Spatial activation and repression of the drosophila vitelline membrane gene VM32E are switched by a complex cis-regulatory system.

The VM32E gene is differently expressed in the distinct cell domains composing the follicular epithelium. Our previous work on the VM32E gene defined the promoter regions required for the control of gene expression in the ventral and dorsal follicle domains. In this report, we present data from a finer dissection of each upstream regulatory region, allowing to draw the functional interactions among different regulatory elements. A 73-bp proximal region (-112/-39) contains regulatory element(s) to dictate the activation of the gene in the follicular epithelium. This region interacts with two other cis-regulatory elements and is absolutely required for their output. The first element (-206/ -113), individually unable to raise reporter expression, elicits gene activity in the ventral domain when joined to the proximal fragment; a second element (-348/-254) joined to the same proximal fragment sustains the full dorsal and ventral activity. Moreover, the ectopic expression driven by some promoter fragments in border or posterior cells uncovers the existence of specific negative regulatory elements. So, the follicular domain specificity of VM32E gene expression is achieved through the combined activities of cell-type specific positive and negative elements.