|Symbols||; CSM1; CSM2; LGMD2R|
|RNA expression pattern|
Desmin is a type III intermediate filament found near the Z line in sarcomeres. It was first described in 1976, first purified in 1977, the gene was cloned in 1989, and the first knockout mouse was created in 1996. Desmin is only expressed in vertebrates, however homologous proteins are found in many organisms. It is a 52kD protein that is a subunit of intermediate filaments in skeletal muscle tissue, smooth muscle tissue, and cardiac muscle tissue.
The function of desmin has been deduced through studies in knockout mice, but the underlying mechanism of its action is not known. These possibilities may be the result of interactions with other proteins and not desmin itself. More research needs to be done on desmin's expression and interactions in the muscle cell in order to determine its exact function.
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.
Desmin is also important in muscle cell architecture and structure since it connects many components of the cytoplasm. The sarcomere is a component of muscle cells composed of actin and myosin motor proteins which allow the cell to contract. Desmin forms a scaffold around the Z-disk of the sarcomere and connects the Z-disk to the subsarcolemmal cytoskeleton (the cytoplasmic part of the muscle cell plasma membrane). It links the myofibrils laterally by connecting the Z-disks. Through its connection to the sarcomere Desmin connects the contractile apparatus to the cell nucleus, mitochondria, and post-synaptic areas of motor endplates. These connections maintain the structural and mechanical integrity of the cell during contraction while also helping in force transmission and longitudinal load bearing. There is some evidence that desmin may also connect the sarcomere to the extracellular matrix (ECM) through desmosomes which could be important in signalling between the ECM and the sarcomere which could regulate muscle contraction and movement.
Finally, desmin may be important in mitochondria function. When desmin is not functioning properly there is improper mitochondrial distribution, number, morphology and function. Since desmin links the mitochondria to the sarcomere it may transmit information about contractions and energy need and through this regulate the aerobic respiration rate of the muscle cell.
When the gene for desmin is knocked out it is no longer able to function properly. Mice with the desmin knockout gene develop normally and are fertile, however soon after birth they begin to show defects in skeletal, smooth and cardiac muscle; in particular the diaphragm and heart are affected. The mice without desmin are weaker and fatigue more easily than wild type mice  but the muscle fibers are less likely to be damaged during contraction  Mice without desmin also have impaired mitochondrial function.
Desmin-related myopathy (DRM or Desminopathy) is a subgroup of the myofibrillar myopathy diseases and is the result of a mutation in the gene that codes for desmin which prevents it from forming protein filaments, instead forming aggregates of desmin and other proteins throughout the cell. Recently, mutations were identified in patients suffered by an arrhythmogenic right ventricular cardiomyopathy (ARVC). Some of these DES mutations like p.N116S or p.E114del cause an aggregation of desmin within the cytoplasma. A mutation p.A120D was discovered in family where several members had a sudden cardiac death. It is also associated with Sarcoma botryoides (rhabdomyosarcoma variant) - a vaginal malignancy composed of spindle-shaped cells that affects girls < 4 years of age.
There are three major domains to this 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.
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- GeneReviews/NIH/NCBI/UW entry on Myofibrillar Myopathy
- Desmin at the US National Library of Medicine Medical Subject Headings (MeSH)
- LOVD mutation database: DES