Biomolecular condensates regulate cellular electrochemical equilibria.

Control of the electrochemical environment in living cells is typically attributed to ion channels. Here, we show that the formation of biomolecular condensates can modulate the electrochemical environment in bacterial cells, which affects cellular processes globally. Condensate formation generates an electric potential gradient, which directly affects the electrochemical properties of a cell, including cytoplasmic pH and membrane potential. Condensate formation also amplifies cell-cell variability of their electrochemical properties due to passive environmental effect. The modulation of the electrochemical equilibria further controls cell-environment interactions, thus directly influencing bacterial survival under antibiotic stress. The condensate-mediated shift in intracellular electrochemical equilibria drives a change of the global gene expression profile. Our work reveals the biochemical functions of condensates, which extend beyond the functions of biomolecules driving and participating in condensate formation, and uncovers a role of condensates in regulating global cellular physiology.

Unlocking the electrochemical functions of biomolecular condensates.

Biomolecular condensation is a key mechanism for organizing cellular processes in a spatiotemporal manner. The phase-transition nature of this process defines a density transition of the whole solution system. However, the physicochemical features and the electrochemical functions brought about by condensate formation are largely unexplored. We here illustrate the fundamental principles of how the formation of condensates generates distinct electrochemical features in the dilute phase, the dense phase and the interfacial region. We discuss the principles by which these distinct chemical and electrochemical environments can modulate biomolecular functions through the effects brought about by water, ions and electric fields. We delineate the potential impacts on cellular behaviors due to the modulation of chemical and electrochemical environments through condensate formation. This Perspective is intended to serve as a general road map to conceptualize condensates as electrochemically active entities and to assess their functions from a physical chemistry aspect.

Programmable synthetic biomolecular condensates for cellular control.

The formation of biomolecular condensates mediated by a coupling of associative and segregative phase transitions plays a critical role in controlling diverse cellular functions in nature. This has inspired the use of phase transitions to design synthetic systems. While design rules of phase transitions have been established for many synthetic intrinsically disordered proteins, most efforts have focused on investigating their phase behaviors in a test tube. Here, we present a rational engineering approach to program the formation and physical properties of synthetic condensates to achieve intended cellular functions. We demonstrate this approach through targeted plasmid sequestration and transcription regulation in bacteria and modulation of a protein circuit in mammalian cells. Our approach lays the foundation for engineering designer condensates for synthetic biology applications.

Biomolecular Condensates are Characterized by Interphase Electric Potentials.

Biomolecular condensates form via processes that combine phase separation and reversible associations of multivalent macromolecules. Condensates can be two- or multiphase systems defined by coexisting dense and dilute phases. Here, we show that solution ions partition asymmetrically across coexisting phases defined by condensates formed by intrinsically disordered proteins or homopolymeric RNA molecules. Our findings were enabled by direct measurements of the activities of cations and anions within coexisting phases of protein and RNA condensates. Asymmetries in ion partitioning between coexisting phases vary with protein sequence, macromolecular composition, salt concentration, and ion type. The Donnan equilibrium set up by the asymmetrical partitioning of solution ions generates interphase electric potentials known as Donnan and Nernst potentials. Our measurements show that the interphase potentials of condensates are of the same order of magnitude as membrane potentials of membrane-bound organelles. Interphase potentials quantify the degree to which microenvironments of coexisting phases are different from one another. Importantly, and based on condensate-specific interphase electric potentials, we reason that condensates are akin to capacitors that store charge. Interphase potentials should lead to electric double layers at condensate interfaces, thereby explaining recent observations of condensate interfaces being electrochemically active.

Study on the influence of a magnetorheological finishing path on the mid-frequency errors of optical element surfaces.

Magnetorheological finishing (MRF) is a deterministic optical processing technique based on CCOS that achieves high removal efficiency and processing accuracy while reducing subsurface damage. This technique still suffers from multiple iterations of processing due to variations in removal efficiency and the inability to fully correct mid-frequency errors below the cut-off frequency of the removal function. For the above problems, this paper attempted to establish the error model of removal function efficiency change for predicting the change of MRF efficiency. Based on the analysis of the distribution of surface shape residuals under different machining paths, a process combining spiral scanning and raster scanning is proposed, which can realize the correction of surface shape and restrain the deterioration of mid-frequency errors. The experimental results show that when the low-frequency errors of fused silica element surface converge rapidly, by optimizing the machining removal coefficient and using the spiral scanning and raster scanning combined method, the PSD analysis results show that the mid-frequency errors of the combined process is lower than the initial value, which expands the process route for the MRF of high-precision optical elements.

Research on the removal characteristics of surface error with different spatial frequency based on shear thickening polishing method.

X-ray mirrors, which are essential for constructing synchrotron radiation light sources, are highly required for full-range spatial wavelength errors. This paper investigated power-law non-Newtonian fluids and pointed out that both three-body removal and shear removal existed in the shear thickening polishing process. Subsequently, this paper calculates the shear force of the power-law non-Newtonian fluid polishing fluid in polishing the surface with different frequency errors. It establishes an MRR model of shear thickening polishing in the frequency domain by combining it with the Archard equation. Then, this model is also applied to optimize the polishing fluid formulation and processing parameters. Finally, the removal effect of the optimized polishing fluid on the mid-frequency ripple error is experimentally verified. On Ф50 mm monocrystalline silicon, the removal of mid-frequency ripple error with a spatial wavelength of 1 mm was achieved by shear thickening polishing technique while converging the surface roughness to 0.14 nm. Finally, the experimental results were applied to monocrystalline silicon with a length of 500 mm. This work provides a new research idea for the existing shear thickening polishing process. It provides theoretical and technical support for removing the mid- and high-frequency errors in high-precision X-ray mirrors.

Visualization of the Charging of Water Droplets Sprayed into Air.

Water droplets are spraying into air using air as a nebulizing gas, and the droplets pass between two parallel metal plates with opposite charges. A high-speed camera records droplet trajectories in the uniform electric field, providing visual evidence for the Lenard effect, that is, smaller droplets are negatively charged whereas larger droplets are positively charged. By analyzing the velocities of the droplets between the metal plates, the charges on the droplets can be estimated. Some key observations include: (1) localized electric fields with intensities on the order of 109 V/m are generated, and charges are expected to jump (micro-lightening) between a positively charged larger droplet and the negatively charged smaller droplet as they separate; (2) the strength of the electric field is sufficiently powerful to ionize gases surrounding the droplets; and (3) observations in an open-air mass spectrometer reveal the presence of ions such as N2+, O2+, NO+, and NO2+. These findings provide new insight into the origins of some atmospheric ions and have implications for understanding ionization processes in the atmosphere and chemical transformations in water droplets, advancing knowledge in the field of aerosol science and water microdroplet chemistry.

Mfsd2a attenuated hypoxic-ischemic brain damage via protection of the blood-brain barrier in mfat-1 transgenic mice.

Previous studies have shown that mfat-1 transgenic mice have protective effects against some central nervous system (CNS) disorders, owing to the high docosahexaenoic acid (DHA) content enriched in their brains. However, whether this protective effect is connected to the blood-brain barrier (BBB) remains unclear. This study aims to investigate the mechanisms of the protective effect against hypoxic-ischemic brain damage (HIBD) of mfat-1 transgenic mice. mfat-1 mice not only demonstrated a significant amelioration of neurological dysfunction and neuronal damage but also partly maintained the physiological permeability of the BBB after HIBD. We initially showed this was associated with elevated major facilitator superfamily domain-containing 2a (Mfsd2a) expression on the BBB, resulting from more lysophosphatidylcholine (LPC)-DHA entering the brain. Wild-type (WT) mice showed a similar Mfsd2a expression trend after long-term feeding with an LPC-DHA-rich diet. Knockdown of Mfsd2a by siRNA intra-cerebroventricular (ICV) injection neutralized the protective effect against HIBD-induced BBB disruption in mfat-1 mice, further validating the protective function of Mfsd2a on BBB. HIBD-induced BBB high permeability was attenuated by Mfsd2a, primarily through a transcellular pathway to decrease caveolae-like vesicle-mediated transcytosis. Taken together, these findings not only reveal that mfat-1 transgenic mice have higher expression of Mfsd2a on the BBB, which partly sustains BBB permeability via vesicular transcytosis to alleviate the severity of HIBD, but also suggest that dietary intake of LPC-DHA may upregulate Mfsd2a expression as a novel therapeutic strategy for BBB dysfunction and survival in HIBD patients.

Double-stranded RNA drives SARS-CoV-2 nucleocapsid protein to undergo phase separation at specific temperatures.

Nucleocapsid protein (N-protein) is required for multiple steps in betacoronaviruses replication. SARS-CoV-2-N-protein condenses with specific viral RNAs at particular temperatures making it a powerful model for deciphering RNA sequence specificity in condensates. We identify two separate and distinct double-stranded, RNA motifs (dsRNA stickers) that promote N-protein condensation. These dsRNA stickers are separately recognized by N-protein's two RNA binding domains (RBDs). RBD1 prefers structured RNA with sequences like the transcription-regulatory sequence (TRS). RBD2 prefers long stretches of dsRNA, independent of sequence. Thus, the two N-protein RBDs interact with distinct dsRNA stickers, and these interactions impart specific droplet physical properties that could support varied viral functions. Specifically, we find that addition of dsRNA lowers the condensation temperature dependent on RBD2 interactions and tunes translational repression. In contrast RBD1 sites are sequences critical for sub-genomic (sg) RNA generation and promote gRNA compression. The density of RBD1 binding motifs in proximity to TRS-L/B sequences is associated with levels of sub-genomic RNA generation. The switch to packaging is likely mediated by RBD1 interactions which generate particles that recapitulate the packaging unit of the virion. Thus, SARS-CoV-2 can achieve biochemical complexity, performing multiple functions in the same cytoplasm, with minimal protein components based on utilizing multiple distinct RNA motifs that control N-protein interactions.

Design and implementation of a dual aspheric integrated shaping element for a high-power fiber laser.

A dual aspheric integrated beam shaper suitable for a high-power laser situation has been designed and realized. The model for this lens was derived theoretically and the performance was evaluated using a detailed simulation. The ultrasonic vibration assisted cutting and the high-precision grinding and polishing technology were used for the processing. The surface accuracy was less than 200 nm measured with a profiler, and the roughness was smaller than 20 nm with the help of the white light interferometer. Shaping experiments were carried out, which verified that the Gaussian beam has uniform intensity distribution with a uniformity of 85.13% in the near field and converges to a point in the far field, which is exactly as expected. It thus provides an actual selection for high-power laser shaping.

Engineering a conformal optical window of a square-to-circular transition isolator.

To realize the flow visualization of shock train structures by Schlieren measurements in a square-to-circular transition isolator, a high-precision conformal optical window was manufactured by fly-cutting technology. According to the light refraction principle, the window's outer surface was iteratively optimized based on the super-elliptic curves of the internal flow channel. Through tolerance analysis and processing parameter optimization, the transmitted wavefront error (RMS value) of the finished window was 0.823λ (λ=632.8n m). Based on a z-type Schlieren apparatus, the high-precision Schlieren measurements were conducted through the window and processed by an image filtering process method. The results promote high-precision Schlieren observation towards square-to-circular transition isolators.

Design and Application of Metal Organic Framework ZIF-90-ZnO-MoS2 Nanohybrid for an Integrated Electrochemical Liquid Biopsy.

Limited healthcare capacity highlights the needs of integrated sensing systems for personalized health-monitoring. However, only limited sensors can be employed for point-of-care applications, emphasizing the lack of a generalizable sensing platform. Here, we report a metal organic framework (MOF) ZIF-90-ZnO-MoS2 nanohybrid-based integrated electrochemical liquid biopsy (ELB) platform capable of direct profiling cancer exosomes from blood. Using a bottom-up approach for sensor design, a series of critical sensing functions is considered and encoded into the MOF material interface by programming the material with different chemical and structural features. The MOF-based ELB platform is able to achieve one-step sensor fabrication, target isolation, nonfouling and high-sensitivity sensing, direct signal transduction, and multiplexed detection. We demonstrated the capability of the designed sensing system on differentiating cancerous groups from healthy controls by analyzing clinical samples from lung cancer patients, providing a generalizable sensing platform.

Prediction of surface roughness and the material removal rate in magnetorheological finishing.

Magnetorheological finishing (MRF) is a sub-aperture polishing process, which is often used to correct surface errors and remove sub-surface damage after grinding. A strong correlation exists between the material removal rate and surface roughness in MRF, but current theoretical models are incapable of predicting these two factors at the same time. In this paper, a theoretical model was developed to describe the material removal rate and surface quality after MRF in order to better understand the material removal mechanism of MRF and explain the relationship between surface roughness and material removal rate. Two modes of experiments (uniform polishing and fixed point polishing) were conducted on monocrystalline silicon to obtain the results of surface roughness and removal rate. The experimental results are highly consistent with the theoretical model calculated results. The theoretical model could be a reference for high-efficiency and ultra-smooth MRF process.

Self-calibration interferometric stitching test method for cylindrical surfaces.

The surface figure accuracy requirement of cylindrical surfaces widely used in rotors of gyroscope, spindles of ultra-precision machine tools and high-energy laser systems is nearly 0.1 µm. Cylindricity measuring instrument that obtains 1-D profile result cannot be utilized for deterministic figuring methods. Interferometric stitching test for cylindrical surfaces utilizes a CGH of which the system error will accumulated to unacceptable extent for large aperture/angular aperture that require many subapertures. To this end, a self-calibration interferometric stitching method for cylindrical surfaces is proposed. The mathematical model of cylindrical surface figure and the completeness condition of self-calibration stitching test of cylindrical surfaces were analyzed theoretically. The effects of shear/stitching motion error and the subapertures lattice on the self-calibration test results were analyzed. Further, a self-calibration interferometric stitching algorithm that can theoretically recover all the necessary components of the system error for testing cylindrical surfaces was proposed. Simulations and experiments on a shaft were conducted to validate the feasibility.

Quasi-absolute interferometric testing of cylinders.

A three-step quasi-absolute testing method for optical cylinders is proposed in this Letter. Three measurements are taken at the so-called cat's eye position and confocal null testing positions with a computer-generated hologram (CGH) rotated around the axis parallel to that of the cylinder. The quasi-absolute surface error of the cylinder is obtained by simple operations including addition/subtraction and flip of the datasets. The uncertainty is traceable to an optical flat. Two different CGHs are used for a convex cylinder and give consistent quasi-absolute testing results of the surface error, which experimentally validates the method.

Impaired generation of mature neurons due to extended expression of Tlx by repressing Sox2 transcriptional activity.

As a master regulator of the dynamic process of adult neurogenesis, timely expression and regulation of the orphan nuclear receptor Tailless (Tlx) is essential. However, there is no study yet to directly investigate the essential role of precise spatiotemporal expressed Tlx. Here, we generated a conditional gain of Tlx expression transgenic mouse model, which allowed the extended Tlx expression in neural stem cells (NSCs) and their progeny by mating with a TlxCreERT2 mouse line. We demonstrate that extended expression of Tlx induced the impaired generation of mature neurons in adult subventricular zone and subgranular zone. Furthermore, we elucidated for the first time that this mutation decreased the endogenous expression of Sox2 by directly binding to its promoter. Restoration experiments further confirmed that Sox2 partially rescued these neuron maturation defects. Together, these findings not only highlight the importance of shutting-off Tlx on time in controlling NSC behavior, but also provide insights for further understanding adult neurogenesis and developing treatment strategies for neurological disorders.

Rapid polishing process for the x ray reflector.

X ray mirrors are symmetrical workpieces along the length and width and are widely used in various optical systems. Unlike the center-symmetric circular mirror, it is more difficult to suppress the edge effect of the x ray mirror during the polishing process, which greatly limits the polishing accuracy and polishing efficiency. Based on this, the unique edge effect of x ray mirrors is investigated in depth in this paper. First, the causes and distribution laws of the edge effect of the x ray mirror were obtained by analyzing the inherent structure of the computer controlled optical surface (CCOS) and the motion trajectory of the polishing tool. Second, a mathematical model was established based on the material removal states of different regions on the x ray mirror. Finally, a combined polishing process based on the influence function of different shaped tools is proposed and experimentally verified. The results show that the edge effect on the x ray mirror is significantly weakened and its surface errors peak to valley (PV) and RMS are increased by 21.5 times and 47.9 times, respectively. This indicates that the combined polishing process has a good suppression effect on the edge effect of the x ray mirror.

Ion beam figuring strategy for aluminum optics with minimal extra material removal.

With the application spectrum moving from infrared to visible light, aluminum optics with complex forms are difficult to fabricate by the majority of existing processing methods. Possessing the highest machining precision and low processing contamination, ion beam figuring (IBF) is a better method for fabrication of aluminum optics. However, the surface roughness deteriorates with the removal depth during IBF. In this study, the extra material removal during the IBF process is studied systematically. Extra material removal consists of two parts, determined by the convolution process and the limitation of the dynamic performance of machining tools. Extra material removal can be reduced by filtering out the surface residual error with a spatial frequency higher than the cut-off frequency and reducing the iterations of the machining process. Then, the executability of the dwell time matrix and the figuring ability of the removal function are analyzed. Adjusting the working parameters (volume removal rate) reduces the requirements for dynamic performance of machining tools. Finally, a minimal material removal processing strategy for aluminum optics based on power spectral density analysis and a spatial frequency filtering method is proposed. A simulation is conducted to verify the feasibility of the proposed strategy. With the same final precision (59.8 nm PV and 4.4 nm RMS), the maximum material removal decreases nearly 36 nm by applying the strategy, which reduces roughness nearly 10 nm. This study promotes the application of IBF in the field of aluminum optics fabrication as well as improves the machining precision of aluminum optics.

Integrative design and processing of a conformal optical window pair in a cylindrical isolator.

In order to perform the flow visualization of a shock train structure by the schlieren imaging method in the cylindrical isolator, to the best of our knowledge, a novel integrative design and processing scheme of an aluminum alloy pipe with an acrylic conformal optical window pair are proposed. The optical ray tracing and wavefront correction methods were applied to design the inner cylindrical surfaces and outer aspherical cylindrical surfaces of the optical window pair for parallel light correction based on the conjoint analysis with the processing capability. Under the tolerance analysis and the optimization of the machining path, the integrative model was fabricated on a three-axis computer numerical control machine using two-axis turning and fast tool servo machining. The wavefront aberration (peak-to-valley value) and wavefront aberration (RMS) of the optical window pair were corrected within 12.189 and 2.658λ (λ=632.8nm) in the observation area which met the requirements of high-precision schlieren observation.

Rapid fabrication technique for aluminum optics by inducing a MRF contamination layer modification with Ar+ ion beam sputtering.

Aluminum optics are widely used in modern optical systems because of high specific stiffness and high reflectance. Magnetorheological finishing (MRF) provides a highly deterministic technology for high precision aluminum optics fabrication. However, the contamination layer will generate on the surface and bring difficulties for the subsequent processes, which highly limit the fabrication efficiency and precision. In this study, characteristics of the contamination layer and its formation process are firstly revealed through experimental and theoretical methods. Impurities such as abrasives are embedded into the aluminum substrate causing increasing surface hardness. The influence of the contaminant layer on machining accuracy and machining efficiency is analyzed in this study. Based on the analysis, ion beam sputtering (IBS) is induced as a contamination layer modification method. Impurities will be preferential sputtered during the process. Surface hardness and brightness will restore to the state before MRF. Moreover, the thickness of the contamination layer reduces dynamically during IBS because of the bombardment-induced Gibbsian segregation and sputter yield amplification mechanism. Consequently, we proposed a combined technique that includes MRF, IBS and smoothing polishing. Comparative experiments are performed on an elliptical shape plane surface. The results indicate that the efficiency has been increased sevenfold and surface precision is also highly improved. Our research will promote the application of aluminum optics to the visible and even ultraviolet band.