platypodia, Platyamoeba stenopodia, Echinamoebia exundans and Vexillifera bacilipedes. In cultures inoculated with material from water samples and from cotton swabs taken from the bottom and walls of the pool the following species of Limax-amoebae could be cloned and identified: Naegleria gruberi, Hartmannella vermiformis, Acanthamoeba castellamii, A. Read moreĪ physiotherapeutical indoor swimmingpool in a hospital was inspected for the presence of potentially pathogenic Limax-amoebae. Starvation-initiated development, leading to encystment, was shown to affect the capacity of the cells to phagocytize, mainly by progressively decreasing the time span over which the cells ingested particles at a constant initial rate. Phagocytosis was depressed by protein in the medium, by increased osmolarity, and by inhibitors of aerobic metabolism. Simultaneously with phagocytosis, comparable numbers of beads accumulated at the cell surface this accumulation did not occur when phagocytosis was inhibited. Beads approximately 1 microm in diameter appeared to be the optimal size for ingestion. pallidum amoebae had the lowest K(p), while the leukocytes had the highest V(p) (max). Comparison with previously published data on Acanthamoeba and guinea pig leukocytes suggested that the P. as well as the maximal velocity itself (V(p) (max)), were made. The kinetics of phagocytosis were determined, and estimates of the concentration of PS beads necessary to achieve half-maximal phagocytic velocity (K(p)). An established quantitative assay of the uptake of polystyrene (PS) beads was shown to be valid for this organism. The phagocytic ability of amoebae of the cellular slime mold Polysphondylium pallidum, grown in shaken suspension, was examined. These data suggest that the molecular mechanism of filopodia formation is conserved throughout evolution from Dictyostelium to mammals and show that lamellipodia and filopodia formation are functionally separable. Moreover, genetic disruption of nap1 or the WAVE-orthologue suppressor of cAMP receptor (scar) in Dictyostelium was also ineffective in preventing filopodia protrusion. Likewise, the Arp2/3-complex, which is essential for lamellipodia protrusion, is dispensable for filopodia formation. Cells depleted of the WAVE-complex component Nck-associated protein 1 (Nap1), and, in consequence, of lamellipodia, exhibited normal filopodia protrusion. Here, we have analyzed filopodia formation in mammalian cells abrogated in expression of essential components of the lamellipodial actin polymerization machinery. A current model of filopodia formation postulates that these structures arise from a dendritic network of lamellipodial actin filaments by selective elongation and bundling. which activates Arp2/3-mediated actin filament nucleation and actin network assembly. In mammals, lamellipodia protrusion downstream of the small GTPase Rac1 requires a multimeric protein assembly, the WAVE-complex. The latter rod-like projections may exert sensory functions and are found in organisms as distant in evolution as mammals and amoeba such as Dictyostelium discoideum.
Cell migration is initiated by plasma membrane protrusions, in the form of lamellipodia and filopodia.