Multipotent adult germline stem cells and embryonic stem cells functional proteomics revealed an important role of eukaryotic initiation factor 5A (Eif5a) in stem cell differentiation

Multipotent adult germline stem cells (maGSCs) are pluripotent cells that can be differentiated into somatic cells of the three primary germ layers. To highlight the protein profile changes associated with stem cell differentiation, retinoic acid (RA) treated mouse stem cells (maGSCs and ESCs) were compared to nontreated stem cells. 2-DE and DIGE reference maps were created, and differentially expressed proteins were further processed for identification. In both stem cell types, the RA induced differentiation resulted in an alteration of 36 proteins of which 18 were down-regulated and might be potential pluripotency associated proteins, whereas the other 18 proteins were up-regulated. These might be correlated to stem cell differentiation. Surprisingly, eukaryotic initiation factor 5A (Eif5a), a protein which is essential for cell proliferation and differentiation, was significantly down-regulated under RA treatment. A time-dependent investigation of Eif5a showed that the RA treatment of stem cells resulted in a significant up-regulation of the Eif5a in the first 48 h followed by a progressive down-regulation thereafter. This effect could be blocked by the hypusination inhibitor ciclopirox olamine (CPX). The alteration of Eif5a hypusination, as confirmed by mass spectrometry, exerts an antiproliferative effect on ESCs and maGSCs in vitro, but does not affect the cell pluripotency. Our data highlights the important role of Eif5a and its hypusination for stem cell differentiation and proliferation.     

Growth Factor erv1-like Modulates Drp1 to Preserve Mitochondrial Dynamics and Function in Mouse Embryonic Stem Cells

The relationship of mitochondrial dynamics and function to pluripotency are rather poorly understood aspects of stem cell biology. Here we show that growth factor erv1-like (Gfer) is involved in preserving mouse embryonic stem cell (ESC) mitochondrial morphology and function. Knockdown (KD) of Gfer in ESCs leads to decreased pluripotency marker expression, embryoid body (EB) formation, cell survival, and loss of mitochondrial function. Mitochondria in Gfer-KD ESCs undergo excessive fragmentation and mitophagy, whereas those in ESCs overexpressing Gfer appear elongated. Levels of the mitochondrial fission GTPase dynamin-related protein 1 (Drp1) are highly elevated in Gfer-KD ESCs and decreased in Gfer-overexpressing cells. Treatment with a specific inhibitor of Drp1 rescues mitochondrial function and apoptosis, whereas expression of Drp1-dominant negative resulted in the restoration of pluripotency marker expression in Gfer-KD ESCs. Altogether, our data reveal a novel prosurvival role for Gfer in maintaining mitochondrial fission–fusion dynamics in pluripotent ESCs.     

Generation and Characterization of Yeast Two-Hybrid cDNA Libraries Derived From Two Distinct Mouse Pluripotent Cell Types

Pluripotent stem cells have the therapeutic potential in future regenerative medicine applications. Therefore, it is highly important to understand the molecular mechanisms governing the pluripotency and differentiation potential of these cells. Our current knowledge of pluripotent cells is largely limited owing to the candidate gene/protein approach rather than studying the complex interactions of the proteins. Experimentally, yeast two-hybrid system (Y2H) is by far the most useful and widely used method to detect the protein–protein interactions in high-throughput screenings. Unfortunately, currently there is no GAL4-based pluripotent stem cell-specific cDNA library available for screening the interaction proteins impeding the large-scale studies. In this study, we report the construction of Y2H cDNA libraries derived from mouse pluripotent embryonic stem cells (ESCs) and multipotent adult germ-line stem cells (maGSCs) in GAL4-based Y2H vector system with very high transformation efficiency. Furthermore, we have constructed two different baits and screened for interaction partners in an effort to characterize the libraries and also as a part of our ongoing studies. Consequently, many putative interaction proteins were identified in both cases and their interaction was further validated by direct-Y2H. The observed interactions between bait proteins and their respective analyzed putative interaction proteins were further confirmed using two independent approaches in mammalian cells, thus highlighting the biological significance of the identified interactor (s). Finally, we would like to make these cDNA libraries as a resource that can be distributed to the research community.     

Generation of functional neurons and glia from multipotent adult mouse germ-line stem cells

Recently, we reported the successful establishment of multipotent adult germ-line stem cells (maGSCs) from cultured adult mouse spermatogonial stem cells. Similar to embryonic stem cells, maGSCs are able to self-renew and differentiate into derivatives of all three germ layers. These properties make maGSCs a potential cell source for the treatment of neural degenerative diseases. In this study, we describe the generation of maGSC-derived proliferating neural precursor cells using growth factor-mediated neural lineage induction. The neural precursors were positive for nestin and Sox1 and could be continuously expanded. Upon further differentiation, they formed functional neurons and glial cells, as demonstrated by expression of lineage-restricted genes and proteins and by electrophysiological properties. Characterization of maGSC-derived neurons revealed the generation of specific subtypes, including GABAergic, glutamatergic, serotonergic, and dopaminergic neurons. Electrophysiological analysis revealed passive and active membrane properties and postsynaptic currents, indicating their functional maturation. Functional networks formed at later stages of differentiation, as evidenced by synaptic transmission of spontaneous neuronal activity. In conclusion, our data demonstrate that maGSCs may be used as a new stem cell source for basic research and biomedical applications.     

Identification of Potential Molecular Determinants of Murine Embryonic Stem Cell Differentiation by a Transposon-Based Approach

Embryonic stem cells (ESCs) are self-renewing pluripotent cells, capable of differentiating into all somatic cell types. The molecular control of self-renewal is relatively well-characterized, whereas how ESCs exit pluripotent state to differentiate is poorly understood. Here we identify two genes are required for differentiation and dozens of intergenic regions that potentially regulate ESC differentiation. We used PiggyBac (PB) transposon-based approach to randomly mutate the genome of ESCs, and generated hundreds of clones that resisted differentiation signals. Each clone was sequenced to determine genomic regions mutated by PB insertion. Intriguingly, many mutations were localized among intergenic regions and we identified two genes are required for differentiation. This study should facilitate further exploration of novel molecular determinants of embryonic stem cell differentiation.     

利用化学小分子实现人胚胎干细胞多能性状态的转化

小鼠胚胎干细胞（Embryonic Stem Cells,ESCs）具有两种不同的多能性状态-原始态多能性（naive pluripotency）和始发态多能性（primed pluripotency）,这两种多能性干细胞在形态、自我更新维持条件、基因表达、表观遗传学特征以及单克隆形成率等方面都存在明显差别。传统条件下分离和培养的人胚胎干细胞（human Embryonic Stem Cells,h ESCs）生物学特征更接近始发态多能性状态,需依赖转基因操作才能获得和维持原始态多能性状态。本研究通过在培养体系中添加化学小分子成功地将已建系的始发态多能性h ESCs转化为原始态多能性干细胞,转化后h ESCs呈紧密、圆形、隆起的三维克隆结构,具有两条活化的X染色体,单克隆形成率提高,基因表达更接近原始态多能性特征。结果提示h ESCs也存在两种多能性状态,不同的体外培养环境可获得具备不同多能性特征的h ESCs。原始态多能性状态的获得使h ESCs在基因治疗、器官再生等领域具有广阔的应用前景,而仅改变培养条件,不依赖基因操作的培养方式大大提高了原始态多能性干细胞应用的安全性。     

X-chromosome inactivation in monkey embryos and pluripotent stem cells

Inactivation of one X chromosome in female mammals (XX) compensates for the reduced dosage of X-linked gene expression in males (XY). However, the inner cell mass (ICM) of mouse preimplantation blastocysts and their in vitro counterparts, pluripotent embryonic stem cells (ESCs), initially maintain two active X chromosomes (XaXa). Random X chromosome inactivation (XCI) takes place in the ICM lineage after implantation or upon differentiation of ESCs, resulting in mosaic tissues composed of two cell types carrying either maternal or paternal active X chromosomes. While the status of XCI in human embryos and ICMs remains unknown, majority of human female ESCs show non-random XCI. We demonstrate here that rhesus monkey ESCs also display monoallelic expression and methylation of X-linked genes in agreement with non-random XCI. However, XIST and other X-linked genes were expressed from both chromosomes in isolated female monkey ICMs indicating that ex vivo pluripotent cells retain XaXa. Intriguingly, the trophectoderm (TE) in preimplantation monkey blastocysts also expressed X-linked genes from both alleles suggesting that, unlike the mouse, primate TE lineage does not support imprinted paternal XCI. Our results provide insights into the species-specific nature of XCI in the primate system and reveal fundamental epigenetic differences between in vitro and ex vivo primate pluripotent cells.     

Cytoskeletal Expression and Remodeling in Pluripotent Stem Cells

Many emerging cell-based therapies are based on pluripotent stem cells, though complete understanding of the properties of these cells is lacking. In these cells, much is still unknown about the cytoskeletal network, which governs the mechanoresponse. The objective of this study was to determine the cytoskeletal state in undifferentiated pluripotent stem cells and remodeling with differentiation. Mouse embryonic stem cells (ESCs) and reprogrammed induced pluripotent stem cells (iPSCs), as well as the original un-reprogrammed embryonic fibroblasts (MEFs), were evaluated for expression of cytoskeletal markers. We found that pluripotent stem cells overall have a less developed cytoskeleton compared to fibroblasts. Gene and protein expression of smooth muscle cell actin, vimentin, lamin A, and nestin were markedly lower for ESCs than MEFs. Whereas, iPSC samples were heterogeneous with most cells expressing patterns of cytoskeletal proteins similar to ESCs with a small subpopulation similar to MEFs. This indicates that dedifferentiation during reprogramming is associated with cytoskeletal remodeling to a less developed state. In differentiation studies, it was found that shear stress-mediated differentiation resulted in an increase in expression of cytoskeletal intermediate filaments in ESCs, but not in iPSC samples. In the embryoid body model of spontaneous differentiation of pluripotent stem cells, however, both ESCs and iPSCs had similar gene expression for cytoskeletal proteins during early differentiation. With further differentiation, however, gene levels were significantly higher for iPSCs compared to ESCs. These results indicate that reprogrammed iPSCs more readily reacquire cytoskeletal proteins compared to the ESCs that need to form the network de novo. The strategic selection of the parental phenotype is thus critical not only in the context of reprogramming but also the ultimate functionality of the iPSC-differentiated cell population. Overall, this increased characterization of the cytoskeleton in pluripotent stem cells will allow for the better understanding and design of stem cell-based therapies.     

Search for nave human pluripotent stem cells

Normal mouse pluripotent stem cells were originally derived from the inner cell mass(ICM) of blastocysts and shown to be the in vitro equivalent of those pre-implantation embryonic cells, and thus were called embryonic stem cells(ESCs). More than a decade later, pluripotent cells were isolated from the ICM of human blastocysts. Despite being called human ESCs, these cells differ significantly from mouse ESCs, including different morphology and mechanisms of control of pluripotency, suggesting distinct embryonic origins of ESCs from the two species. Subsequently, mouse pluripotent stem cells were established from the ICMderived epiblast of post-implantation embryos. These mouse epiblast stem cells(Epi SCs) are morphological and epigenetically more similar to human ESCs. This raised the question of whether cells from the human ICM are in a more advanced differentiation stage than their murine counterpart, or whether the available culture conditions were not adequate to maintain those human cells in their in vivo state, leading to a transition into Epi SC-like cells in vitro. More recently, novel culture conditions allowed the conversion of human ESCs into mouse ESC-like cells called nave(or ground state) human ESCs, and the derivation of nave human ESCs from blastocysts. Here we will review the characteristics of each type of pluripotent stem cells, how(and whether) these relate to different stages of embryonic development, and discuss the potential implications of nave human ESCs in research and therapy.     

Stage-specific germ-cell marker genes are expressed in all mouse pluripotent cell types and emerge early during induced pluripotency

Embryonic stem cells (ESCs) generated from the in-vitro culture of blastocyst stage embryos are known as equivalent to blastocyst inner cell mass (ICM) in-vivo. Though several reports have shown the expression of germ cell/pre-meiotic (GC/PrM) markers in ESCs, their functional relevance for the pluripotency and germ line commitment are largely unknown. In the present study, we used mouse as a model system and systematically analyzed the RNA and protein expression of GC/PrM markers in ESCs and found them to be comparable to the expression of cultured pluripotent cells originated from the germ line. Further, siRNA knockdown experiments have demonstrated the parallel maintenance and independence of pluripotent and GC/PrM networks in ESCs. Through chromatin immunoprecipitation experiments, we observed that pluripotent cells exhibit active chromatin states at GC marker genes and a bivalent chromatin structure at PrM marker genes. Moreover, gene expression analysis during the time course of iPS cells generation revealed that the expression of GC markers precedes pluripotency markers. Collectively, through our observations we hypothesize that the chromatin state and the expression of GC/PrM markers might indicate molecular parallels between in-vivo germ cell specification and pluripotent stem cell generation.