Figure 1.

Alterations in membrane domains during osteoclast activation. Unpolarized, inactive osteoclasts present dispersed podosomes. During osteoclast activation, these podosomes coalesce into a peripheral belt and subsequently into distinct “actin ring” that forms the sealing zone where the osteoclast adheres tightly to the bone surface. Following this, trafficking of late endosomes/lysosomes toward the bone surface result in formation of the ruffled border, the resorptive organelle of the osteoclast. Finally, a membrane domain known as the functional secretory domain forms at the top of the cell, to which transcytotic vesicles formed at the ruffled border are targetted.