Condensation Of Filaments Research Articles

Active condensation of filaments under spatial confinement.

Living systems exhibit self-organization, a phenomenon that enables organisms to perform functions essential for life. The interior of living cells is a crowded environment in which the self-assembly of cytoskeletal networks is spatially constrained by membranes and organelles. Cytoskeletal filaments undergo active condensation in the presence of crosslinking motor proteins. In past studies, confinement has been shown to alter the morphology of active condensates. Here, we perform simulations to explore systems of filaments and crosslinking motors in a variety of confining geometries. We simulate spatial confinement imposed by hard spherical, cylindrical, and planar boundaries. These systems exhibit non-equilibrium condensation behavior where crosslinking motors condense a fraction of the overall filament population, leading to coexistence of vapor and condensed states. We find that the confinement lengthscale modifies the dynamics and condensate morphology. With end-pausing crosslinking motors, filaments self-organize into half asters and fully-symmetric asters under spherical confinement, polarity-sorted bilayers and bottle-brush-like states under cylindrical confinement, and flattened asters under planar confinement. The number of crosslinking motors controls the size and shape of condensates, with flattened asters becoming hollow and ring-like for larger motor number. End pausing plays a key role affecting condensate morphology: systems with end-pausing motors evolve into aster-like condensates while those with non-end-pausing crosslinking motor proteins evolve into disordered clusters and polarity-sorted bundles.

Cysts of the outer root sheath of wool follicles: A study of abnormal keratinization

Cystic enlargements of the outer root sheath in the suprabulbar region of wool follicles have been studied by electron microscopy. The first indication of cyst formation is a perinuclear condensation of filaments in cells that otherwise resemble normal cells of the outer root sheath. Keratohyalin and membrane-coating granules are rarely seen. A mass of keratinized cells progressively differentiates in the cyst. In cells close to the center of the cyst, organelles are centripetally located in the cytoplasm. A gradation of glycogen exists radially in the cyst wall, the higher concentrations being found in peripheral cells. The cyst may eventually reach a diameter of about 150 μ.