Department of Cellular and Molecular Pharmacology, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States
Megan Riel-Mehan
Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, United States
Bi-Chang Chen
Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, United States
Department of Cellular and Molecular Pharmacology, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States
Thomas D Goddard
Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, United States
Thomas E Ferrin
Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, United States
Susan M Nicholson-Dykstra
Department of Biochemistry and Cell Biology, Dartmouth Geisel School of Medicine, Hanover, United States
Henry Higgs
Department of Biochemistry and Cell Biology, Dartmouth Geisel School of Medicine, Hanover, United States
Graham T Johnson
Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, United States; Animated Cell, Allen Institute for Cell Science, Seattle, United States
Eric Betzig
Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, United States
Department of Cellular and Molecular Pharmacology, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States
Leukocytes and other amoeboid cells change shape as they move, forming highly dynamic, actin-filled pseudopods. Although we understand much about the architecture and dynamics of thin lamellipodia made by slow-moving cells on flat surfaces, conventional light microscopy lacks the spatial and temporal resolution required to track complex pseudopods of cells moving in three dimensions. We therefore employed lattice light sheet microscopy to perform three-dimensional, time-lapse imaging of neutrophil-like HL-60 cells crawling through collagen matrices. To analyze three-dimensional pseudopods we: (i) developed fluorescent probe combinations that distinguish cortical actin from dynamic, pseudopod-forming actin networks, and (ii) adapted molecular visualization tools from structural biology to render and analyze complex cell surfaces. Surprisingly, three-dimensional pseudopods turn out to be composed of thin (<0.75 µm), flat sheets that sometimes interleave to form rosettes. Their laminar nature is not templated by an external surface, but likely reflects a linear arrangement of regulatory molecules. Although we find that Arp2/3-dependent pseudopods are dispensable for three-dimensional locomotion, their elimination dramatically decreases the frequency of cell turning, and pseudopod dynamics increase when cells change direction, highlighting the important role pseudopods play in pathfinding.
