During nervous system development, a handful of guidance cues produces a complex neuronal wiring pattern, but exactly how is unclear. Now, on p. 4491,Valérie Castellani and colleagues report that the expression of the repulsive guidance cue semaphorin 3A (Sema3A) by motoneurons sets the sensitivity of their axons to environmental semaphorin sources. Sema3A secreted by peripheral tissues interacts with neuropilin (its receptor) in the growth cones of motoneurons to control motor axon pathfinding, but Sema3A is also expressed by motoneurons themselves during axonal pathfinding. The researchers show that Sema3A overexpression in the neural tube of chick embryos induces the exuberant growth of motor axon projections through normally non-permissive tissues, but that RNAi knockdown of Sema3A in motoneurons inhibits the normal dorsal growth of these neurons. Other experiments indicate that Sema3A expression in motoneurons sets their sensitivity to exogenous Sema3A by regulating neuropilin availability at the growth cone. Thus, the interplay between intrinsic and extrinsic Sema3A may help to organize the axonal pathways of motoneurons.
Inside story on Sema3A and axonal pathfinding
Inside story on Sema3A and axonal pathfinding. Development 15 December 2007; 134 (24): e2404. doi:
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