The goal of the proposed research is to characterize the cells which give rise to the principal neurons, SIF cells and glia in a postmigratory neural crest cell population. Before migration, neural crest cells are multipotent, but earlier studies indicate that neural crest cells in the newly formed rat sympathetic ganglion are committed to neuronal or glial cell fates. One objective of the proposed study is to investigate whether this cell commitment is a common feature of another neural crest derivative, the dorsal root ganglion (DRG). A retroviral lineage marker will be utilized to label precursors and their progeny in dissociated rat embryonic DRG and combined with phenotypic analysis to address whether there are single cells in sensory ganglia that give rise to both neurons and glia. In addition to any lineage restrictions found in precursors, environmental cues also may alter the mature phenotype of DRG cells derived from precursors; we will examine the effects of several such cues, including the presence of purified growth factors and skin target tissue on neuronal differentiation. Within sympathetic ganglia, both principal neurons and small, intensely fluorescent (SIF) cells are generated prenatally within the same ganglion, yet different molecular cues including nerve growth factor (NGF) and glucocorticoids have been proposed to regulate their differentiation. We will test if the sympathetic ganglion possesses a common precursor to neurons and SIF cells, and examine its regulation. In particular, it is not clear how molecular signals are segregated to produce both neurons and SIF cells within one ganglion. As SIF cells mature apposed to ganglionic blood vessels, endothelial cells in addition to glucocorticoids and NGP will be examined for their ability to regulate SIF cell differentiation. As the notochord/ventral neural tube is important in the acquisition of adrenergic traits, we will examine the effects of a transplanted notochord on the establishment of the adrenergic phenotype in chick peripheral ganglia in vivo. While this proposal focuses on the peripheral nervous system, the restriction of neuronal cell fate occurs in both the PNS and CNS, and the cellular and molecular mechanisms which underlie this event are likely to be similar in both regions. Thus, the new information on the genesis of neuronal cell types generated by these experiments will have broad significance in our understanding of how cell diversity is generated in the developing nervous system. These studies will contribute to our understanding of the developmental events that underlie birth defects and mental retardation.
