The Journal of Neuroscience, August 1, 1999, 19(15):6559-6570
Selective Regulation of trkC Expression by NT3 in the Developing
Peripheral Nervous System
Sean
Wyatt,
Gayle
Middleton,
Epaminondas
Doxakis, and
Alun M.
Davies
School of Biological and Medical Sciences, University of St.
Andrews, St. Andrews, Fife KY16 9AJ, Scotland
We have studied the influence of neurotrophin-3 (NT3) on the
expression of its receptor tyrosine kinase, trkC, in embryonic mice. The expression of trkC transcripts encoding full-length and
kinase-deficient receptors was almost entirely restricted to neurons in
the trigeminal ganglion and increased markedly throughout development.
In NT3+/
embryos, the level of trkC
mRNA in the trigeminal ganglion was much lower than that in wild-type
embryos, although there was no significant reduction in the total
number of neurons in the ganglion. This demonstrates that endogenous
NT3 regulates trkC expression in trigeminal neurons independently of
changes in population size. In
NT3
/
embryos, the number of
neurons in the trigeminal ganglion was much lower than in wild-type
embryos, and there was a further reduction in the mean neuronal level
of trkC mRNA. Direct regulation of trkC mRNA expression in cultured
trigeminal neurons was also observed, although the finding that trkC
mRNA levels were sustained better in explant cultures than in
dissociated cultures irrespective of the presence of NT3 suggests that
trkC mRNA expression is regulated by additional factors within the
ganglion. In contrast to trigeminal neurons, the level of trkC mRNA was
sustained at normal levels in neurons of the sympathetic chain of
NT3
/
embryos and was not
increased by NT3 in sympathetic neuron cultures. TrkC mRNA expression
in developing cutaneous tissues was also unaffected by the NT3 null
mutation. In summary, our findings provide the first clear evidence
that the expression of a trk receptor, tyrosine kinase, is regulated by
physiological levels of its ligand in vivo and show that
regulation by NT3 is cell type-specific.
Key words:
Trk receptor; neurotrophin; sensory neuron; sympathetic
neuron; NT3 knock-out; mouse
Copyright © 1999 Society for Neuroscience 0270-6474/99/19156559-12$05.00/0