Figure 1.

Cell segregation and boundary formation. (A) In vitro assay for cell segregation in which two cell populations are dissociated, mixed, and reaggregated. Over a period of time, the intermingled cell populations may segregate from each other. When performed with one population expressing lower levels of cadherin (red) than the other (blue), the former segregate to the outer region of the reaggregate, as predicted by the differential adhesion hypothesis. (B) During normal development, distinct tissues or regional domains within tissues are induced to form at specific locations. In many cases, the border of the adjacent domains is initially fuzzy, and local cell segregation underlies the formation of a sharp interface.