Most neurons have a single axon on one side of their cell body and multiple dendrites on the opposite side. The establishment of this polarisation, which is essential for neuronal function, probably involves both intrinsic and extrinsic factors. Although several intrinsic factors have been identified, the identity of the in vivo extrinsic signals remains unclear. To remedy this situation, Sarah McFarlane and co-workers (p. 2933) have been studying dendrite polarisation in Xenopus retinal ganglion cells (RGCs). They report that neuropilin-1 and plexinA1, which form a holoreceptor for members of the axon guidance family of class III secreted semaphorins (Sema3s), are necessary to bias dendrite extension to the apical side of RGCs in vivo. They report that sema3a and sema3f are expressed on the basal and apical sides of the Xenopus RGC, respectively. Moreover, ectopically expressed Sema3s and inhibition of receptor signalling disrupt dendrite polarisation. The researchers suggest that neuropilin-1 and plexinA1 are co-receptors for an extrinsic cue, probably a Sema3, that directs RGC dendrite polarisation independent of axon polarisation.
- © 2013. Published by The Company of Biologists Ltd