Editors' ChoiceAxon Guidance

Mapping the Neuronal Map

Sci. Signal.  04 Aug 2009:
Vol. 2, Issue 82, pp. ec262
DOI: 10.1126/scisignal.282ec262

In vertebrates, sensory information is topographically represented as a neural map in the brain. How is the neural map formed in the brain? Nearly a half-century ago, Roger Sperry proposed the “chemoaffinity” model, in which the positional cues on the target determine the axonal projection site, thereby establishing the topographic neural map. However, molecular mechanisms of topographic map formation remain controversial. Imai et al. (see the Perspective by Miyamichi and Luo) now report that the topographic map is formed by axon-axon interactions before the axons reach the target. In the mouse olfactory system, the topography of the map is determined by the relative expression levels of a guidance receptor, Neuropilin-1, and its repulsive ligand, Semaphorin-3A, expressed in axons. Topographic organization occurs even in the absence of the target, the olfactory bulb. These findings require that Sperry’s model, which suggests that only the targets determine the topography of neural maps, needs to be reconsidered.

T. Imai, T. Yamazaki, R. Kobayakawa, K. Kobayakawa, T. Abe, M. Suzuki, H. Sakano, Pre-target axon sorting establishes the neural map topography. Science 325, 585–590 (2009).[Abstract] [Full Text]

K. Miyamichi, L. Luo, Brain wiring by presorting axons. Science 325, 544–545 (2009).[Summary] [Full Text]