Fig 8.

Dynamics of podosome-like structures and invadopodia. EGFP-actin transfected cells were followed with wide-field time-lapse imaging for 30 min. 43A podosomes were immobile dot-like structures, whereas 43B invadopodia were complex structures with rapid motion of propelling actin tails (A). Arrows indicate single podosomes or actin comet-embedded invadopodia. Inset: A magnified image of the actin tail marked by an arrow. Time-lapse TIRF imaging showed that podosome-like structures, invadopodia and cell extensions were within the narrow TIRF evanescent field and thus in immediate proximity to the substrate (B). In prolonged 12-hr time-lapse, trafficking of EGFP-actin fluorescence to podosomes seemed sparse and no new podosomes were formed. A halo of fluorescent EGFP-actin (arrows) was detected around podosomes. In contrast, rapid motion was detected in 6-hr time-lapse at the basal surface of 43B cells, including actin filaments (arrowheads). Actin comet-based invadopodia were long-lived (arrow). Some propelling movement of the actin tails could also be detected at this level, as well as undulating movement of the club-ended cell extensions. No similar fluorescent EGFP-actin halo as in 43A cells was detected around invadopodia. Scale bar: 20 μm.