PATTERN-FORMATION IN THE VISUAL CENTERS OF THE DROSOPHILA BRAIN - WINGLESS ACTS VIA DECAPENTAPLEGIC TO SPECIFY THE DORSOVENTRAL AXIS

A stepwise morphogenetic program of cell division and cell fate determ ination generates the precise neuronal architecture of the visual cent ers of the Drosophila brain. Here, we show that the assembly of the ta rget structure for ingrowing retinal axons involves cell-cell interact ions mediated by the secreted product of the wingless (wg) gene. wg, e xpressed in two symmetrical domains of the developing brain, is requir ed to induce and maintain the expression of the secreted decapentapleg ic (dpp) gene product in adjacent domains. wg and dpp function are req uired for target field neurons to adapt their proper fates and to send axons into the developing target structure. These observations implic ate a cascade of diffusible signaling molecules in patterning the visu al centers of the Drosophila brain.