A dying cell (center) gets squeezed out by its neighbors.


Mzacrophages can clean up the detritus of dying cells. But that, say Jody Rosenblatt, Martin Raff, and Louise Cramer (University College London, London, UK), is not the whole story. They have found that cells undergoing apoptosis in an epithelial sheet signal to their neighbors to begin squeezing, in a process that maintains the barrier function of the epithelium while extruding the dying cell. Macrophages may come along only after the dying cell is liberated from its neighbors.

Rosenblatt noticed the squeezing when she was looking at wound healing in epithelial sheets. The fate of apoptosing cells “looked very similar,” she says. In retrospect, she noticed that the literature included accounts of cell sloughing in the gut, and possible cell extrusion in developing fly embryos. “But at the most it would be one sentence in the middle of a discussion,” she says.

Rosenblatt set out to characterize the process more fully. She found that acto- myosin rings form in both the dying and surrounding cells, although only the acto-myosincontraction in the neighboring cells is necessary for extrusion. The neighboring cells are connected via cell–cell junctions so the whole contracting apparatus acts like a purse string.

Apoptotic cells added to a cell monolayer signal early (before any caspase-dependent events) to induce the acto-myosin contraction. Rosenblatt plans to use this in vitro system and the genetics of processes such as dorsal closure to search for the inducing signal. ▪


Rosenblatt, J., et al.
Curr. Biol