WINGLESS ACTS THROUGH THE SHAGGY ZESTE-WHITE-3 KINASE TO DIRECT DORSAL-VENTRAL AXIS FORMATION IN THE DROSOPHILA LEG

The secreted glycoproteins encoded by Wnt genes are thought to functio n as intercellular signaling molecules which convey positional informa tion. Localized expression of Wingless protein is required to specify the fate of ventral cells in the developing Drosophila leg. We report here that Wingless acts through inactivation of the shaggy/zeste white 3 protein kinase to specify ventral cell fate in the leg. Ectopic exp ression of Wingless outside its normal ventral domain has been shown r eorganize the dorsal-ventral axis of the leg in a non-autonomous manne r. Using genetic mosaics, we show that cells that lack shaggy/zeste wh ite 3 activity can influence the fate of neighboring cells to reorgani ze dorsal-ventral pattern in the leg, in the same manner as Wingless-e xpressing cells. Therefore, clones of cells that lack shaggy/zeste whi te 3 activity exhibit all of the organizer activity previously attribu ted to Wingless-expressing cells, but do so without expressing wingles s. We also show that the organizing activity of ventral cells depends upon the location of the clone along the dorsal-ventral axis. These fi ndings suggest that Wingless protein does not function as a morphogen in the dorsal-ventral axis of the leg.