Sympathoadrenal neural crest cells: the known, unknown and forgotten?

Neural crest cells (NCCs) are highly migratory progenitor cells that give rise to a vast array of differentiated cell types. One of their key derivatives is the autonomic nervous system (ANS) that is comprised in part from chromaffin cells of the adrenal medulla and organ of Zuckerkandl, the sympathetic chain and additional prevertebral ganglia such as the celiac ganglia, suprarenal ganglia and mesenteric ganglia. In this review we discuss recent advances toward our understanding of how the NCC precursors of the ANS migrate to their target regions, how they are instructed to differentiate into the correct cell types, and the morphogenetic signals controlling their development. Many of these processes remain enigmatic to developmental biologists worldwide. Taking advantage of lineage tracing mouse models one of our own aims is to address the morphogenetic events underpinning the formation of the ANS and to identify the molecular mechanisms that help to segregate a mixed population of NCCs into pathways specific for the sympathetic ganglia, sensory ganglia or adrenal medulla.