Dynamic actin polymerization drives a variety of morphogenetic events during metazoan development. Members of the WASP/WAVE protein family are central nucleation-promoting factors. They are embedded within regulatory networks of macromolecular complexes controlling Arp2/3-mediated actin nucleation in time and space. WAVE (Wiskott-Aldrich syndrome protein family verprolin-homologous protein) proteins are found in a conserved pentameric heterocomplex that contains Abi, Kette/Nap1, Sra-1/CYFIP, and HSPC300. Formation of the WAVE complex contributes to the localization, activity, and stability of the various WAVE proteins. Here, we established the Bimolecular Fluorescence Complementation (BiFC) technique in Drosophila to determine the subcellular localization of the WAVE complex in living flies. Using different split-YFP combinations, we are able to visualize the formation of the WAVE-Abi complex in vivo. We found that WAVE also forms dimers that are capable of forming higher order clusters with endogenous WAVE complex components. The N-terminal WAVE homology domain (WHD) of the WAVE protein mediates both WAVE-Abi and WAVE-WAVE interactions. Detailed localization analyses show that formation of WAVE complexes specifically takes place at basal cell compartments promoting actin polymerization. In the wing epithelium, hetero-and homooligomeric WAVE complexes co-localize with Integrin and Talin suggesting a role in integrin-mediated cell adhesion. RNAi mediated suppression of single components of the WAVE and the Arp2/3 complex in the wing further suggests that WAVE-dependent Arp2/3-mediated actin nucleation is important for the maintenance of stable integrin junctions.Many biological processes are controlled by networks of interacting proteins organized in macromolecular complexes. Members of the WASP/WAVE 2 protein family are found to be part of such macromolecular complexes coordinating Arp2/3-mediated actin polymerization in time and space (1). Purification of these multiprotein complexes and studies of the underlying protein interactions in vitro have led to significant advances in our understanding of how these molecular machines control actin nucleation. WAVE proteins are found in a pentameric heterocomplex that contains Abi, Kette/ Nap1, Sra-1/CYFIP, and HSPC300 (2). The interactions within the complex are mediated by direct protein-protein interactions (3-6). The central subunit of the WAVE complex represents the Abelson interactor Abi, which directly binds WAVE, HSPC300, and Kette/Nap1 through different domains. Sra-1 is a peripheral subunit recruited by Kette/ Nap1 and links the complex to Rac1 signaling. The WAVE complex is essential for the localization, activity, and stability of the various WAVE proteins (5, 7-11).However, purification and reconstitution experiments are based on the removal of the interacting proteins from their endogenous cellular context. To visualize WAVE complex formation in living flies we established the bimolecular fluorescence complementation (BiFC) technique in Drosophila. The Bi...