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Cell cortex

The cell cortex is a thin, dynamic layer of filamentous actin (F-actin) meshwork that underlies and associates with the plasma membrane in eukaryotic animal cells, serving as a key cytoskeletal structure that maintains cellular shape and mechanical properties.^[1] This cortex typically measures 50–400 nm in thickness and features a network of actin filaments with mesh sizes ranging from 20–300 nm, which can be organized isotropically (randomly oriented) or anisotropically (aligned bundles) depending on the cell type, state, and environmental cues such as adhesion.^[1] Its molecular composition includes actin filaments polymerized by nucleators like formins (for linear filaments) and the Arp2/3 complex (for branched networks), along with cross-linking proteins, nonmuscle myosin II for contractility, and membrane-anchoring elements such as ERM proteins (ezrin, radixin, moesin) or spectrin that tether it to the lipid bilayer.^[1] The cortex's structure and mechanics vary by cellular location and adhesion status; for instance, it is thicker and less bundled in suspended cells compared to adhered cells, where perinuclear regions exhibit greater bundling and stiffness.^[2] Functionally, the cell cortex is essential for generating and resisting mechanical forces, enabling processes such as cell migration, adhesion, division, and differentiation by controlling cortical tension, stiffness, and fluidity.^[2] It contributes to cytokinesis by contracting to form the cleavage furrow and plays a role in maintaining cell polarity and volume regulation through actin remodeling and myosin-driven contractions.^[1] Dysregulation of the cortex can impair these functions, highlighting its importance in cellular homeostasis and response to external stresses.^[2]

Structure and Composition

Definition and Basic Structure

The cell cortex is a thin, actin-rich layer immediately underlying the plasma membrane in eukaryotic animal cells, forming a contractile actomyosin meshwork that provides structural support to the cell surface.^[3] This layer typically measures 100-200 nm in thickness, though values can range from 50-400 nm depending on cell type and physiological state.^[1] It encases the cytoplasm, creating a dynamic boundary that separates the intracellular environment from the exterior.^[4] In terms of basic architecture, the cell cortex integrates closely with the plasma membrane through linker proteins, which anchor the underlying network to the lipid bilayer and maintain its proximity.^[3] This integration forms a cohesive cortical shell, often visualized as a dense, filamentous network oriented parallel to the membrane, as observed in electron microscopy studies of various cell types.^[5] Actin filaments serve as the primary structural elements within this shell, contributing to its overall meshwork organization.^[1] While the cell cortex is a hallmark of animal cells, analogous structures exist in other eukaryotes, such as the cortical actin patches in budding yeast, which perform similar roles in cytoskeletal organization at the plasma membrane.^[6] These patches represent an evolutionary precursor or variant, highlighting conserved actin-based mechanisms across eukaryotic lineages despite differences in complexity.^[6]

Molecular Components

The cell cortex is primarily composed of filamentous actin (F-actin), which forms a dense meshwork serving as the core structural scaffold underlying the plasma membrane. These filaments are assembled through the polymerization of globular actin monomers (G-actin), typically via nucleation-promoting factors such as formins for linear filaments or the Arp2/3 complex for branched networks, resulting in a dynamic yet stable architecture that provides mechanical support to the cell.^[7] In many cell types, formin-nucleated filaments constitute 20-25% of the cortical actin, while Arp2/3-branched filaments make up the remaining 75-80%.^[7] Non-muscle myosin-II acts as the principal motor protein within this actomyosin network, assembling into bipolar minifilaments that slide along adjacent actin filaments to generate contractile forces powered by ATP hydrolysis. This motor activity not only compacts the actin mesh but also enables the cortex to exert tension on the membrane, essential for maintaining cellular integrity. Myosin-II is the primary generator of cortical tension, with its activity modulating the overall stiffness and contractility of the network.^[7]^[8] The actin meshwork is further stabilized by a variety of crosslinking and bundling proteins that regulate filament organization and force transmission. Spectrin, for instance, forms tetramers that crosslink short actin filaments into an isotropic network, particularly prominent in certain cell types like erythrocytes but also contributing to cortical stability in others. Filamin crosslinks actin filaments into orthogonal networks, facilitating stress distribution under mechanical load, while alpha-actinin bundles parallel filaments to enhance alignment and rigidity within the cortex. These proteins collectively determine the mesh size and connectivity, with typical mesh sizes of 100-200 nm.^[7] Direct attachment between the actin cortex and the plasma membrane is mediated by linker proteins, including the ezrin-radixin-moesin (ERM) family, which undergo conformational activation to bind both F-actin and membrane phospholipids or proteins like phosphatidylinositol 4,5-bisphosphate. Ezrin, radixin, and moesin thus anchor the cortex to the membrane, transmitting forces and maintaining spatial organization. Adhesion molecules such as integrins also contribute to cortex-membrane coupling by linking extracellular matrix components to intracellular actin via adaptor proteins, though ERM-mediated links predominate in non-adherent contexts. Myosin-II activity contributes significantly to cortical tension through its contractile effects in balanced networks.^[7]^[8]

Spatial Organization

The cell cortex exhibits both uniform and heterogeneous organization across the cell surface, adapting to functional demands. In migrating cells, the cortical actin meshwork displays a pronounced back-to-front gradient in density, with a sparser arrangement in the lamellipodia at the leading edge compared to the denser mesh in the cell body. This heterogeneity arises from localized regulation of F-actin disassembly by cofilin, which is more active at the front due to phosphatase activity, enabling membrane protrusions essential for directed motility.^[9] In polarized epithelial cells, the cortex is compartmentalized along the apical-basal axis, with distinct molecular compositions and densities mediated by junctional complexes. Tight junctions, positioned apically, and adherens junctions, located more basally, serve as barriers and anchors that segregate apical and basolateral domains, respectively. These junctions, involving proteins like claudins, ZO-1, E-cadherin, and α-catenin, link to the underlying actin cortex, enforcing asymmetric organization and maintaining tissue barrier integrity. The Crumbs and Par polarity complexes further reinforce this compartmentalization by recruiting actin regulators to specific cortical regions.^[10] At the microscale, the cortical thickness varies regionally, as revealed by super-resolution and expansion microscopy techniques. The cortex is typically thinner (~200-250 nm) at protrusions such as lamellipodia and ruffles, facilitating dynamic membrane extensions, while it thickens in areas associated with stress fibers, where bundled actin accumulates to support contractility. These variations, measured with nanometer precision via fluorescence intensity profiling and magnetic bead assays, highlight the cortex's adaptability to local mechanical cues without altering overall filament density uniformly.^[11]^[2] Interactions with intracellular organelles, particularly endosomes and lysosomes, further modulate local cortical density through proximity-dependent remodeling. Late endosomes, upon signaling-induced membrane permeabilization, release cathepsin D into the cytosol near the leading edge, where it nonproteolytically balances cofilin activity to sustain actin turnover and maintain sparse cortical density in protrusions. Similarly, damaged lysosomes recruit connexin43 to reorganize nearby actin into branched networks, increasing local cortical porosity and density to promote organelle docking and exocytosis at the plasma membrane. These organelle-cortex contacts thus create hotspots of heterogeneous organization, influencing overall cortical architecture.^[12]^[13]

Biophysical Properties

Mechanical Properties

The cell cortex exhibits cortical tension primarily generated by the contractile activity of myosin-II minifilaments pulling on crosslinked actin filaments within the actomyosin network.^[14] This tension maintains the structural integrity of the plasma membrane and is quantified in resting cells as approximately 0.1-1 nN/μm, with values around 0.4 nN/μm corresponding to contractile stresses exceeding 1 kPa.^[15]^[16] The cortex displays viscoelastic behavior, combining elastic and viscous components that allow it to deform and recover under mechanical load. Its elasticity is characterized by a Young's modulus typically in the range of 1-10 kPa, reflecting the stiffness contributed by the crosslinked actin meshwork. Recent studies indicate that interactions between actin and vimentin intermediate filaments jointly regulate this viscoelasticity and overall cortical stiffness.^[17]^[18] This viscoelasticity is often modeled using the Kelvin-Voigt framework, which describes the total stress \sigma as the sum of an elastic term and a viscous term proportional to the strain rate:

\sigma = E \varepsilon + \eta \frac{d\varepsilon}{dt}

where E is the elastic modulus, \varepsilon is the strain, \eta is the viscosity, and \frac{d\varepsilon}{dt} is the strain rate.^[19]^[20] Under compressive forces, the cortex can undergo thickness instabilities, including buckling or localized thinning, which arise from imbalances in actomyosin contractility. These phenomena have been observed in experiments applying controlled deformations, such as micropipette aspiration, where the cortex thins non-uniformly in response to suction pressures.^[21] Complementary pinching assays using magnetic beads on live cells further reveal myosin-II-driven instabilities, confirming the cortex's sensitivity to compressive stress. The cortex plays a key role in force transmission, enabling cells to withstand external mechanical stresses without catastrophic failure. Individual actin filaments in the cortical network can endure forces up to approximately 10-100 pN before rupture, providing a threshold that protects the overall structure during deformation.^[22] This resilience is essential for maintaining cortical integrity under physiological loads, such as fluid shear or substrate interactions.

Dynamic Behavior

The dynamic behavior of the cell cortex involves continuous remodeling through actin polymerization and depolymerization cycles, which maintain its structural integrity and responsiveness. Actin polymerization is primarily driven by the Arp2/3 complex, which nucleates branched networks by attaching new filaments to existing ones, while depolymerization is facilitated by cofilin, which severs older ADP-actin filaments to generate new barbed ends for assembly. These cycles exhibit turnover rates ranging from 0.1 to 1 s⁻¹, as measured by fluorescence recovery after photobleaching (FRAP) in reconstituted networks, enabling rapid adaptation to cellular demands.^[23]^[24] Additionally, oxidative stress can induce densification of the actin network in the apical cortex, leading to increased stiffness and altered migration dynamics.^[25] Contractile waves represent another key dynamic feature, characterized by oscillatory patterns of myosin recruitment that propagate across the cortical surface. In starfish oocytes, these surface contraction waves (SCWs) arise from periodic bands of myosin II accumulation, driving localized contractility and propagating at speeds of approximately 0.1 to 1 μm/s, with wavelengths around 20 μm. Such waves facilitate temporal coordination of cortical tension, observed during meiotic maturation.^[26]^[27] The cortex also undergoes rheological transitions from solid-like to fluid-like states, particularly under applied shear, reflecting its viscoelastic nature. These shifts occur over relaxation times of 1 to 10 seconds, governed by actin filament turnover and cross-linker dynamics, allowing the cortex to resist deformation at short timescales while flowing at longer ones during mitotic compression.^[28] Feedback loops further underpin cortical dynamics, as seen in minioscillation models where local contraction events trigger actin disassembly. In these systems, increased material density from contraction slows ingress and promotes net loss of actomyosin components within seconds, generating pulsatile cycles with periods of about 18 seconds that stabilize overall cortical excitability.^[29]

Functions in Cellular Processes

Cell Shape and Integrity

The cell cortex maintains cellular shape and integrity by providing a mechanical scaffold that resists deformation from internal turgor pressure and external forces. In suspended cells, it supports a rounded morphology, while in adherent cells, it adapts to substrate interactions, with regional variations in thickness and stiffness contributing to overall form. Under hypotonic conditions, the cortex can transiently disassemble to permit regulatory volume increase through bleb formation, preventing rupture. Upon return to isotonicity or adaptation, the cortex reforms via actin polymerization. Following mechanical damage, such as laser-induced plasma membrane rupture, actin rapidly accumulates at the wound site within seconds, mediated by nucleators like Arp2/3 and formins, to reinforce the membrane and facilitate repair. This quick response, often completing initial sealing in under 1 minute, ensures cellular homeostasis and prevents lysis.^[30]^[1]

Motility and Migration

The cell cortex drives motility and migration through spatially regulated actin polymerization and actomyosin contractility, enabling cells to generate asymmetric protrusions at the front and retractions at the rear for directed locomotion.^[31] This dynamic remodeling of the cortical actin network couples membrane deformation to intracellular force generation, allowing cells to navigate diverse environments such as tissues or matrices.^[32] In motile cells, the cortex maintains polarity by confining protrusive activity to the leading edge while promoting contraction posteriorly, thus coordinating whole-cell movement over distances spanning tens to hundreds of micrometers.^[33] Lamellipodia formation at the cell front exemplifies the cortex's protrusive function, where the Arp2/3 complex nucleates branched actin filaments that polymerize against the plasma membrane, pushing it forward at rates of 0.1–1 μm/min.^[34] This branching polymerization, activated by upstream signals like Rac GTPases, creates a dense dendritic actin array within the lamellipodium, approximately 1–5 μm wide, that supports persistent extension and adhesion to the substrate via integrins.^[35] Disruption of Arp2/3 activity, as shown in knockout fibroblasts, abolishes lamellipodia and impairs directional protrusion, though overall migration speed remains comparable due to compensatory filopodia-like structures.^[34] These protrusions are essential for mesenchymal migration modes, where cortical actin turnover rates match the protrusion velocity to sustain forward progress.^[36] Cell retraction at the rear relies on myosin-II assembly into bipolar minifilaments that cross-link and slide actin filaments, contracting the cortex to detach the tail from the substrate and propel the cell body forward.^[37] This contractility, regulated by RhoA-ROCK signaling, generates forces on the order of ~100 pN to overcome adhesion and membrane tension, facilitating uropod retraction in polarized cells.^[38] In migrating fibroblasts, myosin-II inhibition reduces rear contractility, leading to elongated tails and slowed overall displacement, highlighting its role in force balance with frontal protrusions.^[39] The cortex's viscoelastic properties ensure that these contractions are tuned to substrate stiffness, preventing excessive deformation during locomotion.^[40] In chemotaxis, polarized cortical flows integrate external gradients to direct migration, with actomyosin contraction at the rear driving retrograde flow that reinforces front-rear asymmetry and orients the cell toward attractants like fMLP or CXCL8.^[41] These flows, arising from instabilities in cortical contractility above a critical Péclet number, transport regulatory molecules such as Rho GTPases to maintain polarity, enabling persistent chemotactic indices above 0.8 in response to gradients of 0.1–1 nM/μm.^[42] In three-dimensional environments, such flows sustain amoeboid migration without adhesions, as observed in tumor cells where rear myosin accumulation correlates with directed velocity.^[41] This mechanism links cortical dynamics to signal amplification, ensuring robust navigation in noisy chemical landscapes.^[32] Neutrophil crawling illustrates cortex-dependent motility in immune response, where rapid lamellipodial extensions and rear contractions enable speeds of 10–20 μm/min toward infection sites in vivo.^[43] Cortical actin remodeling, driven by Cdc42 and Arp2/3, supports pseudopod formation that breaks symmetry in response to chemoattractants, with myosin-II ensuring detachment of the uropod to maintain high persistence.^[44] In confined spaces like capillaries, cortical flows adapt to sustain crawling at average speeds below 50 μm/min, underscoring the cortex's role in force transmission under mechanical stress.^[45] Fibroblast wound healing assays demonstrate collective cortical migration, where leading-edge Arp2/3-driven protrusions close gaps at speeds of ~0.4–0.5 μm/min, coordinated by myosin-II-mediated tension gradients across the sheet.^[46] In these models, cortical integrity ensures synchronized advance, with disruption reducing closure rates by up to 50% and impairing directional persistence.^[34] This process highlights the cortex's integration of mechanical cues from the provisional matrix to guide reparative locomotion.^[47]

Cell Division

During metaphase, the cell cortex undergoes global stiffening mediated by RhoA activation, which promotes cortical retraction and increased rigidity to counteract the outward forces exerted by the mitotic spindle, thereby maintaining a spherical cell shape essential for proper chromosome alignment. This RhoA-driven process involves the recruitment of myosin-II to the cortex, enhancing actomyosin contractility without requiring cell-substrate de-adhesion.^[48] The resulting cortical tension, which can reach pressures of up to 1000 Pa in some systems, ensures mechanical stability against spindle-generated forces estimated at 10-100 pN per microtubule.^[49] In anaphase and telophase, the cortex transitions to localized contractility at the equator, where astral microtubules signal to activate RhoA specifically in the furrow region, leading to the assembly of a myosin-II contractile ring that drives cleavage furrow ingression at rates typically ranging from 0.5 to 2 μm/min in mammalian cells.^[50] This equatorial enrichment of actomyosin, facilitated by guanine nucleotide exchange factors like Ect2, generates the necessary inward force for membrane invagination while polar astral microtubules inhibit contractility to prevent ectopic furrows.00276-6) The ring's contraction, powered by myosin-II motor activity, reduces the intercellular bridge diameter progressively, integrating with centralspindlin signaling from the spindle midzone.^[51] Abscission, the final separation of daughter cells, involves cortical disassembly at the midbody, where endosomal sorting complex required for transport (ESCRT) proteins, particularly ESCRT-III, polymerize to constrict and pinch the membrane, severing the bridge in a process that takes 10-30 minutes.^[52] ESCRT-III filaments recruit the microtubule-severing enzyme spastin to break down the midbody cytoskeleton, enabling membrane fission without compromising cortical integrity elsewhere.^[53] This step ensures complete physical disconnection while preserving the cortex for post-division remodeling. Disruptions in cortical contractility, such as through myosin-II inhibition by blebbistatin, frequently result in cytokinesis failure and multinucleation in HeLa cells, where up to 20-30% of treated cells exhibit multiple nuclei due to incomplete furrow ingression or abscission defects.^[54] Similarly, knockdown of cortical regulators like CLIC4 impairs furrow stability, elevating multinucleation rates and highlighting the cortex's critical role in division fidelity.^[55]

Regulation and Signaling

Key Regulatory Proteins

The cell cortex is modulated by a suite of regulatory proteins that control actin polymerization, myosin activation, and cytoskeletal organization through enzymatic and scaffolding mechanisms. These proteins act as molecular switches and integrators, enabling dynamic responses to cellular cues while maintaining cortical integrity. Central to this regulation are Rho family GTPases, kinases, phosphatases, and scaffold proteins that fine-tune local concentrations and activities to generate patterned cortical behaviors. Rho GTPases serve as master regulators of cortical actin assembly by cycling between GTP-bound active and GDP-bound inactive states, thereby directing distinct actin architectures. RhoA, in its active form, primarily promotes the formation of linear actin filaments in the cortex by activating formin proteins such as mDia1, which nucleate and elongate unbranched filaments essential for contractile structures like stress fibers and the cytokinetic ring.^[56] In contrast, active Rac1 and Cdc42 drive branched actin networks by recruiting and activating the WAVE/Scar complex (for Rac1) or N-WASP (for Cdc42), which in turn stimulate the Arp2/3 complex to generate dendritic actin arrays supporting protrusions and cortical flows.^[57] These GTPases establish spatial gradients of activity across the cortex, with RhoA often peaking at sites of high contractility such as the cell equator during division, enabling patterned self-organization into waves or rings that propagate cortical dynamics.^[58] Myosin activation within the cortical actomyosin network is tightly controlled by kinases and phosphatases that phosphorylate and dephosphorylate the regulatory light chain (MLC) of non-muscle myosin II. Myosin light chain kinase (MLCK) directly phosphorylates MLC at serine 19, enhancing myosin ATPase activity and promoting cortical contractility in response to calcium signals.^[59] Complementing this, RhoA-activated Rho-kinase (ROCK) phosphorylates MLC and inhibits myosin phosphatase, amplifying tension. Conversely, the myosin light chain phosphatase (MLCP), which includes the regulatory subunit MYPT1, dephosphorylates MLC to relax cortical tension, with MYPT1 targeting PP1c to the plasma membrane for localized control during processes like cytokinesis.^[59] This phosphorylation-dephosphorylation cycle allows rapid modulation of cortical stiffness and flow. Scaffold proteins further integrate these regulatory elements by physically linking the cytoskeleton during specific events such as cell division. Anillin exemplifies this role, binding active RhoA, F-actin, myosin II, and septins to stabilize the contractile ring and coordinate actin-septin assemblies at the cortex.^[60] Through its Anillin homology domain, anillin retains GTP-RhoA at the membrane, cycling its residence to sustain effector signaling and prevent premature dissociation, thereby ensuring robust cortical contraction.^[61]

Intracellular Signaling

The cell cortex responds to a variety of intracellular signals that integrate environmental cues with cytoskeletal dynamics, primarily through lipid-based and ion-mediated pathways. Phosphatidylinositol 4,5-bisphosphate (PIP2), a key phosphoinositide enriched in the plasma membrane, serves as a central hub for recruiting effector proteins that modulate actin nucleation and polymerization at the cortical layer. For instance, PIP2 serves as a substrate for phospholipase C (PLC), which is activated by upstream signals and hydrolyzes PIP2 into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG), triggering downstream events that promote or inhibit actin assembly depending on the cellular context; this lipid signaling is crucial for rapid cortical remodeling during processes like phagocytosis or wound healing. Calcium signaling plays a pivotal role in eliciting transient contractions of the actomyosin cortex, often in response to mechanical or chemical stimuli. Transient spikes in cytosolic Ca²⁺ concentration (typically 1-10 μM) propagate as waves across the cortex, activating calmodulin, which binds to and activates myosin light chain kinase (MLCK), enhancing its ability to phosphorylate the regulatory light chain of myosin II and thereby promoting cortical tension. These waves facilitate coordinated responses, such as blebbing in migrating cells or cytokinesis initiation, by linking local Ca²⁺ influx—often from IP3-sensitive stores—to global cortical stiffening. Integrin-mediated adhesion to the extracellular matrix (ECM) transmits signals that reinforce cortical integrity through focal adhesion kinase (FAK) and Src kinase pathways. Upon ECM binding, integrins cluster and activate FAK, which recruits Src to phosphorylate substrates that link the ECM to cortical actin networks, promoting reinforcement and stability; this pathway is essential for maintaining cortical tension in adherent cells under shear stress. Homeostatic feedback mechanisms ensure balanced cortical assembly by preventing excessive actin polymerization. Phosphatase and tensin homolog (PTEN) acts as a negative regulator by dephosphorylating phosphatidylinositol 3,4,5-trisphosphate (PIP3) to PIP2, thereby limiting the recruitment of actin nucleators like the Arp2/3 complex and maintaining cortical homeostasis; disruptions in this loop, such as PTEN loss, lead to aberrant cortical expansion observed in certain pathologies. Rho GTPases serve as key signaling nodes integrating these pathways, though their detailed regulation is covered elsewhere.

Research History and Methods

Historical Discoveries

Early microscopic observations of peripheral structures in cells date back to the late 19th century, with studies on sea urchin eggs contributing to understanding the cell boundary. The cortical reaction, involving exocytosis of cortical granules upon fertilization, was first described by E.B. Harvey in sea urchin eggs in 1910.^[62] These findings laid the groundwork for recognizing the cortex as a specialized layer involved in cellular responses, though initial focus was on fertilization rather than cytoskeletal components. In the 1970s, advances in electron microscopy and biochemical assays revealed the actomyosin composition of the cell cortex. Researchers studying amoeboid movement identified a dense layer of actin filaments and myosin in the peripheral cytoplasm of non-muscle cells like amoebae and slime molds, demonstrating its role in contraction and motility through heavy meromyosin decoration and ATPase activity tests.^[63] These findings established the cortex as an actomyosin network capable of generating contractile forces, with key studies on Physarum polycephalum showing organized filaments in the ectoplasmic zone.^[64] The 1990s brought molecular insights into cortical regulation, particularly through the discovery that Rho GTPases control cortical tension. Alan Hall's group demonstrated in 1992 that Rho activation promotes stress fiber formation and focal adhesions,^[65] with subsequent work in 1994 linking Rho signaling to myosin light chain phosphorylation and enhanced cortical contractility in response to growth factors.^[66] This established Rho as a key regulator of actomyosin dynamics at the cortex, influencing cell shape and adhesion. Proteomic approaches in the early 2000s advanced the molecular identification of the cortex. Studies using mass spectrometry on isolated fractions from model organisms like Dictyostelium discoideum identified key proteins, including actin, myosin II, Arp2/3 complex, and cross-linkers like alpha-actinin, providing maps of the cortical proteome and highlighting its conserved composition across eukaryotes.^[67] These efforts shifted focus from structural description to the regulatory network underlying cortical function.

Modern Techniques

Modern techniques have revolutionized the study of the cell cortex by enabling nanoscale visualization, precise spatiotemporal manipulation, and comprehensive molecular profiling. Super-resolution microscopy methods, such as stimulated emission depletion (STED) and photoactivated localization microscopy (PALM), have been instrumental in resolving the fine architecture of the cortical actin network since the mid-2010s. STED microscopy achieves lateral resolutions of approximately 50 nm, allowing researchers to quantify the density and organization of actin filaments in the cortex of living cells, revealing an asymmetric distribution with a mean width of about 230 nm.^[68] Similarly, PALM variants like interferometric PALM (iPALM) provide resolutions down to 20-30 nm, enabling three-dimensional imaging of individual F-actin filaments in the plasma membrane cortex and demonstrating their branched, mesh-like arrangement with spacing on the order of 20-50 nm.^[69] These approaches have overcome the diffraction limit of conventional light microscopy, facilitating direct observation of filament spacing and dynamics that underpin cortical mechanics.^[70] Optogenetics has emerged as a powerful tool for manipulating cortical contractility with high spatial and temporal precision, particularly through light-inducible activation of RhoA signaling pathways since 2018. By fusing RhoA guanine nucleotide exchange factors (GEFs) to light-sensitive domains like Cry2/CIB1, researchers can trigger localized RhoA activation upon blue light illumination, leading to rapid recruitment of actomyosin components to the cortex and inducing contractions in epithelial cells.^[71] This technique has revealed how RhoA-driven cortical tension regulates cell shape changes and junctional remodeling, with activation causing pulsatile contractions that propagate through epithelial sheets. Such optogenetic perturbations provide reversible control over cortical forces, offering insights into mechanotransduction without the off-target effects of pharmacological agents.^[72] In vitro reconstitution of artificial cortices using actomyosin networks encapsulated in liposomes has allowed isolated study of cortical contractility and shape regulation, with notable advancements from 2021 onward. Researchers at the University of Michigan developed giant unilamellar vesicles (GUVs) loaded with actin, myosin II, and crosslinkers like fascin and α-actinin, mimicking the cortical layer and demonstrating how myosin-driven contractility generates ring-like patterns that deform the membrane into bleb-like protrusions.^[73] These synthetic systems highlight the role of network organization and ATP-dependent myosin activity in active membrane remodeling, with smaller vesicles exhibiting enhanced contractility due to confined geometry. By decoupling the cortex from cellular complexity, such models enable quantitative assessment of force generation and feedback mechanisms in a controlled environment. Integrating proteomics with quantitative imaging has provided a systems-level view of cortical composition and homeostasis, identifying over 200 proteins enriched in the actomyosin cortex and tracking their dynamics across cell cycle stages. A seminal approach combined cortical fractionation, mass spectrometry, and fluorescence microscopy to catalog 163 interphase and 189 mitotic cortical proteins, revealing stable actin and myosin levels despite global remodeling, thus establishing cortical homeostasis. Recent extensions using targeted proteomics have refined this to over 200 actin-associated proteins, quantifying enrichment factors and turnover rates via stable isotope labeling, which show minimal fluctuations in core components like actin and ezrin during interphase-to-mitosis transitions.^[74] These integrated methods underscore the cortex's compositional stability and pave the way for mapping regulatory networks in morphogenesis. As of 2024, advances in cryo-electron tomography have further elucidated the 3D organization of the cortical actin meshwork.^[75]

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Actomyosin forces in cell migration: Moving beyond cell body ...
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We identify, analytically, dynamical instabilities of the cortex and show that they yield steady-state cortical flows, which, in turn, can induce cell migration ...
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Chemotaxis promotes neutrophil participation in cellular defense by enabling neutrophil migration to infected tissue and is controlled by persistent cell ...<|separator|>
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Jan 9, 2025 · Analysis of neutrophil migration in capillaries using live-cell imaging showed that 40% of cells were crawling (speed < 50 µm/min, average speed ...
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Mitotic cells contract actomyosin cortex and generate pressure to ...
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RhoA is required for cortical retraction and rigidity during mitotic cell rounding. ... Hydrostatic pressure and the actomyosin cortex drive mitotic cell rounding ...
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Nonmuscle myosin II exerts tension but does not translocate actin in ...
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A novel coordinated function of Myosin II with GOLPH3 controls ...
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In 1888 he took his first trip to Naples where he made many far-reaching discoveries using sea urchins. Boveri named the centrosome and provided the early ...
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Boveri's long experiment: Sea urchin merogones and the ...
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Rho GTPases and the control of cell behaviour - PubMed
Rho, Rac and Cdc42 can regulate the actin cytoskeleton and gene transcription to promote co-ordinated changes in cell behaviour.Missing: cortical tension 1994
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Dissecting the actin cortex density and membrane-cortex distance in ...
Nanoscale spacing between the plasma membrane and the underlying cortical actin cytoskeleton profoundly modulates cellular morphology, mechanics, and function.
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Three-dimensional Super Resolution Microscopy of F-actin ...
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Simple methods for quantifying super-resolved cortical actin - Nature
Feb 17, 2022 · In conclusion, we demonstrate two simple analysis methods for quantifying cortical actin networks in super-resolved microscopy images. These ...
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RhoA Mediates Epithelial Cell Shape Changes via ...
Here, we study the response to dynamic changes in junctional tension induced by optogenetic activation of RhoA in a model epithelium. We find that RhoA ...
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Shining a Light on RhoA: Optical Control of Cell Contractility - NIH
In summary, optogenetic manipulation of RhoA offers unparalled spatial and temporal control of mechanical perturbations in a cell, with the added benefit of ...
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Proteomic analysis of the actin cortex in interphase and mitosis
In this article, we compared cortices from cells with low and high cortex tensions. We purified cortex-enriched fractions from cells in interphase and mitosis, ...