I propose to analyze how epithelial cell shape is controlled, using the Drosophila peripodial membrane as a model system. Drosophila third instar imaginal discs are a composed of two contiguous layers of cells of distinct morphology: a pseudostratified one, called the proper epithelium (PE), and a squamous epithelium, the peripodial membrane (PM). While the PE has been deeply studied, little is known about the PM. The peripodial membrane has the ability to change its shape in response to ecdysone; it is proposed that this change is responsible for the eversion of the disc during metamorphosis. I propose to study the control of cell shape in the PM by two perspectives. First, I will look for the factors involved in specifying and maintaining the shape of the PM cells. Second, I will examine the dynamic process of disc eversion, and analyse what shape changes the cells undergo, and what factors and cellular rearrangements are responsible for this fundamental morphological process. For this purpose I have developed a technique that allows me to watch dissected live discs, and to follow the eversion in vitro using confocal live imaging. Amongst other mechanisms, I am currently analysing the role of myosin II in this process as well as looking for new factors that may be involved.