cooperating during mechanical challenges, such as cell adhesion and contraction, or compression, stretch and osmolarity fluctuations, creating a cohesive cortex supporting the plasma membrane. Actin territories control protrusions and contractile structures while spectrin territories concentrate in retractile zones and low-actin density/inter-contractile regions, acting as a fence to organize membrane trafficking events. We unveil here the existence of a dynamic interplay between acto-myosin and spectrin cytoskeletons necessary to support a mesoscale organization of the lipid bilayer into spatially-confined cortical territories during cell mechanoresponse.

cell biology↗