Ferreira et al. reveal how Aurora B and the microtubule plus-end binding protein EB3 coordinate cytokinesis and daughter cell adhesion at the end of mitosis.
EB3 and its relative EB1 regulate microtubule dynamics in interphase cells, but they seem to be less important during mitosis. Indeed, Ferreira et al. confirmed that, although cells lacking EB1 and EB3 had problems orienting their mitotic spindles, they passed through mitosis with little delay. EB3-deficient cells ran into trouble as they exited mitosis, however.
In the absence of EB3, the microtubules that form the midbody between separating daughter cells were unstable, causing the midbody to oscillate and partially inhibit cytokinesis. The mitotic kinase Aurora B, which concentrates at the midbody during anaphase, phosphorylated EB3 and promoted its ability to stabilize midbody microtubules.
Most cells lacking EB3 still completed cytokinesis but their daughter cells often failed to spread out and reattach to the underlying substrate. Cortical microtubules grew more in these cells, preventing them from forming stable focal adhesions. In this case, unphosphorylated EB3 was required to restrict cortical microtubule growth and promote daughter cell spreading.
The gradient of Aurora B activity that emanates from the spindle midzone therefore allows phosphorylated EB3 to regulate midbody microtubules, while unphosphorylated EB3 controls cortical microtubule dynamics. By endowing these two microtubule pools with distinct dynamics, EB3 and Aurora B allow cells to coordinate cytokinesis and daughter cell adhesion. Senior author Helder Maiato now wants to investigate how EB3’s numerous binding partners contribute to the protein’s function at different locations of the cell.
Text by Ben Short