Mediates nucleation of actin filaments and thereby promotes actin polymerization (By similarity). Plays a role in the regulation of actin filament length (PubMed:20736303). Required for normal sarcomere organization in the heart, and for normal heart function (By similarity). Can bind at least three actin monomers and thereby provides a nucleus for actin filament formation. Interacts (via N-terminus) with tropomyosin alpha (TPM1) (via N-terminus). May also interact with TPM2 (via N-terminus). Colocalizes with actin filament pointed ends in sarcomeres. Detected close to the M line. First detected in myocardium at HH stage 14. Detected in myocardium and somites at HH stage 17 and 19. Belongs to the tropomodulin family.