Immunocytochemical study of dystrophin at the myotendinous junction

Abstract

Dystrophin is the protein whose deficiency results in Duchenne muscular dystrophy. The protein has homologies with a number of cytoskeletal proteins, is localized at the muscle sarcolemma and it may provide stability to the muscle plasma membrane. Using immunocytochemical techniques, we have studied dystrophin localization at the myotendinous junction, a region of membrane complexity that requires more stability because it is subjected to great mechanical stress during the transmission of contractile force to the tendon. The results showed subsarcolemmal deposits of dystrophin at the junctional folds of the myotendon as well as membrane-associated dystrophin at extrajunctional sarcolemma. The findings suggest that dystrophin may be one of the components linking terminal actin filaments to the subplasmalemmal surface of the junctional folds of the myotendon.

Dystrophin isoforms Dp71 and Dp427 have distinct roles in myogenic cells

“…Although Dp427 contains an N-terminal actin binding domain, it has not been reported to localize along the length of actin filaments, and is restricted to the surface membrane and adhesion zones. 5,10,16,19,24,35,37,42,46,57,61,62,64,69 To confirm that the dystrophin we detected in the SFLS was Dp71 and not Dp427, we also included, in these experiments, an antibody against the rod domain of Dp427 (Dys 2) which would not cross-react with Dp71. As demonstrated in Figure 5e , localization of Dp427 to the SFLS was not observed with this antibody, confirming that the SFLS localization was specific for Dp71.…”

Expression of the Giant Protein AHNAK (Desmoyokin) in Muscle and Lining Epithelial Cells

“…Both of these giant proteins lie close beneath the plasma membrane (Shimada et al 1993;Mussini et al 1995). Dystrophin is part of a multimeric protein complex that links actin on the inside of the cells to extracellular matrix protein through transmembrane proteins (Samitt and Bonilla 1990;Wakayama et al 1993;Norwood et al 2000). Titin is a giant muscle protein.…”

Heterokaryon myotubes with normal mouse and Duchenne nuclei exhibit sarcolemmal dystrophin staining and efficient intracellular free calcium control.

“…It is proposed to exist as a homodimer where anti-parallel dys-trophin monomers interact by their N-terminal domain (a-actinin sequences) with cortical actin filaments and by their C-terminal domain (unique dystrophin sequences) with sarcolemmal glycoproteins (Ervasti and Campbell, 1991). In addition to being expressed at the sarcolemma in muscle fibers, dystrophin is also found at low levels in the triadic junctions (Knudson et al, 1988;Bornemann and Schmalbruch, 1991) and at higher levels at the neuromuscular (Huard et al, 1992) and myotendinous junctions (Samitt and Bonilla, 1990;Tidball and Law, 1991).…”