Expression of the trk proto-oncogene is restricted to the sensory cranial and spinal ganglia of neural crest origin in mouse development.

We have cloned and characterized the mouse homolog of the human trk proto-oncogene, a member of the protein tyrosine kinase (TK) receptor gene family. Here, we present the first report of a trk-encoded mRNA species in vivo. In situ hybridization analysis in the mouse embryo reveals a striking temporal and spatial regulation of trk transcription, with expression confined to the sensory cranial (trigeminal, superior, jugular) and dorsal root ganglia (DRG) of neural crest origin. Recent reports have shown that TK receptors can play regulatory roles in embryonic development. Thus, the developmental mutations W in mouse and torso and sevenless in Drosophila represent genes that code for defective TK receptors. Our data show that trk, a gene associated with malignancy in humans, is a specific marker for a set of neural crest-derived sensory neurons, and are consistent with the hypothesis that this proto-oncogene may have an important role in the development or phenotype of the neurons where it is expressed.