The social life of a mast cell: inter and extracellular networking shape mast cell responses

To fulfill their many tasks as cells of the immune system, mast cells respond to multiple inflammatory stimuli. The latter include chemokines, that trigger mast cell migration to sites of inflammation, and secretagogues, that stimulate mast cell degranulation leading to the release of a variety of inflammatory mediators by regulated exocytosis. Mast cells display remarkable plasticity, whereby their diverse responses are highly coordinated and stimulus dependent. The precise mechanisms responsible for the coordination of mast cell responses and defining their mode of degranulation are still only partially resolved. Here we present evidence for the role of the actin skeleton in coordinating mast cell migration and degranulation. We identify mDia1, a member of the formin family of actin binding proteins, as a novel regulator of mast cell responses that coordinates mast cell chemotaxis and secretion through its actin nucleating activity.