1. Cell Biology
Download icon

Cell cycle entry triggers a switch between two modes of Cdc42 activation during yeast polarization

  1. Kristen L Witte
  2. Devin Strickland
  3. Michael Glotzer  Is a corresponding author
  1. University of Chicago, United States
Research Article
  • Cited 24
  • Views 2,027
  • Annotations
Cite this article as: eLife 2017;6:e26722 doi: 10.7554/eLife.26722

Abstract

Cell polarization underlies many cellular and organismal functions. The GTPase Cdc42 orchestrates polarization in many contexts. In budding yeast, polarization is associated with a focus of Cdc42•GTP which is thought to self sustain by recruiting a complex containing Cla4, a Cdc42-binding effector, Bem1, a scaffold, and Cdc24, a Cdc42 GEF. Using optogenetics, we probe yeast polarization and find that local recruitment of Cdc24 or Bem1 is sufficient to induce polarization by triggering self-sustaining Cdc42 activity. However, the response to these perturbations depends on the recruited molecule, the cell cycle stage, and existing polarization sites. Before cell cycle entry, recruitment of Cdc24, but not Bem1, induces a metastable pool of Cdc42 that is sustained by positive feedback. Upon Cdk1 activation, recruitment of either Cdc24 or Bem1 creates a stable site of polarization that induces budding and inhibits formation of competing sites. Local perturbations have therefore revealed unexpected features of polarity establishment.

Article and author information

Author details

  1. Kristen L Witte

    Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Devin Strickland

    Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Michael Glotzer

    Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, United States
    For correspondence
    mglotzer@uchicago.edu
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-8723-7232

Funding

National Institute of General Medical Sciences (R01GM85087)

  • Michael Glotzer

American Cancer Society (119248-PF-10-134-01-CCG)

  • Devin Strickland

National Institute of General Medical Sciences (T32 GM007183)

  • Kristen L Witte

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Sheila McCormick, University of California-Berkeley, United States

Publication history

  1. Received: March 11, 2017
  2. Accepted: July 4, 2017
  3. Accepted Manuscript published: July 6, 2017 (version 1)
  4. Version of Record published: July 31, 2017 (version 2)

Copyright

© 2017, Witte et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

Metrics

  • 2,027
    Page views
  • 454
    Downloads
  • 24
    Citations

Article citation count generated by polling the highest count across the following sources: Crossref, Scopus, PubMed Central.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Download citations (links to download the citations from this article in formats compatible with various reference manager tools)

Open citations (links to open the citations from this article in various online reference manager services)

Further reading

    1. Biochemistry and Chemical Biology
    2. Cell Biology
    Niladri K Sinha et al.
    Research Article

    Translation of aberrant mRNAs induces ribosomal collisions, thereby triggering pathways for mRNA and nascent peptide degradation and ribosomal rescue. Here we use sucrose gradient fractionation combined with quantitative proteomics to systematically identify proteins associated with collided ribosomes. This approach identified Endothelial differentiation-related factor 1 (EDF1) as a novel protein recruited to collided ribosomes during translational distress. Cryo-electron microscopic analyses of EDF1 and its yeast homolog Mbf1 revealed a conserved 40S ribosomal subunit binding site at the mRNA entry channel near the collision interface. EDF1 recruits the translational repressors GIGYF2 and EIF4E2 to collided ribosomes to initiate a negative-feedback loop that prevents new ribosomes from translating defective mRNAs. Further, EDF1 regulates an immediate-early transcriptional response to ribosomal collisions. Our results uncover mechanisms through which EDF1 coordinates multiple responses of the ribosome-mediated quality control pathway and provide novel insights into the intersection of ribosome-mediated quality control with global transcriptional regulation.

    1. Cell Biology
    2. Microbiology and Infectious Disease
    Mark S Ladinsky et al.
    Research Article Updated

    Fusion of HIV-1 with the membrane of its target cell, an obligate first step in virus infectivity, is mediated by binding of the viral envelope (Env) spike protein to its receptors, CD4 and CCR5/CXCR4, on the cell surface. The process of viral fusion appears to be fast compared with viral egress and has not been visualized by EM. To capture fusion events, the process must be curtailed by trapping Env-receptor binding at an intermediate stage. We have used fusion inhibitors to trap HIV-1 virions attached to target cells by Envs in an extended pre-hairpin intermediate state. Electron tomography revealed HIV-1 virions bound to TZM-bl cells by 2–4 narrow spokes, with slightly more spokes present when evaluated with mutant virions that lacked the Env cytoplasmic tail. These results represent the first direct visualization of the hypothesized pre-hairpin intermediate of HIV-1 Env and improve our understanding of Env-mediated HIV-1 fusion and infection of host cells.