Minipodia, novel structures for extension of the lamella: a high-spatial-resolution video microscopic study.

Extension of leading lamellae has been analyzed by high-spatial- and -time-resolution video microscopy. Many tiny semicircular profiles, hereby named minipodia, have been found at the leading edge of locomoting fibroblasts in culture. These new structures are not "miniruffles" since minipodia seem to originate underneath the leading lamella. Once initiated, minipodia quickly expand and become indistinguishable from what have been known as lamellipodia. The minipodial front becomes the new focal leading edge. So, it appears that leading lamellae do not extend directly themselves, but minipodia protrude underneath them to become new leading edges. These findings are not compatible with the current concept of cell movement, and a new model is proposed.