Expression of the neurotrophic tyrosine kinase receptors,ntrk1andntrk2a, precedes expression of otherntrkgenes in embryonic zebrafish

Abstract

BackgroundThe neurotrophic tyrosine kinase receptor (Ntrk) gene family plays a critical role in the survival of somatosensory neurons. Most vertebrates have threeNtrkgenes each of which encode a Trk receptor: TrkA, TrkB, or TrkC. The function of the Trk receptors is modulated by the p75 neurotrophin receptors (NTRs). Fiventrkgenes and one p75 NTR gene (ngfrb) have been discovered in zebrafish. To date, the expression of these genes in the initial stages of neuron specification have not been investigated.PurposeThe present work used whole mount in situ hybridization to analyze expression of the fiventrkgenes andngfrbin zebrafish at a timepoint when the first sensory neurons of the zebrafish body are being established (16.5 hpf). Because expression of multiple genes were not found at this time point, we also checked expression at 24 hpf to ensure the functionality of our six probes.ResultsAt 16.5 hpf, we found tissue specific expression ofntrk1in cranial ganglia, and tissue specific expression ofntrk2ain cranial ganglia and in the spinal cord. Other genes analyzed at 16.5 hpf were either diffuse or not detected. At 24 hpf, we found expression of bothntrk1andntrk2ain the spinal cord as well as in multiple cranial ganglia, and we identifiedngfrbexpression in cranial ganglia at 24 hpf.ntrk2b,ntrk3aandntrk3bwere detected in the developing brain at 24 hpf.ConclusionThese data are the first to demonstrate thatntrk1andntrk2aare the initial neurotrophic tyrosine kinase receptors expressed in sensory neurons during the development of the zebrafish body, and the first to establish expression patterns ofngfrbduring early zebrafish development. Our data indicate co-expression ofntrk1,ntrk2aandngfrb, and we speculate that these overlapping patterns indicate relatedness of function.