The mechanisms that regulate cell shape are poorly understood, in part because of the limitations of existing experimental models that do not allow for the study of dynamic cellular responses in real time. In this paper, Jean Castillo-Badillo and N. Gautam (Castillo-Badillo and Gautam, 2021) use optogenetic technology to activate RhoA in the centre of mononucleated macrophages, which induces cell shape changes that are associated with cleavage furrow formation. As the cell changes shape, the nucleus is pushed to one side of the cell, while the other side collapses without the mechanical support provided by the nucleus. The non-nucleated side provides a model system for studying how two effectors of RhoA, focal adhesion kinase (FAK) and fascin, an actin-bundling protein, contribute to the maintenance of cell shape in the absence of nuclear support. The authors show that cells overexpressing FAK maintain the adhesion area and are thus able to maintain the furrow – these cells have a similar nucleated and non-nucleated side, although the non-nucleated side is flatter. Fascin, however, regulates the height of the cell by conferring rigidity to the cytoskeleton. Interestingly, it is shown that FAK and fascin must work in conjunction to induce and maintain cell shape changes, and function downstream of RhoA. These data are the first demonstration of how FAK and fascin contribute to regulating cell shape and highlight how optogenetic technology can help to address long-standing questions.