Cloning of a new chicken trkC extracellular isoform and its mRNA expression in E9 sensory and autonomic ganglia.

Neuronal development and maintenance are regulated by trophic interactions with the target tissues and the innervating nerve. The neurotrophin family of polypeptide growth factors, consisting of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4/5 (NT-4/5), are produced in limited amounts in target areas. They bind to tyrosine receptor kinases of the trk family, including trkA, trkB and trkC, which mediate intracellular signalling in the responding neurons. There are reports of different isoforms of trkA, trkB and trkC having different signalling capacities. This study reports a novel deletion of the first cysteine-rich domain in the extracellular part of chicken trkC. We describe the mRNA expression of this isoform compared to non-deleted forms in E9 peripheral ganglia studied by reversetranscriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. We also compare the mRNA expression pattern of two existing signal peptide sequences and the distribution of trkC mRNA detected by the use of a kinase specific probe. The results show that the novel isoform is expressed in peripheral sensory and autonomic ganglia. Moreover both signal peptide forms are detected in these ganglia by RT-PCR. In addition, in situ hybridization results showed a weak mRNA expression of the novel isoform in the E9 dorsal root ganglion (DRG) but not in Remak's ganglion. The two existing signal peptides are equally expressed in the DRG and Remak's ganglion, at labelling densities comparable to those for the full-length catalytic form of trkC.