Downstream effector molecule involved in the transmission of signals from tyrosine kinase receptors and small GTPases to the actin cytoskeleton. Promotes formation of actin filaments. Part of the WAVE complex that regulates lamellipodia formation (PubMed:29961568). The WAVE complex regulates actin filament reorganization via its interaction with the Arp2/3 complex (By similarity). As component of the WAVE1 complex, required for BDNF-NTRK2 endocytic trafficking and signaling from early endosomes (By similarity). Also involved in the regulation of mitochondrial dynamics (PubMed:29961568). {ECO:0000250|UniProtKB:Q8R5H6, ECO:0000269|PubMed:29961568, ECO:0000269|PubMed:9889097}. This is the function of WASF1 (WASP family member 1, Ensembl gene identifier ENSG00000112290).