In previous studies of cell-cell and cell-substratum adhesion, we have identified differences in the behaviour between human skin fibroblasts cultured from normal individuals and patients with Duchenne muscular dystrophy (DMD). In these studies, monolayer cultures were dissociated by trypsinization and no detectable difference was noted in the efficiency of cell dissociation between normal and DMD fibroblast cultures. However, a detailed study by Kent has suggested that Duchenne fibroblasts exhibit increased sensitivity to trypsin. We have re-investigated this finding using an assay that directly measures the number of cells remaining attached to a substratum following trypsinization. In a series of experiments using cultures derived from five normal and five DMD individuals, we can detect no significant difference in the trypsin-induced detachment rates between normal and DMD skin fibroblasts. This observation applies to both growth-phase and stationary-phase cell cultures. This inconsistency with previously reported data on the trypsin-sensitivity of DMD cells is considered in terms of the different assays used and the effects of trypsin on cell-cell and cell-substratum adhesion. The relationship between abnormalities in the behaviour of DMD cells and the localization and primary structure of the DMD gene product are also discussed.
Cultured skin fibroblasts from patients with Duchenne muscular dystrophy (DMD) are more sensitive than normal cells to prolonged exposure to the ionophore monensin. In a cell spreading assay in which cells were preincubated with monensin and subsequently allowed to adhere to and spread on a glass substratum in serum-free medium for 100 min, the mean transformed cell area of normal and DMD cells was 5.97 +/− 0.11 and 5.29 +/− 0.03, respectively. Cultured fibroblasts from carriers of DMD yielded a value of 5.59 +/− 0.03, which is intermediate between, and significantly different from, the values for both normal and DMD cultures. This result would be predicted on the basis of random X-chromosome inactivation in female carriers of this disorder. However, comparison of DMD carrier cell spreading data with data obtained from pooled and summated measurements taken from separate experiments using either normal or DMD fibroblasts suggest a more complex situation. Examination of the variance of the means of cell area for the true carrier population and the summated normal and DMD population provides evidence suggesting that some form of cellular interaction may occur between the two cell genotypes in culture.