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. Author manuscript; available in PMC: 2009 Aug 12.
Published in final edited form as: Curr Opin Neurobiol. 2009 May 27;19(2):174–180. doi: 10.1016/j.conb.2009.04.011

Figure 1.

Figure 1

Topographic map formation in Drosophila. Map formation along the antero-posterior axis is driven by a precise temporal sequence of differentiation, extension, and induction. Photoreceptors differentiate following a wave that begins first at the posterior edge of the retina and spreads anteriorly. They then extend their axons into the lamina following their birth order and induce the differentiation and assembly of target neurons into a columnar array. As each incoming bundle of photoreceptor axons induces its own target column, the number of target columns is precisely matched to the number of photoreceptors that differentiation, and map formation along the A-P axis is ensured by the precise sequence of differentiation in the retina. Dwnt4 is expressed in the ventral lamina, and is regulates dorso-ventral R cell projections.