H1FOO-DD promotes efficiency and uniformity in reprogramming to naive pluripotency.

Heterogeneity among both primed and naive pluripotent stem cell lines remains a major unresolved problem. Here we show that expressing the maternal-specific linker histone H1FOO fused to a destabilizing domain (H1FOO-DD), together with OCT4, SOX2, KLF4, and LMYC, in human somatic cells improves the quality of reprogramming to both primed and naive pluripotency. H1FOO-DD expression was associated with altered chromatin accessibility around pluripotency genes and with suppression of the innate immune response. Notably, H1FOO-DD generates naive induced pluripotent stem cells with lower variation in transcriptome and methylome among clones and a more uniform and superior differentiation potency. Furthermore, we elucidated that upregulation of FKBP1A, driven by these five factors, plays a key role in H1FOO-DD-mediated reprogramming.

Improved Sendai viral system for reprogramming to naive pluripotency.

Naive human induced pluripotent stem cells (iPSCs) can be generated by reprogramming somatic cells with Sendai virus (SeV) vectors. However, only dermal fibroblasts have been successfully reprogrammed this way, and the process requires culture on feeder cells. Moreover, SeV vectors are highly persistent and inhibit subsequent differentiation of iPSCs. Here, we report a modified SeV vector system to generate transgene-free naive human iPSCs with superior differentiation potential. The modified method can be applied not only to fibroblasts but also to other somatic cell types. SeV vectors disappear quickly at early passages, and this approach enables the generation of naive iPSCs in a feeder-free culture. The naive iPSCs generated by this method show better differentiation to trilineage and extra-embryonic trophectoderm than those derived by conventional methods. This method can expand the application of iPSCs to research on early human development and regenerative medicine.

Simple derivation of skeletal muscle from human pluripotent stem cells using temperature-sensitive Sendai virus vector.

Human pluripotent stem cells have the potential to differentiate into various cell types including skeletal muscles (SkM), and they are applied to regenerative medicine or in vitro modelling for intractable diseases. A simple differentiation method is required for SkM cells to accelerate neuromuscular disease studies. Here, we established a simple method to convert human pluripotent stem cells into SkM cells by using temperature-sensitive Sendai virus (SeV) vector encoding myoblast determination protein 1 (SeV-Myod1), a myogenic master transcription factor. SeV-Myod1 treatment converted human embryonic stem cells (ESCs) into SkM cells, which expressed SkM markers including myosin heavy chain (MHC). We then removed the SeV vector by temporal treatment at a high temperature of 38℃, which also accelerated mesodermal differentiation, and found that SkM cells exhibited fibre-like morphology. Finally, after removal of the residual human ESCs by pluripotent stem cell-targeting delivery of cytotoxic compound, we generated SkM cells with 80% MHC positivity and responsiveness to electrical stimulation. This simple method for myogenic differentiation was applicable to human-induced pluripotent stem cells and will be beneficial for investigations of disease mechanisms and drug discovery in the future.

Generation of Motor Neurons from Human ESCs/iPSCs Using Sendai Virus Vectors.

Human motor neurons are important materials for the research of the pathogenesis and drug discovery of motor neuron diseases. Various methods to generate motor neurons (MNs) from embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs) by the addition of signaling molecules have been reported. However, they require multiple steps and complicated processes. Here we describe an approach for generating human MNs from ESCs/iPSCs using a single Sendai virus vector encoding three transcription factors-Lhx3, Ngn2, and Isl1. This approach enabled us to generate MNs in one step, adding Sendai virus vector in culture medium. This simple method significantly reduces the efforts to generate MNs, and it provides a useful tool for motor neuron disease research.

iPSC screening for drug repurposing identifies anti-RNA virus agents modulating host cell susceptibility.

Human pathogenic RNA viruses are threats to public health because they are prone to escaping the human immune system through mutations of genomic RNA, thereby causing local outbreaks and global pandemics of emerging or re-emerging viral diseases. While specific therapeutics and vaccines are being developed, a broad-spectrum therapeutic agent for RNA viruses would be beneficial for targeting newly emerging and mutated RNA viruses. In this study, we conducted a screen of repurposed drugs using Sendai virus (an RNA virus of the family Paramyxoviridae), with human-induced pluripotent stem cells (iPSCs) to explore existing drugs that may present anti-RNA viral activity. Selected hit compounds were evaluated for their efficacy against two important human pathogens: Ebola virus (EBOV) using Huh7 cells and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using Vero E6 cells. Selective estrogen receptor modulators (SERMs), including raloxifene, exhibited antiviral activities against EBOV and SARS-CoV-2. Pioglitazone, a PPARγ agonist, also exhibited antiviral activities against SARS-CoV-2, and both raloxifene and pioglitazone presented a synergistic antiviral effect. Finally, we demonstrated that SERMs blocked entry steps of SARS-CoV-2 into host cells. These findings suggest that the identified FDA-approved drugs can modulate host cell susceptibility against RNA viruses.

Isolation and propagation of enteric neural crest progenitor cells from mouse embryonic stem cells and embryos.

Neural crest is a source of diverse cell types, including the peripheral nervous system. The transcription factor Sox10 is expressed throughout early neural crest. We exploited Sox10 reporter and selection markers created by homologous recombination to investigate the generation, maintenance and expansion of neural crest progenitors. Sox10-GFP-positive cells are produced transiently from mouse embryonic stem (ES) cells by treatment with retinoic acid in combination with Fgf8b and the cytokine leukaemia inhibitory factor (Lif). We found that expression of Sox10 can be maintained using noggin, Wnt3a, Lif and endothelin (NWLE). ES cell-derived Sox10-GFP-positive cells cultured in NWLE exhibit molecular markers of neural crest progenitors. They differentiate into peripheral neurons in vitro and are able to colonise the enteric network in organotypic gut cultures. Neural crest cells purified from embryos using the Sox10 reporter also survive in NWLE, but progressively succumb to differentiation. We therefore applied selection to eliminate differentiating cells. Sox10-selected cells could be clonally expanded, cryopreserved, and multiplied for over 50 days in adherent culture. They remained neurogenic in vitro and in foetal gut grafts. Generation of neural crest from mouse ES cells opens a new route to the identification and validation of determination factors. Furthermore, the ability to propagate undifferentiated progenitors creates an opportunity for experimental dissection of the stimuli and molecular circu that govern neural crest lineage progression. Finally, the demonstration of robust enteric neurogenesis provides a system for investigating and modelling cell therapeutic approaches to neurocristopathies such as Hirschsprung's disease.

Promotion of reprogramming to ground state pluripotency by signal inhibition.

Induced pluripotent stem (iPS) cells are generated from somatic cells by genetic manipulation. Reprogramming entails multiple transgene integrations and occurs apparently stochastically in rare cells over many days. Tissue stem cells may be subject to less-stringent epigenetic restrictions than other cells and might therefore be more amenable to deprogramming. We report that brain-derived neural stem (NS) cells acquire undifferentiated morphology rapidly and at high frequency after a single round of transduction with reprogramming factors. However, critical attributes of true pluripotency--including stable expression of endogenous Oct4 and Nanog, epigenetic erasure of X chromosome silencing in female cells, and ability to colonise chimaeras--were not attained. We therefore applied molecularly defined conditions for the derivation and propagation of authentic pluripotent stem cells from embryos. We combined dual inhibition (2i) of mitogen-activated protein kinase signalling and glycogen synthase kinase-3 (GSK3) with the self-renewal cytokine leukaemia inhibitory factor (LIF). The 2i/LIF condition induced stable up-regulation of Oct4 and Nanog, reactivation of the X chromosome, transgene silencing, and competence for somatic and germline chimaerism. Using 2i /LIF, NS cell reprogramming required only 1-2 integrations of each transgene. Furthermore, transduction with Sox2 and c-Myc is dispensable, and Oct4 and Klf4 are sufficient to convert NS cells into chimaera-forming iPS cells. These findings demonstrate that somatic cell state influences requirements for reprogramming and delineate two phases in the process. The ability to capture pre-pluripotent cells that can advance to ground state pluripotency simply and with high efficiency opens a door to molecular dissection of this remarkable phenomenon.

Generation of osteoblasts and chondrocytes from embryonic stem cells.

The efficient generation of mesenchymal cells such as adipocytes, osteoblasts, and chondrocytes from embryonic stem cells is achieved by following sequential steps: embryoid body formation, retinoic acid (RA) treatment, and exposure to specific reagents for differentiation. RA treatment of embryoid bodies is critical for subsequent mesengenesis. Adipogenesis, osteogenesis, and chondrogenesis occur by culturing outgrowths for 2-3 wk with insulin/triiodothyronine, bone morphogenetic protein/dexamethasone-beta/glycerophosphate/ascorbic acid, and transforming growth factor-beta3/parathyroid hormone/1% fetal bovine serum, respectively. Emergence of these mesenchymal cells using a common initial procedure suggests that embryoid body formation and subsequent RA treatment results in the generation of a common progenitor for osteoblasts and chondrocytes.

Osteogenic and chondrogenic differentiation of embryonic stem cells in response to specific growth factors.

Reliable in vitro conversion of pluripotent embryonic stem (ES) cells into bone and cartilage-forming cells would expand opportunities for experimental investigations of skeletogenesis and could also provide new cellular sources for pharmaceutical screening and for cell therapy applications. Here, we evaluate the generation of mesenchymal cell lineages from mouse ES cells following treatment of embryoid bodies with retinoic acid, previously reported to induce development of adipocyte precursors. We find that retinoic acid reduces mesodermal differentiation but enhances expression of markers of neural crest, an alternative origin of mesenchymal elements. Runx1 and Ptprv appear to provide early markers of mesenchymal potential. Subsequently, different mesenchymal fates are generated in response to particular growth factors. Substitution of the adipogenic factors insulin and triiodothyronine with bone morphogenetic protein (BMP-4) results in suppression of adipogenesis and development of a mature osteogenic phenotype. In contrast, treatment with transforming growth factor-beta (TGF-beta3) promotes chondrogenic differentiation. Thus, the use of appropriate growth factors and culture milieu steers differentiation of ES cell-derived precursors into distinct mesenchymal compartments.

Overexpression of cadherins suppresses pulmonary metastasis of osteosarcoma in vivo.

Osteosarcoma by nature shows aggressive pulmonary metastasis; however, the underlying molecular mechanisms remain unclear. We previously showed that N-cadherin and cadherin-11 (OB-cadherin), which are highly expressed in normal osteoblasts, are anomalously expressed in human osteosarcoma (Kashima et al., Am J Pathol 1999;155:1549-55). In the present study, we examined the role of cadherins in osteosarcoma metastasis using the mouse osteosarcoma cell line Dunn and its highly metastatic subline LM8. Oligonucleotide array and RT-PCR analyses demonstrated that Dunn and LM8 cells did not express appreciable levels of several members of the cadherin family, and Western blot analysis confirmed that Dunn and LM8 cells did not express P-cadherin, E-cadherin, N-cadherin or cadherin-11 protein. We therefore investigated the functional consequences of cadherin overexpression on cell migration and in vivo metastatic potential of LM8 cells. Several LM8 clones were isolated which expressed exogenous N-cadherin and cadherin-11 localized to the cell membrane and able to bind to beta-catenin. Overexpression of N-cadherin or cadherin-11 in LM8 cells did not affect cell proliferation but caused an inhibitory effect on cell migration in vitro. In vivo analysis showed that N-cadherin- and cadherin-11-overexpressing cells exhibited a marked reduction in their ability to form pulmonary metastases, with significant decreases in lung weight and the number and weight of metastatic lesions, as well as the size and weight of primary lesions at the s.c.-inoculated site. These observations demonstrate that disruption of N-cadherin- and cadherin-11-mediated cell-cell adhesion is critical in the pulmonary metastasis of osteosarcoma.

Visualization of whole-mount skeletal expression patterns of LacZ reporters using a tissue clearing protocol.

Gene targeting or trapping constructs that utilize the lacZ gene encoding beta-galactosidase activity to trap promoter expression have become an increasingly important way to disrupt gene function and monitor gene expression. A number of genes targeted in this way have revealed both expected and unexpected developmental abnormalities of the skeleton. The use of X-gal staining to monitor gene expression in developing skeletal structures is hampered in these mutants because, during the critical latter stages of mouse embryonic development, visualization is hindered by the opacity of overlying soft tissue. Here, we report the development of a reliable method to clear exogenous tissue in late-stage embryos and neonates that still preserves skeletal X-gal staining patterns. This protocol reveals (i) specific cell staining in localized regions of developing bone and cartilage in two different genetic models and (ii) that the intensity of X-gal staining is consistent with the level of expression of lacZ. We conclude that this protocol accurately reflects both the specificity and intensity of expression and will facilitate the analysis of mouse skeletal development.