Sbds-null monocytes lack the ability to fuse even at high cell densities. Monocytes were cultured at 2 initial plating densities in 6-well plates, low (5 × 10⁴ cells/well) and high (2.5 × 10⁵ cells/well), to observe the effects of cell density on OCG. Representative photomicrographs (original magnification ×200) of WT (top 2 panels) and Sbds-null (lower 2 panels) cultures are shown on days 2, 4, and 6 of OCG, and representative TRACP-stained images of day 6 WT and Sbds-null cultures are shown on the right. At the 5-fold-higher initial plating density, WT cells formed clearly more large multinucleated osteoclasts than at the lower density. However, this increase in OCG was not observed for Sbds-null cells, suggestive of a fusion defect.