title: Characterization of dip1p reveals a switch in Arp2/3-dependent actin assembly for fission yeast endocytosis.
abstract: BACKGROUND
  During endocytosis in yeast, a choreographed series of discrete local events at the plasma membrane lead to a rapid burst of actin polymerization and the subsequent internalization of an endocytic vesicle. What initiates Arp2/3-dependent actin polymerization in this process is not well understood.
  
  
  RESULTS
  The Schizosaccharomyces pombe WISH/DIP/SPIN90 ortholog dip1p is an actin-patch protein that regulates the temporal sequence of endocytic events. dip1Δ mutants exhibit a novel phenotype in which early events such as WASp localization occur normally but arrival of Arp2/3, actin polymerization, and subsequent steps are delayed and occur with apparently random timing. In studying this mutant, we demonstrate that positive feedback loops of WASp, rapid actin assembly, and Arp2/3 contribute to switch-like behavior that initiates actin polymerization. In the absence of dip1p, a subset of patches is activated concurrently with the "touch" of a neighboring endocytic vesicle.
  
  
  CONCLUSIONS
  These studies reveal a switch-like mechanism responsible for the initiation of actin assembly during endocytosis. This switch may be activated in at least two ways, through a dip1p-dependent mechanism and through contact with another endocytic vesicle.
authors.affiliation: Department of Microbiology & Immunology, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA.
authors.forename: Roshni
authors.initials: R
authors.lastname: Basu
authors.forename: Fred
authors.initials: F
authors.lastname: Chang
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000235:genetics / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism; D004705:Endocytosis / Q000235:genetics*; D000080865:Formins; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D058105:Polymerization; D012568:Schizosaccharomyces / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D018797:Cell Cycle Proteins; C444419:FOR3 protein, S pombe; D000080865:Formins; D008840:Microfilament Proteins; D029702:Schizosaccharomyces pombe Proteins; C417034:Wsp1 protein, S pombe