DIFFERENTIAL EXPRESSION AND FUNCTION OF CADHERIN-LIKE PROTEINS IN THESEA-URCHIN EMBRYO

Cadherins are Ca+2-dependent cell surface proteins involved in the spe cification of the adhesive properties of cells. They are supposed to p lay a critical role in morphogenesis and pattern formation. In this pa per we show that in the sea urchin embryo there are at least two diffe rent cadherins of relative molecular masses 140 and 125 kDa. The 140 k Da cadherin is already present in the fertilized egg and is the sea ur chin equivalent of E-cadherin. The 125 kDa cadherin, which can be dete cted using a broad-spectrum anti-cadherin antibody, appears only at la ter stages of development. In later embryos these two molecules are di stributed differently: E-cadherin is present predominantly in the inva ginating endoderm of the gastrula while the 125 kDa protein is present on the cell surface of most epithelia. Consistently with the observed differences in expression and in distribution, antibodies directed ag ainst these two cadherins differently perturb sea urchin development. For example, when these antibodies are added to early gastrulas only t he antibodies against the 125 kDa component can induce a complete disa ggregation of the ectoderm, while anti E-cadherin antibodies induce an abnormal development of the endoderm while the embryo maintains its b asic integrity. These results are discussed in view of the need for mu ltiple adhesion receptors during pattern formation and embryogenesis.