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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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Expression of the morphological effects of mDia1 is mediated, at least in part, by Rac activity. (A) Co-expression of GFP-N17Rac, a DN mutant of Rac, suppresses expression of the facilitatory effects of FLAG-mDia1-ΔN3 on either axon length (left) in the presence of Y-27632 (50 μM) back to baseline levels. n ≈ 45–137. (B) Inhibition of ROCK activity in the presence of high concentration of SDF-1α (500 ng/ml) increases the GTP-bound form of Rac. ***P < 0.001.
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fig9: Expression of the morphological effects of mDia1 is mediated, at least in part, by Rac activity. (A) Co-expression of GFP-N17Rac, a DN mutant of Rac, suppresses expression of the facilitatory effects of FLAG-mDia1-ΔN3 on either axon length (left) in the presence of Y-27632 (50 μM) back to baseline levels. n ≈ 45–137. (B) Inhibition of ROCK activity in the presence of high concentration of SDF-1α (500 ng/ml) increases the GTP-bound form of Rac. ***P < 0.001.

Mentions: We finally wanted to examine the relevance of mDia1 activity vis-a-vis of Rac, a small GTPase classically found to mediate axon outgrowth. A DN form of Rac, RacN17, was introduced into cerebellar granule cells along with a DA-mDia1 mutant mDia1-ΔN3. Axon elongation facilitated by DA-mDia1 in the presence of Y-27632 was repressed, in the presence of RacN17, back to baseline levels (Fig. 9 A). These findings are most consistent with the idea that Rac may significantly contribute to the mDia effect on axon outgrowth. Thus, mDia may directly regulate Rac or one of its upstream regulators.


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)

Expression of the morphological effects of mDia1 is mediated, at least in part, by Rac activity. (A) Co-expression of GFP-N17Rac, a DN mutant of Rac, suppresses expression of the facilitatory effects of FLAG-mDia1-ΔN3 on either axon length (left) in the presence of Y-27632 (50 μM) back to baseline levels. n ≈ 45–137. (B) Inhibition of ROCK activity in the presence of high concentration of SDF-1α (500 ng/ml) increases the GTP-bound form of Rac. ***P < 0.001.
© Copyright Policy
Related In: Results  -  Collection

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

fig9: Expression of the morphological effects of mDia1 is mediated, at least in part, by Rac activity. (A) Co-expression of GFP-N17Rac, a DN mutant of Rac, suppresses expression of the facilitatory effects of FLAG-mDia1-ΔN3 on either axon length (left) in the presence of Y-27632 (50 μM) back to baseline levels. n ≈ 45–137. (B) Inhibition of ROCK activity in the presence of high concentration of SDF-1α (500 ng/ml) increases the GTP-bound form of Rac. ***P < 0.001.
Mentions: We finally wanted to examine the relevance of mDia1 activity vis-a-vis of Rac, a small GTPase classically found to mediate axon outgrowth. A DN form of Rac, RacN17, was introduced into cerebellar granule cells along with a DA-mDia1 mutant mDia1-ΔN3. Axon elongation facilitated by DA-mDia1 in the presence of Y-27632 was repressed, in the presence of RacN17, back to baseline levels (Fig. 9 A). These findings are most consistent with the idea that Rac may significantly contribute to the mDia effect on axon outgrowth. Thus, mDia may directly regulate Rac or one of its upstream regulators.

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