Actin-binding protein that regulates actin polymerization, filopodia dynamics and increases the branching of proximal dendrites of developing neurons. Interacts with F-actin (By similarity). Interacts with G-actin (By similarity). Localizes to somata and dendrites in cortical neurons (By similarity). Colocalizes with F- and G-actin in lamellipodia (By similarity). Colocalizes in the nucleus with PTK2 (By similarity). The name derives from simia, latin, a female ape, and M, A, T and E, the first four amino acids of the ape orthologs. Belongs to the ABITRAM family.