The NTRK1, NTRK2, and NTRK3 genes encode related single-pass transmembrane receptor tyrosine kinases, high affinity nerve growth factor receptor (TRKA), BDNF/NT-3 growth factor receptor (TRKB), and NT-3 growth factor receptor (TRKC), respectively, that function as high-affinity receptors for neurotrophins. TRK receptors contribute to neuronal development, function, survival, and proliferation during the development and into adulthood. Like other receptor tyrosine kinases, TRK proteins are activated following ligand binding to the extracellular domain of the receptor. Ligands for TRK proteins are the neurotrophins, a family of closely-related secreted proteins that were discovered and classified initially as proteins that were able to promote differentiation and survival in both sympathetic and sensory nerves. 
Signaling via TRK proteins is achieved with specific neurotrophin ligands, which triggers receptor dimerization and phosphorylation, leading to the activation of downstream signaling cascades. Through binding to TRK receptors, neorotrophinss activate Ras, phosphatidylinositol-3 (PI3)-kinase, and phospholipase C-γ1 signaling pathways. By this signaling, neurotrophins ultimately regulate cell fate decisions, axon growth, dendrite growth, and pruning. In addition to the expression in the central nervous system (CNS), TRK proteins have also been identified in non-neuronal normal tissues and cells, including pancreatic beta cells, monocytes, lungs, and bone.

References

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