band about the cell periphery. The resulting arrangement of podosomes is highly interconnected through a dense, radial network of actin filaments that extend between and onto neighboring podosomes. Accumulation of F-actin, vinculin, paxillin, and α-actin within the podosomes of the coalescent band signals the development of a fully matured osteoclast. Upon initiation of bone resorption, the band of podosomes disassembles leaving behind a mesh primarily composed of F-actin which functions as the ‘sealing zone.’ This sealing zone becomes the site of osteoclast attachment to the bone matrix. Inhibition of bone resorption through drug intervention results in the lack of the podosome band during early osteoclast differentiation and ultimate absence of a sealing zone. History In the early 1980s, chicken embryo fibroblasts were transformed using the Rous sarcoma virus (RSV) containing the oncogene v-src. This transformation elicited the relocalization of vinculin and α-actin in the cytoskeleton from focal adhesions forming circular clusters. Later in 1985, it was shown using the same cells that these protein clusters were localized to protrusions in the ventral plasma membrane, were substratum adhesion sites; therefore, these structures were termed podosomes indicating their foot-like character in cells. In 1989, it was demonstrated that these podosomes played a role in matrix degradation. To reflect this newly discovered destructive nature the name invadopodia was given to these dynamic structures. Because both terms invadopodia and podosomes were initially used to reference the identical structures in identical cell lines, there exists confusion about the nomenclature. Typically, when these structures are found in normal cells, they are referred to as podosomes, and when in cancer cells, invadopodia. See also Invadopodia Lamellipodia References External links MBInfo - Podosomes MBInfo - Podosome Assembly Podosomes and Invadopodia at Scirus Topic Pages Cell anatomy Membrane biology