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REVIEW |
1 Program in Developmental and Stem Cell Biology, Hospital for Sick Children Research Institute
2 Department of Molecular Genetics, University of Toronto, MARS Building, Toronto Medical Discovery Tower, 101 College Street, Toronto, Ontario, Canada M5G 1L7
Correspondence should be addressed to J Rossant; Email: janet.rossant{at}sickkids.ca
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Abstract |
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What is pluripotency? |
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Different kinds of pluripotent stem cells exist |
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Pluripotent stem cell lines have been derived from the mouse embryo at several stages. All are capable of differentiating into cells representative of a variety of adult tissue types in various assays, including embryoid body, teratoma, and some can contribute to mouse development in chimeras (Fig. 1). However, in spite of these similarities, many differences have been noted among pluripotent stem cell types. Differences include morphology, gene expression profiles, growth factor requirements, and the ability to contribute to chimeras (Rossant 2008). The best-studied pluripotent stem cell is the ES cell, derived from mouse or human inner cell mass (ICM) at the blastocyst stage (Evans & Kaufman 1981, Martin 1981, Thomson et al. 1998). In addition, self-renewing, pluripotent stem cells, called epiblast stem cells, have been derived from the mouse embryo at a slightly later stage, when the ICM has become the epiblast (Brons et al. 2007, Tesar et al. 2007). Pluripotent mouse embryonic germ cells can be derived from embryo-derived primordial germ cells (PGCs; Matsui et al. 1992), and pluripotent cells have been derived from spontaneously arising embryonal carcinomas (EC cells). In addition, multipotent germline stem cells have been derived from neonatal and adult mouse testes cells (Kanatsu-Shinohara et al. 2004, Guan et al. 2006). Whether a common pluripotency/self-renewal pathway underlies establishment, maintenance, and regulation of all of these cell lines is an area of active research.
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The existence of different kinds of pluripotent stem cells and different reprogramming strategies raises the interesting notion that pluripotency can be achieved in different ways. Recognizing and describing these inherent differences is essential for understanding what makes cells competent to respond to pluripotency factors. Use and comparison of these different cells may thus lead to identification of new molecular regulators of development and pluripotency. Several methods have been used to identify molecular regulators of pluripotency in both stem cell lines and embryos, and these are summarized next.
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Methods for identifying pluripotency factors |
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While the list of pluripotency-associated genes continues to grow, genes involved in cellular reprogramming warrant special attention. The ability of these genes to uniquely initiate a cascade of events leading to the pluripotent stem cell state underscores their fundamental importance at the top of a pluripotency hierarchy. Much consideration has been given to how and why reprogramming even works. Initial speculation raised cautionary caveats about the role of viral integration or cell type in reprogramming. However, non-integrating vectors, excisable vectors, and even soluble proteins, have since been used for factor delivery (Okita et al. 2008, Stadtfeld et al. 2008b, Kaji et al. 2009, Soldner et al. 2009, Woltjen et al. 2009, Zhou et al. 2009). In addition, reprogramming may not involve unique rare, reprogramming-competent cells since many different cell types have been used (Nakagawa et al. 2008, Shi et al. 2008, Silva et al. 2008, Stadtfeld et al. 2008a, Guo et al. 2009), although it is hard to rule out this latter possibility completely. Regardless of the origin of the parental cell, exogenous reprogramming factors are clearly required for expansion of iPS cells. A better understanding of the requirement for these genes in embryos and in ES cells is essential to discussion of how reprogramming works.
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What are the reprogramming factors? |
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While reprogramming factors reset the cellular phenotype from the inside, reprogramming clearly also requires extrinsic signals provided by the cell culture milieu, since all reprogramming events have been performed in ES cell culture conditions. These conditions include growth factors, cytokines, and other signals provided by the cell culture medium, fetal bovine serum, and feeder cells. Together, intrinsic and extrinsic factors maintain pluripotency and guarantee self-renewal. How extrinsic signals are integrated with intrinsically acting factors is not entirely clear, but is an active area of investigation. Possibilities include activation of self-renewal/proliferation genes or repression of prodifferentiation genes. For example, signaling by the cytokine LIF leads to activation of the transcription factor STAT3, which may regulate a suite of ES cell genes (Sekkai et al. 2005, Chen et al. 2008). Bone morphogenetic protein (BMP) or serum suppresses expression of the inhibitors of differentiation (Id) family of transcription factors (Ying et al. 2003). In addition, parallel signaling pathways have been found to connect LIF signaling and transcription factors maintaining pluripotency in ES cells (Niwa et al. 2009). While ES cell signaling pathways will not be discussed further, it is important to keep in mind that they play an essential role in supporting pluripotency. Rather, we will focus on factors delivered into the cell during reprogramming.
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Early embryonic development |
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POU5F1 |
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POU5F1 plays different roles in stem cells at later stages in mouse development. At later stages, Pou5f1 is expressed in multipotent stem cells, including PGCs (Scholer et al. 1990), where it is required for survival (Kehler et al. 2004). These observations led to the proposal that POU5F1 promotes ‘stem cell-ness’ in general. However, Pou5f1 is not required for self-renewal of somatic stem cells in a wide variety of organs (Lengner et al. 2007). Thus, although POU5F1 is an essential reprogramming factor, enabling mature somatic cells to revert to an ES-like state, it does not appear to be required for somatic stem cell self-renewal. This observation underscores intrinsic differences in gain and loss of function assays. Notably, POU5F1 is sufficient to prevent differentiation and expand progenitor cell proliferations when overexpressed in adult epithelia, presumably due to expansion of adult stem cell populations (Hochedlinger et al. 2005). However, in spite of the proposed role for Pou5f1 in maintaining ES cell fates, overexpression of Pou5f1 in ES cells does not maintain their self-renewal in the absence of self-renewal factors such as LIF, but leads to their differentiation (Niwa et al. 2000). This phenotype was proposed to result from titration of other factors by overexpressed Pou5f1 in ES cells. Thus, functional differences in response to POU5F1 exist between adult and ES cells, but the molecular basis for these differences is not understood. One testable hypothesis is that different POU5F1 cofactors exist within ES and adult stem cell populations, and this could alter the response to ectopic POU5F1.
Several key POU5F1 cofactors operating in ES cells are known. According to the current view, POU5F1 acts together with SOX2 and NANOG at the core of a transcription factor network regulating pluripotency in ES cells. These three proteins have been found to co-occupy putative enhancer elements of genes thought to promote pluripotency and repress differentiation (Boyer et al. 2005, Loh et al. 2006). POU5F1 and SOX2 bind transcriptional targets in a protein-DNA ternary complex (Yuan et al. 1995), and promote their own expression (Tomioka et al. 2002, Okumura-Nakanishi et al. 2005), as well as that of Nanog (Kuroda et al. 2005) in ES cells. However, many genes are not co-occupied by all three factors (Boyer et al. 2005, Loh et al. 2006), and thus each gene must have distinct targets as well. The central importance of SOX2 and NANOG to ES and iPS cell biology is recapitulated by the requirement for these genes in early embryogenesis.
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SOX2 |
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Analysis of the requirement for Sox2 in existing ES cell lines has been informative. Reduction of Sox2 levels in established ES cell lines leads to formation of trophoblast-like cells (Li et al. 2007, Masui et al. 2007), supporting the notion that POU5F1 and SOX2 cooperate to repress trophoblast fates in ES cells. Notably, Pou5f1 overexpression can rescue Sox2 deficiency in ES cells (Masui et al. 2007), consistent with the proposal that activation of Pou5f1 expression is a major role of SOX2. However, these observations also suggest that POU5F1/SOX2 dimerization is not essential for activation of pluripotency network genes, although this proposal has not been tested by direct interference of POU5F1/SOX2 binding. Similar to the consequences of Pou5f1 overexpression, overexpression of Sox2 also leads to rapid differentiation of ES cells (Kopp et al. 2008).
The role of Sox2 as a general supporter of stem cell behavior has been examined in other stem cell contexts as well. SOX2 is also highly expressed in progenitor cells throughout the CNS. Sox2 is not absolutely required for neural stem cell self-renewal or multipotency (Miyagi et al. 2008). However, genetic redundancy with other SOX factors may mask its role. Interestingly, in retinal progenitor cells, where Sox2 is the sole SOX factor expressed, Sox2 is required for proliferation and differentiation (Taranova et al. 2006). Beyond regulating proliferation, Sox2 plays important roles in embryo patterning, such as foregut patterning (Que et al. 2007). Thus, Sox2 appears to be regulated in a context-dependent manner to achieve multiple developmental outcomes.
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NANOG |
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The requirement for Nanog in pluripotency has been examined to some extent as well. Deletion of Nanog from existing ES cells does not eliminate their ability to self-renew or contribute to embryos in chimeras (Mitsui et al. 2003, Chambers et al. 2007). Nanog null ES cells exhibit subtle morphological differences and are more prone to differentiate than wild type ES cells (Mitsui et al. 2003, Chambers et al. 2007). Normal populations of ES cells, in fact, appear to express variable levels of NANOG, with those expressing less NANOG being more prone to differentiation and less prone to self-renewal (Hatano et al. 2005, Chambers et al. 2007). Thus, NANOG levels may act as a switch, allowing ES cells to rapidly choose between self-renewal and differentiation. Importantly, Pou5f1 and Sox2 continue to be expressed in ES cells forcibly lacking NANOG, as are all other ES cell markers examined (Chambers et al. 2007). This observation is consistent with the fact that Pou5f1 and Sox2 are alone sufficient to initiate the reprogramming cascade in both mouse and human cells in the absence of ectopic Nanog (Takahashi & Yamanaka 2006, Takahashi et al. 2007). Nonetheless, overexpression of Nanog in mouse ES cells can prevent differentiation in the absence of the critical self-renewal cytokine LIF (Chambers et al. 2003, Mitsui et al. 2003). Thus, Nanog is sufficient, but not necessary for ensuring self-renewal.
The role of Nanog in other stem cell types of the mouse has been examined to a limited extent. Nanog is also expressed in the germline (Hatano et al. 2005), and Nanog mutant ES cells are not detected in the germline beyond embryonic day 11.5 (Chambers et al. 2007), suggesting a requirement for Nanog in germline stem cells. Analysis of the requirement for Nanog in the mouse at later stages should provide interesting insight into its role in adult stem cells, and how these differ from pluripotent stem cells.
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KLF4 |
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KLF4 is sufficient to trigger reprogramming when combined with POU5F1 and SOX2, and supports other KLF factors during pluripotency and self-renewal. Consistent with this, overexpression of Klf4 can reduce ES cell differentiation in some assays (Li et al. 2005). In addition, other KLF factors, such as KLF1, KLF2, and KLF5 can substitute for KLF4 during reprogramming, albeit with lower efficiency (Nakagawa et al. 2008). Genome-wide location analysis revealed that the KLF factors bind putative regulatory elements of Pou5f1, Sox2, Nanog, and many other pluripotency-associated genes (Nakagawa et al. 2008). Thus, KLF may participate in regulating a pluripotency network.
Examination of the requirement for other KLF factors has led to some insight into the connection between KLF factors in ES cells and their establishment in the early embryo. While loss of Klf2 leads to embryonic lethality between embryonic days 12–14 owing to severe hemorrhage (Kuo et al. 1997), loss of Klf5 has a much earlier phenotype. Loss of Klf5 leads to lethality due to trophoblast defects around the blastocyst stage (Ema et al. 2008). ES cells cannot be derived from Klf5 null embryos, even when trophoblast tissues are rescued by tetraploid complementation (Ema et al. 2008). When deleted from existing ES cells, ES cells continue to self-renew, although they are more prone to spontaneously differentiate and proliferate more slowly (Ema et al. 2008). This phenotype was not observed in RNAi knockdown experiments. However, it is not currently clear whether this discrepancy is due to differences between ES cell establishment and maintenance, or simply to the assay in use. Overexpression of Klf4 can rescue Klf5-deficient ES cells Klf5 (Ema et al. 2008), again suggesting some redundancy between these Klf factors.
Since Klf4 and Klf5 play overlapping roles in pluripotency, study of Klf5 may provide insight into the mechanism by which Klf4 promotes pluripotency. One mechanism proposed for KLF5-mediated maintenance of ES cell self-renewal involves the TCL1–AKT pathway. Both TCL1 levels and AKT phosphorylation are reduced in ES cells in the absence of Klf5, and expression of a constitutively active form of AKT partially restores the rate of proliferation to wild-type levels. These observations suggest that KLF factors may regulate self-renewal through regulation of AKT signaling. Alternatively, KLF4 may upregulate Nanog during reprogramming by repressing p53 (Rowland et al. 2005). Elucidating the precise molecular mechanisms underlying the role of KLF factors in maintaining and driving pluripotency will be an exciting avenue for future research.
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ESRRB |
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Both the timing and tissues affected differ between Esrrb and Klf gene family knockouts. Esrrb knockout embryos die around E10.5 with placental defects (Luo et al. 1997). Moreover, deletion of Esrrb strictly within the embryonic lineage rescues this phenotype (Luo et al. 1997), arguing for a specific requirement for Esrrb in the extraembryonic lineage. Genetic redundancy with the related genes Esrra or Esrrg could preclude observation of a requirement for Esrrb in the embryonic lineage. Interestingly, Esrrg, but not Esrra could also promote reprogramming in the presence of POU5F1 and SOX2 (Feng et al. 2009a). Analysis of Esrrb and Esrrg double knockout embryos would therefore be particularly interesting.
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MYC |
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In addition to promoting proliferation and survival of somatic stem cells, MYC may play an important role in ES cell proliferation. Myc levels are decreased as ES cells undergo differentiation during LIF withdrawal, and overexpression of a dominant-negative MYC promotes differentiation (Cartwright et al. 2005). Interestingly, overexpression of stable, non-phosphorylable MYC variant can delay differentiation (Cartwright et al. 2005), suggesting a potential link between proliferation and potency.
Although it is still unclear what role MYC plays during reprogramming, several models have been proposed (Knoepfler 2008). For example, MYC may simply promote proliferation, which could indirectly alter the state of the cell or activity of the reprogramming factors, i.e. MYC-stimulated proliferation could lead to chromatin remodeling, facilitating access of reprogramming factors to pluripotency targets. This hypothesis is consistent with the finding that the related protein MYCN influences chromatin structure in neural stem cells (Knoepfler et al. 2006). Alternatively, MYC may have its own set of pluripotency targets. MYC and the LIF signaling target STAT3 co-occupy putative regulatory elements of many pluripotency-associated genes in ES cells (Kidder et al. 2008). Thus, MYC may help transduce pluripotency-promoting effects of signaling pathways.
While MYC can be omitted completely during reprogramming, its inclusion greatly increases efficiency (Nakagawa et al. 2008). Importantly, fibroblasts express Myc at around 20% of levels expressed in ES cells, and this is increased during reprogramming (Nakagawa et al. 2008), suggesting that endogenous Myc still participates in reprogramming. Nonetheless, it may be safer to avoid use of exogenous Myc, as tumors have been observed to arise in mice generated from iPS cells bearing MYC, but not from those that did not (Takahashi & Yamanaka 2006, Takahashi et al. 2007), although this appears to be cell type-specific (Nakagawa et al. 2008). As an alternative, other MYC paralogs can substitute in the reprogramming mix. For example, MYCL1 (Nakagawa et al. 2008) and MYCN have been used, resulting in reduced tumorigenicity (Blelloch et al. 2007, Nakagawa et al. 2008).
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The microRNA pathway |
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Lin28 is expressed at high levels in both mouse and human ES cells, and is downregulated during their differentiation (Yang & Moss 2003, Richards et al. 2004). Lin28 has recently been found to be necessary and sufficient to inhibit processing of the miRNA let7 in mouse ES cells (Viswanathan et al. 2008). However, levels of pluripotency markers were unchanged (Viswanathan et al. 2008). Nonetheless, Lin28 is able to participate in cellular reprogramming in human cells (Yu et al. 2007) and promote proliferation of tumor cells (Guo et al. 2006). The explanation for this behavior may lie with the fact that LIN28 appears to be capable of regulating Myc through let7, i.e. the miRNA let7 (Mirlet7), which is regulated by LIN28, can target Myc for degradation (Koscianska et al. 2007, Kumar et al. 2007). Consistent with this observation, Lin28 can regulate Myc expression in cultured myoblasts (Polesskaya et al. 2007). These observations are consistent with Lin28 substituting for Myc during reprogramming in human cells. Examination of the requirement for Lin28 during mouse development should help reveal to what extent Lin28 activity is conserved between human and mouse, and whether there are additional Lin28 targets besides Myc.
More recently, a subset of miRNAs was found to increase efficiency of mouse fibroblast reprogramming by POU5F1, SOX2, and KLF4 (Judson et al. 2009). Importantly, these miRNAs, which include members of the miR-290 family, led to an increased proportion of correctly reprogrammed iPS colonies, than when MYC was used. More detailed analysis revealed that the expression of these miRNAs is normally activated during conventional 3 or 4 factor-based reprogramming, but not until relatively late in the process, suggesting that these miRNAs act fairly downstream in the reprogramming process.
Members of the miR-290 family are normally expressed in ES cells and downregulated during their differentiation (Wang et al. 2008). These miRNAs play an important role in cell cycle regulation in self-renewing ES cells (Wang et al. 2008). However, during reprogramming they may act downstream of MYC and subsequent to chromatin remodeling (Judson et al. 2009). The requirement for the miR-290 cluster during embryonic development has not been reported. Partial insight into this issue may be provided by analysis of loss of Dgcr8, an RNA-binding protein specific to the miRNA pathway (Wang et al. 2007). Knockout of Dgcr8 leads to abnormal development by E6.5, and lethality sometime prior to E10 (Wang et al. 2007), consistent with a possible role in early lineage specification.
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Programming and reprogramming in reproduction and human health |
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While the list of genes sufficient to induce pluripotency in mature cell types continues to grow, so do the number of small molecules capable of substituting for one or more of them. Together, these studies will facilitate alternative and possibly safer mechanisms for cellular reprogramming, with the ultimate goal of generating patient-derived stem cells for therapeutic treatment of a variety of human health issues. Meanwhile, examination of the role of these genes during embryonic development in the mouse will help us close the gap between induced pluripotency and fetal health.
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Declaration of interest |
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Funding |
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Acknowledgements |
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Received January 26, 2009
First decision March 23, 2009
Revised manuscript received June 18, 2009
Accepted July 15, 2009
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References |
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Avilion AA, Nicolis SK, Pevny LH, Perez L, Vivian N & Lovell-Badge R 2003 Multipotent cell lineages in early mouse development depend on SOX2 function. Genes and Development 17 126–140.
Bernstein BE, Mikkelsen TS, Xie X, Kamal M, Huebert DJ, Cuff J, Fry B, Meissner A, Wernig M, Plath K et al. 2006 A bivalent chromatin structure marks key developmental genes in embryonic stem cells. Cell 125 315–326.[CrossRef][Web of Science][Medline]
Blelloch R, Venere M, Yen J & Ramalho-Santos M 2007 Generation of induced pluripotent stem cells in the absence of drug selection. Cell Stem Cell 1 245–247.[CrossRef][Web of Science][Medline]
Boyer LA, Lee TI, Cole MF, Johnstone SE, Levine SS, Zucker JP, Guenther MG, Kumar RM, Murray HL, Jenner RG et al. 2005 Core transcriptional regulatory circuitry in human embryonic stem cells. Cell 122 947–956.[CrossRef][Web of Science][Medline]
Brons IG, Smithers LE, Trotter MW, Rugg-Gunn P, Sun B, Chuva de Sousa Lopes SM, Howlett SK, Clarkson A, Ahrlund-Richter L, Pedersen RA et al. 2007 Derivation of pluripotent epiblast stem cells from mammalian embryos. Nature 448 191–195.[CrossRef][Medline]
Cartwright P, McLean C, Sheppard A, Rivett D, Jones K & Dalton S 2005 LIF/STAT3 controls ES cell self-renewal and pluripotency by a Myc-dependent mechanism. Development 132 885–896.
Chambers I, Colby D, Robertson M, Nichols J, Lee S, Tweedie S & Smith A 2003 Functional expression cloning of Nanog, a pluripotency sustaining factor in embryonic stem cells. Cell 113 643–655.[CrossRef][Web of Science][Medline]
Chambers I, Silva J, Colby D, Nichols J, Nijmeijer B, Robertson M, Vrana J, Jones K, Grotewold L & Smith A 2007 Nanog safeguards pluripotency and mediates germline development. Nature 450 1230–1234.[CrossRef][Web of Science][Medline]
Chazaud C, Yamanaka Y, Pawson T & Rossant J 2006 Early lineage segregation between epiblast and primitive endoderm in mouse blastocysts through the Grb2–MAPK pathway. Developmental Cell 10 615–624.[CrossRef][Web of Science][Medline]
Chen X, Xu H, Yuan P, Fang F, Huss M, Vega VB, Wong E, Orlov YL, Zhang W, Jiang J et al. 2008 Integration of external signaling pathways with the core transcriptional network in embryonic stem cells. Cell 133 1106–1117.[CrossRef][Web of Science][Medline]
Davis AC, Wims M, Spotts GD, Hann SR & Bradley A 1993 A null c-myc mutation causes lethality before 10.5 days of gestation in homozygotes and reduced fertility in heterozygous female mice. Genes and Development 7 671–682.
Dubois NC, Adolphe C, Ehninger A, Wang RA, Robertson EJ & Trumpp A 2008 Placental rescue reveals a sole requirement for c-Myc in embryonic erythroblast survival and hematopoietic stem cell function. Development 135 2455–2465.
Ema M, Mori D, Niwa H, Hasegawa Y, Yamanaka Y, Hitoshi S, Mimura J, Kawabe Y, Hosoya T, Morita M et al. 2008 Kruppel-like factor 5 is essential for blastocyst development and the normal self-renewal of mouse ESCs. Cell Stem Cell 3 555–567.[CrossRef][Web of Science][Medline]
Evans MJ & Kaufman MH 1981 Establishment in culture of pluripotential cells from mouse embryos. Nature 292 154–156.[CrossRef][Medline]
Feng B, Jiang J, Kraus P, Ng JH, Heng JC, Chan YS, Yaw LP, Zhang W, Loh YH, Han J et al. 2009a Reprogramming of fibroblasts into induced pluripotent stem cells with orphan nuclear receptor Esrrb. Nature Cell Biology 11 197–203.[CrossRef][Web of Science][Medline]
Feng B, Ng JH, Heng JC & Ng HH 2009b Molecules that promote or enhance reprogramming of somatic cells to induced pluripotent stem cells. Cell Stem Cell 4 301–312.[CrossRef][Web of Science][Medline]
Guan K, Nayernia K, Maier LS, Wagner S, Dressel R, Lee JH, Nolte J, Wolf F, Li M, Engel W et al. 2006 Pluripotency of spermatogonial stem cells from adult mouse testis. Nature 440 1199–1203.[CrossRef][Medline]
Guo Y, Chen Y, Ito H, Watanabe A, Ge X, Kodama T & Aburatani H 2006 Identification and characterization of lin-28 homolog B (LIN28B) in human hepatocellular carcinoma. Gene 384 51–61.[CrossRef][Web of Science][Medline]
Guo G, Yang J, Nichols J, Hall JS, Eyres I, Mansfield W & Smith A 2009 Klf4 reverts developmentally programmed restriction of ground state pluripotency. Development 136 1063–1069.
Hatano SY, Tada M, Kimura H, Yamaguchi S, Kono T, Nakano T, Suemori H, Nakatsuji N & Tada T 2005 Pluripotential competence of cells associated with Nanog activity. Mechanisms of Development 122 67–79.[CrossRef][Web of Science][Medline]
Hochedlinger K, Yamada Y, Beard C & Jaenisch R 2005 Ectopic expression of Oct-4 blocks progenitor-cell differentiation and causes dysplasia in epithelial tissues. Cell 121 465–477.[CrossRef][Web of Science][Medline]
Huangfu D, Osafune K, Maehr R, Guo W, Eijkelenboom A, Chen S, Muhlestein W & Melton DA 2008 Induction of pluripotent stem cells from primary human fibroblasts with only Oct4 and Sox2. Nature Biotechnology 26 1269–1275.[CrossRef][Web of Science][Medline]
Ivanova N, Dobrin R, Lu R, Kotenko I, Levorse J, DeCoste C, Schafer X, Lun Y & Lemischka IR 2006 Dissecting self-renewal in stem cells with RNA interference. Nature 442 533–538.[CrossRef][Medline]
Jiang J, Chan YS, Loh YH, Cai J, Tong GQ, Lim CA, Robson P, Zhong S & Ng HH 2008 A core Klf circuitry regulates self-renewal of embryonic stem cells. Nature Cell Biology 10 353–360.[CrossRef][Web of Science][Medline]
Judson RL, Babiarz JE, Venere M & Blelloch R 2009 Embryonic stem cell-specific microRNAs promote induced pluripotency. Nature Biotechnology 27 459–461.[CrossRef][Web of Science][Medline]
Kaji K, Norrby K, Paca A, Mileikovsky M, Mohseni P & Woltjen K 2009 Virus-free induction of pluripotency and subsequent excision of reprogramming factors. Nature 458 771–775.[CrossRef][Web of Science][Medline]
Kanatsu-Shinohara M, Inoue K, Lee J, Yoshimoto M, Ogonuki N, Miki H, Baba S, Kato T, Kazuki Y, Toyokuni S et al. 2004 Generation of pluripotent stem cells from neonatal mouse testis. Cell 119 1001–1012.[CrossRef][Web of Science][Medline]
Katz JP, Perreault N, Goldstein BG, Lee CS, Labosky PA, Yang VW & Kaestner KH 2002 The zinc-finger transcription factor Klf4 is required for terminal differentiation of goblet cells in the colon. Development 129 2619–2628.
Kehler J, Tolkunova E, Koschorz B, Pesce M, Gentile L, Boiani M, Lomeli H, Nagy A, McLaughlin KJ, Scholer HR et al. 2004 Oct4 is required for primordial germ cell survival. EMBO Reports 5 1078–1083.[CrossRef][Web of Science][Medline]
Kidder BL, Yang J & Palmer S 2008 Stat3 and c-Myc genome-wide promoter occupancy in embryonic stem cells. PLoS ONE 3 e3932.[CrossRef][Medline]
Kim JB, Zaehres H, Wu G, Gentile L, Ko K, Sebastiano V, Arauzo-Bravo MJ, Ruau D, Han DW, Zenke M et al. 2008 Pluripotent stem cells induced from adult neural stem cells by reprogramming with two factors. Nature 454 646–650.[CrossRef][Web of Science][Medline]
Kim JB, Sebastiano V, Wu G, Arauzo-Bravo MJ, Sasse P, Gentile L, Ko K, Ruau D, Ehrich M, van den Boom D et al. 2009 Oct4-induced pluripotency in adult neural stem cells. Cell 136 411–419.[CrossRef][Web of Science][Medline]
Knoepfler PS 2008 Why myc? An unexpected ingredient in the stem cell cocktail. Cell Stem Cell 2 18–21.[CrossRef][Web of Science][Medline]
Knoepfler PS, Cheng PF & Eisenman RN 2002 N-myc is essential during neurogenesis for the rapid expansion of progenitor cell populations and the inhibition of neuronal differentiation. Genes and Development 16 2699–2712.
Knoepfler PS, Zhang XY, Cheng PF, Gafken PR, McMahon SB & Eisenman RN 2006 Myc influences global chromatin structure. EMBO Journal 25 2723–2734.[CrossRef][Web of Science][Medline]
Kopp JL, Ormsbee BD, Desler M & Rizzino A 2008 Small increases in the level of Sox2 trigger the differentiation of mouse embryonic stem cells. Stem Cells 26 903–911.[CrossRef][Web of Science][Medline]
Koscianska E, Baev V, Skreka K, Oikonomaki K, Rusinov V, Tabler M & Kalantidis K 2007 Prediction and preliminary validation of oncogene regulation by miRNAs. BMC Molecular Biology 8 79.[CrossRef][Medline]
Kumar MS, Lu J, Mercer KL, Golub TR & Jacks T 2007 Impaired microRNA processing enhances cellular transformation and tumorigenesis. Nature Genetics 39 673–677.[CrossRef][Web of Science][Medline]
Kuo CT, Veselits ML, Barton KP, Lu MM, Clendenin C & Leiden JM 1997 The LKLF transcription factor is required for normal tunica media formation and blood vessel stabilization during murine embryogenesis. Genes and Development 11 2996–3006.
Kuroda T, Tada M, Kubota H, Kimura H, Hatano SY, Suemori H, Nakatsuji N & Tada T 2005 Octamer and Sox elements are required for transcriptional cis regulation of Nanog gene expression. Molecular and Cellular Biology 25 2475–2485.
Lengner CJ, Camargo FD, Hochedlinger K, Welstead GG, Zaidi S, Gokhale S, Scholer HR, Tomilin A & Jaenisch R 2007 Oct4 expression is not required for mouse somatic stem cell self-renewal. Cell Stem Cell 1 403–415.[CrossRef][Web of Science][Medline]
Li Y, McClintick J, Zhong L, Edenberg HJ, Yoder MC & Chan RJ 2005 Murine embryonic stem cell differentiation is promoted by SOCS-3 and inhibited by the zinc finger transcription factor Klf4. Blood 105 635–637.
Li J, Pan G, Cui K, Liu Y, Xu S & Pei D 2007 A dominant-negative form of mouse SOX2 induces trophectoderm differentiation and progressive polyploidy in mouse embryonic stem cells. Journal of Biological Chemistry 282 19481–19492.
Li W, Wei W, Zhu S, Zhu J, Shi Y, Lin T, Hao E, Hayek A, Deng H & Ding S 2009 Generation of rat and human induced pluripotent stem cells by combining genetic reprogramming and chemical inhibitors. Cell Stem Cell 4 16–19.[CrossRef][Web of Science][Medline]
Liu H, Zhu F, Yong J, Zhang P, Hou P, Li H, Jiang W, Cai J, Liu M, Cui K et al. 2008 Generation of induced pluripotent stem cells from adult rhesus monkey fibroblasts. Cell Stem Cell 3 587–590.[CrossRef][Web of Science][Medline]
Loh YH, Wu Q, Chew JL, Vega VB, Zhang W, Chen X, Bourque G, George J, Leong B, Liu J et al. 2006 The Oct4 and Nanog transcription network regulates pluripotency in mouse embryonic stem cells. Nature Genetics 38 431–440.[CrossRef][Web of Science][Medline]
Luo J, Sladek R, Bader JA, Matthyssen A, Rossant J & Giguere V 1997 Placental abnormalities in mouse embryos lacking the orphan nuclear receptor ERR-beta. Nature 388 778–782.[CrossRef][Medline]
Maherali N & Hochedlinger K 2008 Guidelines and techniques for the generation of induced pluripotent stem cells. Cell Stem Cell 3 595–605.[CrossRef][Web of Science][Medline]
Martin GR 1981 Isolation of a pluripotent cell line from early mouse embryos cultured in medium conditioned by teratocarcinoma stem cells. PNAS 78 7634–7638.
Masui S, Nakatake Y, Toyooka Y, Shimosato D, Yagi R, Takahashi K, Okochi H, Okuda A, Matoba R, Sharov AA et al. 2007 Pluripotency governed by Sox2 via regulation of Oct3/4 expression in mouse embryonic stem cells. Nature Cell Biology 9 625–635.[CrossRef][Web of Science][Medline]
Matsui Y, Zsebo K & Hogan BL 1992 Derivation of pluripotential embryonic stem cells from murine primordial germ cells in culture. Cell 70 841–847.[CrossRef][Web of Science][Medline]
Mitsui K, Tokuzawa Y, Itoh H, Segawa K, Murakami M, Takahashi K, Maruyama M, Maeda M & Yamanaka S 2003 The homeoprotein Nanog is required for maintenance of pluripotency in mouse epiblast and ES cells. Cell 113 631–642.[CrossRef][Web of Science][Medline]
Miyagi S, Masui S, Niwa H, Saito T, Shimazaki T, Okano H, Nishimoto M, Muramatsu M, Iwama A & Okuda A 2008 Consequence of the loss of Sox2 in the developing brain of the mouse. FEBS Letters 582 2811–2815.[CrossRef][Web of Science][Medline]
Nakagawa M, Koyanagi M, Tanabe K, Takahashi K, Ichisaka T, Aoi T, Okita K, Mochiduki Y, Takizawa N & Yamanaka S 2008 Generation of induced pluripotent stem cells without Myc from mouse and human fibroblasts. Nature Biotechnology 26 101–106.[CrossRef][Web of Science][Medline]
Nakatake Y, Fukui N, Iwamatsu Y, Masui S, Takahashi K, Yagi R, Yagi K, Miyazaki J, Matoba R, Ko MS et al. 2006 Klf4 cooperates with Oct3/4 and Sox2 to activate the Lefty1 core promoter in embryonic stem cells. Molecular and Cellular Biology 26 7772–7782.
Nichols J, Zevnik B, Anastassiadis K, Niwa H, Klewe-Nebenius D, Chambers I, Scholer H & Smith A 1998 Formation of pluripotent stem cells in the mammalian embryo depends on the POU transcription factor Oct4. Cell 95 379–391.[CrossRef][Web of Science][Medline]
Niwa H, Miyazaki J & Smith AG 2000 Quantitative expression of Oct-3/4 defines differentiation, dedifferentiation or self-renewal of ES cells. Nature Genetics 24 372–376.[CrossRef][Web of Science][Medline]
Niwa H, Ogawa K, Shimosato D & Adachi K 2009 A parallel circuit of LIF signalling pathways maintains pluripotency of mouse ES cells. Nature 460 118–122.[CrossRef][Web of Science][Medline]
Okita K, Nakagawa M, Hyenjong H, Ichisaka T & Yamanaka S 2008 Generation of mouse induced pluripotent stem cells without viral vectors. Science 322 949–953.
Okumura-Nakanishi S, Saito M, Niwa H & Ishikawa F 2005 Oct-3/4 and Sox2 regulate Oct-3/4 gene in embryonic stem cells. Journal of Biological Chemistry 280 5307–5317.
Park IH, Zhao R, West JA, Yabuuchi A, Huo H, Ince TA, Lerou PH, Lensch MW & Daley GQ 2008 Reprogramming of human somatic cells to pluripotency with defined factors. Nature 451 141–146.[CrossRef][Medline]
Polesskaya A, Cuvellier S, Naguibneva I, Duquet A, Moss EG & Harel-Bellan A 2007 Lin-28 binds IGF-2 mRNA and participates in skeletal myogenesis by increasing translation efficiency. Genes and Development 21 1125–1138.
Que J, Okubo T, Goldenring JR, Nam KT, Kurotani R, Morrisey EE, Taranova O, Pevny LH & Hogan BL 2007 Multiple dose-dependent roles for Sox2 in the patterning and differentiation of anterior foregut endoderm. Development 134 2521–2531.
Richards M, Tan SP, Tan JH, Chan WK & Bongso A 2004 The transcriptome profile of human embryonic stem cells as defined by SAGE. Stem Cells 22 51–64.[CrossRef][Web of Science][Medline]
Rossant J 2008 Stem cells and early lineage development. Cell 132 527–531.[CrossRef][Web of Science][Medline]
Rowland BD, Bernards R & Peeper DS 2005 The KLF4 tumour suppressor is a transcriptional repressor of p53 that acts as a context-dependent oncogene. Nature Cell Biology 7 1074–1082.[Web of Science][Medline]
Scholer HR, Dressler GR, Balling R, Rohdewohld H & Gruss P 1990 Oct-4: a germline-specific transcription factor mapping to the mouse t-complex. EMBO Journal 9 2185–2195.[Web of Science][Medline]
Segre JA, Bauer C & Fuchs E 1999 Klf4 is a transcription factor required for establishing the barrier function of the skin. Nature Genetics 22 356–360.[CrossRef][Web of Science][Medline]
Sekkai D, Gruel G, Herry M, Moucadel V, Constantinescu SN, Albagli O, Tronik-Le Roux D, Vainchenker W & Bennaceur-Griscelli A 2005 Microarray analysis of LIF/Stat3 transcriptional targets in embryonic stem cells. Stem Cells 23 1634–1642.[CrossRef][Web of Science][Medline]
Shi Y, Do JT, Desponts C, Hahm HS, Scholer HR & Ding S 2008 A combined chemical and genetic approach for the generation of induced pluripotent stem cells. Cell Stem Cell 2 525–528.[CrossRef][Web of Science][Medline]
Silva J, Barrandon O, Nichols J, Kawaguchi J, Theunissen TW & Smith A 2008 Promotion of reprogramming to ground state pluripotency by signal inhibition. PLoS Biology 6 e253.[CrossRef][Medline]
Simmons DG & Cross JC 2005 Determinants of trophoblast lineage and cell subtype specification in the mouse placenta. Developmental Biology 284 12–24.[CrossRef][Web of Science][Medline]
Soldner F, Hockemeyer D, Beard C, Gao Q, Bell GW, Cook EG, Hargus G, Blak A, Cooper O, Mitalipova M et al. 2009 Parkinson's disease patient-derived induced pluripotent stem cells free of viral reprogramming factors. Cell 136 964–977.[CrossRef][Web of Science][Medline]
Stadtfeld M, Brennand K & Hochedlinger K 2008a Reprogramming of pancreatic beta cells into induced pluripotent stem cells. Current Biology 18 890–894.[CrossRef][Web of Science][Medline]
Stadtfeld M, Nagaya M, Utikal J, Weir G & Hochedlinger K 2008b Induced pluripotent stem cells generated without viral integration. Science 322 945–949.
Tada M, Takahama Y, Abe K, Nakatsuji N & Tada T 2001 Nuclear reprogramming of somatic cells by in vitro hybridization with ES cells. Current Biology 11 1553–1558.[CrossRef][Web of Science][Medline]
Takahashi K & Yamanaka S 2006 Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell 126 663–676.[CrossRef][Web of Science][Medline]
Takahashi K, Tanabe K, Ohnuki M, Narita M, Ichisaka T, Tomoda K & Yamanaka S 2007 Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell 131 861–872.[CrossRef][Medline]
Taranova OV, Magness ST, Fagan BM, Wu Y, Surzenko N, Hutton SR & Pevny LH 2006 SOX2 is a dose-dependent regulator of retinal neural progenitor competence. Genes and Development 20 1187–1202.
Tesar PJ, Chenoweth JG, Brook FA, Davies TJ, Evans EP, Mack DL, Gardner RL & McKay RD 2007 New cell lines from mouse epiblast share defining features with human embryonic stem cells. Nature 448 196–199.[CrossRef][Medline]
Thomson JA, Itskovitz-Eldor J, Shapiro SS, Waknitz MA, Swiergiel JJ, Marshall VS & Jones JM 1998 Embryonic stem cell lines derived from human blastocysts. Science 282 1145–1147.
Tomioka M, Nishimoto M, Miyagi S, Katayanagi T, Fukui N, Niwa H, Muramatsu M & Okuda A 2002 Identification of Sox-2 regulatory region which is under the control of Oct-3/4-Sox-2 complex. Nucleic Acids Research 30 3202–3213.
Viswanathan SR, Daley GQ & Gregory RI 2008 Selective blockade of microRNA processing by Lin28. Science 320 97–100.
Walker E, Ohishi M, Davey RE, Zhang W, Cassar PA, Tanaka TS, Der SD, Morris Q, Hughes TR, Zandstra PW et al. 2007 Prediction and testing of novel transcriptional networks regulating embryonic stem cell self-renewal and commitment. Cell Stem Cell 1 71–86.[CrossRef][Web of Science][Medline]
Wang J, Rao S, Chu J, Shen X, Levasseur DN, Theunissen TW & Orkin SH 2006 A protein interaction network for pluripotency of embryonic stem cells. Nature 444 364–368.[CrossRef][Medline]
Wang Y, Medvid R, Melton C, Jaenisch R & Blelloch R 2007 DGCR8 is essential for microRNA biogenesis and silencing of embryonic stem cell self-renewal. Nature Genetics 39 380–385.[CrossRef][Web of Science][Medline]
Wang Y, Baskerville S, Shenoy A, Babiarz JE, Baehner L & Blelloch R 2008 Embryonic stem cell-specific microRNAs regulate the G1-S transition and promote rapid proliferation. Nature Genetics 40 1478–1483.[CrossRef][Web of Science][Medline]
Wernig M, Meissner A, Foreman R, Brambrink T, Ku M, Hochedlinger K, Bernstein BE & Jaenisch R 2007 In vitro reprogramming of fibroblasts into a pluripotent ES-cell-like state. Nature 448 318–324.[CrossRef][Medline]
West JA, Viswanthan SR, Yabuuchi A, Cunniff K, Takeuchi A, Park IH, Sero JE, Zhu H, Perez-Atayde A, Frazier AL et al. 2009 A role for Lin28 in primordial germ-cell development and germ-cell malignancy. Nature 460 909–913.[Web of Science][Medline]
Wilmut I, Schnieke AE, McWhir J, Kind AJ & Campbell KH 1997 Viable offspring derived from fetal and adult mammalian cells. Nature 385 810–813.[CrossRef][Medline]
Wilson A, Murphy MJ, Oskarsson T, Kaloulis K, Bettess MD, Oser GM, Pasche AC, Knabenhans C, Macdonald HR & Trumpp A 2004 c-Myc controls the balance between hematopoietic stem cell self-renewal and differentiation. Genes and Development 18 2747–2763.
Woltjen K, Michael IP, Mohseni P, Desai R, Mileikovsky M, Hamalainen R, Cowling R, Wang W, Liu P, Gertsenstein M et al. 2009 piggyBac transposition reprograms fibroblasts to induced pluripotent stem cells. Nature 458 766–770.[CrossRef][Web of Science][Medline]
Yamanaka Y, Ralston A, Stephenson RO & Rossant J 2006 Cell and molecular regulation of the mouse blastocyst. Developmental Dynamics 235 2301–2314.[CrossRef][Web of Science][Medline]
Yang DH & Moss EG 2003 Temporally regulated expression of Lin-28 in diverse tissues of the developing mouse. Gene Expression Patterns 3 719–726.[CrossRef][Web of Science][Medline]
Ying QL, Nichols J, Chambers I & Smith A 2003 BMP induction of Id proteins suppresses differentiation and sustains embryonic stem cell self-renewal in collaboration with STAT3. Cell 115 281–292.[CrossRef][Web of Science][Medline]
Yu J, Vodyanik MA, Smuga-Otto K, Antosiewicz-Bourget J, Frane JL, Tian S, Nie J, Jonsdottir GA, Ruotti V, Stewart R et al. 2007 Induced pluripotent stem cell lines derived from human somatic cells. Science 318 1917–1920.
Yuan H, Corbi N, Basilico C & Dailey L 1995 Developmental-specific activity of the FGF-4 enhancer requires the synergistic action of Sox2 and Oct-3. Genes and Development 9 2635–2645.
Zhou H, Wu S, Joo JY, Zhu S, Han DW, Lin T, Trauger S, Bien G, Yao S, Zhu Y et al. 2009 Generation of induced pluripotent stem cells using recombinant proteins. Cell Stem Cell 4 381–384.[CrossRef][Web of Science][Medline]
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Abstract
What is pluripotency?
