LOCOMOTION OF NEUTROPHIL FRAGMENTS OCCURS BY GRADED RADIAL EXTENSION

The only kinematic description of cell locomotion that relates the dyn amics of actin filaments to whole cell movement is the graded radial e xtension (GRE) model for fish keratocytes, which glide without changin g their shapes or sizes. To test whether the GRE model is applicable t o other cell types, we analyzed the detailed shape changes during loco motion of heat-induced motile fragments of human polymorphonuclear leu kocytes (PMNs). These fragments, called cytokineplasts, were loaded un iformly with a fluorescent cytoplasm-staining dye and their motility a nd shape changes were analyzed by fluorescence-video microscopy and di gital image processing. Two-dimensional (2-D) analysis showed that cyt okineplasts only changed their shapes and sizes slightly and apparentl y maintained their roughly circular shapes, whereas fluorescence-inten sity analysis revealed distinct changes in their cytoplasmic thickness profiles. Furthermore, small structures on the cytoplasmic margins be haved as predicted by the GRE model, which therefore is probably also applicable to the parental PMNs, which show complex shape changes. Thi s is the first indication that the GRE model operates in non-fish-kera tocyte cells and may, therefore, be a universal model of cell locomoti on. (C) 1996 Wiley-Liss, Inc.