Descriptive and experimental analysis of the dispersion of neural crest cells along the dorsolateral path and their entry into ectoderm in the chick embryo.

We have characterized the dispersion of neural crest cells along the dorsolateral path in the trunk of the chicken embryo and experimentally investigated the control of neural crest cell entry into this path. The distribution of putative neural crest cells was analyzed in plastic sections of embryos that had been incubated for 24 hr in HNK-1 antibody, a procedure that we show successfully labels neural crest cells in the dorsolateral path and ectoderm. In accord with earlier observations, crest cells delay entering the dorsolateral path until a day or more after their counterparts have colonized the ventral path. However, once crest cells enter, they disperse rapidly through the path dorsal to the somite but still delay migrating dorsal to the intersegmental space. During dispersion, crest cells invade the ectoderm at sites associated with local disruptions in the basal lamina which may be caused by crest cells. Finally, deleting the dermamyotome releases an inhibition of neural crest cell migration: crest cells enter the dorsolateral path precociously. We speculate that the epithelial dermatome may transiently produce inhibitory substances and that emerging dermis may provide a long-distance, stimulatory cue.