Copurification of actin and desmin from chicken smooth muscle and their copolymerization in vitro to intermediate filaments

Desmin is a 50,000-mol wt protein that is enriched along with 100-A filaments in chicken gizzard that has been extracted with 1 M KI. Although 1 M KI removes most of the actin from gizzard, a small fraction of this protein remains persistently insoluble, along with desmin. The solubility properties of this actin are the same as for desmin: they are both insoluble in high salt concentrations, but are solubilized at low pH or by agents that dissociate hydrophobic bonds. Desmin may be purified by repeated cycles of solubilization by 1 M acetic acid and subsequent precipitation by neutralization to pH 4. During this process, a constant nonstoichiometric ratio of actin to desmin is attained. Gel filtration on Ultrogel AcA34 in the presence of 0.5% Sarkosyl NL-97 reveals nonmonomeric fractions of actin and desmin that comigrate through the column. Gel filtration on Bio-Gel P300 in the presence of 1 M acetic acid reveals that the majority of desmin is monomeric under these conditions. A small fraction of desmin and all of the actin elute with the excluded volume. When the acetic acid is removed from actin-desmin solutions by dialysis, a gel forms that is composed of filaments with diameters of 120-140 A. These filaments react uniformly with both anti-actin and anti-desmin antiserum. These results suggest that desmin is the major subunit of the muscle 100-A filaments and that it may form nonstoichiometric complexes with actin

Immunological Characterization of the Subunit of the 100 angstrom Filaments from Muscle Cells

We report the immunological characterization of the subunit of the intermediate sized (100 angstrom) filaments from muscle cells. The protein as isolated from smooth muscle (chicken gizzard) has an apparent molecular weight of 50,000. It is insoluble in buffers that solubilize myosin and the majority of actin, but becomes soluble in the presence of urea. Under a variety of experimental conditions, that include the presence of 8 M urea, this new protein comigrates with actin during purification studies. The two proteins can be separated from each other by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, and antibodies have been elicited against the 50,000 dalton protein purified by using this technique. These antibodies crossreact with the partially purified protein in urea, but show no detectable cross reaction with actin or myosin. Indirect immunofluorescence reveals that in skeletal muscle this protein is found in close association with the Z lines of the sarcomeres and extends between the Z lines of adjacent myofibrils; it is also associated with filamentous structures that run along the length of a muscle fiber both in close association with the plasma membrane and between myofibrils. These filaments appear to connect myofibrils to each other or to the plasma membrane at the level of their Z lines. In heart muscle, the protein shows the same distribution as in skeletal muscle. In addition, it is found intimately associated with intercalated disks and areas of membrane interaction between laterally associated heart muscle cells. The immunofluorescent localization to the subunit of the 100 angstrom filaments suggests that in muscle cells this molecule may serve to link actin filaments at the level of the Z line (or intercalated disk) with the muscle plasma membrane. We believe that it functions in muscle primarily as a three dimensional matrix which interconnects individual myofibrils to one another and to the plasma membrane at the level of their Z lines. In this manner, this molecule may provide a framework that mechanically integrates all the contractile myofilaments during the contraction and relaxation of muscle. As a means of indicating its linking role in muscle, we have termed the protein desmin (from the Greek delta epsilon sigma µ os = link, bond)

Reconstructing the Forest of Lineage Trees of Diverse Bacterial Communities Using Bio-inspired Image Analysis

Cell segmentation and tracking allow us to extract a plethora of cell attributes from bacterial time-lapse cell movies, thus promoting computational modeling and simulation of biological processes down to the single-cell level. However, to analyze successfully complex cell movies, imaging multiple interacting bacterial clones as they grow and merge to generate overcrowded bacterial communities with thousands of cells in the field of view, segmentation results should be near perfect to warrant good tracking results. We introduce here a fully automated closed-loop bio-inspired computational strategy that exploits prior knowledge about the expected structure of a colony's lineage tree to locate and correct segmentation errors in analyzed movie frames. We show that this correction strategy is effective, resulting in improved cell tracking and consequently trustworthy deep colony lineage trees. Our image analysis approach has the unique capability to keep tracking cells even after clonal subpopulations merge in the movie. This enables the reconstruction of the complete Forest of Lineage Trees (FLT) representation of evolving multi-clonal bacterial communities. Moreover, the percentage of valid cell trajectories extracted from the image analysis almost doubles after segmentation correction. This plethora of trustworthy data extracted from a complex cell movie analysis enables single-cell analytics as a tool for addressing compelling questions for human health, such as understanding the role of single-cell stochasticity in antibiotics resistance without losing site of the inter-cellular interactions and microenvironment effects that may shape it

Topological changes of two-dimensional magnetic textures

We investigate the interaction of magnetic vortices and skyrmions with a spin-polarized current. In a square lattice, fixed classical spins and quantum itinerant electrons, evolve according to the coupled Landau-Lifshitz and Schr\"odinger equations. Changes in the topology occur at microscopic time and length scales, and are shown to be triggered by the nucleation of a nontrivial electron-spin structure at the vortex core.Comment: See supplementary material (high resolution figures and movies) https://drive.google.com/folderview?id=0By4j_RJ9SKLpQ2R5UklXLURvbEE&usp=sharing --- v2: Extended versio