Molecular identification of distinct neurogenic and melanogenic neural crest sublineages.

Clonal and lineage analyses have demonstrated that although some neural crest cells have the ability to generate multiple cell types and display self-renewal ability, other crest cells generate a single or limited repertoire of cell types. However, it is not yet clear when, and in what order, crest cells become specified to adopt a particular fate. We report that the receptor tyrosine kinases TrkC and C-Kit are expressed by distinct neural crest subpopulations in vitro. We then analyzed the lineages of individual receptor-expressing crest cells and found that TrkC-expressing cells that have just emerged from the neural tube give rise to clones containing neurons or glial cells, or both, but never produce melanocytes. A short time later, TrkC-expressing cells only generate pure neuronal clones. By contrast, from their earliest appearance in neural tube outgrowths, C-Kit-expressing cells invariably give rise to clones containing only melanocytes. Our results directly demonstrate that distinct neurogenic and melanogenic sublineages diverge before or soon after crest cells emerge from the neural tube, that fate-restricted precursors are present in nascent neural crest populations and that these sublineages can be distinguished by their cell type-specific expression of receptor tyrosine kinases.

Differentiation and maturation of zebrafish dorsal root and sympathetic ganglion neurons.

The trunk neural crest of vertebrate embryos gives rise to dorsal root ganglion (DRG) sensory neurons and autonomic sympathetic neurons, among other derivatives. We have examined the development of DRG and sympathetic neurons during development in the zebrafish. We found that sensory neurons differentiate rapidly and that their overt neuronal differentiation significantly precedes that of sympathetic neurons in the trunk. Sympathetic neurons in different regions differentiate at different times. The most rostral population, which we call the cervical ganglion, differentiates several days before trunk sympathetic neurons. After undergoing overt neuronal differentiation, sympathetic neurons subsequently express the adrenergic differentiation markers dopamine beta-hydroxylase and tyrosine hydroxylase. A second population of adrenergic nonneuronal cells initially localized with cervical sympathetic neurons appears to represent adrenal chromaffin cells. In more mature fish, these cells were present in clusters within the kidneys. Individual DRG and sympathetic ganglia initially contain few neurons. However, the number of neurons in DRG and sympathetic ganglia increases continuously at least up to 4 weeks of age. Analysis of phosphohistone H3 expression and bromodeoxyuridine incorporation studies suggests that the increases in DRG and sympathetic ganglion neuronal cell number are due wholly or in part to the division of neuronal cells within the ganglia.