Correct positioning of the nucleus is essential for several cell and tissue functions, such as cell migration, division and development. Microtubule motors, the actomyosin network and intermediate filaments all exert forces on the nucleus to ensure proper nuclear localisation; however, whether the net force on the nuclear surface is tensile or compressive has remained unclear. Now, in their work on page , Tanmay Lele and colleagues performed traction-force microscopy analyses of NIH 3T3 fibroblasts cells and of cells, in which the nucleus had been uncoupled from the cytoskeleton by perturbation of the linker of nucleoskeleton-to-cytoskeleton (LINC)-complex. They first showed that the nucleus in migrating fibroblasts localises to the centre point of the traction-force balance, called the point of maximum tension (PMT). This localisation depended on the LINC complex as its disruption led to nuclei lagging behind the PMT by several microns. The authors then measured the traction forces in protruding and retracting cells, which – together – suggest that the nucleus propagates the tensile forces that are transmitted through pulling forces exerted by the cytoskeleton across the length of the cell during migration. This is in contrast to the previously held view that the nucleus is positioned by compressive or shear force and this study, therefore, provides important new insights into the mechanical principles underlying nuclear positioning.
