Tension at intercellular junctions is necessary for accurate orientation of cell division in the epithelium plane

In growing epithelia, divisions are typically oriented in the epithelial plane to drive tissue expansion. In some organs, divisions are then re-oriented so that they occur perpendicular to the epithelium plane to drive tissue stratification and cell differentiation. When uncontrolled, this switch in orientation can lead to defects in tissue organisation and, in the context of cancer, has been suggested to contribute to metastasis. While much is known about the molecular machinery guiding mitotic spindle orientation, less is known about the role of mechanical factors in this process. Here, we use mechanical and chemical perturbations to show that mechanics plays a role in controlling the plane of division. Overall, our data suggest that the orientation of spindles in the epithelium plane requires a threshold level of mechanical tension at intercellular junctions.