sentences:  Cortactin-assisted Arp2/3-nucleated actin branches are most prominent in the actin cortex, around the periphery of the cell.A phosphorylated cortactin monomer binds to, activates, and stabilizes an Arp2/3 complex on preexisting F-actin, which provides a nucleation site for a new actin branch to form from the “mother” filament.Branches formed from cortactin-assisted nucleation sites are very stable; cortactin has been shown to inhibit debranching.