PAIR UP Imaging Science Program, a new framework for a diverse scientific workforce.

PAIR-UP is a new conceptual framework for developing a diverse scientific workforce for the 21st century. PAIR-UP stand for Partnering to Advance Imaging Research for Underrepresented scientists Program. The goal of PAIR-UP is to solve the longstanding and wicked problem of underrepresentation of Black scientists in the imaging science field. PAIR-UP uses a multipronged approach designed to create culturally responsive environments at historically white colleges and universities (HWCUs) where Black scientists are culturally isolated. The PAIR-UP model shows that maintaining a strong cultural identity empowers Black scientists to be more creative and productive and therefore persistent in the discipline.

Inclusivity in cell biology: cultural identity and the power of authenticity.

I am deeply honored to be the recipient of the 2022 ASCB Public Service Award. In addition to my research on the cytoskeleton and molecular motors, I devoted a significant part of my professional career to issues pertaining to diversity, equity, and inclusion (DEI). Diversity of the scientific workforce is essential to accomplish the mission of discovery and innovation required to advance scientific knowledge and improve human health, especially the health of Black communities. This pressing need requires new approaches to address the problem of inclusivity in science. The Black Lives Matter movement and the murder of George Floyd were events that triggered people around the world to begin to reckon with structural racism and new approaches to dismantle it. It is through this momentary lens that I founded the PAIR-UP Imaging Science Program for Black Imaging Scientists. The purpose of PAIR-UP is to improve the professional work environment for Black imaging scientists at R1 institutions by building a self-reinforcing community of Black scientists across institutions committed to helping each other sustain a strong cultural identity. Reenforcing and sustaining a strong cultural identity has the potential to be transformational for the scientists participating in PAIR-UP.

Super-Resolution Imaging of the Actin Cytoskeleton in Living Cells Using TIRF-SIM.

Super-resolution (SR) imaging techniques have advanced rapidly in recent years, but only a subset of these techniques is gentle enough to be used by cell biologists to study living cells with minimal photodamage. Our research is focused on studies of the dynamic remodeling of the actin cytoskeleton in living pancreatic beta cells during insulin secretion. These studies require super-resolution light microscopic techniques that are gentle enough to record rapid changes of the actin cytoskeleton in real time. In this chapter, we describe an SR technique that breaks the diffraction limit of the conventional light microscope called TIRF-SIM. Using this SR techniques, we have been able to show that (1) microvilli on pancreatic beta cells translocate in the plane of the plasma membrane and (2) the cortical actin network reorganizes when cells are stimulated to secrete insulin. We describe the FIJI plugins that were used to process and analyze the TIRF-SIM images to obtain quantitative data.

Publisher Correction: Chimeric peptide EP45 as a dual agonist at GLP-1 and NPY2R receptors.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Chimeric peptide EP45 as a dual agonist at GLP-1 and NPY2R receptors.

We report the design and target validation of chimeric peptide EP45, a novel 45 amino acid monomeric dual agonist peptide that contains amino acid sequence motifs present within the blood glucose-lowering agent exendin-4 (Ex-4) and the appetite-suppressing agent PYY(3-36). In a new high-throughput FRET assay that provides real-time kinetic information concerning levels of cAMP in living cells, EP45 recapitulates the action of Ex-4 to stimulate cAMP production via the glucagon-like peptide-1 receptor (GLP-1R), while also recapitulating the action of PYY(3-36) to inhibit cAMP production via the neuropeptide Y2 receptor (NPY2R). EP45 fails to activate glucagon or GIP receptors, whereas for cells that co-express NPY2R and adenosine A2B receptors, EP45 acts in an NPY2R-mediated manner to suppress stimulatory effects of adenosine on cAMP production. Collectively, such findings are remarkable in that they suggest a new strategy in which the co-existing metabolic disorders of type 2 diabetes and obesity will be treatable using a single peptide such as EP45 that lowers levels of blood glucose by virtue of its GLP-1R-mediated effect, while simultaneously suppressing appetite by virtue of its NPY2R-mediated effect.

Long-Term Live Cell Imaging of Cell Migration: Effects of Pathogenic Fungi on Human Epithelial Cell Migration.

Long-term live cell imaging was used in this study to determine the responses of human epithelial cells to pathogenic biofilms formed by Candida albicans. Epithelial cells of the skin represent the front line of defense against invasive pathogens such as C. albicans but under certain circumstances, especially when the host's immune system is compromised, the skin barrier is breached. The mechanisms by which the fungal pathogen penetrates the skin and invade the deeper layers are not fully understood. In this study we used keratinocytes grown in culture as an in vitro model system to determine changes in host cell migration and the actin cytoskeleton in response to virulence factors produced by biofilms of pathogenic C. albicans. It is clear that changes in epithelial cell migration are part of the response to virulence factors secreted by biofilms of C. albicans and the actin cytoskeleton is the downstream effector that mediates cell migration. Our goal is to understand the mechanism by which virulence factors hijack the signaling pathways of the actin cytoskeleton to alter cell migration and thereby invade host tissues. To understand the dynamic changes of the actin cytoskeleton during infection, we used long-term live cell imaging to obtain spatial and temporal information of actin filament dynamics and to identify signal transduction pathways that regulate the actin cytoskeleton and its associated proteins. Long-term live cell imaging was achieved using a high resolution, multi-mode epifluorescence microscope equipped with specialized light sources, high-speed cameras with high sensitivity detectors, and specific biocompatible fluorescent markers. In addition to the multi-mode epifluorescence microscope, a spinning disk confocal long-term live cell imaging system (Olympus CV1000) equipped with a stage incubator to create a stable in vitro environment for long-term real-time and time-lapse microscopy was used. Detailed descriptions of these two long-term live cell imaging systems are provided.

Voltage-controlled cellular viability of preosteoblasts on polarized cpTi with varying surface oxide thickness.

Cathodic voltage shifts of metallic biomaterials were recently shown to induce cell apoptosis in-vitro. The details of the reduction-based physico-chemical phenomena have not yet been fully elucidated. This study shows how surface oxide thickness of commercially pure titanium affects the voltage viability range, and whether anodic oxidation can extend this range. Cell viability, cytoskeletal organization, and cellular adhesion on bare and anodized Ti, at -500, -400 mV(Ag/AgCl) and open circuit potential were assessed. Surfaces were characterized using contact angle measurement and atomic force microscopy, and the observed cellular response was related to the changes in electrochemical currents, and impedance of the samples. Results show that anodization at 9 V in phosphate buffer saline generates a compact surface oxide with comparable surface roughness and energy to the starting bare surface. The anodized surface extends the viability range at 24h from -400 mV(Ag/AgCl) by about -100 mV, which corresponds to an increase in impedance of the surface from 58 kΩ cm(2) to 29 MΩ cm(2) at -400 mV(Ag/AgCl) and results in low average current densities below 0.1 µA cm(-2). The results demonstrate that the voltage range for cell viability under cathodic polarization is expanded due to anodization of the surface oxide and lowering of cathodic currents.

Electrochemical control of cell death by reduction-induced intrinsic apoptosis and oxidation-induced necrosis on CoCrMo alloy in vitro.

Electrochemical voltage shifts in metallic biomedical implants occur in-vivo due to a number of processes including mechanically assisted corrosion. These excursions may compromise the biocompatibility of metallic implants. Voltages can also be controlled to modulate cell function and fate. The in vitro effect of static voltages on the behavior of MC3T3-E1 pre-osteoblasts cultured on CoCrMo alloy (ASTM-1537) was studied to determine the range of cell viability and mode of cell death beyond the viable range. Cell viability and morphology, changes in actin cytoskeleton, adhesion complexes and nucleus, and mode of cell death (necrosis, or intrinsic or extrinsic apoptosis) were characterized at different voltages ranging from -1000 to +500 mV (Ag/AgCl). Moreover, electrochemical currents and metal ion concentrations at each voltage were measured and related to the observed responses. Results show that cathodic and anodic voltages outside the voltage viability range (-400 < V < +500) lead to primarily intrinsic apoptotic and necrotic cell death, respectively. Cell death is associated with cathodic current densities of 0.1 µA cm(-2) and anodic current densities of 10 µA cm(-2). Significant increase in metallic ions (Co, Cr, Ni, Mo) was seen at +500 mV, and -1000 mV (Cr only) compared to open circuit potential. The number and total projected area of adhesion complexes was also lower on the polarized alloy (p < 0.05). These results show that reduction reactions on CoCrMo alloys leads to apoptosis of cells on the surface and may be a relevant mode of cell death for metallic implants in-vivo.

Human oral keratinocytes: a model system to analyze host-pathogen interactions.

Host-pathogen interactions are complex and dynamic processes that result in a variety of responses. The ability of the host to respond appropriately to the presence of a microbial agent defines the outcome of these interactions. Fungal infections are a problem of growing clinical importance and are responsible for serious health problems in multimorbid patients. Different model systems, including primary cells and cell lines derived from different tissues, are used to study several processes that contribute to the virulence of pathogenic fungi. In this chapter, we describe an in vitro assay to characterize the response of human oral keratinocytes (OKF6/TERT-2) to the presence of the human pathogenic fungus, Candida albicans. The dynamic cellular changes such as expression of differentiation markers can be monitored by epifluorescence deconvolution microscopy. Analyses of immunofluorescence data by linescan analysis and fluorescence intensity measurements are described to identify changes in protein expression levels. The use of this in vitro model system will also provide new information about host cell behavior and identify potential drug targets in the future.

Myosin5a tail associates directly with Rab3A-containing compartments in neurons.

Myosin-Va (Myo5a) is a motor protein associated with synaptic vesicles (SVs) but the mechanism by which it interacts has not yet been identified. A potential class of binding partners are Rab GTPases and Rab3A is known to associate with SVs and is involved in SV trafficking. We performed experiments to determine whether Rab3A interacts with Myo5a and whether it is required for transport of neuronal vesicles. In vitro motility assays performed with axoplasm from the squid giant axon showed a requirement for a Rab GTPase in Myo5a-dependent vesicle transport. Furthermore, mouse recombinant Myo5a tail revealed that it associated with Rab3A in rat brain synaptosomal preparations in vitro and the association was confirmed by immunofluorescence imaging of primary neurons isolated from the frontal cortex of mouse brains. Synaptosomal Rab3A was retained on recombinant GST-tagged Myo5a tail affinity columns in a GTP-dependent manner. Finally, the direct interaction of Myo5a and Rab3A was determined by sedimentation velocity analytical ultracentrifugation using recombinant mouse Myo5a tail and human Rab3A. When both proteins were incubated in the presence of 1 mm GTPγS, Myo5a tail and Rab3A formed a complex and a direct interaction was observed. Further analysis revealed that GTP-bound Rab3A interacts with both the monomeric and dimeric species of the Myo5a tail. However, the interaction between Myo5a tail and nucleotide-free Rab3A did not occur. Thus, our results show that Myo5a and Rab3A are direct binding partners and interact on SVs and that the Myo5a/Rab3A complex is involved in transport of neuronal vesicles.

High resolution multimode light microscopy of cell migration: long-term imaging and analysis.

Cell migration is a multi-step process that involves sequential changes in the cytoskeleton, cell-substrate adhesion and components of the extracellular matrix. In multicellular organisms, directional cell migration is important for normal development, wound healing and immune responses and contributes to disease states such as tumor formation and metastasis. Many cells such as fibroblasts migrate as individuals while others, such as keratinocytes, move as groups or sheets of cells.In this chapter, we use human oral keratinocytes (OKF6/TERT-2) to illustrate the complex patterns of cell migration and its regulation. In culture, sheets of keratinocytes migrate and respond to human pathogens such as Candida albicans. The dynamic changes of the cytoskeleton, cell-cell and cell-substrate interactions that change during an infection for example require observation over long periods of time in order to identify the spatio-temporal coordinated regulation of the cytoskeleton and its associated components as well as the signaling pathways that control them.Microscopic techniques for long-term live cell observation and analysis of cell migration require high-resolution imaging systems that maintain perfect focus and optimal growth conditions (temperature, CO(2)) for cells. We describe two multimode digital imaging systems (VEC-DIC and BioStation IM), both with wide-field epifluorescence and transmitted light objectives for long-term time-lapse imaging and motion analysis.

Stimulation of cell motility and expression of late markers of differentiation in human oral keratinocytes by Candida albicans.

A hallmark of the mucosa of immunocompromized hosts in oral candidiasis is a hyperkeratinized region heavily colonized with fungi at the surface of the terminally differentiated epithelium. To gain insight into the processes important for promoting mucosal invasion by fungi, we characterized the response of keratinocytes to the presence of Candida albicans. Indirect immunofluorescence and kymographic analyses revealed a multifaceted keratinocyte response of OKF6/TERT-2 cells to C. albicans that consisted of: cytoskeletal reorganization within 3 h, motility and cell expansion with formation of E-cadherin-mediated cell-cell adhesions within 6 h, increased expression of late differentiation markers and decreased expression of calprotectin. The initial expansive phase was followed by dissolution of cell-cell adhesions and a decrease in cell size accompanied by loss of E-cadherin. The keratinocyte response depended on soluble factors associated with hyphal growth as demonstrated using the efg1Delta/efg1Delta, cap1Delta/cap1Delta, als3Delta/als3Delta, hwp1Delta/hwp1Deltaand sap4-6Delta/sap4-6Delta mutants and was not observed in the presence of the non-pathogenic yeast, Saccharomyces cerevisiae. These studies show the potential for C. albicans to manipulate the stratified epithelial cells to a state of differentiation that is more permissive of fungal colonization of oral tissue, which is likely to play an important role in the pathogenesis of candidiasis.

Membrane associated nonmuscle myosin II functions as a motor for actin-based vesicle transport in clam oocyte extracts.

Nonmuscle myosin II (Myo2) has been shown to associate with membranes of the trans-Golgi network and to be involved in Golgi to ER retrograde protein transport. Here, we provide evidence that Myo2 not only associates with membranes but functions to transport vesicles on actin filaments (AFs). We used extracts from unactivated clam oocytes for these studies. AFs assembled spontaneously in these extracts and myosin-dependent vesicle transport was observed upon activation. In addition, actin bundles formed and moved relative to each other at an average speed of 0.30 microm/s. Motion analysis revealed that vesicles moved on the spontaneously assembled AFs at speeds greater than 1 microm/s. The motor on these vesicles was identified as a member of the nonmuscle Myo2 family based on sequence determination by Edman chemistry. Vesicles in these extracts were purified by sucrose gradient centrifugation and movement was reconstituted in vitro using skeletal muscle actin coated coverslips. When peripheral membrane proteins of vesicles including Myo2 were removed by salt stripping or when extracts were treated with an antibody specific to clam oocyte nonmuscle Myo2, vesicle movement was inhibited. Blebbistatin, a Myo2 specific inhibitor, also blocked vesicle movement. Myo2 light chain kinase activity was found to be essential for vesicle movement and sliding of actin bundles. Together, our data provide direct evidence that nonmuscle Myo2 is involved in actin-dependent vesicle transport in clam oocytes.

Myosin Vb is required for trafficking of the cystic fibrosis transmembrane conductance regulator in Rab11a-specific apical recycling endosomes in polarized human airway epithelial cells.

Cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl(-) secretion across fluid-transporting epithelia is regulated, in part, by modulating the number of CFTR Cl(-) channels in the plasma membrane by adjusting CFTR endocytosis and recycling. However, the mechanisms that regulate CFTR recycling in airway epithelial cells remain unknown, at least in part, because the recycling itineraries of CFTR in these cells are incompletely understood. In a previous study, we demonstrated that CFTR undergoes trafficking in Rab11a-specific apical recycling endosomes in human airway epithelial cells. Myosin Vb is a plus-end-directed, actin-based mechanoenzyme that facilitates protein trafficking in Rab11a-specific recycling vesicles in several cell model systems. There are no published studies examining the role of myosin Vb in airway epithelial cells. Thus, the goal of this study was to determine whether myosin Vb facilitates CFTR recycling in polarized human airway epithelial cells. Endogenous CFTR formed a complex with endogenous myosin Vb and Rab11a. Silencing myosin Vb by RNA-mediated interference decreased the expression of wild-type CFTR and DeltaF508-CFTR in the apical membrane and decreased CFTR-mediated Cl(-) secretion across polarized human airway epithelial cells. A recombinant tail domain fragment of myosin Vb attenuated the plasma membrane expression of CFTR by arresting CFTR recycling. The dominant-negative effect was dependent on the ability of the myosin Vb tail fragment to interact with Rab11a. Taken together, these data indicate that myosin Vb is required for CFTR recycling in Rab11a-specific apical recycling endosomes in polarized human airway epithelial cells.

The short apical membrane half-life of rescued {Delta}F508-cystic fibrosis transmembrane conductance regulator (CFTR) results from accelerated endocytosis of {Delta}F508-CFTR in polarized human airway epithelial cells.

The most common mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene in individuals with cystic fibrosis, DeltaF508, causes retention of DeltaF508-CFTR in the endoplasmic reticulum and leads to the absence of CFTR Cl(-) channels in the apical plasma membrane. Rescue of DeltaF508-CFTR by reduced temperature or chemical means reveals that the DeltaF508 mutation reduces the half-life of DeltaF508-CFTR in the apical plasma membrane. Because DeltaF508-CFTR retains some Cl(-) channel activity, increased expression of DeltaF508-CFTR in the apical membrane could serve as a potential therapeutic approach for cystic fibrosis. However, little is known about the mechanisms responsible for the short apical membrane half-life of DeltaF508-CFTR in polarized human airway epithelial cells. Accordingly, the goal of this study was to determine the cellular defects in the trafficking of rescued DeltaF508-CFTR that lead to the decreased apical membrane half-life of DeltaF508-CFTR in polarized human airway epithelial cells. We report that in polarized human airway epithelial cells (CFBE41o-) the DeltaF508 mutation increased endocytosis of CFTR from the apical membrane without causing a global endocytic defect or affecting the endocytic recycling of CFTR in the Rab11a-specific apical recycling compartment.

Myosin VI regulates endocytosis of the cystic fibrosis transmembrane conductance regulator.

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic AMP-regulated Cl(-) channel expressed in the apical plasma membrane in fluid-transporting epithelia. Although CFTR is rapidly endocytosed from the apical membrane of polarized epithelial cells and efficiently recycled back to the plasma membrane, little is known about the molecular mechanisms regulating CFTR endocytosis and endocytic recycling. Myosin VI, an actin-dependent, minus-end directed mechanoenzyme, has been implicated in clathrin-mediated endocytosis in epithelial cells. The goal of this study was to determine whether myosin VI regulates CFTR endocytosis. Endogenous, apical membrane CFTR in polarized human airway epithelial cells (Calu-3) formed a complex with myosin VI, the myosin VI adaptor protein Disabled 2 (Dab2), and clathrin. The tail domain of myosin VI, a dominant-negative recombinant fragment, displaced endogenous myosin VI from interacting with Dab2 and CFTR and increased the expression of CFTR in the plasma membrane by reducing CFTR endocytosis. However, the myosin VI tail fragment had no effect on the recycling of endocytosed CFTR or on fluid-phase endocytosis. CFTR endocytosis was decreased by cytochalasin D, an actin-filament depolymerizing agent. Taken together, these data indicate that myosin VI and Dab2 facilitate CFTR endocytosis by a mechanism that requires actin filaments.

Short-range axonal/dendritic transport by myosin-V: A model for vesicle delivery to the synapse.

Myosin-V is a versatile motor involved in short-range axonal/dendritic transport of vesicles in the actin-rich cortex and synaptic regions of nerve cells. It binds to several different kinds of neuronal vesicles by its globular tail domain but the mechanism by which it is recruited to these vesicles is not known. In this study, we used an in vitro motility assay derived from axoplasm of the squid giant axon to study the effects of the globular tail domain on the transport of neuronal vesicles. We found that the globular tail fragment of myosin-V inhibited actin-based vesicle transport by displacing native myosin-V and binding to vesicles. The globular tail domain pulled down kinesin, a known binding partner of myosin-V, in affinity isolation experiments. These data confirmed earlier evidence that kinesin and myosin-V interact to form a hetero-motor complex. The formation of a kinesin/myosin-V hetero-motor complex on vesicles is thought to facilitate the coordination of long-range movement on microtubules and short-range movement on actin filaments. The direct interaction of motors from both filament systems may represent the mechanism by which the transition of vesicles from microtubules to actin filaments is regulated. These results are the first demonstration that the recombinant tail of myosin-V inhibits vesicle transport in an in vitro motility assay. Future experiments are designed to determine the functional significance of the interaction between myosin-V and kinesin and to identify other proteins that bind to the globular tail domain of myosin-V.