Stem cell-based models of early mammalian development

Zheng Y., Yan R.Z., Sun S., Kobayashi M., Xiang L., Yang R., Goedel A., Kang Y., Xue X., Esfahani S.N., Liu Y., Resto Irizarry A.M., Wu W., Li Y., Ji W., et. al.

Summary Despite its clinical and fundamental importance, our understanding of early human development remains limited. Stem cell-derived, embryo-like structures (or embryoids) allowing studies of early development without using natural embryos can potentially help fill the knowledge gap of human development. Herein, transcriptome at the single-cell level of a human embryoid model was profiled at different time points. Molecular maps of lineage diversifications from the pluripotent human epiblast toward the amniotic ectoderm, primitive streak/mesoderm, and primordial germ cells were constructed and compared with in vivo primate data. The comparative transcriptome analyses reveal a critical role of NODAL signaling in human mesoderm and primordial germ cell specification, which is further functionally validated. Through comparative transcriptome analyses and validations with human blastocysts and in vitro cultured cynomolgus embryos, we further proposed stringent criteria for distinguishing between human blastocyst trophectoderm and early amniotic ectoderm cells.

Tarazi S., Aguilera-Castrejon A., Joubran C., Ghanem N., Ashouokhi S., Roncato F., Wildschutz E., Haddad M., Oldak B., Gomez-Cesar E., Livnat N., Viukov S., Lokshtanov D., Naveh-Tassa S., Rose M., et. al.

SummaryIn vitro cultured stem cells with distinct developmental capacities can contribute to embryonic or extraembryonic tissues after microinjection into pre-implantation mammalian embryos. However, whether cultured stem cells can independently give rise to entire gastrulating embryo-like structures with embryonic and extraembryonic compartments remains unknown. Here, we adapt a recently established platform for prolonged ex utero growth of natural embryos to generate mouse post-gastrulation synthetic whole embryo models (sEmbryos), with both embryonic and extraembryonic compartments, starting solely from naive ESCs. This was achieved by co-aggregating non-transduced ESCs, with naive ESCs transiently expressing Cdx2 or Gata4 to promote their priming toward trophectoderm and primitive endoderm lineages, respectively. sEmbryos adequately accomplish gastrulation, advance through key developmental milestones, and develop organ progenitors within complex extraembryonic compartments similar to E8.5 stage mouse embryos. Our findings highlight the plastic potential of naive pluripotent cells to self-organize and functionally reconstitute and model the entire mammalian embryo beyond gastrulation.

Amadei G., Handford C.E., Qiu C., De Jonghe J., Greenfeld H., Tran M., Martin B.K., Chen D., Aguilera-Castrejon A., Hanna J.H., Elowitz M.B., Hollfelder F., Shendure J., Glover D.M., Zernicka-Goetz M.

Embryonic stem (ES) cells can undergo many aspects of mammalian embryogenesis in vitro1–5, but their developmental potential is substantially extended by interactions with extraembryonic stem cells, including trophoblast stem (TS) cells, extraembryonic endoderm stem (XEN) cells and inducible XEN (iXEN) cells6–11. Here we assembled stem cell-derived embryos in vitro from mouse ES cells, TS cells and iXEN cells and showed that they recapitulate the development of whole natural mouse embryo in utero up to day 8.5 post-fertilization. Our embryo model displays headfolds with defined forebrain and midbrain regions and develops a beating heart-like structure, a trunk comprising a neural tube and somites, a tail bud containing neuromesodermal progenitors, a gut tube, and primordial germ cells. This complete embryo model develops within an extraembryonic yolk sac that initiates blood island development. Notably, we demonstrate that the neurulating embryo model assembled from Pax6-knockout ES cells aggregated with wild-type TS cells and iXEN cells recapitulates the ventral domain expansion of the neural tube that occurs in natural, ubiquitous Pax6-knockout embryos. Thus, these complete embryoids are a powerful in vitro model for dissecting the roles of diverse cell lineages and genes in development. Our results demonstrate the self-organization ability of ES cells and two types of extraembryonic stem cells to reconstitute mammalian development through and beyond gastrulation to neurulation and early organogenesis. Synthetic mouse embryos assembled from embryonic stem cells, trophoblast stem cells and induced extraembryonic endoderm stem cells closely recapitulate the development of wild-type and mutant natural mouse embryos up to embryonic day 8.5.

Imamura S., Wen X., Terada S., Yamamoto A., Mutsuda-Zapater K., Sawada K., Yoshimoto K., Tanaka M., Kamei K.

AbstractArtificial human blastoids investigate fundamentals of early embryo development using in vitro models and study the pregnancy failures and birth deficiencies, previously hindered by the need for human embryos. Recent methods on generating blastoids used human naive pluripotent stem cells, which are prone to genomic instability during in vitro culturing. We introduce a simple, robust, and scalable method for generating human blastoids from more stable, human-primed, embryonic stem cells (hESC). Using a non-cell-adhesive hydrogel, hESC aggregates received the chemophysical cellular environment and formed an asymmetric blastoid structure with a cellular distribution similar to that of a human blastocyst. The obtained blastoids also demonstrated the capability of implantation in vitro. This model will allow studies on the underlying mechanisms of human pre- and post-implantation processes, leading to assisted reproductive technology.One-Sentence SummaryBlastoids were generated from human-primed embryonic stem cells using appropriate chemophysical extracellular environments.

Hu Y., Yang Y., Tan P., Zhang Y., Han M., Yu J., Zhang X., Jia Z., Wang D., Li Y., Ma T., Liu K., Ding S.

In mice, only the zygotes and blastomeres from 2-cell embryos are authentic totipotent stem cells (TotiSCs), capable of producing all the differentiated cells in both embryonic and extraembryonic tissues and forming an entire organism1. However, it remains challenging whether and how TotiSCs, representing the very beginning of a life, can be established in vitro in the absence of germline cells. Here, we demonstrate induction and long-term maintenance of TotiSCs from mouse pluripotent stem cells (PSCs) by a combination of three small molecules, TTNPB, 1-Azakenpaullone, and WS6. These cells, which we designated as ciTotiSCs (chemically induced totipotent stem cells), resembled mouse totipotent 2C-embryo stage cells at transcriptome, epigenome and metabolome level. In addition, ciTotiSCs exhibited bidirectional developmental potentials and were able to produce both embryonic and extraembryonic cells in vitro and in teratoma. Furthermore, following injection into 8-cell embryo, ciTotiSCs contributed to both embryonic and extraembryonic lineages with high efficiency. Our chemical approach for TotiSCs induction and maintenance provides a defined in vitro system to manipulate and understand totipotent state towards creating life from non-germline.

Bergmann S., Penfold C.A., Slatery E., Siriwardena D., Drummer C., Clark S., Strawbridge S.E., Kishimoto K., Vickers A., Tewary M., Kohler T.N., Hollfelder F., Reik W., Sasaki E., Behr R., et. al.

Gastrulation controls the emergence of cellular diversity and axis patterning in the early embryo. In mammals, this transformation is orchestrated by dynamic signalling centres at the interface of embryonic and extraembryonic tissues1–3. Elucidating the molecular framework of axis formation in vivo is fundamental for our understanding of human development4–6 and to advance stem-cell-based regenerative approaches7. Here we illuminate early gastrulation of marmoset embryos in utero using spatial transcriptomics and stem-cell-based embryo models. Gaussian process regression-based 3D transcriptomes delineate the emergence of the anterior visceral endoderm, which is hallmarked by conserved (HHEX, LEFTY2, LHX1) and primate-specific (POSTN, SDC4, FZD5) factors. WNT signalling spatially coordinates the formation of the primitive streak in the embryonic disc and is counteracted by SFRP1 and SFRP2 to sustain pluripotency in the anterior domain. Amnion specification occurs at the boundaries of the embryonic disc through ID1, ID2 and ID3 in response to BMP signalling, providing a developmental rationale for amnion differentiation of primate pluripotent stem cells (PSCs). Spatial identity mapping demonstrates that primed marmoset PSCs exhibit the highest similarity to the anterior embryonic disc, whereas naive PSCs resemble the preimplantation epiblast. Our 3D transcriptome models reveal the molecular code of lineage specification in the primate embryo and provide an in vivo reference to decipher human development. 3D transcriptomes reveal the molecular code of lineage specification in the primate embryo and provide an in vivo reference to decipher human development.

Simunovic M., Siggia E.D., Brivanlou A.H.

Our knowledge of the molecular mechanisms surrounding human embryo implantation and gastrulation is lacking, largely due to technical and ethical limitations of experimenting with human embryos. Alternatives to human embryos have been reported, in which 3D clusters of embryonic stem cells are differentiated in a stepwise manner to model aspects of human embryogenesis. Yet it remains challenging to model the events past attachment. We propose a strategy of modeling the post-attachment human embryo by assembling a pre-formed polarized epithelial epiblast and extraembryonic cells, allowing them to self-organize into a structure that mimics the dish-attached human embryo. The model attaches in vitro and, in the absence of exogenous morphogens, breaks anteroposterior symmetry, giving rise to early gastrulation cell types. Our assembloid approach enables in a modular way to upgrade or exchange extraembryonic tissues to access more advanced stages of post-attachment development while complying with ethical policies.

Olmsted Z.T., Paluh J.L.

SummaryMulti-lineage development from gastruloids is enabling unprecedented opportunities to model and study human embryonic processes and is expected to accelerate ex vivo strategies in organ development. Reproducing human cardiogenesis with neurogenesis in a multi-lineage context remains challenging, requiring spatiotemporal input of paracrine and mechanical cues. Here we extend elongating multi-lineage organized (EMLO) gastruloids to include cardiogenesis (EMLOC) and describe interconnected neuro-cardiac lineages in a single gastruloid model. Contractile EMLOCs recapitulate numerous interlinked developmental features including heart tube formation and specialization, cardiomyocyte differentiation and remodeling phases, epicardium, ventricular wall morphogenesis, chamber-like structures and formation of a putative outflow tract. The EMLOC cardiac region, which originates anterior to gut tube primordium, is progressively populated by neurons in a spatial pattern mirroring the known distribution of neurons in the innervated human heart. This human EMLOC model represents a multi-lineage advancement for the study of coincident neurogenesis and cardiogenesis.

Viukov S., Shani T., Bayerl J., Sheban D., Stelzer Y., Novershtern N., Hanna J.

SummaryCells of the trophoblast lineage constitute the major part of placental tissues in higher mammals. Recent derivation of human trophoblast stem cells (TSC) from placental cytotrophoblasts (CT) and from human naïve PSCs opens new opportunities for studying development and function of human placenta. Several recent reports have suggested that naïve human PSCs retain an exclusive potential to give rise to bona fide TSCs. Here we report that inhibition of TGFβ pathway and avoiding WNT stimulation, leads to direct and robust conversion of primed human pluripotent stem cells into TSCs. Systematic side by side comparative analysis showed that the latter are equivalent to previously derived TSC lines. Primed PSC derived TSC lines exhibit self-renewal, are able to differentiate into the main trophoblast lineages, and present RNA and epigenetic profiles that are indistinguishable from the TSC lines derived from placenta or naïve PSCs. Our findings underscore a residual plasticity in primed human PSCs that allows converting directly into pre-implantation extra-embryonic cell lineages.HighlightsPrimed human PSCs readily convert into TSCs upon inhibition of TGF pathwayCHIR inhibits conversion to TSC in primed but not in naive hPSCsPrimed human PSC derived TSCs line are indistinguishable from placental and naïve derived TSCsYAP is sufficient for TSC induction from hPSCs and necessary for TSC maintenance.

Yaman Y.I., Huang R., Ramanathan S.

SummaryAxial development of mammals is a dynamic process involving several coordinated morphogenetic events including axial elongation, somitogenesis, and neural tube formation. How different signals control the dynamics of human axial morphogenesis remains largely unknown. By inducing anteroposterior symmetry breaking of spatially coupled epithelial cysts derived from human pluripotent stem cells, we were able to generate hundreds of axially elongating organoids. Each organoid was composed of a neural tube flanked by presomitic mesoderm that was sequentially segmented into somites. Periodic activation of the somite differentiation gene MESP2 coincided in space and time with anteriorly traveling segmentation clock waves in the presomitic mesoderm of the organoids, recapitulating key aspects of somitogenesis. Through timed perturbations of organoids, we demonstrated that FGF and WNT signaling play distinct roles in axial elongation and somitogenesis, and that the segmentation clock waves are driven by FGF signaling gradients. By generating and perturbing organoids that robustly recapitulate the architecture and dynamics of multiple axial tissues in human embryos, this work offers a means to dissect complex mechanisms underlying human embryogenesis.

Miao Y., Djeffal Y., De Simone A., Zhu K., Silberfeld A., Lee J.G., Rao J., Tarazona O.A., Mongera A., Rigoni P., Diaz-Cuadros M., Song L.M., Di Talia S., Pourquié O.

AbstractThe body of vertebrates displays a segmental organization which is most conspicuous in the periodic organization of the vertebral column and peripheral nerves. This metameric organization is first implemented when somites, which contain the precursors of skeletal muscles and vertebrae, are rhythmically generated from the presomitic mesoderm (PSM). Somites then become subdivided into anterior and posterior compartments essential for vertebral formation and segmental patterning of the peripheral nervous system1–4. How this key somitic subdivision is established remains poorly understood. Here we introduce novel tridimensional culture systems of human pluripotent stem cells (PSCs), called Somitoids and Segmentoids, which can recapitulate the formation of epithelial somite-like structures with antero-posterior (AP) identity. Using these systems, we identified a key organizing function of the segmentation clock in converting temporal rhythmicity into the spatial regularity of anterior and posterior somitic compartments. We show that an initial salt-and-pepper expression pattern of the segmentation gene MESP2 in the newly formed segment is transformed into defined compartments of anterior and posterior identity via an active cell sorting mechanism. Moreover, we demonstrate a large degree of independence of the various patterning modules involved in somitogenesis including the segmentation clock, somite epithelialization and AP polarity patterning. Together we put forward a novel framework accounting for the symmetry breaking process initiating somite polarity patterning. Our work provides a valuable platform to decode general principles of somitogenesis and advance knowledge of human development.

Shao Y., Fu J.

Summary Embryoids and organoids hold great promise for human biology and medicine. Herein, we discuss conceptual and technological frameworks useful for developing high-fidelity embryoids and organoids that display tissue- and organ-level phenotypes and functions, which are critically needed for decoding developmental programs and improving translational applications. Through dissecting the layers of inputs controlling mammalian embryogenesis, we review recent progress in reconstructing multiscale structural orders in embryoids and organoids. Bioengineering tools useful for multiscale, multimodal structural engineering of tissue- and organ-level cellular organization and microenvironment are also discussed to present integrative, bioengineering-directed approaches to achieve next-generation, high-fidelity embryoids and organoids.

Xu Y., Zhao J., Ren Y., Wang X., Lyu Y., Xie B., Sun Y., Yuan X., Liu H., Yang W., Fu Y., Yu Y., Liu Y., Mu R., Li C., et. al.

It is challenging to derive totipotent stem cells in vitro that functionally and molecularly resemble cells from totipotent embryos. Here, we report that a chemical cocktail enables the derivation of totipotent-like stem cells, designated as totipotent potential stem (TPS) cells, from 2-cell mouse embryos and extended pluripotent stem cells, and that these TPS cells can be stably maintained long term in vitro. TPS cells shared features with 2-cell mouse embryos in terms of totipotency markers, transcriptome, chromatin accessibility and DNA methylation patterns. In vivo chimera formation assays show that these cells have embryonic and extraembryonic developmental potentials at the single-cell level. Moreover, TPS cells can be induced into blastocyst-like structures resembling preimplantation mouse blastocysts. Mechanistically, inhibition of HDAC1/2 and DOT1L activity and activation of RARγ signaling are important for inducing and maintaining totipotent features of TPS cells. Our study opens up a new path toward fully capturing totipotent stem cells in vitro.

Rostovskaya M., Andrews S., Reik W., Rugg-Gunn P.J.

In primates, the amnion emerges through cavitation of the epiblast during implantation, whereas in other species it does so later at gastrulation by the folding of the ectoderm. How the mechanisms of amniogenesis diversified during evolution remains unknown. Unexpectedly, single-cell analysis of primate embryos uncovered two transcriptionally and temporally distinct amniogenesis waves. To study this, we employed the naive-to-primed transition of human pluripotent stem cells (hPSCs) to model peri-implantation epiblast development. Partially primed hPSCs transiently gained the ability to differentiate into cavitating epithelium that transcriptionally and morphologically matched the early amnion, whereas fully primed hPSCs produced cells resembling the late amnion instead, thus recapitulating the two independent differentiation waves. The early wave follows a trophectoderm-like pathway and encompasses cavitation, whereas the late wave resembles an ectoderm-like route during gastrulation. The discovery of two independent waves explains how amniogenesis through cavitation could emerge during evolution via duplication of the pre-existing trophectoderm program.

Sanaki-Matsumiya M., Matsuda M., Gritti N., Nakaki F., Sharpe J., Trivedi V., Ebisuya M.

During embryonic development, epithelial cell blocks called somites are periodically formed according to the segmentation clock, becoming the foundation for the segmental pattern of the vertebral column. The process of somitogenesis has recently been recapitulated with murine and human pluripotent stem cells. However, an in vitro model for human somitogenesis coupled with the segmentation clock and epithelialization is still missing. Here, we report the generation of human somitoids, organoids that periodically form pairs of epithelial somite-like structures. Somitoids display clear oscillations of the segmentation clock that coincide with the segmentation of the presomitic mesoderm. The resulting somites show anterior-posterior and apical-basal polarities. Matrigel is essential for epithelialization but dispensable for the differentiation into somite cells. The size of somites is rather constant, irrespective of the initial cell number. The amount of WNT signaling instructs the proportion of mesodermal lineages in somitoids. Somitoids provide a novel platform to study human somitogenesis. Somitogenesis has been well characterized in model organisms, resulting in detailed description of the somite segmentation clock. Here they generate somitogenic organoids from human pluripotent stem cells that recapitulate somitogenesis, periodic segmentation, and proper polarity.

Korody M.L., Hildebrandt T.B.

The northern white rhinoceros (NWR) is functionally extinct, with only two nonreproductive females remaining. However, because of the foresight of scientists, cryopreserved cells and reproductive tissues may aid in the recovery of this species. An ambitious program of natural and artificial gametes and in vitro embryo generation was first outlined in 2015, and many of the proposed steps have been achieved. Multiple induced pluripotent stem cell lines have been established, primordial germ cell–like cells have been generated, oocytes have been collected from the remaining females, blastocysts have been cryopreserved, and the closely related southern white rhinoceros (SWR) is being established as a surrogate. Recently, the first successful embryo transfer in SWR demonstrated that embryos can be generated by in vitro fertilization and cryopreserved. We explore progress to date in using advanced cellular technologies to save the NWR and highlight the necessary next steps to ensure a viable population for reintroduction. We roll out a holistic rescue approach for a charismatic megavertebrate that includes the most advanced cellular technologies, which can provide a blueprint for other critically endangered mammals. We also provide a detailed discussion of the remaining questions in such an upgraded conservation program.

Oh D., Hong N., Eun K., Lee J., Cai L., Kim M., Choi H., Jawad A., Ham J., Park M.G., Kim B., Lee S.C., Moon C., Kim H., Hyun S.

AbstractMelanoma is a serious type of skin cancer that originates from melanocytes. Rodent melanoma models have provided valuable insights into melanoma pathology; however, they often lack applicability to humans owing to genetic, anatomical, physiological, and metabolic differences. Herein, we developed a transgenic porcine melanoma model that closely resembles humans via somatic cell nuclear transfer (SCNT). Our model features the conditional oncogenes cassettes, TP53R167H and human BRAFV600E, controlled by melanocyte-specific CreER recombinase. After SCNT, transgenic embryos developed normally, with the capacity to develop porcine embryonic stem cells. Seven transgenic piglets with oncogene cassettes were born through embryo transfer. We demonstrated that Cre recombination-mediated oncogene activation remarkably triggered the mitogen-activated protein kinase pathway in vitro. Notably, intradermal injection of 4-hydroxytamoxifen activated oncogene cassettes in vivo, resulting in melanocytic lesions resembling hyperpigmented nevi with increased proliferative properties similar to early human melanomas. This melanoma-inducing system, heritably transmitted to offspring, supports large-scale studies. The novel porcine model provides a valuable tool for elucidating melanoma development and metastasis mechanism, advancing translational medicine, and facilitating preclinical evaluation of new anticancer drugs.

Choi H.K., Moon S.

Xue X., Liu Y., Fu J.

Stem cell-based embryo models, which recapitulate symmetry breaking, pattern formation and tissue morphogenesis during early development, provide promising experimental tools to study the development of mammalian species, including humans. Despite considerable progress in embryo modelling using cultured stem cells, generating embryo models with high fidelity, efficiency, controllability, and in vivo-like cellular organization and tissue architecture remains challenging. This is largely due to intrinsic variabilities in self-organization and differentiation of mammalian stem cells in uncontrolled culture environments. In this Review, we argue that bioengineering tools, which are powerful for controlling topological boundaries and dynamic chemical and mechanical signals, can efficiently guide symmetry breaking, pattern formation, tissue morphogenesis and tissue–tissue interactions. We discuss pattern formation and morphogenesis during embryonic development and examine different embryo models to highlight the importance of bioengineering strategies in developing models with improved efficiency, reproducibility, controllability, complexity and in vivo relevance. Stem cell-based embryo models can recapitulate developmental processes such as tissue patterning and morphogenetic events from pre-implantation to early organogenesis. This Review discusses how bioengineering approaches can be used to generate more efficient, controllable, reproducible and scalable embryo models.

Zhi M., Gao D., Yao Y., Zhao Z., Wang Y., He P., Feng Z., Zhang J., Huang Z., Gu W., Zhao J., Zhang H., Wang S., Li X., Zhang Q., et. al.

The establishment of epiblast-derived pluripotent stem cells (PSCs) from cattle, which are important domestic animals that provide humans with milk and meat while also serving as bioreactors for producing valuable proteins, poses a challenge due to the unclear molecular signaling required for embryonic epiblast development and maintenance of PSC self-renewal. Here, we selected six key stages of bovine embryo development (E5, E6, E7, E10, E12, and E14) to track changes in pluripotency and the dependence on signaling pathways via modified single-cell transcription sequencing technology. The remarkable similarity of the gene expression patterns between cattle and pigs during embryonic lineage development contributed to the successful establishment of bovine epiblast stem cells (bEpiSCs) using 3i/LAF (WNTi, GSK3βi, SRCi, LIF, Activin A, and FGF2) culture system. The generated bEpiSCs exhibited consistent expression patterns of formative epiblast pluripotency genes and maintained clonal morphology, normal karyotypes, and proliferative capacity for more than 112 passages. Moreover, these cells exhibited high-efficiency teratoma formation as well as the ability to differentiate into various cell lineages. The potential of bEpiSCs for myogenic differentiation, primordial germ cell like cells (PGCLCs) induction, and as donor cells for cell nuclear transfer was also assessed, indicating their promise in advancing cell-cultured meat production, gene editing, and animal breeding.

Kim Y., Kim I., Shin K.

AbstractRecent discoveries in stem cell and developmental biology have introduced a new era marked by the generation of in vitro models that recapitulate early mammalian development, providing unprecedented opportunities for extensive research in embryogenesis. Here, we present an overview of current techniques that model early mammalian embryogenesis, specifically noting models created from stem cells derived from two significant species: Homo sapiens, for its high relevance, and Mus musculus, a historically common and technically advanced model organism. We aim to provide a holistic understanding of these in vitro models by tracing the historical background of the progress made in stem cell biology and discussing the fundamental underlying principles. At each developmental stage, we present corresponding in vitro models that recapitulate the in vivo embryo and further discuss how these models may be used to model diseases. Through a discussion of these models as well as their potential applications and future challenges, we hope to demonstrate how these innovative advances in stem cell research may be further developed to actualize a model to be used in clinical practice.

Rossant J., Fu J.

Scientists should carefully consider whether embryo models based on human stem cells are essential to their work because of the associated practical and ethical challenges. Scientists should carefully consider whether embryo models based on human stem cells are essential to their work because of the associated practical and ethical challenges.

Muter J., Lynch V.J., McCoy R.C., Brosens J.J.

ABSTRACT Embryo implantation in humans is interstitial, meaning the entire conceptus embeds in the endometrium before the placental trophoblast invades beyond the uterine mucosa into the underlying inner myometrium. Once implanted, embryo survival pivots on the transformation of the endometrium into an anti-inflammatory placental bed, termed decidua, under homeostatic control of uterine natural killer cells. Here, we examine the evolutionary context of embryo implantation and elaborate on uterine remodelling before and after conception in humans. We also discuss the interactions between the embryo and the decidualising endometrium that regulate interstitial implantation and determine embryo fitness. Together, this Review highlights the precarious but adaptable nature of the implantation process.

Ren Z., Ku T., Ren M., Liang J., Ning X., Xu H., Ren D., Zhou Q., Sang N.

The increasing production and extensive application of chemicals have led to their unintended release and contamination in the environment, posing a hazardous threat to wildlife and human health. Numerous studies have demonstrated that developmental toxicity could be induced by various emerging chemicals, causing abnormal embryonic and placental development, adverse pregnancy outcomes, obesity, and dysfunction of lipid metabolism in neonates. Given the currently-available experimental technology for developmental toxicological studies, an in vitro model based on stem cells showed promising performance in high-throughput screening of the early-stage developmental toxicity of emerging chemicals. In this review, the deleterious effects of environmental pollutants on stem cells were systemically assorted from the aspects of cytological dysfunction, self-renewal impairment, perturbation in embryoid body(EB) formation, and disruption of committed lineage differentiation. The toxicological data on the molecular level, including the altered expressions of gene and protein biomarkers, epigenomic regulation, and enhanced oxidative stress, were collected and summarized to provide the mechanism explanation for the link between environmental pollutant exposure and unfavorable phenotypes in stem cells. The advantage of the stem cell model in developmental toxicological studies was specifically emphasized. And the perspectives for stem cells were ultimately highlighted in the research field of environmental toxicology, especially developmental toxicology during the early stage of life.

Mihailovic S., Wolff S.C., Kedziora K.M., Smiddy N.M., Redick M.A., Wang Y., Lin G.K., Zikry T.M., Simon J., Ptacek T., Allbritton N.L., Beltran A.S., Purvis J.E.

SummaryThe human transcription factors OCT4, SOX2, and NANOG form a core signaling network critical for maintaining stem cell pluripotency and self-renewal potential. The spatiotemporal expression dynamics of these pluripotency factors throughout differentiation is unclear, limiting our understanding of stem cell fate decisions. Here, we combined CRISPR/Cas9-mediated gene editing with microraft array technology to generate human embryonic stem cell lines with endogenously tagged fluorophores for OCT4, SOX2, and NANOG. Fluorescence time-lapse imaging revealed that pluripotent stem cells show gastrulation-like patterning without direct chemical induction. Directed differentiation to the three primary germ layers—endoderm, mesoderm, and ectoderm—revealed distinct spatiotemporal patterns of SOX2 and NANOG expression in single cells. Finally, we captured dynamic changes in cell morphology during ectoderm differentiation corresponding to the formation of neural rosettes. This study provides a robust method for generating live-cell reporters in human stem cells and describes the single-cell dynamics of human pluripotency factors during differentiation.

Huch M., Gouti M.

ABSTRACT In June 2022, the second meeting on ‘Engineering Multicellular Systems’, organized by the European Molecular Biology Laboratory and the Institute of Bioengineering of Catalonia, took place in Barcelona. Stem cell and systems biologists, physicists and engineers from all over the world gathered to discuss how recent breakthroughs in organoid technologies, engineering and mechanobiology are boosting our understanding of early morphogenesis, organogenesis and organ function with applications in tissue engineering, disease modeling and drug screening. The meeting was organized with sustainability in mind, and included an ethics session and an outreach public activity.

Wells J.M.