Mechanisms of adhesion among cells of the early chick blastoderm. Role of calcium ions in the adhesion of extraembryonic endoderm cells

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Abstract
Cells from the extraembryonic endoderm of the gastrulating chick embryo adhere to one another in the absence of divalent cations. The addition of Mg2+ ions to the medium has no effect on the aggregation kinetics but the addition of Ca2+ ions increases the number of cells which aggregate and also stabilizes adhesion. Some aggregation also occurs when cells are suspended in saline devoid of Ca2+ and Mg2+ ions and supplemented with EGTA, a Ca2+ ion complexing agent, but adhesion is not stabilized. Shear sensitive and shear resistant bonds form in Ca-containing as well as in EGTA-containing saline. These results suggest that extraembryonic endoderm cells have Ca2+ indepedent and Ca2+ dependent mechanisms of adhesion.