Xenopus cadherin-11 restrains cranial neural crest migration and influences neural crest specification.
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 (deltacXcad-11) or extracellular (deltaeXcad-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 beta-catenin-binding site (deltacXcad-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-I and N-Tubulin). Beta-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, deltaeXcad-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 deltaeXcad-11 and beta-catenin was able to rescue the loss of twist expression, indicating that Wnt/beta-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/beta-catenin signalling is required to sustain twist expression during migration, it is not sufficient to block neural differentiation in non-migrating grafts.
Borchers
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Department of Genetics, Stanford University, CA 94305-5120, USA.
David
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Wedlich
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D000818:Animals; D001665:Binding Sites; D015820:Cadherins / Q000096:biosynthesis* / Q000502:physiology*; D002448:Cell Adhesion; D002454:Cell Differentiation; D019070:Cell Lineage; D002465:Cell Movement; D003593:Cytoplasm / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000737:chemistry; D004625:Embryo, Nonmammalian / Q000378:metabolism; D005982:Glutathione Transferase; D049452:Green Fluorescent Proteins; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008164:Luminescent Proteins / Q000096:biosynthesis; D008856:Microscopy, Fluorescence; D009154:Mutation; D009432:Neural Crest / Q000166:cytology* / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D015534:Trans-Activators; D014981:Xenopus; D029867:Xenopus Proteins; D051176:beta Catenin
C495266:CTNNB1 protein, Xenopus; D015820:Cadherins; D003598:Cytoskeletal Proteins; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D029867:Xenopus Proteins; D051176:beta Catenin; D049452:Green Fluorescent Proteins; C086960:osteoblast cadherin; D005982:Glutathione Transferase