Explore the vast range of titles available.

Nano-sized metal particles are attracting much interest in industrial and biomedical applications due to the recent progress and development of nanotechnology, and the surface-modifications by appropriate polymers are key techniques to stably express their characteristics. Herein, we applied cyclic poly(ethylene glycol) ( c -PEG), having no chemical inhomogeneity, to provide a polymer topology-dependent stabilization for the surface-modification of gold nanoparticles (AuNPs) through physisorption. By simply mixing c -PEG, but not linear counterparts, enables AuNPs to maintain dispersibility through freezing, lyophilization, or heating. Surprisingly, c -PEG endowed AuNPs with even better dispersion stability than thiolated PEG (HS–PEG–OMe). The stronger affinity of c -PEG was confirmed by DLS, ζ-potential, and FT-IR. Furthermore, the c -PEG system exhibited prolonged blood circulation and enhanced tumor accumulation in mice. Our data suggests that c -PEG induces physisorption on AuNPs, supplying sufficient stability toward bio-medical applications, and would be an alternative approach to the gold–sulfur chemisorption. Many nanoparticles are stabilised by chemical functionalisation with poly(ethylene glycol) (PEG). Here, the authors report on the functionalisation of gold nanoparticles by the physical absorption of cyclic PEG and demonstrate superior stabilisation against heating, freezing and lyophilisation.

The epiblast (EPI) is the origin of all somatic and germ cells in mammals, and of pluripotent stem cells in vitro . To explore the ontogeny of human and primate pluripotency, here we perform comprehensive single-cell RNA sequencing for pre- and post-implantation EPI development in cynomolgus monkeys ( Macaca fascicularis ). We show that after specification in the blastocysts, EPI from cynomolgus monkeys (cyEPI) undergoes major transcriptome changes on implantation. Thereafter, while generating gastrulating cells, cyEPI stably maintains its transcriptome over a week, retains a unique set of pluripotency genes and acquires properties for ‘neuron differentiation’. Human and monkey pluripotent stem cells show the highest similarity to post-implantation late cyEPI, which, despite co-existing with gastrulating cells, bears characteristics of pre-gastrulating mouse EPI and epiblast-like cells in vitro . These findings not only reveal the divergence and coherence of EPI development, but also identify a developmental coordinate of the spectrum of pluripotency among key species, providing a basis for better regulation of human pluripotency in vitro . Using a single-cell sequencing analysis in monkey embryos, and comparing the genes expressed during early development in this species with those in mice and in human pluripotent stem cells, the authors define characteristics of pluripotency ontogeny across mammalian species. Species differences in developing pluripotent stem cells Using a single-cell-sequencing-based analysis in monkey embryos, and comparing the genes expressed during early development in this species and what is known from mouse and human studies, Mitinori Saitou and colleagues define characteristics of pluripotency ontogeny across mammalian species. They show that, surprisingly, monkey cells undergoing neuronal differentiation continue to express genes associated with pluripotency during gastrulation. The analysis also provides insights into the comparative properties of developmental-stage pluripotent stem cells in key species that will help to establish a basis for better regulation of human pluripotency in vitro .

Human pluripotent stem cells (hPSCs) have been induced into human primordial germ cell–like cells (hPGCLCs) in vitro, the first step toward human in vitro gametogenesis. Yamashiro et al. went a step closer to generating mature gametes by culturing hPSCs with mouse embryonic ovarian somatic cells in xenogeneic reconstituted ovaries (see the Perspective by Gill and Peters). Over a period of 4 months, hPGCLCs underwent hallmark epigenetic reprogramming and differentiated progressively into cells closely resembling human oogonia, an immediate embryonic precursor for human oocytes. This study creates opportunities for human germ cell research and provides a foundation for human in vitro gametogenesis. Science , this issue p. 356 ; see also p. 291 Human primordial germ cell–like cells differentiate into oogonia in xenogeneic reconstituted ovaries in vitro. Human in vitro gametogenesis may transform reproductive medicine. Human pluripotent stem cells (hPSCs) have been induced into primordial germ cell–like cells (hPGCLCs); however, further differentiation to a mature germ cell has not been achieved. Here, we show that hPGCLCs differentiate progressively into oogonia-like cells during a long-term in vitro culture (approximately 4 months) in xenogeneic reconstituted ovaries with mouse embryonic ovarian somatic cells. The hPGCLC-derived oogonia display hallmarks of epigenetic reprogramming—genome-wide DNA demethylation, imprint erasure, and extinguishment of aberrant DNA methylation in hPSCs—and acquire an immediate precursory state for meiotic recombination. Furthermore, the inactive X chromosome shows a progressive demethylation and reactivation, albeit partially. These findings establish the germline competence of hPSCs and provide a critical step toward human in vitro gametogenesis.

De novo establishment of DNA methylation is accomplished by DNMT3A and DNMT3B. Here, we analyze de novo DNA methylation in mouse embryonic fibroblasts (2i-MEFs) derived from DNA-hypomethylated 2i/L ES cells with genetic ablation of Dnmt3a or Dnmt3b . We identify 355 and 333 uniquely unmethylated genes in Dnmt3a and Dnmt3b knockout (KO) 2i-MEFs, respectively. We find that Dnmt3a is exclusively required for de novo methylation at both TSS regions and gene bodies of Polycomb group (PcG) target developmental genes, while Dnmt3b has a dominant role on the X chromosome. Consistent with this, tissue-specific DNA methylation at PcG target genes is substantially reduced in Dnmt3a KO embryos. Finally, we find that human patients with DNMT3 mutations exhibit reduced DNA methylation at regions that are hypomethylated in Dnmt3 KO 2i-MEFs. In conclusion, here we report a set of unique de novo DNA methylation target sites for both DNMT3 enzymes during mammalian development that overlap with hypomethylated sites in human patients. De novo DNA methylation is carried out by DNMT3A and DNMT3B, but the distinct functions of these two enzymes is poorly understood. Here the authors present a comprehensive, genome-wide identification of target sites for de novo DNA methylation by the DNMT3A and DNMT3B in mouse ES cells and embryos, identifying unique de novo DNA methylation target sites for both DNMT3 enzymes.

Derivation of female mouse embryonic stem cells under certain conditions induces a loss of DNA methylation and erasure of genomic imprints, which are not recovered and that may contribute to observed impaired development. Stem cell development inhibitors MEK1/2 and GSK3β inhibitors enhance derivation of mouse embryonic stem cells (ES cells) in a ground state of pluripotency that closely resembles the inner cell mass of the pre-implantation embryo. However, the effect of long-term culture under these conditions on the developmental potential of ES cells is unclear. Yashuiro Yamada and colleagues show that derivation of female ES cells under these conditions induces a loss of DNA methylation and erasure of genomic imprints, which are not recovered following differentiation. In parallel, the authors show that 2i-ES cells have impaired embryonic and placental development. The group also develops a culture medium that preserves the genomic features of female 2i-ES cells. Elsewhere in this issue, Konrad Hochedlinger and colleagues also show how these culture conditions lead to detrimental changes in epigenetic features, genomic stability and in vivo developmental potential and suggest an alternative inhibitor that preserves the genomic integrity of the ES cells. Inhibitors of Mek1/2 and Gsk3β, known as 2i, enhance the derivation of embryonic stem (ES) cells and promote ground-state pluripotency in rodents 1 , 2 . Here we show that the derivation of female mouse ES cells in the presence of 2i and leukaemia inhibitory factor (2i/L ES cells) results in a widespread loss of DNA methylation, including a massive erasure of genomic imprints. Despite this global loss of DNA methylation, early-passage 2i/L ES cells efficiently differentiate into somatic cells, and this process requires genome-wide de novo DNA methylation. However, the majority of imprinting control regions (ICRs) remain unmethylated in 2i/L-ES-cell-derived differentiated cells. Consistently, 2i/L ES cells exhibit impaired autonomous embryonic and placental development by tetraploid embryo complementation or nuclear transplantation. We identified the derivation conditions of female ES cells that display 2i/L-ES-cell-like transcriptional signatures while preserving gamete-derived DNA methylation and autonomous developmental potential. Upon prolonged culture, however, female ES cells exhibited ICR demethylation regardless of culture conditions. Our results provide insights into the derivation of female ES cells reminiscent of the inner cell mass of preimplantation embryos.

Conjugated polymer nanoparticles (CP NPs) attract attention as nanoscale materials used for a variety of applications. In relation to this, the internal structure of CP NPs is an important factor for their properties, and numerous investigations have been carried out to control their nanomorphology. Here, we report the formation of CP NPs from defect-free cyclic poly(3-hexylthiophene) (c-P3HT) using a microfluidic device, and the effect of polymer topology on their structural and solvatochromic properties was investigated. CP NPs from c-P3HT exhibited reduced particle sizes and hypsochromic shifts in the absorption spectrum when compared to CP NPs obtained from corresponding linear P3HT (l-P3HT). Furthermore, steady responses in the solvatochromism of CP NPs from c-P3HT were observed, while those from l-P3HT displayed molecular weight dependency. These topology effects were caused by the change in the conjugation length, solubility, and crystallinity upon cyclization. Grazing incidence X-ray scattering (GIXS) studies of spin-coated P3HT films further showed a reduced interchain order and a larger proportion of face-on molecular orientation on a substrate for c-P3HTs. The various distinct structures observed for c-P3HT indicate the use of polymer topology as a means of nanostructure regulation.

Skeletal muscle stem cells (MuSCs), the major source for skeletal muscle regeneration in vertebrates, are in a state of cell cycle arrest in adult skeletal muscles. Prior evidence suggests that embryonic muscle progenitors proliferate and differentiate to form myofibres and also self-renew, implying that MuSCs, derived from these cells, acquire quiescence later during development. Depletion of Dicer in adult MuSCs promoted their exit from quiescence, suggesting microRNAs are involved in the maintenance of quiescence. Here we identified miR-195 and miR-497 that induce cell cycle arrest by targeting cell cycle genes, Cdc25 and Ccnd . Reduced expression of MyoD in juvenile MuSCs, as a result of overexpressed miR-195/497 or attenuated Cdc25/Ccnd, revealed an intimate link between quiescence and suppression of myogenesis in MuSCs. Transplantation of cultured MuSCs treated with miR-195/497 contributed more efficiently to regenerating muscles of dystrophin-deficient mice, indicating the potential utility of miR-195/497 for stem cell therapies. Skeletal muscle stem cells are in a state of cell cycle arrest in adult skeletal muscles and are stimulated to proliferate and differentiate in response to injury or pathology. Here the authors identify two microRNAs, miR-195 and miR-497, which induce cell cycle arrest in the stem cells and suppress myogenesis.

Epigenetic reprogramming resets parental epigenetic memories and differentiates primordial germ cells (PGCs) into mitotic pro-spermatogonia or oogonia. This process ensures sexually dimorphic germ cell development for totipotency 1 . In vitro reconstitution of epigenetic reprogramming in humans remains a fundamental challenge. Here we establish a strategy for inducing epigenetic reprogramming and differentiation of pluripotent stem-cell-derived human PGC-like cells (hPGCLCs) into mitotic pro-spermatogonia or oogonia, coupled with their extensive amplification (about >10 10 -fold). Bone morphogenetic protein (BMP) signalling is a key driver of these processes. BMP-driven hPGCLC differentiation involves attenuation of the MAPK (ERK) pathway and both de novo and maintenance DNA methyltransferase activities, which probably promote replication-coupled, passive DNA demethylation. hPGCLCs deficient in TET1, an active DNA demethylase abundant in human germ cells 2 , 3 , differentiate into extraembryonic cells, including amnion, with de-repression of key genes that bear bivalent promoters. These cells fail to fully activate genes vital for spermatogenesis and oogenesis, and their promoters remain methylated. Our study provides a framework for epigenetic reprogramming in humans and an important advance in human biology. Through the generation of abundant mitotic pro-spermatogonia and oogonia-like cells, our results also represent a milestone for human in vitro gametogenesis research and its potential translation into reproductive medicine. A new strategy that involves signalling-molecule-driven differentiation can induce epigenetic reprogramming of human pluripotent stem cell-derived primordial germ cell-like cells to pro-spermatogonia and oogonia-like cells with massive propagation and high efficiency.

Recently, several studies using cultures of human embryos together with single-cell RNA-seq analyses have revealed differences between humans and mice, necessitating the study of human embryos 1 – 8 . Despite the importance of human embryology, ethical and legal restrictions have limited post-implantation-stage studies. Thus, recent efforts have focused on developing in vitro self-organizing models using human stem cells 9 – 17 . Here, we report genetic and non-genetic approaches to generate authentic hypoblast cells (naive hPSC-derived hypoblast-like cells (nHyCs))—known to give rise to one of the two extraembryonic tissues essential for embryonic development—from naive human pluripotent stem cells (hPSCs). Our nHyCs spontaneously assemble with naive hPSCs to form a three-dimensional bilaminar structure (bilaminoids) with a pro-amniotic-like cavity. In the presence of additional naive hPSC-derived analogues of the second extraembryonic tissue, the trophectoderm, the efficiency of bilaminoid formation increases from 20% to 40%, and the epiblast within the bilaminoids continues to develop in response to trophectoderm-secreted IL-6. Furthermore, we show that bilaminoids robustly recapitulate the patterning of the anterior–posterior axis and the formation of cells reflecting the pregastrula stage, the emergence of which can be shaped by genetically manipulating the DKK1/OTX2 hypoblast-like domain. We have therefore successfully modelled and identified the mechanisms by which the two extraembryonic tissues efficiently guide the stage-specific growth and progression of the epiblast as it establishes the post-implantation landmarks of human embryogenesis. Authentic hypoblast cells created from naive human pluripotent stem cells (hPSCs) spontaneously assemble with naive hPSCs to form a three-dimensional bilaminar structure (bilaminoids) with a pro-amniotic-like cavity.

The structure of written texts is analyzed by focusing on word sequences. As a method, word sequences in texts are transformed into rank sequences of the occurrence frequency of each word and return maps are drawn. The features of word sequences are extracted by comparing with the surrogate data, i.e., a sequence in which all the words are randomly rearranged. A total of 140 written texts consisting of ten languages are selected for analysis. To characterize the distribution in the return map quantitatively, two characteristic quantities are defined, the distance between the original distribution and surrogate distribution, and the correlation coefficient of the adjacent word ranks. The results show that there is a negative correlation in the rank of adjacent words in almost all languages, and features of return maps of the same language texts are similar. A clustering structure which implies the relation to language (sub)family is observed. A mathematical model is proposed for reproducing features of the return map for multiple languages. The numerical simulations achieve results similar to those of the real data quantitatively. GraphicAbstract