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Evidence exists for a primary defect in the muscle plasma membrane of persons with Duchenne muscular dystrophy (DMD), although the molecular basis of the defect is unknown [ 5 ] . Studies from our laboratory [8, [6] found that the organization of microtubules, a component of the cytoskeleton, was diminished in cardiac fibroblasts from chickens with muscular dystrophy. The conclusions of both studies have been questioned [l, 2, 71, making the situation unclear. We studied the organization of microtubules and microfilaments in muscle cultures from patients with D M D to clarify some of these issues.Two biopsies from patients clinically diagnosed as having D M D were used. Biopsy 1 was from a 5-year-old boy examined at the Hospital for Sick Children, London, and biopsy 2 was from a 6-year-old boy een at the Wilhemina Gasthuis of the Akademische Ziekenhuis, Amsterdam, Holland. Mononucleated cells were released from the muscle specimens as previously described [ 101 and were seeded onto Lux plastic dishes. The celi numbers were increased by subculturing, and cultures were plated on Petriperm dishes. The distribution of microtubules and microfilaments was determined by indirect immunofluorescence with rabbit anti-rat brain tubulin and rabbit anti-pig skeletal muscle actin antibodies, followed by fluoresceinconjugated goat anti-rabbit IgG. For immunofluorescence the cells were fixed with 3 % formaldehyde in phosphatebuffered saline for 30 minutes, followed by extraction with methanol at -20°C prior to staining. Figure 1 shows that muscle cultures from D M D patients have an elaborate distribution of microfilaments similar to that found in other cultured cells such as fibroblasts [j]. The majority of cells displayed this distribution of stress fibers. Figure 2 shows the distribution of microtubules in muscle cultures from D M D biopsy 2; similar results were found for biopsy 1 and also control skin fibroblast cultures. The observed distribution of microtubules is much like the known distribution

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