Revealing chiral cell motility by 3D Riesz transform-differential interference contrast microscopy and computational kinematic analysis

Chirality Quantification for High-Performance Nanophotonic Biosensors

Recent advancements in chiral metabolomics have facilitated the discovery of disease biomarkers through the enantioselective measurement of metabolites, offering new opportunities for diagnosis, prognosis, and personalized medicine. Although chiral photonic nanomaterials have emerged as promising platforms for chiral biosensing, enhancing sensitivity and enabling the detection of biomolecules at extremely low concentrations, a deeper understanding of the relationship between structural and optical chirality is crucial for optimizing these platforms. This perspective examines recent methods for quantifying chirality, including the Hausdorff Chirality Measure (HCM), Continuous Chirality Measure (CCM), Osipov-Pickup-Dunmur (OPD), and Graph-Theoretical Chirality (GTC) measure. These approaches have advanced the understanding of chirality in both materials and biomolecules, as well as its correlation with optical responses. This work emphasizes the role of chiral quantification in improving biosensor performance and explores the potential of near-field chiroptical studies to enhance sensor capabilities. Finally, this work addresses key challenges and outline future research directions for advancing chiral biosensors, with a focus on improving nano-bio interface interactions to drive the development of next-generation sensing technologies.

Nonlinear differential interference contrast imaging

Differential interference contrast (DIC) imaging is essential in both biological research and medical diagnostics. Despite considerable progress in theoretical and experimental frameworks, limited by the inefficient cameras, achieving direct DIC imaging with infrared (IR) illumination remains a formidable challenge. However, infrared DIC imaging is urgent for diverse fields. Here, we creatively leverage the walk-off effect, a limitation in nonlinear optics, to solve this obstacle and present the nonlinear DIC imaging. The critical component of our scheme is a nonlinear beam displacer (NBD) made up of two quadrature-cascaded type I nonlinear crystals. When the infrared beam carrying object information passes through the proposed NBD, it undergoes nonlinear coupling with the pump beam and then generates two orthogonally polarized visible beams with a slight spatial displacement dominated by the walk-off effect. Accordingly, by selecting polarization, the lateral shear interference for realizing DIC imaging can be realized, and thus the phase discontinuities of the object can be visualized with infrared illumination. Our finding brings DIC imaging technology into the realm of upconversion infrared imaging, paving the way for infrared phase microscopy imaging.

Filopodia: integrating cellular functions with theoretical models

Filopodia, widely distributed on cell surfaces, are distinguished by their dynamic extensions, playing pivotal roles in a myriad of biological processes. Their functions span from mechanosensing and guidance to cell-cell communication during cellular organization in the early embryo. Filopodia have significant roles in pathogenic processes, such as cancer invasion and viral dissemination. Molecular mapping of the filopodome has revealed generic components essential for filopodia functions. In parallel, recent insights into biophysical mechanisms governing filopodia dynamics have provided the foundation for broader investigations of filopodia's biological functions. We highlight recent discoveries of engagement of filopodia in various stages of development and pathogenesis and present an overview of intricate molecular and physical features of these cellular structures across a spectrum of cellular activities.

Dynamics of multicellular swirling on micropatterned substrates

Chirality plays a crucial role in biology, as it is highly conserved and fundamentally important in the developmental process. To better understand the relationship between the chirality of individual cells and that of tissues and organisms, we develop a generalized mechanics model of chiral polarized particles to investigate the swirling dynamics of cell populations on substrates. Our analysis reveals that cells with the same chirality can form distinct chiral patterns on ring-shaped or rectangular substrates. Interestingly, our studies indicate that an excessively strong or weak individual cellular chirality hinders the formation of such chiral patterns. Our studies also indicate that there exists the influence distance of substrate boundaries in chiral patterns. Smaller influence distances are observed when cell-cell interactions are weaker. Conversely, when cell-cell interactions are too strong, multiple cells tend to be stacked together, preventing the formation of chiral patterns on substrates in our analysis. Additionally, we demonstrate that the interaction between cells and substrate boundaries effectively controls the chiral distribution of cellular orientations on ring-shaped substrates. This research highlights the significance of coordinating boundary features, individual cellular chirality, and cell-cell interactions in governing the chiral movement of cell populations and provides valuable mechanics insights into comprehending the intricate connection between the chirality of single cells and that of tissues and organisms.

Membrane-bound myosin IC drives the chiral rotation of the gliding actin filament around its longitudinal axis

Myosin IC, a single-headed member of the myosin I family, specifically interacts with anionic phosphatidylinositol 4,5-bisphosphate (PI[4,5]P2) in the cell membrane via the pleckstrin homology domain located in the myosin IC tail. Myosin IC is widely expressed and physically links the cell membrane to the actin cytoskeleton; it plays various roles in membrane-associated physiological processes, including establishing cellular chirality, lipid transportation, and mechanosensing. In this study, we evaluated the motility of full-length myosin IC of Drosophila melanogaster via the three-dimensional tracking of quantum dots bound to actin filaments that glided over a membrane-bound myosin IC-coated surface. The results revealed that myosin IC drove a left-handed rotational motion in the gliding actin filament around its longitudinal axis, indicating that myosin IC generated a torque perpendicular to the gliding direction of the actin filament. The quantification of the rotational motion of actin filaments on fluid membranes containing different PI(4,5)P2 concentrations revealed that the rotational pitch was longer at lower PI(4,5)P2 concentrations. These results suggest that the torque generated by membrane-bound myosin IC molecules can be modulated based on the phospholipid composition of the cell membrane.

Chiral growth of adherent filopodia

Adherent filopodia are elongated finger-like membrane protrusions, extending from the edges of diverse cell types and participating in cell adhesion, spreading, migration, and environmental sensing. The formation and elongation of filopodia are driven by the polymerization of parallel actin filaments, comprising the filopodia cytoskeletal core. Here, we report that adherent filopodia, formed during the spreading of cultured cells on galectin-8-coated substrates, tend to change the direction of their extension in a chiral fashion, acquiring a left-bent shape. Cryoelectron tomography examination indicated that turning of the filopodia tip to the left is accompanied by the displacement of the actin core bundle to the right of the filopodia midline. Reduction of the adhesion to galectin-8 by treatment with thiodigalactoside abolished this filopodia chirality. By modulating the expression of a variety of actin-associated filopodia proteins, we identified myosin-X and formin DAAM1 as major filopodia chirality promoting factors. Formin mDia1, actin filament elongation factor VASP, and actin filament cross-linker fascin were also shown to be involved. Thus, the simple actin cytoskeleton of filopodia, together with a small number of associated proteins are sufficient to drive a complex navigation process, manifested by the development of left-right asymmetry in these cellular protrusions.

The Actin Crosslinker Fascin Regulates Cell Chirality

The left-right (L-R) asymmetry of the cells, or cell chirality, is a well-known intrinsic property derived from the dynamic organization of the actin cytoskeleton. Cell chirality can be regulated by actin-binding proteins such as α-actinin-1 and can also be mediated by certain signaling pathways, such as protein kinase C (PKC) signaling. Fascin, an actin crosslinker known to mediate parallel bundling of actin filaments, appears as a prominent candidate in cell chirality regulation, given its role in facilitating cell migration as an important PKC substrate. Here, it is shown that the chirality of NIH/3T3 cells can be altered by PKC activation and fascin manipulation. With either small-molecule drug inhibition or genetic knockdown of fascin, the chirality of 3T3 cells is reversed from a clockwise (CW) bias to a counterclockwise (CCW) bias on ring-shaped micropatterns, accompanied by the reversal in cell directional migration. The Ser-39 fascin-actin binding sites are further explored in cell chirality regulation. The findings of this study reveal the critical role of fascin as an important intermediator in cell chirality, shedding novel insights into the mechanisms of L-R asymmetric cell migration and multicellular morphogenesis.

Single-shot isotropic differential interference contrast microscopy

Differential interference contrast (DIC) microscopy allows high-contrast, low-phototoxicity, and label-free imaging of transparent biological objects, and has been applied in the field of cellular morphology, cell segmentation, particle tracking, optical measurement and others. Commercial DIC microscopy based on Nomarski or Wollaston prism resorts to the interference of two polarized waves with a lateral differential offset (shear) and axial phase shift (bias). However, the shear generated by these prisms is limited to the rectilinear direction, unfortunately resulting in anisotropic contrast imaging. Here we propose an ultracompact metasurface-assisted isotropic DIC (i-DIC) microscopy based on a grand original pattern of radial shear interferometry, that converts the rectilinear shear into rotationally symmetric along radial direction, enabling single-shot isotropic imaging capabilities. The i-DIC presents a complementary fusion of typical meta-optics, traditional microscopes and integrated optical system, and showcases the promising and synergetic advancements in edge detection, particle motion tracking, and label-free cellular imaging.

Recognition of 3D Chiral Microenvironments for Myoblast Differentiation

Cell chirality plays a critical role in the linkage between molecular chirality and the asymmetrical biological functions of body organs. However, enantioselective interactions between cell chirality and the extracellular environment are not yet fully understood. In this study, we investigated the effects of structurally chiral extracellular microenvironments on cellular alignments and differentiations. Twisted wrinkle-shaped chiral micropatterns were prepared using biaxial and asymmetric buckling methods, wherein structural handedness was determined from the orientation of the tilt angle between the first and second microwrinkles. Myoblasts were separately cultured on two enantiomeric chiral micropatterns in a mirror-reflected shape. Cells cultured on the left-handed chiral micropatterns preferred alignments along the direction of the second microwrinkle, with a relatively deeper valley than that of the first microwrinkle. The aligned cells on the left-handed pattern showed higher differentiation rates, as assessed by fusion indices and marker protein expression levels, than those cultured on right-handed chiral micropatterns. These results suggest that myoblasts exhibit enantioselective recognition of structurally chiral microenvironments, which can promote cellular alignments and differentiation.

Cell Chirality as a Novel Measure for Cytotoxicity

Cytotoxicity assessment has great importance in both research and pharmaceutical development. The mainstream in vitro cytotoxicity assays are mostly biochemical assays that evaluate a specific cellular activity such as proliferation and apoptosis. Few assays assess toxicity by characterizing overall functional outcomes in cellular physiology such as multicellular morphogenesis. The intrinsic cellular chiral bias (also known as cell chirality, left-right asymmetry, or handedness), which determines cellular polarization along the left-right axis, is demonstrated to play important roles in development and disease. This chiral property of cells gives insights not only into functions of individual cells, such as motility and polarity but also into emerging behaviors of cell clusters, such as collective cell migration. Therefore, cell chirality characterization can be potentially used as a biomarker for assessing the overall effects of pharmaceutical drugs and environmental factors on the health of the cell. In this review article, the current in vitro techniques for cell chirality characterization and their applications are discussed and the advantages and limitations of these cell chirality assays as potential tools for detecting cytotoxicity are discussed.

Cells/colony motion of oral keratinocytes determined by non-invasive and quantitative measurement using optical flow predicts epithelial regenerative capacity

Cells/colony motion determined by non-invasive, quantitative measurements using the optical flow (OF) algorithm can indicate the oral keratinocyte proliferative capacity in early-phase primary cultures. This study aimed to determine a threshold for the cells/colony motion index to detect substandard cell populations in a subsequent subculture before manufacturing a tissue-engineered oral mucosa graft and to investigate the correlation with the epithelial regenerative capacity. The distinctive proliferating pattern of first-passage [passage 1 (p1)] cells reveals the motion of p1 cells/colonies, which can be measured in a non-invasive, quantitative manner using OF with fewer full-screen imaging analyses and cell segmentations. Our results demonstrate that the motion index lower than 40 μm/h reflects cellular damages by experimental metabolic challenges although this value shall only apply in case of our culture system. Nonetheless, the motion index can be used as the threshold to determine the quality of cultured cells while it may be affected by any different culture conditions. Because the p1 cells/colony motion index is correlated with epithelial regenerative capacity, it is a reliable index for quality control of oral keratinocytes.

Exploration of possible cell chirality using material techniques of surface patterning

Consistent left-right (LR) asymmetry or chirality is critical for embryonic development and function maintenance. While chirality on either molecular or organism level has been well established, that on the cellular level has remained an open question for a long time. Although it remains unclear whether chirality exists universally on the cellular level, valuable efforts have recently been made to explore this fundamental topic pertinent to both cell biology and biomaterial science. The development of material fabrication techniques, surface patterning, in particular, has afforded a unique platform to study cell-material interactions. By using patterning techniques, chirality on the cellular level has been examined for cell clusters and single cells in vitro in well-designed experiments. In this review, we first introduce typical fabrication techniques of surface patterning suitable for cell studies and then summarize the main aspects of preliminary evidence of cell chirality on patterned surfaces to date. We finally indicate the limitations of the studies conducted thus far and describe the perspectives of future research in this challenging field. STATEMENT OF SIGNIFICANCE: While both biomacromolecules and organisms can exhibit chirality, it is not yet conclusive whether a cell has left-right (LR) asymmetry. It is important yet challenging to study and reveal the possible existence of cell chirality. By using the technique of surface patterning, the recent decade has witnessed progress in the exploration of possible cell chirality within cell clusters and single cells. Herein, some important preliminary evidence of cell chirality is collected and analyzed. The open questions and perspectives are also described to promote further investigations of cell chirality in biomaterials.

Digital image processing to detect subtle motion in stony coral

Coral reef ecosystems support significant biological activities and harbor huge diversity, but they are facing a severe crisis driven by anthropogenic activities and climate change. An important behavioral trait of the coral holobiont is coral motion, which may play an essential role in feeding, competition, reproduction, and thus survival and fitness. Therefore, characterizing coral behavior through motion analysis will aid our understanding of basic biological and physical coral functions. However, tissue motion in the stony scleractinian corals that contribute most to coral reef construction are subtle and may be imperceptible to both the human eye and commonly used imaging techniques. Here we propose and apply a systematic approach to quantify and visualize subtle coral motion across a series of light and dark cycles in the scleractinian coral Montipora capricornis. We use digital image correlation and optical flow techniques to quantify and characterize minute coral motions under different light conditions. In addition, as a visualization tool, motion magnification algorithm magnifies coral motions in different frequencies, which explicitly displays the distinctive dynamic modes of coral movement. Specifically, our assessment of displacement, strain, optical flow, and mode shape quantify coral motion under different light conditions, and they all show that M. capricornis exhibits more active motions at night compared to day. Our approach provides an unprecedented insight into micro-scale coral movement and behavior through macro-scale digital imaging, thus offering a useful empirical toolset for the coral research community.

Effects of Alzheimer's Disease-Related Proteins on the Chirality of Brain Endothelial Cells

Introduction

Cell chirality is an intrinsic cellular property that determines the directionality of cellular polarization along the left-right axis. We recently show that endothelial cell chirality can influence intercellular junction formation and alter trans-endothelial permeability, depending on the uniformity of the chirality of adjacent cells, which suggests a potential role for cell chirality in neurodegenerative diseases with blood-brain barrier (BBB) dysfunctions, such as Alzheimer's disease (AD). In this study, we determined the effects of AD-related proteins amyloid-β (Aβ), tau, and apolipoprotein E4 (ApoE4) on the chiral bias of the endothelial cell component in BBB.

Methods

We first examined the chiral bias and effects of protein kinase C (PKC)-mediated chiral alterations of human brain microvascular endothelial cells (hBMECs) using the ring micropattern chirality assay. We then investigated the effects of Aβ, tau, and ApoE4 on hBMEC chirality using chirality assay and biased organelle positions.

Results

The hBMECs have a strong clockwise chiral bias, which can be reversed by protein kinase C (PKC) activation. Treatment with tau significantly disrupted the chiral bias of hBMECs with altered cellular polarization. In contrast, neither ApoE4 nor Aβ-42 caused significant changes in cell chirality.

Conclusions

We conclude that tau might cause BBB dysfunction by disrupting cell polarization and chiral morphogenesis, while the effects of ApoE4 and Aβ-42 on BBB integrity might be chirality-independent. The potential involvement of chiral morphogenesis in tau-mediated BBB dysfunction in AD provides a novel perspective in vascular dysfunction in tauopathies such as AD, chronic traumatic encephalopathy, progressive supranuclear palsy, and frontotemporal dementia.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-021-00669-w.

Cell chirality in cardiovascular development and disease

The cardiovascular system demonstrates left-right (LR) asymmetry: most notably, the LR asymmetric looping of the bilaterally symmetric linear heart tube. Similarly, the orientation of the aortic arch is asymmetric as well. Perturbations to the asymmetry have been associated with several congenital heart malformations and vascular disorders. The source of the asymmetry, however, is not clear. Cell chirality, a recently discovered and intrinsic LR asymmetric cellular morphological property, has been implicated in the heart looping and vascular barrier function. In this paper, we summarize recent advances in the field of cell chirality and describe various approaches developed for studying cell chirality at multi- and single-cell levels. We also examine research progress in asymmetric cardiovascular development and associated malformations. Finally, we review evidence connecting cell chirality to cardiac looping and vascular permeability and provide thoughts on future research directions for cell chirality in the context of cardiovascular development and disease.

Early Committed Clockwise Cell Chirality Upregulates Adipogenic Differentiation of Mesenchymal Stem Cells

Cell chirality is observed with diverse forms and coordinates various left-right (LR) asymmetry in tissue morphogenesis. To give rise to such diversity, cell chirality may be coupled with cell differentiation. Here, using micropatterned human mesenchymal stem cells (hMSCs), an early committed clockwise (CW) cell chirality that can itself upregulate the adipogenic differentiation is reported. hMSC chirality enables a positively tilted chiral orientation on micropatterned stripes. When cultured as single cells on circular micropatterns, an anticlockwise (ACW)-biased nucleus rotation and swirling pattern of actin filament are observed. Interestingly, with adipogenic induction for 3-6 days, such chirality is reversed to negative chiral orientation and CW-biased rotation, which is earlier than the maturation of other differentiation markers, and consistently expressed in terminally differentiated adipocytes. Using latrunculin A (LatA), cytochalasin D (CD), and nocodazole (Noco) that forces a CW-biased actin filament and nucleus rotation resembling the early differentiated chirality upon adipogenic induction, an upregulation of adipogenic differentiation is found. The result demonstrates that the early differentiated chirality may serve as a mechanical precursor to engage the lineage commitment, suggesting a feedback mechanism of chiral actin in regulating cell differentiation and LR morphogenesis.

Neuronal Signaling Involved in Neuronal Polarization and Growth: Lipid Rafts and Phosphorylation

Neuronal polarization and growth are developmental processes that occur during neuronal cell differentiation. The molecular signaling mechanisms involved in these events in in vivo mammalian brain remain unclear. Also, cellular events of the neuronal polarization process within a given neuron are thought to be constituted of many independent intracellular signal transduction pathways (the "tug-of-war" model). However, in vivo results suggest that such pathways should be cooperative with one another among a given group of neurons in a region of the brain. Lipid rafts, specific membrane domains with low fluidity, are candidates for the hotspots of such intracellular signaling. Among the signals reported to be involved in polarization, a number are thought to be present or translocated to the lipid rafts in response to extracellular signals. As part of our analysis, we discuss how such novel molecular mechanisms are combined for effective regulation of neuronal polarization and growth, focusing on the significance of the lipid rafts, including results based on recently introduced methods.

Effect of static magnetic field on DNA synthesis: The interplay between DNA chirality and magnetic field left-right asymmetry

Interactions between magnetic fields (MFs) and living cells may stimulate a large variety of cellular responses to a MF, while the underlying intracellular mechanisms still remain a great puzzle. On a fundamental level, the MF - cell interaction is affected by the two broken symmetries: (a) left-right (LR) asymmetry of the MF and (b) chirality of DNA molecules carrying electric charges and subjected to the Lorentz force when moving in a MF. Here we report on the chirality-driven effect of static magnetic fields (SMFs) on DNA synthesis. This newly discovered effect reveals how the interplay between two fundamental features of symmetry in living and inanimate nature-DNA chirality and the inherent features of MFs to distinguish the left and right-manifests itself in different DNA synthesis rates in the upward and downward SMFs, consequently resulting in unequal cell proliferation for the two directions of the field. The interplay between DNA chirality and MF LR asymmetry will provide fundamental knowledge for many MF-induced biological phenotypes.

Reorientation behavior in the helical motility of light-responsive spiral droplets

The physico-chemical processes supporting life's purposeful movement remain essentially unknown. Self-propelling chiral droplets offer a minimalistic model of swimming cells and, in surfactant-rich water, droplets of chiral nematic liquid crystals follow the threads of a screw. We demonstrate that the geometry of their trajectory is determined by both the number of turns in, and the handedness of, their spiral organization. Using molecular motors as photo-invertible chiral dopants allows converting between right-handed and left-handed trajectories dynamically, and droplets subjected to such an inversion reorient in a direction that is also encoded by the number of spiral turns. This motile behavior stems from dynamic transmission of chirality, from the artificial molecular motors to the liquid crystal in confinement and eventually to the helical trajectory, in analogy with the chirality-operated motion and reorientation of swimming cells and unicellular organisms.

Noninvasive measurement of cell/colony motion using image analysis methods to evaluate the proliferative capacity of oral keratinocytes as a tool for quality control in regenerative medicine

Image-based cell/colony analyses offer promising solutions to compensate for the lack of quality control (QC) tools for noninvasive monitoring of cultured cells, a regulatory challenge in regenerative medicine. Here, the feasibility of two image analysis algorithms, optical flow and normalised cross-correlation, to noninvasively measure cell/colony motion in human primary oral keratinocytes for screening the proliferative capacity of cells in the early phases of cell culture were examined. We applied our software to movies converted from 96 consecutive time-lapse phase-contrast images of an oral keratinocyte culture. After segmenting the growing colonies, two indices were calculated based on each algorithm. The correlation between each index of the colonies and their proliferative capacity was evaluated. The software was able to assess cell/colony motion noninvasively, and each index reflected the observed cell kinetics. A positive linear correlation was found between cell/colony motion and proliferative capacity, indicating that both algorithms are potential tools for QC.

Cell organelle-based analysis of cell chirality

The maintenance of tight endothelial junctions requires the establishment of proper cell polarity, which includes not only the apicobasal and front-rear polarity but also the left-right (L-R) polarity. The cell possesses an intrinsic mechanism of orienting the L-R axis with respect to the other axes, following a left-hand or right-hand rule, termed cell chirality. We have previously reported that endothelial cells exhibit a clockwise or rightward bias on ring-shaped micropatterns. Now we further characterize the chirality of individual endothelial cells on micropatterns by analyzing the L-R positioning of the cell centroid relative to the nucleus-centrosome axis. Our results show that the centroids of endothelial cells preferably polarized towards the right side of the nucleus-centrosome axis. This bias is consistent with cell chirality characterized by other methods. These results suggest that the positioning of cell organelles is intrinsically L-R biased inside individual cells. This L-R bias provides an opportunity for determining cell chirality in situ, even in vivo, without the limitations of using isolated cells in in vitro engineered platforms.

Cells with Broken Left–Right Symmetry: Roles of Intrinsic Cell Chirality in Left–Right Asymmetric Epithelial Morphogenesis

Chirality is a fundamental feature in biology, from the molecular to the organismal level. An animal has chirality in the left–right asymmetric structure and function of its body. In general, chirality occurring at the molecular and organ/organism scales has been studied separately. However, recently, chirality was found at the cellular level in various species. This “cell chirality” can serve as a link between molecular chirality and that of an organ or animal. Cell chirality is observed in the structure, motility, and cytoplasmic dynamics of cells and the mechanisms of cell chirality formation are beginning to be understood. In all cases studied so far, proteins that interact chirally with F-actin, such as formin and myosin I, play essential roles in cell chirality formation or the switching of a cell’s enantiomorphic state. Thus, the chirality of F-actin may represent the ultimate origin of cell chirality. Links between cell chirality and left–right body asymmetry are also starting to be revealed in various animal species. In this review, the mechanisms of cell chirality formation and its roles in left–right asymmetric development are discussed, with a focus on the fruit fly Drosophila, in which many of the pioneering studies were conducted.

Chiral Neuronal Motility: The Missing Link between Molecular Chirality and Brain Asymmetry

Left–right brain asymmetry is a fundamental property observed across phyla from invertebrates to humans, but the mechanisms underlying its formation are still largely unknown. Rapid progress in our knowledge of the formation of body asymmetry suggests that brain asymmetry might be controlled by the same mechanisms. However, most of the functional brain laterality, including language processing and handedness, does not share common mechanisms with visceral asymmetry. Accumulating evidence indicates that asymmetry is manifested as chirality at the single cellular level. In neurons, the growth cone filopodia at the tips of neurites exhibit a myosin V-dependent, left-helical, and right-screw rotation, which drives the clockwise circular growth of neurites on adhesive substrates. Here, I propose an alternative model for the formation of brain asymmetry that is based on chiral neuronal motility. According to this chiral neuron model, the molecular chirality of actin filaments and myosin motors is converted into chiral neuronal motility, which is in turn transformed into the left–right asymmetry of neural circuits and lateralized brain functions. I also introduce automated, numerical, and quantitative methods to analyze the chirality and the left–right asymmetry that would enable the efficient testing of the model and to accelerate future investigations in this field.

Molecular basis of the functions of the mammalian neuronal growth cone revealed using new methods

The neuronal growth cone is a highly motile, specialized structure for extending neuronal processes. This structure is essential for nerve growth, axon pathfinding, and accurate synaptogenesis. Growth cones are important not only during development but also for plasticity-dependent synaptogenesis and neuronal circuit rearrangement following neural injury in the mature brain. However, the molecular details of mammalian growth cone function are poorly understood. This review examines molecular findings on the function of the growth cone as a result of the introduction of novel methods such superresolution microscopy and (phospho)proteomics. These results increase the scope of our understating of the molecular mechanisms of growth cone behavior in the mammalian brain.

Intrinsic cellular chirality regulates left-right symmetry breaking during cardiac looping

The vertebrate body plan is overall symmetrical but left-right (LR) asymmetric in the shape and positioning of internal organs. Although several theories have been proposed, the biophysical mechanisms underlying LR asymmetry are still unclear, especially the role of cell chirality, the LR asymmetry at the cellular level, on organ asymmetry. Here with developing chicken embryos, we examine whether intrinsic cell chirality or handedness regulates cardiac C looping. Using a recently established biomaterial-based 3D culture platform, we demonstrate that chick cardiac cells before and during C looping are intrinsically chiral and exhibit dominant clockwise rotation in vitro. We further show that cells in the developing myocardium are chiral as evident by a rightward bias of cell alignment and a rightward polarization of the Golgi complex, correlating with the direction of cardiac tube rotation. In addition, there is an LR polarized distribution of N-cadherin and myosin II in the myocardium before the onset of cardiac looping. More interestingly, the reversal of cell chirality via activation of the protein kinase C signaling pathway reverses the directionality of cardiac looping, accompanied by a reversal in cellular biases on the cardiac tube. Our results suggest that myocardial cell chirality regulates cellular LR symmetry breaking in the heart tube and the resultant directionality of cardiac looping. Our study provides evidence of an intrinsic cellular chiral bias leading to LR symmetry breaking during directional tissue rotation in vertebrate development.

Lineage-Specific Chiral Biases of Human Embryonic Stem Cells during Differentiation

Left-right symmetry breaking is a complex developmental process and an important part of embryonic axis development. As of yet, the biophysical mechanism behind LR asymmetry establishment remains elusive for the overall asymmetry of embryos as well as for the organ-specific asymmetry. Here, we demonstrate that inherent cellular chirality is observable in the cells of early embryonic stages using a 3D Matrigel bilayer system. Differentiation of human embryonic stem cells to three lineages corresponding to heart, intestine, and neural tissues demonstrates phenotype-specific inherent chiral biases, complementing the current knowledge regarding organ development. The existence of inherent cellular chirality early in development and its correlation with organ asymmetry implicate cell chirality as a possible regulator in LR symmetry breaking.

Epithelial Cell Chirality Revealed by Three-Dimensional Spontaneous Rotation

Our understanding of the left-right (LR) asymmetry of embryonic development, in particular the contribution of intrinsic handedness of the cell or cell chirality, is limited due to the confounding systematic and environmental factors during morphogenesis and a ack of physiologically relevant in vitro 3D platforms. Here we report an efficient two-layered biomaterial platform for determining the chirality of individual cells, cell aggregates, and self-organized hollow epithelial spheroids. This bioengineered niche provides a uniform defined axis allowing for cells to rotate spontaneously with a directional bias toward either clockwise or counterclockwise directions. Mechanistic studies reveal an actin-dependent, cell-intrinsic property of 3D chirality that can be mediated by actin cross-linking via α-actinin-1. Our findings suggest that the gradient of extracellular matrix is an important biophysicochemical cue influencing cell polarity and chirality. Engineered biomaterial systems can serve as an effective platform for studying developmental asymmetry and screening for environmental factors causing birth defects.

Dual-wavelength oblique back-illumination microscopy for the non-invasive imaging and quantification of blood in collection and storage bags

There is currently no low-cost method to quantitatively assess the contents of a blood bag without breaching the bag and potentially damaging the sample. Towards this end, we adapt oblique back-illumination microscopy (OBM) to rapidly, inexpensively, and non-invasively screen blood bags for red blood cell (RBC) morphology and white blood cell (WBC) count. OBM has been recently introduced as a tomographic technique that produces high-resolution wide-field images based on phase-gradient and transmission. Here we modify this technique to include illumination at dual wavelengths to facilitate spectral analysis for cell classification. Further, we apply a modified 2D Hilbert transform to recover the phase information from the phase-gradient images for facile cell segmentation. Blood cells are classified as WBCs and RBCs, and counted based on shape, absorption spectrum, and phase profile using an automated algorithm. This work has important implications for the non-invasive assessment of (1) cell viability in storage bags for transfusion applications and (2) suitability of a cord blood collection bag for stem cell therapy applications.

Growth Cone Phosphoproteomics Reveals that GAP-43 Phosphorylated by JNK Is a Marker of Axon Growth and Regeneration

Neuronal growth cones are essential for nerve growth and regeneration, as well as for the formation and rearrangement of the neural network. To elucidate phosphorylation-dependent signaling pathways and establish useful molecular markers for axon growth and regeneration, we performed a phosphoproteomics study of mammalian growth cones, which identified >30,000 phosphopeptides of ∼1,200 proteins. The phosphorylation sites were highly proline directed and primarily MAPK dependent, owing to the activation of JNK, suggesting that proteins that undergo proline-directed phosphorylation mediate nerve growth in the mammalian brain. Bioinformatics analysis revealed that phosphoproteins were enriched in microtubules and the cortical cytoskeleton. The most frequently phosphorylated site was S96 of GAP-43 (growth-associated protein 43-kDa), a vertebrate-specific protein involved in axon growth. This previously uncharacterized phosphorylation site was JNK dependent. S96 phosphorylation was specifically detected in growing and regenerating axons as the most frequent target of JNK signaling; thus it represents a promising new molecular marker for mammalian axonal growth and regeneration.

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Phosphoproteomics of mammalian growth cone membranes reveals activation of MAPK

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JNK is the activated MAPK in growth cones and phosphorylates S96 of GAP-43

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pS96 of GAP-43, the most frequent site, is observed in growing axons

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pS96 is biochemically detected in the regenerating axons of the peripheral nerves

Cell Chirality Drives Left-Right Asymmetric Morphogenesis

Most macromolecules found in cells are chiral, meaning that they cannot be superimposed onto their mirror image. However, cells themselves can also be chiral, a subject that has received little attention until very recently. In our studies on the mechanisms of left-right (LR) asymmetric development in Drosophila, we discovered that cells can have an intrinsic chirality to their structure, and that this “cell chirality” is generally responsible for the LR asymmetric development of certain organs in this species. The actin cytoskeleton plays important roles in the formation of cell chirality. In addition, Myosin31DF (Myo31DF), which encodes Drosophila Myosin ID, was identified as a molecular switch for cell chirality. In other invertebrate species, including snails and Caenorhabditis elegans, chirality of the blastomeres, another type of cell chirality, determines the LR asymmetry of structures in the body. Thus, chirality at the cellular level may broadly contribute to LR asymmetric development in various invertebrate species. Recently, cell chirality was also reported for various vertebrate cultured cells, and studies suggested that cell chirality is evolutionarily conserved, including the essential role of the actin cytoskeleton. Although the biological roles of cell chirality in vertebrates remain unknown, it may control LR asymmetric development or other morphogenetic events. The investigation of cell chirality has just begun, and this new field should provide valuable new insights in biology and medicine.