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Trends Cell Biol. 2008 Dec;18(12):597-603. doi: 10.1016/j.tcb.2008.09.005. Epub 2008 Oct 24.

Axon guidance: asymmetric signaling orients polarized outgrowth.

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Department of Pathology, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, NJ 08854-5635, USA.


A network of connections is established as neural circuits form between neurons. To make these connections, neurons initiate asymmetric axon outgrowth in response to extracellular guidance cues. Within the specialized growth cones of migrating axons, F-actin and microtubules asymmetrically accumulate where an axon projects forward. Although many guidance cues, receptors and intracellular signaling components that are required for axon guidance have been identified, the means by which the asymmetry is established and maintained is unclear. Here, we discuss recent studies in invertebrate and vertebrate organisms that define a signaling module comprising UNC-6 (the Caenorhabditis elegans ortholog of netrin), UNC-40 (the C. elegans ortholog of DCC), PI3K, Rac and MIG-10 (the C. elegans ortholog of lamellipodin) and we consider how this module could establish polarized outgrowth in response to guidance cues.

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