Mediates nucleation of actin filaments and thereby promotes actin polymerization (By similarity). Plays a role in the regulation of actin filament length (PubMed:26487682). Required for normal sarcomere organization in the heart, and for normal heart function (PubMed:26487682, PubMed:27274810). 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) (PubMed:17572376). Colocalizes with actin filaments in sarcomeres. Detected close to the M line. Detected in neonate heart (at protein level) (PubMed:26487682). Detected in embryonic heart and in pharyngeal arches (PubMed:26487682). Detected in adult heart (PubMed:27274810). Mutant mice are born at the expected Mendelian rate. All die between 15 to 33 days after birth due to early-onset dilated cardiomyopathy. Cardiac muscle thin filaments are shorter than in wild-type, both in embryonic heart and in pups 6 or 15 days after birth. Hearts appear grossly normal at birth, but after 15 days, they display enlarged left ventricles with thin ventricle walls and resuced systolic performance. In contrast, there are no differences in thin filament length in skeletal muscle (PubMed:26487682). Insertion of a transposon in the first, non-coding exon decreases Lmod2 expression by 90% in females and by over 95% in males and gives rise to a phenotype that is closely similar to that of complete gene disruption, except that mutant mice die between three and nine weeks after birth (PubMed:27274810). Belongs to the tropomodulin family. Extended N-terminus.