IN MOUSE-BRAIN PROFILIN-I AND PROFILIN-II ASSOCIATE WITH REGULATORS OF THE ENDOCYTIC PATHWAY AND ACTIN ASSEMBLY

Profilins are thought to be essential for regulation of actin assembly , However, the functions of profilins in mammalian tissues are not wel l understood, In mice profilin I is expressed ubiquitously while profi lin II is expressed at high levels only in brain, In extracts from mou se brain, profilin I and profilin II can form complexes with regulator s of endocytosis, synaptic vesicle recycling and actin assembly, Using mass spectrometry and database searching we characterized a number of ligands for profilin I and profilin II from mouse brain extracts incl uding dynamin I, clathrin, synapsin, Rho-associated coiled-coil kinase , the Rac-associated protein NAP1 and a member of the NSF/sec18 family , In vivo, profilins co-localize with dynamin I and synapsin in axonal and dendritic processes, Our findings strongly suggest that in brain profilin I and profilin II complexes link the actin cytoskeleton and e ndocytic membrane how directing actin and clathrin assembly to distinc t membrane domains.