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Updated: Jul 11, 2026

Use of pHluorin to Assess the Dynamics of Axon Guidance Receptors in Cell Culture and in the Chick Embryo
Published on: January 12, 2014
Plexin B mediates axon guidance in Drosophila by simultaneously inhibiting active Rac and enhancing RhoA signaling
H Hu1, T F Marton, C S Goodman
1Howard Hughes Medical Institute, Division of Neurobiology, Department of Molecular and Cell Biology, 519 LSA, University of California, Berkeley, CA 94720, USA.
Abstract:
Plexins are neuronal receptors for the repulsive axon guidance molecule Semaphorins. Previous studies showed that Plexin B (PlexB) binds directly to the active, GTP-bound form of the Rac GTPase. Here, we define a seven amino acid sequence in PlexB required for Rac(GTP) binding. The interaction of PlexB with Rac(GTP) is necessary for Plexin-mediated axon guidance in vivo. A different region of PlexB binds to RhoA. Dosage-sensitive genetic interactions suggest that PlexB suppresses Rac activity and enhances RhoA activity. Biochemical evidence indicates that PlexB sequesters Rac(GTP) from its downstream effector PAK. These results suggest a model whereby PlexB mediates repulsion by coordinately regulating two small GTPases in opposite directions: PlexB binds to Rac(GTP) and downregulates its output by blocking its access to PAK and, at the same time, binds to and increases the output of RhoA.
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