Receptor tyrosine kinase involved in nervous system and probably heart development. Upon binding of its ligand NTF3/neurotrophin-3, NTRK3 autophosphorylates and activates different signaling pathways, including the phosphatidylinositol 3-kinase/AKT and the MAPK pathways, that control cell survival and differentiation (By similarity). The KT and KD isoforms fail to stimulate transformation, process outgrowth or survival. Isoform KI25 exhibits tyrosine phosphorylation in the absence of ligand and is unable to mediate survival of neuronal cells (PubMed:8060621). ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Exists in a dynamic equilibrium between monomeric (low affinity) and dimeric (high affinity) structures (By similarity). Interacts with PTPRS (PubMed:17967490, PubMed:25385546). Additional isoforms seem to exist. Expression occurs in the embryonal day 2 (E2) embryo with increasing levels later in development. In the E9 embryo highest levels are found in brain and spinal cord with intermediate levels in eye, heart, gut and muscle. Low levels are found in kidney, liver, skin and yolk sac. Ligand-mediated auto-phosphorylation. The kinase domain is of 19 aa instead of 39aa in the isoform alpha-KD due to a frameshift. Belongs to the protein kinase superfamily. Tyr protein kinase family. Insulin receptor subfamily.