Short-term retention of actin filament binding proteins on lamellipodial actin bundles

Actin filaments are organised into sub-compartments of meshwork and bundles in lamellipodia. Localisation of fascin, the LIM and SH3 domain protein 1 (lasp-1), and lasp-2 to the bundles suggest their involvement in that organisation; however, their contributions remain unclear. We have compared the turnover of these proteins with actin at the bundle. After photobleaching, EGFP-actin recovered inwards from the bundle tip, consistent with the retrograde flow by treadmilling. In contrast, the recovery of EGFP-fascin, -lasp-1 and -lasp-2 occurred from the anterograde direction. These results suggest that these molecules would participate in the stabilisation of bundles but not in initiation.