Semaphorin3A accelerates neuronal polarity in vitro and in its absence the orientation of DRG neuronal polarity in vivo is distorted

Axon guidance cues are critical for neuronal circuitry formation. Guidance molecules may repel or attract axons directly by effecting growth cone motility, or by impinging on neuronal polarity. In Semaphorin3A null mice. many axonal errors are detected, most prominently in DRG neurons. It has been generally assumed the repellent properties of Semaphorin3A are the cause of these erroneous axonal projections. Here we show that, in semaphorin3A-null mice, the initial trajectory of neurons in the DRG is abnormal, suggesting that Semaphorin3A may instruct neuronal polarity. In corroboration, in vitro Semaphorin3A dramatically increases neuronal polarization, as indicated by GSK3 beta and Rac1 subcellular localization in DRG neurons. Polarization effects of Semaphorin3A are regulated by activated MAPK, as indicated by p-MAPK 42/44 polarization and the need for its activity for Rac1 and GSK3 beta polarization. Taken together, our findings suggest that Semaphorin3A plays a role in the formation of neuronal polarity, in addition to its classic repellent role. (c) 2007 Elsevier Inc. All rights reserved.