One Signal for Attraction and Repulsion

Abstract

Pyramidal neurons have an asymmetric morphology with the apical dendrites oriented toward the pial (outer) surface of the cortex and the axon oriented toward the subcortical white matter (see the accompanying news and views article by Strittmatter). Axons of pyramidal neurons are directed away from a gradient of the chemorepellant Semaphorin 3A (Sema3A) acting through the Neuropilin-1 receptor. Polleux, Morrow, and Ghosh show that the same signal, Sema3A, also acts as a chemoattractant to direct the orientation of the dendrites of pyramidal neurons. Antibodies against the Neuropilin-1 receptor blocked the chemoattractive effect of Sema3A for dendrites, suggesting that chemoattraction and chemorepulsion are mediated by the same receptor. Elevation of cyclic guanosine monophosphate converts the Sema3A signal from repulsion to attraction in other systems, thus, the authors investigated whether guanylyl cyclase may be important for mediating the chemoattractive effect in pyramidal neurons. Soluble guanylyl cyclase is asymmetrically oriented with high levels at the pole of the cell where the dendrite is generated. Pharmacological inhibition of guanylyl cyclase or protein kinase G blocked oriented growth of the dendrites, but did not disrupt the oriented growth of the axons in pyramidal neurons. Thus, the same extracellular signal (Sema3A) is used for both chemoattraction and chemorepulsion via a mechanism involving asymmetric distribution of downstream signaling elements Polleux, F., Morrow, T., and Ghosh, A. (2000) Semaphorin 3A is a chemoattractant for cortical apical dendrites. Nature 404 : 567-573. [Online Journal] Strittmatter, S.M. (2000) Dendrites go up, axons go down. Nature 404 : 557-558. [Online Journal]