Expression of the chicken retinoid X receptor-gamma gene in migrating cranial neural crest cells.

We have used in situ hybridisation to whole chick embryos with digoxygenin-labelled probes to investigate the distribution of RXR-gamma transcripts during neural crest cell migration in the developing head and the anterior of the trunk (the vagal region), where neural crest cells make a substantial contribution. We have found that RXR-gamma transcripts are a good marker for migrating neural crest cells in the chick embryo. RXR-gamma transcripts were first detected in cells that had recently emerged from the neural crest, providing an earlier marker for neural crest cells than the HNK-1 epitope. The pattern of RXR-gamma transcript distribution is dynamic in the developing chick head, and changes in a pattern which is coincident with the migration of cells containing RXR-gamma transcripts and the gradual restriction of RXR-gamma transcripts to specific differentiating neural crest derivatives. Transcripts appeared to be present initially in migrating neural crest cells thoughout the developing head, but gradually became restricted to some crest-derived populations and absent from others. By stage 15, RXR-gamma transcripts were not detectable in neural-crest-derived ectomesenchymal cells, although they were still found in cells contributing to the cranial ganglia and their roots.