DIFFERENTIAL PERTURBATIONS IN THE MORPHOGENESIS OF ANTERIOR STRUCTURES INDUCED BY OVEREXPRESSION OF TRUNCATED XB-CADHERIN AND N-CADHERIN INXENOPUS EMBRYOS

Cadherins, a family of Ca-dependent adhesion molecules, have been prop osed to act as regulators of morphogenetic processes and to be major e ffecters in the maintenance of tissue integrity. In this study, we hav e compared the effects of the expression of two truncated cadherins du ring early neurogenesis in Xenopus laevis. mRNA encoding deleted forms of XB- and N-cadherin lacking most of the extracellular domain were i njected into the four animal dorsal blastomeres of 32-cell stage Xenop us embryos. These truncated cadherins altered the cohesion of cells de rived from the injected blastomeres and induced morphogenetic defects in the anterior neural tissue to which they chiefly contributed. Trunc ated XB-cadherin was more efficient than N-cadherin in inducing these perturbations. Moreover, the coexpression of both truncated cadherins had additive perturbation effects on neural development. The two trunc ated cadherins can interact with the three known catenins, but with di stinct affinities. These results suggest that the adhesive signal medi ated by cadherins can be perturbed by overexpressing their cytoplasmic domains by competing with different affinity with catenins and/or a c ommon anchor structure. Therefore, the correct regulation of cadherin function through the cytoplasmic domain appears to be a crucial step i n the formation of the neural tissue.