INTERACTION BETWEEN DORSAL AND VENTRAL CELLS IN THE IMAGINAL DISC DIRECTS WING DEVELOPMENT IN DROSOPHILA

The adult appendages of Drosophila develop from imaginal discs. An ear ly step in disc patterning involves the formation of developmental bou ndaries that subdivide the discs into compartments. Anterior and poste rior compartments are established in the embryo. Later in development a new boundary originates to subdivide the wing disc into dorsal and v entral compartments, which correspond to the dorsal and ventral surfac es of the adult wing. We report here that spatially localized expressi on of the homeobox gene apterous (ap) specifies the identity of dorsal cells in the wing. The boundary of cell lineage restriction between d orsal and ventral compartments coincides with the limit of the domain of ap expression. Using genetic mosaics, we show that juxtaposition of dorsal and ventral cells induces formation of the wing margin. We pre sent evidence that the dorsal-ventral boundary promotes growth and ser ves as a pattern-organizing center in the wing disc.