FIGURE 9.

Cells expressing the C566S PMEL mutant, but not the C301S mutant, exhibit decreased fibril formation relative to those expressing wild type PMEL. HeLa cells transiently transfected with wild-type PMEL, the C301S mutant, or the C566S mutant were analyzed by transmission electron microscopy. A, example of a multivesicular body (MVB) with intraluminal vesicles (arrowheads). B, example of a multivesicular body with fibrils, intraluminal vesicles (arrowheads), and a small multilamellar structure commonly found in late endosomes and lysosomes (asterisk). C, fibril-containing organelles and multivesicular bodies without any evidence of fibril formation were quantified in at least one field of view/cell, and the percentage of fibril-containing multivesicular bodies was calculated for each cell. Box plots show the combined results of three experiments with the line in the center representing the median, the box representing the 25th and 75th percentiles, and the whiskers denoting the minimum and maximum values. Statistics were performed using a two-tailed unpaired t test comparing each mutant to wild-type PMEL. Scale bars are 500 nm.