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Visualizing Membrane Ruffle Formation using Scanning Electron Microscopy
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Visualizing Membrane Ruffle Formation using Scanning Electron Microscopy

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Ruffles limit diffusion in the plasma membrane during macropinosome formation

Timothy P Welliver1, S Laura Chang, Jennifer J Linderman

  • 1Program in Immunology, University of Michigan Medical School, Ann Arbor, MI 48109-5620, USA.

Journal of Cell Science
|December 24, 2011
PubMed

Insights

Circular ruffles in macrophages concentrate signaling molecules, enhancing cell communication. This actin-driven process is crucial for forming macropinosomes and amplifying cellular signals.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biophysics

Background:

  • Macropinosome formation is vital for cellular processes like nutrient uptake and immune surveillance.
  • Macrophage-colony-stimulating factor (M-CSF) triggers signaling pathways essential for macropinosome formation.
  • Circular ruffles are actin-rich plasma membrane structures involved in cellular signaling.

Purpose of the Study:

  • To investigate the role of circular ruffles in restricting the lateral diffusion of membrane proteins.
  • To understand how circular ruffles contribute to signal amplification during macropinosome formation.
  • To test the hypothesis that actin-mediated confinement within circular ruffles is essential for Rac1 activation.

Main Methods:

  • Utilized murine macrophages stimulated with M-CSF.
  • Disrupted actin polymerization using latrunculin B to assess its effect on ruffling and Rac1 activity.
  • Monitored the diffusion of photoactivatable green fluorescent protein targeted to the membrane (PAGFP-MEM) in live cells.

Main Results:

  • M-CSF stimulation induced the formation of circular ruffles, concentrating signaling molecules.
  • Latrunculin B inhibited ruffling and localized Rac1 activation, indicating actin's role in signaling.
  • Circular ruffles retained PAGFP-MEM within their domains, suggesting confinement of membrane proteins.
  • Diffusion within macropinocytic cups was not inhibited, but ruffles acted as barriers.

Conclusions:

  • Circular ruffles act as signaling microdomains by confining essential membrane proteins.
  • Actin-mediated confinement within circular ruffles amplifies Rac1 signaling through positive feedback.
  • This organized signaling within ruffles facilitates the contractile events required for macropinosome closure.

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