Figure 1.

Orienting cell divisions. (A) The existence of external forces in a tissue induces internal stresses that deform cells. This deformation may then orient cells divisions. (B) In cells adhering to a substrate, experiments on isolated cells cultured on patterned substrates have shown that the rounded cell body may keep the memory of its adherent geometry through actin-rich retraction fibers, which pull on the cell cortex. (B′) Somehow, the pulling forces are transmitted to the astral microtubules, which results in orienting the mitotic spindle. (C) Observations of unperturbed embryos, as well as recent experiments in confined geometries, have highlighted how cells sense their shape to orient the mitotic spindle. (C′) The shape of cells can be sensed by astral microtubules, which extend to the cell cortex and generate a global torque and force to orient the centrosomes and nucleus, or spindle, depending on whether the alignment occurs before or after nuclear envelope breakdown.