Fig. 4. Individual podosome lifespan depends on the substrate flexibility. (A) 3T3 fibroblast observed by fluorescence microscopy exhibiting an actin cluster. (B-E) Movement of the cluster over 3 minutes revealed an apparent motion induced by appearance and disappearance of non-moving podosomes (circled). (F) The lifespan of podosomes calculated by averaging the lifespan of about ten podosomes per cell, and for each substrate type (n=68 for 0.08% gel; n=63 for 0.2% gel; and n=99 for glass). Data are expressed as mean ± s.d. Bars, 20 µm (A); 10 µm (B-E).