The shape, size, and architecture of the nucleus determines the output of transcriptional programmes. As such, the ability of the nucleus to resist deformation and maintain its shape is essential for homeostasis. Conversely, changes in nuclear shape can alter transcription and cell state. The ability of cells to deform their nuclei is also essential for cells to invade confined spaces. But how cells set the extent of nuclear deformability in response to their environment is unclear. Here we show that the cell-cell adhesion protein JAM3 regulates nuclear shape. In epithelial cells, JAM3 is required for maintenance of nuclear shape by organizing microtubule polymers and promoting LMNA stabilization in the nuclear membrane. Depletion of JAM3 in normal epithelial cells leads to dysmorphic nuclei, which leads to differentiation into a mesenchymal-like state. Inhibiting the actions of kinesins in JAM3 depleted cells restores nuclear morphology and prevents differentiation into the mesenchymal-like state. Critically, JAM3 expression is predictive of disease progression. Thus JAM3 is a molecule which allows cells to control cell fates in response to the presence of neighbouring cells by tuning the extent of nuclear deformability.

The cell-cell adhesion protein JAM3 determines nuclear deformability by regulating microtubule organization