The transcriptional activator Klf5 recruits p300-mediated H3K27ac for maintaining trophoblast stem cell pluripotency.

The effective proliferation and differentiation of trophoblast stem cells (TSCs) is indispensable for the development of the placenta, which is the key to maintaining normal fetal growth during pregnancy. Kruppel-like factor 5 (Klf5) is implicated in the activation of pluripotency gene expression in embryonic stem cells (ESCs), yet its function in TSCs is poorly understood. Here, we showed that Klf5 knockdown resulted in the downregulation of core TSC-specific genes, consequently causing rapid differentiation of TSCs. Consistently, Klf5-depleted embryos lost the ability to establish TSCs in vitro. At the molecular level, Klf5 preferentially occupied the proximal promoter regions and maintained an open chromatin architecture of key TSC-specific genes. Deprivation of Klf5 impaired the enrichment of p300, a major histone acetyl transferase of H3 lysine 27 acetylation (H3K27ac), and further reduced the occupancy of H3K27ac at promoter regions, leading to decreased transcriptional activity of TSC pluripotency genes. Thus, our findings highlight a novel mechanism of Klf5 in regulating the self-renewal and differentiation of TSCs and provide a reference for understanding placental development and improving pregnancy rates.

Epsilon-near-zero gratings for polarization selectivity.

Zero-index materials have emerged as a topic of significant scientific interest in recent years. In this Letter, we investigate the electromagnetic properties of epsilon-near-zero (ENZ) gratings composed of materials with near-zero effective permittivity. Our study reveals that ENZ gratings exhibit a unique polarization selectivity that is opposite to that observed in perfect conductor gratings. Furthermore, we demonstrate that hybrid gratings combining perfect conductors and ENZ materials can block omnidirectional electromagnetic waves of any polarization. In addition, we propose a practical design of the ENZ and hybrid gratings based on dielectric ENZ MMs, exhibiting excellent polarization selectivity and blocking effect. Our research presents a promising approach for the flexible manipulation of polarizations using ENZ gratings.

Broadband binary-reflection-phase metasurfaces with undistorted transmission wavefront via mirror symmetry.

In this work, we report the realization of broadband binary-reflection-phase metasurfaces that simultaneously exhibit undistorted transmission wavefront. Such a unique functionality is bestowed by leveraging mirror symmetry in the metasurface design. Under the normal incidence of waves polarized along the mirror surface, a broadband binary-phase pattern with π phase difference is induced in the cross-polarized reflection, while the co-polarized transmission and reflection are unaffected by the binary-phase pattern. Consequently, the cross-polarized reflection can be flexibly manipulated by designing the binary-phase pattern, without distorting the wavefront in transmission. The phenomena of reflected-beam splitting and undistorted transmission wavefront are hereby experimentally validated in a broad bandwidth from 8 GHz to 13 GHz. Our findings reveal a unique mechanism to realize independent manipulation of reflection with undistorted transmission wavefront in a broad spectrum, which has potential implications in meta-domes and reconfigurable intelligent surfaces.

Selective autophagic degradation of ACLY (ATP citrate lyase) maintains citrate homeostasis and promotes oocyte maturation.

Macroautophagy/autophagy is a cellular and energy homeostatic mechanism that contributes to maintain the number of primordial follicles, germ cell survival, and anti-ovarian aging. However, it remains unknown whether autophagy in granulosa cells affects oocyte maturation. Here, we show a clear tendency of reduced autophagy level in human granulosa cells from women of advanced maternal age, implying a potential negative correlation between autophagy levels and oocyte quality. We therefore established a co-culture system and show that either pharmacological inhibition or genetic ablation of autophagy in granulosa cells negatively affect oocyte quality and fertilization ability. Moreover, our metabolomics analysis indicates that the adverse impact of autophagy impairment on oocyte quality is mediated by downregulated citrate levels, while exogenous supplementation of citrate can significantly restore the oocyte maturation. Mechanistically, we found that ACLY (ATP citrate lyase), which is a crucial enzyme catalyzing the cleavage of citrate, was preferentially associated with K63-linked ubiquitin chains and recognized by the autophagy receptor protein SQSTM1/p62 for selective autophagic degradation. In human follicles, the autophagy level in granulosa cells was downregulated with maternal aging, accompanied by decreased citrate in the follicular fluid, implying a potential correlation between citrate metabolism and oocyte quality. We also show that elevated citrate levels in porcine follicular fluid promote oocyte maturation. Collectively, our data reveal that autophagy in granulosa cells is a beneficial mechanism to maintain a certain degree of citrate by selectively targeting ACLY during oocyte maturation.Abbreviations: 3-MA: 3-methyladenine; ACLY: ATP citrate lyase; AMA: advanced maternal age; CG: cortical granule; CHX: cycloheximide; CQ: chloroquine; CS: citrate synthase; COCs: cumulus-oocyte-complexes; GCM: granulosa cell monolayer; GV: germinal vesicle; MII: metaphase II stage of meiosis; PB1: first polar body; ROS: reactive oxygen species; shRNA: small hairpin RNA; SQSTM1/p62: sequestosome 1; TCA: tricarboxylic acid; TOMM20/TOM20: translocase of outer mitochondrial membrane 20; UBA: ubiquitin-associated domain; Ub: ubiquitin; WT: wild-type.

Hierarchical Accumulation of Histone Variant H2A.Z Regulates Transcriptional States and Histone Modifications in Early Mammalian Embryos.

Early embryos undergo extensive epigenetic reprogramming to achieve gamete-to-embryo transition, which involves the loading and removal of histone variant H2A.Z on chromatin. However, how does H2A.Z regulate gene expression and histone modifications during preimplantation development remains unrevealed. Here, by using ultra-low-input native chromatin immunoprecipitation and sequencing, the genome-wide distribution of H2A.Z is delineated in mouse oocytes and early embryos. These landscapes indicate that paternal H2A.Z is removed upon fertilization, followed by unbiased accumulation on parental genomes during zygotic genome activation (ZGA). Remarkably, H2A.Z exhibits hierarchical accumulation as different peak types at promoters: promoters with double H2A.Z peaks are colocalized with H3K4me3 and indicate transcriptional activation; promoters with a single H2A.Z peak are more likely to occupy bivalent marks (H3K4me3+H3K27me3) and indicate development gene suppression; promoters with no H2A.Z accumulation exhibit persisting gene silencing in early embryos. Moreover, H2A.Z depletion changes the enrichment of histone modifications and RNA polymerase II binding at promoters, resulting in abnormal gene expression and developmental arrest during lineage commitment. Furthermore, similar transcription and accumulation patterns between mouse and porcine embryos indicate that a dual role of H2A.Z in regulating the epigenome required for proper gene expression is conserved during mammalian preimplantation development.

ATG7-mediated autophagy facilitates embryonic stem cell exit from naive pluripotency and marks commitment to differentiation.

Macroautophagy/autophagy is a conserved cellular mechanism to degrade unneeded cytoplasmic proteins and organelles to recycle their components, and it is critical for embryonic stem cell (ESC) self-renewal and somatic cell reprogramming. Whereas autophagy is essential for early development of embryos, no information exists regarding its functions during the transition from naive-to-primed pluripotency. Here, by using an in vitro transition model of ESCs to epiblast-like cells (EpiLCs), we find that dynamic changes in ATG7-dependent autophagy are critical for the naive-to-primed transition, and are also necessary for germline specification. RNA-seq and ATAC-seq profiling reveal that NANOG acts as a barrier to prevent pluripotency transition, and autophagy-dependent NANOG degradation is important for dismantling the naive pluripotency expression program through decommissioning of naive-associated active enhancers. Mechanistically, we found that autophagy receptor protein SQSTM1/p62 translocated into the nucleus during the pluripotency transition period and is preferentially associated with K63 ubiquitinated NANOG for selective protein degradation. In vivo, loss of autophagy by ATG7 depletion disrupts peri-implantation development and causes increased chromatin association of NANOG, which affects neuronal differentiation by competitively binding to OTX2-specific neuroectodermal development-associated regions. Taken together, our findings reveal that autophagy-dependent degradation of NANOG plays a critical role in regulating exit from the naive state and marks distinct cell fate allocation during lineage specification.Abbreviations: 3-MA: 3-methyladenine; EpiLC: epiblast-like cell; ESC: embryonic stem cell; PGC: primordial germ cell.

Defective chromatin architectures in embryonic stem cells derived from somatic cell nuclear transfer impair their differentiation potentials.

Nuclear transfer embryonic stem cells (ntESCs) hold enormous promise for individual-specific regenerative medicine. However, the chromatin states of ntESCs remain poorly characterized. In this study, we employed ATAC-seq and Hi-C techniques to explore the chromatin accessibility and three-dimensional (3D) genome organization of ntESCs. The results show that the chromatin accessibility and genome structures of somatic cells are re-arranged to ESC-like states overall in ntESCs, including compartments, topologically associating domains (TADs) and chromatin loops. However, compared to fertilized ESCs (fESCs), ntESCs show some abnormal openness and structures that have not been reprogrammed completely, which impair the differentiation potential of ntESCs. The histone modification H3K9me3 may be involved in abnormal structures in ntESCs, including incorrect compartment switches and incomplete TAD rebuilding. Moreover, ntESCs and iPSCs show high similarity in 3D genome structures, while a few differences are detected due to different somatic cell origins and reprogramming mechanisms. Through systematic analyses, our study provides a global view of chromatin accessibility and 3D genome organization in ntESCs, which can further facilitate the understanding of the similarities and differences between ntESCs and fESCs.

TDG is a pig-specific epigenetic regulator with insensitivity to H3K9 and H3K27 demethylation in nuclear transfer embryos.

Pig cloning by somatic cell nuclear transfer (SCNT) frequently undergoes incomplete epigenetic remodeling during the maternal-to-zygotic transition, which leads to a significant embryonic loss before implantation. Here, we generated the first genome-wide landscapes of histone methylation in pig SCNT embryos. Excessive H3K9me3 and H3K27me3, but not H3K4me3, were observed in the genomic regions with unfaithful embryonic genome activation and donor-cell-specific gene silencing. A combination of H3K9 demethylase KDM4A and GSK126, an inhibitor of H3K27me3 writer, were able to remove these epigenetic barriers and restore the global transcriptome in SCNT embryos. More importantly, thymine DNA glycosylase (TDG) was defined as a pig-specific epigenetic regulator for nuclear reprogramming, which was not reactivated by H3K9me3 and H3K27me3 removal. Both combined treatment and transient TDG overexpression promoted DNA demethylation and enhanced the blastocyst-forming rates of SCNT embryos, thus offering valuable methods to increase the cloning efficiency of genome-edited pigs for agricultural and biomedical purposes.

Derivation of feeder-free human extended pluripotent stem cells.

Human extended pluripotent stem cells (EPSCs), with bidirectional chimeric ability to contribute to both embryonic and extraembryonic lineages, can be obtained and maintained by converting conventional pluripotent stem cells using chemicals. However, the transition system is based on inactivated mouse fibroblasts, and the underlying mechanism is not clear. Here we report a Matrigel-based feeder-free method to convert human embryonic stem cells and induced pluripotent stem cells into EPSCs and demonstrate the extended pluripotency in terms of molecular features, chimeric ability, and transcriptome. We further identify chemicals targeting glycolysis and histone methyltransferase to facilitate the conversion to and maintenance of feeder-free EPSCs. Altogether, our data not only establish a feeder-free system to generate human EPSCs, which should facilitate the mechanistic studies of extended pluripotency and further applications, but also provide additional insights into the transitions among different pluripotent states.

An Experimental Investigation of Steel Surface Topography Transfer by Cold Rolling.

Automobile and household appliance panels require steel strips with extremely high-quality surfaces. Therefore, an in-depth study of the surface topography transfer of the steel strip during the rolling process is of considerable significance for improving product quality. In this study, the scale-invariant feature transform (SIFT) algorithm is used to realize the large-field stitching and the correspondence measurement of the surface topography of the roll and strip. The surface topography transfer mechanism and microconvex change law during cold rolling are revealed. Further analysis is conducted regarding the effects of different reduction rates and the initial surface topography of the roll on the formation of strip surface topography. Experimental results reveal that the furrow phenomenon occurs during the rolling process owing to the backward slip effect but is eliminated by the elastoplastic deformation of the matrix and the forward slip action. No furrow occurred along the width direction of the strip. With an increase in the rolling reduction rate, the transfer rate increases, and the strip surface topography is closer to the roll surface topography. Under the same rolling roughness condition and a small reduction rate (5%), the transfer degree increases remarkably with a rise in the reduction rate and increases slowly as the reduction rate continues to grow (from 7% to 10%). This study serves as a theoretical basis for the subsequent improvement of the surface quality of cold rolled strips.

Induction of autophagy promotes porcine parthenogenetic embryo development under low oxygen conditions.

Autophagy plays an important role in embryo development; however, only limited information is available on how autophagy specifically regulates embryo development, especially under low oxygen culture conditions. In this study we used parthenogenetic activation (PA) of porcine embryos to test the hypothesis that a low oxygen concentration (5%) could promote porcine embryo development by activating autophagy. Immunofluorescence staining revealed that low oxygen tension activated autophagy and alleviated oxidative stress in porcine PA embryos. Development was significantly affected when autophagy was blocked by 3-methyladenine, even under low oxygen culture conditions, with increased reactive oxygen species levels and malondialdehyde content. Furthermore, the decreased expression of pluripotency-associated genes induced by autophagy inhibition could be recovered by treatment with the antioxidant vitamin C. Together, these results demonstrate that low oxygen-induced autophagy regulates embryo development through antioxidant mechanisms in the pig.

Resveratrol delays postovulatory aging of mouse oocytes through activating mitophagy.

Resveratrol (3,5,4'-trihydroxystilbene, RSV) is a natural potential anti-aging polyphenolic compound frequently used as a nutritional supplement against several diseases. However, the underlying mechanisms by which resveratrol regulates postovulatory aging of oocytes are still insufficiently known. In this study, we found that resveratrol could delay postovulatory aging and improve developmental competence of oocytes through activating selective mitophagy in the mouse. Resveratrol could maintain spindle morphology but it disturbed cortical granule (CG) distribution during oocyte aging. This might be due to upregulated mitophagy, since blocking mitophagy by cyclosporin A (CsA) treatment affected oocyte quality by damaging mitochondrial function and it decreased embryonic development. In addition, we also observed an involvement of FoxO3a in regulating mitophagy in aging oocytes following resveratrol treatment. Taken together, our results provide evidence that mitophagy induced by resveratrol is a potential mechanism to protect against postovulatory oocyte aging.