DEVELOPMENTAL EXPRESSION OF TRKC, THE NEUROTROPHIN-3 RECEPTOR, IN THEMAMMALIAN NERVOUS-SYSTEM

The mammalian trkC gene encodes a tyrosine protein kinase that serves as a functional receptor for neurotrophin-3 (NT-3). Here, we report th at trkC is widely expressed in the developing and adult nervous system . Using in situ hybridization, we first detect trkC transcripts in the telencephalon and spinal cord of embryonic day 9.5 mouse embryos. In later embryonic development, trkC is expressed in various structures o f the CNS including the caudatoputamen, septal nuclei, cerebellum, and brainstem. In the PNS, trkC hybridization appears to correlate, both temporally and spatially, with the outgrowth of axons toward their per ipheral targets. trkC transcripts were also identified in the autonomo us enteric nervous system as well as in some non-neural tissues such a s the wall of the aorta and the acini of the submaxillary and sublingu al glands. In the adult mouse, trkC gene expression is heterogeneously distributed throughout the brain, with highest levels in limbic and d iencephalic structures. These results indicate that the trkC gene is w idely expressed in the three identified branches of the mammalian nerv ous system and appears to correlate with the expression of NT-3, its c ognate ligand. The apparent colocalization of trkC transcripts with NT -3 raises the possibility this neurotrophin exerts its trophic effects by a paracrine and/or autocrine mechanism.