Cell-substrate contacts in cultured chick embryonic cells: an interference reflection study.

Cell-substrate contacts in explants of different regions of early chick tissues were investigated using the technique of interference reflection microscopy. All the explants spread as epithelial sheets. During initial spreading a peripheral zone of 2-3 cells formed broad contacts with the substrate. In spread explants some cells in the centre made broad substrate contacts. A mat of extracellular material containing fibronectin was found under the explants. Focal contacts and focal adhesions increased in number during culture, and stress fibres were associated with them. These changes in cell contacts appeared more quickly in some tissues than in others. After 24 h, explants of hypoblast and definitive endoblast could easily be distinguished but by 7 days they were very similar. In the absence of serum, specialized cell contacts developed more quickly; in higher concentrations of serum, more slowly. Confrontations between explants were also examined. The most conspicuous feature was that cells in invading explants normally underlapped invaded cells. Invasion from above by an unspread explant could occur even if the invaded explant had formed many focal adhesions.