Topographical control of cell behaviour : 1. Simple step cues

The photolithographic techniques of the microelectronics industry have allowed us to fabricate patterned plastic substrata to investigate contact guidance of animal tissue cells. The reactions of cells to single steps on a substratum were examined using time-lapse videorecording and scanning electron microscopy. BHK cells and chick embryonic neural cell processes exhibited gradual inhibition of crossing steps with a concomitant increase in alignment at steps dependent on increasing step height. Comparison of these cells' reactions, with those of chick heart fibroblasts and rabbit neutrophils, at a 5 fan step revealed that the influence of topography is also dependent on cell type, the neutrophils being relatively unaffected. The presence of an adhesive difference at a series of steps altered BHK cells' reactions such that the frequency of crossing was dependent on the direction of approach to a step. Although our data are consistent with Dunn & Heath's proposal (1976) that the inflexibility of the cytoskeleton of a moving cell's protrusion is the cellular property determining such reactions to topography, we have found that, on encountering a topographical feature, the response of a cell may be predictable on a probabilistic basis, i.e. the topographical feature reduces the probability of a cell making a successful protrusion and contact in a given direction, that even the largest features tested did not act as absolute barriers to cell locomotion since a small proportion of a population of cells were able to overcome them, and that other guidance cues could significantly alter a cell's response. Even in situations where it is not the primary cue in directing cell locomotion, topographical control may be an important factor during morphogenesis since it must, at the very least, influence the efficiency of other cues.