COMPARTMENTS, WINGLESS AND ENGRAILED - PATTERNING THE VENTRAL EPIDERMIS OF DROSOPHILA EMBRYOS

Recent experiments on the wing disc of Drosophila have shown that cell s at the interface between the anterior and posterior compartments dri ve pattern formation by becoming the source of a morphogen, Here we as k whether this model applies to the ventral embryonic epidermis, First , we show that interfaces between posterior (engrailed ON) and anterio r (engrailed OFF) cells are required for pattern formation, Second, we provide evidence that Wingless could play the role of the morphogen, at least within part of the segmental pattern. We looked at the cuticu lar structures that develop after different levels of uniform Wingless activity are added back to unsegmented embryos (wingless(-) engrailed (-)). Because it is rich in landmarks, the T1 segment is a good region to analyse, There, we find that the cuticle formed depends on the amo unt of added Wingless activity, For example, a high concentration of W ingless gives the cuticle elements normally found near the top of the presumed gradient. Unsegmented embryos are much shorter than wild type . If Wingless activity is added in stripes, the embryos are longer tha n if it is added uniformly, We suggest that the Wingless gradient land scape affects the size of the embryo, so that steep slopes would allow cells to survive and divide, while an even distribution of morphogen would promote cell death, Supporting the hypothesis that Wingless acts as a morphogen, we find that these stripes affect, at a distance, the type of cuticle formed and the planar polarity of the cells.