Highlights in basic autonomic neuroscience: Development of autonomic neurons — From the neural crest to circuit formation

Abstract

Neural crest cells arise fromdorsal regions of the neural tube, delaminate and migrate to many target sites. In the trunk, neural crest cells follow distinct pathways to form multiple derivatives, including neurons and glia in sympathetic and dorsal root ganglia and melanocytes in the skin. The earliest migrating cells proceed ventrally to the sympathetic ganglia, while later migrating cells populate the dorsal root ganglia, and last of all, pre-specified melanoblasts migrate along a dorsolateral pathway. Multiple molecular differences have been identified between neural crest following the dorsolateral pathway compared to those migrating ventrally. Krispin and colleagues examined in detail the emergence of neural crest cells from the dorsal region of the neural tube by labeling and lineage tracing small numbers of cells in the dorsal neural tube (by electroporating a GFP construct or with DiI) at a specified axial level at defined stages of development in chick embryos. Following labeling of dorsal neural tube cells shortly prior to the initial migration of neural crest cells, all of the labeled cells exited the neural tube in ~90% of the experiments. This suggested a ventral to dorsal relocation of cells in the dorsal neural tube, rather than asymmetric cell division in which one daughter cell emigrated as a neural crest cell while the other daughter cell remained within the neural tube. Time lapse imaging of the neural tube opened along themiddle and flattened into a hemi-tube showed movement of labeled cells from ventral to dorsal. When cells at distinct sites within the dorsal 30% of the neural tube were labeled shortly prior to initial migration, a strong correlation was observed between the dorsoventral positionwithin the neural tube and the final localization of the labeled cells. These results suggest that within the neural tube there is a progressive ventral to dorsal relocation of cells prior to neural crest cell delamination, and that the roof plate is formed from the cells that have relocated dorsally after the dorsolaterally migrating melanoblasts have exited the neural tube. The authors concluded that there is a dynamic spatiotemporal fate map in the dorsal neural tube shortly prior to and during neural crest emigration. Finally,