Noncontact estimation of intercellular breaking force using a femtosecond laser impulse quantified by atomic force microscopy

Relief of pain in mice by an antibody with high affinity for cell adhesion molecule 1 on nerves

AIMS

Cell adhesion molecule 1 (CADM1) is a member of the immunoglobulin superfamily and is abundantly expressed on nerve fibers. Recently, the anti-CADM1 ectodomain antibody 3E1 has proven useful as a drug delivery vector for CADM1-expressing cells in vitro. When injected subcutaneously into mice, whether 3E1 accumulates on nerve fibers and serves as an analgesic was examined.

MAIN METHODS

Injected 3E1 was detected by immunohistochemistry and double immunofluorescence. Analgesic effects were verified by a formalin-induced chemical-inflammatory pain test and video-recorded behavior analysis that were performed 6, 12, and 24 h after antibody injection. Primary cultures of mouse dorsal root ganglion (DRG) cells were incubated with 3E1 and expressions of CADM1 and its key downstream molecules were examined by Western blot analyses and live cell imaging. DRG cells were loaded with a Ca2+ fluorescent indicator Fluo-8 and a femtosecond laser pulse was irradiated near the cell body to mechanically stimulate the nerves.

KEY FINDINGS

Subcutaneously injected 3E1 was widely localized almost exclusively on peripheral nerve fibers in the dermis. In formalin tests, 3E1-injected mice exhibited less pain-related behavior than control mice. When 3E1 was added to DRG cell cultures, it localized to neurites and resulted in decreased expression of CADM1, increased phosphorylation of Src and Akt, and CADM1-3E1 complex formation. Femtosecond laser-induced stimulation transmission along neurites was clearly visualized by Fluo-8 fluorescence in control cells, whereas it was markedly suppressed in 3E1-treated cells.

SIGNIFICANCE

3E1 was suggested to be a potential long-acting analgesic based on its high affinity for CADM1.

Potential Contribution of Cell Adhesion Molecule 1 to the Binding of SARS-CoV-2 Spike Protein to Mouse Nasal Mucosa

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) first infects the host nasal mucosa, where the viral spike protein binds to angiotensin-converting enzyme 2 (ACE2) on the mucosal cells. This study aimed at searching host cell surface molecules that could contribute to the infection in two views; abundance on host cells and affinity to the spike protein. Since the nasal mucosa is lined by respiratory and olfactory epithelia, and both express an immunoglobulin superfamily member cell adhesion molecule 1 (CADM1), whether CADM1 would participate in the spike protein binding was examined. Immunohistochemistry on the mouse nasal cavity detected CADM1 strongly in the olfactory epithelium at cell-cell contacts and on the apical surface but just faintly in the respiratory epithelium. In contrast, ACE2 was detected in the respiratory, not olfactory, epithelium. When mice were administered intranasally with SARS-CoV-2 S1 spike protein and an anti-CADM1 ectodomain antibody separately, both were detected exclusively on the olfactory, not respiratory, epithelium. Then, the antibody and S1 spike protein were administered intranasally to mice in this order with an interval of 1 h. After 3 h, S1 spike protein was detected as a protein aggregate floating in the nasal cavity. Next, S1 spike protein labeled with fluorescein was added to the monolayer cultures of epithelial cells exogenously expressing ACE2 or CADM1. Quantitative detection of fluorescein bound to the cells revealed that S1 spike protein bound to CADM1 with affinity half as high as to ACE2. Consistently, docking simulation analyses revealed that S1 spike protein could bind to CADM1 three-quarters as strongly as to ACE2 and that the interface of ACE2 was similar in both binding modes. Collectively, intranasal S1 spike protein appeared to prefer to accumulate on the olfactory epithelium, and CADM1 was suggested to contribute to this preference of S1 spike protein based on the molecular abundance and affinity.

Microsecond cell triple-sorting enabled by multiple pulse irradiation of femtosecond laser

Femtosecond-laser-assisted cell manipulation, as one of the high throughput cell sorting techniques, is tailored for single-step multiple sorting based on controllable impulsive force. In this paper, femtosecond laser pulses are focused within a pocket structure and they induce an impulse force acting on the flowing objects. The impulsive force is shown to be controllable by a new method to adjust the femtosecond pulse properties. This allows precise streamline manipulation of objects having various physical qualities (e.g., weight and volume). The pulse energy, pulse number, and pulse interval of the femtosecond laser are altered to determine the impulsive force strength. The method is validated in single cell or bead triple-sorting experiments and its capability to perform streamline manipulation in as little as 10 μs is shown. The shift profiles of the beads acting under the impulsive force are studied in order to better understand the sorting mechanism. Additionally, beads and cells with different fluorescence intensities are successfully detected and directed into different microchannels, with maximum success rates of 90% and 64.5%, respectively. To sum up, all results suggest that this method has the potential to sort arbitrary subpopulations by altering the number of femtosecond pulses and that it takes the first step toward developing a single-step multi-selective system.

Indigo plant leaf extract inhibits the binding of SARS‑CoV‑2 spike protein to angiotensin‑converting enzyme 2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) uses its S1 spike protein to bind to angiotensin-converting enzyme 2 (ACE2) on human cells in the first step of cell entry. Tryptanthrin, extracted from leaves of the indigo plant, Polygonum tinctorium, using d-limonene (17.3 µg/ml), is considered to inhibit ACE2-mediated cell entry of another type of coronavirus, HCoV-NL63. The current study examined whether this extract could inhibit the binding of the SARS-CoV-2 spike protein to ACE2. Binding was quantified as cell-bound fluorescence intensity in live cell cultures in which canine kidney MDCK cells overexpressing ACE2 were incubated with fluorescein-labeled S1 spike protein. When indigo extract, together with S1 protein, was added at 8,650x and 17,300x dilutions, fluorescence intensity decreased in a dose- and S1 extract-dependent manner, without affecting cell viability. When 4.0-nM tryptanthrin was added instead of the indigo extract, fluorescence intensity also decreased, but to a lesser degree than with indigo extract. Docking simulation analyses revealed that tryptanthrin readily bound to the receptor-binding domain of the S1 protein, and identified 2- and 7-amino acid sequences as the preferred binding sites. The indigo extract appeared to inhibit S1-ACE2 binding at high dilutions, and evidently contained other inhibitory elements as well as tryptanthrin. This extract may be useful for the prevention or treatment of SARS-CoV-2 infection.

Filopodium-derived vesicles produced by MIM enhance the migration of recipient cells

Extracellular vesicles (EVs) are classified as large EVs (l-EVs, or microvesicles) and small EVs (s-EVs, or exosomes). S-EVs are thought to be generated from endosomes through a process that mainly depends on the ESCRT protein complex, including ALG-2 interacting protein X (ALIX). However, the mechanisms of l-EV generation from the plasma membrane have not been identified. Membrane curvatures are generated by the bin-amphiphysin-rvs (BAR) family proteins, among which the inverse BAR (I-BAR) proteins are involved in filopodial protrusions. Here, we show that the I-BAR proteins, including missing in metastasis (MIM), generate l-EVs by scission of filopodia. Interestingly, MIM-containing l-EV production was promoted by in vivo equivalent external forces and by the suppression of ALIX, suggesting an alternative mechanism of vesicle formation to s-EVs. The MIM-dependent l-EVs contained lysophospholipids and proteins, including IRS4 and Rac1, which stimulated the migration of recipient cells through lamellipodia formation. Thus, these filopodia-dependent l-EVs, which we named as filopodia-derived vesicles (FDVs), modify cellular behavior.

Hydrodynamic particle focusing enhanced by femtosecond laser deep grooving at low Reynolds numbers

Microfluidic focusing of particles (both synthetic and biological), which enables precise control over the positions of particles in a tightly focused stream, is a prerequisite step for the downstream processing, such as detection, trapping and separation. In this study, we propose a novel hydrodynamic focusing method by taking advantage of open v-shaped microstructures on a glass substrate engraved by femtosecond pulse (fs) laser. The fs laser engraved microstructures were capable of focusing polystyrene particles and live cells in rectangular microchannels at relatively low Reynolds numbers (Re). Numerical simulations were performed to explain the mechanisms of particle focusing and experiments were carried out to investigate the effects of groove depth, groove number and flow rate on the performance of the groove-embedded microchannel for particle focusing. We found out that 10-µm polystyrene particles are directed toward the channel center under the effects of the groove-induced secondary flows in low-Re flows, e.g. Re < 1. Moreover, we achieved continuous focusing of live cells with different sizes ranging from 10 to 15 µm, i.e. human T-cell lymphoma Jurkat cells, rat adrenal pheochromocytoma PC12 cells and dog kidney MDCK cells. The glass grooves fabricated by fs laser are expected to be integrated with on-chip detection components, such as contact imaging and fluorescence lifetime-resolved imaging, for various biological and biomedical applications, where particle focusing at a relatively low flow rate is desirable.

Forces to Drive Neuronal Migration Steps

To establish and maintain proper brain architecture and elaborate neural networks, neurons undergo massive migration. As a unique feature of their migration, neurons move in a saltatory manner by repeating two distinct steps: extension of the leading process and translocation of the cell body. Neurons must therefore generate forces to extend the leading process as well as to translocate the cell body. In addition, neurons need to switch these forces alternately in order to orchestrate their saltatory movement. Recent studies with mechanobiological analyses, including traction force microscopy, cell detachment analyses, live-cell imaging, and loss-of-function analyses, have begun to reveal the forces required for these steps and the molecular mechanics underlying them. Spatiotemporally organized forces produced between cells and their extracellular environment, as well as forces produced within cells, play pivotal roles to drive these neuronal migration steps. Traction force produced by the leading process growth cone extends the leading processes. On the other hand, mechanical tension of the leading process, together with reduction in the adhesion force at the rear and the forces to drive nucleokinesis, translocates the cell body. Traction forces are generated by mechanical coupling between actin filament retrograde flow and the extracellular environment through clutch and adhesion molecules. Forces generated by actomyosin and dynein contribute to the nucleokinesis. In addition to the forces generated in cell-intrinsic manners, external forces provided by neighboring migratory cells coordinate cell movement during collective migration. Here, we review our current understanding of the forces that drive neuronal migration steps and describe the molecular machineries that generate these forces for neuronal migration.

Re-evaluation of physical interaction between plant peroxisomes and other organelles using live-cell imaging techniques

The dynamic behavior of organelles is essential for plant survival under various environmental conditions. Plant organelles, with various functions, migrate along actin filaments and contact other types of organelles, leading to physical interactions at a specific site called the membrane contact site. Recent studies have revealed the importance of physical interactions in maintaining efficient metabolite flow between organelles. In this review, we first summarize peroxisome function under different environmental conditions and growth stages to understand organelle interactions. We then discuss current knowledge regarding the interactions between peroxisome and other organelles, i.e., the oil bodies, chloroplast, and mitochondria from the perspective of metabolic and physiological regulation, with reference to various organelle interactions and techniques for estimating organelle interactions occurring in plant cells.

A simple and static preservation system for shipping retinal pigment epithelium cell sheets

The ability to move cells and tissues from bench to bedside is an essential aspect of regenerative medicine. In this study, we propose a simple and static shipping system to deliver tissue-engineered cell sheets. Notably, this system is electronic-device-free and simplified to minimize the number of packing and opening steps involved. Shipping conditions were optimized, and application and verification of the system were performed using human iPS cell-derived or fetal retinal pigment epithelium (RPE) cell sheets. The temperature of the compartments within the insulated container was stable at various conditions, and filling up the cell vessel with medium effectively prevented turbulence-induced mechanical damage to the RPE cell sheets. Furthermore, no abnormal changes were observed in RPE morphology, transepithelial electrical resistance, or mRNA expression after transit by train and car. Taken together, our simple shipping system has the potential to minimize the costs and human error associated with bench to bedside tissue transfer. This specially designed regenerative tissue shipping system, validated for use in this field, can be used without any special training. This study provides a procedure for easily sharing engineered tissues with the goal of promoting collaboration between laboratories and hospitals and enhancing patient care.

Geometry, packing, and evolutionary paths to increased multicellular size

The evolutionary transition to multicellularity transformed life on earth, heralding the evolution of large, complex organisms. Recent experiments demonstrated that laboratory-evolved multicellular "snowflake yeast" readily overcome the physical barriers that limit cluster size by modifying cellular geometry [Jacobeen et al., Nat. Phys. 14, 286 (2018)10.1038/s41567-017-0002-y]. However, it is unclear why this route to large size is observed, rather than an evolved increase in intercellular bond strength. Here, we use a geometric model of the snowflake yeast growth form to examine the geometric efficiency of increasing size by modifying geometry and bond strength. We find that changing geometry is a far more efficient route to large size than evolving increased intercellular adhesion. In fact, increasing cellular aspect ratio is on average ∼13 times more effective than increasing bond strength at increasing the number of cells in a cluster. Modifying other geometric parameters, such as the geometric arrangement of mother and daughter cells, also had larger effects on cluster size than increasing bond strength. Simulations reveal that as cells reproduce, internal stress in the cluster increases rapidly; thus, increasing bond strength provides diminishing returns in cluster size. Conversely, as cells become more elongated, cellular packing density within the cluster decreases, which substantially decreases the rate of internal stress accumulation. This suggests that geometrically imposed physical constraints may have been a key early selective force guiding the emergence of multicellular complexity.

Modest Static Pressure Suppresses Columnar Epithelial Cell Growth in Association with Cell Shape and Cytoskeletal Modifications

Intraluminal pressure elevation can cause degenerative disorders, such as ileus and hydronephrosis, and the threshold is fairly low and constant, 20–30 cm H₂O. We previously devised a novel two-chamber culture system subjecting cells cultured on a semipermeable membrane to increased culture medium height (water pressure up to 60 cm H₂O). Here, we sought to determine how a continuous pressure load of ~30 cm H₂O affects proliferating epithelial cells with special interest in the link with cell morphology. We cultured several different cell lines using the low static pressure-loadable two-chamber system, and examined cell growth, cell cycle, and cell morphology. Madin–Darby canine kidney (MDCK) columnar epithelial cells were growth-suppressed in a manner dependent on static water pressure ranging from 2 to 50 cm H₂O, without cell cycle arrest at any specific phase. Two other types of columnar epithelial cells exhibited similar phenotypes. By contrast, spherical epithelial and mesenchymal cells were not growth-suppressed, even at 50 cm H₂O. Phalloidin staining revealed that 50 cm H₂O pressure load vertically flattened and laterally widened columnar epithelial cells and made actin fiber distribution sparse, without affecting total phalloidin intensity per cell. When the mucosal protectant irsogladine maleate (100 nM) was added to 50-cm-high culture medium, MDCK cells were reduced in volume and their doubling time shortened. Cell proliferation and morphology are known to be regulated by the Hippo signaling pathway. A pressure load of 50 cm H₂O enhanced serine-127 phosphorylation and cytoplasmic retention of YAP, the major constituent of this pathway, suggesting that Hippo pathway was involved in the pressure-induced cell growth suppression. RNA sequencing of MDCK cells showed that a 50 cm H₂O pressure load upregulated keratin 14, an intermediate filament, 12-fold. This upregulation was confirmed at the protein level by immunofluorescence, suggesting a role in cytoskeletal reinforcement. These results provide evidence that cell morphology and the cytoskeleton are closely linked to cell growth. Pathological intraluminal pressure elevation may cause mucosal degeneration by acting directly on this linkage and the Hippo pathway.

Quantitative analysis of mechanical force required for cell extrusion in zebrafish embryonic epithelia

When cells in epithelial sheets are damaged by intrinsic or extrinsic causes, they are eliminated by extrusion from the sheet. Cell extrusion, which is required for maintenance of tissue integrity, is the consequence of contraction of actomyosin rings, as demonstrated by both molecular/cellular biological experimentation and numerical simulation. However, quantitative evaluation of actomyosin contraction has not been performed because of the lack of a suitable direct measurement system. In this study, we developed a new method using a femtosecond laser to quantify the contraction force of the actomyosin ring during cell extrusion in zebrafish embryonic epithelia. In this system, an epithelial cell in zebrafish embryo is first damaged by direct femtosecond laser irradiation. Next, a femtosecond laser-induced impulsive force is loaded onto the actomyosin ring, and the contraction force is quantified to be on the order of kPa as a unit of pressure. We found that cell extrusion was delayed when the contraction force was slightly attenuated, suggesting that a relatively small force is sufficient to drive cell extrusion. Thus, our method is suitable for the relative quantitative evaluation of mechanical dynamics in the process of cell extrusion, and in principle the method is applicable to similar phenomena in different tissues and organs of various species.

Summary: In this study a novel in vivo force quantification system was developed, which succeeded in estimating the magnitude of force required for extrusion of a dying cell from zebrafish embryonic epithelia.

Time-Course Statistical Evaluation of Intercellular Adhesion Maturation by Femtosecond Laser Impulse

The maturation of intercellular adhesion is an essential process for establishing the signal transduction network in living cells. Although the maturation is naturally considered to enhance the signal transduction, the relationship between the signal transduction and the maturation process has not been revealed in detail using time-course data. Here, using a coculture of mast cells and neurites, differences in maturation between individual cells were estimated as a function of the adhesion strength by our original single-cell measurement method utilizing a laser-induced impulsive force. When an intense femtosecond laser is focused into a culture medium under a microscope, shock and stress waves are generated at the laser focal point that exert an impulsive force on individual cells. In our method, this impulse is used to break the adhesion between a mast cell and a neurite. The magnitude of the impulse is then quantified by a local force-measurement system utilizing an atomic force microscope, and the adhesion strength is estimated from the threshold of the impulse required to break the adhesion. The measurement is conducted within 1 min/cell, and thus, data on the individual differences of the adhesion strength can be obtained within only a few hours. Coculturing of neurites and mast cells for 4 h resulted in a specific adhesion that was stronger than the nonspecific adhesions between the substrate and mast cells. In the time-course investigation, we identified two distinct temporal patterns of adhesion: 1) the strength at 24 h was the same as the initial strength; and 2) the strength increased threefold from baseline and became saturated within 24 h. Based on these results, the distribution of CADM1 adhesion molecules in the neurites was suggested to be inhomogeneous, and the relationship between adhesion maturation and the signal-transduction process was considered.

Splicing Regulation of Pro-Inflammatory Cytokines and Chemokines: At the Interface of the Neuroendocrine and Immune Systems

Alternative splicing plays a key role in posttranscriptional regulation of gene expression, allowing a single gene to encode multiple protein isoforms. As such, alternative splicing amplifies the coding capacity of the genome enormously, generates protein diversity, and alters protein function. More than 90% of human genes undergo alternative splicing, and alternative splicing is especially prevalent in the nervous and immune systems, tissues where cells need to react swiftly and adapt to changes in the environment through carefully regulated mechanisms of cell differentiation, migration, targeting, and activation. Given its prevalence and complexity, this highly regulated mode of gene expression is prone to be affected by disease. In the following review, we look at how alternative splicing of signaling molecules—cytokines and their receptors—changes in different pathological conditions, from chronic inflammation to neurologic disorders, providing means of functional interaction between the immune and neuroendocrine systems. Switches in alternative splicing patterns can be very dynamic and can produce signaling molecules with distinct or antagonistic functions and localization to different subcellular compartments. This newly discovered link expands our understanding of the biology of immune and neuroendocrine cells, and has the potential to open new windows of opportunity for treatment of neurodegenerative disorders.

Dynamics of the Light-Dependent Transition of Plant Peroxisomes

Peroxisomes are present in almost all plant cells. These organelles are involved in various metabolic processes, such as lipid catabolism and photorespiration. A notable feature of plant peroxisomes is their flexible adaptive responses to environmental conditions such as light. When plants shift from heterotrophic to autotrophic growth during the post-germinative stage, peroxisomes undergo a dynamic response, i.e. enzymes involved in lipid catabolism are replaced with photorespiratory enzymes. Although the detailed molecular mechanisms underlying the functional transition of peroxisomes have previously been unclear, recent analyses at the cellular level have enabled this detailed machinery to be characterized. During the functional transition, obsolete enzymes are degraded inside peroxisomes by Lon protease, while newly synthesized enzymes are transported into peroxisomes. In parallel, mature and oxidized peroxisomes are eliminated via autophagy; this functional transition occurs in an efficient manner. Moreover, it has become clear that quality control mechanisms are important for the peroxisomal response to environmental stimuli. In this review, we highlight recent advances in elucidating the molecular mechanisms required for the regulation of peroxisomal roles in response to changes in environmental conditions.

Physical interaction between peroxisomes and chloroplasts elucidated by in situ laser analysis

Life on earth relies upon photosynthesis, which consumes carbon dioxide and generates oxygen and carbohydrates. Photosynthesis is sustained by a dynamic environment within the plant cell involving numerous organelles with cytoplasmic streaming. Physiological studies of chloroplasts, mitochondria and peroxisomes show that these organelles actively communicate during photorespiration, a process by which by-products produced by photosynthesis are salvaged. Nevertheless, the mechanisms enabling efficient exchange of metabolites have not been clearly defined. We found that peroxisomes along chloroplasts changed shape from spherical to elliptical and their interaction area increased during photorespiration. We applied a recent femtosecond laser technology to analyse adhesion between the organelles inside palisade mesophyll cells of Arabidopsis leaves and succeeded in estimating their physical interactions under different environmental conditions. This is the first application of this estimation method within living cells. Our findings suggest that photosynthetic-dependent interactions play a critical role in ensuring efficient metabolite flow during photorespiration.

In situ quantification of living cell adhesion forces: single cell force spectroscopy with a nanotweezer

A novel method is presented for in situ quantification of living cell adhesion forces using a homemade nanorobotic system provided with two independently actuated probes that form a dual-probe nanotweezer capable of pick-and-place manipulation of a single living cell in an aqueous environment. Compared with single-cell force spectroscopy (SCFS) based on traditional atomic force microscopy (AFM), cell immobilization via chemical trapping is unnecessary and the test cell can be efficiently released using the nanotweezer to significantly enhance production of the SCFS. Benefiting from the accurate force sensing capability of AFM, the nanotweezer allows reliable force measurement ranging from picoNewtons to microNewtons and is sufficiently sensitive to characterize short- and long-term adhesion of cell-cell and cell-substrate adhesions. Capabilities of the nanotweezer have been validated through experimental qualification of cell-substrate and cell-cell adhesion events of C2C12 cells (mouse myoblast adherent) with different contact times.

Increased expression of cell adhesion molecule 1 by mast cells as a cause of enhanced nerve-mast cell interaction in a hapten-induced mouse model of atopic dermatitis

BACKGROUND

Neuroimmunological disorders are involved in the pathogenesis of atopic dermatitis (AD), partly through enhanced sensory nerve-skin mast cell interaction. Cell adhesion molecule 1 (CADM1) is a mast-cell adhesion molecule that mediates the adhesion to, and communication with, sympathetic nerves.

OBJECTIVES

To investigate the role of mast cell CADM1 in the pathogenesis of AD, CADM1 expression levels by comparing between lesional and nonlesional skin mast cells of an AD mouse model, which was developed by repeated application of trinitrochlorobenzene, and to examine, in cocultures, how the alterations in CADM1 detected in lesional mast cells might affect the sensory nerve-mast cell interaction.

METHODS

AD-like lesional and nonlesional skin mast cells were collected separately by laser capture microdissection. CADM1 expression was examined by reverse transcription-polymerase chain reaction and CADM1 immunohistochemistry. In cocultures, adhesion between dorsal root ganglion (DRG) neurites and IC2 mast cells was analysed by loading a femtosecond laser-induced impulsive force on neurite-attendant IC2 cells, while cellular communication was monitored as the IC2 cellular response ([Ca(2+)]i increase) after nerve-specific stimulant-induced DRG activation.

RESULTS

AD-like lesional mast cells expressed three-fold more CADM1 transcripts than nonlesional cells. This was supported at the protein level, shown by immunohistochemistry. In coculture, CADM1 overexpression in IC2 cells strengthened DRG neurite-IC2 cell adhesion and doubled the population of IC2 cells responding to DRG activation. A function-blocking anti-CADM1 antibody abolished these effects in a dose-dependent manner.

CONCLUSIONS

Increased expression of CADM1 in mast cells appeared to be a cause of enhanced sensory nerve-mast cell interaction in a hapten-induced mouse model of AD.

Measurements of elastic modulus for human anterior lens capsule with atomic force microscopy: the effect of loading force

The purpose of the study was to appraise the effect of loading force magnitude on the determination of the elastic modulus of the anterior lens capsule through atomic force microscopy. Four human anterior lens capsules taken during phacoemulsification cataract surgery were studied, free of epithelial cells, with atomic force microscopy. For the experiment, five different indentation loading forces were applied to near areas of the specimen. Experimental data was exported and analyzed according to the Hertz model to obtain the Young's modulus with regards to the elastic behavior of the material. Force-distance curves were acquired by applying a load of 2, 5, 10, 20 and 30 nN. When examining the results it was evident that determination of Young's modulus of the anterior lens capsule is dependent on the loading force concerning the examined range. Loading forces of 10 and 20 nN led to results without significant difference (p > 0.05) and more reproducible (coefficients of variation 12.4 and 11.7 %, respectively).

On fundamental cellular processes for emergence of collective epithelial movement

In all animals, collective cell movement is an essential process in many events, including wound healing and embryonic development. However, our understanding of what characterizes the emergence of multicellular collective behavior is still far from complete. In this article we showed the fundamental cellular processes that drive collective cell movement by means of integrated approaches, including precise quantification measurements and mathematical modeling of measured data. First, we observed the dependence of the collective behaviors of cultured human skin cells on Ca²⁺ concentrations. When the culturing area confined by a PDMS sheet was suddenly expanded by removing the sheet, the group of cells moved to the expanded area with higher collectivity at higher Ca²⁺ concentrations. Next, we quantitatively measured cellular responses to the Ca²⁺ treatments, such as cell growth, cell division, and the strength of intercellular adhesion. Using a femtosecond-laser-based assay, an original method for estimating intercellular adhesion, we found that the strength of intercellular adhesion has an approximately 13-fold range in our treatments. Incorporating the quantitative data into a mathematical model, we then confirmed that the model well reproduced the multicellular behaviors we observed, demonstrating that the strength of intercellular adhesion sufficiently determines the generation of collective cell movement. Finally, we performed extensive numerical experiments, and the results suggested that the emergence of collective cell movement is derived by an optimal balance between the strength of intercellular adhesion and the intensity of cell migration.

Submicrosecond time resolution atomic force microscopy for probing nanoscale dynamics

We propose, simulate, and experimentally validate a new mechanical detection method to analyze atomic force microscopy (AFM) cantilever motion that enables noncontact discrimination of transient events with ~100 ns temporal resolution without the need for custom AFM probes, specialized instrumentation, or expensive add-on hardware. As an example application, we use the method to screen thermally annealed poly(3-hexylthiophene):phenyl-C(61)-butyric acid methyl ester photovoltaic devices under realistic testing conditions over a technologically relevant performance window. We show that variations in device efficiency and nanoscale transient charging behavior are correlated, thereby linking local dynamics with device behavior. We anticipate that this method will find application in scanning probe experiments of dynamic local mechanical, electronic, magnetic, and biophysical phenomena.

Photoporation of biomolecules into single cells in living vertebrate embryos induced by a femtosecond laser amplifier

Introduction of biomolecules into cells in living animals is one of the most important techniques in molecular and developmental biology research, and has potentially broad biomedical implications. Here we report that biomolecules can be introduced into single cells in living vertebrate embryos by photoporation using a femtosecond laser amplifier with a high pulse energy and a low repetition rate. First, we confirmed the efficiency of this photoporation technique by introducing dextran, morpholino oligonucleotides, or DNA plasmids into targeted single cells of zebrafish, chick, shark, and mouse embryos. Second, we demonstrated that femtosecond laser irradiation efficiently delivered DNA plasmids into single neurons of chick embryos. Finally, we successfully manipulated the fate of single neurons in zebrafish embryos by delivering mRNA. Our observations suggest that photoporation using a femtosecond laser with a high pulse energy and low repetition rate offers a novel way to manipulate the function(s) of individual cells in a wide range of vertebrate embryos by introduction of selected biomolecules.

Enhanced nerve-mast cell interaction by a neuronal short isoform of cell adhesion molecule-1

Close apposition of nerve and mast cells is viewed as a functional unit of neuro-immune mechanisms, and it is sustained by trans-homophilic binding of cell adhesion molecule-1 (CADM1), an Ig superfamily member. Cerebral nerve-mast cell interaction might be developmentally modulated, because the alternative splicing pattern of four (a-d) types of CADM1 transcripts drastically changed during development of the mouse cerebrum: developing cerebrums expressed CADM1b and CADM1c exclusively, while mature cerebrums expressed CADM1d additionally and predominantly. To probe how individual isoforms are involved in nerve-mast cell interaction, Neuro2a neuroblastoma cells that express CADM1c endogenously were modified to express additionally either CADM1b (Neuro2a-CADM1b) or CADM1d (Neuro2a-CADM1d), and they were cocultured with mouse bone marrow-derived mast cells (BMMCs) and BMMC-derived cell line IC-2 cells, both of which expressed CADM1c. BMMCs were found to adhere to Neuro2a-CADM1d neurites more firmly than to Neuro2a-CADM1b neurites when the adhesive strengths were estimated from the femtosecond laser-induced impulsive forces minimally required for detaching BMMCs. GFP-tagging and crosslinking experiments revealed that the firmer adhesion site consisted of an assembly of CADM1d cis-homodimers. When Neuro2a cells were specifically activated by histamine, intracellular Ca(2+) concentration was increased in 63 and 38% of CADM1c-expressing IC-2 cells that attached to the CADM1d assembly site and elsewhere, respectively. These results indicate that CADM1d is a specific neuronal isoform that enhances nerve-mast cell interaction, and they suggest that nerve-mast cell interaction may be reinforced as the brain grows mature because CADM1d becomes predominant.