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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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A DN mDia1 mutant interferes with SDF-1α–dependent axon elongation. (A) Coexpression of the GFP-mDia1-ΔN3(HindIII) mutant abolished the effect of FLAG-mDia1-ΔN3 expression on axon length (left). n ≈ 33–80. (B and C) The effect of GFP-mDia1-ΔN3(HindIII) overexpression was examined on SDF-1α–facilitated axon elongation in the presence of Y-27632. A potent inhibition on both SDF-1α–dependent axon elongation (B and C, left) and axon initiation (B and C, right) was detected. n ≈ 35–145. Bars, 5 μm.
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fig7: A DN mDia1 mutant interferes with SDF-1α–dependent axon elongation. (A) Coexpression of the GFP-mDia1-ΔN3(HindIII) mutant abolished the effect of FLAG-mDia1-ΔN3 expression on axon length (left). n ≈ 33–80. (B and C) The effect of GFP-mDia1-ΔN3(HindIII) overexpression was examined on SDF-1α–facilitated axon elongation in the presence of Y-27632. A potent inhibition on both SDF-1α–dependent axon elongation (B and C, left) and axon initiation (B and C, right) was detected. n ≈ 35–145. Bars, 5 μm.

Mentions: We next examined the contribution of endogenous mDia1 on SDF-1α–stimulated axon elongation by use of a dominant-negative (DN) form of mDia1, mDia1-ΔN3(HindIII) (Fig. 4 A; Tsuji et al., 2002). This mutant was able to abolish the effect of DA-mDia1 on axon length (Fig. 7 A). DN-mDia1 also inhibited axon numbers back to baseline levels (Fig. 7 A); however, since DA-mDia1 had little effect per se (Fig. 6 D), we currently favor the simplest view that rather than acting on the axonogenesis itself, mDia's axon elongating activity may be required in order to visualize even the smallest process. Consistently, when this DN mutant was transfected in neurons stimulated with SDF-1α in the presence of Y-27632, both axon number and axon length were significantly diminished (Fig. 7, B and C). Together, these results support the notion that axon elongation induced by SDF-1α may be regulated in an mDia-dependent manner.


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)

A DN mDia1 mutant interferes with SDF-1α–dependent axon elongation. (A) Coexpression of the GFP-mDia1-ΔN3(HindIII) mutant abolished the effect of FLAG-mDia1-ΔN3 expression on axon length (left). n ≈ 33–80. (B and C) The effect of GFP-mDia1-ΔN3(HindIII) overexpression was examined on SDF-1α–facilitated axon elongation in the presence of Y-27632. A potent inhibition on both SDF-1α–dependent axon elongation (B and C, left) and axon initiation (B and C, right) was detected. n ≈ 35–145. Bars, 5 μm.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2172896&req=5

fig7: A DN mDia1 mutant interferes with SDF-1α–dependent axon elongation. (A) Coexpression of the GFP-mDia1-ΔN3(HindIII) mutant abolished the effect of FLAG-mDia1-ΔN3 expression on axon length (left). n ≈ 33–80. (B and C) The effect of GFP-mDia1-ΔN3(HindIII) overexpression was examined on SDF-1α–facilitated axon elongation in the presence of Y-27632. A potent inhibition on both SDF-1α–dependent axon elongation (B and C, left) and axon initiation (B and C, right) was detected. n ≈ 35–145. Bars, 5 μm.
Mentions: We next examined the contribution of endogenous mDia1 on SDF-1α–stimulated axon elongation by use of a dominant-negative (DN) form of mDia1, mDia1-ΔN3(HindIII) (Fig. 4 A; Tsuji et al., 2002). This mutant was able to abolish the effect of DA-mDia1 on axon length (Fig. 7 A). DN-mDia1 also inhibited axon numbers back to baseline levels (Fig. 7 A); however, since DA-mDia1 had little effect per se (Fig. 6 D), we currently favor the simplest view that rather than acting on the axonogenesis itself, mDia's axon elongating activity may be required in order to visualize even the smallest process. Consistently, when this DN mutant was transfected in neurons stimulated with SDF-1α in the presence of Y-27632, both axon number and axon length were significantly diminished (Fig. 7, B and C). Together, these results support the notion that axon elongation induced by SDF-1α may be regulated in an mDia-dependent manner.

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