Fig. 2. Podosome fusion, fission and sliding. (A) Podosome fusion within a cluster. Frames from a GFP-actin movie show two neighboring podosomes (0-60", arrows) that approach each other and fuse (75-105", arrowheads). (B) Podosome fission within a cluster. Frames from a GFP-actin movie show podosome splitting (0-30", arrows), creating two daughter podosomes (45"-75", arrowheads). (C) Apparent sliding motion of a podosome within a cluster. Frames from a GFP-actin movie are shown. Podosomes recorded at three time points are marked with different artificial colors (arrows indicate the original localization of the podosome). Time-lapse movies of cells expressing (D) GFP-actin or (E) YFP-paxillin analyzed by temporal autocorrelation techniques. The green line represents the correlation decay time constant (1/e). Five cells were analyzed for every podosome pattern. The blue line represents cluster podosomes and the red line represents SZL structure podosomes. (D) GFP-actin cluster podosomes decayed after 105 seconds; GFP-actin SZL structure decayed after 30 seconds. (E) YFP-paxillin in the cluster decayed after 195 seconds; YFP-paxillin in the SZL structure decayed after 225 seconds. Bars, 1 µm.