THE ROLE OF APTEROUS IN THE CONTROL OF DORSOVENTRAL COMPARTMENTALIZATION AND PS INTEGRIN GENE-EXPRESSION IN THE DEVELOPING WING OF DROSOPHILA

During the development of Drosophila appendages from imaginal discs li neage restrictions appear that prevent dividing cells from crossing be tween regionally distinct compartments. These compartments correspond not only to regions of cell lineage restrictions but also to regions o f specific gene expression. When compartments were first discovered, i t was proposed that their formation relied on compartment-specific 'se lector' gene activity; engrailed is thought to play such a role for th e early-arising anterior-posterior restriction. Recent results suggest that the dorsally expressed transcription factor encoded by apterous may control dorsoventral identity in the wing. In this study we use mo saic analysis to show that apterous maintains the late-arising dorsove ntral lineage restriction in a manner that strongly supports the selec tor gene hypothesis: loss of apterous function from dorsal cells after the formation of the boundary causes them to cross into the ventral c ompartment. Moreover, we show that apterous plays a role controlling p atterns of gene expression in the developing wing disc. The PS1 and PS 2 integrins are normally expressed in primarily dorsal-specific and ve ntral-specific patterns, respectively. We show that ectopic expression of apterous induces ectopic ventral expression of PS1 integrin and al pha(PS1) mRNA, while loss of apterous can induce the ectopic dorsal ex pression of PS2 integrin. Thus, apterous plays a selector-like role bo th in terms of the control of lineage restrictions and the regulation of downstream gene expression.