ORIGINS OF THE AVIAN NEURAL CREST - THE ROLE OF NEURAL PLATE-EPIDERMAL INTERACTIONS

We have investigated the lineage and tissue interactions that result i n avian neural crest cell formation from the ectoderm. Presumptive neu ral plate was grafted adjacent to non-neural ectoderm in whole embryo culture to examine the role of tissue interactions in ontogeny of the neural crest. Our results show that juxtaposition of nonneural ectoder m and presumptive neural plate induces the formation of neural crest c ells. Quail/chick recombinations demonstrate that both the prospective neural plate and the prospective epidermis can contribute to the neur al crest. When similar neural plate/epidermal confrontations are perfo rmed in tissue culture to look at the formation of neural crest deriva tives, juxtaposition of epidermis with either early (stages 4-5) or la ter (stages 6-10) neural plate results in the generation of both melan ocytes and sympathoadrenal cells. Interestingly, neural plates isolate d from early stages form no neural crest cells, whereas those isolated later give rise to melanocytes but not crest-derived sympathoadrenal cells. Single cell lineage analysis was performed to determine the tim e at which the neural crest lineage diverges from the epidermal lineag e and to elucidate the timing of neural plate/epidermis interactions d uring normal development. Our results from stage 8 to 10+ embryos show that the neural plate/neural crest lineage segregates from the epider mis around the time of neural tube closure, suggesting that neural ind uction is still underway at open neural plate stages.