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Control of axon elongation via an SDF-1alpha/Rho/mDia pathway in cultured cerebellar granule neurons.

Arakawa Y, Bito H, Furuyashiki T, Tsuji T, Takemoto-Kimura S, Kimura K, Nozaki K, Hashimoto N, Narumiya S - J. Cell Biol. (2003)

Bottom Line: SDF-1alpha-induced axon elongating activity under ROCK inhibition was replicated by the dominant-active form of the mammalian homologue of the Drosophila gene Diaphanous (mDia)1 and counteracted by its dominant-negative form.Furthermore, RNAi knockdown of mDia1 abolished SDF-1alpha-induced axon elongation.Together, our results support a critical role for an SDF-1alpha/Rho/mDia1 pathway in mediating axon elongation.

View Article: PubMed Central - PubMed

Affiliation: Dept. of Pharmacology, Kyoto University Faculty of Medicine, Yoshida, Sakyo-ku, Kyoto 606-8315, Japan.

ABSTRACT
Rho-GTPase has been implicated in axon outgrowth. However, not all of the critical steps controlled by Rho have been well characterized. Using cultured cerebellar granule neurons, we show here that stromal cell-derived factor (SDF)-1alpha, a neural chemokine, is a physiological ligand that can turn on two distinct Rho-dependent pathways with opposite consequences. A low concentration of the ligand stimulated a Rho-dependent pathway that mediated facilitation of axon elongation. In contrast, Rho/ROCK activation achieved by a higher concentration of SDF-1alpha caused repression of axon formation and induced no more increase in axon length. However, even at this higher concentration a Rho-dependent axon elongating activity could be recovered upon removal of ROCK activity using Y-27632. SDF-1alpha-induced axon elongating activity under ROCK inhibition was replicated by the dominant-active form of the mammalian homologue of the Drosophila gene Diaphanous (mDia)1 and counteracted by its dominant-negative form. Furthermore, RNAi knockdown of mDia1 abolished SDF-1alpha-induced axon elongation. Together, our results support a critical role for an SDF-1alpha/Rho/mDia1 pathway in mediating axon elongation.

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Distinct C3 dose effectiveness on axon elongation and axon number in cultured cerebellar granule neurons. Axon elongation reveals a bell-shaped C3 responsiveness consistent with the presence of two opposing effects downstream of Rho. However, the C3 effect on axon number is saturated at doses over 10 μg/ml. n ≈115–424; ***P < 0.001.
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fig2: Distinct C3 dose effectiveness on axon elongation and axon number in cultured cerebellar granule neurons. Axon elongation reveals a bell-shaped C3 responsiveness consistent with the presence of two opposing effects downstream of Rho. However, the C3 effect on axon number is saturated at doses over 10 μg/ml. n ≈115–424; ***P < 0.001.

Mentions: To test whether the biphasic responsiveness could be accounted for by the existence of distinct thresholds of activation of two separate Rho effectors, we carefully reexamined the dose–response relationship between C3 concentration and resulting axon length. The sampling number was increased substantially in order to detect even small differences that might have been overlooked before. At 10 μg/ml of C3, a significant increase in axon length and number was achieved (Fig. 2) . When the dose was augmented to 30–50 μg/ml, this facilitation in axon length was substantially diminished compared with 10 μg/ml treatment, though a small but significant net increase was still detectable; however, no additional effect was seen on axon number (Fig. 2). Therefore, different concentrations of active Rho were likely to gear two distinct pathways, repression and facilitation of axon extension, via two distinct Rho effectors. In contrast, only one Rho effector was likely to contribute to axon number control (Fig. 2), consistent with our previous work (Bito et al., 2000). A similar C3 dose–response curve was also reported in PC-12 cells (Winton et al., 2002).


Control of axon elongation via an SDF-1alpha/Rho/mDia pathway in cultured cerebellar granule neurons.

Arakawa Y, Bito H, Furuyashiki T, Tsuji T, Takemoto-Kimura S, Kimura K, Nozaki K, Hashimoto N, Narumiya S - J. Cell Biol. (2003)

Distinct C3 dose effectiveness on axon elongation and axon number in cultured cerebellar granule neurons. Axon elongation reveals a bell-shaped C3 responsiveness consistent with the presence of two opposing effects downstream of Rho. However, the C3 effect on axon number is saturated at doses over 10 μg/ml. n ≈115–424; ***P < 0.001.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172896&req=5

fig2: Distinct C3 dose effectiveness on axon elongation and axon number in cultured cerebellar granule neurons. Axon elongation reveals a bell-shaped C3 responsiveness consistent with the presence of two opposing effects downstream of Rho. However, the C3 effect on axon number is saturated at doses over 10 μg/ml. n ≈115–424; ***P < 0.001.
Mentions: To test whether the biphasic responsiveness could be accounted for by the existence of distinct thresholds of activation of two separate Rho effectors, we carefully reexamined the dose–response relationship between C3 concentration and resulting axon length. The sampling number was increased substantially in order to detect even small differences that might have been overlooked before. At 10 μg/ml of C3, a significant increase in axon length and number was achieved (Fig. 2) . When the dose was augmented to 30–50 μg/ml, this facilitation in axon length was substantially diminished compared with 10 μg/ml treatment, though a small but significant net increase was still detectable; however, no additional effect was seen on axon number (Fig. 2). Therefore, different concentrations of active Rho were likely to gear two distinct pathways, repression and facilitation of axon extension, via two distinct Rho effectors. In contrast, only one Rho effector was likely to contribute to axon number control (Fig. 2), consistent with our previous work (Bito et al., 2000). A similar C3 dose–response curve was also reported in PC-12 cells (Winton et al., 2002).

Bottom Line: SDF-1alpha-induced axon elongating activity under ROCK inhibition was replicated by the dominant-active form of the mammalian homologue of the Drosophila gene Diaphanous (mDia)1 and counteracted by its dominant-negative form.Furthermore, RNAi knockdown of mDia1 abolished SDF-1alpha-induced axon elongation.Together, our results support a critical role for an SDF-1alpha/Rho/mDia1 pathway in mediating axon elongation.

View Article: PubMed Central - PubMed

Affiliation: Dept. of Pharmacology, Kyoto University Faculty of Medicine, Yoshida, Sakyo-ku, Kyoto 606-8315, Japan.

ABSTRACT
Rho-GTPase has been implicated in axon outgrowth. However, not all of the critical steps controlled by Rho have been well characterized. Using cultured cerebellar granule neurons, we show here that stromal cell-derived factor (SDF)-1alpha, a neural chemokine, is a physiological ligand that can turn on two distinct Rho-dependent pathways with opposite consequences. A low concentration of the ligand stimulated a Rho-dependent pathway that mediated facilitation of axon elongation. In contrast, Rho/ROCK activation achieved by a higher concentration of SDF-1alpha caused repression of axon formation and induced no more increase in axon length. However, even at this higher concentration a Rho-dependent axon elongating activity could be recovered upon removal of ROCK activity using Y-27632. SDF-1alpha-induced axon elongating activity under ROCK inhibition was replicated by the dominant-active form of the mammalian homologue of the Drosophila gene Diaphanous (mDia)1 and counteracted by its dominant-negative form. Furthermore, RNAi knockdown of mDia1 abolished SDF-1alpha-induced axon elongation. Together, our results support a critical role for an SDF-1alpha/Rho/mDia1 pathway in mediating axon elongation.

Show MeSH