Decisive role of mDia-family formins in cell cortex function of highly adherent cells.

Cortical formins, pivotal for the assembly of linear actin filaments beneath the membrane, exert only minor effects on unconfined cell migration of weakly and moderately adherent cells. However, their impact on migration and mechanostability of highly adherent cells remains poorly understood. Here, we demonstrate that loss of cortical actin filaments generated by the formins mDia1 and mDia3 drastically compromises cell migration and mechanics in highly adherent fibroblasts.

Differential interference with actin-binding protein function by acute Cytochalasin B.

Dynamic actin filament remodeling is crucial for a plethora of fundamental cell biological processes, ranging from cell division and migration to cell communication, intracellular trafficking or tissue development. Cytochalasin B and -D are fungal secondary metabolites frequently used for interference with such processes. Although generally assumed to block actin filament polymerization at their rapidly growing barbed ends and compete with regulators at these sites, our molecular understanding of their precise effects in dynamic actin structures is scarce.

Structural basis for subversion of host cell actin cytoskeleton during infection.

Secreted bacterial type III secretion system (T3SS) proteins are essential for successful infection by many human pathogens. Both T3SS translocator SipC and effector SipA are critical for infection by subversion of the host cell cytoskeleton, but the precise molecular interplay between them remains unknown. Here, using cryo-electron microscopy, we show that SipA binds along the F-actin grooves with a unique binding pattern.

Epithelial restitution in 3D - Revealing biomechanical and physiochemical dynamics in intestinal organoids via fs laser nanosurgery.

Intestinal organoids represent a three-dimensional cell culture system mimicking the mammalian intestine. The application of single-cell ablation for defined wounding via a femtosecond laser system within the crypt base allowed us to study cell dynamics during epithelial restitution. Neighboring cells formed a contractile actin ring encircling the damaged cell, changed the cellular aspect ratio, and immediately closed the barrier.

Unleashed Actin Assembly in Capping Protein-Deficient B16-F1 Cells Enables Identification of Multiple Factors Contributing to Filopodium Formation.

Background: Filopodia are dynamic, finger-like actin-filament bundles that overcome membrane tension by forces generated through actin polymerization at their tips to allow extension of these structures a few microns beyond the cell periphery. Actin assembly of these protrusions is regulated by accessory proteins including heterodimeric capping protein (CP) or Ena/VASP actin polymerases to either terminate or promote filament growth. Accordingly, the depletion of CP in B16-F1 melanoma cells was previously shown to cause an explosive formation of filopodia.

Convergence of Ras- and Rac-regulated formin pathways is pivotal for phagosome formation and particle uptake in .

Macroendocytosis comprising phagocytosis and macropinocytosis is an actin-driven process regulated by small GTPases that depend on the dynamic reorganization of the membrane that protrudes and internalizes extracellular material by cup-shaped structures. To effectively capture, enwrap, and internalize their targets, these cups are arranged into a peripheral ring or ruffle of protruding actin sheets emerging from an actin-rich, nonprotrusive zone at its base. Despite extensive knowledge of the mechanism driving actin assembly of the branched network at the protrusive cup edge, which is initiated by the actin-related protein (Arp) 2/3 complex downstream of Rac signaling, our understanding of actin assembly in the base is still incomplete.

ArpC5 isoforms regulate Arp2/3 complex-dependent protrusion through differential Ena/VASP positioning.

Regulation of the Arp2/3 complex is required for productive nucleation of branched actin networks. An emerging aspect of regulation is the incorporation of subunit isoforms into the Arp2/3 complex. Specifically, both ArpC5 subunit isoforms, ArpC5 and ArpC5L, have been reported to fine-tune nucleation activity and branch junction stability.

Ena/VASP clustering at microspike tips involves lamellipodin but not I-BAR proteins, and absolutely requires unconventional myosin-X.

Sheet-like membrane protrusions at the leading edge, termed lamellipodia, drive 2D-cell migration using active actin polymerization. Microspikes comprise actin-filament bundles embedded within lamellipodia, but the molecular mechanisms driving their formation and their potential functional relevance have remained elusive. Microspike formation requires the specific activity of clustered Ena/VASP proteins at their tips to enable processive actin assembly in the presence of capping protein, but the factors and mechanisms mediating Ena/VASP clustering are poorly understood.

Tension-dependent RHGF-1 recruitment to stress fibers drives robust spermathecal tissue contraction.

Contractile epithelial tubes are found in various organs, such as lung airways and blood capillaries. Their ability to sense luminal pressure and respond with adequate contractility is essential for their physiology, and its mis-regulation results in diseases such as asthma and hypertension. Here, we describe a mechanoresponsive regulatory pathway downstream of tissue stretching that controls contraction of the C.

Inhibition of Arp2/3 Complex after ADP-Ribosylation of Arp2 by Binary Toxins.

Clostridioides bacteria are responsible for life threatening infections. Here, we show that in addition to actin, the binary toxins CDT, C2I, and Iota from , , and , respectively, ADP-ribosylate the actin-related protein Arp2 of Arp2/3 complex and its additional components ArpC1, ArpC2, and ArpC4/5. The Arp2/3 complex is composed of seven subunits and stimulates the formation of branched actin filament networks.

Calcium bursts allow rapid reorganization of EFhD2/Swip-1 cross-linked actin networks in epithelial wound closure.

Changes in cell morphology require the dynamic remodeling of the actin cytoskeleton. Calcium fluxes have been suggested as an important signal to rapidly relay information to the actin cytoskeleton, but the underlying mechanisms remain poorly understood. Here, we identify the EF-hand domain containing protein EFhD2/Swip-1 as a conserved lamellipodial protein strongly upregulated in Drosophila macrophages at the onset of metamorphosis when macrophage behavior shifts from quiescent to migratory state.

Frameshift mutation S368fs in the gene encoding cytoskeletal β-actin leads to ACTB-associated syndromic thrombocytopenia by impairing actin dynamics.

Heterozygous dominant mutations in the ubiquitously produced cytoskeletal β-actin isoform lead to a broad range of human disease phenotypes, which are currently classified as three distinct clinical entities termed Baraitser-Winter-Cerebrofrontofacial syndrome (BWCFF), ACTB-associated pleiotropic malformation syndrome with intellectual disability (ACTB-PMSID), and ACTB-associated syndromic thrombocytopenia (ACTB-AST). The latter two are distinguishable from BWCFF by the presence of milder craniofacial features and less pronounced developmental abnormalities, or the absence of craniofacial features in combination with a characteristic thrombocytopenia with platelet anisotropy. Production and correct function of β-actin is required for multiple essential processes in all types of cells.

Ena/VASP proteins in cell edge protrusion, migration and adhesion.

The tightly coordinated, spatiotemporal control of actin filament remodeling provides the basis of fundamental cellular processes, such as cell migration and adhesion. Specific protein assemblies, composed of various actin-binding proteins, are thought to operate in these processes to nucleate and elongate new filaments, arrange them into complex three-dimensional (3D) arrays and recycle them to replenish the actin monomer pool. Actin filament assembly is not only necessary to generate pushing forces against the leading edge membrane or to propel pathogens through the cytoplasm, but also coincides with the generation of stress fibers (SFs) and focal adhesions (FAs) that generate, transmit and sense mechanical tension.

VASP boosts protrusive activity of macroendocytic cups and drives phagosome rocketing after internalization.

Ena/VASP proteins are powerful actin polymerases that drive the processive elongation of actin filaments. Members of this protein family have been implicated in a variety of important cellular processes including axon guidance, cell migration and adhesion. However, the specific function of these proteins in macroendocytosis, comprising macropinocytosis and phagocytosis remain rather poorly understood.

Laboratory Detection and Initial Diagnosis of Monoclonal Gammopathies.

Context.—: The process for identifying patients with monoclonal gammopathies is complex. Initial detection of a monoclonal immunoglobulin protein (M protein) in the serum or urine often requires compilation of analytical data from several areas of the laboratory.

Single-Dilution COVID-19 Antibody Test with Qualitative and Quantitative Readouts.

The coronavirus disease 2019 (COVID-19) global pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to place an immense burden on societies and health care systems. A key component of COVID-19 control efforts is serological testing to determine the community prevalence of SARS-CoV-2 exposure and quantify individual immune responses to prior SARS-CoV-2 infection or vaccination. Here, we describe a laboratory-developed antibody test that uses readily available research-grade reagents to detect SARS-CoV-2 exposure in patient blood samples with high sensitivity and specificity.

Loss of Hem1 disrupts macrophage function and impacts migration, phagocytosis, and integrin-mediated adhesion.

Hematopoietic-specific protein 1 (Hem1) is an essential subunit of the WAVE regulatory complex (WRC) in immune cells. WRC is crucial for Arp2/3 complex activation and the protrusion of branched actin filament networks. Moreover, Hem1 loss of function in immune cells causes autoimmune diseases in humans.

Capping protein is dispensable for polarized actin network growth and actin-based motility.

Heterodimeric capping protein (CP) binds the rapidly growing barbed ends of actin filaments and prevents the addition (or loss) of subunits. Capping activity is generally considered to be essential for actin-based motility induced by Arp2/3 complex nucleation. By stopping barbed end growth, CP favors nucleation of daughter filaments at the functionalized surface where the Arp2/3 complex is activated, thus creating polarized network growth, which is necessary for movement.

Lamellipodin tunes cell migration by stabilizing protrusions and promoting adhesion formation.

Efficient migration on adhesive surfaces involves the protrusion of lamellipodial actin networks and their subsequent stabilization by nascent adhesions. The actin-binding protein lamellipodin (Lpd) is thought to play a critical role in lamellipodium protrusion, by delivering Ena/VASP proteins onto the growing plus ends of actin filaments and by interacting with the WAVE regulatory complex, an activator of the Arp2/3 complex, at the leading edge. Using B16-F1 melanoma cell lines, we demonstrate that genetic ablation of Lpd compromises protrusion efficiency and coincident cell migration without altering essential parameters of lamellipodia, including their maximal rate of forward advancement and actin polymerization.