g., Feng et al., 2004 and Benzing et al., 2000). Therefore, our results suggest a model ( Figure 10) in which Sema/Plex interactions activate PlexA GAP activity, which inactivates Ras/Rap and disables Integrin-mediated adhesion. However, these Sema/Plex-mediated effects are subject to regulation, such that increasing cAMP levels activates PlexA-bound PKA to phosphorylate PlexA and provide a binding site for 14-3-3ε. These PlexA-14-3-3ε interactions occlude PlexA GAP-mediated inactivation of Ras family GTPases and restore Integrin-dependent adhesion.

In conclusion, we have identified a simple mechanism that allows multiple axon guidance signals to be incorporated during axon guidance. Neuronal growth cones encounter both Selleckchem EPZ 6438 attractive and repulsive guidance cues but the molecular pathways and biochemical mechanisms that integrate these antagonistic cues and enable a discrete steering event are incompletely understood. One way in which to integrate these disparate signals is to allow different axon guidance receptors to directly modulate each other’s function (e.g., Stein and Tessier-Lavigne, 2001). Another means is to tightly regulate the cell surface expression of specific receptors and thereby actively prevent axons from seeing certain guidance cues (e.g., Kidd et al., 1998, Brittis

et al., 2002, Keleman et al., 2002, Nawabi et al., 2010, Chen et al., 2008 and Yang et al., 2009). Still further results are not simply explained by relatively slow modulatory mechanisms like receptor trafficking, endocytosis, and local protein synthesis but indicate that interpreting a particular guidance cue is susceptible to rapid Cyclopamine intracellular modulation by other, distinct, signaling pathways (e.g., Song et al., 1998, Dontchev and Letourneau, 2002, Terman and Kolodkin, 2004, Parra and Zou, 2010 and Xu et al., 2010). Our results now indicate a means to allow

for such intracellular signaling crosstalk events and present a logic by which axon guidance signaling pathways override one another. Given this molecular link between such key regulators of axon pathfinding as cyclic nucleotides, phosphorylation, and GTPases, our observations on silencing Sema/Plex-mediated repulsive axon guidance also suggest approaches to neutralize axonal growth inhibition Parvulin and encourage axon regeneration. Yeast two-hybrid setup, protein expression analyses, and screening were performed following standard procedures (Terman et al., 2002). Drosophila husbandry, genetics, imaging, and characterization of axon guidance were performed using standard methods ( Terman et al., 2002 and Hung et al., 2010). GST pull-down (Oinuma et al., 2004) and coimmunoprecipitation (Terman et al., 2002) assays were performed using standard approaches. GDP and GTPγS-preloading was assessed by GST pull-down assays using GST-RBD proteins (Diekmann and Hall, 1995 and Benard et al., 1999).