The assembly dynamics of the actin cytoskeleton is crucial for most morphogenetic processes that occur at both cellular and organism levels in eukaryotes. As a consequence, defects in actin dynamics and organization have been implicated in a variety of human diseases. However, our understanding of how actin is regulated in different physiological processes remains limited due to the extraordinary complexity and dynamic nature of the actin cytoskeletal system. The Arp2/3 complex is thought to be a major key element of actin filament nucleation and the formation of branched dendritic networks at the leading edge of motile cells. The role of Arp2/3 complex in these processes can only be understood through studies of the key molecular steps in the Arp2/3-mediated actin nucleation and branch formation. In this Program Project we aim at understanding the detailed structural mechanisms by which the Arp2/3 complex mediates the formation of actin branch junctions and the role of the Arp2/3 complex in vertebrate cell motility. We have assembled a highly synergistic team of Pis with complimentary expertise to achieve these goals through collaborative efforts. This sub-project (Volkmann lab) will contribute the development and application of a diverse set of computational tools for the reconstruction, analysis, and modeling of structural states and distribution patterns. Using these tools we will combine information from various data sources generated by all members of the Program Project to obtain (i) high-resolution models of the intermediates of the branch formation process and of the fully assembled branch itself;(ii) a dynamic, energetically self-consistent, structural model of the transition pathway from the inactive state of the Arp2/3 complex to the fully assembled branch in the dendritic network, and (iii) structural differences between different cell types and between wild-type cells and defective mutants by multi-dimensional and dynamical characterization of Arp2/3-complex and actin-filament distribution patterns in living eukaryotic cells.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Program Projects (P01)
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Special Emphasis Panel (ZRG1-CB-D)
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Yale University
New Haven
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Volkmann, Niels (2014) The joys and perils of flexible fitting. Adv Exp Med Biol 805:137-55
Volkmann, Niels; Page, Christopher; Li, Rong et al. (2014) Three-dimensional reconstructions of actin filaments capped by Arp2/3 complex. Eur J Cell Biol 93:179-83
Xu, Xiao-Ping; Slaughter, Brian D; Volkmann, Niels (2013) Probabilistic determination of probe locations from distance data. J Struct Biol 184:75-82
Xu, X-P; Zhai, D; Kim, E et al. (2013) Three-dimensional structure of Bax-mediated pores in membrane bilayers. Cell Death Dis 4:e683
Yi, Kexi; Rubinstein, Boris; Li, Rong (2013) Symmetry breaking and polarity establishment during mouse oocyte maturation. Philos Trans R Soc Lond B Biol Sci 368:20130002
Li, Rong; Albertini, David F (2013) The road to maturation: somatic cell interaction and self-organization of the mammalian oocyte. Nat Rev Mol Cell Biol 14:141-52
Pollard, Thomas D; De La Cruz, Enrique M (2013) Take advantage of time in your experiments: a guide to simple, informative kinetics assays. Mol Biol Cell 24:1103-10
Yi, Kexi; Rubinstein, Boris; Unruh, Jay R et al. (2013) Sequential actin-based pushing forces drive meiosis I chromosome migration and symmetry breaking in oocytes. J Cell Biol 200:567-76
Volkmann, Niels (2012) Putting structure into context: fitting of atomic models into electron microscopic and electron tomographic reconstructions. Curr Opin Cell Biol 24:141-7
Suraneni, Praveen; Rubinstein, Boris; Unruh, Jay R et al. (2012) The Arp2/3 complex is required for lamellipodia extension and directional fibroblast cell migration. J Cell Biol 197:239-51

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