Professor Cui develops new physical and chemical approaches to study biological processes in neurons, with particular focus on long-range signal propagation in axons and its implications in neurodegenerative disease. Methods of interest include live imaging of vesicular transport, magnetic and optical manipulation of axonal traffic, single-molecule fluorescence imaging, photo-lithography, electrophysiological recordings and a microfluidic neuronal platform for studying axonal transport.
Bianxiao Cui studied materials science and engineering at the University of Science & Technology of China (B.S. 1998) before pursuing doctoral study in physical chemistry at the University of Chicago (Ph.D. 2002). In thesis work under Prof. Stuart Rice, she explored dynamic heterogeneity and phase transition in colloidal liquids. She moved to California in 2002 to perform postdoctoral research with Prof. Steven Chu on single-molecule imaging of nerve growth factor signal transduction in neurons. She joined the Stanford Department of Chemistry as Assistant Professor in 2008, and in 2015 became Associate Professor. She was recently awarded the National Science Foundation INSPIRE Award for interdisciplinary research, as well as the NSF New Innovator and CAREER Awards, among others.
Current work in the Cui Lab seeks to understand neuronal signal propagation, with three major research directions: 1) investigating axonal transport processes using optical imaging, magnetic and optical trapping, and a microfluidic platform; 2) developing vertical nanopillar-based electric and optic sensors for sensitive detection of biological functions; 3) using optogentics to investigate temporal and spatial control of intracellular signaling pathways.
Single-molecule imaging of vesicle transport in axons
Defective axonal transport of materials between the neuronal cell body and synapse, such as accumulation of cargo or slower transport rate, has been linked with a range of neurodegenerative diseases. Cui lab members are investigating molecular mechanisms associated with retrograde axonal transport of neurotrophins, and the coordination of this essential process by molecular motors and regulatory proteins. The lab is developing a novel technique that permits external manipulation of axonal transport via magnetic and optical forces, affording new approaches to investigate the linkages between axonal transport and neuronal health and function.
Nano-bio interface: probing live cells with nanopillar sensors
Applying nanotechnology to new frontiers in biological science, the Cui Lab and other groups have shown that vertical nanopillars protruding from a flat surface support cell survival and can be used as subcellular sensors to probe biological processes in live cells. Ongoing work in the lab explores nanopillars as electric sensors, optical sensors and structural probes.
Optic control of intracellular signaling pathways
Cells constantly process environmental cues such as growth factors to determine cell fate, e.g. survival, proliferation, differentiation, migration, and apoptosis. To ensure proper conversion of a specific environmental input into a distinct cellular output, the activation of intracellular signaling pathways is tightly regulated in space and time. Compared with our understanding of proteins involved in various signaling pathways, much less is known about how these temporal and spatial aspects influence cell behavior, largely due to a lack of effective tools to precisely regulate signaling pathways in space and time. In the Cui Lab, light-gated protein-protein interaction systems are used to control the activation and inactivation of intracellular signaling pathways, providing unprecedented precision in temporal and spatial observations.
Please visit the Cui Lab website to learn more.
Affiliated Faculty and Scientific Leadership Council Member, Stanford Bio-X (2014 - Present)
Honors & Awards
Michael and Kate Barany Award, Biophysical Society (2018)
NSF INSPIRE award, National Science Foundation (2013)
NIH New Innovator Award, National Institutes of Health (2012)
Hellman Scholar, Hellman Foundation (2011)
NSF CAREER award, National Science Foundation (2011)
Packard Fellowships for Science and Engineering, David and Lucile Packard Foundation (2009)
Searle Scholar Award, Searle Scholars Program (2009)
Dreyfus New Faculty Award, Camille & Henry Dreyfus foundation (2008)
Terman Fellowship, Stanford University (2008)
NIH Pathway to Independence Career Award, National Institutes of Health (2006)
Postdoc, Stanford University Department of Physics, Biophysics (2002)
Ph.D., University of Chicago, Physical Chemistry (2002)
M.S., University of Chicago, Chemistry (2000)
B.S., University of Science & Technology of China, Material Sci. & Eng. (1998)
Current Research and Scholarly Interests
We are developing various physical and chemical approaches to study biological processes in neurons. There are three major research directions: (1) Investigating the axonal transport process using optical imging, magnetic and optical trapping, and microfluidic platform; (2) Developing vertical nanopillar-based electric and optic sensors for sensitive detection of biological functions; (3) Using optogentic approach to investigate temporal and spatial control of intracellular signaling pathways.
- Advanced Physical Chemistry
CHEM 273 (Win)
- Physical Chemistry I
CHEM 171 (Spr)
- Research Progress in Physical Chemistry
CHEM 278A (Win)
- Research Progress in Physical Chemistry
CHEM 278B (Win)
Independent Studies (6)
- Advanced Undergraduate Research
CHEM 190 (Aut, Win, Spr, Sum)
- Directed Instruction/Reading
CHEM 110 (Aut, Win, Spr, Sum)
- Directed Reading in Biophysics
BIOPHYS 399 (Aut, Win, Spr, Sum)
- Graduate Research
BIOPHYS 300 (Aut, Win, Spr, Sum)
- Research and Special Advanced Work
CHEM 200 (Aut, Win, Spr, Sum)
- Research in Chemistry
CHEM 301 (Aut, Win, Spr, Sum)
- Advanced Undergraduate Research
Prior Year Courses
- Advanced Physical Chemistry
CHEM 273 (Win)
- Physical Chemistry I
CHEM 171 (Spr)
- Research Progress in Physical Chemistry
CHEM 278A (Win)
- Research Progress in Physical Chemistry
CHEM 278B (Win)
- Advanced Physical Chemistry
CHEM 273 (Win)
- Research Progress in Physical Chemistry
CHEM 278A (Win)
- Research Progress in Physical Chemistry
CHEM 278B (Win)
- Advanced Physical Chemistry
Graduate and Fellowship Programs
Nanoscale manipulation of membrane curvature for probing endocytosis in live cells.
Clathrin-mediated endocytosis (CME) involves nanoscale bending and inward budding of the plasma membrane, by which cells regulate both the distribution of membrane proteins and the entry of extracellular species. Extensive studies have shown that CME proteins actively modulate the plasma membrane curvature. However, the reciprocal regulation of how the plasma membrane curvature affects the activities of endocytic proteins is much less explored, despite studies suggesting that membrane curvature itself can trigger biochemical reactions. This gap in our understanding is largely due to technical challenges in precisely controlling the membrane curvature in live cells. In this work, we use patterned nanostructures to generate well-defined membrane curvatures ranging from +50 nm to -500 nm radius of curvature. We find that the positively curved membranes are CME hotspots, and that key CME proteins, clathrin and dynamin, show a strong preference towards positive membrane curvatures with a radius <200 nm. Of ten CME-related proteins we examined, all show preferences for positively curved membrane. In contrast, other membrane-associated proteins and non-CME endocytic protein caveolin1 show no such curvature preference. Therefore, nanostructured substrates constitute a novel tool for investigating curvature-dependent processes in live cells.
View details for DOI 10.1038/nnano.2017.98
View details for PubMedID 28581510
Control of cerebral ischemia with magnetic nanoparticles.
2017; 14 (2): 160-166
The precise manipulation of microcirculation in mice can facilitate mechanistic studies of brain injury and repair after ischemia, but this manipulation remains a technical challenge, particularly in conscious mice. We developed a technology that uses micromagnets to induce aggregation of magnetic nanoparticles to reversibly occlude blood flow in microvessels. This allowed induction of ischemia in a specific cortical region of conscious mice of any postnatal age, including perinatal and neonatal stages, with precise spatiotemporal control but without surgical intervention of the skull or artery. When combined with longitudinal live-imaging approaches, this technology facilitated the discovery of a feature of the ischemic cascade: selective loss of smooth muscle cells in juveniles but not adults shortly after onset of ischemia and during blood reperfusion.
View details for DOI 10.1038/nmeth.4105
View details for PubMedID 27941784
Dual-Functional Lipid Coating for the Nanopillar-Based Capture of Circulating Tumor Cells with High Purity and Efficiency
2017; 33 (4): 1097-1104
Clinical studies of circulating tumor cells (CTC) have stringent demands for high capture purity and high capture efficiency. Nanostructured surfaces have been shown to significantly increase the capture efficiency yet suffer from low capture purity. Here we introduce a dual-functional lipid coating on nanostructured surfaces. The lipid coating serves both as an effective passivation layer that helps prevent nonspecific cell adhesion and as a functionalized layer for antibody-based specific cell capture. In addition, the fluidity of lipid bilayers enables antibody clustering that enhances the cell-surface interaction for efficient cell capture. As a result, the lipid-coating method helps promote both the capture efficiency and capture purity of nanostructure-based CTC capture.
View details for DOI 10.1021/acs.langmuir.6b03903
View details for Web of Science ID 000393269700032
View details for PubMedID 28059522
Imaging electric field dynamics with graphene optoelectronics
The use of electric fields for signalling and control in liquids is widespread, spanning bioelectric activity in cells to electrical manipulation of microstructures in lab-on-a-chip devices. However, an appropriate tool to resolve the spatio-temporal distribution of electric fields over a large dynamic range has yet to be developed. Here we present a label-free method to image local electric fields in real time and under ambient conditions. Our technique combines the unique gate-variable optical transitions of graphene with a critically coupled planar waveguide platform that enables highly sensitive detection of local electric fields with a voltage sensitivity of a few microvolts, a spatial resolution of tens of micrometres and a frequency response over tens of kilohertz. Our imaging platform enables parallel detection of electric fields over a large field of view and can be tailored to broad applications spanning lab-on-a-chip device engineering to analysis of bioelectric phenomena.
View details for DOI 10.1038/ncomms13704
View details for Web of Science ID 000389853500001
View details for PubMedID 27982125
View details for PubMedCentralID PMC5172231
The Timing of Raf/ERK and AKT Activation in Protecting PC12 Cells against Oxidative Stress
2016; 11 (4)
Acute brain injuries such as ischemic stroke or traumatic brain injury often cause massive neural death and irreversible brain damage with grave consequences. Previous studies have established that a key participant in the events leading to neural death is the excessive production of reactive oxygen species. Protecting neuronal cells by activating their endogenous defense mechanisms is an attractive treatment strategy for acute brain injuries. In this work, we investigate how the precise timing of the Raf/ERK and the AKT pathway activation affects their protective effects against oxidative stress. For this purpose, we employed optogenetic systems that use light to precisely and reversibly activate either the Raf/ERK or the AKT pathway. We find that preconditioning activation of the Raf/ERK or the AKT pathway immediately before oxidant exposure provides significant protection to cells. Notably, a 15-minute transient activation of the Raf/ERK pathway is able to protect PC12 cells against oxidant strike that is applied 12 hours later, while the transient activation of the AKT pathway fails to protect PC12 cells in such a scenario. On the other hand, if the pathways are activated after the oxidative insult, i.e. postconditioning, the AKT pathway conveys greater protective effect than the Raf/ERK pathway. We find that postconditioning AKT activation has an optimal delay period of 2 hours. When the AKT pathway is activated 30min after the oxidative insult, it exhibits very little protective effect. Therefore, the precise timing of the pathway activation is crucial in determining its protective effect against oxidative injury. The optogenetic platform, with its precise temporal control and its ability to activate specific pathways, is ideal for the mechanistic dissection of intracellular pathways in protection against oxidative stress.
View details for DOI 10.1371/journal.pone.0153487
View details for Web of Science ID 000374291800022
View details for PubMedID 27082641
- A close look at axonal transport: Cargos slow down when crossing stationary organelles NEUROSCIENCE LETTERS 2016; 610: 110-116
- Nanoparticle-assisted optical tethering of endosomes reveals the cooperative function of dyneins in retrograde axonal transport SCIENTIFIC REPORTS 2015; 5
- A skin-inspired organic digital mechanoreceptor SCIENCE 2015; 350 (6258): 313-?
- The Dual Characteristics of Light-Induced Cryptochrome 2, Homo-oligomerization and Heterodimerization, for Optogenetic Manipulation in Mammalian Cells. ACS synthetic biology 2015; 4 (10): 1124-1135
Activity-dependent BDNF release via endocytic pathways is regulated by synaptotagmin-6 and complexin.
Proceedings of the National Academy of Sciences of the United States of America
2015; 112 (32): E4475-84
Brain-derived neurotrophic factor (BDNF) is known to modulate synapse development and plasticity, but the source of synaptic BDNF and molecular mechanisms regulating BDNF release remain unclear. Using exogenous BDNF tagged with quantum dots (BDNF-QDs), we found that endocytosed BDNF-QDs were preferentially localized to postsynaptic sites in the dendrite of cultured hippocampal neurons. Repetitive neuronal spiking induced the release of BDNF-QDs at these sites, and this process required activation of glutamate receptors. Down-regulating complexin 1/2 (Cpx1/2) expression eliminated activity-induced BDNF-QD secretion, although the overall activity-independent secretion was elevated. Among eight synaptotagmin (Syt) isoforms examined, down-regulation of only Syt6 impaired activity-induced BDNF-QD secretion. In contrast, activity-induced release of endogenously synthesized BDNF did not depend on Syt6. Thus, neuronal activity could trigger the release of endosomal BDNF from postsynaptic dendrites in a Cpx- and Syt6-dependent manner, and endosomes containing BDNF may serve as a source of BDNF for activity-dependent synaptic modulation.
View details for DOI 10.1073/pnas.1511830112
View details for PubMedID 26216953
Efficient Radioisotope Energy Transfer by Gold Nanoclusters for Molecular Imaging
2015; 11 (32): 4002-4008
Beta-emitting isotopes Fluorine-18 and Yttrium-90 are tested for their potential to stimulate gold nanoclusters conjugated with blood serum proteins (AuNCs). AuNCs excited by either medical radioisotope are found to be highly effective ionizing radiation energy transfer mediators, suitable for in vivo optical imaging. AuNCs synthesized with protein templates convert beta-decaying radioisotope energy into tissue-penetrating optical signals between 620 and 800 nm. Optical signals are not detected from AuNCs incubated with Technetium-99m, a pure gamma emitter that is used as a control. Optical emission from AuNCs is not proportional to Cerenkov radiation, indicating that the energy transfer between the radionuclide and AuNC is only partially mediated by Cerenkov photons. A direct Coulombic interaction is proposed as a novel and significant mechanism of energy transfer between decaying radionuclides and AuNCs.
View details for DOI 10.1002/smll.201500907
View details for Web of Science ID 000360226300016
Retrograde NGF Axonal Transport-Motor Coordination in the Unidirectional Motility Regime
2015; 108 (11): 2691-2703
We present a detailed motion analysis of retrograde nerve growth factor (NGF) endosomes in axons to show that mechanical tugs-of-war and intracellular motor regulation are complimentary features of the near-unidirectional endosome directionality. We used quantum dots to fluorescently label NGF and acquired trajectories of retrograde quantum-dot-NGF-endosomes with <20-nm accuracy at 32 Hz in microfluidic neuron cultures. Using a combination of transient motion analysis and Bayesian parsing, we partitioned the trajectories into sustained periods of retrograde (dynein-driven) motion, constrained pauses, and brief anterograde (kinesin-driven) reversals. The data shows many aspects of mechanical tugs-of-war and multiple-motor mechanics in NGF-endosome transport. However, we found that stochastic mechanical models based on in vitro parameters cannot simulate the experimental data, unless the microtubule-binding affinity of kinesins on the endosome is tuned down by 10 times. Specifically, the simulations suggest that the NGF-endosomes are driven on average by 5-6 active dyneins and 1-2 downregulated kinesins. This is also supported by the dynamics of endosomes detaching under load in axons, showcasing the cooperativity of multiple dyneins and the subdued activity of kinesins. We discuss the possible motor coordination mechanism consistent with motor regulation and tugs-of-war for future investigations.
View details for DOI 10.1016/j.bpj.2015.04.036
View details for Web of Science ID 000355668800010
View details for PubMedID 26039170
- Nanotechnology and neurophysiology CURRENT OPINION IN NEUROBIOLOGY 2015; 32: 132-140
Vertical nanopillars for in situ probing of nuclear mechanics in adherent cells.
2015; 10 (6): 554-562
The mechanical stability and deformability of the cell nucleus are crucial to many biological processes, including migration, proliferation and polarization. In vivo, the cell nucleus is frequently subjected to deformation on a variety of length and time scales, but current techniques for studying nuclear mechanics do not provide access to subnuclear deformation in live functioning cells. Here we introduce arrays of vertical nanopillars as a new method for the in situ study of nuclear deformability and the mechanical coupling between the cell membrane and the nucleus in live cells. Our measurements show that nanopillar-induced nuclear deformation is determined by nuclear stiffness, as well as opposing effects from actin and intermediate filaments. Furthermore, the depth, width and curvature of nuclear deformation can be controlled by varying the geometry of the nanopillar array. Overall, vertical nanopillar arrays constitute a novel approach for non-invasive, subcellular perturbation of nuclear mechanics and mechanotransduction in live cells.
View details for DOI 10.1038/nnano.2015.88
View details for PubMedID 25984833
Optogenetic Control of Molecular Motors and Organelle Distributions in Cells
CHEMISTRY & BIOLOGY
2015; 22 (5): 671-682
Intracellular transport and distribution of organelles play important roles in diverse cellular functions, including cell polarization, intracellular signaling, cell survival, and apoptosis. Here, we report an optogenetic strategy to control the transport and distribution of organelles by light. This is achieved by optically recruiting molecular motors onto organelles through the heterodimerization of Arabidopsis thaliana cryptochrome 2 (CRY2) and its interacting partner CIB1. CRY2 and CIB1 dimerize within subseconds upon exposure to blue light, which requires no exogenous ligands and low intensity of light. We demonstrate that mitochondria, peroxisomes, and lysosomes can be driven toward the cell periphery upon light-induced recruitment of kinesin, or toward the cell nucleus upon recruitment of dynein. Light-induced motor recruitment and organelle movements are repeatable, reversible, and can be achieved at subcellular regions. This light-controlled organelle redistribution provides a new strategy for studying the causal roles of organelle transport and distribution in cellular functions in living cells.
View details for DOI 10.1016/j.chembiol.2015.04.014
View details for Web of Science ID 000355153900015
View details for PubMedID 25963241
- Optogenetic control of intracellular signaling pathways TRENDS IN BIOTECHNOLOGY 2015; 33 (2): 92-100
U0126 Protects Cells against Oxidative Stress Independent of Its Function as a MEK Inhibitor
ACS CHEMICAL NEUROSCIENCE
2015; 6 (1): 130-137
U0126 is a potent and selective inhibitor of MEK1 and MEK2 kinases. It has been widely used as an inhibitor for the Ras/Raf/MEK/ERK signaling pathway with over 5000 references on the NCBI PubMed database. In particular, U0126 has been used in a number of studies to show that inhibition of the Raf/MEK/ERK pathway protects neuronal cells against oxidative stress. Here, we report that U0126 can function as an antioxidant that protects PC12 cells against a number of different oxidative-stress inducers. This protective effect of U0126 is independent of its function as a MEK inhibitor, as several other MEK inhibitors failed to show similar protective effects. U0126 reduces reactive oxygen species (ROS) in cells. We further demonstrate that U0126 is a direct ROS scavenger in vitro, and the oxidation products of U0126 exhibit fluorescence. Our finding that U0126 is a strong antioxidant signals caution for its future usage as a MEK inhibitor and for interpreting some previous results.
View details for DOI 10.1021/cn500288n
View details for Web of Science ID 000348338900016
View details for PubMedID 25544156
Enhancing the nanomaterial bio-interface by addition of mesoscale secondary features: crinkling of carbon nanotube films to create subcellular ridges.
2014; 8 (12): 11958-11965
Biological cells often interact with their local environment through subcellular structures at a scale of tens to hundreds of nanometers. This study investigated whether topographic features fabricated at a similar scale would impact cellular functions by promoting the interaction between subcellular structures and nanomaterials. Crinkling of carbon nanotube films by solvent-induced swelling and shrinkage of substrate resulted in the formation of ridge features at the subcellular scale on both flat and three-dimensional substrates. Biological cells grown upon these crinkled CNT films had enhanced activity: neuronal cells grew to higher density and displayed greater cell polarization; exoelectrogenic micro-organisms transferred electrons more efficiently. The results indicate that crinkling of thin CNT films creates secondary mesoscale features that enhance attachment, growth, and electron transfer.
View details for DOI 10.1021/nn504898p
View details for PubMedID 25415858
Chemically defined generation of human cardiomyocytes.
2014; 11 (8): 855-860
Existing methods for human induced pluripotent stem cell (hiPSC) cardiac differentiation are efficient but require complex, undefined medium constituents that hinder further elucidation of the molecular mechanisms of cardiomyogenesis. Using hiPSCs derived under chemically defined conditions on synthetic matrices, we systematically developed an optimized cardiac differentiation strategy, using a chemically defined medium consisting of just three components: the basal medium RPMI 1640, L-ascorbic acid 2-phosphate and rice-derived recombinant human albumin. Along with small molecule-based induction of differentiation, this protocol produced contractile sheets of up to 95% TNNT2(+) cardiomyocytes at a yield of up to 100 cardiomyocytes for every input pluripotent cell and was effective in 11 hiPSC lines tested. This chemically defined platform for cardiac specification of hiPSCs will allow the elucidation of cardiomyocyte macromolecular and metabolic requirements and will provide a minimal system for the study of maturation and subtype specification.
View details for DOI 10.1038/nmeth.2999
View details for PubMedID 24930130
Lighting up FGFR signaling.
Chemistry & biology
2014; 21 (7): 806-808
In this issue of Chemistry & Biology, Kim and colleagues describe their work on optogenetic control of fibroblast growth factor receptor (FGFR) signaling. By engineering a chimeric receptor, the authors demonstrate that FGFR intracellular signaling can be controlled in space and time by blue light.
View details for DOI 10.1016/j.chembiol.2014.07.004
View details for PubMedID 25036775
- Divergence of the long-wavelength collective diffusion coefficient in quasi-one- and quasi-two-dimensional colloidal suspensions PHYSICAL REVIEW E 2014; 89 (2)
- Iridium oxide nanotube electrodes for sensitive and prolonged intracellular measurement of action potentials. Nature communications 2014; 5: 3206-?
- NANOWIRE TRANSISTORS Room for manoeuvre NATURE NANOTECHNOLOGY 2014; 9 (2): 94-96
Iridium oxide nanotube electrodes for sensitive and prolonged intracellular measurement of action potentials.
2014; 5: 3206-?
Intracellular recording of action potentials is important to understand electrically-excitable cells. Recently, vertical nanoelectrodes have been developed to achieve highly sensitive, minimally invasive and large-scale intracellular recording. It has been demonstrated that the vertical geometry is crucial for the enhanced signal detection. Here we develop nanoelectrodes of a new geometry, namely nanotubes of iridium oxide. When cardiomyocytes are cultured upon those nanotubes, the cell membrane not only wraps around the vertical tubes but also protrudes deep into the hollow centre. We show that this nanotube geometry enhances cell-electrode coupling and results in larger signals than solid nanoelectrodes. The nanotube electrodes also afford much longer intracellular access and are minimally invasive, making it possible to achieve stable recording up to an hour in a single session and more than 8 days of consecutive daily recording. This study suggests that the nanoelectrode performance can be significantly improved by optimizing the electrode geometry.
View details for DOI 10.1038/ncomms4206
View details for PubMedID 24487777
- Light-Mediated Kinetic Control Reveals the Temporal Effect of the Raf/MEK/ERK Pathway in PC12 Cell Neurite Outgrowth. PloS one 2014; 9 (3)
Hard X-ray-induced optical luminescence via biomolecule-directed metal clusters
2014; 50 (27): 3549-3551
Here, we demonstrate that biomolecule-directed metal clusters are applicable in the study of hard X-ray excited optical luminescence, promising a new direction in the development of novel X-ray-activated imaging probes.
View details for DOI 10.1039/c3cc48661c
View details for Web of Science ID 000332483200003
View details for PubMedID 24463467
Light-mediated kinetic control reveals the temporal effect of the Raf/MEK/ERK pathway in PC12 cell neurite outgrowth.
2014; 9 (3)
It has been proposed that differential activation kinetics allows cells to use a common set of signaling pathways to specify distinct cellular outcomes. For example, nerve growth factor (NGF) and epidermal growth factor (EGF) induce different activation kinetics of the Raf/MEK/ERK signaling pathway and result in differentiation and proliferation, respectively. However, a direct and quantitative linkage between the temporal profile of Raf/MEK/ERK activation and the cellular outputs has not been established due to a lack of means to precisely perturb its signaling kinetics. Here, we construct a light-gated protein-protein interaction system to regulate the activation pattern of the Raf/MEK/ERK signaling pathway. Light-induced activation of the Raf/MEK/ERK cascade leads to significant neurite outgrowth in rat PC12 pheochromocytoma cell lines in the absence of growth factors. Compared with NGF stimulation, light stimulation induces longer but fewer neurites. Intermittent on/off illumination reveals that cells achieve maximum neurite outgrowth if the off-time duration per cycle is shorter than 45 min. Overall, light-mediated kinetic control enables precise dissection of the temporal dimension within the intracellular signal transduction network.
View details for DOI 10.1371/journal.pone.0092917
View details for PubMedID 24667437
X-ray excitable luminescent polymer dots doped with an iridium(iii) complex.
2013; 49 (39): 4319-4321
In this study, cyclometalated iridium(III) complex-doped polymer dots were synthesized and shown to emit luminescence upon X-ray irradiation, potentially serving as a new probe for molecular imaging during X-ray computed tomography.
View details for DOI 10.1039/c2cc37169c
View details for PubMedID 23320256
- Defective Axonal Transport of Rab7 GTPase Results in Dysregulated Trophic Signaling JOURNAL OF NEUROSCIENCE 2013; 33 (17): 7451-7462
Light-Controlled Mitogen-Activated Protein Kinase (MAPK) Signaling Pathway in Live Cells
57th Annual Meeting of the Biophysical-Society
CELL PRESS. 2013: 679A–679A
View details for Web of Science ID 000316074306435
Characterization of the Cell-Nanopillar Interface by Transmission Electron Microscopy
2012; 12 (11): 5815-5820
Vertically aligned nanopillars can serve as excellent electrical, optical and mechanical platforms for biological studies. However, revealing the nature of the interface between the cell and the nanopillar is very challenging. In particular, a matter of debate is whether the cell membrane remains intact around the nanopillar. Here we present a detailed characterization of the cell-nanopillar interface by transmission electron microscopy. We examined cortical neurons growing on nanopillars with diameter 50-500 nm and heights 0.5-2 μm. We found that on nanopillars less than 300 nm in diameter, the cell membrane wraps around the entirety of the nanopillar without the nanopillar penetrating into the interior of the cell. On the other hand, the cell sits on top of arrays of larger, closely spaced nanopillars. We also observed that the membrane-surface gap of both cell bodies and neurites is smaller for nanopillars than for a flat substrate. These results support a tight interaction between the cell membrane and the nanopillars and previous findings of excellent sealing in electrophysiology recordings using nanopillar electrodes.
View details for DOI 10.1021/nl303163y
View details for Web of Science ID 000311244400064
View details for PubMedID 23030066
Intracellular recording of action potentials by nanopillar electroporation
2012; 7 (3): 185-190
Action potentials have a central role in the nervous system and in many cellular processes, notably those involving ion channels. The accurate measurement of action potentials requires efficient coupling between the cell membrane and the measuring electrodes. Intracellular recording methods such as patch clamping involve measuring the voltage or current across the cell membrane by accessing the cell interior with an electrode, allowing both the amplitude and shape of the action potentials to be recorded faithfully with high signal-to-noise ratios. However, the invasive nature of intracellular methods usually limits the recording time to a few hours, and their complexity makes it difficult to simultaneously record more than a few cells. Extracellular recording methods, such as multielectrode arrays and multitransistor arrays, are non-invasive and allow long-term and multiplexed measurements. However, extracellular recording sacrifices the one-to-one correspondence between the cells and electrodes, and also suffers from significantly reduced signal strength and quality. Extracellular techniques are not, therefore, able to record action potentials with the accuracy needed to explore the properties of ion channels. As a result, the pharmacological screening of ion-channel drugs is usually performed by low-throughput intracellular recording methods. The use of nanowire transistors, nanotube-coupled transistors and micro gold-spine and related electrodes can significantly improve the signal strength of recorded action potentials. Here, we show that vertical nanopillar electrodes can record both the extracellular and intracellular action potentials of cultured cardiomyocytes over a long period of time with excellent signal strength and quality. Moreover, it is possible to repeatedly switch between extracellular and intracellular recording by nanoscale electroporation and resealing processes. Furthermore, vertical nanopillar electrodes can detect subtle changes in action potentials induced by drugs that target ion channels.
View details for DOI 10.1038/NNANO.2012.8
View details for Web of Science ID 000301186300012
View details for PubMedID 22327876
View details for PubMedCentralID PMC3356686
Neurotrophin Signaling via Long-Distance Axonal Transport
ANNUAL REVIEW OF PHYSICAL CHEMISTRY, VOL 63
2012; 63: 571-594
Neurotrophins are a family of target-derived growth factors that support survival, development, and maintenance of innervating neurons. Owing to the unique architecture of neurons, neurotrophins that act locally on the axonal terminals must convey their signals across the entire axon for subsequent regulation of gene transcription in the cell nucleus. This long-distance retrograde signaling, a motor-driven process that can take hours or days, has been a subject of intense interest. In the last decade, live-cell imaging with high sensitivity has significantly increased our capability to track the transport of neurotrophins, their receptors, and subsequent signals in real time. This review summarizes recent research progress in understanding neurotrophin-receptor interactions at the axonal terminal and their transport dynamics along the axon. We emphasize high-resolution studies at the single-molecule level and also discuss recent technical advances in the field.
View details for DOI 10.1146/annurev-physchem-032511-143704
View details for Web of Science ID 000304203500026
View details for PubMedID 22404590
Functional characterization and axonal transport of quantum dot labeled BDNF
2012; 4 (8): 953-960
Brain derived neurotrophic factor (BDNF) plays a key role in the growth, development and maintenance of the central and peripheral nervous systems. Exogenous BDNF activates its membrane receptors at the axon terminal, and subsequently sends regulation signals to the cell body. To understand how a BDNF signal propagates in neurons, it is important to follow the trafficking of BDNF after it is internalized at the axon terminal. Here we labeled BDNF with bright, photostable quantum dots (QD-BDNF) and followed the axonal transport of QD-BDNF in real time in hippocampal neurons. We showed that QD-BDNF was able to bind BDNF receptors and activate downstream signaling pathways. When QD-BDNF was applied to the distal axons of hippocampal neurons, it was observed to be actively transported toward the cell body at an average speed of 1.11 ± 0.05 μm s(-1). A closer examination revealed that QD-BDNF was transported by both discrete endosomes and multivesicular body-like structures. Our results showed that QD-BDNF could be used to track the movement of exogenous BDNF in neurons over long distances and to study the signaling organelles that contain BDNF.
View details for DOI 10.1039/c2ib20062g
View details for Web of Science ID 000306708500014
View details for PubMedID 22772872
Diarylethene doped biocompatible polymer dots for fluorescence switching
2012; 48 (27): 3285-3287
The photochromic molecule diarylethene works as a "toggle switch" for biocompatible fluorescence polymer dots and enables fluorescence switching in biological samples.
View details for DOI 10.1039/c2cc18085e
View details for Web of Science ID 000301057400004
View details for PubMedID 22294244
Automated Image Analysis for Tracking Cargo Transport in Axons
MICROSCOPY RESEARCH AND TECHNIQUE
2011; 74 (7): 605-613
The dynamics of cargo movement in axons encodes crucial information about the underlying regulatory mechanisms of the axonal transport process in neurons, a central problem in understanding many neurodegenerative diseases. Quantitative analysis of cargo dynamics in axons usually includes three steps: (1) acquiring time-lapse image series, (2) localizing individual cargos at each time step, and (3) constructing dynamic trajectories for kinetic analysis. Currently, the later two steps are usually carried out with substantial human intervention. This article presents a method of automatic image analysis aiming for constructing cargo trajectories with higher data processing throughput, better spatial resolution, and minimal human intervention. The method is based on novel applications of several algorithms including 2D kymograph construction, seed points detection, trajectory curve tracing, back-projection to extract spatial information, and position refining using a 2D Gaussian fitting. This method is sufficiently robust for usage on images with low signal-to-noise ratio, such as those from single molecule experiments. The method was experimentally validated by tracking the axonal transport of quantum dot and DiI fluorophore-labeled vesicles in dorsal root ganglia neurons.
View details for DOI 10.1002/jemt.20934
View details for Web of Science ID 000292570900005
View details for PubMedID 20945466
A Microfluidic Positioning Chamber for Long-Term Live-Cell Imaging
MICROSCOPY RESEARCH AND TECHNIQUE
2011; 74 (6): 496-501
We report a microfluidic positioning chamber (MPC) that can rapidly and repeatedly relocate the same imaging area on a microscope stage. The "roof" of the microfluidic chamber was printed with serials of coordinate numbers that act as positioning marks for mammalian cells that grow attached to the "floor" of the microfluidic chamber. MPC cell culture chamber provided a simple solution for tracking the same cell or groups of cells over days or weeks. The positioning marks were used to register time-lapse images of the same imaging area to single-pixel accuracy. Using MPC cell culture chamber, we tracked the migration, division, and differentiation of individual PC12 cells for over a week using bright field and fluorescence imaging.
View details for DOI 10.1002/jemt.20937
View details for Web of Science ID 000291539200004
View details for PubMedID 20936672
View details for PubMedCentralID PMC3021629
Vertical nanopillars for highly localized fluorescence imaging
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2011; 108 (10): 3894-3899
Observing individual molecules in a complex environment by fluorescence microscopy is becoming increasingly important in biological and medical research, for which critical reduction of observation volume is required. Here, we demonstrate the use of vertically aligned silicon dioxide nanopillars to achieve below-the-diffraction-limit observation volume in vitro and inside live cells. With a diameter much smaller than the wavelength of visible light, a transparent silicon dioxide nanopillar embedded in a nontransparent substrate restricts the propagation of light and affords evanescence wave excitation along its vertical surface. This effect creates highly confined illumination volume that selectively excites fluorescence molecules in the vicinity of the nanopillar. We show that this nanopillar illumination can be used for in vitro single-molecule detection at high fluorophore concentrations. In addition, we demonstrate that vertical nanopillars interface tightly with live cells and function as highly localized light sources inside the cell. Furthermore, specific chemical modification of the nanopillar surface makes it possible to locally recruit proteins of interest and simultaneously observe their behavior within the complex, crowded environment of the cell.
View details for DOI 10.1073/pnas.1015589108
View details for Web of Science ID 000288120400019
View details for PubMedID 21368157
View details for PubMedCentralID PMC3054026
Real-time visualization of axonal transport in neurons.
Methods in molecular biology (Clifton, N.J.)
2011; 670: 231-243
The normal function of neurons depends on the integrity of microtubule-dependent transport of cellular materials and organelles to/from their cell bodies or axon terminus. In this chapter, we describe the design and implementation of a fluorescence imaging method to visualize axonal transport in neurons directly. We combine a pseudo total internal reflection microscopy, quantum dot fluorescence labeling, microfluidic neuronal culture chamber, and single molecule detection methods to achieve a high spatial and temporal resolution in tracking nerve growth factor transport in dorsal root ganglia neurons.
View details for DOI 10.1007/978-1-60761-744-0_16
View details for PubMedID 20967594
Tau Reduction Prevents A beta-Induced Defects in Axonal Transport
2010; 330 (6001): 198-U52
Amyloid-β (Aβ) peptides, derived from the amyloid precursor protein, and the microtubule-associated protein tau are key pathogenic factors in Alzheimer's disease (AD). How exactly they impair cognitive functions is unknown. We assessed the effects of Aβ and tau on axonal transport of mitochondria and the neurotrophin receptor TrkA, cargoes that are critical for neuronal function and survival and whose distributions are altered in AD. Aβ oligomers rapidly inhibited axonal transport of these cargoes in wild-type neurons. Lowering tau levels prevented these defects without affecting baseline axonal transport. Thus, Aβ requires tau to impair axonal transport, and tau reduction protects against Aβ-induced axonal transport defects.
View details for DOI 10.1126/science.1194653
View details for Web of Science ID 000282644600034
View details for PubMedID 20829454
Noninvasive Neuron Pinning with Nanopillar Arrays
2010; 10 (10): 4020-4024
Cell migration in a cultured neuronal network presents an obstacle to selectively measuring the activity of the same neuron over a long period of time. Here we report the use of nanopillar arrays to pin the position of neurons in a noninvasive manner. Vertical nanopillars protruding from the surface serve as geometrically better focal adhesion points for cell attachment than a flat surface. The cell body mobility is significantly reduced from 57.8 μm on a flat surface to 3.9 μm on nanopillars over a 5 day period. Yet, neurons growing on nanopillar arrays show a growth pattern that does not differ in any significant way from that seen on a flat substrate. Notably, while the cell bodies of neurons are efficiently anchored by the nanopillars, the axons and dendrites are free to grow and elongate into the surrounding area to develop a neuronal network, which opens up opportunities for long-term study of the same neurons in connected networks.
View details for DOI 10.1021/nl101950x
View details for Web of Science ID 000282727600038
View details for PubMedID 20815404
View details for PubMedCentralID PMC2955158
Hydrodynamic interactions in ribbon channels: From quasi-one-dimensional to quasi-two-dimensional behavior
PHYSICAL REVIEW E
2010; 82 (3)
We present a study of the dynamics of confined suspensions whose dimensionality is intermediate between quasi-one-dimensional and quasi-two-dimensional (q2D) using microfluidic channels of various widths. The crossover between the two limiting behaviors is found to occur to different extent for different dynamic correlations between a pair of particles. In particular, the transverse coupling diffusion coefficient of particle pairs significantly deviates from its q2D form even in surprisingly wide channels.
View details for DOI 10.1103/PhysRevE.82.031403
View details for Web of Science ID 000281741000002
View details for PubMedID 21230073
Single-molecule imaging of NGF axonal transport in microfluidic devices
LAB ON A CHIP
2010; 10 (19): 2566-2573
Nerve growth factor (NGF) signaling begins at the nerve terminal, where it binds and activates membrane receptors and subsequently carries the cell-survival signal to the cell body through the axon. A recent study revealed that the majority of endosomes contain a single NGF molecule, which makes single-molecule imaging an essential tool for NGF studies. Despite being an increasingly popular technique, single-molecule imaging in live cells is often limited by background fluorescence. Here, we employed a microfluidic culture platform to achieve background reduction for single-molecule imaging in live neurons. Microfluidic devices guide the growth of neurons and allow separately controlled microenvironment for cell bodies or axon termini. Designs of microfluidic devices were optimized and a three-compartment device successfully achieved direct observation of axonal transport of single NGF when quantum dot labeled NGF (Qdot-NGF) was applied only to the distal-axon compartment while imaging was carried out exclusively in the cell-body compartment. Qdot-NGF was shown to move exclusively toward the cell body with a characteristic stop-and-go pattern of movements. Measurements at various temperatures show that the rate of NGF retrograde transport decreased exponentially over the range of 36-14 degrees C. A 10 degrees C decrease in temperature resulted in a threefold decrease in the rate of NGF retrograde transport. Our successful measurements of NGF transport suggest that the microfluidic device can serve as a unique platform for single-molecule imaging of molecular processes in neurons.
View details for DOI 10.1039/c003385e
View details for Web of Science ID 000281614900012
View details for PubMedID 20623041
Optically Resolving Individual Microtubules in Live Axons
2009; 17 (11): 1433-1441
Microtubules are essential cytoskeletal tracks for cargo transportation in axons and also serve as the primary structural scaffold of neurons. Structural assembly, stability, and dynamics of axonal microtubules are of great interest for understanding neuronal functions and pathologies. However, microtubules are so densely packed in axons that their separations are well below the diffraction limit of light, which precludes using optical microscopy for live-cell studies. Here, we present a single-molecule imaging method capable of resolving individual microtubules in live axons. In our method, unlabeled microtubules are revealed by following individual axonal cargos that travel along them. We resolved more than six microtubules in a 1 microm diameter axon by real-time tracking of endosomes containing quantum dots. Our live-cell study also provided direct evidence that endosomes switch between microtubules while traveling along axons, which has been proposed to be the primary means for axonal cargos to effectively navigate through the crowded axoplasmic environment.
View details for DOI 10.1016/j.str.2009.09.008
View details for Web of Science ID 000272011500005
View details for PubMedID 19913478
The Quasi-One-Dimensional Colloid Fluid Revisited
JOURNAL OF PHYSICAL CHEMISTRY B
2009; 113 (42): 13742-13751
We report the results of studies of the pair correlation function and equation of state of a quasi-one-dimensional colloid suspension, focusing attention on the behavior in the density range near close packing. Our data show that, despite deviations from true one-dimensional geometry, the colloid fluid is well described as a hard rod Tonks fluid. In our experimental realization, the colloid suspension does not wet the confining walls, one consequence of which is a surface tension induced weak attractive interaction between the particles. The reality of this interaction is confirmed after correction of the raw experimental data for overlap of the optical images of particles that are nearly in contact and by an alternative particle location algorithm based on edge location.
View details for DOI 10.1021/jp9018734
View details for Web of Science ID 000270670800010
View details for PubMedID 19569626
Structure of quasi-one-dimensional ribbon colloid suspensions
PHYSICAL REVIEW E
2009; 79 (3)
We report the results of an experimental study of a colloid fluid confined to a quasi-one-dimensional (q1D) ribbon channel as a function of channel width and colloid density. Our findings confirm the principal predictions of previous theoretical studies of such systems. These are (1) that the density distribution of the liquid transverse to the ribbon channel exhibits stratification; (2) that even at the highest density the order along the strata, as measured by the longitudinal pair correlation function, is characteristic of a liquid; and (3) the q1D pair correlation functions in different strata exhibit anisotropic behavior resembling that found in a Monte Carlo simulation for the in-plane pair correlation function of a hard sphere fluid in a planar slit.
View details for DOI 10.1103/PhysRevE.79.031406
View details for Web of Science ID 000264767300067
View details for PubMedID 19391943
The coming of age of axonal neurotrophin signaling endosomes
JOURNAL OF PROTEOMICS
2009; 72 (1): 46-55
Neurons of both the central and the peripheral nervous system are critically dependent on neurotrophic signals for their survival and differentiation. The trophic signal is originated at the axonal terminals that innervate the target(s). It has been well established that the signal must be retrogradely transported back to the cell body to exert its trophic effect. Among the many forms of transmitted signals, the signaling endosome serves as a primary means to ensure that the retrograde signal is delivered to the cell body with sufficient fidelity and specificity. Recent evidence suggests that disruption of axonal transport of neurotrophin signals may contribute to neurodegenerative diseases such as Alzheimer's disease and Down syndrome. However, the identity of the endocytic vesicular carrier(s), and the mechanisms involved in retrogradely transporting the signaling complexes remain a matter of debate. In this review, we summarize current insights that are mainly based on classical hypothesis-driven research, and we emphasize the urgent needs to carry out proteomics to resolve the controversies in the field.
View details for DOI 10.1016/j.jprot.2008.10.007
View details for Web of Science ID 000264320700006
View details for PubMedID 19028611
View details for PubMedCentralID PMC2677075
Anomalous behavior of the depletion potential in quasi-two-dimensional binary mixtures
PHYSICAL REVIEW E
2005; 72 (2)
We report an experimental determination of the depletion interaction between a pair of large colloid particles present in a binary colloid mixture that has a high density of large particles and is tightly confined between two parallel plates, as a function of the small colloid particle density. The bare interaction between the large particles in the one component large colloid suspension, and the effective potential between the large particles in the binary colloid suspension represented as a pseudo-one-component fluid, were obtained by inverting the Ornstein-Zernike equation with the hypernetted chain closure. The depletion interaction is defined by subtracting the bare potential from the effective potential at fixed large colloid density. We find that the depletion potential in the quasi-two-dimensional (Q2D) system is purely attractive and short ranged as described by Asakura-Oosawa model. However, the depth of the depletion potential is found to be almost an order of magnitude larger than the counterpart depletion potential predicted for the same density and diameter ratio in a three-dimensional system. Although it is expected that the confining walls in the Q2D geometry enhance the excluded volume effects that generate entropic attraction, the observed enhancement is much larger than predicted for a Q2D binary mixture of hard spheres. We speculate that this anomalously strong confinement-induced depletion potential is a signature of characteristics of the real confined binary colloid mixture that are not included in any extant theory of the depletion interaction, specifically the omission of the role of the solvent in those theories. One such characteristic could be differential wall or particle wetting that generates a wall induced one-particle effective potential that confines the centers of the small particles to lie closer to the midplane between the walls than expected from the wall separation and the direct particle-wall interaction, thereby enhancing the depletion interaction.
View details for DOI 10.1103/PhysRevE.72.021402
View details for Web of Science ID 000231564000027
View details for PubMedID 16196560