Fig. 1.

Guidance of cells by a global gradient, e.g., in classic chemotaxis (A) and by a surface with 2-μm-spaced ridges of sawteeth of length 6 μm, height 1.8 μm, and width 630 nm (B–F). (A) A global gradient must be maintained over a distance that is much larger than the cell length. (B) Side-view scanning electron micrograph of sawteeth. (C and D) Top-view bright-field (C) and confocal (D) micrographs of a cAR1-YFP–expressing cell on sawteeth. The dashed line in C delineates the cell boundary. (E) Side-view confocal micrographs of different cross-sections of a cAR1-YFP–expressing cell on sawteeth. The gray background schematic represents the sawtooth surface. Each image was obtained at a plane perpendicular to the surface in the position of the dashed line of the color of the image border. (Scale bars: B–E, 3 μm.) (F) Centroid motion tracks of 25 representative cells over 18 min. All tracks were translated to begin at the black dot. The height of each sawtooth increases from left to right. (Scale bar: 20 μm.)