Formation of junctions and cell sorting in aggregates of chick and mouse cells

The frequency of desmosome formation was examined in aggregates of old cells, which form many junctions, combined with young cells, which form few. Cells of chick corneal epithelium and mouse epidermis, which can be distinguished morphologically, were combined. Desmosomes between these cell types are stable. Further, young cells make more desmosomes than they otherwise would on those surfaces adjoining old cells. Desmosomes increase in number in aggregates while cell sorting is occurring. Cells consistently sort, with those which form most desmosomes lying internally. Gap junctions and intermediate junctions are also present, but are uncommon. A carbohydrate cell-surface coat has regenerated by the time desmosome formation starts. The possible relation of desmosome formation to cell sorting is discussed.