Search results for "Lamellipodium"
showing 10 items of 11 documents
Numerical Treatment of the Filament-Based Lamellipodium Model (FBLM)
2017
We describe in this work the numerical treatment of the Filament-Based Lamellipodium Model (FBLM). This model is a two-phase two-dimensional continuum model, describing the dynamics of two interacting families of locally parallel F-actin filaments. It includes, among others, the bending stiffness of the filaments, adhesion to the substrate, and the cross-links connecting the two families. The numerical method proposed is a Finite Element Method (FEM) developed specifically for the needs of this problem. It is comprised of composite Lagrange–Hermite two-dimensional elements defined over a two-dimensional space. We present some elements of the FEM and emphasize in the numerical treatment of t…
Profilin 1 is required for abscission during late cytokinesis of chondrocytes
2009
Profilins are key factors for dynamic rearrangements of the actin cytoskeleton. However, the functions of profilins in differentiated mammalian cells are uncertain because profilin deficiency is early embryonic lethal for higher eukaryotes. To examine profilin function in chondrocytes, we disrupted the profilin 1 gene in cartilage (Col2pfn1). Homozygous Col2pfn1 mice develop progressive chondrodysplasia caused by disorganization of the growth plate and defective chondrocyte cytokinesis, indicated by the appearance of binucleated cells. Surprisingly, Col2pfn1 chondrocytes assemble and contract actomyosin rings normally during cell division; however, they display defects during late cytokines…
Chemotaxis and Haptotaxis on Cellular Level
2018
Chemotaxis and haptotaxis have been a main theme in the macroscopic study of bacterial and cellular motility. In this work, we use a successful model that describes cellular motility and investigate the influence these processes have on the shape and motility of fast migrating cells. We note that, despite the biological and modelling differences of chemotaxis and haptotaxis, the cells exhibit many similarities in their migration. In particular, after an initial adjustment phase, the cells obtain a stable shape, similar in both cases, and move with constant velocity.
Loss of endocytic clathrin-coated pits upon acute depletion of phosphatidylinositol 4,5-bisphosphate.
2007
Phosphatidylinositol 4,5-bisphosphate [PI(4,5) P 2 ], a phosphoinositide concentrated predominantly in the plasma membrane, binds endocytic clathrin adaptors, many of their accessory factors, and a variety of actin-regulatory proteins. Here we have used fluorescent fusion proteins and total internal reflection fluorescence microscopy to investigate the effect of acute PI(4,5) P 2 breakdown on the dynamics of endocytic clathrin-coated pit components and of the actin regulatory complex, Arp2/3. PI(4,5) P 2 breakdown was achieved by the inducible recruitment to the plasma membrane of an inositol 5-phosphatase module through the rapamycin/FRB/FKBP system or by treatment with ionomycin. PI(4,5)…
Dissection of keratin dynamics: different contributions of the actin and microtubule systems.
2005
It has only recently been recognized that intermediate filaments (IFs) and their assembly intermediates are highly motile cytoskeletal components with cell-type- and isotype-specific characteristics. To elucidate the cell-type-independent contribution of actin filaments and microtubules to these motile properties, fluorescent epithelial IF keratin polypeptides were introduced into non-epithelial, adrenal cortex-derived SW13 cells. Time-lapse fluorescence microscopy of stably transfected SW13 cell lines synthesizing fluorescent human keratin 8 and 18 chimeras HK8-CFP and HK18-YFP revealed extended filament networks that are entirely composed of transgene products and exhibit the same dynamic…
The Ras/Raf-1/MEK1/ERK Signaling Pathway Coupled to Integrin Expression Mediates Cholinergic Regulation of Keratinocyte Directional Migration
2005
The physiologic mechanisms that determine directionality of lateral migration are a subject of intense research. Galvanotropism in a direct current (DC) electric field represents a natural model of cell re-orientation toward the direction of future migration. Keratinocyte migration is regulated through both the nicotinic and muscarinic classes of acetylcholine (ACh) receptors. We sought to identify the signaling pathway mediating the cholinergic regulation of chemotaxis and galvanotropism. The pharmacologic and molecular modifiers of the Ras/Raf-1/MEK1/ERK signaling pathway altered both chemotaxis toward choline and galvanotropism toward the cathode in a similar way, indicating that the sam…
Profilin 1 is required for peripheral nervous system myelination
2014
Myelination allows rapid saltatory propagation of action potentials along the axon and is an essential prerequisite for the normal functioning of the nervous system. During peripheral nervous system (PNS) development, myelin-forming Schwann cells (SCs) generate radial lamellipodia to sort and ensheath axons. This process requires controlled cytoskeletal remodeling, and we show that SC lamellipodia formation depends on the function of profilin 1 (Pfn1), an actin-binding protein involved in microfilament polymerization. Pfn1 is inhibited upon phosphorylation by ROCK, a downstream effector of the integrin linked kinase pathway. Thus, a dramatic reduction of radial lamellipodia formation is obs…
An Extended Filament Based Lamellipodium Model Produces Various Moving Cell Shapes in the Presence of Chemotactic Signals
2015
The Filament Based Lamellipodium Model (FBLM) is a two-phase two-dimensional continuum model, describing the dynamcis of two interacting families of locally parallel actin filaments (C.Schmeiser and D.Oelz, How do cells move? Mathematical modeling of cytoskeleton dynamics and cell migration. Cell mechanics: from single scale-based models to multiscale modeling. Chapman and Hall, 2010). It contains accounts of the filaments' bending stiffness, of adhesion to the substrate, and of cross-links connecting the two families. An extension of the model is presented with contributions from nucleation of filaments by branching, from capping, from contraction by actin-myosin interaction, and from a pr…
Focal adhesions are hotspots for keratin filament precursor formation
2006
Recent studies showed that keratin filament (KF) formation originates primarily from sites close to the actin-rich cell cortex. To further characterize these sites, we performed multicolor fluorescence imaging of living cells and found drastically increased KF assembly in regions of elevated actin turnover, i.e., in lamellipodia. Abundant KF precursors (KFPs) appeared within these areas at the distal tips of actin stress fibers, moving alongside the stress fibers until their integration into the peripheral KF network. The earliest KFPs were detected next to actin-anchoring focal adhesions (FAs) and were only seen after the establishment of FAs in emerging lamellipodia. Tight spatiotemporal …
Follicle Cells of Styela plicata Eggs (Ascidiacea)
2001
Styela plicata eggs are surrounded by large follicle cells that at LM appear as highly vacuolated and columnar in shape; at the apical end of each cell lies a very large and clear vacuole, half of which extends inward. Electron microscope observations show a Single layer of largely spaced box-like follicle cells; the close cell-cell contact at their base is realized by interdigitations. The cell surface shows a peculiar structure, more developed in the latero-basal regions, consisting of a complex of membrane extensions, i.e. microvilli, filopodia and lamellipodia. Filopodia irradiate in all directions towards the adjacent cells and the outermost vitelline coat, thus creating a complex netw…