A paired oocyte adhesion assay reveals the homophilic binding properties of the Xenopus maternal cadherins, XBU- and EP-cadherin

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.

Immunocytochemical studies of the interactions of cadherins and catenins in the earlyXenopus embryo

“…Antisense oligodeoxynucleotides, directed against a sequence within the 3Ј untranslated region of both maternal cadherin mRNAs, were injected into isolated stage VI oocytes. This treatment effectively depletes oocytes of cadherin mRNA (Mü nchberg et al, 1997). The oocytes were matured in vitro and fertilized by injection of demembranated sperm nuclei (Kroll and Amaya, 1996).…”

“…The antisense oligodeoxynucleotide was directed against a sequence in the 3Ј untranslated region of the mRNAs of maternal cadherins EP/C and XB/U. As described by Mü nchberg et al (1997), this sequence represents a region that is identical in both cadherins. A complementary sense oligodeoxynucleotide was used for control purposes.…”

“…Although they share significant sequence homology, they are distinguished by their specific homophilic binding capacity (Mü nchberg et al, 1997). However, distinct functions for the two cadherins in the early embryo have yet to be demonstrated.…”