Desmin is a protein that in humans is encoded by the DES gene. Desmin is a muscle-specific, type III intermediate filament that integrates the sarcolemma, Z disk, and nuclear membrane in sarcomeres and regulates sarcomere architecture. Structure Desmin is a 53.5 kD protein composed of 470 amino acids, encoded by the human DES gene located on the long arm of chromosome 2. There are three major domains to the desmin protein: a conserved alpha helix rod, a variable non alpha helix head, and a carboxy-terminal tail. Desmin, as all intermediate filaments, shows no polarity when assembled. The rod domain consists of 308 amino acids with parallel alpha helical coiled coil dimers and three linkers to disrupt it. The rod domain connects to the head domain. The head domain 84 amino acids with many arginine, serine, and aromatic residues is important in filament assembly and dimer-dimer interactions. The tail domain is responsible for the integration of filaments and interaction with proteins and organelles. Desmin is only expressed in vertebrates, however homologous proteins are found in many organisms. Desmin is a subunit of intermediate filaments in cardiac muscle, skeletal muscle and smooth muscle tissue. In cardiac muscle, desmin is present in Z-discs and intercalated discs. Desmin has been shown to interact with desmoplakin and αB-crystallin. Function Desmin was first described in 1976, first purified in 1977, the gene was cloned in 1989, and the first knockout mouse was created in 1996. The function of desmin has been deduced through studies in knockout mice. Desmin is one of the earliest protein markers for muscle tissue in embryogenesis as it is detected in the somites. Although it is present early in the development of muscle cells, it is only expressed at low levels, and increases as the cell nears terminal differentiation. A similar protein, vimentin, is present in higher amounts during embryogenesis while desmin is present in higher amounts after differentiation. This suggests that there may be some interaction between the two in determining muscle cell differentiation. However desmin knockout mice develop normally and only experience defects later in life. Since desmin is expressed at a low level during differentiation another protein may be able to compensate for desmin's function early in development but not later on. In adult desmin-null mice, hearts from 10 week-old animals showed drastic alterations in muscle architecture, including a misalignment of myofibrils and disorganization and swelling of mitochondria; findings