Posterior-to-anterior transformation in engrailed wing imaginal disks of Drosophila

Abstract

Segments in the Drosophila adult are divided into clonally distinct anterior and posterior compartments^1–5. Mutations at the engrailed locus can affect the pattern of cuticular structures in the posterior compartments of segments, but have no obvious effect on anterior structures^4–12; for example, bristles that are normally seen only on the anterior wing margin in wild-type flies can be found on the posterior margin of engrailed wings. These and clonal analysis data led to the hypothesis that engrailed causes a transformation of posterior to anterior identity in the wing cells⁶. Despite some striking examples of this transformation, a common engrailed phenotype is the disruption or elimination of posterior pattern elements, without a clear replacement by anterior structures^8–13; this, together with indications that localized cell death can mimic some of the observed posterior-to-anterior transformations¹⁴, has led some investigators to question the original engrailed hypothesis¹². Recently, monoclonal antibodies displaying region-specific binding patterns on the wing imaginal disk have been described^15–17, and one of these antibodies in particular provides a novel probe for the engrailed phenotype in the larval precursors of the adult wing. Here I compare the antibody binding patterns on engrailed and wild-type wing disks. The results strongly support the notion that engrailed mutations cause a posterior-to-anterior transformation in these cells.