title: A cell number-counting factor regulates the cytoskeleton and cell motility in Dictyostelium.
abstract: Little is known about how a morphogenetic rearrangement of a tissue is affected by individual cells. Starving Dictyostelium discoideum cells aggregate to form dendritic streams, which then break up into groups of approximately 2 x 10(4) cells. Cell number is sensed at this developmental stage by using counting factor (CF), a secreted complex of polypeptides. A high extracellular concentration of CF indicates that there is a large number of cells, which then causes the aggregation stream to break up. Computer simulations indicated that stream breakup could be caused by CF decreasing cell-cell adhesion and/or increasing cell motility, and we observed that CF does indeed decrease cell-cell adhesion. We find here that CF increases cell motility. In Dictyostelium, motility is mediated by actin and myosin. CF increases the amounts of polymerized actin and the ABP-120 actin-crosslinking protein. Partially inhibiting motility by using drugs that interfere with actin polymerization reduces stream dissipation, resulting in fewer stream breaks and thus larger groups. CF also potentiates the phosphorylation and redistribution of myosin while repressing its basal level of assembly. The computer simulations indicated that a narrower distribution of group sizes results when a secreted factor modulates both adhesion and motility. CF thus seems to induce the morphogenesis of streams into evenly sized groups by increasing actin polymerization, ABP-120 levels, and myosin phosphorylation and decreasing adhesion and myosin polymerization.
authors.affiliation: Department of Biochemistry and Cell Biology, MS-140, Rice University, Houston, TX 77005-1892, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Tang
authors.forename: Tong
authors.initials: T
authors.lastname: Gao
authors.forename: Catherine
authors.initials: C
authors.lastname: McCollum
authors.forename: Wonhee
authors.initials: W
authors.lastname: Jang
authors.forename: Michael G
authors.initials: MG
authors.lastname: Vicker
authors.forename: Robin R
authors.initials: RR
authors.lastname: Ammann
authors.forename: Richard H
authors.initials: RH
authors.lastname: Gomer
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D030801:Animals, Genetically Modified; D002448:Cell Adhesion / Q000502:physiology; D002449:Cell Aggregation / Q000502:physiology; D002452:Cell Count / Q000379:methods; D003198:Computer Simulation; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000502:physiology*; D004023:Dictyostelium / Q000166:cytology / Q000254:growth & development* / Q000502:physiology; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics; D009024:Morphogenesis; D009068:Movement / Q000187:drug effects; D009219:Myosin-Light-Chain Kinase / Q000235:genetics; D009218:Myosins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation
chemical_list: D000199:Actins; D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins; D015638:Cytochalasin D; D009219:Myosin-Light-Chain Kinase; D009218:Myosins