Disease relevance of DMD

• Dystrophin is a very large muscle protein (approximately 400 kd) the deficiency of which is responsible for Duchenne muscular dystrophy [1].
• We have determined the cell types likely to express the pathogenic effects of this neuromuscular disease by determining the pattern of dystrophin expression in normal cells [2].
• Mutations in dystrophin cause muscular dystrophy but also affect the CNS, including information processing in the retina [3].
• Cultured dorsal root ganglion, spinal cord, and ciliary ganglion neurons show immunoreactivity for dystrophin, both in cell bodies and along fibers [4].
• The complexity of the relation between dystrophin mutations and the cell-specific loss of dystrophin expression can result in patients having cardiomyopathy and no myopathy [5].

High impact information on DMD

• We find that all physiological types of muscle cells express dystrophin at similar levels, and that the dystrophin content of various tissues correlates with the myogenic cell population of each tissue [2].
• This simple bipartite domain organization contrasts with the more complex organization of the skeletal muscle sarcolemma: smooth muscle thus offers itself as a useful system for localizing, among other components, potential interacting partners of dystrophin [6].
• Complementary distributions of vinculin and dystrophin define two distinct sarcolemma domains in smooth muscle [6].
• We show here by immunofluorescence and immunoelectron microscopy that dystrophin is specifically localized in the caveolae-rich domains of the smooth muscle sarcolemma, together with the caveolae-associated molecule caveolin [6].
• Thus, a chimeric protein containing the NH2-terminal region of dystrophin (residues 1-233) fused to alpha-actinin residues 244-888 localized to actin-containing structures when expressed in Cos cells [7].

Biological context of DMD

• Nucleotide sequence of chicken dystrophin cDNA [8].
• In the brain, Dp71 is the most abundant protein product of the DMD gene and by alternative splicing of exon 78 two isoforms can be expressed, Dp71d and Dp71f [9].
• Analysis of 800 residues of deduced amino acid sequence at the amino-terminal end revealed a strikingly conserved domain of integral of 230 residues that shows a high degree of sequence similarity to the amino-terminal domains of alpha actinin and dystrophin [10].
• The Dictyostelium gelation factor shares a putative actin binding site with alpha-actinins and dystrophin and also has a rod domain containing six 100-residue motifs that appear to have a cross-beta conformation [11].
• Analysis of the actin-binding domain of alpha-actinin by mutagenesis and demonstration that dystrophin contains a functionally homologous domain [7].

Anatomical context of DMD

• Desmin has been shown to associate with the sarcolemma in specific structures, such as neuromuscular junctions and the dystrophin-associated protein complex [12].
• Polyclonal antibodies were first prepared from a dystrophin fragment derived from the chicken skeletal muscle gene (residues 1173-1728) [13].
• A dystrophin-enriched membrane preparation from chicken gizzard muscle was then purified by passing it through an affinity chromatography column made with the anti-dystrophin antibodies [13].
• Dystrophin has been shown to occur in Torpedo electrocyte [Chang, H. W., Bock, E. & Bonilla, E. (1989) J. Biol. Chem. 264, 20831-20834], a highly polarized syncytium that is embryologically derived from skeletal muscle and displays functionally distinct plasma membrane domains on its innervated and noninnervated faces [14].
• These observations suggest that the alpha 5 beta 1 integrin is involved in the adhesion of muscle to the extracellular matrix, the organization of the dystrophin-containing lattice, and the organization of nascent myofibrils which emanate from the focal contact- and stress fiber-like structures in muscle [15].

Associations of DMD with chemical compounds

• Finally, we have established that the NH2-terminal domain of dystrophin is functionally as well as structurally homologous to that in alpha-actinin [7].
• In developing electrocytes (45-mm embryo), dystrophin is already detectable at the acetylcholine receptor-rich ventral pole of the cells before the entry of the electromotor axons [14].
• In the present study, we investigated the subcellular distribution of dystrophin in the adult electrocyte from Torpedo marmorata and the evolution of its distribution during embryogenesis [14].
• Like dystrophin, utrophin has been shown to be associated with a membrane-bound glycoprotein complex [16].
• However, dystrophin, which displayed a diffuse distribution earlier, now colocalized with the alpha 5 beta 1 integrin in the punctate lattice [15].

Physical interactions of DMD

• Under these conditions dystrophin bound talin with high affinity (Kd 3.5 nM) [17].

Co-localisations of DMD

• These intensely stained striations and scattered patches of dystrophin were colocalized with those of vinculin [18].

Other interactions of DMD

• The interaction of dystrophin with purified talin from chicken gizzard was tested by solid phase immunoassay [17].
• These data suggest that utrophin could replace dystrophin functionally in dystrophic muscle [16].
• We were able to precisely determine the dystrophin distribution along the plasmalemma whereas caldesmon molecules were present in the cytoplasm [19].

Analytical, diagnostic and therapeutic context of DMD

• We also find that the dystrophic chicken does not represent an animal model for dystrophin deficiency [2].
• Isolated dystrophin molecules as seen by electron microscopy [13].
• Dystrophin was examined at the protein level by immunocytochemistry and at the transcriptional level by a semiquantitative reverse transcriptase-polymerase chain reaction analysis [4].
• The time-course of protease degradation was examined by Western immunoblot using three polyclonal sera which were characterized as being specific to the central (residues 1173-1728) and two distal parts of the molecule ie specific to the N-terminal (residues 43-760) or the C-terminal (residues 3357-3660) extremities of the dystrophin molecule [20].
• Furthermore, co-sedimentation and solid phase immunoassay experiments both demonstrated that native dystrophin binds purified actin from rabbit skeletal muscle [17].

References