A protein trap insertion using a yellow fluorescent protein (YFP) tag was used to observe dpy protein expression in the larval imaginal discs and in pupae. In the imaginal discs, dpy is found in a dense meshwork covering the apical surface of the epithelium. It is more restricted in the pupal wing. At the onset of hinge contraction (18 hr APF), it is restricted to the wing margin and along the trajectories of wing veins L3 and L5. It is also observed at the extreme distal tips of the pupal legs and antennae. As tissue contraction proceeds, dpy expression occurs uniformly over the apical surface of epithelium.