Phagocytosis: Rac and roll over the corpses

Programmed cell death or apoptosis plays a fundamental role during animal development and metamorphosis, and in tissue homeostasis in the adult. This process comprises two distinct and sequential steps: the death of cells and their subsequent removal by phagocytosis. Removing excess cells before lysis allows cell numbers to be regulated without the release of potentially toxic intracellular contents, thereby preserving tissue integrity and function. Uptake of apoptotic cells is performed either by neighbouring mesenchymal or epithelial cells or by specialized, highly motile phagocytes. Recent findings in the nematode Caenorhabditis elegans, an organism with no specialized phagocytes, reveal intriguing mechanistic similarities between apoptotic cell uptake and the pathfinding process that occurs during a particular form of cellular migration. The same molecular actors influence these two independent processes, and their mammalian homologs — Rac1, DOCK180 and CrkII — are known regulators of cell motility and integrin signaling.