Biology subjects

Tang, M.-X.

Publications and source records attributed to Tang, M.-X..

10 recordsLinked to original sources

bioRxiv2026

Cerebrovascular Structure-Flow Gradients Revealed by Volumetric Ultrasound Localization Microscopy

Characterizing the joint organization of microscale cerebrovascular structure and flow in vivo is challenging. Volumetric ultrasound localization microscopy (ULM) provides spatially resolved measures of microvascular structure and flow from the same acquisition, but how these features are jointly organized across brain networks remains unclear. Here, we characterized local vascular phenotypes from transcranial volumetric ULM in mice and examined whether they contained reproducible low-dimensional organization. Local measures of vascular structure and flow dynamics were summarized within corresponding brain regions across mice. Subject-specific vascular phenotype similarity matrices were combined into a group-consensus graph and analyzed using diffusion embedding. Two leading gradients, showing distinct spatial distributions across brain networks, were reproducibly recovered across subject and spatial scales. The principal gradient was associated with local vascular density and flow complexity, defining a vascular structure-related axis. The secondary gradient was associated with flow speed and acceleration, defining a flow-dynamics-related axis. These gradients provide a low-dimensional representation of the cerebrovascular structure and flow and provide a reference for studying coordinated vascular changes across disease, aging, and intervention.

neuroscience↗

bioRxiv2024

Achieving Single Cell Acoustic Localisation with Deactivation Super Resolution

Super-resolution optical microscopy enables optical imaging of cells, molecules and other biological structures beyond the diffraction limit. However, no similar method exists to super-resolve specific cells with ultrasound. Here we introduce Deactivation Super Resolution (DSR), an ultrasound imaging method that uses the acoustic deactivation of genetically encodable contrast agents to super-resolve individual cells with ultrasound as they navigate through structures that cannot be resolved by conventional imaging methods. DSR takes advantage of gas vesicles, which are air-filled sub-micron protein particles that can be expressed in genetically engineered cells to produce ultrasound contrast. Our experimental results show that DSR can distinguish sub-wavelength microstructures that standard B-mode ultrasound images fail to resolve by super- localizing individual mammalian cells. This study provides a proof of concept for the potential of DSR to serve as a super- resolution ultrasound technique for individual cell localization, opening new horizons in the field.

bioengineering↗

bioRxiv2024

Enhanced Ultrasound Image Formation with Computationally Efficient Cross-Angular Delay Multiply and Sum Beamforming

Ultrasound imaging is a valuable clinical tool. It is commonly achieved using the delay and sum beamformer algorithm, which takes the signals received by an array of sensors and generates an image estimating the spatial distribution of the signal sources. This algorithm, while computationally efficient, has limited resolution and suffers from high side lobes. Nonlinear processing has proven to be an effective way to enhance the image quality produced by beamforming in a computationally efficient manner. In this work, we describe a new beamforming algorithm called Cross-Angular Delay Multiply and Sum, which takes advantage of nonlinear compounding to enhance contrast and resolution. This is then implemented with a mathematical reformulation to produce images with tighter point spread functions and enhanced contrast at a low computational cost. We tested this new algorithm over a range of in vitro and in vivo scenarios for both conventional B-Mode and amplitude modulation imaging, and for two types of ultrasound contrast agents, demonstrating its potential for clinical settings.

bioengineering↗

bioRxiv2023

LLPS condensates of Fha initiate the inside-out assembly of the type VI secretion system

The type VI secretion system (T6SS) is one of the most powerful nanomachines employed by Gram-negative pathogens for penetrating diverse cell envelopes, including bacteria and fungi, to deliver potent effectors into target cells. While the membrane-anchored contractile tubular structure of the T6SS is well characterized, the assembly process remains poorly understood. The prevailing model suggests that the assembly of T6SS initiates from its outer-membrane component. Here, we report a distinct model that the cytoplasmic protein Fha initiates T6SS assembly in Acidovorax citrulli, an important plant pathogen. Fha dictates the formation of the inner-membrane complex and the baseplate, and directly interacts with these key components. Importantly, imaging and biochemical assays reveal that Fha undergoes liquid-liquid phase separation (LLPS), forming condensates that selectively recruit essential T6SS proteins, which are otherwise dispersed in cells. Fha also exhibited conserved functions in human pathogens Vibrio cholerae and Pseudomonas aeruginosa. These findings unveil an inside-first LLPS-driven model for T6SS assembly and suggest LLPS might be broadly involved in mediating the assembly of bacterial macromolecular complexes and facilitating interspecies interactions and pathogenesis. Significance statementThe T6SS plays a pivotal role in interspecies competition and host-microbe interactions by delivering toxins to various prokaryotes and eukaryotes. Its crucial function relies on a membrane-anchored macromolecular structure comprising at least 13 conserved components. However, the mechanisms governing the efficient assembly of its diverse cytosolic and membrane-bound components remain elusive. Here, we identify Fha, a conserved cytosolic protein, as a key initiator of T6SS assembly. Fha recruits multiple structural and effector components, forming LLPS condensates. Fha homologs of plant and human pathogens exhibit conserved functions. Our findings not only unveil an inside-first assembly model for the T6SS, initiating from inner-membrane and baseplate components, but also suggest LLPS may have a broader impact on bacterial physiology beyond intracellular activities.

microbiology↗

bioRxiv2022

Systematic mutagenesis reveals critical effector functions in the assembly and dueling of the H1-T6SS in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an important human pathogen that can cause severe wound and lung infections. It employs the type VI secretion system (H1-T6SS) as a molecular weapon to carry out a unique dueling response to deliver toxic effectors to neighboring sister cells or other microbes after sensing an external attack. However, the underlying mechanism for such dueling is not fully understood. Here, we examined the role of all H1-T6SS effectors and VgrG proteins in assembly and signal sensing by ectopic expression, combinatorial deletion and point mutations, and imaging analyses. Expression of effectors targeting the cell wall and membrane resulted in increased H1-T6SS assembly. Deletion of individual effector and vgrG genes had minor- to-moderate effects on H1-T6SS assembly and dueling activities. The dueling response was detectable in the P. aeruginosa mutant lacking all H1-T6SS effector activities. In addition, double deletions of vgrG1a with either vgrG1b or vgrG1c and double deletions of effector genes tse5 and tse6 severely reduced T6SS assembly and dueling activities, suggesting their critical role in T6SS assembly. Collectively, these data highlight the diverse roles of effectors in not only dictating antibacterial functions but also their differential contributions to the assembly of the complex H1-T6SS apparatus.

microbiology↗

bioRxiv2022

A dueling-competent signal-sensing module guides precise delivery of cargo proteins into target cells by engineered Pseudomonas aeruginosa

To recognize and manipulate a specific microbe of a crowded community is a highly challenging task in synthetic biology. Here, we introduce a highly-selective protein delivery platform, termed DUEC, which responds to direct contact of attacking cells by engineering the tit-for-tat/dueling response of H1-T6SS (type VI secretion system) in Pseudomonas aeruginosa. Using a Cre-recombinase-dependent reporter, we screened H1-T6SS secreted substrates and developed Tse6N as the most effective secretion tag for Cre delivery. DUEC cells can discriminately deliver the Tse6N-Cre cargo into the cytosol of T6SS+ but not T6SS- Vibrio cholerae cells in a mixed population. These data demonstrate that the DUEC cell is not only a prototypical physical-contact sensor and delivery platform but also may be coupled with recombination-based circuits with the potential for complex tasks in mixed microbial communities.

microbiology↗

bioRxiv2022

Concurrent assessment of individual motoneuron discharges and muscle unit displacement velocity in humans by high-density EMG and ultrafast ultrasound

ObjectiveThe study of human neuromechanical control at the motor unit (MU) level has predominantly focussed on electrical activity and force generation, whilst the link between these, the muscle deformation, has not been widely studied. An important example of this is excitation-contraction coupling (E-C coupling) - the process by which electrical excitation is converted into contraction in the muscle fibres. Despite this being a clear marker for progression of certain diseases, it cannot be measured in vivo in natural contractions. To address this, we analyse the kinematics of muscle units in natural contractions. ApproachWe combine high density surface electromyography (HDsEMG) and ultrafast ultrasound (US) recordings of a mildly contracted muscle (tibialis anterior) to measure the deformation of the muscular tissue caused by individual MU twitches (decomposed from the HDsEMG). With a novel analysis on the US images we identified, with high spatio-temporal precision, the velocity maps associated with single muscle unit movements. From the individual MU profiles obtained from the velocity maps the region of movement, the duration of the mechanical twitch, the total and active contraction times, and the activation time (equivalent to E-C coupling) were computed. Main resultsThe E-C coupling was 3.8 {+/-} 3.0 ms (n = 390), providing the first measurement of this value in for single MUs in non-stimulated contractions. Furthermore, the experimental measures provided the first evidence of single muscle unit twisting during voluntary contractions and showed the presence of MUs with territories with multiple distinct split regions across the muscle region. SignificanceWe show that the combined use of HDsEMG and ultrafast US can allow for the study of kinematics of individual MU twitches, including measurement of the excitation-contraction coupling time under natural neural control conditions. These measurements and characterisations open new avenues for study of neuromechanics in healthy and pathological conditions.

bioengineering↗

bioRxiv2021

Breaching the cell-envelope barriers of gram-positive and fungal microbes by a type VI secretion system in Acidovorax citrulli

The type VI secretion system (T6SS) is a double-tubular toxin-injection nanomachine widely found in gram-negative human and plant pathogens. The current model depicts that the T6SS spear-like Hcp tube is powered by the contraction of an outer sheath to drill through the envelope of a neighboring cell, achieving cytosol to cytosol delivery. However, gram-positive bacteria seem to be impenetrable to such T6SS action. Here we report that a plant pathogen Acidovorax citrulli (AC) deploys a highly potent T6SS to kill a range of bacteria including Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Mycobacterium smegmatis as well as fungal species including Candida albicans and Pichia pastoris. Using bioinformatic and biochemical assays, we identified a group of T6SS effectors and characterized one effector RhsB that is critical for interspecies interaction. We report that RhsB contains a conserved YD-repeat domain and a C-terminal nuclease domain. Toxicity of RhsB was neutralized by its downstream immunity proteins through direct interaction. RhsB was cleaved at the C-terminal end and a catalytic mutation within the internal aspartic protease abolished such cleavage. Collectively, the T6SS of AC displays potent activities to penetrate the cell envelope barriers of gram-positive and fungal species, highlighting the greatly expanded capabilities of T6SS in modulating microbiome compositions in complex environments.

microbiology↗

bioRxiv2021

Abiotic factors modulate interspecies competition mediated by the type VI secretion system effectors in Vibrio cholerae

Vibrio cholerae, the etiological pathogen of cholera, relies on its type VI secretion system (T6SS) as an effective weapon to survive in highly competitive communities. The anti-bacterial and anti-eukaryotic functions of T6SS depend on its secreted effectors that target multiple essential cellular processes. However, the mechanisms that account for effector diversity and different effectiveness during interspecies competition remain elusive. Here, we report that environmental cations and temperature play a key role in dictating effector-mediated competition of Vibrio cholerae. We found that V. cholerae could employ its cell-wall-targeting effector TseH to outcompete the otherwise resistant Escherichia coli and the V. cholerae immunity deletion mutant{Delta} tsiH when Ca2+ and Mg2+ were supplemented. The E. coli {Delta}phoQ mutant was more sensitive to TseH-mediated killing during competition, suggesting the metal-sensing PhoPQ two-component system is protective to E. coli from TseH activity. Using transcriptome analysis, we found multiple stress response systems, including acid stress response, oxidative stress response, and osmotic stress response, were activated in E. coli expressing TseH in comparison with E. coli expressing the inactive mutant TseHH64A. The membrane-targeting lipase effector TseL also exhibited reduced killing against E. coli when divalent cations were removed. In addition, competition analysis of E. coli with V. cholerae single-effector active strains reveals a temperature-dependent susceptibility of E. coli to effectors, VasX, VgrG3, and TseL. These findings suggest that abiotic factors, that V. cholerae frequently encounters in natural habitats, play a crucial role in dictating the competitive fitness conferred by the type VI secretion system in complex multispecies communities.

microbiology↗

bioRxiv2019

Full-waveform inversion imaging of the human brain

Magnetic resonance imaging and X-ray computed tomography provide the two principal methods available for imaging the brain at high spatial resolution, but these methods are not easily portable and cannot be applied safely to all patients. Ultrasound imaging is portable and universally safe, but existing modalities cannot image usefully inside the adult human skull. We use in-silico simulations to demonstrate that full-waveform inversion, a computational technique originally developed in geophysics, is able to generate accurate three-dimensional images of the brain with sub-millimetre resolution. This approach overcomes the familiar problems of conventional ultrasound neuroimaging by using: transcranial ultrasound that is not obscured by strong reflections from the skull, low frequencies that are readily transmitted with good signal-to-noise ratio, an accurate wave equation that properly accounts for the physics of wave propagation, and an accurate model of the skull that compensates properly for wavefront distortion. Laboratory ultrasound data, using ex-vivo human skulls, demonstrate that our computational experiments mimic the penetration and signal-to-noise ratios expected in clinical applications. This form of non-invasive neuroimaging has the potential for the rapid diagnosis of stroke and head trauma, and for the provision of routine monitoring of a wide range of neurological conditions.

neuroscience↗