Expressing TrkC from the TrkA locus causes a subset of dorsal root ganglia neurons to switch fate

Abstract

Tactile information is perceived by a heterogeneous population of specialized neurons. Neurotrophin receptors (the receptor tyrosine kinases, Trks) mark the major classes of these sensory neurons: TrkA is expressed in neurons that sense temperature and noxious stimuli, and TrkC is expressed in proprioceptive neurons that sense body position. Neurotrophin signaling through these receptors is required for cell survival. To test whether neurotrophins have an instructive role in sensory specification, we expressed rat TrkC from the TrkA (also known as Ntrk1) locus in mice. The surviving presumptive TrkA-expressing neurons adopted a proprioceptive phenotype, indicating that neurotrophin signaling can specify sensory neuron subtypes.Neurotrophins are well-characterized growth factors required for the survival of developing sensory neurons by signaling through a class of receptor tyrosine kinases 1-3 . The Trk receptors are specifically expressed in functionally distinct neurons of the dorsal root ganglia (DRG). TrkA, the receptor for nerve growth factor (NGF) is expressed in nociceptive and thermoceptive sensory neurons; TrkC, the high-affinity receptor for neurotrophin-3 (NT-3), is expressed in proprioceptive neurons; and TrkB, the receptor for brain-derived neurotrophic factor (BDNF) and NT-4, is expressed in less specifically characterized touch neurons. Each Trk receptor is required for the survival of the distinct class of neurons that it marks, consistent with a permissive role of neurotrophin signaling in neuronal survival. Various studies have suggested that Trk signaling is also involved in instructive steps of DRG development 4 . For example, neurotrophins are able to guide DRG axons in culture, and Bax -/-; TrkA -/-or Bax -/-;NT3 -/-DRG neurons, which are rescued from apoptosis by the lack of functional Bax protein, fail to develop properly 5-10 . To directly test whether signaling by a specific Trk can specify the subtype of DRG neurons in vivo, we designed a knock-in construct that expresses rat TrkC protein from the mouse TrkA locus while inactivating native TrkA expression. Table 2 and Fig. 4e-h).To further demonstrate that an effect on survival of existing proprioceptive neurons cannot account for the phenotype observed in TrkA TrkC/TrkC mice, we crossed the knock-in mice to Bax -/-mice. The deletion of Bax rescues DRG neurons from apoptosis, but does not cause the formation of extra proprioceptive neurons, as judged by the number of muscle spindles 10 (also compare parvalbumin and spindle counts in wild-type and Bax -/-mice; Tables 1 and 2). Notably, we observed a five-fold increase in parvalbumin-positive L5 DRGs and a seven-fold increase in muscle spindles in the soleus muscle of TrkA TrkC/TrkC ;Bax -/-mice when compared to Bax -/-mice ( Functional endogenous TrkC is required for the phenotypic switchIn an attempt to visualize the projection patterns of the ectopic proprioceptive neurons, we analyzed TrkA τlacZ/TrkC compound heterozygous mice. The TrkA-positive DRG neuronal projections are...

Trk receptor signaling and sensory neuron fate are perturbed in human neuropathy caused by Gars mutations

“…7C). A previous study has shown that expression of TrkC from the TrkA locus caused a developmental fate switch in DRG sensory subtypes (63). Given that GlyRS is expressed during early development (11,12), and that arborization of nociceptive neurons is developmentally impaired in CMT2D mice (Fig.…”

B-RAF kinase drives developmental axon growth and promotes axon regeneration in the injured mature CNS

“…Pritchard (University of Leicester, Leicester, England, UK; Mercer et al, 2005). The TrkA taulacZ mouse was provided by L. Reichardt (University of California, San Francisco, San Francisco, CA; Moqrich et al, 2004). Nestin-Cre deleter and Bax-null mice were generated in R. Klein's laboratory (Max Planck Institute of Neurobiology, Martinsried, Germany; Tronche et al, 1999) and S.J.…”

“…At E13.5, the branching pattern of sensory nerves in the skin was not changed by kaB-RAF expression (Fig. 1, H (Moqrich et al, 2004). Because TrkA expression is absent in homozygous TrkA taulacZ/taulacZ mice, we refer to the "TrkA taulacZ/taulacZ " as "TrkA / " in the text below.…”

“…Removal of the Bax gene blocks apoptosis in embryonic DRG neurons, rescuing them from cell death that is otherwise observed in the absence of TrkA signaling. The Bax / background thus allows for the molecular dissection of signaling pathways that specifically affect axon growth (Knudson et al, 1995;Lentz et al, 1999;Patel et al, 2000;Markus et al, 2002;Kuruvilla et al, 2004;Moqrich et al, 2004). In TrkA / : Bax / mice, DRG neurons survive, but sensory afferent innervation in the skin is completely abolished (Fig.…”

Direct Involvement of Arachidonic Acid in the Development of Ear Edema via TRPV3

“…Key words: arachidonic acid, cyclooxygenase 2, edema, lipoxygenase, TRPV3 2 Experimental 2.1 Mice C57BL TRPV3-/-mice were constructed according to a previous report 14 . C57BL TRPV3-/-mice were crossed with ICR mice for several generations to produce ICR TRPV3-/-mice, because ICR mice are useful for analyzing ear edema.…”