Early Cell Fate Decisions of Human Embryonic Stem Cells and Mouse Epiblast Stem Cells Are Controlled by the Same Signalling Pathways

Human embryonic stem cells have unique value for regenerative medicine, as they are capable of differentiating into a broad variety of cell types. Therefore, defining the signalling pathways that control early cell fate decisions of pluripotent stem cells represents a major task. Moreover, modelling the early steps of embryonic development in vitro may provide the best approach to produce cell types with native properties. Here, we analysed the function of key developmental growth factors such as Activin, FGF and BMP in the control of early cell fate decisions of human pluripotent stem cells. This analysis resulted in the development and validation of chemically defined culture conditions for achieving specification of human embryonic stem cells into neuroectoderm, mesendoderm and into extra-embryonic tissues. Importantly, these defined culture conditions are devoid of factors that could obscure analysis of developmental mechanisms or render the resulting tissues incompatible with future clinical applications. Importantly, the growth factor roles defined using these culture conditions similarly drove differentiation of mouse epiblast stem cells derived from post implantation embryos, thereby reinforcing the hypothesis that epiblast stem cells share a common embryonic identity with human pluripotent stem cells. Therefore the defined growth factor conditions described here represent an essential step toward the production of mature cell types from pluripotent stem cells in conditions fully compatible with clinical use ant also provide a general approach for modelling the early steps of mammalian embryonic development.     

Live Imaging of Whole Mouse Embryos during Gastrulation: Migration Analyses of Epiblast and Mesodermal Cells

During gastrulation in the mouse embryo, dynamic cell movements including epiblast invagination and mesodermal layer expansion lead to the establishment of the three-layered body plan. The precise details of these movements, however, are sometimes elusive, because of the limitations in live imaging. To overcome this problem, we developed techniques to enable observation of living mouse embryos with digital scanned light sheet microscope (DSLM). The achieved deep and high time-resolution images of GFP-expressing nuclei and following 3D tracking analysis revealed the following findings: (i) Interkinetic nuclear migration (INM) occurs in the epiblast at embryonic day (E)6 and 6.5. (ii) INM-like migration occurs in the E5.5 embryo, when the epiblast is a monolayer and not yet pseudostratified. (iii) Primary driving force for INM at E6.5 is not pressure from neighboring nuclei. (iv) Mesodermal cells migrate not as a sheet but as individual cells without coordination.     

Activin Regulates Self-renewal and Differentiation of Trophoblast Stem Cells by Down-regulating the X Chromosome Gene Bcor

The development of a functional placenta is largely dependent upon proper proliferation and differentiation of trophoblast stem cells (TSCs). Activin signaling has long been regarded to play important roles during this process, but the exact mechanism is largely unknown. Here, we demonstrate that the X chromosome gene BCL-6 corepressor (Bcor) is a critical downstream effector of activin to fine-tune mouse TSC fate decision. Bcor was specifically down-regulated by activin A in TSCs in a dose-dependent manner, and immediately up-regulated upon TSC differentiation. Knockdown of Bcor partially compensated for the absence of activin A in maintaining the self-renewal of TSCs together with FGF4, while promoting syncytiotrophoblast differentiation in the absence of FGF4. Moreover, the impaired trophoblast giant cell and spongiotrophoblast differentiation upon Bcor knockdown also resembled the function of activin. Reporter analysis showed that BCOR inhibited the expression of the key trophoblast regulator genes Eomes and Cebpa by binding to their promoter regions. Our findings provide us with a better understanding of placental development and placenta-related diseases.     

Human Embryonic Stem Cells Do Not Change Their X Inactivation Status during Differentiation

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Changes in Laminin Expression Pattern during Early Differentiation of Human Embryonic Stem Cells

Laminin isoforms laminin-511 and -521 are expressed by human embryonic stem cells (hESC) and can be used as a growth matrix to culture these cells under pluripotent conditions. However, the expression of these laminins during the induction of hESC differentiation has not been studied in detail. Furthermore, the data regarding the expression pattern of laminin chains in differentiating hESC is scarce. In the current study we aimed to fill this gap and investigated the potential changes in laminin expression during early hESC differentiation induced by retinoic acid (RA). We found that laminin-511 but not -521 accumulates in the committed cells during early steps of hESC differentiation. We also performed a comprehensive analysis of the laminin chain repertoire and found that pluripotent hESC express a more diverse range of laminin chains than shown previously. In particular, we provide the evidence that in addition to α1, α5, β1, β2 and γ1 chains, hESC express α2, α3, β3, γ2 and γ3 chain proteins and mRNA. Additionally, we found that a variant of laminin α3 chain—145 kDa—accumulated in RA-treated hESC showing that these cells produce prevalently specifically modified version of α3 chain in early phase of differentiation.     

Live Imaging of Apoptotic Cell Clearance during Drosophila Embryogenesis

The proper elimination of unwanted or aberrant cells through apoptosis and subsequent phagocytosis (apoptotic cell clearance) is crucial for normal development in all metazoan organisms. Apoptotic cell clearance is a highly dynamic process intimately associated with cell death; unengulfed apoptotic cells are barely seen in vivo under normal conditions. In order to understand the different steps of apoptotic cell clearance and to compare ''professional'' phagocytes - macrophages and dendritic cells to ''non-professional'' - tissue-resident neighboring cells, in vivo live imaging of the process is extremely valuable. Here we describe a protocol for studying apoptotic cell clearance in live Drosophila embryos. To follow the dynamics of different steps in phagocytosis we use specific markers for apoptotic cells and phagocytes. In addition, we can monitor two phagocyte systems in parallel: ''professional'' macrophages and ''semi-professional'' glia in the developing central nervous system (CNS). The method described here employs the Drosophila embryo as an excellent model for real time studies of apoptotic cell clearance.     

mTORC1 Is Essential for Early Steps during Schwann Cell Differentiation of Amniotic Fluid Stem Cells and Regulates Lipogenic Gene Expression

Schwann cell development is hallmarked by the induction of a lipogenic profile. Here we used amniotic fluid stem (AFS) cells and focused on the mechanisms occurring during early steps of differentiation along the Schwann cell lineage. Therefore, we initiated Schwann cell differentiation in AFS cells and monitored as well as modulated the activity of the mechanistic target of rapamycin (mTOR) pathway, the major regulator of anabolic processes. Our results show that mTOR complex 1 (mTORC1) activity is essential for glial marker expression and expression of Sterol Regulatory Element-Binding Protein (SREBP) target genes. Moreover, SREBP target gene activation by statin treatment promoted lipogenic gene expression, induced mTORC1 activation and stimulated Schwann cell differentiation. To investigate mTORC1 downstream signaling we expressed a mutant S6K1, which subsequently induced the expression of the Schwann cell marker S100b, but did not affect lipogenic gene expression. This suggests that S6K1 dependent and independent pathways downstream of mTORC1 drive AFS cells to early Schwann cell differentiation and lipogenic gene expression. In conclusion our results propose that future strategies for peripheral nervous system regeneration will depend on ways to efficiently induce the mTORC1 pathway.     

Live Cell Imaging of Early Autophagy Events: Omegasomes and Beyond

Autophagy is a cellular response triggered by the lack of nutrients, especially the absence of amino acids. Autophagy is defined by the formation of double membrane structures, called autophagosomes, that sequester cytoplasm, long-lived proteins and protein aggregates, defective organelles, and even viruses or bacteria. Autophagosomes eventually fuse with lysosomes leading to bulk degradation of their content, with the produced nutrients being recycled back to the cytoplasm. Therefore, autophagy is crucial for cell homeostasis, and dysregulation of autophagy can lead to disease, most notably neurodegeneration, ageing and cancer.Autophagosome formation is a very elaborate process, for which cells have allocated a specific group of proteins, called the core autophagy machinery. The core autophagy machinery is functionally complemented by additional proteins involved in diverse cellular processes, e.g. in membrane trafficking, in mitochondrial and lysosomal biology. Coordination of these proteins for the formation and degradation of autophagosomes constitutes the highly dynamic and sophisticated response of autophagy. Live cell imaging allows one to follow the molecular contribution of each autophagy-related protein down to the level of a single autophagosome formation event and in real time, therefore this technique offers a high temporal and spatial resolution.Here we use a cell line stably expressing GFP-DFCP1, to establish a spatial and temporal context for our analysis. DFCP1 marks omegasomes, which are precursor structures leading to autophagosomes formation. A protein of interest (POI) can be marked with either a red or cyan fluorescent tag. Different organelles, like the ER, mitochondria and lysosomes, are all involved in different steps of autophagosome formation, and can be marked using a specific tracker dye. Time-lapse microscopy of autophagy in this experimental set up, allows information to be extracted about the fourth dimension, i.e. time. Hence we can follow the contribution of the POI to autophagy in space and time.     

Collagen Type I Improves the Differentiation of Human Embryonic Stem Cells towards Definitive Endoderm

Human embryonic stem cells have the ability to generate all cell types in the body and can potentially provide an unlimited source of cells for cell replacement therapy to treat degenerative diseases such as diabetes. Current differentiation protocols of human embryonic stem cells towards insulin producing beta cells focus on soluble molecules whereas the impact of cell-matrix interactions has been mainly unattended. In this study almost 500 different extracellular matrix protein combinations were screened to systemically identify extracellular matrix proteins that influence differentiation of human embryonic stem cells to the definitive endoderm lineage. The percentage of definitive endoderm cells after differentiation on collagen I and fibronectin was >85% and 65%, respectively. The cells on collagen I substrates displayed different morphology and gene expression during differentiation as assessed by time lapse studies compared to cells on the other tested substrates. Global gene expression analysis showed that cells differentiated on collagen I were largely similar to cells on fibronectin after completed differentiation. Collectively, the data suggest that collagen I induces a more rapid and consistent differentiation of stem cells to definitive endoderm. The results shed light on the importance of extracellular matrix proteins for differentiation and also points to a cost effective and easy method to improve differentiation.     

Cultivation and Differentiation Change Nuclear Localization of Chromosome Centromeres in Human Mesenchymal Stem Cells

Chromosome arrangement in the interphase nucleus is not accidental. Strong evidences support that nuclear localization is an important mechanism of epigenetic regulation of gene expression. The purpose of this research was to identify differences in the localization of centromeres of chromosomes 6, 12, 18 and X in human mesenchymal stem cells depending on differentiation and cultivating time. We analyzed centromere positions in more than 4000 nuclei in 19 mesenchymal stem cell cultures before and after prolonged cultivation and after differentiation into osteogenic and adipogenic directions. We found a centromere reposition of HSAX at late passages and after differentiation in osteogenic direction as well as of HSA12 and HSA18 after adipogenic differentiation. The observed changes of the nuclear structure are new nuclear characteristics of the studied cells which may reflect regulatory changes of gene expression during the studied processes.     

胚胎干细胞在体外模拟心肌生长环境中向心肌分化

目的:探讨获得大量成熟同质有功能的心肌细胞(cardiomyocytes,CMs)的方法.方法:胚胎干细胞(embryonic stem cells,ESCs)经悬滴培养法形成拟胚体(embryoid bodies,EBs),将EBs用抗坏血酸处理后与天然心肌细胞共培养诱导ESCs的分化,采用免疫组化、流式细胞技术、RT-PCR、超微分析等方法分析分化细胞(ESC-derived CMs,ESCMs)的结构和功能.结果:共培养组,常规组和对照组中有(90.1±3.40)%,(29.6±6.03)%和(20.1±3.82)%的EBs表现节律性收缩,差异有统计学意义(P＜0.05).在体外模拟的心脏微环境中,不但跳动EBs的数目明显增加,且单个跳动EBs中含有功能CMs的百分比也明显增加.兴奋收缩的自律性能维持更长时间,在后期分化得到的有功能ESCMs在细胞形态上接近于天然的心肌细胞.结论:心脏微环境是促使ESCs特定地分化为CMs的关键因素,抗坏血酸处理和共培养诱导策略可使ESCs定向分化为CMs.     

Imaging of Nucleolar Dynamics During the Cell Cycle of Cancer Cells in Live Mice

The synthesis and assembly of ribosomal subunits take place in the nucleolus. The nucleolus forms in the nucleus around the repeated ribosomal gene clusters and undergoes cyclic changes during the cell cycle. Although the nucleolus is easily visualized by light microscopy of cells in vitro, the nucleolus has not been imaged in cells in vivo. We report here development of a mouse model to visualize the nucleolus cycle of cancer cells in live mice. HT-1080 human fibrosarcoma cells were labeled in the nucleus with histone H2B-GFP and with retroviral RFP in the cytoplasm. The nucleolus was visualized by contrast to the fluorescence of GFP expressed in the nucleus. HT-1080 dual-color cells were seeded on the surface of a skin-flap of nude mice. The inside surface of the skin-flap was directly imaged with a laser scanning microscope 24 hours after seeding. The nucleoli of the cancer cells were clearly imaged in real-time. The appearance of the nucleoli changed dramatically during the cell cycle. During mitosis, the nucleolus disappeared. After mitosis, the nucleoli decreased in number and increased in size. The nucleolus appears to have a major role in cell cycle regulation effected at least in part by sequestering proteins which affect cell cycle progression. Nucleolar imaging could be used for more precise determination of cancer-cell position in the cell cycle in vivo.     

间充质干细胞的细胞成像技术比较与应用

间充质干细胞是一类具有强大增殖、多向分化潜能和免疫调节能力的多功能细胞,研究显示间充质干细胞移植可能治疗多种难治性疾病,例如帕金森病、脊髓损伤以及肿瘤等。但是,人们对移植后的细胞在宿主内的存活、分布、增殖、分化、免疫排斥反应以及成瘤特性等问题尚不清楚,所以许多疾病经过细胞移植治疗后的进展及转归情况仍难以获得确切的科学证据。而细胞成像技术(包括放射性核素成像、超声成像、磁共振成像以及光学成像)可以在体外或者体内实现对间充质干细胞实时、无创的示踪,在以间充质干细胞为研究基础的细胞移植治疗和细胞组织再生的医学领域里有着巨大的应用潜力。该文综述近十年来细胞成像技术应用于示踪间充质干细胞移植疗法的研究进展,旨在比较当下多种热门细胞成像技术的优劣,进而找寻更合适的干细胞示踪策略,为干细胞移植治疗的基础和临床研究提供进一步的理论证据支持和研究思路。