Expression of cofilin isoforms during development of mouse striated muscles

Cofilin (CF) is an actin regulatory protein that plays a critical role in a ctin filament dynamics in a variety of cells. Two cofilin isoforms, muscle- type (M-CF) and nonmuscle-type (NM-CF) encoded by different genes, exist in mammals; in the adult, the former is predominantly expressed in muscle tis sues, while the latter is distributed in various non-muscle tissues (Ono et al., 1994). In this study, we examined cofilin isoform expression during s keletal and cardiac muscle development in mice using cDNA probes and antibo dies which distinguish the isoforms. We found that the expression of M-CF w as initiated in terminally differentiated myogenic cells in both the myotom e and limb buds. In myogenic cell cultures, its expression occurred coupled with myotube formation. NM-CF was expressed in developing skeletal and car diac muscles but disappeared from skeletal muscle during postnatal developm ent, while its expression persisted in the heart, even in adult mice. A sim ilar situation was observed in the heart of other mammals. Thus, it is like ly that the both cofilin isoforms are involved in the regulation of actin a ssembly during myofibrillogenesis. Only M-CF could be involved in actin dyn amics in mature skeletal muscle, while both isoforms could be in the mature heart.