Shrub's double life in epithelial cell division

Septate junctions (SJs) form a permeability barrier in epithelia that must be maintained when cells within the tissue divide. During cytokinesis, the nascent daughter cells maintain SJ contact with their neighbours via finger-like protrusions (FLPs) that attach to the midbody, a transient structure connecting the daughter cells. Prior to abscission, the midbody is released from the FLPs via SJ remodelling. Here, Roland Le Borgne and colleagues use fast-cycling Drosophila sensory organ precursor cells (SOPs) to explore the role of Shrub, an ESCRT-III complex component, in this process. They follow SOP cytokinesis using live imaging and show that cytoplasmic isolation (when free diffusion between the dividing daughter cells ceases) occurs before midbody release, suggesting that these two processes are decoupled. Shrub-GFP localises to the midbody and FLPs, and depleting Shrub delays midbody release and cytoplasmic isolation. By contrast, depletion of the SJ component Coracle results in these processes occurring prematurely. Intriguingly, depleting Coracle also results in increased recruitment of Shrub-GFP to FLPs, whereas depleting Shrub leads to aberrant localisation of SJ components. From their data, the authors postulate that the pool of Shrub at the midbody of the dividing cell plays a cell-autonomous role in abscission, whereas the Shrub localised at the neighbouring cell FLPs is involved in SJ remodelling.