The Journal of Neuroscience, June 15, 1999, 19(12):4739-4747
TrkB Isoforms with Distinct Neurotrophin Specificities Are
Expressed in Predominantly Nonoverlapping Populations of Avian Dorsal
Root Ganglion Neurons
Kristen L.
Boeshore,
Carol N.
Luckey,
Richard E.
Zigmond, and
Thomas H.
Large
Department of Neurosciences and Visual Sciences Research Center,
Case Western Reserve University School of Medicine, Cleveland,
Ohio 44106-4975
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.
Key words:
trkB; alternative splicing; dorsal root ganglia; neurotrophin specificity; single-cell RT-PCR; chicken
Copyright © 1999 Society for Neuroscience 0270-6474/99/19124739-09$05.00/0