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sorting out

phenomenon observed to occur when mixed aggregates of dissimilar embryonic cell types are formed in vitro. The original aggregate sorts out so that similar cells come together into homotypic domains, usually with one cell type sorting out to form a central mass that is surrounded by the other cell type. Much controversy has arisen over the years as to the underlying mechanism, whether there is specificity in the adhesive interactions (which would imply tissue specific receptor ligand interactions) or whether it is sufficient to suppose that there are quantitative differences in homo and hetero typic adhesion (the differential adhesion hypothesis). With the exception perhaps of the main protagonists, most cell biologists consider that there are probably elements both of tissue specificity (cAMs) and of quantitative adhesive differences involved.