The Role of Stress Fibers in the Shape Determination Mechanism of Fish Keratocytes

Crawling cells have characteristic shapes that are a function of their cell types. How their different shapes are determined is an interesting question. Fish epithelial keratocytes are an ideal material for investigating cell shape determination, because they maintain a nearly constant fan shape during their crawling locomotion. We compared the shape and related molecular mechanisms in keratocytes from different fish species to elucidate the key mechanisms that determine cell shape. Wide keratocytes from cichlids applied large traction forces at the rear due to large focal adhesions, and showed a spatially loose gradient associated with actin retrograde flow rate, whereas round keratocytes from black tetra applied low traction forces at the rear small focal adhesions and showed a spatially steep gradient of actin retrograde flow rate. Laser ablation of stress fibers (contractile fibers connected to rear focal adhesions) in wide keratocytes from cichlids increased the actin retrograde flow rate and led to slowed leading-edge extension near the ablated region. Thus, stress fibers might play an important role in the mechanism of maintaining cell shape by regulating the actin retrograde flow rate.

Spatiotemporal coordinated hierarchical properties of cellular protrusion revealed by multiscale analysis

We present a methodology for integrative multiscale analysis to highlight hierarchical properties of cellular protrusion and mechanochemical interactions in cellular protrusion based on live cell imaging data with high spatiotemporal resolution. As an appropriate experimental system, we selected non-polarized full-moon-shaped keratocytes that present balanced protrusion around the entire cell periphery at the cellular scale simultaneously with active protrusion and retraction at the subcellular scale. We achieved the observation of a whole cell with sub-micrometer spatial precision and sub-second time resolution for three minutes or more. The multiscale characteristics of cell peripheral activity and those of the cell peripheral shape were extracted from an identical image sequence by estimating the cell protrusion rates and the cell peripheral curvatures at various differential intervals. The spatiotemporal maps of the cell protrusion rates demonstrated a spatiotemporally nested structure of travelling waves of active protruding regions at the cellular and subcellular scales. Moreover, correlation analysis demonstrated the relationship between the cell protrusion rate and peripheral curvature at the subcellular scale. The novel integrative methodology presented here well highlighted the hierarchical properties of organized cellular protrusion, and further provided insight about the underlying mechanochemical interactions between the cell membrane and the actin filaments under the membrane.

Characteristics of motility-based filtering of adherent cells on microgrooved surfaces

Topographical features are known to physically affect cell behavior and are expected to have great potential for non-invasive control of such behavior. To provide a design concept of a microstructured surface for elaborate non-invasive control of cell migration, we systematically analyzed the effect of microgrooves on cell migration. We fabricated silicon microstructured surfaces covered with SiO(2) with microgrooves of various sizes, and characterized the behavior of cells moving from the flat surface to the grooved surface. The intersecting microgrooves with well-defined groove width absorbed or repelled cells precisely according to the angle of approach of the cell to the boundary with the grooved surface. This filtering process was explained by the difference in the magnitude of the lamellar dragging effect resulting from the number of the grooves interacting with the lamella of the cell. This study provides a framework to tailor the microgrooved surface for non-invasive control of cell migration with label-free detection of a specific property of the target cells. This should offer significant benefits to biomedical research and applications.