Stuck in the divide

A contractile actin ring does most of the work during cytokinesis, but microtubule-to-membrane anchoring is also needed as two cells pinch away from each other. Tomas et al. (page 813) now show that a protein called annexin 11 may act as a bridge during this last separation event by interacting with both the microtubule-binding CHO1 kinesin-like protein and membranes.

Annexins are Ca²⁺-dependent proteins that function in a variety of cellular processes. The team finds that cells lacking annexin 11 fail to separate during division and die via apoptosis. Annexin 11–depleted cells remained joined via long thin extensions that do not resemble the functional midbodies characteristic of cells going through a normal cytokinesis. Annexin 11 and CHO1 coimmunoprecipitated and colocalized to the midbody in wild-type cells.

Annexin 11 has membrane fusogenic activity in vitro and so could be involved in the fusion of membrane vesicles at the cleavage furrow. But direct evidence for such an in vivo function is lacking, leading the authors to suspect that CHO1 and annexin 11 bring together microtubules and the cell membrane to execute the final phase of cell division. ▪