Expression of the neurotrophic tyrosine kinase receptors, and , precedes expression of other genes in embryonic zebrafish.

BACKGROUND

The neurotrophic tyrosine kinase receptor () gene family plays a critical role in the survival of somatosensory neurons. Most vertebrates have three genes 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). Five genes and one p75 NTR gene () have been discovered in zebrafish. To date, the expression of these genes in the initial stages of neuron specification have not been investigated.

PURPOSE

The present work used whole mount in situ hybridization to analyze expression of the five genes and in 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.

RESULTS

At 16.5 hpf, we found tissue specific expression of in cranial ganglia, and tissue specific expression of in 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 both and in the spinal cord as well as in multiple cranial ganglia, and we identified expression in cranial ganglia at 24 hpf. , and were detected in the developing brain at 24 hpf.

CONCLUSION

These data are the first to demonstrate that and are the initial neurotrophic tyrosine kinase receptors expressed in sensory neurons during the development of the zebrafish body, and the first to establish expression patterns of during early zebrafish development. Our data indicate co-expression of , and , and we speculate that these overlapping patterns indicate relatedness of function.