利用piggyBac转座子制备牛成体多能干细胞诱导技术研究

通过逆转录病毒等媒介表达核转录因子Oct4、Sox2、Klf4、c-Myc可将体细胞重编程为诱导多能干细胞(induced pluripotent stem cells, iPSc)。时至今日,已经报道了小鼠、人、大鼠、猪、羊、马、牛的iPS细胞,但大动物iPS的多能性特别是嵌合体形成和生殖细胞传代还没有得到确认。与逆转录病毒等不同的是,piggyBac转座子转染效率高且无病毒源性、操作简单,可以在转座酶的存在下被安全切除。首次尝试了采用piggyBac转座子携带鼠源Oct4、Sox2、Klf4、c-Myc、Rarg和Lrh16个核转录因子诱导胎牛成纤维细胞,成功获得牛类iPS细胞,其形态与小鼠胚胎干细胞相似,克隆边界清晰、呈丘状、克隆内细胞致密、核大。RT-PCR与免疫组织化学染色分析均显示牛类iPS细胞表达多能性基因。该类细胞体外诱导分化可形成类胚体EB,且表达3个胚层的基因;体内诱导分化可形成畸胎瘤,苏木精、伊红染色显示瘤体有三胚层的分化。上述结果显示利用piggyBac转座子制备牛多潜能干细胞诱导技术可行,产生的牛类iPS细胞具有潜在多能性。     

Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors

Differentiated cells can be reprogrammed to an embryonic-like state by transfer of nuclear contents into oocytes or by fusion with embryonic stem (ES) cells. Little is known about factors that induce this reprogramming. Here, we demonstrate induction of pluripotent stem cells from mouse embryonic or adult fibroblasts by introducing four factors, Oct3/4, Sox2, c-Myc, and Klf4, under ES cell culture conditions. Unexpectedly, Nanog was dispensable. These cells, which we designated iPS (induced pluripotent stem) cells, exhibit the morphology and growth properties of ES cells and express ES cell marker genes. Subcutaneous transplantation of iPS cells into nude mice resulted in tumors containing a variety of tissues from all three germ layers. Following injection into blastocysts, iPS cells contributed to mouse embryonic development. These data demonstrate that pluripotent stem cells can be directly generated from fibroblast cultures by the addition of only a few defined factors.     

Emerging roles of microRNAs in the control of embryonic stem cells and the generation of induced pluripotent stem cells

MicroRNAs (miRNAs) have emerged as critical regulators of gene expression. These small, non-coding RNAs are believed to regulate more than a third of all protein coding genes, and they have been implicated in the control of virtually all biological processes, including the biology of stem cells. The essential roles of miRNAs in the control of pluripotent stem cells were clearly established by the finding that embryonic stem (ES) cells lacking proteins required for miRNA biogenesis exhibit defects in proliferation and differentiation. Subsequently, the function of numerous miRNAs has been shown to control the fate of ES cells and to directly influence critical gene regulatory networks controlled by pluripotency factors Sox2, Oct4, and Nanog. Moreover, a growing list of tissue-specific miRNAs, which are silenced or not processed fully in ES cells, has been found to promote differentiation upon their expression and proper processing. The importance of miRNAs for ES cells is further indicated by the exciting discovery that specific miRNA mimics or miRNA inhibitors promote the reprogramming of somatic cells into induced pluripotent stem (iPS) cells. Although some progress has been made during the past two years in our understanding of the contribution of specific miRNAs during reprogramming, further progress is needed since it is highly likely that miRNAs play even wider roles in the generation of iPS cells than currently appreciated. This review examines recent developments related to the roles of miRNAs in the biology of pluripotent stem cells. In addition, we posit that more than a dozen additional miRNAs are excellent candidates for influencing the generation of iPS cells as well as for providing new insights into the process of reprogramming.     

n-Butylidenephthalide (BP) Maintains Stem Cell Pluripotency by Activating Jak2/Stat3 Pathway and Increases the Efficiency of iPS Cells Generation

In 2006, induced pluripotent stem (iPS) cells were generated from somatic cells by introducing Oct4, Sox2, c-Myc and Klf4. The original process was inefficient; maintaining the pluripotency of embryonic stem (ES) and iPS cell cultures required an expensive reagent-leukemia induced factor (LIF). Our goal is to find a pure compound that not only maintains ES and iPS cell pluripotency, but also increases iPS cell generation efficiency. From 15 candidate compounds we determined that 10 μg/ml n-Butylidenephthalide (BP), an Angelica sinensis extract, triggers the up-regulation of Oct4 and Sox2 gene expression levels in MEF cells. We used ES and iPS cells treated with different concentrations of BP to test its usefulness for maintaining stem cell pluripotency. Results indicate higher expression levels of several stem cell markers in BP-treated ES and iPS cells compared to controls that did not contain LIF, including alkaline phosphatase, SSEA1, and Nanog. Embryoid body formation and differentiation results confirm that BP containing medium culture was capable of maintaining ES cell pluripotency after six time passage. Microarray analysis data identified PPAR, ECM, and Jak-Stat signaling as the top three deregulated pathways. We subsequently determined that phosphorylated Jak2 and phosphorylated Stat3 protein levels increased following BP treatment and suppressed with the Jak2 inhibitor, AG490. The gene expression levels of cytokines associated with the Jak2-Stat3 pathway were also up-regulated. Last, we used pou5f1-GFP MEF cells to test iPS generation efficiency following BP treatment. Our data demonstrate the ability of BP to maintain stem cell pluripotency via the Jak2-Stat3 pathway by inducing cytokine expression levels, at the same time improving iPS generation efficiency.     

Characterization of bovine induced pluripotent stem cells by lentiviral transduction of reprogramming factor fusion proteins

Pluripotent stem cells from domesticated animals have potential applications in transgenic breeding. Here, we describe induced pluripotent stem (iPS) cells derived from bovine fetal fibroblasts by lentiviral transduction of Oct4, Sox2, Klf4 and c-Myc defined-factor fusion proteins. Bovine iPS cells showed typical colony morphology, normal karyotypes, stained positively for alkaline phosphatase (AP) and expressed Oct4, Nanog and SSEA1. The CpG in the promoter regions of Oct4 and Nanog were highly unmethylated in bovine iPS cells compared to the fibroblasts. The cells were able to differentiate into cell types of all three germ layers in vitro and in vivo. In addition, these cells were induced into female germ cells under defined culture conditions and expressed early and late female germ cell-specific genes Vasa, Dazl, Gdf9, Nobox, Zp2, and Zp3. Our data suggest that bovine iPS cells were generated from bovine fetal fibroblasts with defined-factor fusion proteins mediated by lentivirus and have potential applications in bovine transgenic breeding and gene-modified animals.     

Direct reprogramming of genetically unmodified fibroblasts into pluripotent stem cells

In vitro reprogramming of somatic cells into a pluripotent embryonic stem cell-like state has been achieved through retroviral transduction of murine fibroblasts with Oct4, Sox2, c-myc and Klf4. In these experiments, the rare 'induced pluripotent stem' (iPS) cells were isolated by stringent selection for activation of a neomycin-resistance gene inserted into the endogenous Oct4 (also known as Pou5f1) or Nanog loci. Direct isolation of pluripotent cells from cultured somatic cells is of potential therapeutic interest, but translation to human systems would be hindered by the requirement for transgenic donors in the present iPS isolation protocol. Here we demonstrate that reprogrammed pluripotent cells can be isolated from genetically unmodified somatic donor cells solely based upon morphological criteria.     

A novel strategy to derive iPS cells from porcine fibroblasts

Induced pluripotent stem (iPS) cell technology demonstrates that somatic cells can be reprogrammed to a pluripotent state by over-expressing four reprogramming factors. This technology has created an interest in deriving iPS cells from domesticated animals such as pigs, sheep and cattle. Moloney murine leukemia retrovirus vectors have been widely used to generate and study mouse iPS cells. However, this retrovirus system infects only mouse and rat cells, which limits its use in establishing iPS cells from other mammals. In our study, we demonstrate a novel retrovirus strategy to efficiently generate porcine iPS cells from embryonic fibroblasts. We transfected four human reprogramming factors (Oct4, Sox2, Klf4 and Myc) into fibroblasts in one step by using a VSV-G envelope-coated pantropic retrovirus that was easily packaged by GP2-293 cells. We established six embryonic stem (ES)-like cell lines in human ES cell medium supplemented with bFGF. Colonies showed a similar morphology to human ES cells with a high nuclei-cytoplasm ratio and phase-bright flat colonies. Porcine iPS cells could form embryoid bodies in vitro and differentiate into the three germ layers in vivo by forming teratomas in immunodeficient mice.     

Mouse meningiocytes express Sox2 and yield high efficiency of chimeras after nuclear reprogramming with exogenous factors

Induced pluripotent stem cell technology, also termed iPS, is an emerging approach to reprogram cells into an embryonic stem cell-like state by viral transduction with defined combinations of factors. iPS cells share most characteristics of embryonic stem cells, counting pluripotency and self-renewal, and have so far been obtained from mouse and humans, including patients with genetic diseases. Remarkably, autologous transplantation of cell lineages derived from iPS cells will eliminate the possibility of immunological rejection, as well as current ethical issues surrounding human embryonic stem cell research. However, before iPS can be used for clinical purposes, technical problems must be overcome. Among other considerations, full and homogeneous iPS reprogramming is an important prerequisite. However, despite the fact that cells from several mouse tissues can be successfully induced to iPS, the overall efficiency of chimera formation of these clones remains low even if selection for Oct4 or Nanog expression is applied. In this report, we demonstrate that cells from the mouse meningeal membranes express elevated levels of the embryonic master regulator Sox2 and are highly amenable to iPS. Meningeal iPS clones, generated without selection, are fully and homogeneously reprogrammed based on DNA methylation analysis and 100% chimera competent. Our results define a population of somatic cells that are ready to undergo iPS, thus highlighting a very attractive cell type for iPS research and application.     

人诱导性多潜能干细胞(iPS细胞)系的建立

掌握建立人iPS细胞系(induced pluripotent stem cells,iPSCs)的技术,以便为人肿瘤细胞重编程为iPS细胞建立技术平台.在人胚胎干细胞的培养条件下,通过携带Oct4、Sox2、c-Myc、Klf44个混合因子的慢病毒感染人皮肤成纤维细胞(CCD-1079SK细胞),从而诱导成干细胞样的克隆.根据人胚胎干细胞的特性进行如下鉴定:克隆形态、碱性磷酸酶活性、核型和CCD-1079SK细胞来源的克隆拟胚体(embryoid bodies,EBs)形成及分化等.结果显示,在人胚胎干细胞的培养环境中,导入Oct4、Sox2、c-Myc、Klf44个因子的CCD-1079SK细胞产生了一株iPSC克隆,这株iPSC克隆在细胞形态、增殖能力、胚胎细胞特异性表面抗原以及基因表达与人胚胎干细胞相似,此外,iPSC克隆在体外悬浮培养中形成拟胚体并分化成3个胚层.人iPS细胞系的成功建立为利用iPS细胞技术开展肿瘤细胞重编程研究奠定了坚实基础.     

Induction of pluripotent stem cells from primary human fibroblasts with only Oct4 and Sox2

Ectopic expression of defined sets of genetic factors can reprogram somatic cells to induced pluripotent stem (iPS) cells that closely resemble embryonic stem (ES) cells. The low efficiency with which iPS cells are derived hinders studies on the molecular mechanism of reprogramming, and integration of viral transgenes, in particular the oncogenes c-Myc and Klf4, may handicap this method for human therapeutic applications. Here we report that valproic acid (VPA), a histone deacetylase inhibitor, enables reprogramming of primary human fibroblasts with only two factors, Oct4 and Sox2, without the need for the oncogenes c-Myc or Klf4. The two factor-induced human iPS cells resemble human ES cells in pluripotency, global gene expression profiles and epigenetic states. These results support the possibility of reprogramming through purely chemical means, which would make therapeutic use of reprogrammed cells safer and more practical.