Neurotrophin receptor tgenes are expressed in developing dorsal root ganglia

Department of Neurology, Washington University Medical School, St. Louis, Missouri 63110.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 10/1993; 13(9):4029-41.
Source: PubMed


All members of the neurotrophin family of neuronal growth factors promote survival and neurite outgrowth of dorsal root ganglion (DRG) neurons in vitro. The trk family of protooncogenes encodes receptors that are now thought to mediate the biological effects of neurotrophins. In order to learn more about the dependence of DRG neurons on neurotrophins in vivo, we have studied mRNA expression of members of the trk family in developing DRGs in embryonic and postnatal rats. We show here that neurotrophin receptors are expressed in thoracic and lumbar DRGs by embryonic day 13 (E13), which is only 24-48 hr after neurogenesis begins in these ganglia. Distinct patterns of expression of trkA, trkB, and trkC are readily apparent by E15. At this age, 40% of thoracic DRG neurons express trkA. In contrast, trkB and trkC are expressed by only 6% and 8%, respectively, of thoracic DRG neurons. These percentages change little between E15 and postnatal day 1. Although absolute numbers of DRG neurons expressing neurotrophin receptors are greater in lumbar than in thoracic ganglia, the ratios of DRG neurons expressing different members of the trk family are similar in the two regions. The different trks are expressed by distinct populations of DRG neurons from E15 onward. trkA is expressed predominantly by small neurons with darkly staining cytoplasm. trkB and trkC are expressed by large, lightly staining neurons. Size-frequency histograms show that trkA is expressed by neurons of variable sizes, but particularly by neurons at the smallest end of the spectrum. In contrast, trkC is expressed predominantly by large DRG neurons, including those with the largest soma areas. trkB is expressed by DRG neurons of intermediate size. Our results show that a majority of DRG neurons express mRNA for at least one member of the trk protooncogene family. Furthermore, trk expression occurs in a time frame consistent with the idea that trks mediate responses of DRG neurons to neurotrophins that are synthesized in both the periphery and spinal cord at early developmental stages. Finally, different populations of DRG neurons express different trks. We hypothesize that DRG neurons subserving different functions express different trks, and that trk expression of a particular class of DRG neurons determines its neurotrophin dependence during development.

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Available from: Steven L Carroll, Oct 06, 2015
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    • ") , and the calcium - binding protein Pv , a proprioceptive sensory neuron marker ( Mu et al . , 1993 ; Honda , 1995 ) ."
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    ABSTRACT: Commissural neurons project across the midline at all levels of the central nervous system (CNS), providing bilateral communication critical for the coordination of motor activity and sensory perception. Midline crossing at the spinal ventral midline has been extensively studied and has revealed that multiple developmental lineages contribute to this commissural neuron population. Ventral midline crossing occurs in a manner dependent on Robo3 regulation of Robo/Slit signaling and the ventral commissure is absent in the spinal cord and hindbrain of Robo3 mutants. Midline crossing in the spinal cord is not limited to the ventral midline, however. While prior anatomical studies provide evidence that commissural axons also cross the midline dorsally, little is known of the genetic and molecular properties of dorsally-crossing neurons or of the mechanisms that regulate dorsal midline crossing. In this study, we describe a commissural neuron population that crosses the spinal dorsal midline during the last quarter of embryogenesis in discrete fiber bundles present throughout the rostrocaudal extent of the spinal cord. Using immunohistochemistry, neurotracing, and mouse genetics, we show that this commissural neuron population includes spinal inhibitory neurons and sensory nociceptors. While the floor plate and roof plate are dispensable for dorsal midline crossing, we show that this population depends on Robo/Slit signaling yet crosses the dorsal midline in a Robo3-independent manner. The dorsally-crossing commissural neuron population we describe suggests a substrate circuitry for pain processing in the dorsal spinal cord.
    Frontiers in Neural Circuits 08/2015; 9:36. DOI:10.3389/fncir.2015.00036 · 3.60 Impact Factor
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    • "Surprisingly, EGFP- and ISL1/2-double-positive cells were noted inside the spinal cord near the DREZ of Six1/4 EGFP/EGFP (n = 19, Figure 3J,L), whereas these cells were hardly observed in Six1/4 +/EGFP (n = 17, Figure 3I,K). The EGFP- and ISL1/2-double-positive cells in Six1/4 EGFP/EGFP also showed immunofluorescence signal for NTRK3 (TrkC) (n = 6, Figure 3N,P), a marker of proprioceptive neurons of the DRG [60]. By contrast, the NTRK3 signal was observed only in the axonal bundle of DREZ in the spinal cords of Six1/4 +/EGFP (n = 5, Figure 3M,O). "
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    BMC Biology 05/2014; 12(1):40. DOI:10.1186/1741-7007-12-40 · 7.98 Impact Factor
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    • "In addition to SC-mediated augmentation of regeneration, there may also be a direct effect upon neurons that promote axonal sprouting. NT-3 and its high-affinity receptor, TrkC, are present in high numbers of spinal motor neurons and in a subpopulation of large diameter primary sensory neurons.36,37 Furthermore, NT-3 is internalized and retrogradely transported from the periphery to motoneuron cell bodies.38 "
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