Quantitative evaluation of tissue-specific cell adhesion at the level of a single cell pair

Tissue specificity of cell adhesion was directly characterized in a unit cell interaction using a novel laser trapping cell manipulator in combination with a fixed micropipet. We quantified the adhesive specificity of endodermal and ectodermal epithelial cells from Hydra, which are known to sort out within hours after being dissociated and then randomly reaggregate. It was shown that homotypic pairs of cells from the same tissue source could adhere to each other within a certain period, while heterotypic pairs could not form an adhesion. It was also found that the adhesion probability was higher in endodermal epithelial cell pairs than in ectodermal epithelial cell pairs. The former pairs could adhere with a contact period of less than 30 sec, while 60% of the latter remained nonadherent even after a 6-min forced contact. The adhesive strength of the latter was estimated to be as large as 30 pN, while that of the former was much larger than 50 pN. The tissue-specific adhesivity quantitatively measured provides a new insight into the mechanism of cell sorting.