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Abstract

The homophilic nature of cadherin-mediated cell-cell adhesion provides an organism with the opportunity of altering the adhesive capabilities of its cells by selectively modulating the expression of different cadherin types. Differential cadherin expression is of major importance in regulating the cell rearrangements involved in the processes which shape tissues and organs during embryogenesis. The pregastrula embryo of Xenopus laevis expresses two maternally supplied cadherins: XB/U-cadherin and EP-cadherin. Since these two proteins are almost 92% identical at the amino acid level, it was unclear whether heterophilic interactions between them were possible. Different functional roles can only be ascribed to the two cadherins if the possibility of heterophilic binding between them can be excluded. We describe a simple and straightforward assay which can be used to assess interactions between adhesion molecules. A combination of antisense oligonucleotide and enzyme treatments eliminates endogenous cadherins in Xenopus oocytes and subsequent injection of a specific mRNA yields oocytes carrying only one or the other cadherin. After removal of the vitelline membranes, two oocytes expressing the appropriate cadherins will adhere to one another when they are placed in close contact. By scoring for adhesion in homotypic and heterotypic pairings, we demonstrate that XB/U-cadherin and EP-cadherin do not interact with one another.