How Well Can an Amoeba Climb?

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 97; no. 18; pp. 10020 - 10025
• Main Authors: Fukui, Y, Uyeda, T Q, Kitayama, C, Inoué, S
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 29.08.2000; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences
• Subjects: Actins; Amoeba; Amoeba - physiology; Animals; Biological Sciences; Buoyancy; Calibration; Cell lines; Cellular biology; Centrifugation; Centrifugation - methods; Density; Dictyostelium - genetics; Dictyostelium - physiology; Dictyostelium discoideum; Embryonic cells; Gene Deletion; Mass; Microscopes; Microscopy, Polarization - methods; Movement - physiology; Mutation; Myosin Heavy Chains - genetics; Myosins - genetics; Myosins - physiology; Organisms; Stall
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.97.18.10020

We report here our efforts to measure the crawling force generated by cells undergoing amoeboid locomotion. In a centrifuge microscope, acceleration was increased until amoebae of Dictyostelium discoideum were "stalled" or no longer able to "climb up". The "apparent weight" of the amoebae at stalling rpm in myosin mutants depended on the presence of myosin II (but not myosins IA and IB) and paralleled the cortical strength of the cells. Surprisingly, however, the cell stalled not only in low-density media as expected but also in media with densities greater than the cell density where the buoyant force should push the amoeba upward. We find that the leading pseudopod is bent under centrifugal force in all stalled amoebae, suggesting that this pseudopod is very dense indeed. This finding also suggests that directional cell locomotion against resistive forces requires a turgid forward-pointing pseudopod, most likely sustained by cortical actomyosin II.