Girdin controls the pace of 3D tracheal cell intercalation by coupling adherens junctions to the actin cytoskeleton in <i>Drosophila</i>

Morphogenesis is orchestrated through coordinated cell movements, including cell intercalation, which drives extensive changes in cell shape and position. This process requires precise regulation of interactions between adherens junctions (AJs) and the cortical actin network to generate the necessary mechanical forces. Although the Myosin molecular motor II plays a central role in generating morphogenetic forces, it is dispensable for processes such as dorsal branch morphogenesis in the Drosophila tracheal system, where coordinated cell migration and three-dimensional intercalation rely on alternative, yet poorly characterised mechanisms of force generation. Here, we show that Vinculin and Ajuba LIM protein, two key regulators of mechano-transduction and cell adhesion, do not localise to AJs of dorsal branches, while the cytoskeletal adaptor Girdin does. We demonstrate that the function of Girdin relies on AJ components α-Catenin and E-Cadherin, and is specifically required in tracheal cells to ensure the proper pace of cell intercalation. In addition, Girdin contributes to the actin network enrichment at AJs. Its role as an integral AJ component is further elucidated through the development of a novel genetic tool that enables in vivo cell-specific actin depolymerisation.