Jauregui LA, Joe AY, Pistunova K, Wild DS, High AA, Zhou Y, Scuri G, De Greve K, Sushko A, Yu C-H, et al. Electrical control of interlayer exciton dynamics in atomically thin heterostructures. Science. 2019;336 (6467) :870-875.
Publisher's VersionAbstractA van der Waals heterostructure built from atomically thin semiconducting transition metal dichalcogenides (TMDs) enables the formation of excitons from electrons and holes in distinct layers, producing interlayer excitons with large binding energy and a long lifetime. By employing heterostructures of monolayer TMDs, we realize optical and electrical generation of long-lived neutral and charged interlayer excitons. We demonstrate that neutral interlayer excitons can propagate across the entire sample and that their propagation can be controlled by excitation power and gate electrodes. We also use devices with ohmic contacts to facilitate the drift motion of charged interlayer excitons. The electrical generation and control of excitons provide a route for achieving quantum manipulation of bosonic composite particles with complete electrical tunability.
Download Paper Fürthauer S, Lemma B, Foster PJ, Ems-McClung SC, Yu7 C-H, Walczak CE, Dogic Z, Needleman DJ, Shelley MJ.
Self-straining of actively crosslinked microtubule networks. Nature Physics. 2019.
AbstractCytoskeletal networks are foundational examples of active matter and central to self-organized structures in the cell. In vivo, these networks are active and densely crosslinked. Relating their large-scale dynamics to the properties of their constituents remains an unsolved problem. Here, we study an in vitro active gel made from aligned microtubules and XCTK2 kinesin motors. Using photobleaching, we demonstrate that the gel’s aligned microtubules, driven by motors, continually slide past each other at a speed independent of the local microtubule polarity and motor concentration. This phenomenon is also observed, and remains unexplained, in spindles. We derive a general framework for coarse graining microtubule gels crosslinked by molecular motors from microscopic considerations. Using microtubule–microtubule coupling through a force–velocity relationship for kinesin, this theory naturally explains the experimental results: motors generate an active strain rate in regions of changing polarity, which allows microtubules of opposite polarities to slide past each other without stressing the material.
Download Paper Needleman D, Shelley M.
The stormy fluid dynamics of the living cell. Physics Today. 2019;72 (9).
Publisher's VersionAbstractCell biology has its beginnings in the first observations of cells through primitive microscopes and in the formulation of cell theory, which postulates that cells are the fundamental building blocks of life. Light microscopes showed that the insides of cells contained complex structures, such as nuclei, spindles, and chromosomes. The advent of electron microscopy in the mid 20th century brought the first truly detailed views of cell innards. Images revealed complexity at all observable scales, including cell-spanning networks of polymers, intricate organelles made of membranes, and a variety of micron- to nanometer-sized sacs and granules such as vesicles, lipid droplets, and ribosomes. (For a glossary of cellular components, see the Quick Study by Ned Wingreen, PHYSICS TODAY, September 2006, page 80.) Those structures are immersed in or part of the aqueous cytoplasm—the cell’s fluidic medium.
Download Paper MBoC Paper of the Year Award Winner: Yu C-H*, Redemann* S, Wu H-Y, Kiewisz R, Yoo TY, Conway W, Farhadifar R, Müller-Reichert T, Needleman D.
Central-spindle microtubules are strongly coupled to chromosomes during both anaphase A and anaphase B. Molecular Biology of the Cell. 2019;30 :2503-2514.
Publisher's VersionAbstract
Spindle microtubules, whose dynamics vary over time and at different locations, cooperatively drive chromosome segregation. Measurements of microtubule dynamics and spindle ultrastructure can provide insight into the behaviors of microtubules, helping elucidate the mechanism of chromosome segregation. Much work has focused on the dynamics and organization of kinetochore microtubules, that is, on the region between chromosomes and poles. In comparison, microtubules in the central-spindle region, between segregating chromosomes, have been less thoroughly characterized. Here, we report measurements of the movement of central-spindle microtubules during chromosome segregation in human mitotic spindles and Caenorhabditis elegans mitotic and female meiotic spindles. We found that these central-spindle microtubules slide apart at the same speed as chromosomes, even as chromosomes move toward spindle poles. In these systems, damaging central-spindle microtubules by laser ablation caused an immediate and complete cessation of chromosome motion, suggesting a strong coupling between central-spindle microtubules and chromosomes. Electron tomographic reconstruction revealed that the analyzed anaphase spindles all contain microtubules with both ends between segregating chromosomes. Our results provide new dynamical, functional, and ultrastructural characterizations of central-spindle microtubules during chromosome segregation in diverse spindles and suggest that central-spindle microtubules and chromosomes are strongly coupled in anaphase.
Download Paper ascb_newsletter_december_2020.pdf Sanchez T, Zhang M, Needleman D, Seli E.
Metabolic imaging via fluorescence lifetime imaging microscopy for egg and embryo assessment. Fertility and Sterility. 2019;111 (2) :212 - 218.
Publisher's VersionAbstractCurrent strategies for embryo assessment in the assisted reproductive technology laboratories rely primarily on morphologic parameters that have limited accuracy for determining embryo viability. Even with the addition of invasive diagnostic interventions such as preimplantation genetic testing for aneuploidy alone or in combination with mitochondrial DNA copy number assessment, at least one third of embryos fail to implant. Therefore, at a time when the clinical benefits of single ET are widely accepted, improving viability assessment of embryos is ever more important. Building on the previous work demonstrating the importance of metabolic state in oocytes and embryos, metabolic imaging via fluorescence lifetime imaging microscopy offers new and potentially useful diagnostic method by detecting natural fluorescence of FAD and NADH, the two electron transporters that play a central role in oxidative phosphorylation. Recent studies demonstrate that fluorescence lifetime imaging microscopy can detect oocyte and embryo metabolic function and dysfunction in a multitude of experimental models and provide encouraging evidence for use in scientific investigation and possibly for clinical application.
Download Paper Foster PJ, Fürthauer S, Shelley MJ, Needleman DJ.
From cytoskeletal assemblies to living materials. Current Opinion in Cell Biology. 2019;56 :109–114.
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