Ehrlicher, A. J. ; Krishnan, R. ; Guo, M. ; Bidan, C. M. ; Weitz, D. A. ; Pollak, M. R. Alpha-actinin binding kinetics modulate cellular dynamics and force generation. Proceedings of the National Academy of Sciences 2015, 112, 6619-6624. Publisher's VersionAbstract

The actin cytoskeleton is a key element of cell structure and movement whose properties are determined by a host of accessory proteins. Actin cross-linking proteins create a connected network from individual actin filaments, and though the mechanical effects of cross-linker binding affinity on actin networks have been investigated in reconstituted systems, their impact on cellular forces is unknown. Here we show that the binding affinity of the actin cross-linker α-actinin 4 (ACTN4) in cells modulates cytoplasmic mobility, cellular movement, and traction forces. Using fluorescence recovery after photobleaching, we show that an ACTN4 mutation that causes human kidney disease roughly triples the wild-type binding affinity of ACTN4 to F-actin in cells, increasing the dissociation time from 29 ± 13 to 86 ± 29 s. This increased affinity creates a less dynamic cytoplasm, as demonstrated by reduced intracellular microsphere movement, and an approximate halving of cell speed. Surprisingly, these less motile cells generate larger forces. Using traction force microscopy, we show that increased binding affinity of ACTN4 increases the average contractile stress (from 1.8 ± 0.7 to 4.7 ± 0.5 kPa), and the average strain energy (0.4 ± 0.2 to 2.1 ± 0.4 pJ). We speculate that these changes may be explained by an increased solid-like nature of the cytoskeleton, where myosin activity is more partitioned into tension and less is dissipated through filament sliding. These findings demonstrate the impact of cross-linker point mutations on cell dynamics and forces, and suggest mechanisms by which such physical defects lead to human disease.

Hackelbusch, S. ; Rossow, T. ; Steinhilber, D. ; Weitz, D. A. ; Seiffert, S. Hybrid Microgels with Thermo-Tunable Elasticity for Controllable Cell Confinement. Advanced Healthcare Materials 2015, n/a–n/a. Publisher's Version 2015_advhealthcaremater_hackelbusch.pdf
Gaudreault, R. ; Di Cesare, N. ; van de Ven, T. G. M. ; Weitz, D. A. Structure and Strength of Flocs of Precipitated Calcium Carbonate Induced by Various Polymers Used in Papermaking. Industrial & Engineering Chemistry Research 2015, null. Publisher's Version 2015_iec_caudreault.pdf
Klein, A.  M. ; Mazutis, L. ; Akartuna, I. ; Tallapragada, N. ; Veres, A. ; Li, V. ; Peshkin, L. ; Weitz, D.  A. ; Kirschner, M.  W. Droplet Barcoding for Single-Cell Transcriptomics Applied to Embryonic Stem Cells. Cell 2015, 161, 1187 - 1201. Publisher's Version 2015_cell_klein.pdf
Macosko, E.  Z. ; Basu, A. ; Satija, R. ; Nemesh, J. ; Shekhar, K. ; Goldman, M. ; Tirosh, I. ; Bialas, A.  R. ; Kamitaki, N. ; Martersteck, E.  M. ; et al. Highly Parallel Genome-wide Expression Profiling of Individual Cells Using Nanoliter Droplets. Cell 2015, 161, 1202 - 1214. Publisher's Version 2015_cell_macosko.pdf
Zhou, Y. ; Park, J. ; Shi, J. ; Chhowalla, M. ; Park, H. ; Weitz, D. A. ; Ramanathan, S. Control of Emergent Properties at a Correlated Oxide Interface with Graphene. Nano Letters 2015, 15, 1627-1634. Publisher's Version 2015_nanoletter_zhou.pdf
Russell, E. R. ; Spaepen, F. ; Weitz, D. A. Anisotropic elasticity of experimental colloidal Wigner crystals. Phys. Rev. E 2015, 91, 032310. Publisher's Version 2015_pre_russell.pdf
Bannwarth, M. B. ; Utech, S. ; Ebert, S. ; Weitz, D. A. ; Crespy, D. ; Landfester, K. Colloidal Polymers with Controlled Sequence and Branching Constructed from Magnetic Field Assembled Nanoparticles. ACS Nano 2015, 9 2720-2728. Publisher's Version 2015_acsnano_bannwarth.pdf

PMID: 25695858

Kanai, T. ; Boon, N. ; Lu, P. J. ; Sloutskin, E. ; Schofield, A. B. ; Smallenburg, F. ; van Roij, R. ; Dijkstra, M. ; Weitz, D. A. Crystallization and reentrant melting of charged colloids in nonpolar solvents. Phys. Rev. E 2015, 91, 030301. Publisher's Version 2015_pre_kanai.pdf
Lee, W. C. ; Kim, K. ; Park, J. ; Koo, J. ; Jeong, H. Y. ; Lee, H. ; Weitz, D. A. ; Zettl, A. ; Takeuchi, S. Graphene-templated directional growth of an inorganic nanowire. Nature Nanotechnology 2015, 10, 423-428. 2015_natnanotech_lee.pdf
Fischer, A. E. ; Wu, S. K. ; Proescher, J. B. G. ; Rotem, A. ; Chang, C. B. ; Zhang, H. ; Tao, Y. ; Mehoke, T. S. ; Thielen, P. M. ; Kolawole, A. O. ; et al. A high-throughput drop microfluidic system for virus culture and analysis. Journal of Virological Methods 2015, 213, 111-117.Abstract

High mutation rates and short replication times lead to rapid evolution in RNA viruses. New tools for high-throughput culture and analysis of viral phenotypes will enable more effective studies of viral evolutionary processes. A water-in-oil drop microfluidic system to study virus–cell interactions at the single event level on a massively parallel scale is described here. Murine norovirus (MNV-1) particles were co-encapsulated with individual RAW 264.7 cells in 65 pL aqueous drops formed by flow focusing in 50 μm microchannels. At low multiplicity of infection (MOI), viral titers increased greatly, reaching a maximum 18 h post-encapsulation. This system was employed to evaluate MNV-1 escape from a neutralizing monoclonal antibody (clone A6.2). Further, the system was validated as a means for testing escape from antibody neutralization using a series of viral point mutants. Finally, the replicative capacity of single viral particles in drops under antibody stress was tested. Under standard conditions, many RNA virus stocks harbor minority populations of genotypic and phenotypic variants, resulting in quasispecies. These data show that when single cells are encapsulated with single viral particles under antibody stress without competition from other virions, the number of resulting infectious particles is nearly equivalent to the number of viral genomes present. These findings suggest that lower fitness virions can infect cells successfully and replicate, indicating that the microfluidics system may serve as an effective tool for isolating mutants that escape evolutionary stressors.

Köster, S. ; Weitz, D. A. ; Goldman, R. D. ; Aebi, U. ; Herrmann, H. Intermediate filament mechanics in vitro and in the cell: from coiled coils to filaments, fibers and networks. Current Opinion in Cell Biology 2015, 32, 82-91.Abstract

Intermediate filament proteins form filaments, fibers and networks both in the cytoplasm and the nucleus of metazoan cells. Their general structural building plan accommodates highly varying amino acid sequences to yield extended dimeric α-helical coiled coils of highly conserved design. These ‘rod’ particles are the basic building blocks of intrinsically flexible, filamentous structures that are able to resist high mechanical stresses, that is, bending and stretching to a considerable degree, both in vitro and in the cell. Biophysical and computer modeling studies are beginning to unfold detailed structural and mechanical insights into these major supramolecular assemblies of cell architecture, not only in the ‘test tube’ but also in the cellular and tissue context.

Zieringer, M. A. ; Carroll, N. J. ; Abbaspourrad, A. ; Koehler, S. A. ; Weitz, D. A. Microcapsules for Enhanced Cargo Retention and Diversity. Small 2015, n/a–n/a. Publisher's Version 2015_small_microcapsules_for_cargo_retention.pdf
Polenz, I. ; Weitz, D. A. ; Baret, J. - C. Polyurea Microcapsules in Microfluidics: Surfactant Control of Soft Membranes. Langmuir 2015, 31, 1127–1134. Publisher's Version 2015_langmuir_polyurea_microcapsules.pdf

PMID: 25531127

Akartuna, I. ; Aubrecht, D. M. ; Kodger, T. E. ; Weitz, D. A. Chemically induced coalescence in droplet-based microfluidics. Lab Chip 2015, -. Publisher's VersionAbstract

We present a new microfluidic method to coalesce pairs of surfactant-stabilized water-in-fluorocarbon oil droplets. We achieve this through the local addition of a poor solvent for the surfactant{,} perfluorobutanol{,} which induces cohesion between droplet interfaces causing them to merge. The efficiency of this technique is comparable to existing techniques providing an alternative method to coalesce pairs of droplets.

Shimanovich, U. ; Efimov, I. ; Mason, T. O. ; Flagmeier, P. ; Buell, A. K. ; Gedanken, A. ; Linse, S. ; Åkerfeldt, K. S. ; Dobson, C. M. ; Weitz, D. A. ; et al. Protein Microgels from Amyloid Fibril Networks. ACS Nano 2015, Article ASAP. Publisher's Version [PDF]

PMID: 25469621

Ostafe, R. ; Prodanovic, R. ; Lloyd Ung, W. ; Weitz, D. A. ; Fischer, R. A high-throughput cellulase screening system based on droplet microfluidics. Biomicrofluidics 2014, 8 041102. Publisher's Version [PDF]
Fan, J. ; Li, Y. ; Bisoyi, H. K. ; Zola, R. S. ; Yang, Deng-ke, B. T. J. W. D. A. L. Q. Light-Directing Omnidirectional Circularly Polarized Reflection from Liquid-Crystal Droplets. Angewandte Chemie International Edition 2014. 2014_angew_fan.pdf
Kim, S. - H. ; Park, J. - G. ; Choi, T. M. ; Manoharan, V. N. ; Weitz, D. A. Osmotic-pressure-controlled concentration of colloidal particles in thin-shelled capsules. Nature communications 2014, 5 3068. 2014_natcomm_kim.pdf
Deng, N. - N. ; Wang, W. ; Ju, X. - J. ; Xie, R. ; Weitz, D. A. ; Chu, L. - Y. Reply to the ‘Comment on “Wetting-induced formation of controllable monodisperse multiple emulsions in microfluidics”’by J. Guzowski and P. Garstecki, Lab Chip, 2014, 14, DOI: 10.1039/C3LC51229K. Lab on a Chip 2014, 14, 1479–1480. 2014_loc_deng_rtc.pdf