Dynamic expression of neurotrophin receptors during sensory neuron genesisand differentiation

To identify potential functions for neurotrophins during sensory neuron gen esis and differentiation, we determined the temporal and spatial protein ex pression patterns of neurotrophin receptors throughout the process of senso ry neurogenesis in the dorsal root ganglia (DRG). We show that neurotrophin receptors are expressed early, being first detected on subsets of migratin g neural crest cells, and that trkC is among the earliest markers of neural lineage specification. In the immature DRG, we find that both trkC and p75 (NTR) are expressed on subsets of dividing progenitor cells in vivo. Furthe rmore, our data directly reveal distinct patterns of trk receptor expressio n by individual sensory neurons from the time of their inception with all e arly arising cells initially being trkC(+), some subsets of whom also coexp ress either trkA or trkB or both. As sensory neurons innervate their target s and establish their mature identities, the spectrum of trk receptors expr essed by individual neurons is altered. The stereotyped trk receptor expres sion profiles identified here may potentially correspond to distinct lineag es of sensory neurons. These data, in conjunction with other studies, argue for multiple functions for neurotrophins during the process of sensory neu ron differentiation, including effects on both neural crest and DRG mitotic ally active progenitor cells, in addition to possibly influencing the estab lishment of sensory neuron identity. (C) 2000 Academic Press.