Development of SF6 as a Formal Electrophilic Fluorinating Reagent for Photocatalyzed Oxidative Fluorination of Phosphine Oxides.

Organophosphorus-fluorine compounds are of significant utility across biology, pharmacy, and chemical synthesis. Here, we introduce a photocatalyzed oxidative-fluorination approach employing SF6 as a formal electrophilic fluorinating reagent. It offers an innovative pathway to forge P(O)-F bonds. Notably, sulfur hexafluoride plays a dual role as both the oxidant and the fluorinating reagent under mild conditions in this transformation. Meanwhile, this method contributes to environmental sustainability by consuming a notorious greenhouse gas, underscoring the ecological benefits of our approach.

Population pharmacokinetics of fluconazole for prevention or treatment of invasive candidiasis in Chinese young infants.

The dosing of fluconazole for young infants remains empirical because of the limited pharmacokinetic (PK) data. We aimed to establish a population PK model and assess the systematic exposure-response of commonly used regimens of fluconazole in Chinese infants. We included infants with a postnatal age of less than 120 days and received intravenous fluconazole. Both scheduled and scavenged plasma samples were collected, and fluconzaole concentration was determined by a validated ultra-performance liquid chromatography-tandem mass spectrometry assay. Population PK analysis was conducted using Phoenix NLME, and then Monte Carlo simulation was conducted to predict the probability of target attainment (PTA) of empirically used regimens of both prophylactic and therapeutic purposes. Based on 304 plasma samples from 183 young infants, fluconazole concentration data was best described by a one-compartment model with first-order elimination. Gestational Age (GA), postnatal age (PNA), and body weight (BW) were included in the final model as CL = 0.02*(GA/214)2.77*(PNA/13)0.24*exp(nCL); V = 1.56*(BW/1435)0.90*exp(nV). Model validation revealed the final model had qualified stability and acceptable predictive properties. Monte Carlo simulation indicated that under the same minimum inhibitory concentration (MIC) value and administration regimen, PTA decreased with GA and PNA. The commonly used prophylactic regimens can meet the clinical need, while higher doses might be needed for treatment of invasive candidiasis. This population PK model of fluconazole discriminated the impact of GA and PNA on CL and BW on V. Dosing adjustment was needed according to the GA and PNA of infants to achieve targeted exposures.

Efficient Green Spin Light-Emitting Diodes Enabled by Ultrafast Energy- and Spin-Funneling in Chiral Perovskites.

Introducing molecular chirality into perovskite crystal structures has enabled the control of carrier spin states, giving rise to circularly polarized luminescence (CPL) in thin films and circularly polarized electroluminescence (CPEL) in LEDs. Spin-LEDs can be fabricated either through a spin-filtering layer enabled by chiral-induced spin selectivity or a chiral emissive layer. The former requires a high degree of spin polarization and a compatible spinterface for efficient spin injection, which might not be easily integrated into LEDs. Alternatively, a chiral emissive layer can also generate circularly polarized electroluminescence, but the efficiency remains low and the fundamental mechanism is elusive. In this work, we report an efficient green LED based on quasi-two-dimensional (quasi-2D) chiral perovskites as the emitting layer (EML), where CPEL is directly produced without separate carrier spin injection. The optimized chiral perovskite thin films exhibited strong CPL at 535 nm with a photoluminescence quantum yield (PLQY) of 91% and a photoluminescence dissymmetry factor (glum) of 8.6 × 10-2. Efficient green spin-LEDs were successfully demonstrated, with a large EL dissymmetry factor (gEL) of 7.8 × 10-2 and a maximum external quantum efficiency (EQE) of 13.5% at room temperature. Ultrafast transient absorption (TA) spectroscopic study shows that the CPEL is generated from a rapid energy transfer accompanied by spin transfer from 2D to 3D perovskites. Our study not only demonstrates a reliable approach to achieve high performance spin-LEDs but also reveals the fundamental mechanism of CPEL with an emissive layer of chiral perovskites.

NLRX1 Inhibits LPS-Induced Microglial Death via Inducing p62-Dependent HO-1 Expression, Inhibiting MLKL and Activating PARP-1.

The activation of microglia and the production of cytokines are key factors contributing to progressive neurodegeneration. Despite the well-recognized neuronal programmed cell death regulated by microglial activation, the death of microglia themselves is less investigated. Nucleotide-binding oligomerization domain, leucine-rich repeat-containing X1 (NLRX1) functions as a scaffolding protein and is involved in various central nervous system diseases. In this study, we used the SM826 microglial cells to understand the role of NLRX1 in lipopolysaccharide (LPS)-induced cell death. We found LPS-induced cell death is blocked by necrostatin-1 and zVAD. Meanwhile, LPS can activate poly (ADP-ribose) polymerase-1 (PARP-1) to reduce DNA damage and induce heme oxygenase (HO)-1 expression to counteract cell death. NLRX1 silencing and PARP-1 inhibition by olaparib enhance LPS-induced SM826 microglial cell death in an additive manner. Less PARylation and higher DNA damage are observed in NLRX1-silencing cells. Moreover, LPS-induced HO-1 gene and protein expression through the p62-Keap1-Nrf2 axis are attenuated by NLRX1 silencing. In addition, the Nrf2-mediated positive feedback regulation of p62 is accordingly reduced by NLRX1 silencing. Of note, NLRX1 silencing does not affect LPS-induced cellular reactive oxygen species (ROS) production but increases mixed lineage kinase domain-like pseudokinase (MLKL) activation and cell necroptosis. In addition, NLRX1 silencing blocks bafilomycin A1-induced PARP-1 activation. Taken together, for the first time, we demonstrate the role of NLRX1 in protecting microglia from LPS-induced cell death. The underlying protective mechanisms of NLRX1 include upregulating LPS-induced HO-1 expression via Nrf2-dependent p62 expression and downstream Keap1-Nrf2 axis, mediating PARP-1 activation for DNA repair via ROS- and autophagy-independent pathway, and reducing MLKL activation.

Tuning Spin-Polarized Lifetime at High Carrier Density through Deformation Potential in Dion-Jacobson-Phase Perovskites.

The control of spin relaxation mechanisms is of great importance for spintronics applications as well as for fundamental studies. Layered metal-halide perovskites represent an emerging class of semiconductors with rich optical spin physics, showing potential for spintronic applications. However, a major hurdle arises in layered metal-halide perovskites with strong spin-orbit coupling, where the spin lifetime becomes extremely short due to D'yakonov-Perel' scattering and Bir-Aronov-Pikus at high carrier density. Using the circularly polarized pump-probe transient reflection technique, we experimentally reveal the important scattering for spin relaxation beyond the electron-hole exchange strength in the Dion-Jacobson (DJ)-type 2D perovskites (3AMP)(MA)n-1PbnI3n+1 [3AMP = 3-(aminomethyl)piperidinium, n = 1-4]. Despite a more than 10-fold increase in carrier concentration, the spin lifetimes for n = 3 and 4 are effectively maintained. We reveal neutral impurity and polar optical phonon scatterings as significant contributors to the momentum relaxation rate. Furthermore, we show that more octahedral distortions induce a larger deformation potential which is reflected on the acoustic phonon properties. Coherent acoustic phonon analysis indicates that the polaronic effect is crucial in achieving control over the scattering mechanism and ensuring spin lifetime protection, highlighting the potential of DJ-phase perovskites for spintronic applications.

Research progress of post-acute sequelae after SARS-CoV-2 infection.

SARS-CoV-2 has spread rapidly worldwide and infected hundreds of millions of people worldwide. With the increasing number of COVID-19 patients discharged from hospitals, the emergence of its associated complications, sequelae, has become a new global health crisis secondary to acute infection. For the time being, such complications and sequelae are collectively called "Post-acute sequelae after SARS-CoV-2 infection (PASC)", also referred to as "long COVID" syndrome. Similar to the acute infection period of COVID-19, there is also heterogeneity in PASC. This article reviews the various long-term complications and sequelae observed in multiple organ systems caused by COVID-19, pathophysiological mechanisms, diagnosis, and treatment of PASC, aiming to raise awareness of PASC and optimize management strategies.

Amorphous-Like Ultralow Thermal Transport in Crystalline Argyrodite Cu7PS6.

Due to their amorphous-like ultralow lattice thermal conductivity both below and above the superionic phase transition, crystalline Cu- and Ag-based superionic argyrodites have garnered widespread attention as promising thermoelectric materials. However, despite their intriguing properties, quantifying their lattice thermal conductivities and a comprehensive understanding of the microscopic dynamics that drive these extraordinary properties are still lacking. Here, an integrated experimental and theoretical approach is adopted to reveal the presence of Cu-dominated low-energy optical phonons in the Cu-based argyrodite Cu7PS6. These phonons yield strong acoustic-optical phonon scattering through avoided crossing, enabling ultralow lattice thermal conductivity. The Unified Theory of thermal transport is employed to analyze heat conduction and successfully reproduce the experimental amorphous-like ultralow lattice thermal conductivities, ranging from 0.43 to 0.58 W m-1 K-1, in the temperature range of 100-400 K. The study reveals that the amorphous-like ultralow thermal conductivity of Cu7PS6 stems from a significantly dominant wave-like conduction mechanism. Moreover, the simulations elucidate the wave-like thermal transport mainly results from the contribution of Cu-associated low-energy overlapping optical phonons. This study highlights the crucial role of low-energy and overlapping optical modes in facilitating amorphous-like ultralow thermal transport, providing a thorough understanding of the underlying complex dynamics of argyrodites.

Channel-wise attention enhanced and structural similarity constrained cycleGAN for effective synthetic CT generation from head and neck MRI images.

BACKGROUND: Magnetic resonance imaging (MRI) plays an increasingly important role in radiotherapy, enhancing the accuracy of target and organs at risk delineation, but the absence of electron density information limits its further clinical application. Therefore, the aim of this study is to develop and evaluate a novel unsupervised network (cycleSimulationGAN) for unpaired MR-to-CT synthesis. METHODS: The proposed cycleSimulationGAN in this work integrates contour consistency loss function and channel-wise attention mechanism to synthesize high-quality CT-like images. Specially, the proposed cycleSimulationGAN constrains the structural similarity between the synthetic and input images for better structural retention characteristics. Additionally, we propose to equip a novel channel-wise attention mechanism based on the traditional generator of GAN to enhance the feature representation capability of deep network and extract more effective features. The mean absolute error (MAE) of Hounsfield Units (HU), peak signal-to-noise ratio (PSNR), root-mean-square error (RMSE) and structural similarity index (SSIM) were calculated between synthetic CT (sCT) and ground truth (GT) CT images to quantify the overall sCT performance. RESULTS: One hundred and sixty nasopharyngeal carcinoma (NPC) patients who underwent volumetric-modulated arc radiotherapy (VMAT) were enrolled in this study. The generated sCT of our method were more consistent with the GT compared with other methods in terms of visual inspection. The average MAE, RMSE, PSNR, and SSIM calculated over twenty patients were 61.88 ± 1.42, 116.85 ± 3.42, 36.23 ± 0.52 and 0.985 ± 0.002 for the proposed method. The four image quality assessment metrics were significantly improved by our approach compared to conventional cycleGAN, the proposed cycleSimulationGAN produces significantly better synthetic results except for SSIM in bone. CONCLUSIONS: We developed a novel cycleSimulationGAN model that can effectively create sCT images, making them comparable to GT images, which could potentially benefit the MRI-based treatment planning.

Modulating hot carrier cooling and extraction with A-site organic cations in perovskites.

Hot carrier solar cells could offer a solution to achieve high efficiency solar cells. Due to the hot-phonon bottleneck in perovskites, the hot carrier lifetime could reach hundreds of ps. Such that exploring perovskites could be a good way to promote hot carrier technology. With the incorporation of large organic cations, the hot carrier lifetime can be improved. By using ultrafast transient spectroscopy, the hot carrier relaxation and extraction kinetics are measured. From the transient kinetics, 2-phenyl-acetamidine cation based perovskites exhibit the highest initial carrier temperature, longest carrier relaxation, and slowest hot carrier relaxation. Such superior behavior could be attributed to reduced electron-phonon coupling induced by lattice strain, which is a result of the large organic cation and also a possible surface electronic state change. Our discovery exhibits the potential to use large organic cations for the use of hot carrier perovskite solar cells.

Enhancing osteoporosis treatment with engineered mesenchymal stem cell-derived extracellular vesicles: mechanisms and advances.

As societal aging intensifies, the incidence of osteoporosis (OP) continually rises. OP is a skeletal disorder characterized by reduced bone mass, deteriorated bone tissue microstructure, and consequently increased bone fragility and fracture susceptibility, typically evaluated using bone mineral density (BMD) and T-score. Not only does OP diminish patients' quality of life, but it also imposes a substantial economic burden on society. Conventional pharmacological treatments yield limited efficacy and severe adverse reactions. In contemporary academic discourse, mesenchymal stem cells (MSCs) derived extracellular vesicles (EVs) have surfaced as auspicious novel therapeutic modalities for OP. EVs can convey information through the cargo they carry and have been demonstrated to be a crucial medium for intercellular communication, playing a significant role in maintaining the homeostasis of the bone microenvironment. Furthermore, various research findings provide evidence that engineered strategies can enhance the therapeutic effects of EVs in OP treatment. While numerous reviews have explored the progress and potential of EVs in treating degenerative bone diseases, research on using EVs to address OP remains in the early stages of basic experimentation. This paper reviews advancements in utilizing MSCs and their derived EVs for OP treatment. It systematically examines the most extensively researched MSC-derived EVs for treating OP, delving not only into the molecular mechanisms of EV-based OP therapy but also conducting a comparative analysis of the strengths and limitations of EVs sourced from various cell origins. Additionally, the paper emphasizes the technical and engineering strategies necessary for leveraging EVs in OP treatment, offering insights and recommendations for future research endeavors.

Mortality risk of people living with HIV under hypothetical intervention scenarios of PM2.5 and HIV severity: a prospective cohort study.

This study estimated and compared mortality risks among people living with HIV (PLWH) under the real-world and hypothetical scenarios of PM2.5 concentrations and HIV severity. An open cohort from all PLWH receiving antiretroviral therapy in Sichuan during 2010-2019 was constructed, resulting in 541,515 person-years. Annual mean concentrations of PM2.5 were estimated and linked to PLWH by their residential address. The parametric g-formula were used to assess 3- and 5-year mortality risks under the real-world and hypothetical scenarios of PM2.5 (10-35, 35-50, 50-75 µg/m3) and CD4 concentrations (0-200, 200-500, 500-800, 800-1100 counts/µl). The estimated 3- and 5-year mortality risks among the PLWH were 14.43 % and 19.38 %, respectively, which would decrease substantially when annual PM2.5 concentration were reduced to between 10 and 35 µg/m3 (risk difference [RD] = -3.23 % and - 4.06 %) and would increase when PM2.5 concentration were elevated to between 50 and 75 µg/m3 (RD = 3.59 % and 5.04 %). The mortality risk would increase when CD4 concentration were reduced to <200 counts/µl (RD = 15.90 % and 20.27 %) and would decrease when CD4 concentration were ≥ 200 counts/µl, especially to between 800 and 1100 counts/µl (RD = -9.01 % and - 11.75 %). The elevated concentration of PM2.5 may disproportionately affect individuals with immune deficiency, especially those with more severity. The findings would serve as justifications for future intervention design and policy making to alleviate air pollution and improve environmental justice and health equity.

Copper ions reinforced flexible carboxymethylcellulose/polyethyleneimine composite films with enhanced mechanical properties, UV-shielding performance, thermal stability, solvent resistance, and antibacterial activity.

A composite film (CMC/PEI) consisting of anionic carboxymethylcellulose (CMC) and cationic polyethyleneimine (PEI) can be easily produced through the solution casting method using self-assembly based on electrostatic interaction and hydrogen bonding. Subsequently, the resulting CMC/PEI polyelectrolyte composite film with a network structure was crosslinked with divalent Cu2+ ions through ionic and coordination bonds, resulting in a strengthened Cu(II)@CMC/PEI film. The composite film was characterized based on its structural, surface, thermal, UV protection, antibacterial, and degradation aspects. The results demonstrated this film has impressive mechanical properties, remarkable solvent resistance, good antibacterial properties, and excellent UV-shielding performance by completely blocking ultraviolet light with wavelengths below 360 nm. These properties can be attributed to the presence of Cu2+ ions and PEI in the film. This work is valuable for the development of novel UV-shielding materials and should contribute to the design of carboxymethylcellulose composite films with desirable properties and exceptional performance.

Identifying complementary and alternative medicine recommendations for anxiety treatment and care: a systematic review and critical assessment of comprehensive clinical practice guidelines.

Background: Clinical practice guidelines (CPGs) are used to guide decision-making, especially regarding complementary and alternative medicine (CAM) therapies that are unfamiliar to orthodox healthcare providers. This systematic review aimed to critically review and summarise CAM recommendations associated with anxiety management included in the existing CPGs. Methods: Seven databases, websites of six international guidelines developing institutions, and the National Centre for Complementary and Integrative Health website were systematically searched. Their reporting and methodological quality were evaluated using the Reporting Items for practice Guidelines in Healthcare checklist and the Appraisal of Guidelines for Research and Evaluation (2nd version) instrument, respectively. Results: Ten CPGs were included, with reporting rates between 51.4 and 88.6%. Seven of these were of moderate to high methodological quality. Seventeen CAM modalities were implicated, involving phytotherapeutics, mind-body practice, art therapy, and homeopathy. Applied relaxation was included in 70% CPGs, which varied in degree of support for its use in the treatment of generalised anxiety disorder. There were few recommendations for other therapies/products. Light therapy was not recommended for use in generalised anxiety disorder, and St John's wort and mindfulness were not recommended for use in social anxiety disorder in individual guidelines. Recommendations for the applicability of other therapies/products for treating a specific anxiety disorder were commonly graded as "unclear, unambiguous, or uncertain". No CAM recommendations were provided for separation anxiety disorder, specific phobia or selective mutism. Conclusion: Available guidelines are limited in providing logically explained graded CAM recommendations for anxiety treatment and care. A lack of high-quality evidence and multidisciplinary consultation during the guideline development are two major reasons. High quality and reliable clinical evidence and the engagement of a range of interdisciplinary stakeholders are needed for future CPG development and updating. Systematic review registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022373694, identifier CRD42022373694.

Higher Delta variant-specific neutralizing antibodies prevented infection in close contacts vaccinated with ancestral mRNA vaccines during the SARS-CoV-2 Delta wave.

Identification of the risk factors and the high-risk groups which are most vulnerable is critical in COVID-19 disease management at a population level. Evaluating the efficacy of vaccination against infections is necessary to determine booster vaccination strategies for better protection in high-risk groups. In this study, we recruited 158 mRNA-vaccinated individuals during the Delta wave of SARS-CoV-2 infections in Singapore and examined the antibody profiles of infected individuals. We found that, despite high exposure due to communal living conditions in proximity, 4% of individuals (6/158) had PCR-confirmed infections and 96% (152/158) remained uninfected. Time-course analysis of the antibody profile at the start and the end of quarantine period showed Delta-specific boosting of anti-spike antibody response in 57% of the uninfected individuals (86/152). In the remaining 43% of the uninfected individuals (66/152) with no Delta-specific antibody boost, we found a higher Delta-specific antibody response at the start of quarantine period, which correlated with higher Delta pseudovirus neutralizing capacity. Our findings indicate that a higher basal variant-specific antibody response in the mRNA-vaccinated individuals contributes to better protection against infections by the new emerging SARS-CoV-2 variants.

Self-Healing of Poly(vinyl Alcohol)/Poly(acrylic Acid)-Polytetrahydrofuran-Poly(acrylic Acid) Blend Boosted via Shape Memory.

The self-healable polymers that can repair physical damage autonomously to extend their lifetime and reduce maintenance costs are promising intelligent materials. However, utilizing shape memory to facilitate self-repair is unusual at present. In this work, a series of poly(acrylic acid)-polytetrahydrofuran-poly(acrylic acid) polymers (PAA-PTMG-PAA, diPAA-PTMG) are synthesized as a switching phase and healing accelerator to blend into poly(vinyl alcohol) (PVA). The water swelling rate of the blend is up to 400.0% at 1/1 molecular weight ratio of PTMG/PAA and 20.0 wt % blend ratio of diPAA-PTMG to PVA, and its crystallization is changed significantly under wet conditions. The blend membrane exhibits not only a good hydrothermal-response shape memory effect but also a favorable self-healing behavior. The tensile strength and elongation at break are 12.4 MPa and 320.0% after healing at 25 °C, respectively. In particular, the wound membrane can achieve a better self-healing effect with the assistance of shape memory at 37 °C, and the elongation at the break increased to 515.9% after healing. The membrane is not cytotoxic, so it will be a promising biomedical material.

Gut Microbiota Metabolite 3-Indolepropionic Acid Directly Activates Hepatic Stellate Cells by ROS/JNK/p38 Signaling Pathways.

There has been a growing interest in studying the communication of gut microbial metabolites between the gut and the liver as liver fibrosis progresses. Although 3-Indolepropionic acid (IPA) is regarded as a clinically valuable gut metabolite for the treatment of certain chronic diseases, the effects of oral administration of IPA on hepatic fibrosis in different animal models have been conflicting. While some mechanisms have been proposed to explain these contradictory effects, the direct impact of IPA on hepatic fibrosis remains unclear. In this study, we found that IPA could directly activate LX-2 human hepatic stellate cells in vitro. IPA upregulated the expression of fibrogenic marker genes and promoted the features associated with HSCs activation, including proliferation and contractility. IPA also increased reactive oxygen species (ROS) in mitochondria and the expression of inflammation-related genes in LX-2 cells. However, when a ROS-blocking agent was used, these effects were reduced. p38 and JNK, the downstream signaling cascades of ROS, were found to be required for the activation of LX-2 induced by IPA. These findings suggest that IPA can directly activate hepatic stellate cells through ROS-induced JNK and p38 signaling pathways.

Nickel-Catalyzed Asymmetric Decarboxyarylation with NHP Esters of α-Amino Acid to Chiral Benzylamines.

A nickel-catalyzed asymmetric decarboxyarylation of NHP esters via reductive cross-coupling has been established. Utilizing the NHP of amino acid esters as radical precursors furnishes a new protocol in which structurally diverse chiral benzylamines could be accessible. This method has demonstrated excellent catalytic efficiency, high enantioselective control, mild conditions, and good functional group tolerance, thus enabling the late-stage modification of bioactive molecules and pharmaceuticals.

Ultrafast Hole Transfer in Graphitic Carbon Nitride Imide Enabling Efficient H2O2 Photoproduction.

Solar-driven photocatalysis is a promising approach for renewable energy application. H2O2 photocatalysis by metal-free graphitic carbon nitride has been gaining attention. Compared with traditional thermal catalysis, metal-free graphitic carbon nitride photocatalysis could lower material cost and achieve greener production of H2O2. Also, to better guide photocatalyst design, a fundamental understanding of the reaction mechanism is needed. Here, we develop a series of model cost-effective metal-free H2O2 photocatalysts made from graphitic carbon nitride (melem) and common imide groups. With 4,4'-oxydiphthalic anhydride (ODPA)-modified g-C3N4, a H2O2 yield rate of 10781 µmol/h·g·L could be achieved. Transient absorption and ex situ Fourier transform infrared (FTIR) measurements revealed an ultrafast charge transfer from the melem core to water with ∼3 ps to form unique N-OH intermediates. The electron withdrawing ability of the anhydride group plays a role in governing the rate of electron transfer, ensuring efficient charge separation. Our strategy represents a new way to achieve a low material cost, simple synthesizing strategy, good environment impact, and high H2O2 production for renewable energy application.

Cell-type specific regulator RBPMS switches alternative splicing via higher-order oligomerization and heterotypic interactions with other splicing regulators.

Alternative pre-mRNA splicing decisions are regulated by RNA binding proteins (RBPs) that can activate or repress regulated splice sites. Repressive RBPs typically harness multivalent interactions to bind stably to target RNAs. Multivalency can be achieved by homomeric oligomerization and heteromeric interactions with other RBPs, often mediated by intrinsically disordered regions (IDRs), and by possessing multiple RNA binding domains. Cell-specific splicing decisions often involve the action of widely expressed RBPs, which are able to bind multivalently around target exons, but without effect in the absence of a cell-specific regulator. To address how cell-specific regulators can collaborate with constitutive RBPs in alternative splicing regulation, we used the smooth-muscle specific regulator RBPMS. Recombinant RBPMS is sufficient to confer smooth muscle cell specific alternative splicing of Tpm1 exon 3 in cell-free assays by preventing assembly of ATP-dependent splicing complexes. This activity depends upon a C-terminal IDR that facilitates dynamic higher-order self-assembly, cooperative binding to multivalent RNA and interactions with widely expressed splicing co-regulators, including MBNL1 and RBFOX2, allowing cooperative assembly of stable cell-specific regulatory complexes.