POSITIVE AND NEGATIVE CONTROL OF SERRATE EXPRESSION DURING EARLY DEVELOPMENT OF THE DROSOPHILA WING

The product of the Drosophila gene Serrate acts as a short-range signa l during wing development to induce the organising centre at the dorsa l/ventral compartment boundary, from which growth and patterning of th e wing is controlled. Regulatory elements reflecting the early Serrate expression in the dorsal compartment of the wing disc have recently b een confined to a genomic fragment in the 5'-upstream region of the ge ne. Here we present data to suggest that this fragment responds to var ious positive and negative inputs required for the early Serrate expre ssion. First, activation and maintenance of expression in the dorsal c ompartment of the wing discs of second and early third instar larvae d epends on apterous, as revealed by reporter gene expression in discs e ither lacking or ectopically expressing apterous. Second, transcriptio nal downregulation during third larval instar is mediated by hiiragi. Finally, this regulatory element responds to Delta signalling in a non autonomous way to maintain Serrate expression along the dorsal margin. The results clearly show that some of the previously described transa ctivators of Serrate protein expression, e.g. fringe, act on elements required for later aspects of Serrate expression (C) 1998 Elsevier Sci ence Ireland Ltd. All rights reserved.