Abstract
In the peripheral nervous system, enteric and sympathetic neurons develop from multipotent neural crest cells. While local environmental signals in the gut and in the region of the sympathetic ganglia play a role in the choice of cell fate, little is known about the mechanisms that underlie restriction to specific neuronal phenotypes. We investigated the divergence and restriction of the enteric and sympathetic neuronal lineages using immuno-isolated neural crest-derived cells from the gut and sympathetic ganglia. Analysis of neuronal and lineage-specific mRNAs and proteins indicated that neural crest-derived cells from the gut and sympathetic ganglia had initiated neuronal differentiation and phenotypic divergence by E14.5 in the rat. We investigated the developmental potential of these cells using expression of tyrosine hydroxylase as a marker for a sympathetic phenotype. Tyrosine hydroxylase expression was examined in neurons that developed from sympathetic and enteric neuroblasts under the following culture conditions: culture alone; coculture with gut monolayers to promote enteric differentiation; or coculture with dorsal aorta monolayers to promote noradrenergic differentiation. Both enteric and sympathetic neuroblasts displayed developmental plasticity at E14.5. Sympathetic neuroblasts downregulated tyrosine hydroxylase in response to signals from the gut environment and enteric neuroblasts increased expression of tyrosine hydroxylase when grown on dorsal aorta or in the absence of other cell types. Tracking of individual sympathetic cells displaying a neuronal morphology at the time of plating indicated that neuroblasts retained phenotypic plasticity even after initial neuronal differentiation had occurred. By E19.5 both enteric and sympathetic neuroblasts had undergone a significant loss of their developmental potential, with most neuroblasts retaining their lineage-specific phenotype in all environments tested. Together our data indicate that the developmental potential of enteric and sympathetic neuroblasts becomes restricted over time and that this restriction takes place not as a consequence of initial neuronal differentiation but during the period of neuronal maturation. Further, we have characterized a default pathway of adrenergic differentiation in the enteric nervous system and have defined a transient requirement for gut-derived factors in the maintenance of the enteric neuronal phenotype.