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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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SDF-1α–induced axon elongation is antagonized by ROCK. 12-h exposure to high concentration (500 ng/ml) of SDF-1α represses axonogenesis (A, top, and B, right). Addition of 50 μM Y-27632, a specific ROCK inhibitor, blocked this SDF-1α–induced inhibition of axonogenesis (A, bottom, and B, right). Under the same condition, SDF-1α significantly facilitated axon elongation in ROCK-inhibited neurons (B, left), while having little effect on axon numbers (B, right). n ≈ 82–74. ***Compared with untreated cells or ###compared with Y-27632-treated cells; P < 0.001. Bars, 5 μm.
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fig3: SDF-1α–induced axon elongation is antagonized by ROCK. 12-h exposure to high concentration (500 ng/ml) of SDF-1α represses axonogenesis (A, top, and B, right). Addition of 50 μM Y-27632, a specific ROCK inhibitor, blocked this SDF-1α–induced inhibition of axonogenesis (A, bottom, and B, right). Under the same condition, SDF-1α significantly facilitated axon elongation in ROCK-inhibited neurons (B, left), while having little effect on axon numbers (B, right). n ≈ 82–74. ***Compared with untreated cells or ###compared with Y-27632-treated cells; P < 0.001. Bars, 5 μm.

Mentions: What are these two Rho effectors? The finding that SDF-1α seemed to antagonize axonogenesis at higher doses in a Rho-dependent manner (Fig. 1 B) was in keeping with our previous finding that Rho/ROCK signaling critically regulates axon numbers (Bito et al., 2000). To test whether ROCK, a Rho-associated kinase (Narumiya et al., 1997; Bito et al., 2000; Ishizaki et al., 2000), was indeed mediating the SDF-1α effect, we bath-applied 50 μM Y-27632, a potent and selective ROCK inhibitor (Uehata et al., 1997; Ishizaki et al., 2000). As expected, treatment with Y-27632 reversed the negative SDF-1α effect on axon numbers, indicating that SDF-1α is indeed able to activate ROCK (Fig. 3, A and B) . Surprisingly, however, exposure to SDF-1α in the presence of the ROCK inhibitor now resulted in a significant net increase in axon extension (Fig. 3, A and B). Thus, SDF-1α activated a novel ROCK-independent, yet C3-sensitive, effector pathway that was coupled to axon elongation.


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)

SDF-1α–induced axon elongation is antagonized by ROCK. 12-h exposure to high concentration (500 ng/ml) of SDF-1α represses axonogenesis (A, top, and B, right). Addition of 50 μM Y-27632, a specific ROCK inhibitor, blocked this SDF-1α–induced inhibition of axonogenesis (A, bottom, and B, right). Under the same condition, SDF-1α significantly facilitated axon elongation in ROCK-inhibited neurons (B, left), while having little effect on axon numbers (B, right). n ≈ 82–74. ***Compared with untreated cells or ###compared with Y-27632-treated cells; P < 0.001. Bars, 5 μm.
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Related In: Results  -  Collection

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fig3: SDF-1α–induced axon elongation is antagonized by ROCK. 12-h exposure to high concentration (500 ng/ml) of SDF-1α represses axonogenesis (A, top, and B, right). Addition of 50 μM Y-27632, a specific ROCK inhibitor, blocked this SDF-1α–induced inhibition of axonogenesis (A, bottom, and B, right). Under the same condition, SDF-1α significantly facilitated axon elongation in ROCK-inhibited neurons (B, left), while having little effect on axon numbers (B, right). n ≈ 82–74. ***Compared with untreated cells or ###compared with Y-27632-treated cells; P < 0.001. Bars, 5 μm.
Mentions: What are these two Rho effectors? The finding that SDF-1α seemed to antagonize axonogenesis at higher doses in a Rho-dependent manner (Fig. 1 B) was in keeping with our previous finding that Rho/ROCK signaling critically regulates axon numbers (Bito et al., 2000). To test whether ROCK, a Rho-associated kinase (Narumiya et al., 1997; Bito et al., 2000; Ishizaki et al., 2000), was indeed mediating the SDF-1α effect, we bath-applied 50 μM Y-27632, a potent and selective ROCK inhibitor (Uehata et al., 1997; Ishizaki et al., 2000). As expected, treatment with Y-27632 reversed the negative SDF-1α effect on axon numbers, indicating that SDF-1α is indeed able to activate ROCK (Fig. 3, A and B) . Surprisingly, however, exposure to SDF-1α in the presence of the ROCK inhibitor now resulted in a significant net increase in axon extension (Fig. 3, A and B). Thus, SDF-1α activated a novel ROCK-independent, yet C3-sensitive, effector pathway that was coupled to axon elongation.

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
Related in: MedlinePlus