title: TrkB isoforms with distinct neurotrophin specificities are expressed in predominantly nonoverlapping populations of avian dorsal root ganglion neurons.
abstract: Alternative splicing of the avian trkB receptor generates an extracellular deletion (ED) isoform missing 11 amino acids from the neurotrophin-binding domain of the full-length (FL) receptor. When expressed in fibroblasts, the ED isoform exhibited restricted neurotrophin specificity compared with that of the FL receptor. Brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4) activated the FL receptor, as determined by tyrosine phosphorylation. However, only BDNF was capable of significant activation of the ED isoform, although to a reduced level. Because positively charged residues in NT-3 are important for binding to trkB, two negatively charged aspartate residues within the 11 amino acid motif of FL trkB were mutated to examine the role of electrostatic interactions on ligand binding. As found for the ED isoform, the FL mutated receptor displayed a similar loss of NT-3- and NT-4-mediated activation, in addition to a diminished responsiveness to BDNF. Because of these profound effects on ligand specificity, reverse transcription-PCR was used to understand the expression of the FL and ED receptor isoforms at the level of single neurons. The predominant expression pattern of either FL or ED isoforms in single embryonic DRG neurons establishes the existence of two subpopulations exhibiting differential responsiveness to trkB ligands, indicating that regulated splicing of the extracellular domain of trkB may serve as a mechanism to restrict neuronal responsiveness to the neurotrophins.
authors.affiliation: Department of Neurosciences and Visual Sciences Research Center, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4975, USA.
authors.forename: K L
authors.initials: KL
authors.lastname: Boeshore
authors.forename: C N
authors.initials: CN
authors.lastname: Luckey
authors.forename: R E
authors.initials: RE
authors.lastname: Zigmond
authors.forename: T H
authors.initials: TH
authors.lastname: Large
mesh_terms: D017398:Alternative Splicing / Q000502:physiology; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000502:physiology; D000818:Animals; D001224:Aspartic Acid; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism / Q000494:pharmacology; D002642:Chick Embryo; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D005727:Ganglia, Spinal / Q000166:cytology; D017353:Gene Deletion; D007536:Isomerism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D009414:Nerve Growth Factors / Q000378:metabolism* / Q000494:pharmacology; D009474:Neurons / Q000737:chemistry* / Q000502:physiology; D018696:Neuroprotective Agents / Q000737:chemistry / Q000378:metabolism*; D020933:Neurotrophin 3; D011485:Protein Binding / Q000187:drug effects / Q000235:genetics; D017434:Protein Structure, Tertiary; D020794:Receptor Protein-Tyrosine Kinases / Q000737:chemistry / Q000235:genetics*; D020801:Receptor, Ciliary Neurotrophic Factor; D017475:Receptors, Nerve Growth Factor / Q000737:chemistry / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D008565:Membrane Proteins; D009414:Nerve Growth Factors; D018696:Neuroprotective Agents; D020933:Neurotrophin 3; D020801:Receptor, Ciliary Neurotrophic Factor; D017475:Receptors, Nerve Growth Factor; D001224:Aspartic Acid; D020794:Receptor Protein-Tyrosine Kinases; C073922:neurotrophin 4