Medial cell mixing during axial morphogenesis of the amphibian embryo requires cadherin function.

A truncated form of Xenopus E-cadherin (deltaE-cad) comprising the cytoplasmic and transmembrane domains was overexpressed generating a dominant negative mutation in the urodelan amphibian embryo Pleurodeles waltl. deltaE-cad mRNA and rhodamine-lysinated-dextran (RLDx) cell lineage tracer were microinjected into 32-cell stage blastomeres which contribute principally to the notochord and central nervous system. deltaE-cad expression causes defects in forebrain and hindbrain formation coupled with the development of supernumerary vesicles. Duplication of the notochord also occurs due to the retardation of medial cell intercalation with correlated duplications of spinal cord and somites. These results emphasize the role of cadherins in mediating cell-cell adhesion in early amphibian embryogenesis. They extend to Pleurodeles the observations made in Xenopus, illustrating that despite differences in morphogenetic processes, the molecular mechanisms are conserved in these two species.