Environmental signals and cell fate specification in premigratory neural crest

Neural crest cells are multipotent progenitors, capable of producing divers e cell types upon differentiation. Recent studies have identified significa nt heterogeneity in both the fates produced and genes expressed by differen t premigratory crest cells. While these cells may be specified toward parti cular fates prior to migration, transplant studies show that some may still be capable of respecification at this time. Here we summarize evidence tha t extracellular signals in the local environment may act to specify premigr atory crest and thus generate diversity in the population. Three main class es of signals-Wnts, BMP2/BMP4 and TGF beta 1,2,3-have been shown to directl y influence the production of particular neural crest cell fates, and all a re expressed near the premigratory crest. This system may therefore provide a good model for integration of multiple signaling pathways during embryon ic cell fate specification. (C) 2000 John Wiley & Sons, Inc.