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Developmental waves of mechanosensitivity acquisition in sensory neuron subtypes during embryonic development.

Lechner SG, Frenzel H, Wang R, Lewin GR - EMBO J. (2009)

Bottom Line: Sensory neurons that are mechanoreceptors or proprioceptors acquire mature mechanotransduction indistinguishable from the adult already at E13.In contrast, most nociceptive (pain sensing) sensory neurons acquire mechanosensitive competence as a result of exposure to target-derived nerve growth factor.The highly regulated process of mechanosensory acquisition unveiled here, reveals new strategies to identify molecules required for sensory neuron mechanotransduction.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Max-Delbrück Center for Molecular Medicine, Berlin-Buch, Germany.

ABSTRACT
Somatic sensation relies on the transduction of physical stimuli into electrical signals by sensory neurons of the dorsal root ganglia. Little is known about how and when during development different types of sensory neurons acquire transduction competence. We directly investigated the emergence of electrical excitability and mechanosensitivity of embryonic and postnatal mouse sensory neurons. We show that sensory neurons acquire mechanotransduction competence coincident with peripheral target innervation. Mechanotransduction competence arises in different sensory lineages in waves, coordinated by distinct developmental mechanisms. Sensory neurons that are mechanoreceptors or proprioceptors acquire mature mechanotransduction indistinguishable from the adult already at E13. This process is independent of neurotrophin-3 and may be driven by a genetic program. In contrast, most nociceptive (pain sensing) sensory neurons acquire mechanosensitive competence as a result of exposure to target-derived nerve growth factor. The highly regulated process of mechanosensory acquisition unveiled here, reveals new strategies to identify molecules required for sensory neuron mechanotransduction.

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In vitro acquisition of mechanosensitivity. (A) Recordings were made from E10.5, E11.5 and E12.5 cultures treated with NGF, BDNF and NT-3 for 24 h. The cell diameter of each patched neuron is plotted, and the symbol colour indicates the type of current exhibited by a particular cell (see inset). (B, C) Stacked histograms showing the proportions of neurons with RA- or IA-mechanosensitive currents, the neurotrophin treatment is indicated for each bar, the number of cells recorded is indicated above each column. (C) Note that neurons from E11.5 require 48 h in culture before mechanosensitive currents appear in large neurons. (D) The proportion of large diameter neurons with an RA-current recorded in acutely dissociated DRG cultures from wild-type and NT-3−/− mice. (E) Schema summarizing the key findings in A–D.
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f5: In vitro acquisition of mechanosensitivity. (A) Recordings were made from E10.5, E11.5 and E12.5 cultures treated with NGF, BDNF and NT-3 for 24 h. The cell diameter of each patched neuron is plotted, and the symbol colour indicates the type of current exhibited by a particular cell (see inset). (B, C) Stacked histograms showing the proportions of neurons with RA- or IA-mechanosensitive currents, the neurotrophin treatment is indicated for each bar, the number of cells recorded is indicated above each column. (C) Note that neurons from E11.5 require 48 h in culture before mechanosensitive currents appear in large neurons. (D) The proportion of large diameter neurons with an RA-current recorded in acutely dissociated DRG cultures from wild-type and NT-3−/− mice. (E) Schema summarizing the key findings in A–D.

Mentions: To test whether time in culture and neurotrophins might contribute to the acquisition of mechanosensitivity, we cultured sensory neurons from non-mechanosensitive stages (E10.5 to E12.5) for 24 h. Culture media were supplemented with NGF, BDNF and NT-3 (10 ng/ml). After 24 h in culture, neurons from E10.5 embryos did not acquire mechanosensitive currents and those from E11.5 only rarely (13%, 3/23 tested neurons). In contrast, the majority (77%, 17/22 tested neurons) of E12.5 neurons acquired mechanosensitive currents after 24 h in culture (Figure 5A). We cultured neurons from E12.5 embryos with single neurotrophins (Figure 5B). Incubation with BDNF had no inductive effect on mechanosensitivity, but in these cultures only few cells survived up to 24 h. We found that 24 h after incubation with NGF or NT-3 many cells possessed a mechanosensitive current; 73% (27/37 tested neurons) and 49% (18/37 tested neurons) when treated with NGF and NT-3, respectively. Between E10.5 and E12.5 many DRG neurons are TrkC+ (Farinas et al, 1996), but mechanosensitive currents were only observed after NT-3 was added to E12.5 DRG cultures. Thus, we wondered whether mechanosensitive currents appear as a function of developmental age and to this end we incubated neurons from E11.5 embryos for 24 or 48 h in NT-3 alone. Interestingly, only after 48 h in culture did a significant number of sensory neurons (71%, 12/17 tested neurons) acquire mechanosensitive currents (Figure 5C and E). These data are suggestive of an intrinsic program that leads to the acquisition of a mechanosensitive current starting from E13.5 in mechanoreceptors. It is known that NT-3/TrkC signalling acts very early in gangliogenesis to control neuronal number, and it is, therefore, conceivable that NT-3 signals are required to initiate a mechanotransduction program in mechanoreceptors. We tested this idea directly by isolating sensory neurons from NT-3−/− mutant embryos at E13.5 and asked whether such neurons possess a mechanosensitive RA-current. We found that the number of large neurons with narrow APs that possess an RA-current at this stage is indistinguishable from controls (Figure 5D). Thus, NT-3 is not obligatory for the mechanosensory development of the first mechanoreceptor population (Figure 5D and E).


Developmental waves of mechanosensitivity acquisition in sensory neuron subtypes during embryonic development.

Lechner SG, Frenzel H, Wang R, Lewin GR - EMBO J. (2009)

In vitro acquisition of mechanosensitivity. (A) Recordings were made from E10.5, E11.5 and E12.5 cultures treated with NGF, BDNF and NT-3 for 24 h. The cell diameter of each patched neuron is plotted, and the symbol colour indicates the type of current exhibited by a particular cell (see inset). (B, C) Stacked histograms showing the proportions of neurons with RA- or IA-mechanosensitive currents, the neurotrophin treatment is indicated for each bar, the number of cells recorded is indicated above each column. (C) Note that neurons from E11.5 require 48 h in culture before mechanosensitive currents appear in large neurons. (D) The proportion of large diameter neurons with an RA-current recorded in acutely dissociated DRG cultures from wild-type and NT-3−/− mice. (E) Schema summarizing the key findings in A–D.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2664657&req=5

f5: In vitro acquisition of mechanosensitivity. (A) Recordings were made from E10.5, E11.5 and E12.5 cultures treated with NGF, BDNF and NT-3 for 24 h. The cell diameter of each patched neuron is plotted, and the symbol colour indicates the type of current exhibited by a particular cell (see inset). (B, C) Stacked histograms showing the proportions of neurons with RA- or IA-mechanosensitive currents, the neurotrophin treatment is indicated for each bar, the number of cells recorded is indicated above each column. (C) Note that neurons from E11.5 require 48 h in culture before mechanosensitive currents appear in large neurons. (D) The proportion of large diameter neurons with an RA-current recorded in acutely dissociated DRG cultures from wild-type and NT-3−/− mice. (E) Schema summarizing the key findings in A–D.
Mentions: To test whether time in culture and neurotrophins might contribute to the acquisition of mechanosensitivity, we cultured sensory neurons from non-mechanosensitive stages (E10.5 to E12.5) for 24 h. Culture media were supplemented with NGF, BDNF and NT-3 (10 ng/ml). After 24 h in culture, neurons from E10.5 embryos did not acquire mechanosensitive currents and those from E11.5 only rarely (13%, 3/23 tested neurons). In contrast, the majority (77%, 17/22 tested neurons) of E12.5 neurons acquired mechanosensitive currents after 24 h in culture (Figure 5A). We cultured neurons from E12.5 embryos with single neurotrophins (Figure 5B). Incubation with BDNF had no inductive effect on mechanosensitivity, but in these cultures only few cells survived up to 24 h. We found that 24 h after incubation with NGF or NT-3 many cells possessed a mechanosensitive current; 73% (27/37 tested neurons) and 49% (18/37 tested neurons) when treated with NGF and NT-3, respectively. Between E10.5 and E12.5 many DRG neurons are TrkC+ (Farinas et al, 1996), but mechanosensitive currents were only observed after NT-3 was added to E12.5 DRG cultures. Thus, we wondered whether mechanosensitive currents appear as a function of developmental age and to this end we incubated neurons from E11.5 embryos for 24 or 48 h in NT-3 alone. Interestingly, only after 48 h in culture did a significant number of sensory neurons (71%, 12/17 tested neurons) acquire mechanosensitive currents (Figure 5C and E). These data are suggestive of an intrinsic program that leads to the acquisition of a mechanosensitive current starting from E13.5 in mechanoreceptors. It is known that NT-3/TrkC signalling acts very early in gangliogenesis to control neuronal number, and it is, therefore, conceivable that NT-3 signals are required to initiate a mechanotransduction program in mechanoreceptors. We tested this idea directly by isolating sensory neurons from NT-3−/− mutant embryos at E13.5 and asked whether such neurons possess a mechanosensitive RA-current. We found that the number of large neurons with narrow APs that possess an RA-current at this stage is indistinguishable from controls (Figure 5D). Thus, NT-3 is not obligatory for the mechanosensory development of the first mechanoreceptor population (Figure 5D and E).

Bottom Line: Sensory neurons that are mechanoreceptors or proprioceptors acquire mature mechanotransduction indistinguishable from the adult already at E13.In contrast, most nociceptive (pain sensing) sensory neurons acquire mechanosensitive competence as a result of exposure to target-derived nerve growth factor.The highly regulated process of mechanosensory acquisition unveiled here, reveals new strategies to identify molecules required for sensory neuron mechanotransduction.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Max-Delbrück Center for Molecular Medicine, Berlin-Buch, Germany.

ABSTRACT
Somatic sensation relies on the transduction of physical stimuli into electrical signals by sensory neurons of the dorsal root ganglia. Little is known about how and when during development different types of sensory neurons acquire transduction competence. We directly investigated the emergence of electrical excitability and mechanosensitivity of embryonic and postnatal mouse sensory neurons. We show that sensory neurons acquire mechanotransduction competence coincident with peripheral target innervation. Mechanotransduction competence arises in different sensory lineages in waves, coordinated by distinct developmental mechanisms. Sensory neurons that are mechanoreceptors or proprioceptors acquire mature mechanotransduction indistinguishable from the adult already at E13. This process is independent of neurotrophin-3 and may be driven by a genetic program. In contrast, most nociceptive (pain sensing) sensory neurons acquire mechanosensitive competence as a result of exposure to target-derived nerve growth factor. The highly regulated process of mechanosensory acquisition unveiled here, reveals new strategies to identify molecules required for sensory neuron mechanotransduction.

Show MeSH
Related in: MedlinePlus