Although both spreading and migration involve actin polymerization and protrusion, cell locomotion is complex and requires cell polarity, contraction, and deadhesion, none of which are needed for spreading. PI3K at the leading edge of a cell is important for generating PIP₃. Localized PIP₃ binds specific actin regulatory proteins and leads to F-actin assembly. PTEN is an inositol phosphatase localized at the trailing edge of the migrating cell that dephosphorylates PIP₃ into PIP₂.