Rac1-Mediated Endocytosis during Ephrin-A2- and Semaphorin 3A-Induced Growth Cone Collapse

Abstract

Negative guidance molecules are important for guiding the growth of axons and ultimately for determining the wiring pattern in the developing nervous system. In tissue culture, growth cones at the tips of growing axons collapse in response to negative guidance molecules, such as ephrin-A2 and semaphorin 3A. The small GTPase Rac1 is involved in growth cone collapse, but the nature of its role is not clear. Rac1 activity assays showed that Rac1 is transiently inactivated after treatment with ephrin-A2. Ephrin-induced growth cone collapse, however, correlated with resumption of Rac1 activity. We demonstrate that Rac1 is required for endocytosis of the growth cone plasma membrane and reorganization of F-actin but not for the depolymerization of F-actin during growth cone collapse in response to ephrin-A2 and semaphorin 3A. Rac1, however, does not regulate constitutive endocytosis in growth cones. These findings show that in response to negative guidance molecules, the function of Rac1 changes from promoting actin polymerization associated with axon growth to driving endocytosis of the plasma membrane, resulting in growth cone collapse. Furthermore, Rac1 antisense injected into the embryonic chick eye in vivo caused the retinotectal projection to develop without normal topography in a manner consistent with Rac1 having an obligatory role in mediating ephrin signaling.

Rac1 and RhoA Promote Neurite Outgrowth through Formation and Stabilization of Growth Cone Point Contacts

“…Although many studies have demonstrated the importance of Rac1 for axon outgrowth and guidance (Kuhn et al, 1998;Jurney et al, 2002;Ng et al, 2002;Shekerabi and Kennedy, 2002), these studies have focused on the role of Rac1 in promoting actin polymerization during leading edge protrusion and endocytosis. Here, we show that Rac1 also supports axon outgrowth by promoting point contact formation, which leads to stabilization of protrusions.…”

TUC-4b, a Novel TUC Family Variant, Regulates Neurite Outgrowth and Associates with Vesicles in the Growth Cone

“…The small GTPase Rac1 is required for growth cone collapse; however, it does not mediate actin depolymerization during collapse. Rather, Rac1 mediates endocytosis during growth cone collapse (Jin and Strittmatter, 1997;Jurney et al, 2002). Together, these data suggest that endocytosis is part of the biological mechanism that mediates the response to repulsive guidance cues.…”

“…Stimulation of growth cones by semaphorins or ephrins induces endocytosis in the growth cone (Fournier et al, 2000;Jurney et al, 2002). However, endocytosis is not stimulated by cytochalasin B, suggesting that endocytosis is not a nonspecific consequence of collapse but rather the specific result of intracellular signaling in response to guidance cues.…”

Release of MICAL Autoinhibition by Semaphorin-Plexin Signaling Promotes Interaction with Collapsin Response Mediator Protein

“…Recent work has made it clear that Sema3A signaling involves several intracellular pathways mediating a variety of cellular responses (for review, see Pasterkamp and Kolodkin, 2003). After the binding of Sema3A to the coreceptor complex consisting of members of the Plexin-A (PlexA) and neuropilin-1 (NRP1) families of proteins (He and Tessier-Lavigne, 1997;Kolodkin et al, 1997;Takahashi et al, 1999;Tamagnone et al, 1999), neuronal growth cones collapse as a result of the dramatic rearrangement of the actin cytoskeleton and endocytosis of the plasma membrane (Luo et al, 1993;Fournier et al, 2000;Jurney et al, 2002;Castellani et al, 2004). A role for Rho-like GTPases (Jin and Strittmatter, 1997;Zanata et al, 2002;Turner et al, 2004;Toyofuku et al, 2005), protein phosphorylation (Aizawa et al, 2001;Eickholt et al, 2002;Mitsui et al, 2002;Sasaki et al, 2002), RanBPM (Togashi et al, 2006), and members of the collapsin response mediator protein (CRMP) family (Goshima et al, 1995;Deo et al, 2004) have all been shown to play a role in Sema3A signal transduction.…”