Playing a essential role in the fission of tubules that serve as transport intermediates during endosome sorting, the WASH complex is present at the surface of endosomes and functions to recruit and activate the Arp2/3 complex for induction of actin polymerization. FAM21, Putative WASH complex subunit FAM21, is a component of the WASH complex. Having undergone evolutionary duplication, four highly homologous family members exist including FAM21A, FAM21B, FAM21C and FAM21D. FAM21 links the WASH complex to endosomes and is required for WASM-dependent retromer-mediated sorting. Also, by directly interacting with CapZ, FAM21 inhibits its anti-capping activity, thereby regulating actin dynamics.