Stem cells

  • Letter |

    TET1 is an enzyme that catalyses the conversion of 5-methylcytosine of DNA to 5-hydroxymethylcytosine, raising the possibility that it is involved in mediating DNA demethylation. These authors show that Tet1 is involved in mouse embryonic stem cell maintenance and specification of the inner cell mass. It is required to maintain both the expression of Nanog in embryonic stem cells and the Nanog promoter in a hypomethylated state, supporting a role for Tet1 in regulating DNA methylation.

    • Shinsuke Ito
    • , Ana C. D’Alessio
    •  & Yi Zhang
  • Letter |

    The thymus contains thymic epithelial cells (TECs), which form a complex three-dimensional network organized into cortical and medullary compartments. It is shown here that these cells are plastic. Clonogenic TECs can acquire new properties when exposed to the skin microenvironment; under such conditions, they can permanently adopt the fate of hair follicle multipotent stem cells. Hence, microenvironmental cues can be sufficient to re-direct epithelial cell fate.

    • Paola Bonfanti
    • , Stéphanie Claudinot
    •  & Yann Barrandon
  • Article |

    Gene activation may involve the formation of a DNA loop that connects enhancer-bound transcription factors with the transcription apparatus at the core promoter. But this process is not well understood. Here, two proteins, mediator and cohesin, are shown to connect the enhancers and core promoters of active genes in embryonic stem cells. These proteins seem to generate cell-type-specific DNA loops linked to the gene expression program of each cell.

    • Michael H. Kagey
    • , Jamie J. Newman
    •  & Richard A. Young
  • Letter |

    During haematopoiesis, multipotent progenitors differentiate into progressively restricted myeloid or lymphoid progenitors. A comprehensive genome-wide DNA methylation analysis of haematopoietic cell populations with well-characterized differentiation potentials reveals remarkable epigenetic plasticity during lymphoid and myeloid restriction.

    • Hong Ji
    • , Lauren I. R. Ehrlich
    •  & Andrew P. Feinberg
  • Article |

    The identity of the cells that form the haematopoietic stem cell (HSC) niche in bone marrow has been unclear. These authors identify nestin-expressing mesenchymal stem cells as niche-forming cells. These nestin-expressing cells show a close physical association with HSCs and express high levels of genes involved in HSC maintenance, and their depletion reduces bone marrow homing of haematopoietic progenitors.

    • Simón Méndez-Ferrer
    • , Tatyana V. Michurina
    •  & Paul S. Frenette
  • Letter |

    The rat is a animal model widely used for studying human physiology and disease, but functional genomics and genetic research have been stifled by the limited availability of gene targeting tools. These authors have established gene targeting by homologous recombination in rat embryonic stem cells, and have generated p53 gene knockout rats for the first time.

    • Chang Tong
    • , Ping Li
    •  & Qi-Long Ying
  • Letter |

    The retinoblastoma tumour suppressor protein pRb can suppress the activity of certain transcription factors and potentiate the activity of others, and has been shown to affect the differentiation of different cell lineages in vitro. These authors show that the Rb gene has a role in driving bone cell formation or brown adipose tissue formation in vivo.

    • Eliezer Calo
    • , Jose A. Quintero-Estades
    •  & Jacqueline A. Lees
  • Article |

    Pluripotent stem cells can be generated in the laboratory through somatic cell nuclear transfer (generating nuclear transfer embryonic stem cells, ntESCs) or transcription-factor-based reprogramming (producing induced pluripotent stem cells, iPSCs). These methods reset the methylation signature of the genome — but to what extent? Here it is found that mouse iPSCs 'remember' the methylation status of their tissue of origin, but the methylation of ntESCs is more similar to that of naturally produced ES cells.

    • K. Kim
    • , A. Doi
    •  & G. Q. Daley
  • Letter |

    Ependymoma is a type of neural tumour that arises throughout the central nervous system. Using comparative transcriptomics in mouse and human tumours, these authors home in on mutations that are specific to individual tumour subgroups. In doing so, they generate the first mouse model of ependymoma and demonstrate the power of interspecific genomic comparisons to interrogate cancer subgroups.

    • Robert A. Johnson
    • , Karen D. Wright
    •  & Richard J. Gilbertson
  • Brief Communications Arising |

    • Sabine Conrad
    • , Markus Renninger
    •  & Thomas Skutella
  • Letter |

    Reproductive history influences breast cancer risk but the cellular mechanisms are unclear. Here it is shown that ovarian hormones regulate the size of the mammary stem cell pool in mice. The size of this pool increases when progesterone levels increase during the reproductive cycle. Progesterone probably regulates stem cell numbers through a paracrine mechanism involving induction of RANKL and Wnt in luminal cells.

    • Purna A. Joshi
    • , Hartland W. Jackson
    •  & Rama Khokha
  • Letter |

    The generation of induced pluripotent stem cells (iPSCs) from patients with defined genetic disorders promises to help the basic understanding of complex diseases and the development of therapeutics. Here iPSCs have been generated from patients with LEOPARD syndrome, a developmental disorder with pleiomorphic effects on several tissues and organs. The iPSCs are characterized and the phenotype of cardiomyocytes derived from these cells is investigated.

    • Xonia Carvajal-Vergara
    • , Ana Sevilla
    •  & Ihor R. Lemischka
  • Article |

    Induced pluripotent stem cells (iPSCs) are generated by the enforced expression of particular transcription factors in somatic cells. The extent to which such cells are equivalent to embryonic stem (ES) cells is an open question. Here, genetically identical mouse ES cells and iPSCs have been compared; the overall expression patterns of messenger RNAs and microRNAs are the same, with the exception of a few transcripts encoded within an imprinted gene cluster on chromosome 12qF1.

    • Matthias Stadtfeld
    • , Effie Apostolou
    •  & Konrad Hochedlinger
  • Letter |

    The ovarian hormones oestrogen and progesterone increase breast cancer risk but the cellular mechanisms are unclear. Here it is shown that the size of the mammary stem cell pool in mice is regulated by steroid hormone signalling, although these cells lack the receptors for oestrogen and progesterone. The augmented pool could lead to clonal expansion of a mutated cell, possibly accounting for the increased incidence of breast cancer associated with pregnancy.

    • Marie-Liesse Asselin-Labat
    • , François Vaillant
    •  & Jane E. Visvader
  • Letter |

    Several non-haematopoietic-cell-derived cytokines, including interleukin (IL)25, have been implicated in inducing T helper 2 (TH2) cell-dependent inflammation, but their precise role has been unclear. Here, IL25 is shown to promote the accumulation of multipotent progenitor cells in gut-associated lymphoid tissue. These cells can give rise to macrophage or granulocyte lineages that promote the differentiation of TH2 cells and contribute to protective immunity against helminth infections.

    • Steven A. Saenz
    • , Mark C. Siracusa
    •  & David Artis
  • Article |

    Zscan4 is shown to be involved in maintaining telomeres in embryonic stem (ES) cells. Only 5% of ES cells express Zscan4 at a given time, but nearly all ES cells activate Zscan4 at least once within nine passages. The transient Zscan4-positive state is associated with rapid telomere extension by telomere recombination and upregulation of meiosis–specific homologous recombination genes. Knocking down Zscan4 shortens telomeres, increases karyotype abnormalities and spontaneous sister chromatid exchange, and slows down cell proliferation until reaching crisis by eight passages.

    • Michal Zalzman
    • , Geppino Falco
    •  & Minoru S. H. Ko
  • Letter |

    To study the changes in chromatin structure that accompany zygotic genome activation and pluripotency during the maternal–zygotic transition (MZT), the genomic locations of histone H3 modifications and RNA polymerase II have been mapped during this transition in zebrafish embryos. H3 lysine 27 trimethylation and H3 lysine 4 trimethylation are only detected after MZT; evidence is provided that the bivalent chromatin domains found in cultured embryonic stem cells also exist in embryos.

    • Nadine L. Vastenhouw
    • , Yong Zhang
    •  & Alexander F. Schier
  • Brief Communications Arising |

    • François Majo
    • , Ariane Rochat
    •  & Yann Barrandon
  • Letter |

    Here, iPS cell technology is used to study the mechanisms underlying dyskeratosis congenita in humans. Reprogramming restores telomere elongation in dyskeratosis congenita cells despite genetic lesions affecting telomerase. The reprogrammed cells were able to overcome a critical limitation in telomerase RNA component (TERC) levels to restore telomere maintenance and self-renewal, and multiple telomerase components are targeted by pluripotency-associated transcription factors.

    • Suneet Agarwal
    • , Yuin-Han Loh
    •  & George Q. Daley
  • Letter |

    Endogenous retroviruses (ERVs) are widely dispersed in mammalian genomes, and are silenced in somatic cells by DNA methylation. Here, an ERV silencing pathway independent of DNA methylation is shown to operate in embryonic stem cells. The pathway involves the histone H3K9 methyltransferase ESET and might be important for ERV silencing during the stages in embryogenesis when DNA methylation is reprogrammed.

    • Toshiyuki Matsui
    • , Danny Leung
    •  & Yoichi Shinkai
  • Letter |

    One of two papers showing the generation of haematopoietic stem cells (HSCs) from the ventral wall of the dorsal aorta in live zebrafish embryos. Here, combined fluorescent reporter transgenes, confocal time-lapse microscopy and flow cytometry identify and isolate the stepwise intermediates as aortic haemogenic endothelium transitions to nascent HSCs. HSCs generated from this haemogenic endothelium are the lineal founders of virtually all of the adult haematopoietic system.

    • Julien Y. Bertrand
    • , Neil C. Chi
    •  & David Traver
  • Letter |

    De novo emergence of phenotypically defined haematopoietic stem cells (Sca1+, c kit+, CD41+) directly from ventral aortic haemogenic endothelial cells is shown in mice. Although the study did not visualize live embryos, it instead developed a dissection procedure to visualize the deeply located aorta.

    • Jean-Charles Boisset
    • , Wiggert van Cappellen
    •  & Catherine Robin
  • Letter |

    The transcription factor Tbx3 is shown to significantly improve the quality of induced pluripotent stem (iPS) cells. Tbx3 binding sites in embryonic stem cells are present in genes involved in pluripotency and reprogramming factors. Furthermore, there are intrinsic qualitative differences in iPS cells generated by different methods in terms of their pluripotency, thus highlighting the need to rigorously characterize iPS cells beyond in vitro studies.

    • Jianyong Han
    • , Ping Yuan
    •  & Bing Lim
  • Article |

    Age-associated changes in stem cell supportive niche cells are shown to deregulate normal haematopoiesis by causing haematopoietic stem cell dysfunction. Age-dependent defects in niche cells are systemically regulated and can be reversed by exposure to a young circulation or by neutralization of the conserved longevity regulator, insulin-like growth factor-1, in the marrow microenvironment.

    • Shane R. Mayack
    • , Jennifer L. Shadrach
    •  & Amy J. Wagers
  • Letter |

    Progenitor cells sustain the capacity of self-renewing tissues for proliferation while suppressing cell cycle exit and terminal differentiation. DNA methylation is one potential epigenetic mechanism for the cellular memory needed to preserve the somatic progenitor state through cell divisions. The DNA methyltransferase 1 and other regulators of DNA methylation are now shown to be essential for epidermal progenitor cell function.

    • George L. Sen
    • , Jason A. Reuter
    •  & Paul A. Khavari
  • Letter |

    Much of the mammalian genome is derived from retroelements, a significant proportion of which are endogenous retroviruses (ERVs). ERVs are transcriptionally silenced during early embryogenesis by histone and DNA methylation, but the initiators of this process are largely unknown. Here, deletion of KAP1 is shown to lead to a marked upregulation of a range of ERVs in mouse embryonic stem cells and in early embryos.

    • Helen M. Rowe
    • , Johan Jakobsson
    •  & Didier Trono
  • Letter |

    Polycomb proteins have a key role in regulating the expression of genes essential for development, differentiation and maintenance of cell fates. Here, Polycomb repressive complex 2 (PRC2) is shown to form a complex with JARID2, a Jumonji domain protein. JARID2 is required for the binding of Polycomb proteins to target genes in embryonic stem cells as well as for the proper differentiation of ES cells.

    • Diego Pasini
    • , Paul A. C. Cloos
    •  & Kristian Helin
  • Article |

    The differentiation of an embryonic stem cell (ESC) requires both suppression of the self-renewal process and activation of the specific differentiation pathway. The let-7 family of microRNAs (miRNAs) are now shown to suppress the self-renewal program in cells that are normally unable to silence this program, whereas introduction of ESC cell cycle regulating miRNAs blocks the action of let-7. Thus, the interplay between these two groups of miRNAs dictates cell fate.

    • Collin Melton
    • , Robert L. Judson
    •  & Robert Blelloch