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Kurt Anderson

Publications and source records attributed to Kurt Anderson.

6 recordsLinked to original sources
PubMed2005

Subsecond reorganization of the actin network in cell motility and chemotaxis.

Actin networks are continuously reorganized in cells that rapidly change their shape. Applying total internal reflection fluorescence microscopy at acquisition rates of 10-20 Hz, we measured an average growth rate of 3 microm.sec(-1) for filamentous actin structures throughout the entire substrate-attached cortex of Dictyostelium cells. New filaments often proceed along preexisting ones, resulting in bundle formation concurrent with filament growth. In cells that orientate in a gradient of chemoattractant, prominent assemblies of actin enriched in the Arp2/3 complex are inserted into the network, primarily at the base of filopods that point into the direction of the gradient. We propose that high turnover rates of actin filaments confer the plasticity to the cell cortex that is required for rapid accommodation to external stimuli.

Actin-Related Protein 2↗
PubMed2004

Mobile actin clusters and traveling waves in cells recovering from actin depolymerization.

At the leading edge of a motile cell, actin polymerizes in close apposition to the plasma membrane. Here we ask how the machinery for force generation at a leading edge is established de novo after the global depolymerization of actin. The depolymerization is accomplished by latrunculin A, and the reorganization of actin upon removal of the drug is visualized in Dictyostelium cells by total internal reflection fluorescence microscopy. The actin filament system is reorganized in three steps. First, F-actin assembles into globular complexes that move along the bottom surface of the cells at velocities up to 10 microm/min. These clusters are transient structures that eventually disassemble, fuse, or divide. In a second step, clusters merge into a contiguous zone at the cell border that spreads and gives rise to actin waves traveling on a planar membrane. Finally, normal cell shape and motility are resumed. These data show that the initiation of actin polymerization is separated in Dictyostelium from front protrusion, and that the coupling of polymerization to protrusion is a later step in the reconstitution of a leading edge.

Actins↗
PubMed2004

Dynamic actin patterns and Arp2/3 assembly at the substrate-attached surface of motile cells.

BACKGROUND: In the cortical region of motile cells, the actin network rapidly reorganizes as required for movement in various directions and for cell-to-substrate adhesion. The analysis of actin network dynamics requires the combination of high-resolution imaging with a specific fluorescent probe that highlights the filamentous actin structures in live cells. RESULTS: Combining total internal reflection fluorescence (TIRF) microscopy with a method for labeling actin filaments, we analyze the dynamics of actin patterns in the highly motile cells of Dictyostelium. A rapidly restructured network of single or bundled actin filaments provides a scaffold for the assembly of differentiated actin complexes. Recruitment of the Arp2/3 complex characterizes stationary foci with a lifetime of 7-10 s and traveling waves. These structures are also formed in the absence of myosin-II. Arp2/3-actin assemblies similar to those driving the protrusion of a leading edge form freely at the inner face of the plasma membrane. CONCLUSIONS: The actin system of highly motile cells runs far from equilibrium and generates a multitude of patterns within a dynamic filamentous network. Traveling waves are the most complicated patterns based on recruitment of the Arp2/3 complex. They are governed by the propagated induction of actin polymerization. We hypothesize that the actin system autonomously generates primordia of specialized structures such as phagocytic cups or lamellipodia. These primordia would represent an activated state of the actin system and enable cells to respond within seconds to local stimuli by chemotaxis or phagocytic-cup formation.

Actins↗
PubMed2002

Tensile stress stimulates microtubule outgrowth in living cells.

Cell motility is driven by the sum of asymmetric traction forces exerted on the substrate through adhesion foci that interface with the actin cytoskeleton. Establishment of this asymmetry involves microtubules, which exert a destabilising effect on adhesion foci via targeting events. Here, we demonstrate the existence of a mechano-sensing mechanism that signals microtubule polymerisation and guidance of the microtubules towards adhesion sites under increased stress. Stress was applied either by manipulating the body of cells moving on glass with a microneedle or by stretching a flexible substrate that cells were migrating on. We propose a model for this mechano-sensing phenomenon whereby microtubule polymerisation is stimulated and guided through the interaction of a microtubule tip complex with actin filaments under tension.

Actin Cytoskeleton↗
PubMedDate not supplied

Observing structure, function and assembly of single proteins by AFM.

Single molecule experiments provide insight into the individuality of biological macromolecules, their unique function, reaction pathways, trajectories and molecular interactions. The exceptional signal-to-noise ratio of the atomic force microscope allows individual proteins to be imaged under physiologically relevant conditions at a lateral resolution of 0.5-1nm and a vertical resolution of 0.1-0.2nm. Recently, it has become possible to observe single molecule events using this technique. This capability is reviewed on various water-soluble and membrane proteins. Examples of the observation of function, variability, and assembly of single proteins are discussed. Statistical analysis is important to extend conclusions derived from single molecule experiments to protein species. Such approaches allow the classification of protein conformations and movements. Recent developments of probe microscopy techniques allow simultaneous measurement of multiple signals on individual macromolecules, and greatly extend the range of experiments possible for probing biological systems at the molecular level. Biologists exploring molecular mechanisms will benefit from a burgeoning of scanning probe microscopes and of their future combination with molecular biological experiments.

Biophysical Phenomena↗