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Different requirements for GFRα2-signaling in three populations of cutaneous sensory neurons.

Kupari J, Airaksinen MS - PLoS ONE (2014)

Bottom Line: In contrast to the nonpeptidergic neurons, GFRα2 is not required for the target innervation of C-LTMRs and Aβ-LTMRs in the back skin.These results suggest that different factors drive target innervation in these three populations of neurons.In addition, the observation that the large Ret-positive DRG neurons lack GFRα2 immunoreactivity in mature animals suggests that these neurons switch their GFRα signaling pathways during postnatal development.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biomedicine, Anatomy, University of Helsinki, Helsinki, Finland.

ABSTRACT
Many primary sensory neurons in mouse dorsal root ganglia (DRG) express one or several GFRα's, the ligand-binding receptors of the GDNF family, and their common signaling receptor Ret. GFRα2, the principal receptor for neurturin, is expressed in most of the small nonpeptidergic DRG neurons, but also in some large DRG neurons that start to express Ret earlier. Previously, GFRα2 has been shown to be crucial for the soma size of small nonpeptidergic nociceptors and for their target innervation of glabrous epidermis. However, little is known about this receptor in other Ret-expressing DRG neuron populations. Here we have investigated two populations of Ret-positive low-threshold mechanoreceptors that innervate different types of hair follicles on mouse back skin: the small C-LTMRs and the large Aβ-LTMRs. Using GFRα2-KO mice and immunohistochemistry we found that, similar to the nonpeptidergic nociceptors, GFRα2 controls the cell size but not the survival of both C-LTMRs and Aβ-LTMRs. In contrast to the nonpeptidergic neurons, GFRα2 is not required for the target innervation of C-LTMRs and Aβ-LTMRs in the back skin. These results suggest that different factors drive target innervation in these three populations of neurons. In addition, the observation that the large Ret-positive DRG neurons lack GFRα2 immunoreactivity in mature animals suggests that these neurons switch their GFRα signaling pathways during postnatal development.

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TH+ DRG neurons in GFRα2-KO mice are smaller.(A–C) TH and GFRα2 colocalize in a subpopulation of thoracic DRG neurons. (D) Nearly all TH+ neurons express GFRα2 (red bar). TH+ neurons comprise ∼37% of all GFRα2 neurons (green bar). Analysis was done from three animals and three ganglia in total. (E–H) The number of TH+ neurons in thoracic DRGs is similar between the genotypes (G: WT 533±59, KO 555±24; positive neurons per DRG, n = 3 animals/genotype, U-test) but the size is smaller in the knock-out animals (H: WT 196±14 µm2, KO 120±8 µm2; three animals and 200 cells/genotype in total, chi-square -test). Scale bar: 50 µm.
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pone-0104764-g002: TH+ DRG neurons in GFRα2-KO mice are smaller.(A–C) TH and GFRα2 colocalize in a subpopulation of thoracic DRG neurons. (D) Nearly all TH+ neurons express GFRα2 (red bar). TH+ neurons comprise ∼37% of all GFRα2 neurons (green bar). Analysis was done from three animals and three ganglia in total. (E–H) The number of TH+ neurons in thoracic DRGs is similar between the genotypes (G: WT 533±59, KO 555±24; positive neurons per DRG, n = 3 animals/genotype, U-test) but the size is smaller in the knock-out animals (H: WT 196±14 µm2, KO 120±8 µm2; three animals and 200 cells/genotype in total, chi-square -test). Scale bar: 50 µm.

Mentions: A distinct class of C-LTMRs that expresses vesicular glutamate transporter VGlut3 [11] and tyrosine hydroxylase (TH) [12] constitutes a subpopulation of nonpeptidergic C-fibers. This population of neurons has also been reported to express GFRα2 and Ret, but not to bind IB4 or express any of the Mas-related G-protein receptors, making them a separate population from the nonpeptidergic nociceptors [12]. Using immunohistochemistry and two different antibodies, we confirmed that a significant population of thoracic DRG neurons expresses TH in wild-type mice (Fig. 2A, E and Fig. S4). Co-staining showed that nearly all of the TH+ DRG neurons expressed GFRα2 (Fig. 2B–D). Vice versa, the TH+ neurons totaled to a roughly one third of all GFRα2+ neurons (Fig. 2D). To investigate if GFRα2 is required for TH expression or survival of these DRG neurons, we quantified the numbers of TH+ neurons in thoracic DRGs of both wild-type and GFRα2-KO animals. Firstly, intense TH+ immunoreactivity was found on a subpopulation of neurons in KO DRGs, indicating that GFRα2-signaling is not a requirement for TH expression (Fig. 2F). Secondly, no significant differences were found in the number estimates of TH+ neurons per DRG between the genotypes, suggesting that GFRα2 is not required for TH+ neuron survival (Fig. 2G). We then performed a cell size distribution analysis, which showed that the TH+ neurons were significantly smaller in the GFRα2-KO animals (Fig. 2H).


Different requirements for GFRα2-signaling in three populations of cutaneous sensory neurons.

Kupari J, Airaksinen MS - PLoS ONE (2014)

TH+ DRG neurons in GFRα2-KO mice are smaller.(A–C) TH and GFRα2 colocalize in a subpopulation of thoracic DRG neurons. (D) Nearly all TH+ neurons express GFRα2 (red bar). TH+ neurons comprise ∼37% of all GFRα2 neurons (green bar). Analysis was done from three animals and three ganglia in total. (E–H) The number of TH+ neurons in thoracic DRGs is similar between the genotypes (G: WT 533±59, KO 555±24; positive neurons per DRG, n = 3 animals/genotype, U-test) but the size is smaller in the knock-out animals (H: WT 196±14 µm2, KO 120±8 µm2; three animals and 200 cells/genotype in total, chi-square -test). Scale bar: 50 µm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4128720&req=5

pone-0104764-g002: TH+ DRG neurons in GFRα2-KO mice are smaller.(A–C) TH and GFRα2 colocalize in a subpopulation of thoracic DRG neurons. (D) Nearly all TH+ neurons express GFRα2 (red bar). TH+ neurons comprise ∼37% of all GFRα2 neurons (green bar). Analysis was done from three animals and three ganglia in total. (E–H) The number of TH+ neurons in thoracic DRGs is similar between the genotypes (G: WT 533±59, KO 555±24; positive neurons per DRG, n = 3 animals/genotype, U-test) but the size is smaller in the knock-out animals (H: WT 196±14 µm2, KO 120±8 µm2; three animals and 200 cells/genotype in total, chi-square -test). Scale bar: 50 µm.
Mentions: A distinct class of C-LTMRs that expresses vesicular glutamate transporter VGlut3 [11] and tyrosine hydroxylase (TH) [12] constitutes a subpopulation of nonpeptidergic C-fibers. This population of neurons has also been reported to express GFRα2 and Ret, but not to bind IB4 or express any of the Mas-related G-protein receptors, making them a separate population from the nonpeptidergic nociceptors [12]. Using immunohistochemistry and two different antibodies, we confirmed that a significant population of thoracic DRG neurons expresses TH in wild-type mice (Fig. 2A, E and Fig. S4). Co-staining showed that nearly all of the TH+ DRG neurons expressed GFRα2 (Fig. 2B–D). Vice versa, the TH+ neurons totaled to a roughly one third of all GFRα2+ neurons (Fig. 2D). To investigate if GFRα2 is required for TH expression or survival of these DRG neurons, we quantified the numbers of TH+ neurons in thoracic DRGs of both wild-type and GFRα2-KO animals. Firstly, intense TH+ immunoreactivity was found on a subpopulation of neurons in KO DRGs, indicating that GFRα2-signaling is not a requirement for TH expression (Fig. 2F). Secondly, no significant differences were found in the number estimates of TH+ neurons per DRG between the genotypes, suggesting that GFRα2 is not required for TH+ neuron survival (Fig. 2G). We then performed a cell size distribution analysis, which showed that the TH+ neurons were significantly smaller in the GFRα2-KO animals (Fig. 2H).

Bottom Line: In contrast to the nonpeptidergic neurons, GFRα2 is not required for the target innervation of C-LTMRs and Aβ-LTMRs in the back skin.These results suggest that different factors drive target innervation in these three populations of neurons.In addition, the observation that the large Ret-positive DRG neurons lack GFRα2 immunoreactivity in mature animals suggests that these neurons switch their GFRα signaling pathways during postnatal development.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biomedicine, Anatomy, University of Helsinki, Helsinki, Finland.

ABSTRACT
Many primary sensory neurons in mouse dorsal root ganglia (DRG) express one or several GFRα's, the ligand-binding receptors of the GDNF family, and their common signaling receptor Ret. GFRα2, the principal receptor for neurturin, is expressed in most of the small nonpeptidergic DRG neurons, but also in some large DRG neurons that start to express Ret earlier. Previously, GFRα2 has been shown to be crucial for the soma size of small nonpeptidergic nociceptors and for their target innervation of glabrous epidermis. However, little is known about this receptor in other Ret-expressing DRG neuron populations. Here we have investigated two populations of Ret-positive low-threshold mechanoreceptors that innervate different types of hair follicles on mouse back skin: the small C-LTMRs and the large Aβ-LTMRs. Using GFRα2-KO mice and immunohistochemistry we found that, similar to the nonpeptidergic nociceptors, GFRα2 controls the cell size but not the survival of both C-LTMRs and Aβ-LTMRs. In contrast to the nonpeptidergic neurons, GFRα2 is not required for the target innervation of C-LTMRs and Aβ-LTMRs in the back skin. These results suggest that different factors drive target innervation in these three populations of neurons. In addition, the observation that the large Ret-positive DRG neurons lack GFRα2 immunoreactivity in mature animals suggests that these neurons switch their GFRα signaling pathways during postnatal development.

Show MeSH
Related in: MedlinePlus