TCF7L2 acts as a molecular switch in midbrain to control mammal vocalization through its DNA binding domain but not transcription activation domain.

Vocalization is an essential medium for social signaling in birds and mammals. Periaqueductal gray (PAG) a conserved midbrain structure is believed to be responsible for innate vocalizations, but its molecular regulation remains largely unknown. Here, through a mouse forward genetic screening we identified one of the key Wnt/ß-catenin effectors TCF7L2/TCF4 controls ultrasonic vocalization (USV) production and syllable complexity during maternal deprivation and sexual encounter. Early developmental expression of TCF7L2 in PAG excitatory neurons is necessary for the complex trait, while TCF7L2 loss reduces neuronal gene expressions and synaptic transmission in PAG. TCF7L2-mediated vocal control is independent of its ß-catenin-binding domain but dependent of its DNA binding ability. Patient mutations associated with developmental disorders, including autism spectrum disorders, disrupt the transcriptional repression effect of TCF7L2, while mice carrying those mutations display severe USV impairments. Therefore, we conclude that TCF7L2 orchestrates gene expression in midbrain to control vocal production through its DNA binding but not transcription activation domain.

Sub-3 nm Aluminum Nanocrystals Exhibiting Cluster-Like Optical Properties.

Metal nanoclusters with distinct photophysical and photochemical properties have drawn intense research interests for their applications in optoelectronics, catalysis, and biomedicine. Herein, strong evidence is provided that light metal is capable of generating comparable optical responses of noble metal nanoclusters, but at much shorter wavelength. Air-stable, size-uniform, sub-3 nm aluminum nanocrystals are prepared with simple solution based synthetic procedures, with photoluminescence located in the ultraviolet range and short exciton lifetime. Partial modulation of the photoluminescence is achieved, indicating the key role of surface oxides. This work is envisioned to inspire new frontiers of nanocluster research with light metals.

Nanometre imaging of Fe3GeTe2 ferromagnetic domain walls.

Fe3GeTe2 is a layered crystal which has recently been shown to maintain its itinerant ferromagnetic properties even when atomically thin. Here, differential phase contrast scanning transmission electron microscopy is used to investigate the domain structure in a Fe3GeTe2 cross-sectional lamella at temperatures ranging from 95 to 250 K and at nanometre spatial resolution. Below the experimentally determined Curie temperature (T C) of 191 K, stripe domains magnetised along 〈0001〉, bounded with 180◦ Bloch type domain walls, are observed, transitioning to mixed Bloch-Néel type where the cross-sectional thickness is reduced below 50 nm. When warming towards T C, these domains undergo slight restructuring towards uniform size, before abruptly fading at T C. Localised loss of ferromagnetic order is seen over time, hypothesised to be a frustration of ferromagnetic order from ambient oxidation and basal cracking, which could enable selective modification of the magnetic properties for device applications.

In vivo stress granule misprocessing evidenced in a FUS knock-in ALS mouse model.

Many RNA-binding proteins, including TDP-43, FUS, and TIA1, are stress granule components, dysfunction of which causes amyotrophic lateral sclerosis (ALS). However, whether a mutant RNA-binding protein disrupts stress granule processing in vivo in pathogenesis is unknown. Here we establish a FUS ALS mutation, p.R521C, knock-in mouse model that carries impaired motor ability and late-onset motor neuron loss. In disease-susceptible neurons, stress induces mislocalization of mutant FUS into stress granules and upregulation of ubiquitin, two hallmarks of disease pathology. Additionally, stress aggravates motor performance decline in the mutant mouse. By using two-photon imaging in TIA1-EGFP transduced animals, we document more intensely TIA1-EGFP-positive granules formed hours but cleared weeks after stress challenge in neurons in the mutant cortex. Moreover, neurons with severe granule misprocessing die days after stress challenge. Therefore, we argue that stress granule misprocessing is pathogenic in ALS, and the model we provide here is sound for further disease mechanistic study.

The effect of hydrodynamics on the succession of autotrophic and heterotrophic organisms of biofilms in river ecosystems.

Biofilms were cultivated for a 68-day period under different hydrodynamic conditions, and the effect of hydrodynamics on the succession of autotrophic and heterotrophic organisms of biofilms was investigated. Five obvious stages were observed during biofilm formation. At Stage I, the attachment of algae was delayed, especially under turbulent conditions. After Stage II, algal density and heterotrophic biomass of biofilms increased, which were obvious under turbulent flow. Therefore, the algal density and heterotrophic biomass of biofilms were largest under turbulent condition, followed by laminar condition, and then transitional condition. Diatoms were dominant in all flumes and were most abundant under turbulent conditions. The proportion of cyanobacteria was highest under laminar conditions. The ratio of aerobic to anaerobic bacteria decreased and their co-existence could facilitate the nitrification and denitrification in the biofilm. The ratio of monounsaturated fatty acids to saturated fatty acids was highest under turbulent conditions on the 15th day. While the ratio was highest under laminar condition on the 48th day, the high ratio indicates the high ability of biofilm to obtain nutrients, which affect the growth of algae. The regulation of hydrodynamics is a useful technology which can affect the growth of the microorganisms of biofilm, and further improve water quality.

[Effects of different storage conditions on edible quality and antioxidant activity of Polygonatum cyrtonema flowers].

The flower of Polygonatum cyrtonema has good edible and medicinal values. In this study, four samples of P. cyrtonema flowers from different regions were selected as test materials. The contents, composition and antioxidant activities of lipid-soluble pigments and alcohol-soluble components were determined under different light and temperature conditions, which help to reveal the discoloration reason and the composition variation patterns during storage. The results showed that light and temperature had different effects on the lipid-soluble pigments and alcohol-soluble components in the dried flowers during storage. After storage for 4 weeks, the contents of total chlorophyll, carotenoids, phenols and saponins in the samples exposed to light respectively decreased by 62.62%, 66.4%, 68.7% and 43.4% compared with those in the dark. The decreases in the contents of chlorophyll a, chlorophyll b, lutein, ß-carotene and zeaxanthin were 64.64%, 56.74%, 59.2%, 77.7% and 45.4%, respectively. The contents of pigments and components in the samples stored at-20 ℃ were significantly higher than those at room temperature and 4 ℃, indicating that low temperature was conductive to the stability of lipid-soluble pigments and alcohol-soluble components. The samples stored at low temperature and in the dark had the strongest free radical scavenging activity. The results suggest that P. cyrtonema dried flowers should be stored in low temperature environment without light, which can slow down the degradation of internal components. The study provides a theoretical basis for the production, processing and storage of P. cyrtonema flowers.

Enhanced interfacial Dzyaloshinskii-Moriya interactions in annealed Pt/Co/MgO structures.

The interfacial Dzyaloshinskii-Moriya interaction (iDMI) is attracting great interest for spintronics. An iDMI constant larger than 3 mJ m-2 is expected to minimize the size of skyrmions and to optimize the domain-wall dynamics. In this study, we experimentally demonstrate a giant iDMI in Pt/Co/X/MgO ultra-thin film structures with perpendicular magnetization. The iDMI constants were measured using a field-driven creep regime domain expansion method. The enhancement of iDMI with an atomically thin insertion of Ta and Mg is comprehensively understood with the help of ab-initio calculations. Thermal annealing has been used to crystallize the MgO thin layer to improve the tunneling magneto-resistance (TMR), but interestingly it also provides a further increase of the iDMI constant. An increase of the iDMI constant of up to 3.3 mJ m-2 is shown, which is promising for the scaling down of skyrmion electronics.

Photo-induced excitonic structure renormalization and broadband absorption in monolayer tungsten disulphide.

Atomically thin transition metal dichalcogenides (TMDCs) have emerged as a new class of two-dimensional (2D) material for novel optoelectronic applications. In particular, 2D TMDCs are viewed as intriguing and appealing materials to construct Q-switching and mode-locked modulators, due to their broadband saturable absorption even of photon energy below their excitonic energies. However, the dynamics and mechanism of saturable absorption inside TMDCs has yet to be investigated. In this paper, the relaxation dynamics of monolayer tungsten disulphide (WS2) was investigated considering different excitonic transitions. WS2 illustrates dramatic changes in optical responses when excited by intense laser pulses, which are characterized by the broadband photo-induced nonresonance absorption and the giant excitonic bands renormalization process. The experimental results show that strong photo-induced restructuring of excitonic bands has picosecond lifetime and full recovery of optical responses takes hundreds of picosecond. Additionally, our observations reveal that heavy renormalization and overlap of excitonic bands are induced by strong many-body Coulomb interactions. Moreover, the broadband absorption feature of WS2 opens up new applications in broadband saturable absorbers and ultrafast photonic devices.

Nonlinear absorption and temperature-dependent fluorescence of perovskite FAPbBr3 nanocrystal.

Recent progress in solar cell and light-emitting devices makes halide perovskite a research hot spot in optics. In this Letter, the nonlinear absorption and fluorescence properties of FAPbBr3 nanocrystal, one typical organometallic halide perovskite, have been investigated via Z-scan measurements and a density-dependent photoluminescence (PL) spectrum. The FAPbBr3 nanocrystal exhibits nonlinear absorption under the excitation of 800 nm, whose photon energy is below the bandgap of FAPbBr3. The significant absorption is experimentally confirmed to be induced by two-photon absorption (TPA), and the TPA coefficient is measured to be ∼0.0042 cm/GW. Moreover, the PL induced by TPA in FAPbBr3 nanocrystal shows different temperature-dependent behaviors in the range of 90 to 350 K. The peaks of the PL spectrum remain nearly constant at 100-160 K, with a very shallow trough at around 150 K, while a linear blue shift (0.496 meV/K) of the spectrum is observed when temperature is above 160 K. These temperature-dependent fluorescence behaviors can be ascribed to the structural phase transition at about 150 K and the contribution of thermal expansion. Moreover, the exciton binding energy around 160 meV and the optical phonon energy of 15.3 meV are also extracted from the temperature-dependent PL data.

Ultrafast saturable absorption of MoS2 nanosheets under different pulse-width excitation conditions.

The newly raised two-dimensional material MoS2 is regarded as an ideal candidate for saturated absorbers. Here, the open-aperture Z-scan method is used to study the saturation absorption (SA) response of monolayer and multilayer MoS2, considering laser irradiation with different pulse widths. Specifically, in cases of 10 ns and 10 ps laser pulses, the accumulative nonlinearity [e.g., free carrier absorption (FCA)] coupled with SA is found in both monolayer and multilayer MoS2. However, under a 65 fs pulse laser, the instantaneous nonlinearity [e.g., two-photon absorption (TPA)] and the SA effect turn to play a significant role. Additionally, the saturation of both TPA and FCA is observed in MoS2. Importantly, the modulation depth of MoS2 shows different change trends by adjusting the laser pulse width.

Broadband ultrafast nonlinear absorption and ultra-long exciton relaxation time of black phosphorus quantum dots.

Black phosphorus (BP) has recently attracted significant attention for its brilliant physical and chemical features. The remarkable strong light-matter interaction and tunable direct wide range band-gap make it an ideal candidate in various application regions, especially saturable absorbers. In this paper, ultrasmall black phosphorus quantum dots (BPQDs), a unique form of phosphorus nanostructures, with average size of 5.7 ± 0.8 nm are synthesized. Compared with BP nanosheets (BPNs) with similar thickness, the ultrafast nonlinear optical (NLO) absorption properties and excited carrier dynamics are investigated in wide spectra. Beyond the saturation absorption (SA), giant two photon absorption (TPA) is observed in BPQDs. BPQDs exhibit quite different excitation intensity and wavelength dependent nonlinear optical (NLO) response from BPNs, which is attributed to the quantum confinement and edge effects. The BPQDs show broadband photon-induced absorption (PIA) under the probe wavelength from 470 nm to 850 nm and a fast and a slow decay time are obtained as long as 92 ± 10 ps and 1100 ± 100 ps, respectively. The substantial independence for ultra-long time scales of pump intensity and temperature reveals that the carrier recombination mechanism may be attributed to a defect-assisted Auger capture process. These findings will help to develop optoelectronic and photonic devices operating in the infrared and visible wavelength region.

Temperature-dependent excitonic photoluminescence excited by two-photon absorption in perovskite CsPbBr3 quantum dots.

Recently, lead halide perovskite quantum dots have been reported with potential for photovoltaic and optoelectronic applications due to their excellent luminescent properties. Herein excitonic photoluminescence (PL) excited by two-photon absorption in perovskite CsPbBr3 quantum dots (QDs) has been studied at a broad temperature range, from 80 to 380 K. Two-photon absorption has been investigated and the absorption coefficient is up to 0.085 cm/GW at room temperature. Moreover, the PL spectrum excited by two-photon absorption shows a linear blue-shift (0.32 meV/K) below the temperature of 220 K. However, for higher temperatures, the PL peak approaches a roughly constant value and shows temperature-independent chromaticity up to 380 K. This behavior is distinct from the general red-shift for semiconductors and can be attributed to the result of thermal expansion, electron-phonon interaction and structural phase transition around 360 K. The strong nonlinear absorption and temperature-independent chromaticity of CsPbBr3 QDs observed in temperature range from 220 to 380 K will offer new opportunities in nonlinear photonics, light-harvesting, and light-emitting devices.

Giant nonlinear absorption and excited carrier dynamics of black phosphorus few-layer nanosheets in broadband spectra.

Layered black phosphorus nanosheets (BPNs) offer potential uses in nanoelectronic and photonics applications. This work demonstrates giant saturable absorption (SA) and two-photon absorption (TPA) of BPNs under femtosecond visible-to-mid-infrared laser-pulse excitation. In addition, the excited carrier dynamics of BPNs were also studied with ultrafast pump-probe technology. Measurements demonstrated that the nonlinear absorption properties of BPNs strongly depend on excitation wavelength and intensity. BPNs moved from SA to TPA under increasing laser intensities at 800, 1160, 1300, and 1550 nm but showed a purely TPA response at 2000 nm, as gauged by measuring BPN nonlinear absorption coefficients. The BPNs showed broadband photon-induced absorption (PIA) signals from 470 to 700 nm, and the excited carrier recombination time was determined to be 150±10 ps. The excitation intensity dependence of excited carrier dynamics were also studied.

Z-scan measurement of the nonlinear refractive index of monolayer WS(2).

Transition metal dichalcogenides (TMDCs), such as tungsten disulfide (WS(2)), are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into two-dimensional layers of single unit cell thickness. Recent advances in nanoscale materials characterization and few layer TMDCs' unique optical properties make them a research hot-spot in nonlinear optics. In this work, the nonlinear refractive index of monolayer WS(2) has been characterized with Z-scan measurement under 800nm femtosecond pulsed laser excitation, and a value of n2 ≃ (8.1 ± 0.41) × 10(-13)m(2)/W is obtained. A shift from saturable absorption to reverse saturable absorption was observed at higher input pump intensities in the experiments. The transition process was analyzed using a phenomenological model based on two photon absorption, and the two photon absorption coefficient was estimated about (3.7±0.28)×10(-6)m/W.

Characterization of nonlinear properties of black phosphorus nanoplatelets with femtosecond pulsed Z-scan measurements.

The nonlinear properties of black phosphorus (BP) nanoplatelets (NPs) have been characterized with Z-scan measurements under 800-nm femtosecond pulsed laser excitation. A transition from saturable absorption (SA) to reverse saturable absorption (RSA) with the increase of laser intensity was observed in the open-aperture (OA) measurements. Simultaneously, closed-aperture (CA) measurements were carried out to investigate the nonlinear refractive index of BP NPs together, and a value of n(2) ≃(6.8±0.2)×10(-13) m2/W was obtained. The nonlinear absorption properties were analyzed according to the band structure of BP. A theoretical analysis based on SA and two-photon absorption (TPA) was used to determine the nonlinear absorption coefficients from the experimental results, and the TPA coefficient at 800 nm was estimated about (4.5±0.2)×10(-10) m/W.

Z-scan measurement of nonlinear optical properties of BiOCl nanosheets.

Bismuth oxyhalides, such as bismuth oxychlorides (BiOCl), are layered materials with [Bi2O2]2+ layers sandwiched between two sheets of Cl ions. Much work has focused on the potential for bismuth oxyhalides to be a photocatalyst, but their nonlinear optical properties are rarely studied. In this work, the nonlinear refractive index of BiOCl nanosheets has been characterized with Z-scan measurement under 800 nm femtosecond pulsed laser excitation. A shift from saturable absorption to reverse saturable absorption was observed at higher input pump intensities in the experiments. The transition process was analyzed using a phenomenological model based on saturable absorption and two-photon absorption.

Structure of a PLS-class pentatricopeptide repeat protein provides insights into mechanism of RNA recognition.

Pentatricopeptide repeat (PPR) proteins are sequence-specific RNA-binding proteins that form a pervasive family of proteins conserved in yeast, plants, and humans. The plant PPR proteins are grouped mainly into the P and PLS classes. Here, we report the crystal structure of a PLS-class PPR protein from Arabidopsis thaliana called THA8L (THA8-like) at 2.0 Å. THA8L resembles THA8 (thylakoid assembly 8), a protein that is required for the splicing of specific group II introns of genes involved in biogenesis of chloroplast thylakoid membranes. The THA8L structure contains three P-type PPR motifs flanked by one L-type motif and one S-type motif. We identified several putative THA8L-binding sites, enriched with purine sequences, in the group II introns. Importantly, THA8L has strong binding preference for single-stranded RNA over single-stranded DNA or double-stranded RNA. Structural analysis revealed that THA8L contains two extensive patches of positively charged residues next to the residues that are proposed to comprise the RNA-binding codes. Mutations in these two positively charged patches greatly reduced THA8L RNA-binding activity. On the basis of these data, we constructed a model of THA8L-RNA binding that is dependent on two forces: one is the interaction between nucleotide bases and specific amino acids in the PPR motifs (codes), and the other is the interaction between the negatively charged RNA backbone and positively charged residues of PPR motifs. Together, these results further our understanding of the mechanism of PPR protein-RNA interactions.

Nanoscale Metal Particle Modified Single-Atom Catalyst: Synthesis, Characterization, and Application.

Single-atom catalysts (SACs) have attracted considerable attention in heterogeneous catalysis because of their well-defined active sites, maximum atomic utilization efficiency, and unique unsaturated coordinated structures. However, their effectiveness is limited to reactions requiring active sites containing multiple metal atoms. Furthermore, the loading amounts of single-atom sites must be restricted to prevent aggregation, which can adversely affect the catalytic performance despite the high activity of the individual atoms. The introduction of nanoscale metal particles (NMPs) into SACs (NMP-SACs) has proven to be an efficient approach for improving their catalytic performance. A comprehensive review is urgently needed to systematically introduce the synthesis, characterization, and application of NMP-SACs and the mechanisms behind their superior catalytic performance. This review first presents and classifies the different mechanisms through which NMPs enhance the performance of SACs. It then summarizes the currently reported synthetic strategies and state-of-the-art characterization techniques of NMP-SACs. Moreover, their application in electro/thermo/photocatalysis, and the reasons for their superior performance are discussed. Finally, the challenges and perspectives of NMP-SACs for the future design of advanced catalysts are addressed.