Factors directing the expression of sympathetic nerve traits in cells of neural crest origin.

Abstract

AbstractIt has been assumed that the phenotype expressed by a particular cell of neural crest origin is determined by the tissues comprising the final site of that crest cell. To test this premise as it applies to differentiation of sympathetic ganglioblasts, the future site of the primary sympathetic ganglia was ablated from embryonic axial trunks and the remaining tissues including the migrating crest cells were grown on chorioallantoic membranes of host chicks. Despite removal of the ultimate site of the primary sympathetic chains, catecholamine‐containing cells, identified by a fluorescent test, differentiated ectopically.These results suggest that tissues along the migratory route rather than the tissues comprising the definitive site direct catecholamine synthesis in crest cells. To test this possibility, segments of neural tubes containing neural crest were grown alone or combined with somites on the chorioallantoic membrane. It was found that sympathoblast differentiation requires the presence of somitic mesoderm. In addition, ablation of the ventral neural tube drastically reduces the quantity of sympathetic nervous tissue formed in the presence of somites. Whether the ventral neural tube affects the crest cells directly or affects the capacity of the somites to influence crest cell differentiation is as yet undetermined. Control experiments indicate that mesoderm from other sources will not substitute for the somites in eliciting differentiation of sympathoblasts. These experiments support the hypothesis that neural crest cells give rise to sympathetic neurons in response to conditions imposed while the cells migrate ventrally.