Excitons in semiconductors, bound pairs of excited electrons and holes, can form the basis for new classes of quantum optoelectronic devices. A 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. Employing heterostructures of monolayer TMDs, we realize optical and electrical generation of long-lived neutral and charged interlayer excitons. We demonstrate the transport of neutral interlayer excitons across the whole sample that can be controlled by excitation power and gate electrodes. We also realize the drift motion of charged interlayer excitons using Ohmic-contacted devices. The electrical generation and control of excitons provides a new route for realizing quantum manipulation of bosonic composite particles with complete electrical tunability.As bosonic composite particles, long-lived excitons can be potentially utilized for the realization of coherent quantum many-body systems (1, 2) or as quantum information carriers (3,4). In conventional semiconductors, the exciton lifetime can be increased by constructing double quantum well (DQW) heterostructures, where spatially separated electrons and holes form interlayer excitons (IEs) across the quantum wells (5-10). Strongly bound IEs can also be formed in atomically thin DQW. By stacking two

Concentration gradients of soluble proteins are believed to be responsible for control of morphogenesis of subcellular systems, but the mechanisms that generate the spatial organization of these subcellular gradients remain poorly understood. Here, we use a newly developed multipoint fluorescence fluctuation spectroscopy technique to study the ras-related nuclear protein (Ran) pathway, which forms soluble gradients around chromosomes in mitosis and is thought to spatially regulate microtubule behaviors during spindle assembly. We found that the distribution of components of the Ran pathway that influence microtubule behaviors is determined by their interactions with microtubules, resulting in microtubule nucleators being localized by the microtubules whose formation they stimulate. Modeling and perturbation experiments show that this feedback makes the length of the spindle insensitive to the length scale of the Ran gradient, allows the spindle to assemble outside the peak of the Ran gradient, and explains the scaling of the spindle with cell size. Such feedback between soluble signaling pathways and the mechanics of the cytoskeleton may be a general feature of subcellular organization.RanGTP gradient | spatial organization | microtubule nucleation | feedback loop | spindle size C ells exhibit internal order over a range of length scales (1). The manners in which nanometer-sized proteins specify micrometer-scale subcellular organization remain poorly understood. Either mechanics or chemistry could in principle produce order at length scales of cellular dimensions. The simplest mechanical phenomena result from the cytoskeleton: Filaments can be microns long and thus their individual lengths may even be sufficient to specify large-scale subcellular organization. Chemical processes can produce large, defined length scales through the interplay between diffusion and reactions (2). The simplest reaction-diffusion phenomenon, which has been widely discussed in the context of subcellular organization, is a scenario in which a signaling molecule is phosphorylated at one location in a cell and diffuses away and gradually dephosphorylates (3). Simple mathematical models of such source-sink scenarios predict that the resulting steady-state profile will be an exponentially decreasing gradient of the phosphorylated form around the source, with a length scale of λ = ffiffiffiffiffiffiffiffi ffi D=k p , where D is the diffusion coefficient of the signaling molecule and k is the rate of dephosphorylation (3). λ is the average distance a molecule diffuses before it is dephosphorylated.Although mechanics and chemistry are individually sufficient to give rise to structure at micrometer-length scales, increasing evidence suggests that the joint contribution of both of them leads to novel phenomena that might be important for subcellular organization: The interactions of diffusible molecules with the cytoskeleton can alter their mobility and localization, greatly modifying reaction-diffusion processes (4-8); large-scale patterns can...

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.

Imaging the activity of neurons that are widely distributed across brain regions deep in scattering tissue at high speed remains challenging. Here, we introduce an open-source system with Dual Independent Enhanced Scan Engines for Large field-of-view Two-Photon imaging (Diesel2p). Combining optical design, adaptive optics, and temporal multiplexing, the system offers subcellular resolution over a large field-of-view of ~25 mm2, encompassing distances up to 7 mm, with independent scan engines. We demonstrate the flexibility and various use cases of this system for calcium imaging of neurons in the living brain.