title: A RabGAP regulates life-cycle duration via trimeric G-protein cascades in Dictyostelium discoideum.
abstract: BACKGROUND
  The life-cycle of cellular slime molds comprises chronobiologically regulated processes. During the growth phase, the amoeboid cells proliferate at a definite rate. Upon starvation, they synthesize cAMP as both first and second messengers in signalling pathways and form aggregates, migrating slugs, and fruiting bodies, consisting of spores and stalk cells, within 24 h. In Dictyostelium discoideum, because most growth-specific events cease during development, proliferative and heterochronic mutations are not considered to be interrelated and no genetic factor governing the entire life-cycle duration has ever been identified.
  
  
  RESULTS
  Using yeast 2-hybrid library screening, we isolated a Dictyostelium discoideum RabGAP, Dd Rbg-3, as a candidate molecule by which the Dictyostelium Gα2 subunit directs its effects. Rab GTPase-activating protein, RabGAP, acts as a negative regulator of Rab small GTPases, which orchestrate the intracellular membrane trafficking involved in cell proliferation. Deletion mutants of Dd rbg-3 exhibited an increased growth rate and a shortened developmental period, while an overexpression mutant demonstrated the opposite effects. We also show that Dd Rbg-3 interacts with 2 Gα subunits in an activity-dependent manner in vitro. Furthermore, both human and Caenorhabditis elegans rbg-3 homologs complemented the Dd rbg-3-deletion phenotype in D. discoideum, indicating that similar pathways may be generally conserved in multicellular organisms.
  
  
  CONCLUSIONS
  Our findings suggest that Dd Rbg-3 acts as a key element regulating the duration of D. discoideum life-span potentially via trimeric G-protein cascades.
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Kuwayama
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Japan ; Japan Science and Technology Agency, Core Research for Evolutional Science and Technology, Toyonaka, Japan.
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Miyanaga
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
authors.forename: Hideko
authors.initials: H
authors.lastname: Urushihara
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Japan ; Japan Science and Technology Agency, Core Research for Evolutional Science and Technology, Toyonaka, Japan ; Quantitative Biology Center, RIKEN, Osaka, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ueda
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans; D049109:Cell Proliferation; D004023:Dictyostelium / Q000235:genetics* / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000235:genetics* / Q000378:metabolism; D017353:Gene Deletion; D005786:Gene Expression Regulation; D005816:Genetic Complementation Test; D006801:Humans; D008018:Life Cycle Stages / Q000235:genetics*; D008869:Microtubule-Associated Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D011485:Protein Binding; D055503:Protein Multimerization; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction; D020798:Two-Hybrid System Techniques
chemical_list: D020690:GTPase-Activating Proteins; D008869:Microtubule-Associated Proteins; D015800:Protozoan Proteins