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Xenopus cadherin-11 restrains cranial neural crest migration and influences neural crest specification

¹ Department of Genetics, Stanford University, Stanford, CA 94305-5120, USA
² Department of Biochemistry, University of Ulm, Germany
^* Author for correspondence at present address: Institute of Zoology II, University Karlsruhe (e-mail: doris.wedlich{at}zi2.uni-karlsruhe.de

Accepted 21 May 2001

Cranial neural crest (CNC) cells migrate extensively, typically in a pattern of cell streams. In Xenopus, these cells express the adhesion molecule Xcadherin-11 (Xcad-11) as they begin to emigrate from the neural fold. In order to study the function of this molecule, we have overexpressed wild-type Xcad-11 as well as Xcad-11 mutants with cytoplasmic (cXcad-11) or extracellular (eXcad-11) deletions. Green fluorescent protein (GFP) was used to mark injected cells. We then transplanted parts of the fluorescent CNC at the premigratory stage into non-injected host embryos. This altered not only migration, but also the expression of neural crest markers.

Migration of transplanted cranial neural crest cells was blocked when full-length Xcad-11 or its mutant lacking the ß-catenin-binding site (cXcad-11) was overexpressed. In addition, the expression of neural crest markers (AP-2, Snail and twist) diminished within the first four hours after grafting, and disappeared completely after 18 hours. Instead, these grafts expressed neural markers (2G9, nrp-1 and N-Tubulin). ß-catenin co-expression, heterotopic transplantation of CNC cells into the pharyngeal pouch area or both in combination failed to prevent neural differentiation of the grafts.

By contrast, eXcad-11 overexpression resulted in premature emigration of cells from the transplants. The AP-2 and Snail patterns remained unaffected in these migrating grafts, while twist expression was strongly reduced. Co-expression of eXcad-11 and ß-catenin was able to rescue the loss of twist expression, indicating that Wnt/ß-catenin signalling is required to maintain twist expression during migration.

These results show that migration is a prerequisite for neural crest differentiation. Endogenous Xcad-11 delays CNC migration. Xcad-11 expression must, however, be balanced, as overexpression prevents migration and leads to neural marker expression. Although Wnt/ß-catenin signalling is required to sustain twist expression during migration, it is not sufficient to block neural differentiation in non-migrating grafts.

Key words: Cadherin, Neural crest, Migration, Xenopus