Initiation of lamellipodia and ruffles involves cooperation between mDia1 and the Arp2/3 complex

J Cell Sci. 2015 Oct 15;128(20):3796-810. doi: 10.1242/jcs.176768. Epub 2015 Sep 8.


Protrusion of lamellipodia and ruffles requires polymerization of branched actin filaments by the Arp2/3 complex. Although regulation of Arp2/3 complex activity has been extensively investigated, the mechanism of initiation of lamellipodia and ruffles remains poorly understood. Here, we show that mDia1 acts in concert with the Arp2/3 complex to promote initiation of lamellipodia and ruffles. We find that mDia1 is an epidermal growth factor (EGF)-regulated actin nucleator involved in membrane ruffling using a combination of knockdown and rescue experiments. At the molecular level, mDia1 polymerizes linear actin filaments, activating the Arp2/3 complex, and localizes within nascent and mature membrane ruffles. We employ functional complementation experiments and optogenetics to show that mDia1 cooperates with the Arp2/3 complex in initiating lamellipodia and ruffles. Finally, we show that genetic and pharmacological interference with this cooperation hampers ruffling and cell migration. Thus, we propose that the lamellipodium- and ruffle-initiating machinery consists of two actin nucleators that act sequentially to regulate membrane protrusion and cell migration.

Keywords: Actin; Arp2/3; Cell migration; Lamellipodia; Ruffles; mDia1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin-Related Protein 2-3 Complex / genetics
  • Actin-Related Protein 2-3 Complex / metabolism*
  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism*
  • Animals
  • COS Cells
  • Cell Membrane Structures / genetics
  • Cell Membrane Structures / metabolism*
  • Chlorocebus aethiops
  • Formins
  • HeLa Cells
  • Humans
  • Pseudopodia / genetics
  • Pseudopodia / metabolism*


  • Actin-Related Protein 2-3 Complex
  • Adaptor Proteins, Signal Transducing
  • DIAPH1 protein, human
  • Formins