Redundancy of lamellipodia in locomoting Walker carcinosarcoma cells

Locomoting metazoan cells usually form lamellipodia at the leading front an d it is widely accepted that lamellipodia are required for locomotion. In t his case, suppression of lamellipodia must stop locomotion. However, the ex periments show that lamellipodia are redundant for locomotion of Walker car cinosarcoma cells. Low latrunculin A concentrations (10(-7) M) transform po larised locomoting cells with lamellipodia into cells without morphological ly recognisable protrusions showing an increased speed of locomotion and a reduced amount of cellular F-actin. Whereas untreated cells show a fairly l inear distribution of F-actin along the plasma membrane, cells lacking morp hologically recognizable protrusions at the front show modifications at the front consisting in an irregular distribution of F-actin with formation of small or large patches of F-actin alternating with small or large gaps in the F-actin layer. This is associated with a reduced resistance to deformat ion pressure at the front of the cell. High concentrations of latrunculin A (>10(-7) M) compromising contraction at the rear stop locomotion, suggesti ng that cortical contraction is important for locomotion to occur in these cells. The results are consistent with the view that actin polymerization i s important for formation of lamellipodia but they are not compatible with the view that lamellipodia are essential for locomotion of Walker carcinosa rcoma cells. A unifying hypothesis for the formation of different types of protrusions is proposed. Cell Motil. Cytoskeleton 46:247-256, 2000. (C) 200 0 Wiley-Liss, Inc.