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A mechanism for 1,4-Benzoquinone-induced genotoxicity.

Benzene is a common environmental toxin and its metabolite, 1-4-Benzoquinone (BQ) causes hematopoietic cancers like myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). BQ has not been comprehensively assessed for its impact on genome maintenance, limiting our understanding of the true health risks associated with benzene exposure and our ability to identify people with increased sensitivity to this genotoxin. Here we analyze the impact BQ exposure has on wild type and DNA repair-defective mouse embryonic stem (ES) cells and wild type human cells. We find that double strand break (DSB) repair and replication fork maintenance pathways including homologous recombination (HR) and Fanconi anemia (FA) suppress BQ toxicity. BQ-induced damage efficiently stalls replication forks, yet poorly induces ATR/DNA-PKCS responses. Furthermore, the pattern of BQ-induced γH2AX and 53BP1foci is consistent with the formation of poly(ADP-ribose) polymerase 1 (PARP1)-stabilized regressed replication forks. At a biochemical level, BQ inhibited topoisomerase 1 (topo1)-mediated DNA ligation and nicking in vitro; thus providing mechanism for the cellular phenotype. These data are consistent with a model that proposes BQ interferes with type I topoisomerase's ability to maintain replication fork restart and progression leading to chromosomal instability that has the potential to cause hematopoietic cancers like MDS and AML.

Animals

Glycolytic activity instructs germ layer proportions through regulation of Nodal and Wnt signaling.

Metabolic pathways can influence cell fate decisions, yet their regulative role during embryonic development remains poorly understood. Here, we demonstrate an instructive role of glycolytic activity in regulating signaling pathways involved in mesoderm and endoderm specification. Using a mouse embryonic stem cell (mESC)-based in vitro model for gastrulation, we found that glycolysis inhibition increases ectodermal cell fates at the expense of mesodermal and endodermal lineages. We demonstrate that this relationship is dose dependent, enabling metabolic control of germ layer proportions through exogenous glucose levels. We further show that glycolysis acts as an upstream regulator of Nodal and Wnt signaling and that its influence on cell fate specification can be decoupled from its effects on growth. Finally, we confirm the generality of our findings using a human gastrulation model. Our work underscores the dependence of signaling pathways on metabolic conditions and provides mechanistic insight into the nutritional regulation of cell fate decision-making.

Glycolysis

Dual-patterned pluripotent stem cells self-organize into a human embryo model with extended anterior-posterior patterning.

Human gastruloids are a powerful class of stem cell-derived models that recapitulate key features of early embryonic development, including symmetry breaking and the emergence of three germ layers1-3. However, they lack anterior embryonic structures and coordinated axial organization4-6. To address this limitation, we pre-patterned human pluripotent stem cells (hPSCs) by exposing them to either anterior (FGF2) or posterior (CHIR99021 [CHIR] & retinoic acid [RA]) cues. Upon mixing, these dual-patterned hPSCs interacted and self-organized into elongated structures with both anterior and posterior features-which we term anterior-posterior (AP) human gastruloids. Anteriorly pre-treated cells robustly intercalated into posteriorly pre-treated cells, collectively giving rise to a continuum of neural tissues-including a brain-like domain, a neural tube-like structure, and neuro-mesodermal progenitors (NMPs)-with segmented somites arrayed bilaterally. Single cell RNA sequencing (scRNA-seq) revealed that human AP gastruloids contain cell types resembling the midbrain-hindbrain boundary (MHB), regionalized hindbrain structures (i .e. rhombomeres 1-8), regionalized neural crest (i.e. cranial, vagal, trunk)7,8 and head mesoderm. Transcriptomic comparisons to primate embryos revealed that human AP gastruloids most closely resemble Carnegie stage 11 (CS11) embryos. While they lack a notochord and full dorsal-ventral polarity, human AP gastruloids recapitulate key spatial and temporal features of early neurulation and somitogenesis. Perturbation of folic acid metabolism or rho-associated kinase (ROCK) signaling induced spinal cord defects, phenocopying aspects of spina bifida and other neural tube defects, highlighting this model's potential for studying congenital disorders9. AP gastruloids may serve as a simple, robust, scalable platform for modeling coordinated human AP body axis development. More broadly, our results suggest that controlled interactions between differentially prepatterned progenitors can initiate self-organization of complex body axis features. The "pattern-and-mix" strategy may serve as a generalizable framework for assembling spatially organized stem cell models of mammalian development.

Journal Article

Lentiviral Transduction of Embryonic Stem Cells.

Lentiviral vectors provide an efficient and reliable method for stable gene knockdown in embryonic stem cells (ESCs) through RNA interference. Here, we describe a detailed protocol for lentiviral transduction of mouse ESCs using lentiviral shRNA expression vectors. The protocol encompasses lentiviral particle production in HEK-293T packaging cells, determination of viral titer, transduction of ESCs cultured under feeder-free conditions, and selection of stably transduced cells. Additionally, we describe methods for evaluating transduction efficiency using fluorescence microscopy and flow cytometry, as well as for assessing gene knockdown efficacy by quantitative real-time PCR (Q-RT-PCR). This protocol is suitable for functional genomic studies in pluripotent stem cells and can be adapted for other difficult-to-transfect cell types.

Lentivirus

Decoding bipotency: a transient regulatory state bridging totipotency and lineage commitment.

Early mammalian embryogenesis entails a coordinated transition from totipotency to the first lineage bifurcation, giving rise to embryonic lineages and the extra-embryonic trophectoderm. The mechanisms by which totipotency is resolved into lineage-primed states remain incompletely understood. Emerging evidence supports a non-binary model in which cells traverse a continuum of potency states, passing through a transient bipotent intermediate that retains both embryonic and extra-embryonic potential while exiting totipotency. Here, we synthesize recent advances in the mechanisms that establish, maintain, and resolve bipotency. We emphasize the coordinated roles of transposable elements, transcription factors, and signaling pathways in regulating this transition. We also highlight newly developed bipotent stem cell models and their implications in generating advanced embryo models in vitro. Notably, current insights are largely derived from mouse systems; given key differences between mouse and human early embryogenesis, extending these findings to human models remains a critical next step.

Animals

Integrator promotes the association of TFIID and RNA polymerase II to maintain pluripotency during development.

The mechanisms by which the expression of pluripotency and Polycomb networks are harmonized to allow the transition from pluripotency to a differentiated state have not been fully elucidated. Integrator complex regulates transcription pause release and RNA processing in metazoans. We show that Integrator is required for stemness and plays a critical role as early as day 2 in embryonic development. While the catalytic endonuclease activity enhances cellular reprogramming, Integrator recruits RNA polymerase II (RNAPII) to promoters and super enhancers of pluripotency and Polycomb genes. Integrator coordinates expression of pluripotency and Polycomb networks by fostering the association of RNAPII and basal transcription factors. We pinpoint a critical role for TATA-binding protein-associated factors (TAFs) in Integrator entry into the preinitiation complex. Taken together, beyond its role in RNAPII pause release, Integrator recruitment of RNAPII ensures an orderly cellular differentiation during development.

RNA Polymerase II

Genome-wide chromatin recording resolves dynamic cell state changes.

Understanding how the chromatin state of a cell influences its future behavior is a major challenge throughout biology. However, most chromatin profiling methods are limited to endpoint assays. Here, we present LagTag, a method for recovery of earlier and endpoint chromatin states in the same mammalian cells. In this approach, transient activity of bacterial adenine methyltransferase fusions records the DNA-binding profiles of chromatin-associated proteins of interest at earlier time points. Subsequent tagmentation and sequencing recover the earlier chromatin profile from adenine methylation profiles, alongside endpoint profiles of endogenous chromatin-associated proteins. We verified that LagTag profiles aligned with those from established methods in mouse and human cells. We then applied LagTag to record and recover dynamic chromatin state transitions during mouse embryonic stem cell differentiation, capturing transcriptional signatures from pre- and post-differentiation time points within the same cell population. LagTag thus provides a foundation for temporally resolved chromatin profiling. A record of this paper's transparent peer review process is included in the supplemental information.

chromatin organization

Genome-wide chromatin recording resolves dynamic cell state changes.

Understanding how the chromatin state of a cell influences its future behavior is a major challenge throughout biology. However, most chromatin profiling methods are limited to endpoint assays. Here, we present LagTag, a method for recovery of earlier and endpoint chromatin states in the same mammalian cells. In this approach, transient expression of bacterial adenine methyltransferase fusions records the DNA binding profiles of chromatin-associated proteins of interest at earlier timepoints. Subsequent tagmentation and sequencing recovers the earlier chromatin profile from adenine methylation profiles, alongside endpoint profiles of endogenous chromatin-associated proteins. We verified that LagTag profiles aligned with those from established methods in mouse and human cells. We then applied LagTag to record and recover dynamic chromatin state transitions during mouse embryonic stem cell differentiation, capturing transcriptional signatures from pre- and post-differentiation timepoints within the same cell population. LagTag thus provides a foundation for temporally resolved chromatin profiling.

Journal Article

From stem cells to somites: Revealing genetic and exogenous factors of human embryogenesis.

Stem-cell-based human embryo models offer an ethically tractable platform for studying early human development. This study employs somitoids, three-dimensional models of human somitogenesis, to investigate how transcriptional programs and culture conditions influence somite formation and segmentation. We show that pre-differentiation culture medium impacts the developmental potential of induced pluripotent stem cells (iPSCs), with StemFit medium and Matrigel embedding outperforming mTeSR Plus medium in generating robust somite-like structures. Strikingly, these differences arise despite only subtle changes in transcriptomic and time-resolved proteomic profiles. P300-based proximity labeling also reveals a largely overlapping set of chromatin-associated regulators across iPSC conditions. In somitoids, enhancer-associated profiling highlights factors linked to somitogenesis, including MESP2 and TBX6. Knockout of three identified regulators, BPTF, RBPJ, and CITED2, demonstrate their essential roles in somite formation. Together, these findings highlight how culture conditions and enhancer-associated networks influence early human development and demonstrate somitoids as a scalable system for functional genomics.

Humans

Biology of testicular tumors.

Testicular tumors arise from the germ cell line and therefore exhibit characteristics of both neoplastic and normal growth and differentiation. Experimental model systems of animal and human tumors have been reviewed with emphasis on the biologic characteristics of these tumors. The embryonal carcinoma cell is the totipotential stem cell that resembles normal germ cells in many ways and is capable of differentiating along the somatic pathways to form endoderm, mesoderm and ectoderm cell types (teratoma) or along extraembryonic pathways to form trophoblast (choriocarcinoma) or yolk sac (endodermal sinus tumor). Markers of the extraembryonic cell types have been defined, and the cell surface characteristics of embryonal carcinoma cells are being intensively studied. Clarification of the biology of testicular tumors will provide the basis for future rational therapy.

Animals

Hemopoietic events in human embryonic spleens at early gestational stages.

The appearance of hemopoietic progenitor cells in human embryonic spleens at early gestational stages was observed with a transmission electron microscope. In spleens of 6- to 7-week-old embryos hemocytoblasts, proerythroblasts and megakarycotyic precursors were identified, located between the mesenchymal cells, suggesting that hemopoiesis in the embryonic spleen is an extravascular process. The relationship between hemopoietic and mesenchymal cells in the embryonic spleen is discussed.

Erythroblasts

A single small molecule-based human embryo model reveals V-ATPase requirement in mammalian blastocyst cavitation.

Human naïve pluripotent stem cells (nPSCs) can be induced by various combinations of signaling factors to generate blastocyst-like structures, termed blastoids. Despite rapid progress in human blastoid models, their potential to uncover fundamental mechanisms of early human development remains limited, leaving key morphogenetic processes poorly understood. Here, we describe a simple and robust system in which dimethyl sulfoxide (DMSO) alone induces blastoid formation from human nPSCs. This model recapitulates key pre- and post-implantation features and exhibits enhanced polar trophectoderm (TE) organization, more efficient attachment within an implantation-relevant window, improved epiblast lumenogenesis associated with amniotic cavity formation, and more robust, sustained expansion of embryonic lineages following attachment. Using this system, we reveal a previously unrecognized mechanism underlying TE cavitation and identify lysosome-associated genes - particularly subunits of the proton pump V-ATPase - as essential regulators of blastoid cavitation. DMSO treatment upregulates key V-ATPase subunits (ATP6V0A4 and ATP6V1B1), which are also enriched in the TE of human embryos. Genetic or pharmacological inhibition of V-ATPase activity disrupts lysosomal acidification, blocks intracellular vacuole formation, and impairs blastoid cavitation, whereas overexpression of V-ATPase subunits rescues this phenotype. Furthermore, genetic and pharmacological perturbations of V-ATPase function significantly compromise cavitation in both mouse and human blastocysts. Finally, DMSO treatment induces membrane biomechanical changes characteristic of early embryonic development, suggesting a mode of action distinct from conventional small-molecule, signaling pathway-based induction strategies. This simple DMSO-based blastoid model recapitulates key aspects of human blastocyst development and reveals a conserved requirement for V-ATPase-mediated lysosomal acidification during early mammalian embryogenesis.

Humans

Intimate contact between human yolk sac endoderm and haemopoietic precursor cells.

Although the localization of embryonic haemopoietic cells in the endodermal epithelium of the human yolk sac had been discovered several decades ago, the nature and significance of the localization were dubious, and it was supposed that light microscopic pictures represent technical artifacts. Our ultamicrographs now demonstrate that at 16--26 mm CR-length there is an intimate contact between yolk sac endoderm and free haemopoietic precursor cells: apart from interdigitations various types of intercellular contact could be discovered. These contacts, especially the gap-like ones with associated electron dense cytoplasmic areas speak for intercellular communication, i.e., the role of endoderm in early human embryonic haematopoiesis appears likely. The demonstrability of these contacts, however, does not mean that endodermal associations are indispensable for haemopoietic differentiation.

Endoderm

RNA splicing evidence enables robust classification of BRCA1 exon 18 variants: Results from the ENIGMA consortium.

The Evidence-based Network for the Interpretation of Germline Mutant Alleles (ENIGMA) research consortium conducted a comprehensive study to characterize spliceogenic variants in BRCA1 exon 18. The absence of systematic RNA-based assessment for these variants has led to inconsistent interpretation, limiting accurate classification and management of individuals and their families. The splicing profile of 166 variants was assessed using minigene assays; 32 were additionally analyzed in blood-derived RNA from 51 individuals and 18 in mouse embryonic stem cell (mESC)-based assays to evaluate homology-directed repair (HDR) capacity. mRNA assessment by RT-PCR in blood samples and minigene assays showed a significant positive correlation, with splicing analysis in mESCs displaying highly concordant results. The mESC-based HDR assay showed that the in-frame exon 18 skipping (&#x394;18) transcript encodes a non-functional protein lacking rescue activity. Linear regression analysis using mESC splicing and functional data indicated that &#x2265;59% of full-length (FL) levels and <34% of &#x394;18 were associated with benign HDR activity. These thresholds differ from those recommended by the ClinGen ENIGMA BRCA1 and BRCA2 Variant Curation Expert Panel American College of Medical Genetics and Genomics (ACMG)/Association for Molecular Pathology (AMP) specifications for applying BP7_strong(RNA): >30% functional transcripts or <70% non-functional transcripts. Incorporation of RNA splicing evidence into variant interpretation increased pathogenic (28.6%-31.7%) and benign (3.7%-24.4%) classifications while reducing likely pathogenic (19.5%-17.7%), uncertain (18.9%-8.5%), and likely benign (29.3%-17.7%) categories. Experimental mRNA profiling impacted the interpretation of 34% of variants and resolved uncertainty in approximately 10% of cases. Exon 18 skipping was less tolerated, indicating that the degree of splice perturbation required to impair BRCA1 function may depend on the nature of the resulting non-functional transcript.

Humans

Crosstalk between the Wnt pathway and other signaling pathways.

The Wnt/&#x3b2;-catenin signaling pathway is a deeply conserved regulatory network that governs embryonic development, stem cell maintenance, and tissue homeostasis. Aberrant activation of the Wingless/Integrated protein (Wnt) signaling is a hallmark of numerous human diseases, most prominently in colorectal cancer, where it cooperates with additional oncogenic pathways to drive tumor initiation, progression, and therapeutic resistance (See Supplementary Table 1 for a list of the abbreviations used in this manuscript and their definitions.). Increasing evidence indicates that Wnt signaling does not function as an isolated linear cascade but rather as an integrative signaling hub that dynamically interfaces with major signaling pathways, including the RAS-RAF-MAPK and PI3K-AKT-mTOR pathways. Rat Sarcoma protein (RAS)- Rapidly Accelerated Fibrosarcoma protein (RAF)- Mitogen-Activated Protein Kinase (MAPK) and Phosphoinositide 3-Kinase (PI3K)- Ak strain transforming protein (AKT)- Mechanistic Target of Rapamycin (mTOR) pathways. These interactions occur at multiple molecular levels, encompassing shared kinases, transcriptional regulators, metabolic nodes, and cytoskeletal components, thereby coordinating proliferative, metabolic, and migratory programs. In this review, we synthesize current mechanistic and clinical insights into the crosstalk between Wnt signaling and the RAS-RAF-MAPK and PI3K-AKT-mTOR pathways, with particular emphasis on colorectal cancer. We discuss how these signaling networks converge to regulate &#x3b2;-catenin stability, transcriptional activity, cell adhesion, and metabolic reprogramming, thereby generating oncogenic phenotypes that cannot be explained by activation of individual pathways alone. To illustrate the evolutionary conservation and biological significance of these interactions, we integrate developmental paradigms from early Xenopus embryogenesis, where Wnt signaling governs zygotic genome activation, body axis formation, and the regulation of cell growth, protein stability, and biomass accumulation. Finally, we examine how an improved understanding of Wnt-centered signaling networks is informing emerging therapeutic strategies, including combinatorial pathway inhibition and nanoparticle-based drug delivery. Collectively, this review highlights Wnt signaling as a central integrator of developmental and oncogenic programs, providing a conceptual framework for understanding signaling network crosstalk and identifying new therapeutic opportunities in cancer.

Humans

A human-specific non-coding RNA for EFHC1, an epilepsy-associated gene, regulates neural stem cell proliferation for cortical development.

Epilepsy is a prevalent brain disorder in humans but rarely occurs naturally in other species, highlighting the potential for human-specific mechanisms in its pathogenesis, and thus, current animal models fail to recapitulate human symptoms. Comparing RNA sequencing (RNA-seq) datasets from human and mouse neural stem cells (NSCs), we identified EFHC1, a juvenile myoclonic epilepsy gene, as exhibiting a human-biased expression. EFHC1 knockdown reduced human NSC proliferation, while its overexpression in mouse embryonic brains increased cortical NSC number. Mechanistically, EFHC1 prevented endoplasmic reticulum stress, thereby reducing inflammatory activation of p38 MAPK and promoting continuous proliferation of human NSCs. We also identified pancEFHC1, a bidirectional promoter-associated non-coding RNA (pancRNA), located at the human EFHC1 promoter. Knockdown of pancEFHC1 in human NSCs increased DNA methylation to reduce EFHC1 expression, with the resulting phenotype rescued by EFHC1 overexpression. We propose that the evolutionary acquisition of pancEFHC1 has introduced a complex regulatory mechanism for EFHC1 expression that allows distinguishing it in humans.

Humans

Hemopoietic stem cells bear sperm-associated antigens.

A fluorescence-activated cell sorter has been used to sort out enriched populations of murine hemopoietic stem cells from mouse bone marrow, based on fluorescence of cells labeled with various antisera. Significant positive enrichment for stem cells was obtained with rabbit anti-human brain, human anti-human sperm and mouse anti-mouse F9 sera but not with mouse anti-mouse Ia serum. These results support the hypothesis that the hemopoietic stem cell exhibits 'unique' surface antigens cross-reactive with sperm, brain and embryonic antigens.

Animals

Generation of an induced pluripotent stem cell line, LGMi002-A, from a Bardet-Biedl Syndrome patient with a BBS5 homozygous pathogenic variant.

The human induced pluripotent stem cell (iPSC) line, iPSC-BBS5stbg1, derived from a patient with a Bardet-Biedl Syndrome (BBS) phenotype and carrying a BBS5 homozygous pathogenic variant: c.123delA, p.Gly42Glufs*11 is described. The reprogramming of the patient's dermal fibroblasts was achieved using the non-integrative Sendai virus system delivering the OCT4, SOX2, KLF4 and c-MYC (OSKM) transcription factors. The established iPSC line iPSC-BBS5stbg1 displays typical iPSC morphology, maintains genomic stability, and demonstrates the ability to differentiate into cell types representative of the three embryonic germ layers. This iPSC line constitutes robust and relevant cellular model for studying BBS-associated disease mechanisms and ciliary dysfunction.

Humans