Filopodia numbers impact chemotactic migration speed

Summary Migrating cells sense and respond to external chemical and physical cues, enabling them to efficiently reach their destinations. Filopodia are slender actin-filled membrane protrusions implicated in interacting with the extracellular environment in many contexts, such as neuronal growth cone guidance and the capture of prey by immune cells and unicellular organisms. The role of filopodia in chemotactic guidance in fast-moving amoeboid cells has not been well-studied. The social amoeba Dictyostelium relies on chemotaxis for development and finding food, making it an excellent system for investigating the role of filopodia in amoeboid chemotaxis. Stimulation of amoebae with the chemoattractant cAMP activates a transient increase of filopodia formation by recruiting the filopodial myosin DdMyo7 to the cell cortex. Filopodia formation is biased towards the source of chemoattractant, yet myo7 null cells that lack filopodia exhibit normal directional migration. However, cells either lacking filopodia or having increased numbers of filopodia move more slowly than those with wildtype numbers of filopodia. Thus, while filopodia are dispensable for detection of chemical gradients by amoeboid cells, changes in filopodia number can impact their migration speed possibly due to altering cell-substrate adhesion. In brief Filopodia formation in chemotactic amoeboid cells is stimulated by chemoattractant and biased towards the gradient source. Lack of filopodia does not impair directed migration but rather reduces cell speed. Changes in filopodia number correlate with the speed of chemotactic cells suggesting a role for these extension in tuning adhesion for optimal migration. Highlights Filopodia formation in chemotactic amoeboid cells is biased towards the source of the gradient. Chemotactic Dictyostelium amoebae lacking filopodia migrate with directional persistence. Migration speed is altered by filopodia number.