The role of bone morphogenetic proteins in sympathetic neuron development

The generation of specific neuronal subtypes from neural stem cells is one of the dominating themes in developmental neurobiology. In the last years, key signaling pathways have been identified that are involved in the generic control of neurogenesis. In addition, genes were found that selectively control the specification and differentiation of specific types of neurons. The development of sympathetic neurons from neural crest-derived precursors has been investigated over the years in great detail at molecular and cellular levels and thus represents one of the best understood models of neuron generation. The present review summarizes results demonstrating the role of the extrinsic signaling molecules, bone morphogenetic proteins (BMPs), and of their downstream transcription factors in the generation and differentiation of noradrenergic sympathetic neurons. How these signaling pathways are modified to generate other nonnoradrenergic neuron types of the autonomic nervous system is discussed in the context of recent studies of the development of parasympathetic neurons. Finally, evidence is reviewed that implicates BMPs at later stages of sympathetic neuron differentiation, in the control of dendrite formation.