Delamination of premigratory neural crest cells depends on a balance between BMP/noggin and on successful G1/S transition. Here, we report that BMP regulates G1/S transition and consequent crest delamination through canonical Wnt signaling. Noggin overexpression inhibits G1/S transition and blocking G1/S abrogates BMP-induced delamination; moreover, transcription of Wnt1 is stimulated by BMP and by the developing somites, which concomitantly inhibit noggin production. Interfering with β-catenin and LEF/TCF inhibits G1/S transition, neural crest delamination and transcription of various BMPdependent genes, which include Cad6B, Pax3 and Msx1, but not that of Slug, Sox9 or FoxD3. Hence, we propose that developing somites inhibit noggin transcription in the dorsal tube, resulting in activation of BMP and consequent Wnt1 production. Canonical Wnt signaling in turn stimulates G1/S transition and generation of neural crest cell motility independently of its proposed role in earlier neural crest specification. Research article 5328 NC delamination and overexpression of β-catenin rescues NC delamination in noggin-inhibited neural primordia. Thus, BMP-dependent Wnt signaling is necessary for NC delamination. Materials and methods EmbryosChick (Gallus gallus) and quail (Coturnix coturnix Japonica) eggs were from commercial sources.In ovo grafting of noggin-secreting cells CHO cells producing Xenopus noggin and dhfr-CHO control cells were grown as previously described (Lamb et al., 1993; SelaDonenfeld and Kalcheim, 2002). To establish confluent monolayers, cells were replated on eight-well chamber slides (Lab-Tek), grown in serum-containing medium for 2 days and then transferred to serumfree medium until explantation of neural primordia. For grafting purposes, confluent cultures were harvested and pelleted. The vitelline membrane of 16-to 20-somite stage chick embryos was removed. A slit was performed along the dorsal edge of the neural tube at levels corresponding either to the rostral segmental plate and two last formed epithelial somites, or along the caudal half of the segmental plate. Concentrated cell suspensions were applied on top of the neural tube with a micropipette. Cell implants were performed under an Olympus dissecting microscope with a ϫ40 total magnification. Embryos were further incubated for 8-10 or 20-24 hours and then fixed for immunocytochemistry and/or in situ hybridization.

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