title: Actin-cytoskeleton dynamics in non-monotonic cell spreading.
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.
authors.affiliation: Department für Physik, Ludwig-Maximilians-Universität, München, Germany.
authors.forename: Doris
authors.initials: D
authors.lastname: Heinrich
authors.forename: Simon
authors.initials: S
authors.lastname: Youssef
authors.forename: Britta
authors.initials: B
authors.lastname: Schroth-Diez
authors.forename: Ulrike
authors.initials: U
authors.lastname: Engel
authors.forename: Daniel
authors.initials: D
authors.lastname: Aydin
authors.forename: Jacques
authors.initials: J
authors.lastname: Blümmel
authors.forename: Joachim P
authors.initials: JP
authors.lastname: Spatz
authors.forename: Günther
authors.initials: G
authors.lastname: Gerisch
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives / Q000378:metabolism; D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000818:Animals; D002448:Cell Adhesion; D002454:Cell Differentiation; D002460:Cell Line; D002465:Cell Movement; D002966:Clathrin / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism*; D004023:Dictyostelium / Q000166:cytology* / Q000378:metabolism*; D024461:Myosin Type I / Q000378:metabolism; D013379:Substrate Specificity; D054378:Acetogenins
chemical_list: D015107:4-Butyrolactone; D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D002966:Clathrin; D024461:Myosin Type I; C438920:coronin acetogenin; D054378:Acetogenins