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What Are Stem Cells?
(Released December 2004)

  by Preeti Gokal Kochar  


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  1. Specific Knockdown of Oct4 and beta 2-microglobulin Expression by RNA Interference in Human Embryonic Stem Cells and Embryonic Carcinoma Cells

    Matin, Maryam M; Walsh, James R; Gokhale, Paul J; Draper, Jonathan S; Bahrami, Ahmad R; Morton, Ian; Moore, Harry D; Andrews, Peter W

    Stem Cells [Stem Cells]. Vol. 22, no. 5, pp. 659-668. Sep 2004.

    We have used RNA interference (RNAi) to downregulate beta 2-microglobulin and Oct4 in human embryonal carcinoma (hEC) cells and embryonic stem (hES) cells, demonstrating that RNAi is an effective tool for regulating specific gene activity in these human stem cells. The knockdown of Oct4 but not beta 2- microglobulin expression in both EC and ES cells resulted in their differentiation, as indicated by a marked change in morphology, growth rate, and surface antigen phenotype, with respect to SSEA1, SSEA3, and TRA-1-60 expression. Expression of hCG and Gcm1 was also induced following knockdown of Oct4 expression, in both 2102Ep hEC cells and in H7 and H14 hES cells, consistent with the conclusion that, as in the mouse, Oct4 is required to maintain the undifferentiated stem cell state, and that differentiation to trophectoderm occurs in its absence. NTERA2 hEC cells also differentiated, but not to trophectoderm, suggesting their equivalence to a later stage of embryogenesis than other hEC and hES cells.

  2. Strategies for Directing the Differentiation of Stem Cells Into the Osteogenic Lineage In Vitro

    Heng, Boon Chin; Cao, Tong; Stanton, LW; Robson, P; Olsen, B

    Journal of Bone and Mineral Research [J. Bone Miner. Res.]. Vol. 19, no. 9, pp. 1379-1394. Sep 2004.

    A major area in regenerative medicine is the application of stem cells in bone reconstruction and bone tissue engineering. This will require well-defined and efficient protocols for directing the differentiation of stem cells into the osteogenic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages on transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying osteogenesis and bone development, and facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for bone-related biomaterials and drugs could also use protocols developed for the osteogenic differentiation of stem cells. This review critically examines the various strategies that could be used to direct the differentiation of stem cells into the osteogenic lineage in vitro.

  3. Combined effects of Matrigel super(TM) and growth factors on maintaining undifferentiated murine embryonic stem cells for embryotoxicity testing

    Greenlee, AR; Kronenwetter-Koepel, TA; Kaiser, SJ; Ellis, TM; Liu, K

    Toxicology In Vitro [Toxicol. In Vitro]. Vol. 18, no. 4, pp. 543-553. Aug 2004.

    Undifferentiated, murine embryonic stem (mES) cells have shown promise as a substrate for identifying embryotoxic chemicals and for studying mechanisms of early developmental injury. However, long-term maintenance of mES cells in an undifferentiated state is problematic. The present study evaluates the combination of Matrigel super(TM) matrix and three growth factors for this purpose. Biomarkers of mES cell pluripotency, apoptosis, chromosome number and cardiomyocyte differentiation were monitored over 119 population doublings. D3 mES cells retained undifferentiated characteristics, including sustained expression of alkaline phosphatase and stage specific embryonic antigen-1 (SSEA- 1) and continued transcription of Pou5f1 (Oct-4). Cell viability remained at [gt-or-equal, slanted]95% and population-doubling times averaged 14.3 h over 10 weeks of observation. Caspase-3 activation, a marker of cellular death by apoptosis, was measured in early- and late-passage mES cells. Early- passage cells showed dose-responsive caspase-3 activation following exposure to sodium arsenite, whereas caspase-3 activation of late-passage cells dropped to background levels at toxicant dosages above 50 ppb. Aneuploidy and impaired differentiation into beating cardiomyocytes were noted for late-passage mES cells. Matrigel super(TM), combined with growth factors, may sustain undifferentiated mES cells. However, aneuploidy, reduced caspase-3 activation, and inability to differentiate suggests further modifications to the culture system may be needed for long-term propagation of cells for embryotoxicity endpoints.

  4. Nanoliter-scale synthesis of arrayed biomaterials and application to human embryonic stem cells

    Anderson, Daniel G; Levenberg, Shulamit; Langer, Robert

    Nature Biotechnology [Nat. Biotechnol.]. Vol. 22, no. 7, pp. 863-866. Jul 2004.

    Identification of biomaterials that support appropriate cellular attachment, proliferation and gene expression patterns is critical for tissue engineering and cell therapy. Here we describe an approach for rapid, nanoliter-scale synthesis of biomaterials and characterization of their interactions with cells. We simultaneously characterize over 1,700 human embryonic stem cell-material interactions and identify a host of unexpected materials effects that offer new levels of control over human embryonic stem cell behavior.

  5. Efficient Transfection of Embryonic and Adult Stem Cells

    Lakshmipathy, Uma; Pelacho, Beatriz; Sudo, Kazuhiro; Linehan, Jonathan L; Coucouvanis, Electra; Kaufman, Dan S; Verfaillie, Catherine M

    Stem Cells [Stem Cells]. Vol. 22, no. 4, pp. 531-543. Jul 2004.

    The ability of embryonic stem cells and adult stem cells to differentiate into specific cell types holds immense potential for therapeutic use in cell and gene therapy. Realization of this potential depends on efficient and optimized protocols for genetic manipulation of stem cells. In the study reported here, we demonstrate the use of nucleofection as a method to introduce plasmid DNA into embryonic and adult stem cells with significantly greater efficiency than electroporation or lipid-based transfection methods have. Using enhanced green fluorescent protein (eGFP) as a reporter gene, mouse embryonic stem cells were transfected both transiently and stably at a rate nearly 10-fold higher than conventional methods. The transfected cells retained their stem cell properties, including continued expression of the stem cell markers SSEA1, Oct4, and Rex1; formation of embryoid bodies; differentiation into cardiomyocytes in the presence of appropriate inducers; and, when injected into developing blastocysts, contribution to chimeras. Higher levels of transfection were also obtained with human embryonic carcinoma and human embryonic stem cells. Particularly hard-to-transfect adult stem cells, including bone marrow and multipotent adult progenitor cells, were also transfected efficiently by the method of nucleofection. Based on our results, we conclude that nucleofection is superior to currently available methods for introducing plasmid DNA into a variety of embryonic and adult stem cells. The high levels of transfection achieved by nucleofection will enable its use as a rapid screening tool to evaluate the effect of ectopically expressed transcription factors on tissue- specific differentiation of stem cells.

  6. Human embryonic stem cells express a unique set of microRNAs

    Suh, M-R; Lee, Y; Kim, JY; Kim, S-K; Moon, S-H; Lee, JY; Cha, K-Y; Chung, HM; Yoon, HS; Moon, SY; Kim, VN; Kim, K-S

    Developmental Biology [Dev. Biol.]. Vol. 270, no. 2, pp. 488-498. Jun 2004.

    Human embryonic stem (hES) cells are pluripotent cell lines established from the explanted inner cell mass of human blastocysts. Despite their importance for human embryology and regenerative medicine, studies on hES cells, unlike those on mouse ES (mES) cells, have been hampered by difficulties in culture and by scant knowledge concerning the regulatory mechanism. Recent evidence from plants and animals indicates small RNAs of approximately 22 nucleotides (nt), collectively named microRNAs, play important roles in developmental regulation. Here we describe 36 miRNAs (from 32 stem-loops) identified by cDNA cloning in hES cells. Importantly, most of the newly cloned miRNAs are specifically expressed in hES cells and downregulated during development into embryoid bodies (EBs), while miRNAs previously reported from other human cell types are poorly expressed in hES cells. We further show that some of the ES-specific miRNA genes are highly related to each other, organized as clusters, and transcribed as polycistronic primary transcripts. These miRNA gene families have murine homologues that have similar genomic organizations and expression patterns, suggesting that they may operate key regulatory networks conserved in mammalian pluripotent stem cells. The newly identified hES-specific miRNAs may also serve as molecular markers for the early embryonic stage and for undifferentiated hES cells.

  7. Navigating the pathway from embryonic stem cells to beta cells

    Stoffel, M; Vallier, L; Pedersen, RA*

    Seminars in Cell & Developmental Biology [Semin. Cell Dev. Biol.]. Vol. 15, no. 3, pp. 327-336. Jun 2004.

    The compelling goal of using in vitro differentiation of stem cells to obtain replacement pancreatic beta cells that are clinically effective in treating diabetes has until now eluded researchers. This difficulty raises the question of whether more effective strategies are available. We propose that the native embryonic pathway leading to the definitive endoderm lineage, and continuing on to the endocrine pancreas, is the one most likely to succeed for the in vitro differentiation of embryonic stem cells. We question however whether gain-of-function approaches involving genes necessary for beta cell development are destined to work effectively, and suggest alternative approaches to identifying conditions sufficient for in vitro beta cell differentiation.

  8. Increased apoptosis in differentiating p27-deficient mouse embryonic stem cells

    Bryja, V; Pachernik, J; Soucek, K; Horvath, V; Dvorak, P; Hampl, A

    Cellular and Molecular Life Sciences [Cell. Mol. Life Sci.]. Vol. 61, no. 11, pp. 1384-1400. Jun 2004.

    In mouse embryonic stem (mES) cells, the expression of p27 is elevated when differentiation is induced. Using mES cells lacking p27 we tested the importance of p27 for the regulation of three critical cellular processes: proliferation, differentiation, and apoptosis. Although cell cycle distribution, DNA synthesis, and the activity of key G1/S-regulating cyclin-dependent kinases remained unaltered in p27-deficient ES cells during retinoic acid-induced differentiation, the amounts of cyclin D2 and D3 in such cells were much lower compared with normal mES cells. The onset of differentiation induces apoptosis in p27-deficient cells, the extent of which can be reduced by artificially increasing the level of cyclin D3. We suggest that the role of p27 in at least some differentiation pathways of mES cells is to prevent apoptosis, and that it is not involved in slowing cell cycle progression. We also propose that the pro-survival function of p27 is realized via regulation of metabolism of D-type cyclin(s).

  9. A hierarchical order of factors in the generation of FLK1- and SCL-expressing hematopoietic and endothelial progenitors from embryonic stem cells

    Park, C; Afrikanova, I; Chung, YS; Zhang, WJ; Arentson, E; Fong, GH; Rosendahl, A; Choi, K*

    Development [Development]. Vol. 131, no. 11, pp. 2749-2762. 1 Jun 2004.

    The receptor tyrosine kinase FLK1 and the transcription factor SCL play crucial roles in the establishment of hematopoietic and endothelial cell lineages in mice. We have previously used an in vitro differentiation model of embryonic stem (ES) cells and demonstrated that hematopoietic and endothelial cells develop via sequentially generated FLK1 super(+) and SCL super(+) cells. To gain a better understanding of cellular and molecular events leading to hematopoietic specification, we examined factors necessary for FLK1 super(+) and SCL cell induction in serum-free conditions. We demonstrate that bone morphogenetic protein (BMP) 4 was required for the generation of FLK1 super(+) and SCL super(+) cells, and that vascular endothelial growth factor (VEGF) was necessary for the expansion and differentiation of SCL-expressing hematopoietic progenitors. Consistently, Flk1-deficient ES cells responded to BMP4 and generated TER119 super(+) and CD31 super(+) cells, but they failed to expand in response to VEGF. The Smad1/5 and map kinase pathways were activated by BMP4 and VEGF, respectively. The overexpression of SMAD6 in ES cells resulted in a reduction of FLK1 super(+) cells. In addition, a MAP kinase kinase 1 specific inhibitor blocked the expansion of SCL super(+) cells in response to VEGF. Finally, VEGF mediated expansion of hematopoietic and endothelial cell progenitors was inhibited by TGF beta 1, but was augmented by activin A. Our studies suggest that hematopoietic and endothelial commitment from the mesoderm occurs via BMP4-mediated signals and that expansion and/or differentiation of such progenitors is achieved by an interplay of VEGF, TGF beta 1 and activin A signaling.

  10. Disruption of MKK4 signaling reveals its tumor-suppressor role in embryonic stem cells

    Cazillis, M; Bringuier, A-F; Delautier, D; Buisine, M; Bernuau, D; Gespach, C; Groyer, A

    Oncogene [Oncogene]. Vol. 23, no. 27, pp. 4735-4744. 10 Jun 2004.

    The dual Ser/Thr kinase MKK4 and its downstream targets JNK and p38 regulate critical cellular functions during embryogenesis and development. MKK4 has been identified as a putative tumor-suppressor gene in human solid tumors of breast, prostate and pancreas. To clarify the mechanisms underlying the transforming potential of molecular defects targeting MKK4, we have generated totipotent embryonic stem (ES) cells expressing the dominant-negative mutant DN-MKK4 sub(Ala), S257A/T261A. Stably transfected DN-MKK4-ES cells exhibit a transformed fibroblast-like morphology, reduced proliferation rate, were no more submitted to cell contact inhibition, were growing in soft agar, and were much more tumorigenic than parental ES cells in athymic nude mice. These phenotypic changes: (i) are consistent with the protection of DN-MKK4-transfected ES cells from spontaneous, cell density-dependent, and stress-induced apoptosis (DAPI staining and poly (ADP-ribose) polymerase (PARP) cleavage) and (ii) correlated with alterations in JNK, p38, and Erk-1/-2 MAPK/SAPK signaling. Taken together, our data provide a new mechanism linking the MKK4 signaling pathways to cancer progression and identify MKK4 as a tumor-suppressor gene implicated in several transforming functions.

  11. Specification of the Retinal Fate of Mouse Embryonic Stem Cells by Ectopic Expression of Rx/rax, a Homeobox Gene

    Tabata, Y; Ouchi, Y; Kamiya, H; Manabe, T; Arai, K-I; Watanabe, S*

    Molecular and Cellular Biology [Mol. Cell. Biol.]. Vol. 24, no. 10, pp. 4513-4521. May 2004.

    With the goal of generating retinal cells from mouse embryonic stem (ES) cells by exogenous gene transfer, we introduced the Rx/rax transcription factor, which is expressed in immature retinal cells, into feeder-free mouse ES cells (CCE). CCE cells expressing Rx/rax as well as enhanced green fluorescent protein (CCE-RX/E cells) proliferated and remained in the undifferentiated state in the presence of leukemia inhibitory factor, as did parental ES cells. We made use of mouse embryo retinal explant cultures to address the differentiation ability of grafted ES cells. Dissociated embryoid bodies were treated with retinoic acid for use as donor cells and cocultured with retina explants for 2 weeks. In contrast to the parental CCE cells, which could not migrate into host retinal cultures, CCE-RX/E cells migrated into the host retina and extended their process-like structures between the host retinal cells. Most of the grafted CCE- RX/E cells became located in the ganglion cell and inner plexiform layers and expressed ganglion and horizontal cell markers. Furthermore, these grafted cells had the electrophysiological properties expected of ganglion cells. Our data thus suggest that subpopulations of retinal neurons can be generated in retinal explant cultures from grafted mouse ES cells ectopically expressing the transcription factor Rx/rax.