Regulating wing formation through the vestigial gene of Drosophila melanogaster

How fields of cells within an organism are patterned and assigned identities to form complex structures, such as legs and wings, is a fundamental question in developmental biology. In this thesis I have focused on the wing of the model insect Drosophila melanogaster, specifically on how genetic information for patterning this structure is interpreted at the DNA level to determine an appendage's identity. The wing-specific gene vestigial is necessary for wing formation, since loss of vestigial results in loss of wings. I ectopically expressed this gene in the developing fly and found that Vestigial is capable of transdetermining other imaginal-disc-derived tissues---such as legs, eyes, antennae, and genitalia---to wing tissue. Mis-regulation of vestigial has a dramatic and specific effect on fly development, suggesting that vestigial is central to determining wing identity. The proper regulation of this gene is therefore an essential feature of the fly's wing developmental pathway. vestigial is expressed in the wing under the control of two complementary cis regulatory elements. I investigated the regulation of vestigial through one of these elements: the quadrant enhancer (vgQ). By examining the expression patterns of a series of deletion reporter constructs, I learned that vgQ requires at least two positive regulatory inputs, in addition to the known input of Decapentaplegic (Dpp) through its effector protein Mad. No direct negative regulatory inputs were discovered. A combination of genetic and biochemical data suggests that the direct regulatory inputs into vgQ are Dpp through Mad, Vestigial itself, through the Vestigial/Scalloped complex, and the Drifter POU domain protein. Other genetic inputs, such as Notch and wingless, appear to be indirect, i.e. not through direct binding of their nuclear effector protein to the vg Q DNA.