The actin filament nucleator Arp2/3 complex is activated at cortical sites in S. pombe to assemble branched actin networks that drive endocytosis. Arp2/3 complex activators Wsp1 and Dip1 are required for proper actin assembly at endocytic sites, but how they coordinately control Arp2/3-mediated actin assembly is unknown. Alone, Dip1 activates Arp2/3 complex without preexisting actin filaments to nucleate 'seed' filaments that activate Wsp1-bound Arp2/3 complex, thereby initiating branched actin network assembly. In contrast, because Wsp1 requires pre-existing filaments to activate, it has been assumed to function exclusively in propagating actin networks by stimulating branching from pre-existing filaments. Here we show that Wsp1 is important not only for propagation, but also for initiation of endocytic actin networks. Using single molecule TIRF microscopy we show that Wsp1 synergizes with Dip1 to co-activate Arp2/3 complex. Synergistic coactivation does not require pre-existing actin filaments, explaining how Wsp1 contributes to actin network initiation in cells.
- Brad J Nolen
- Connor John Balzer
- Luke A Helgeson
- Connor John Balzer
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Alphee Michelot, Institut de Biologie du Développement, France
- Received: June 26, 2020
- Accepted: November 10, 2020
- Accepted Manuscript published: November 12, 2020 (version 1)
© 2020, Balzer 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.
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