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ABSTRACT: Myeloid ecotropic viral integration site 1 (Meis1) forms a heterodimer with Pbx1 that augments Hox-dependent gene expression and is associated with leukemogenesis and HSC self-renewal. Here we identified 2 independent actions of Meis1 in hematopoietic development: one regulating cellular proliferation and the other involved in megakaryocyte lineage development. First, we found that endogenous Mesp1 indirectly induces Meis1 and Meis2 in endothelial cells derived from embryonic stem cells. Overexpression of Meis1 and Meis2 greatly enhanced the formation of hematopoietic colonies from embryonic stem cells, with the exception of erythroid colonies, by maintaining hematopoietic progenitor cells in a state of proliferation. Second, overexpression of Meis1 repressed the development of early erythroid progenitors, acting in vivo at the megakaryocyte-erythroid progenitor stage to skew development away from erythroid generation and toward megakaryocyte development. This previously unrecognized action of Meis1 may explain the embryonic lethality observed in Meis1(-/-) mice that arises from failure of lymphatic-venous separation and can result as a consequence of defective platelet generation. These results show that Meis1 exerts 2 independent functions, with its role in proliferation of hematopoietic progenitors acting earlier in development from its influence on the fate choice at the megakaryocyte-erythroid progenitor between megakaryocytic and erythroid development.
Blood 06/2012; 120(2):335-46. · 9.90 Impact Factor
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ABSTRACT: Expression of the transcription factor Snail is required for normal vasculogenesis in the developing mouse embryo. In addition, tumors expressing Snail have been associated with a more malignant phenotype, with both increased invasive properties and angiogenesis. Although the relationship between Snail and vasculogenesis has been noted, no mechanistic analysis has been elucidated. Here, we show that in addition to inducing an epithelial mesenchymal transition, Snail promotes the cell-autonomous induction of Flk1(+) endothelial cells in an early subset of differentiating mouse embryonic stem (ES) cells. Cells that become Flk1+ in response to Snail have a transcriptional profile specific to Gata6+primitive endoderm, but not the early Nanog+epiblast. We further show that Snail's ability to promote Flk1(+) endothelium depends on fibroblast growth factor signaling as well as the repression of the microRNA-200 (miR-200) family, which directly targets the 3' UTRs of Flk1 and Ets1. Together, our results show that Snail is capable of inducing Flk1+ lineage commitment in a subset of differentiating ES cells through the down-regulation of the miR-200 family. We hypothesize that this mechanism of Snail-induced vasculogenesis may be conserved in both the early developing embryo and malignant cancers.
Stem cells and development 08/2011; 21(2):167-76. · 4.15 Impact Factor
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ABSTRACT: The reprogramming of somatic cells to inducible pluripotent stem cells requires a mesenchymal-to-epithelial transition. While differentiating ESCs can undergo the reverse process or epithelial-to-mesenchymal transition (EMT), little is known about the role of EMT in ESC differentiation and fate commitment. Here, we show that Snail homolog 1 (Snail) is expressed during ESC differentiation and is capable of inducing EMT on day 2 of ESC differentiation. Induction of EMT by Snail promotes mesoderm commitment while repressing markers of the primitive ectoderm and epiblast. Snail's impact on differentiation can be partly explained through its regulation of a number of ESC-associated microRNAs, including the microRNA-200 (miR-200) family. The miR-200 family is normally expressed in ESCs but is downregulated in a Wnt-dependent manner during EMT. Maintenance of miR-200 expression stalls differentiating ESCs at the epiblast-like stem cell (EpiSC) stage. Consistent with a role for activin in maintaining the EpiSC state, we find that inhibition of activin signaling decreases miR-200 expression and allows EMT to proceed with a bias toward neuroectoderm commitment. Furthermore, miR-200 requires activin to efficiently maintain cells at the epiblast stage. Together, these findings demonstrate that Snail and miR-200 act in opposition to regulate EMT and exit from the EpiSC stage toward induction of germ layer fates. By modulating expression levels of Snail, activin, and miR-200, we are able to control the order in which cells undergo EMT and transition out of the EpiSC state.
Stem Cells 03/2011; 29(5):764-76. · 7.78 Impact Factor
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R Coleman Lindsley,
Jennifer G Gill,
Theresa L Murphy, Ellen M Langer,
Mi Cai,
Mona Mashayekhi,
Wei Wang,
Noriko Niwa,
Jeanne M Nerbonne,
Michael Kyba,
Kenneth M Murphy
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ABSTRACT: Wnt signaling is required for development of mesoderm-derived lineages and expression of transcription factors associated with the primitive streak. In a functional screen, we examined the mesoderm-inducing capacity of transcription factors whose expression was Wnt-dependent in differentiating ESCs. In contrast to many inactive factors, we found that mesoderm posterior 1 (Mesp1) promoted mesoderm development independently of Wnt signaling. Transient Mesp1 expression in ESCs promotes changes associated with epithelial-mesenchymal transition (EMT) and induction of Snai1, consistent with a role in gastrulation. Mesp1 expression also restricted the potential fates derived from ESCs, generating mesoderm progenitors with cardiovascular, but not hematopoietic, potential. Thus, in addition to its effects on EMT, Mesp1 may be capable of generating the recently identified multipotent cardiovascular progenitor from ESCs in vitro.
Cell stem cell 08/2008; 3(1):55-68. · 23.56 Impact Factor
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ABSTRACT: The SNAIL transcription factor contains C-terminal tandem zinc finger motifs and an N-terminal SNAG repression domain. The members of the SNAIL family have recently emerged as major contributors to the processes of development and metastasis via the regulation of epithelial-mesenchymal transition events during embryonic development and tumor progression. However, the mechanisms by which SNAIL represses gene expression are largely undefined. Previously we demonstrated that the AJUBA family of LIM proteins function as corepressors for SNAIL and, as such, may serve as a platform for the assembly of chromatin-modifying factors. Here, we describe the identification of the protein arginine methyltransferase 5 (PRMT5) as an effector recruited to SNAIL through an interaction with AJUBA that functions to repress the SNAIL target gene, E-cadherin. PRMT5 binds to the non-LIM region of AJUBA and is translocated into the nucleus in a SNAIL- and AJUBA-dependent manner. The depletion of PRMT5 in p19 cells stimulates E-cadherin expression, and the SNAIL, AJUBA, and PRMT5 ternary complex can be found at the proximal promoter region of the E-cadherin gene, concomitant with increased arginine methylation of histones at the locus. Together, these data suggest that PRMT5 is an effector of SNAIL-dependent gene repression.
Molecular and cellular biology 06/2008; 28(10):3198-207. · 6.06 Impact Factor
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ABSTRACT: Snail family transcriptional repressors regulate epithelial mesenchymal transitions during physiological and pathological processes. A conserved SNAG repression domain present in all vertebrate Snail proteins is necessary for repressor complex assembly. Here, we identify the Ajuba family of LIM proteins as functional corepressors of the Snail family via an interaction with the SNAG domain. Ajuba LIM proteins interact with Snail in the nucleus on endogenous E-cadherin promoters and contribute to Snail-dependent repression of E-cadherin. Using Xenopus neural crest as a model of in vivo Snail- or Slug-induced EMT, we demonstrate that Ajuba LIM proteins contribute to neural crest development as Snail/Slug corepressors and are required for in vivo Snail/Slug function. Because Ajuba LIM proteins are also components of adherens junctions and contribute to their assembly or stability, their functional interaction with Snail proteins in the nucleus suggests that Ajuba LIM proteins are important regulators of epithelia dynamics communicating surface events with nuclear responses.
Developmental cell 04/2008; 14(3):424-36. · 13.36 Impact Factor
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ABSTRACT: The SNAG repression domain is comprised of a highly conserved 21-amino acid sequence, is named for its presence in the Snail/growth factor independence-1 class of zinc finger transcription factors, and is present in a variety of proto-oncogenic transcription factors and developmental regulators. The prototype SNAG domain containing oncogene, growth factor independence-1, is responsible for the development of T cell thymomas. The SNAIL proteins also encode the SNAG domain and play key roles in epithelial mesenchymal differentiation events during development and metastasis. Significantly, these oncogenic functions require a functional SNAG domain. The molecular mechanisms of SNAG domain-mediated transcriptional repression are largely unknown. Using a yeast two-hybrid strategy, we identified Ajuba, a multiple LIM domain protein that can function as a corepressor for the SNAG domain. Ajuba interacts with the SNAG domain in vitro and in vivo, colocalizes with it, and enhances SNAG-mediated transcriptional repression. Ajuba shuttles between the cytoplasm and the nucleus and may form a novel intracellular signaling system. Using an integrated reporter gene combined with chromatin immunoprecipitation, we observed rapid, SNAG-dependent assembly of a multiprotein complex that included Ajuba, SNAG, and histone modifications consistent with the repressed state. Thus, SNAG domain proteins may bind Ajuba, trapping it in the nucleus where it functions as an adapter or molecular scaffold for the assembly of macromolecular repression complexes at target promoters.
Cancer Research 11/2007; 67(19):9097-106. · 7.86 Impact Factor
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Benjamin E Deverman,
Brian L Cook,
Scott R Manson,
Robert A Niederhoff, Ellen M Langer,
Ivana Rosová,
Laura A Kulans,
Xiaoyun Fu,
Justin S Weinberg,
Jay W Heinecke,
Kevin A Roth,
Steven J Weintraub
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ABSTRACT: The therapeutic value of DNA-damaging antineoplastic agents is dependent upon their ability to induce tumor cell apoptosis while sparing most normal tissues. Here, we show that a component of the apoptotic response to these agents in several different types of tumor cells is the deamidation of two asparagines in the unstructured loop of Bcl-xL, and we demonstrate that deamidation of these asparagines imports susceptibility to apoptosis by disrupting the ability of Bcl-xL to block the proapoptotic activity of BH3 domain-only proteins. Conversely, Bcl-xL deamidation is actively suppressed in fibroblasts, and suppression of deamidation is an essential component of their resistance to DNA damage-induced apoptosis. Our results suggest that the regulation of Bcl-xL deamidation has a critical role in the tumor-specific activity of DNA-damaging antineoplastic agents.
Cell 11/2002; 111(1):51-62. · 32.40 Impact Factor
