The wingless signalling pathway and the patterning of the wing margin in Drosophila.

The margin of the wing of Drosophila is defined and patterned from a stripe of cells expressing the wingless (wg) gene that is established during the third larval instar in the developing wing blade. The expression of the genes cut and achaete in a small domain in the prospective wing margin region reflects the activity of wg and probably mediate its function. Our results indicate that, in the wing margin, the wingless signal requires the activity of at least three genes: armadillo (arm), dishevelled (dsh) and shaggy (sgg) and that the functional relationship between these genes and wg is the same as that which exist during the patterning of the larval epidermis. These observations indicate that arm, dsh and sgg encode elements of a unique 'wingless signalling pathway' that is used several times throughout development.