A major focus of my laboratory is to understand how cytoskeletal polymers help a collection of macromolecules work together to establish a common identity: to become a living cell. Grants to my laboratory from NIGMS have funded work on several basic cell biological processes, in both eukaryotes and prokaryotes, including: (i) the assembly and function of force-generating `lamellipodial' actin networks that drive membrane movements in eukaryotic cells (GM061010 and an NDC Roadmap Grant); (ii) the actin nucleating activity and biological function of Spire-family proteins (GM075287); (iii) the architecture and function of actin-based structures in the nucleus (GM061010); and (iv) DNA segregation in bacterial cells, driven by assembly of cytoskeletal polymers (GM095263 and GM079556). A MIRA grant funding all these projects would enable us redirect energy previously devoted to maintaining multiple R0-1 grants into doing more original work. To understand how molecular properties govern the architecture and function of living cells, we perform quantitative studies at multiple size scales: (i) single-molecule and bulk biochemical studies of cytoskeletal components; (ii) biophysical and microscopical studies of complex cellular structures reconstituted in vitro; and (iii) cell biological and high-resolution microscopy studies of cytoskeletal systems in living cells. Broadly speaking, the ongoing work that would be supported by this grant can be divided into four parts: 1. Studies of prokaryotic cytoskeletal systems. Prokaryotic genomes encode more than forty classes of actin-like proteins (ALPs). We have studied the assembly and function of three eubacterial ALPs (ParM, AlfA, and Alp7A) and we are currently working to understand the role of ALPs in archaea. 2. Studies of dendritic actin networks assembled by: the Arp2/3 complex, WASP/WAVE-family proteins, Ena/VASP, formins, capping protein, cofilin, and profilin. In addition to powering some types of cell locomotion, this `dendritic network motor' also contributes to phagocytosis, endocytosis, movement of intracellular pathogens, and healing of membrane ruptures. Among other things, we are currently working to understand the mechanisms by which these networks generate and adapt to mechanical forces. 3. Studies of fast amoeboid migration. We combine `Evolutionary Cell Biology' approaches with 3D Bessel Beam microscopy to understand how cells generate complex membrane dynamics and then harness them for rapid movement. Briefly, we employ comparative genomics and cell biological studies of widely divergent (non-model) organisms to uncover molecular and biophysical mechanisms of cell movement. 4. Studies of the assembly and function of actin filaments in eukaryotic nuclei. We recently discovered nuclear actin filaments created by Fmn2 and Spire-family molecules in response to DNA damage. These filaments contribute to rapid clearance of double-strand DNA breaks (Belin and Mullins, submitted) and we are working to understand their functions and to work out the signaling pathways that create them.

Public Health Relevance

Organization and cooperation are fundamental to life. At the most microscopic level, individual molecules must interact, cooperate, and self-organize to create living cells. The goal of this proposal is to understand how the self-assembly of actin-based cytoskeletal structures helps organize the contents of cells; gives them shape; and enables them to move.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Unknown (R35)
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Special Emphasis Panel (ZGM1)
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Ainsztein, Alexandra M
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University of California San Francisco
Schools of Medicine
San Francisco
United States
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Fritz-Laylin, Lillian K; Lord, Samuel J; Kakley, Mallory et al. (2018) Concise Language Promotes Clear Thinking about Cell Shape and Locomotion. Bioessays 40:e1700225
Bieling, Peter; Hansen, Scott D; Akin, Orkun et al. (2018) WH2 and proline-rich domains of WASP-family proteins collaborate to accelerate actin filament elongation. EMBO J 37:102-121
Fritz-Laylin, Lillian K; Riel-Mehan, Megan; Chen, Bi-Chang et al. (2017) Actin-based protrusions of migrating neutrophils are intrinsically lamellar and facilitate direction changes. Elife 6:
Díaz-Celis, César; Risca, Viviana I; Hurtado, Felipe et al. (2017) Bacterial Tubulins A and B Exhibit Polarized Growth, Mixed-Polarity Bundling, and Destabilization by GTP Hydrolysis. J Bacteriol 199:
Fritz-Laylin, Lillian K; Lord, Samuel J; Mullins, R Dyche (2017) WASP and SCAR are evolutionarily conserved in actin-filled pseudopod-based motility. J Cell Biol 216:1673-1688
Fritz-Laylin, Lillian K; Lord, Samuel J; Mullins, R Dyche (2017) Our evolving view of cell motility. Cell Cycle 16:1735-1736
Bieling, Peter; Li, Tai-De; Weichsel, Julian et al. (2016) Force Feedback Controls Motor Activity and Mechanical Properties of Self-Assembling Branched Actin Networks. Cell 164:115-127
Köster, Darius Vasco; Husain, Kabir; Iljazi, Elda et al. (2016) Actomyosin dynamics drive local membrane component organization in an in vitro active composite layer. Proc Natl Acad Sci U S A 113:E1645-54
Hansen, Scott D; Mullins, R Dyche (2015) Lamellipodin promotes actin assembly by clustering Ena/VASP proteins and tethering them to actin filaments. Elife 4:
Belin, Brittany J; Lee, Terri; Mullins, R Dyche (2015) DNA damage induces nuclear actin filament assembly by Formin -2 and Spire-½ that promotes efficient DNA repair. [corrected]. Elife 4:e07735