胚胎干细胞自我复制及亚全能分化特性维持的分子机制

微环境中的各种细胞因子与细胞内的多种转录因子通过一定的信号系统相互作用构成网络, 共同调控胚胎干细胞的自我复制. 本文对维持胚胎干细胞(embryonic stem cells, ESCs)亚全能分化特性的相关分子、信号通路以及它们的作用方式进行了综述, 探讨了胚胎干细胞自我复制及亚全能分化特性维持的分子机制.     

早期胚胎细胞谱系研究——揭示生命发育早期的黑盒子

哺乳动物的早期胚胎发育,通过多个层次的细胞命运决定,建立了胚胎器官发生、形态建成的整体发育蓝图,是生命体最重要的分子事件之一。早期胚胎发育过程伴随了全能性的维持和分化,以及各种多能干细胞命运的次序决定,任何发育进程上的缺陷都会对整个胚胎个体产生深远的影响。因此,研究早期胚胎谱系建立的过程、不同胚层和组织前体细胞的命运决定及其发生与发展的调控机制,不仅仅是面对国家人口政策的变化以及优生优育的需求,预防和减少早期发育疾病,还能够指导胚胎干细胞及各种多能干细胞的分化和进一步转化医学应用,因而具有极其重要的生物学意义。     

人胚胎干细胞建系和培养的研究进展

人胚胎干细胞(human embryonic stem cell,hESc)在再生医学、药物筛选和发育生物学等领域具有重要的研究和应用价值.本文对人胚胎干细胞建系方法的现状包括胚胎来源、内细胞团分离方法、以及人胚胎干细胞培养体系的改进作了介绍,讨论了与全能性维持和定向分化有关的信号通路的研究进展,以及胚胎干细胞研究中伦理问题的争议.     

胚胎干细胞的体外诱导分化模型

胚胎干细胞是具有全能性及无限制的自我更新与分化能力的一类特殊的细胞群体 ,它能通过祖细胞为中介 ,分化为各种类型的体细胞 ,可重演体内干细胞的分化过程。自 80年代从小鼠囊胚的内细胞团分离到胚胎干细胞并建系到现在已建立了神经细胞、肌肉细胞、上皮细胞、造血细胞等体外分化体系。将胚胎干细胞体外分化成为可利用的分化模型 ,无论从组织结构、细胞及分子水平都体现了体内分化过程的体外重演 ,再加上胚胎干细胞系具有体系简单 ,影响因子少 ,可控制 ,便于研究等特点 ,因此可用于研究早期胚胎发育和细胞分化调控 ;可成为器官移植和修复…     

Nanog基因的功能与调控

胚胎干细胞的无限增殖能力和亚全能性决定了它在再生医学、新药开发及发育生物学基础研究中具有巨大的应用前景。探索维持胚胎干细胞亚全能性的因子及其网络的调控功能成为胚胎干细胞生物学研究的热点。已研究发现多个与维持胚胎干细胞亚全能性相关的基因如Oct4,Nanog,Sox2等,其中Nanog是2003年5月末发现的一个基因,它对维持胚胎干细胞亚全能性起关键性作用,能够独立于LIF／Stat3维持ICM和胚胎干细胞的亚全能性。几年来,Nanog的生物学功能及其与Oct4,Sox2等亚全能性维持基因之间的相互作用关系已有较为深入的研究,并发现多个调控Nanog表达的转录因子,从而进一步明晰Nanog与已知调控胚胎发育的信号通路之间的关系。在综述Nanog基因的表达特征和功能的基础上、重点探讨Nanog基因表达调控以及Oct4,Sox2等亚全能性维持基因之间的相互作用关系,并对未来的研究趋势予以展望。     

利用胚胎干细胞分化的拟胚体研究小鼠早期胚胎发育过程

小鼠胚胎干细胞(ES细胞)具有分化的全能性已经得到广泛共识。ES细胞在体外分化所形成的拟胚体在结构上能够模仿早期胚胎发育过程,包括在内细胞团表面形成内胚层、柱状上皮细胞的分化,以及中央空腔的形成。本文介绍利用拟胚体研究小鼠早期胚胎发育过程中各个胚胎阶段的发育、细胞程序性死亡的发生及TGF-β信号在胚胎发育过程中的作用。     

Nanog基因的功能与调控研究进展

胚胎干细胞的无限增殖能力和亚全能性决定了它在再生医学、新药开发及发育生物学基础研究中具有巨大的应用前景。探索维持胚胎干细胞亚全能性的因子及其网络的调控功能成为胚胎干细胞生物学研究的热点。已研究发现多个与维持胚胎干细胞亚全能性相关的基因如Oct4, Nanog, Sox2等,其中Nanog是2003年5月末发现的一个基因,它对维持胚胎干细胞亚全能性起关键性作用,能够独立于L1F/Stat3维持ICM和胚胎干细胞的亚全能性。几年来,Nanog的生物学功能及其与 Oct4, Sox2等亚全能性维持基因之间的相互作用关系已有较为深入的研究,并发现多个调控Nanog表达的转录因子,从而进一步明晰Nanog与已知调控胚胎发育的信号通路之间的关系。本文在综述Nanog基因的表达特征和功能的基础上、重点探讨Nanog基因表达调控以及Oct4, Sox2等亚全能性维持基因之间的相互作用关系,并对未来的研究趋势予以展望。     

维持胚胎干细胞生物学特性的分子调控机制

胚胎干(embryonic stem,ES)细胞来源于植入前的胚胎.在体外培养条件下,可保持分化成机体各种类型细胞的能力,即全能性.因此,胚胎干细胞被广泛用作研究胚胎发生、发育的细胞模型,也是目前开展细胞移植性治疗研究的重要来源.揭示维持ES细胞自我更新和全能性的分子调控机制,是ES细胞基础研究和临床治疗基础研究的重要领域.目前研究发现,不同的信号通路、转录因子及其通过激活ES细胞特异性表达谱对维持ES细胞多能性、自我更新发挥关键作用。     

MicroRNA调控造血干细胞发育

造血干细胞是目前研究最为深入的成体干细胞,是极富应用前景的研究领域,然而其维持自我更新以及多向分化潜能的分子机制尚不明.MicroRNA (miRNA)是一类崭新的调控性非编码小分子RNA,在监控生物体个体发育和细胞增殖、分化进程中起着重要作用.miRNA参与包括胚胎干细胞和多种成体干细胞的发育进程,人类造血干细胞及其发育过程中也存在特征性miRNA表达谱,参与调控造血干细胞发育进程,以miRNA为分子靶点的防治造血功能低下疾患的研究具有广阔的应用前景.     

胚胎干细胞向造血细胞分化研究

胚胎干（embryonic stem,ES）细胞是来源于囊胚的内细胞团（inner cell mass,ICM）,具有发育的全能性或多能性,能嵌合到早期胚胎,在体内可以参与各种组织发育甚至包括生殖细胞;在体外分化培养条件下,可以顺序分化出各种组织细胞,与体内完整胚胎发育过程相符合,而且可以通过调节ES细胞某些基因的表达而调节其分化。因此,ES细胞是研究哺乳动物早期胚胎发育、细胞分化及其关键基因鉴定的理想模型。另外,胚胎生殖脊（embryonic germ,EG）细胞系也具有同样的生物学特性,它是由早期胚胎的原始生殖脊（primordial germ,PG）细胞建株而来。最近研究显示：ES细胞在体外不但可以分化为所有造血细胞系,而且还可以分化为具有长期增殖能力的造血干细胞。作者就胚胎干细胞向造血细胞和造血干细胞分化及其诱导因子和调控基因的表达作一综述。     

MicroRNA对胚胎干细胞的多能性网络调控

胚胎干细胞(Embryonic stem cells, ESCs)是一类能够无限增殖和诱导分化为多种类型细胞的干细胞。MicroRNA(miRNA)是一类内源性具有调控基因表达功能的非编码RNA, 在ESCs增殖和分化过程中起重要作用。MiRNA可以通过对ESCs多能性网络中的转录因子、细胞周期、表观遗传学、信号转导等方面调控, 促使ESCs维持多能性状态。文章重点综述了miRNA的生成过程、调控ESCs多能性的主要miRNA家族以及miRNA对ESCs多能性网络调控作用等内容。     

Association of telomere length with authentic pluripotency of ES/iPS cells

Telomerase and telomeres are important for indefinite replication of stem cells. Recently, telomeres of somatic cells were found to be reprogrammed to elongate in induced pluripotent stem cells (iPSCs). The role of telomeres in developmental pluripotency in vivo of embryonic stem cells (ESCs) or iPSCs, however, has not been directly addressed. We show that ESCs with long telomeres exhibit authentic developmental pluripotency, as evidenced by generation of complete ESC pups as well as germline-competent chimeras, the most stringent tests available in rodents. ESCs with short telomeres show reduced teratoma formation and chimera production, and fail to generate complete ESC pups. Telomere lengths are highly correlated (r > 0.8) with the developmental pluripotency of ESCs. Short telomeres decrease the proliferative rate or capacity of ESCs, alter the expression of genes related to telomere epigenetics, down-regulate genes important for embryogenesis and disrupt germ cell differentiation. Moreover, iPSCs with longer telomeres generate chimeras with higher efficiency than those with short telomeres. Our data show that functional telomeres are essential for the developmental pluripotency of ESCs/iPSCs and suggest that telomere length may provide a valuable marker to evaluate stem cell pluripotency, particularly when the stringent tests are not feasible.     

Histone h1 depletion impairs embryonic stem cell differentiation

Pluripotent embryonic stem cells (ESCs) are known to possess a relatively open chromatin structure; yet, despite efforts to characterize the chromatin signatures of ESCs, the role of chromatin compaction in stem cell fate and function remains elusive. Linker histone H1 is important for higher-order chromatin folding and is essential for mammalian embryogenesis. To investigate the role of H1 and chromatin compaction in stem cell pluripotency and differentiation, we examine the differentiation of embryonic stem cells that are depleted of multiple H1 subtypes. H1c/H1d/H1e triple null ESCs are more resistant to spontaneous differentiation in adherent monolayer culture upon removal of leukemia inhibitory factor. Similarly, the majority of the triple-H1 null embryoid bodies (EBs) lack morphological structures representing the three germ layers and retain gene expression signatures characteristic of undifferentiated ESCs. Furthermore, upon neural differentiation of EBs, triple-H1 null cell cultures are deficient in neurite outgrowth and lack efficient activation of neural markers. Finally, we discover that triple-H1 null embryos and EBs fail to fully repress the expression of the pluripotency genes in comparison with wild-type controls and that H1 depletion impairs DNA methylation and changes of histone marks at promoter regions necessary for efficiently silencing pluripotency gene Oct4 during stem cell differentiation and embryogenesis. In summary, we demonstrate that H1 plays a critical role in pluripotent stem cell differentiation, and our results suggest that H1 and chromatin compaction may mediate pluripotent stem cell differentiation through epigenetic repression of the pluripotency genes.     

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.     

Proteomic analysis of membrane proteins expressed specifically in pluripotent murine embryonic stem cells

Embryonic stem cells (ESCs) are established from the inner cell mass of preimplantation embryos, are capable of self‐renewal, and exhibit pluripotency. Given these unique properties, ESCs are expected to have therapeutic potential in regenerative medicine and as a powerful tool for in vitro differentiation studies of stem cells. Various growth factors and extracellular matrix components regulate the pluripotency and differentiation of ESC progenies. Thus, the cell surface receptors that bind these regulatory factors are crucial for the precise regulation of stem cells. To identify membrane proteins that are involved in the regulation of pluripotent stem cells, the membrane proteins of murine ESCs cultured with or without leukemia inhibitory factor (LIF) were purified and analyzed by quantitative proteomics. 2‐D PAGE‐based analysis using fluorescently labeled proteins and shotgun‐based analysis with isotope‐labeled peptides identified 338 proteins, including transmembrane, membrane‐binding, and extracellular proteins, which were expressed specifically in pluripotent or differentiated murine ESCs. Functions of the identified proteins revealed cell adhesion molecules, channels, and receptors, which are expected to play important roles in the maintenance of murine ESC pluripotency. Membrane proteins that are expressed in pluripotent ESCs but not in differentiated cells such as Slc16a1 and Bsg could be useful for the selection of the stem cells in vitro.     

DEPTOR Is a Stemness Factor That Regulates Pluripotency of Embryonic Stem Cells

The mammalian target of rapamycin (mTOR) pathway regulates stem cell regeneration and differentiation in response to growth factors, nutrients, cellular energetics, and various extrinsic stressors. Inhibition of mTOR activity has been shown to enhance the regenerative potential of pluripotent stem cells. DEPTOR is the only known endogenous inhibitor of all known cellular mTOR functions. We show that DEPTOR plays a key role in maintaining stem cell pluripotency by limiting mTOR activity in undifferentiated embryonic stem cells (ESCs). DEPTOR levels dramatically decrease with differentiation of mouse ESCs, and knockdown of DEPTOR is sufficient to promote ESC differentiation. A strong decrease in DEPTOR expression is also observed during human ESCs differentiation. Furthermore, reduction in DEPTOR level during differentiation is accompanied by a corresponding increase in mTOR complex 1 activity in mouse ESCs. Our data provide evidence that DEPTOR is a novel stemness factor that promotes pluripotency and self-renewal in ESCs by inhibiting mTOR signaling.