Dynamic Tethering Research Articles

Nanohoops Favour Light‐Induced Energy Transfer over Charge Separation in Porphyrin/[10]CPP/Fullerene Rotaxanes

Abstract[2]Rotaxanes offer unique opportunities for studying and modulating charge separation and energy transfer, because the mechanical bond allows the robust, yet spatially dynamic tethering of photoactive groups. In this work, we synthesized [2]rotaxane triads comprising a central (aza)[10]CPP⊃C60 bis‐adduct complex and two zinc porphyrin stoppers to address how the movable nanohoop affects light‐induced charge separation and energy transfer between the rotaxane subcomponents. We found that neither the parent nanohoop [10]CPP nor its electron‐deficient analogue aza[10]CPP actively participate in charge separation. In contrast, the nanohoops completely prevented through‐space charge separation. This result is likely due to supramolecular “shielding”, because charge separation was observed in the thread that acted as reference dyad. On the other hand, the suppression of electron transfer allowed the observation of energy transfer from the porphyrin triplet to the fullerene triplet state with a lifetime of ca. 25 μs. The presence of the interlocked nanohoops therefore leads to a dramatic switch between charge separation and energy transfer. We suggest that our results explain observations made by others in photovoltaic devices comprising nanohoops and may pave the way toward strategic uses of mechanically interlocked architectures in devices that feature (triplet) energy transfer.

Nanohoops Favour Light-Induced Energy Transfer over Charge Separation in Porphyrin/[10]CPP/Fullerene Rotaxanes.

[2]Rotaxanes offer unique opportunities for studying and modulating charge separation and energy transfer, because the mechanical bond allows the robust, yet spatially dynamic tethering of photoactive groups. In this work, we synthesized [2]rotaxane triads comprising a central (aza)[10]CPP⊃C60 bis-adduct complex and two zinc porphyrin stoppers to address how the movable nanohoop affects light-induced charge separation and energy transfer between the rotaxane subcomponents. We found that neither the parent nanohoop [10]CPP nor its electron-deficient analogue aza[10]CPP actively participate in charge separation. In contrast, the nanohoops completely prevented through-space charge separation. This result is likely due to supramolecular "shielding", because charge separation was observed in the thread that acted as reference dyad. On the other hand, the suppression of electron transfer allowed the observation of energy transfer from the porphyrin triplet to the fullerene triplet state with a lifetime of ca. 25 μs. The presence of the interlocked nanohoops therefore leads to a dramatic switch between charge separation and energy transfer. We suggest that our results explain observations made by others in photovoltaic devices comprising nanohoops and may pave the way toward strategic uses of mechanically interlocked architectures in devices that feature (triplet) energy transfer.

Long-term Results of the Treatment of Scapholunate Instability with Dynamic Extensor Carpi Radialis Brevis Tenodesis

Background: Scapholunate dissociation is the most common form of carpal instability. This retrospective case series aimed to assess long-term results obtained by treating scapholunate instability with dynamic tenodesis using the entire extensor carpi radialis brevis tendon, which is detached from the base of the third metacarpal, rerouted in the third extensor compartment, and fixed at the distal portion of the scaphoid to maintain reduced rotatory subluxation. Methods: Nine patients with scapholunate instability were treated. We reviewed eight patients with a mean follow-up of 12 years. One subgroup of four patients was affected by static scapholunate instability, and the other by dynamic scapholunate instability. Disability of the Arm, Shoulder, and Hand score, Patient Rated Wrist Evaluation score, modified Mayo score, and radiographs were used to determine functional and anatomical outcomes. Results: Excellent functional results did not correlate with radiological outcome in patients with static scapholunate instability. In this subgroup, scapholunate angle and gap and radiolunate angle improved in average but remained in the pathologic range. In only one of these patients, osteoarthritis was observed. In the subgroup of patients affected by dynamic instability, very good functional outcomes correlate with radiological results, except in one patient who developed arthritic changes. Conclusions: Dynamic tethering of the scaphoid with the extensor carpi radialis brevis tendon might be indicated in the treatment not only in patients affected by dynamic scapholunate instability but also in patients with static instability. Prospective studies with a larger number of patients are required to evaluate this method.

TAOK2 is an ER-localized kinase that catalyzes the dynamic tethering of ER to microtubules.

SUMMARYThe endoplasmic reticulum (ER) depends on extensive association with the microtubule (MT) cytoskeleton for its structure and mitotic inheritance. However, mechanisms that underlie coupling of ER membranes to MTs are poorly understood. We have identified thousand and one amino acid kinase 2 (TAOK2) as a pleiotropic protein kinase that mediates tethering of ER to MTs. In human cells, TAOK2 localizes in distinct ER subdomains via transmembrane helices and an adjacent amphipathic region. Through its C-terminal tail, TAOK2 directly binds MTs, coupling ER membranes to the MT cytoskeleton. In TAOK2 knockout cells, although ER-membrane dynamics are increased, movement of ER along growing MT plus ends is disrupted. ER-MT tethering is tightly regulated by catalytic activity of TAOK2, perturbation of which leads to defects in ER morphology, association with MTs, and cell division. Our study identifies TAOK2 as an ER-MT tether and reveals a kinase-regulated mechanism for control of ER dynamics.

Moving the ER tip by tip.

Endoplasmic reticulum (ER) and microtubule (MT) interactions have been observed in different cell types. However, how these interactions are regulated remains unknown. In this issue of Developmental Cell, Nourbakhsh etal. show that an ER-localized kinase, TAOK2, catalyzes the dynamic tethering of the ER tip to the MT tip.

TAOK2 is an ER kinase that catalyzes the dynamic tethering of ER to microtubules

The endoplasmic reticulum (ER) extensively associates with the microtubule cytoskeleton. Although integral to its many functions, mechanisms through which the ER tethers to microtubules and regulates its coupling dynamics with the cytoskeleton are poorly understood. Herein we report that TAOK2 is an ER-resident multifunctional protein kinase required for tethering of ER membranes to microtubules. Using biochemical and super-resolution imaging techniques, we show that TAOK2 is a multipass membrane-spanning kinase localized in distinct ER domains via four transmembrane and amphipathic helices. Using in vitro and cellular assays, we find that TAOK2 directly binds microtubules with high affinity. We define the minimal TAOK2 determinants that induce ER-microtubule tethering. While TAOK2 knockout cells exhibit decreased ER stability and disrupted movement of ER along growing microtubule plus-ends, motor-mediated ER motility is not affected. ER-microtubule tethering is tightly regulated by the catalytic activity of TAOK2 in interphase and mitotic cells. Perturbation of TAOK2 activity leads to defects in ER morphology and cell division. Our study identifies TAOK2 as an ER-microtubule tether, and reveals a kinase-regulated mechanism for control of ER dynamics critical for cell growth and division.

Tangling and instability effect analysis of initial in-plane/out-of-plane angles on electrodynamic tether deployment under gravity gradient

The space debris occupies the orbit resources greatly, which seriously threats the safety of spacecraft for its high risks of collisions. Many theories about space debris removal have been put forward in recent years. The Electro Dynamic Tether (EDT), which can be deployed under gravity gradient, is considered to be an effective method to remove debris in low orbit for its low power consumption. However, in order to generate sufficient Lorentz force, the EDT needs to be deployed to several kilometers, which increases the risks of tangling and the instability of the EDT system. In the deployment process, different initial in-plane/out-of-plane angles, caused by direction error at initial release or the initial selection of ejection, affect the motion of EDT system seriously. In order to solve these problems, firstly, this paper establishes the dynamic model of the EDT system. Then, based on the model, safety metrics of avoiding tangling and assessing system stability during EDT deployment stage are designed toquantitatively evaluate the EDT system security. Finally, several numerical simulations are established to determine the safety ranges of the initial in-plane/out-of-plane angles on the EDT deployment.

Dysferlin-deficient myotubes show tethering of different membrane compartments characterized by TMEM16E and DHPRα

TMEM16E deficiency has been shown to be responsible for human limb-girdle muscular dystrophy LGMD2L. We found that endogenous TMEM16E co-localized with caveolin-3 at cytoplasmic vesicular compartments in a myotube from C2C12 cells (C2C12 myotube) without forming a molecular complex. In contrast, a myotube from murine myoblastic dysferlin-deficient GREG cells (GREG myotube) showed not only co-localization but also constitutive association of caveolin-3 and TMEM16E. GREG myotubes also displayed constitutive association of TMEM16E with DHPRα, which reside in different membrane compartments, indicating increased contact of the different vesicular membrane compartments. Τhese results suggest that a dynamic tethering of different membrane compartments might represent a distorted membrane damage repairing process in the absence of dysferlin.

ESCRT-III/Vps4 Controls Heterochromatin-Nuclear Envelope Attachments.

SummaryEukaryotic genomes are organized within the nucleus through interactions with inner nuclear membrane (INM) proteins. How chromatin tethering to the INM is controlled in interphase and how this process contributes to subsequent mitotic nuclear envelope (NE) remodeling remains unclear. We have probed these fundamental questions using the fission yeast Schizosaccharomyces japonicus, which breaks and reforms the NE during mitosis. We show that attachments between heterochromatin and the transmembrane Lem2-Nur1 complex at the INM are remodeled in interphase by the ESCRT-III/Vps4 machinery. Failure of ESCRT-III/Vps4 to release Lem2-Nur1 from heterochromatin leads to persistent association of chromosomes with the INM throughout mitosis. At mitotic exit, such trapping of Lem2-Nur1 on heterochromatin prevents it from re-establishing nucleocytoplasmic compartmentalization. Our work identifies the Lem2-Nur1 complex as a substrate for the nuclear ESCRT machinery and explains how the dynamic tethering of chromosomes to the INM is linked to the establishment of nuclear compartmentalization.

Visualizing Dynamic Tethering of Argonaute to Single mRNA in Live Human Cells Reveals the Mechanism of Mirna-mediated Translational Silencing

Visualizing Dynamic Tethering of Argonaute to Single mRNA in Live Human Cells Reveals the Mechanism of Mirna-mediated Translational Silencing

Motor Reattachment Kinetics Play a Dominant Role in Multimotor-Driven Cargo Transport

Kinesin-based cargo transport in cells frequently involves the coordinated activity of multiple motors, including kinesins from different families that move at different speeds. However, compared to the progress at the single-molecule level, mechanisms by which multiple kinesins coordinate their activity during cargo transport are poorly understood. To understand these multimotor coordination mechanisms, defined pairs of kinesin-1 and kinesin-2 motors were assembled on DNA scaffolds and their motility examined in vitro. Although less processive than kinesin-1 at the single-molecule level, addition of kinesin-2 motors more effectively amplified cargo run lengths. By applying the law of total expectation to cargo binding durations in ADP, the kinesin-2 microtubule reattachment rate was shown to be fourfold faster than that of kinesin-1. This difference in microtubule binding rates was also observed in solution by stopped-flow. High-resolution tracking of a gold-nanoparticle-labeled motor with 1 ms and 2 nm precision revealed that kinesin-2 motors detach and rebind to the microtubule much more frequently than does kinesin-1. Finally, compared to cargo transported by two kinesin-1, cargo transported by two kinesin-2 motors more effectively navigated roadblocks on the microtubule track. These results highlight the importance of motor reattachment kinetics during multimotor transport and suggest a coordinated transport model in which kinesin-1 motors step effectively against loads whereas kinesin-2 motors rapidly unbind and rebind to the microtubule. This dynamic tethering by kinesin-2 maintains the cargo near the microtubule and enables effective navigation along crowded microtubules.

An Intrinsically Disordered APLF Links Ku, DNA-PKcs, and XRCC4-DNA Ligase IV in an Extended Flexible Non-homologous End Joining Complex

DNA double-strand break (DSB) repair by non-homologous end joining (NHEJ) in human cells is initiated by Ku heterodimer binding to a DSB, followed by recruitment of core NHEJ factors including DNA-dependent protein kinase catalytic subunit (DNA-PKcs), XRCC4-like factor (XLF), and XRCC4 (X4)-DNA ligase IV (L4). Ku also interacts with accessory factors such as aprataxin and polynucleotide kinase/phosphatase-like factor (APLF). Yet, how these factors interact to tether, process, and ligate DSB ends while allowing regulation and chromatin interactions remains enigmatic. Here, small angle X-ray scattering (SAXS) and mutational analyses show APLF is largely an intrinsically disordered protein that binds Ku, Ku/DNA-PKcs (DNA-PK), and X4L4 within an extended flexible NHEJ core complex. X4L4 assembles with Ku heterodimers linked to DNA-PKcs via flexible Ku80 C-terminal regions (Ku80CTR) in a complex stabilized through APLF interactions with Ku, DNA-PK, and X4L4. Collective results unveil the solution architecture of the six-protein complex and suggest cooperative assembly of an extended flexible NHEJ core complex that supports APLF accessibility while possibly providing flexible attachment of the core complex to chromatin. The resulting dynamic tethering furthermore, provides geometric access of L4 catalytic domains to the DNA ends during ligation and of DNA-PKcs for targeted phosphorylation of other NHEJ proteins as well as trans-phosphorylation of DNA-PKcs on the opposing DSB without disrupting the core ligation complex. Overall the results shed light on evolutionary conservation of Ku, X4, and L4 activities, while explaining the observation that Ku80CTR and DNA-PKcs only occur in a subset of higher eukaryotes.

Dynactin Functions as Both a Dynamic Tether and Brake during Dynein-Driven Motility

Dynactin is a large multi-subunit complex that is an important cofactor for cytoplasmic dynein in cellular processes including organelle trafficking and mitosis. Dynactin increases the processivity of dynein and also targets dynein to specific cellular locations. Although the role of dynactin in dynein-mediated processes is well established, the underlying mechanisms involved are unknown. Here, we use single molecule approaches to investigate the contribution of the dynactin subunit p150Glued to dynein motor function. We first characterized the motility of purified GFP-tagged mammalian dynein isolated from a knock-in mouse brain tissue (Zhang et al., 2013). Consistent with previous reports (Mallik et al., 2005; Ross et al., 2006), single molecules of dynein-GFP switch stochastically from processive to diffusive states of motion. We analyzed this motion by a novel algorithm that we developed to parse trajectories into different states and found that dynein is processive 60% of the time. To examine the activation of dynein by dynactin, we investigated the formation and co-migration of a dynein-p150Glued co-complex using dual-color TIRF microscopy. We provide direct evidence that p150Glued is sufficient to recruit and tether dynein to the microtubule and that this recruitment is concentration-dependent; p150Glued increases the on-rate and decreases the off-rate of dynein from microtubules. Single molecule imaging of motility in cell extracts demonstrates that the CAP-Gly domain of dynactin is essential for the decreased detachment rate of the dynein-dynactin complex from the microtubule and also acts as a brake to slow the dynein motor. Consistent with this important role, two neurodegenerative disease-causing mutations in the CAP-Gly domain abrogate these functions in our assays. Together, these observations support a model in which dynactin enhances the initial recruitment of dynein onto microtubules and promotes the sustained engagement of dynein with its cytoskeletal track.

Cargo recognition and cargo-mediated regulation of unconventional myosins.

Organized motions are hallmarks of living organisms. Such motions range from collective cell movements during development and muscle contractions at the macroscopic scale all the way down to cellular cargo (e.g., various biomolecules and organelles) transportation and mechanoforce sensing at more microscopic scales. Energy required for these biological motions is almost invariably provided by cellular chemical fuels in the form of nucleotide triphosphate. Biological systems have designed a group of nanoscale engines, known as molecular motors, to convert cellular chemical fuels into mechanical energy. Molecular motors come in various forms including cytoskeleton motors (myosin, kinesin, and dynein), nucleic-acid-based motors, cellular membrane-based rotary motors, and so on. The main focus of this Account is one subfamily of actin filament-based motors called unconventional myosins (other than muscle myosin II, the remaining myosins are collectively referred to as unconventional myosins). In general, myosins can use ATP to fuel two types of mechanomotions: dynamic tethering actin filaments with various cellular compartments or structures and actin filament-based intracellular transport. In contrast to rich knowledge accumulated over many decades on ATP hydrolyzing motor heads and their interactions with actin filaments, how various myosins recognize their specific cargoes and whether and how cargoes can in return regulate functions of motors are less understood. Nonetheless, a series of biochemical and structural investigations in the past few years, including works from our own laboratory, begin to shed lights on these latter questions. Some myosins (e.g., myosin-VI) can function both as cellular transporters and as mechanical tethers. To function as a processive transporter, myosins need to form dimers or multimers. To be a mechanical tether, a monomeric myosin is sufficient. It has been shown for myosin-VI that its cellular cargo proteins can play critical roles in determining the motor properties. Dab2, an adaptor protein linking endocytic vesicles with actin-filament-bound myosin-VI, can induce the motor to form a transport competent dimer. Such a cargo-mediated dimerization mechanism has also been observed in other myosins including myosin-V and myosin-VIIa. The tail domains of myosins are very diverse both in their lengths and protein domain compositions and thus enable motors to engage a broad range of different cellular cargoes. Remarkably, the cargo binding tail of one myosin alone often can bind to multiple distinct target proteins. A series of atomic structures of myosin-V/cargo complexes solved recently reveals that the globular cargo binding tail of the motor contains a number of nonoverlapping target recognition sites for binding to its cargoes including melanophilin, vesicle adaptors RILPL2, and vesicle-bound GTPase Rab11. The structures of the MyTH4-FERM tandems from myosin-VIIa and myosin-X in complex with their respective targets reveal that MyTH4 and FERM domains extensively interact with each other forming structural and functional supramodules in both motors and demonstrate that the structurally similar MyTH4-FERM tandems of the two motors display totally different target binding modes. These structural studies have also shed light on why numerous mutations found in these myosins can cause devastating human diseases such as deafness and blindness, intellectual disabilities, immune disorders, and diabetes.

Advances in Muscle Physiology and Pathophysiology

During the recent years, unprecedented amounts of new knowledge have seen the light, revealing key factors that modulate the essential processes of the structure and function of muscle. The assembly of the sarcomeric and extrasarcomeric cytoskeleton, the formation of internal membrane systems and their contribution to the regulation of Ca2+ homeostasis, the molecular dissection of specialized sarcolemmal microdomains, and the anchoring of the intracellular cytoskeletal network with the extracellular matrix are only some of the themes where rapid progress has been made. Advanced genetic, molecular, cellular, biochemical, genomic, and proteomic approaches, using diverse animal models, have unraveled the intricate details of these complex pathways both during health and disease and highlighted new questions and challenges. The breadth of new information has been overwhelming yet exciting, emphasizing once again the absolute need for development of sophisticated, multidisciplinary, and integrated approaches to study the roles of subproteomes rather than individual proteins during development and in adulthood, under normal and stress conditions. In this volume, we invited authors who study muscle structure and function from different perspectives and angles to contribute original and review articles. A wide array of topics is discussed in this special issue, including the regulated assembly of myofibrils, the biomechanical and biophysical properties of sarcomeric contraction, the dynamic tethering of thin and thick filaments and the unique, compensatory, or even redundant roles of their accessory proteins, the giant sarcomeric proteins, and their roles as molecular blueprints and sensors, the sarcolemma and its role in the mechanical and electrochemical coupling of neighboring cells, the tripartite regulation of Ca2+ cycling orchestrated by the activities of the t-tubules, sarcoplasmic reticulum, and mitochondria, the roles of exercise, fatigue and injury in muscle contraction, and the isolation and use of muscle stem cells. Importantly, many of these processes are altered, compromised, or dysregulated in different forms of skeletal and cardiac myopathies and dystrophies. Some of these are discussed as well. The editors of this special issue are indebted to all the authors who provided either original data or a comprehensive review of the previous and recent literature, making this special issue appealing to a diverse audience of muscle researchers. Our goal was to touch on different aspects of muscle physiology and pathophysiology at the molecular, cellular, organ, and organismal level. We are delighted to see the outcome of our call in the form of this special volume, and we hope that it will provide a wealthy source of knowledge and information and further stimulate muscle research at all different fronts. Aikaterini Kontrogianni-Konstantopoulos Guy Benian Henk Granzier

2D31 Storage Strategy of a Long Tape Tether and Analysis of Deployment Behaviour

Electro Dynamic Tether (EDT) system is one of the non-chemical propulsion systems on low earth orbit (LEO) in the future. The tether technologies rocket experiment (T-REx) mission was proposed, which is the first attempt in the world to employ a bare tape tether. The sounding rocket S520-25th is provided for the T-REx mission. In this mission, the tape tether is stored in a storage box in a foldaway manner, which is a new concept of tether deployment schemes. To expand EDT system feasibility, a small satellite mission of EDT system, following T-REx mission, is planned, in which a bare tape tether of 3km stored in the folding manner will be deployed. However, shape of the foldaway tape tether storage is concerned to affect the design of the spacecraft in case that the tether length becomes longer, and simple expansion of scale will not be able to cope with this problem. In this paper, in order to improve store efficiency, we expand foldaway manner to the two dimensions, called "cross-shift foldaway storage." To evaluate deployment performance, the tape tether is described as a discriminate model with springs and dampers.

Viewpoint Animation With a Dynamic Tether for Supporting Navigation in a Virtual Environment

This study examined the concept of dynamic viewpoint tethering for enhancing performance in 3-D avatar control tasks. Dynamic viewpoint tethering refers to a viewpoint animation technique that couples a display viewpoint to a controlled avatar through a virtual tether. A dynamic tether, modeled as a mass spring damper system, can potentially generate desirable viewpoint behavior because of its ability to produce frequency-separated viewpoint responses. This study investigated the impact of a tether's rigidity and damping properties on users' navigational performance. Twelve participants took part in a simulated 3-D aerial navigational task. Performance was evaluated with respect to local guidance and global awareness. Root mean square error scores revealed a decrease in local guidance performance when (a) the tether was either severely underdamped or overdamped and (b) the tether's rigidity approached either zero or infinity. In addition, (c) global performance was better for higher-frequency forcing functions. Critical damping and medium rigidity can be optimized during design for enhancing users' navigational efficiency. Guidelines generated from this study support future viewpoint design in interactive virtual reality applications.

Myosin-Vb functions as a dynamic tether for peripheral endocytic compartments during transferrin trafficking

BackgroundMyosin-Vb has been shown to be involved in the recycling of diverse proteins in multiple cell types. Studies on transferrin trafficking in HeLa cells using a dominant-negative myosin-Vb tail fragment suggested that myosin-Vb was required for recycling from perinuclear compartments to the plasma membrane. However, chemical-genetic, dominant-negative experiments, in which myosin-Vb was specifically induced to bind to actin, suggested that the initial hypothesis was incorrect both in its site and mode of myosin-Vb action. Instead, the chemical-genetic data suggested that myosin-Vb functions in the actin-rich periphery as a dynamic tether on peripheral endosomes, retarding transferrin transport to perinuclear compartments.ResultsIn this study, we employed both approaches, with the addition of overexpression of full-length wild-type myosin-Vb and switching the order of myosin-Vb inhibition and transferrin loading, to distinguish between these hypotheses. Overexpression of full-length myosin-Vb produced large peripheral endosomes. Chemical-genetic inhibition of myosin-Vb after loading with transferrin did not prevent movement of transferrin from perinuclear compartments; however, virtually all myosin-Vb-decorated particles, including those moving on microtubules, were halted by the inhibition. Overexpression of the myosin-Vb tail caused a less-peripheral distribution of early endosome antigen-1 (EEA1).ConclusionAll results favored the peripheral dynamic tethering hypothesis.

Viewpoint Optimisation for Virtual Environment Navigation Using Dynamic Tethering - A Study of Tether Rigidity

Much research has been carried out on providing navigational aids and improving users' wayfinding ability across a variety of navigation related tasks. In this study, we focus on investigating users' navigational performance with respect to the display frame of reference in a large scale virtual environment. Dynamic viewpoint tethering is proposed as a means to improve user control and reduce the need for mental rotations, thus facilitating the acquisition of configurational knowledge about the virtual space.The modelling of dynamic viewpoint tethering is explained and recent research findings are presented. Twelve volunteers participated in an experiment in which they were instructed to control an aircraft-shaped cursor flying through a set of virtual tunnels (local guidance) and to answer questions about the environment (global awareness). Experimental results showed that neither the very loose dynamic tether nor the completely rigid tether supported the best control performance. Rather, an optimal tether configuration lies at the centre of the rigidity continuum. Research results are discussed from the point of view of design of navigational system interfaces.

Viewpoint Optimisation for Navigation Using Dynamic Teher

Dynamic viewpoint tethering is an innovative display technique which has been proposed to support effective navigation in large-scale virtual environments, by integrating information from different frames of reference. In this paper, we explain the modelling of a dynamic tether and report our latest research findings in investigating the optimal parametric values of tether configuration and their relations to human users' navigational performance. Tethered displays with different parametric configurations were compared. Participants were instructed to control an aircraft-shaped cursor flying in a virtual tunnel and to answer questions about the environment. The results revealed that critically damped tethers supported the best local guidance performance. No significant global awareness performance differences were observed under all display conditions.