Developmental Regulation of Full‐length trkC in the Rat Sciatic Nerve

In order to gain insight into potential roles of neurotrophins in Schwann cell biology, the expression of neurotrophin receptors of the frk gene family was investigated in rat sciatic nerve development. This analysis revealed differential regulation of truncated and full‐length receptors. TrkA was undetectable even when analysed with a sensitive reverse transcriptase‐polymerase chain reaction (RT‐PCR) method. TrkB was present at the mRNA as well as protein level only in its truncated form. Surprisingly, multiple isoforms of trkC, including full‐length forms, were detected in early postnatal nerve. Specific antibodies detected truncated and full‐length trkC proteins in Western blotting, and RT‐PCR revealed the presence of two full‐length isoforms, one of them containing the 14 amino acid kinase insert. In situ hybridisation localized the expression of trkC to a subpopulation of Schwann cells. TrkC receptors are expressed already in nerves from day‐16 embryos. In contrast to early postnatal stages, full‐length trkC receptors are no longer expressed in adult nerves, which, however, maintain expression of truncated trkC transcripts. The presence of trkC kinases in peripheral nerve suggests a role for neurotrophin‐3, the only known trkC ligand, in peripheral nerve development.