Since WASp is required for directional migration of macrophages in response to CSF-1 [16] and defects in the first peak of actin polymerization in carcinoma cells is correlated with defective directional sensing [24], we proceeded to monitor the chemotactic responses of shControl, shWASp and Y291F cells in response to a directional source of CSF-1 using a micropipette. Here, WAS is linked to carcinoma.