Apoptosis is a form of programmed cell death potentially activated in all cells. This cellular process relies on the activation of a conserved pathway in which inhibitors and activators act together to precisely regulate the effector caspases which are proteases responsible for degrading the dying cell. Initially viewed as random destructors of the cell, recent evidences suggest that caspases orchestrate a sequential cellular degradation. First, they can either activate or inactivate a huge number of substrates; second, caspase cleavages lead to the appearance of stable peptides, hinting at their active role during cell death; third, a vast majority of caspase substrates are interacting proteins, indicating that caspases target specific complexes in the cell. For example, caspases specifically cleave cell adhesion components to allow a clean elimination of the dying cell. Reciprocally, loss of cell adhesion can induce cell death. This particular induction of the apoptotic pathway is called anoikis and is viewed as a secure mechanism impeding the dissemination of cells in inappropriate location and the potential development of metastasis. Furthermore, in normal conditions, anoikis is important for the turnover of epithelial cells. Here we propose to study the connection of apoptosis with cell anchorage in normal physiological conditions. Interestingly, previous data strongly suggest that apoptosis in the Drosophila leg joint is induced by a process of anoikis. The leg joint formation requires a local apoptosis witch is precede by a reorganization of cell adhesion, which strongly suggests that cells die as a consequence of cell detachment. Anoikis has been essentially studied in cultured cells, showing the importance of cell-cell and cell- matrix adhesion in the process, but its regulation in a whole tissue is mostly unexplored. The approach proposed here will allow us to bypass the limitations of other studies that rely on tissue culture experiment, where cells are selected on their capacity to survive outside their normal environment and/or in a context of artificial resistance or induction of apoptosis. Our system provides us the opportunity to study apoptosis and/or anoikis regulation in vivo in a whole organism, during the development of leg joint structure in Drosophila. We propose to analyze how apoptosis is induced in the future leg joint through three distinct and complementary approaches that will combine time-lapse experiments to follow the general shape and cellular rearrangement during the whole process of fold formation, together with a more detailed analysis of cell ultrastructural organization by electron microscopy and genetic methods to modify cell adhesion properties: 1. The first goal is to elucidate the mechanism by which two pathways known to play an essential role in leg joint formation, Dpp and Notch, trigger apoptosis non-autonomously in the future leg joint. 2. Second, we will determine the hierarchy between cell detachment and cell death in the presumptive joint. 3. To further study how cell adhesion is regulated in this morphogenetic process, we will analyze the potential function of genes involved in modification of cell adhesion during epithelial-mesenchymal transition (EMT) in leg joint formation. It is anticipated that these in vivo approaches will provide important new insights into the cellular consequences of impaired anoikis within a physiological context. This will greatly advance our understanding of how anoikis is induced, and how defects in this process affect tissue morphogenesis. Furthermore, as the acquiring of resistance towards anoikis is a major characteristic of malignant cells, this work may also identify new targets for cancer therapies.