Whether chromatin stretching and decondensing by physiological forces affects gene expression is unclear. Tajik et al. used 3D magnetic twisting cytometry to apply force to chromatin in Chinese hamster ovary cells carrying a genomic insertion of an array of DHFR genes. Each DHFR gene contained lac-operator repeats that, when bound by GFP–lac repressors, enabled visualization of chromatin stretching as increased distance between GFP spots. Applying local shear stresses to focal adhesions on the cell surface induced chromatin stretching, depending on the angle (directionality) of the force. Chromatin stretching induced DHFR expression within seconds, measured by mRNA FISH, as well as the expression of a tested endogenous gene. Force transmission to chromatin depended on cytoskeletal tension, the LINC (linker of nucleoskeleton and cytoskeleton) complex and the nuclear lamina.