Delayed fluorescence from inverted singlet and triplet excited states.

Hund's multiplicity rule states that a higher spin state has a lower energy for a given electronic configuration1. Rephrasing this rule for molecular excited states predicts a positive energy gap between spin-singlet and spin-triplet excited states, as has been consistent with numerous experimental observations over almost a century. Here we report a fluorescent molecule that disobeys Hund's rule and has a negative singlet-triplet energy gap of -11 ± 2 meV. The energy inversion of the singlet and triplet excited states results in delayed fluorescence with short time constants of 0.2 µs, which anomalously decrease with decreasing temperature owing to the emissive singlet character of the lowest-energy excited state. Organic light-emitting diodes (OLEDs) using this molecule exhibited a fast transient electroluminescence decay with a peak external quantum efficiency of 17%, demonstrating its potential implications for optoelectronic devices, including displays, lighting and lasers.

Population structure and adaptability analysis of Schizothorax o'connori based on whole-genome resequencing.

BACKGROUND: Schizothorax o'connori is an endemic fish distributed in the upper and lower reaches of the Yarlung Zangbo River in China. It has experienced a fourth round of whole gene replication events and is a good model for exploring the genetic differentiation and environmental adaptability of fish in the Qinghai-Tibet Plateau. The uplift of the Qinghai-Tibet Plateau has led to changes in the river system, thereby affecting gene exchange and population differentiation between fish populations. With the release of fish whole genome data, whole genome resequencing has been widely used in genetic evolutionary analysis and screening of selected genes in fish, which can better elucidate the genetic basis and molecular environmental adaptation mechanisms of fish. Therefore, our purpose of this study was to understand the population structure and adaptive characteristics of S. o'connori using the whole-genome resequencing method. RESULTS: The results showed that 23,602,746 SNPs were identified from seven populations, mostly distributed on chromosomes 2 and 23. There was no significant genetic differentiation between the populations, and the genetic diversity was relatively low. However, the Zangga population could be separated from the Bomi, Linzhi, and Milin populations in the cluster analysis. Based on historical dynamics analysis of the population, the size of the ancestral population of S. o'connori was affected by the late accelerated uplift of the Qinghai Tibet Plateau and the Fourth Glacial Age. The selected sites were mostly enriched in pathways related to DNA repair and energy metabolism. CONCLUSION: Overall, the whole-genome resequencing analysis provides valuable insights into the population structure and adaptive characteristics of S. o'connori. There was no obvious genetic differentiation at the genome level between the S. o'connori populations upstream and downstream of the Yarlung Zangbo River. The current distribution pattern and genetic diversity are influenced by the late accelerated uplift of the Qinghai Tibet Plateau and the Fourth Ice Age. The selected sites of S. o'connori are enriched in the energy metabolism and DNA repair pathways to adapt to the low temperature and strong ultraviolet radiation environment at high altitude.

Modifying electronic and optical properties of violet phosphorus through variable fluorine coverage.

We present a comprehensive investigation of the electronic properties of fluorinated monolayer violet phosphorus using first-principles calculations. Our results reveal a strong dependence of the electronic properties on the different fluorine coverages of fluorination. As the fluorine coverage increases, monolayer violet phosphorus undergoes a significant transition from a wide direct bandgap semiconductor to a narrow indirect bandgap semiconductor. Moreover, both semi-fluorinated and fully fluorinated monolayer violet phosphorus exhibit advantageous semiconducting characteristics, with a tunable bandgap of 0.50 ~ 1.04 eV under biaxial strain ranging from -6% to 6%. Notably, the fully fluorinated monolayer violet phosphorus demonstrates a higher coefficient of light absorption within the visible range. Therefore, our findings highlight the tunability of monolayer violet phosphorus properties through the absorption of various fluorine coverages, providing valuable insights for the design and development of novel semiconductor devices based on this material.

Large valley splitting induced by spin-orbit coupling effects in monolayer W2NSCl.

Two-dimensional (2D) valley materials are promising materials for writing and storing information. The search for 2D materials with large valley splitting is essential for the development of spintronics and valley electronics. In this study, we theoretically design 2D W2NSCl MXenes with large valley splitting based on first-principle calculations. Due to the strong spin-orbit coupling (SOC) and the broken inversion symmetry, the W2NSCl monolayer exhibits valley splitting values of 491 meV and 83 meV at K/K' of the valence and conduction bands, respectively. The valley splitting of W2NSCl is robust to biaxial strain. Because of the broken mirror symmetry of W2NSCl, there is a Rashba effect at Γ with a Rashba parameter of 1.019 V Å. Based on the maximum localization of the Wannier function, we found the non-zero Berry curvature at K/K'. Furthermore, the non-zero Berry curvature at the K/K' valley increases monotonically with an external strain from -4% to 4%. Our finding shows that W2NSCl is a candidate material for valley electronics and spintronics applications.

Plasmon-modulated bistable second-harmonic generation in a nonlinear microcavity coupled to a metallic nanoparticle.

Multiple nonlinear effects with second-harmonic (SH) generation and optical bistability (OB) are highly desired but rather rare due to insufficient intrinsic nonlinearity in most nonlinear media. Here, a nonlinear microcavity coupled to a metallic nanoparticle (MNP) is suggested to realize the bistable SH generation. When two counterpropagating driving fields are injected into the cavity, a traditional SH pathway is constructed via the two-photon process of fundamental-harmonic (FH) photons. In addition, we report the coexistence between the SH and OB effects under the condition that the strong excitation and the detuning management for the driving fields boost system nonlinear responses. In the presence of a control field toward the MNP, our calculation finds that the traditional and plasmon-induced SH pathways in the present system allow enhancing the SH conversion efficiency and reducing the OB thresholds simultaneously. With the control field intensity increasing, a linear growth rate for the SH efficiency maximum is achieved. Furthermore, the relative phase between the driving and control fields has profound effects on modulating the bistable SH efficiency, the bistable interval and the thresholds.

Theoretical prediction of valley spin splitting in two-dimensional Janus MSiGeZ4 (M = Cr and W; Z = N, P, and As).

With the exploration of valleytronic materials in MA2Z4 structures, larger valley spin splitting has become a hot topic of research. Based on first-principles calculations, we predicted six valleytronic 2D (two-dimensional) Janus MSiGeZ4 (M = Cr and W; Z = N, P, and As) materials. The valley spin splitting value of WSiGeZ4 (Z = N, P, and As) can reach more than 400 meV, which is favorable for the practical application of valleytronics. Two-dimensional WSiGeZ4 (Z = N, P, and As) materials are dynamically and mechanically stable and have an abundance of electronic properties. The two-dimensional Janus WSiGeZ4 (Z = N, P, and As) structures comprise both direct and indirect bandgap semiconductor materials. Among them, WSiGeN4 is an indirect bandgap semiconductor material with a bandgap of 1.654 eV and WSiGeP4 is a direct bandgap semiconductor material. The valley spin splitting originates from the symmetry breaking of the material structure and the spin-orbit coupling effect of the transition metal, which is manifested as the Berry curvature. In particular, the Berry curvature of 2D Janus WSiGeP4 and WSiGeAs4 is as high as 300 Bohr2, which is quite large. The W atom has more d-orbital electrons than the Cr atom, and the SOC (spin-orbit coupling) effect is stronger; thus, the valley spin splitting value CrSiGeZ4 of WSiGeZ4 is more than 300 meV, which is quite large. In addition, the bandgap and valley spin splitting of WSiGeZ4 (Z = N, P, and As) can be significantly modulated by applying a biaxial strain. Our study shows that WSiGeZ4 (Z = N, P, and As) has great potential for valleytronic applications.

Computational Design of Multiple Resonance-Type BN Molecules for Inverted Singlet and Triplet Excited States.

A computational design of linearly extended multiple resonance (MR)-type BN molecules based on DABNA-1 is proposed herein in the quest to find potential candidates that exhibit a negative singlet-triplet gap (ΔEST) and a large oscillator strength value. The impact of a proper account of the electron correlation in the lowest singlet and triplet excited states is systematically investigated by using double-hybrid functionals within the TD-DFT framework, as well as wavefunction-based methods (EOM-CCSD and SCS-CC2), since this contribution plays an essential role in driving the magnitude of the ΔEST in MR-TADF and inverted singlet-triplet gap compounds. Our results point out a gradual reduction of the ΔEST gap with respect to the increasing sum of the number of B and N atoms, reaching negative ΔEST values for some molecules as a function of their size. The double-hybrid functionals reproduce the gap with only slight deviation compared to available experimental data for DABNA-1, ν-DABNA, and mDBCz and nicely agree with high-level quantum mechanical methods (e.g., EOM-CCSD and SCS-CC2). Larger oscillator strengths are found compared to the azaphenalene-type molecules, also exhibiting the inversion of their singlet and triplet excited states. We hope this study can serve as a motivation for further design of the molecules showing negative ΔEST based on boron- and nitrogen-doped polyaromatic hydrocarbons.

Organotin mixtures reveal interactions that modulate adipogenic differentiation in 3T3-L1 preadipocytes.

Organotin chemicals (butyltins and phenyltins) are the most widely used organometallic chemicals worldwide and are used in industrial applications, such as biocides and anti-fouling paints. Tributyltin (TBT) and more recently, dibutyltin (DBT) and triphenyltin (TPT) have been reported to stimulate adipogenic differentiation. Although these chemicals co-exist in the environment, their effect in combination remains unknown. We first investigated the adipogenic effect of eight organotin chemicals (monobutyltin (MBT), DBT, TBT, tetrabutyltin (TeBT), monophenyltin (MPT), diphenyltin (DPT), TPT, and tin chloride (SnCl4)) in the 3T3-L1 preadipocyte cell line in single exposures at two doses (10 and 50 ng/ml). Only three out of the eight organotins induced adipogenic differentiation with TBT eliciting the strongest adipogenic differentiation (in a dose-dependent manner) followed by TPT and DBT, as demonstrated by lipid accumulation and gene expression. We then hypothesized that, in combination (TBT, DBT, and TPT), adipogenic effects will be exacerbated compared to single exposures. However, at the higher dose (50 ng/ml), TBT-induced differentiation was reduced by TPT and DBT when in dual or triple combination. We tested whether TPT or DBT would interfere with adipogenic differentiation stimulated by a peroxisome proliferator-activated receptor (PPARγ) agonist (rosiglitazone) or a glucocorticoid receptor agonist (dexamethasone). Both DBT50 and TPT50 reduced rosiglitazone-, but not dexamethasone-stimulated adipogenic differentiation. In conclusion, DBT and TPT interfere with TBT's adipogenic differentiation possibly via PPARγ signaling. These findings highlight the antagonistic effects among organotins and the need to understand the effects and mechanism of action of complex organotin mixtures on adipogenic outcomes.

Study of Interference Detection of Rail Transit Wireless Communication System Based on Fourth-Order Cyclic Cumulant.

The wireless communication system is used to provide dispatching, control, communication and other services for rail transit operations. In practice, interference from other wireless communication systems will affect the normal operation of trains, so it is an urgent problem to study the interference detection algorithms for rail transit applications. In this paper, the fourth-order cyclic cumulant (FOCC) of signals with different modulation modes is analyzed for the narrow-band wireless communications system of rail transit. Based on the analysis results, an adjacent-frequency interference detection algorithm is proposed according to the FOCC of the received signal within the predetermined cyclic frequency range. To detect interference with the same carrier frequency, a same-frequency interference detection algorithm using the relationship between the FOCC and the received power is proposed. The performance of the proposed detection algorithms in terms of correct rate and computational complexity is analyzed and compared with the traditional second-order statistical methods. Simulation results show that when an interference signal coexists with the expected signal, the correct rates of the adjacent-frequency and the same-frequency interference detection algorithms are greater than 90% when the signal-to-noise ratio (SNR) is higher than 2 dB and -4 dB, respectively. Under the practical rail transit wireless channel with multipath propagation and the Doppler effect, the correct rates of the adjacent-frequency and the same-frequency interference detection algorithms are greater than 90% when the SNR is higher than 3 dB and 7 dB, respectively. Compared with the existing second-order statistical methods, the proposed method can detect both the adjacent-frequency and the same-frequency interference when the interference signals coexist with the expected signal. Although the computational complexity of the proposed method is increased, it is acceptable in the application of rail transit wireless communication interference detection.

FoxH1 Represses the Promoter Activity of cyp19a1a in the Ricefield Eel (Monopterus albus).

Forkhead box H1 (FoxH1) is a sexually dimorphic gene in Oreochromis niloticus, Oplegnathus fasciatus, and Acanthopagrus latus, indicating that it is essential for gonadal development. In the present study, the molecular characteristics and potential function of FoxH1 and the activation of the cyp19a1a promoter in vitro were evaluated in Monopterus albus. The levels of foxh1 in the ovaries were three times higher than those in the testes and were regulated by gonadotropins (Follicle-Stimulating Hormone and Human Chorionic Gonadotropin). FoxH1 colocalized with Cyp19a1a in the oocytes and granulosa cells of middle and late vitellogenic follicles. In addition, three FoxH1 binding sites were identified in the proximal promoter of cyp19a1a, namely, FH1 (-871/-860), FH2 (-535/-524), and FH3 (-218/-207). FoxH1 overexpression significantly attenuated the activity of the cyp19a1a promoter in CHO cells, and FH1/2 mutation increased promoter activity. Taken together, these results suggest that FoxH1 may act as an important regulator in the ovarian development of M. albus by repressing cyp19a1a promoter activity, which provides a foundation for the study of FoxH1 function in bony fish reproductive processes.

Ferroelectric polarization effect on the photocatalytic activity of Bi0.9Ca0.1FeO3/CdS S-scheme nanocomposites.

BiFeO3 (BFO), as a kind of narrow band-gap semiconductor material, has gradually emerged advantages in the application of photocatalysis. In this paper, Ca doped BFO nanoparticles Bi0.9Ca0.1FeO3 (BCFO) were prepared by sol-gel method. And BCFO and CdS nanocomposites with two morphologies were obtained by controlling the time of loading CdS under a low temperature liquid phase process. It is found that the band gap becomes narrower after doping Ca into BFO, which is conducive to the absorption of visible light. Among all the samples, the composite of CdS nanowires and BCFO nanoparticles obtained by reaction time of 10 min has the best photocatalytic performance. The degradation rate of Methyl Orange solution was 94% after 90 min under visible light irradiation, which was much higher than that of pure BCFO and CdS. Furthermore, significant enhancement in the degradation rate (100% degradation in 60 min) can be achieved in poled samples after electric polarization process. The highest degradation rate is due to the promoted separation of photogenerated carriers induced by the internal polarization field and the formation of S-scheme heterostructure between BCFO and CdS. Such BCFO-CdS nanocomposites may bring new insights into designing highly efficient photocatalyst.

Identification, characterization and functional analysis of gonadal long noncoding RNAs in a protogynous hermaphroditic teleost fish, the ricefield eel (Monopterus albus).

BACKGROUND: An increasing number of long noncoding RNAs (lncRNAs) have been found to play important roles in sex differentiation and gonad development by regulating gene expression at the epigenetic, transcriptional and posttranscriptional levels. The ricefield eel, Monopterus albus, is a protogynous hermaphroditic fish that undergoes a sequential sex change from female to male. However, the roles of lncRNA in the sex change is unclear. RESULTS: Herein, we performed RNA sequencing to analyse lncRNA expression patterns in five different stages of M. albus development to investigate the roles of lncRNAs in the sex change process. A total of 12,746 lncRNAs (1503 known lncRNAs and 11,243 new lncRNAs) and 2901 differentially expressed lncRNAs (DE-lncRNAs) were identified in the gonads. The target genes of the DE-lncRNAs included foxo1, foxm1, smad3, foxr1, camk4, ar and tgfb3, which were mainly enriched in signalling pathways related to gonadal development, such as the insulin signalling pathway, MAPK signalling pathway, and calcium signalling pathway. We selected 5 highly expressed DE-lncRNAs (LOC109952131, LOC109953466, LOC109954337, LOC109954360 and LOC109958454) for full length amplification and expression pattern verification. They were all expressed at higher levels in ovaries and intersex gonads than in testes, and exhibited specific time-dependent expression in ovarian tissue incubated with follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG). The results of quantitative real-time PCR (qRT-PCR) analysis and a dual-luciferase assay showed that znf207, as the gene targeted by LOC109958454, was expressed in multiple tissues and gonadal developmental stages of M. albus, and its expression was also inhibited by the hormones FSH and hCG. CONCLUSIONS: These results provide new insights into the role of lncRNAs in gonad development, especially regarding natural sex changes in fish, which will be useful for enhancing our understanding of sequential hermaphroditism and sex changes in the ricefield eel (M. albus) and other teleosts.

The organotin triphenyltin disrupts cholesterol signaling in mammalian ovarian steroidogenic cells through a combination of LXR and RXR modulation.

Organotins, a chemical family with over 30 congeners to which humans are directly exposed to through food consumption, are a chemical class widely used as stabilizers in polyvinyl chloride, and biocides in antifouling products. Aside from tributyltin (TBT), toxicological information on other organotin congeners, such as triphenyltin (TPT), remains scarce. Our previous work has demonstrated that TBT can interfere with cholesterol trafficking in steroidogenic cells. Given their structural similarities, we hypothesized that TPT, similar to TBT, disrupts intracellular cholesterol transport and impairs steroidogenesis in ovarian theca cells. To test this, human and ovine primary ovarian theca cells were isolated, purified and exposed to TPT at environmentally relevant doses (1 or 10 ng/ml) in pre-luteinized (48 h exposure) or luteinizing cells (72 h exposure). Intracellular cholesterol levels, progesterone, and testosterone secretion and gene expression of nuclear receptors, cholesterol transporters, and steroidogenic enzymes were evaluated. In ovine cells, TPT upregulated StAR, ABCA1, and SREBF1 mRNA and ABCA1 protein in both pre-luteinized and luteinized stages. TPT did not alter intracellular cholesterol or testosterone synthesis, but upregulated progesterone production. Inhibitor and shRNA knockdown approaches were then used to evaluate the role of retinoid X receptor (RXR) and liver X receptor (LXR) on TPT's effects. TPT upregulated ABCA1 and StAR expression was blocked by both LXR and RXR antagonists. TPT's effect on ABCA1 expression was reduced in LXRß and RXRß knockdown theca cells. Similar findings were obtained with primary human theca cells. No synergistic effect of TBT and TPT was observed. In conclusion, at an environmentally relevant dose, TPT upregulates theca cell cholesterol transporter ABCA1 expression via RXR and LXR pathways. Similar effects of TPT on human and sheep theca cells supports its conserved mechanism across mammalian theca cells.

Pressure effects on the anomalous thermal transport and anharmonic lattice dynamics of CsX (X = Cl, Br, and I).

The lattice thermal conductivity of CsX (X = Cl, Br, and I) and its pressure dependence are investigated using first-principles third-order anharmonic force constants. Contrary to the expectation that compounds with heavier atoms usually exhibit lower lattice thermal conductivity (kL), the kL of CsI is higher than those of CsCl and CsBr. This anomalous behavior is examined by analyzing the group velocity, phonon lifetime, three-phonon scattering phase space and Grüneisen parameters. The higher kL of CsI can be attributed to its longer phonon lifetimes due to weaker absorption processes in the range of 1 ∼ 2.1 THz. It is found that the lattice thermal conductivity of CsI is more sensitive to hydrostatic pressure, and the kL of CsI becomes lower than those of CsCl and CsBr at -2 GPa due to the shorter phonon lifetimes and the smaller group velocities. Moreover, the changes in the bulk modulus and Bader charge of CsX are also discussed to provide further insight into its anomalous thermal behavior.

Prediction of a new two-dimensional valleytronic semiconductor MoGe2P4 with large valley spin splitting.

Recently, MoSi2N4 with large valley spin splitting was experimentally synthesized. However, materials with large valley spin splitting are still rare. We predict a new two-dimensional (2D) MoGe2P4 material. It has large valley spin splitting and excellent optical absorption properties. The results show that 2D MoGe2P4 is a direct semiconductor with a bandgap of 887 meV. Its valley spin splitting (ΔV) at the top of the valence band is 153 meV because of the inversion symmetry breaking and spin-orbit coupling (SOC). 2D MoGe2P4 transforms from a semiconductor to a metal under a biaxial strain of 6%. ΔV increases monotonically from 137 meV to 157 meV under biaxial strain. In addition, the lowest exciton state of 2D MoGe2P4 is near 770 nm, and the optical absorption coefficient in the ultraviolet range is higher than that of MoS2. Our results suggest that 2D MoGe2P4 has excellent potential for applications in valley electronics and optoelectronic devices.

Tunable magnetoelectric coupling and electrical features in an ultrathin Cr2Si2Te6/In2Se3 heterostructure.

Two-dimensional (2D) van der Waals (vdW) heterostructures based on multiferroic materials have potential applications in novel low-dimensional spintronic devices. In this work, we have investigated a strong magnetoelectric coupling and electrical dependence between single layer (1L) Cr2Si2Te6 and In2Se3. By switching the direction of ferroelectric polarization in In2Se3, we observed a significant magneto-crystalline anisotropy energy (MAE) enhancement of Cr2Si2Te6. The analysis of the spin-resolved orbital-decomposed band structure shows stronger magnetoelectric coupling between the In2Se3 and Cr2Si2Te6 layers. The modulation of the electrical features could also be achieved in the switching of the ferroelectric polarization. Furthermore, the switching of Ohmic-Schottky contacts in the heterojunction with different polarization states was successfully achieved under the effect of strain engineering. Based on these findings, we design a novel 2D ferroelectric-ferromagnetic heterojunction that exploits the controllability and nonvolatility of ferroelectrics to modulate the electrical properties of the device. These findings indicate the high application potential of Cr2Si2Te6/In2Se3 multiferroic heterojunctions in spintronics.

Spin-Orbit Torque Nano-oscillators by Dipole-Field-Localized Spin Wave Modes.

We demonstrate a high-quality spin-orbit torque nano-oscillator comprised of spin wave modes confined by the magnetic field by the strongly inhomogeneous dipole field of a nearby micromagnet. This approach enables variable spatial confinement and systematic tuning of magnon spectrum and spectral separations for studying the impact of multimode interactions on auto-oscillations. We find these dipole-field-localized spin wave modes exhibit good characteristic properties as auto-oscillators─narrow line width and large amplitude─while persisting up to room temperature. We find that the line width of the lowest-lying localized mode is approximately proportional to temperature in good agreement with theoretical analysis of the impact of thermal fluctuations. This demonstration of a clean oscillator with tunable properties provides a powerful tool for understanding the fundamental limitations and line width contributions to improve future spin-Hall oscillators.

Bisphenol S Impairs Invasion and Proliferation of Extravillous Trophoblasts Cells by Interfering with Epidermal Growth Factor Receptor Signaling.

The placenta supports fetal growth and is vulnerable to exogenous chemical exposures. We have previously demonstrated that exposure to the emerging chemical bisphenol S (BPS) can alter placental endocrine function. Mechanistically, we have demonstrated that BPS interferes with epidermal growth factor receptor (EGFR) signaling, reducing placenta cell fusion. Extravillous trophoblasts (EVTs), a placenta cell type that aids with vascular remodeling, require EGF to invade into the maternal endometrium. We hypothesized that BPS would impair EGF-mediated invasion and proliferation in EVTs. Using human EVTs (HTR-8/SVneo cells), we tested whether BPS could inhibit the EGF response by blocking EGFR activation. We also evaluated functional endpoints of EGFR signaling, including EGF endocytosis, cell invasion and proliferation, and endovascular differentiation. We demonstrated that BPS blocked EGF-induced phosphorylation of EGFR by acting as a competitive antagonist to EGFR. Transwell assay and a three-dimensional microfluidic chip invasion assay revealed that BPS exposure can block EGF-mediated cell invasion. BPS also blocked EGF-mediated proliferation and endovascular differentiation. In conclusion, BPS can prevent EGF-mediated EVT proliferation and invasion through EGFR antagonism. Given the role of EGFR in trophoblast proliferation and differentiation during placental development, our findings suggest that maternal exposure to BPS may contribute to placental dysfunction via EGFR-mediated mechanisms.

Cyt-C Mediated Mitochondrial Pathway Plays an Important Role in Oocyte Apoptosis in Ricefield Eel (Monopterus albus).

Apoptosis plays a key role in the effective removal of excessive and defective germ cells, which is essential for sequential hermaphroditism and sex change in vertebrates. The ricefield eel, Monopterus albus is a protogynous hermaphroditic fish that undergoes a sequential sex change from female to male. Previous studies have demonstrated that apoptosis is involved in sex change in M. albus. However, the apoptotic signaling pathway is unclear. In the current study, we explored the underlying mechanism of apoptosis during gonadal development and focused on the role of the mitochondrial apoptosis signaling pathway in sex change in M. albus. Flow cytometry was performed to detect apoptosis in gonads at five sexual stages and ovary tissues exposed to hydrogen peroxide (H2O2) in vitro. Then the expression patterns of key genes and proteins in the mitochondrial pathway, death receptor pathway and endoplasmic reticulum (ER) pathway were examined. The results showed that the apoptosis rate was significantly increased in the early intersexual stage and then decreased with the natural sex change from female to male. Quantitative real-time PCR revealed that bax, tnfr1, and calpain were mainly expressed in the five stages. ELISA demonstrated that the relative content of cytochrome-c (cyt-c) in the mitochondrial pathway was significantly higher than that of caspase8 and caspase12, with a peak in the early intersexual stage, while the levels of caspase8 and caspase12 peaked in the late intersexual stage. Interestingly, the Pearson's coefficient between cyt-c and the apoptosis rate was 0.705, which suggests that these factors are closely related during the gonadal development of M. albus. Furthermore, the cyt-c signal was found to be increased in the intersexual stage by immunohistochemistry. After incubation with H2O2, the mRNA expression of mitochondrial pathway molecules such as bax, apaf-1, and caspase3 increased in ovary tissues. In conclusion, the present results suggest that the mitochondrial apoptotic pathway may play a more important role than the other apoptotic pathways in sex change in M. albus.

Expression Patterns and Gonadotropin Regulation of the TGF-ß II Receptor (Bmpr2) during Ovarian Development in the Ricefield Eel Monopterus albus.

Bmpr2 plays a central role in the regulation of reproductive development in mammals, but its role during ovarian development in fish is still unclear. To ascertain the function of bmpr2 in ovarian development in the ricefield eel, we isolated and characterized the bmpr2 cDNA sequence; the localization of Bmpr2 protein was determined by immunohistochemical staining; and the expression patterns of bmpr2 in ovarian tissue incubated with FSH and hCG in vitro were analyzed. The full-length bmpr2 cDNA was 3311 bp, with 1061 amino acids encoded. Compared to other tissues, bmpr2 was abundantly expressed in the ovary and highly expressed in the early yolk accumulation (EV) stages of the ovary. In addition, a positive signal for Bmpr2 was detected in the cytoplasm of oocytes in primary growth (PG) and EV stages. In vitro, the expression level of gdf9, the ligand of bmpr2, in the 10 ng/mL FSH treatment group was significantly higher after incubation for 4 h than after incubation for different durations. However, bmpr2 expression in the 10 ng/mL FSH treatment group at 2 h, 4 h and 10 h was significantly lower. Importantly, the expression level of bmpr2 and gdf9 in the 100 IU/mL hCG group had similar changes that were significantly decreased at 4 h and 10 h. In summary, Bmpr2 might play a pivotal role in ovarian growth in the ricefield eel, and these results provide a better understanding of the function of bmpr2 in ovarian development and the basic data for further exploration of the regulatory mechanism of gdf9 in oocyte development.