Cell–cell fusion is initiated at 48 h after RANKL treatment with morphological changes. (A) Confocal images of the time sequence of RAW 264.7 cells after RANKL addition, stained with phalloidin (magenta) and DAPI (gray). Multinucleated cells are surrounded by dotted lines. Scale bar: 50 μm. (B) Quantification of fusion index in A. For box plots inside violin plots, circles, boxes, and whiskers indicate median values, interquartile range (25–75%), and SD, respectively. n = 30 fields of view for each time point. (C) Representative confocal images of mononuclear cells without or with RANKL treatment for 84 h, stained with phalloidin (green), WGA (magenta), and DRAQ5 (blue). Scale bar: 10 μm. WGA, wheat germ agglutinin.