THE INDUCTION OF NEUROTROPHIN AND TRK RECEPTOR MESSENGER-RNA EXPRESSION DURING EARLY AVIAN EMBRYOGENESIS

Nerve growth factor, brain-derived neurotrophic factor and neurotrophi n-3, designated neurotrophins, are a family of neurotrophic factors, h aving important functions in the survival of embryonic and adult neuro nal subpopulations. Through the trk family of receptors, these neurotr ophins utilize phosphotyrosine-mediated signal transduction. We have u sed RT-PCR to detect the expression of mRNA for the above neurotrophin s and their respective receptors, namely trkA, trkB and trkC in embryo nic stages 1-8 of chicken development. While trkA and trkC mRNAs were expressed from stage 1 onwards, NGF and NT-3 mRNAs were expressed only at stages 3 and 51 respectively. In contrast, BDNF mRNA was expressed at stage 1, being the only neurotrophin expressed prior to expression of its respective receptor trkB. However, the latter was not expresse d until stage 8. These results indicate an earlier expression of some but not all trk proto-oncogenes, suggesting that the two different rec eptor mRNAs expressed i.e. trkA and trkC in conjunction with BDNF. at stage 1, may act in aspects of very early embryonic development, such as gastrulation. Thereafter, mRNAs for trkB, NGF and NT-3 art expresse d reflecting their later action in early embryonic development.