Tropomodulin function and thin filament assembly in cardiac myocytes.

The regulation of thin filament length is a fundamental property of all striated muscles. Tropomodulin is an actin and tropomyosin binding protein that is exclusively associated with the free (pointed) ends of thin filaments. In vitro and in vivo studies reveal that tropomodulin is an actin filament pointed end capping protein, which is required to maintain the final length of thin filaments and is essential for contractile activity in embryonic chick cardiac myocytes. Understanding the mechanisms of thin filament assembly, as well as determining the roles of proteins modulating actin filament dynamics, is important for future considerations of the molecular bases for myopathies seen in various types of heart disease.