Actin-cytoskeleton dynamics in non-monotonic cell spreading |
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| Authors: | Doris Heinrich Simon Youssef Britta Schroth-Diez Ulrike Engel Daniel Aydin Jacques Blümmel Joachim P Spatz Günther Gerisch |
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| Institution: | 1.Department für Physik; Ludwig-Maximilians-Universität; München, Germany;2.Max Planck Institute of Molecular Cell Biology and Genetics; Dresden, Germany;3.Nikon Imaging Center at the University of Heidelberg; Heidelberg, Germany;4.Max Planck Institute for Metals Research; Department of New Materials and Biosystems; Stuttgart, Germany;5.Department of Biophysical Chemistry; University of Heidelberg;6.Max-Planck-Institut für Biochemie; Martinsried, Germany |
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| Abstract: | The spreading of motile cells on a substrate surface is accompanied by reorganization of their actin network. We show that spreading in the highly motile cells of Dictyostelium is non-monotonic, and thus differs from the passage of spreading cells through a regular series of stages. Quantification of the gain and loss of contact area revealed fluctuating forces of protrusion and retraction that dominate the interaction of Dictyostelium cells with a substrate. The molecular basis of these fluctuations is elucidated by dual-fluorescence labeling of filamentous actin together with proteins that highlight specific activities in the actin system. Front-to-tail polarity is established by the sorting out of myosin-II from regions where dense actin assemblies are accumulating. Myosin-IB identifies protruding front regions, and the Arp2/3 complex localizes to lamellipodia protruded from the fronts. Coronin is used as a sensitive indicator of actin disassembly to visualize the delicate balance of polymerization and depolymerization in spreading cells. Short-lived actin patches that co-localize with clathrin suggest that membrane internalization occurs even when the substrate-attached cell surface expands. We conclude that non-monotonic cell spreading is characterized by spatiotemporal patterns formed by motor proteins together with regulatory proteins that either promote or terminate actin polymerization on the scale of seconds.Key words: actin cytoskeleton, Arp 2/3 complex, cell adhesion, cell spreading, Coronin, Dictyostelium, myosin, self-organization, clathrin |
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