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Genome -wide identification of SCL's target genes in Megakaryocyte progenitors

ABSTRACT: Megakaryopoiesis is a complex process that involves major cellular changes and relies on controlled coordination of cellular proliferation and differentiation. These mechanisms are orchestrated in part by transcriptional regulators. The key hematopoietic transcription factor SCL/TAL1 is required for specification of the megakaryocytic lineage from hematopoietic progenitors. Here, we report that it also critically controls terminal megakaryocyte maturation. In vivo depletion of SCL specifically in the megakaryocytic lineage affects all key attributes of megakaryocyte progenitors (MkPs), namely proliferation, ploidisation, cytoplasmic maturation, as well as platelet production. Genome-wide expression analysis reveals increased expression of the cell cycle regulator p21 in Scl-deleted MkPs. Importantly, P21 knockdown-mediated rescue assays in Scl-deleted MkPs show full restoration of cell cycle progression and partial rescue of the nuclear and cytoplasmic maturation defects. Therefore, SCL-mediated transcriptional control of p21 is critical for maturation of MkPs. Our study provides a mechanistic link between one of the major hematopoietic transcriptional regulators, cell cycle progression and megakaryocytic differentiation.

ORGANISM(S): Mus musculus

PROVIDER: GSE24969 | GEO | 2011/07/11

SECONDARY ACCESSION(S): PRJNA131897

REPOSITORIES: GEO

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Project description:The bHLH transcription factor stem cell leukemia gene (Scl) is a master regulator for hematopoiesis essential for hematopoietic specification and proper differentiation of the erythroid and megakaryocyte lineages. However, the critical downstream targets of Scl remain undefined. Here, we identified a novel Scl target gene, transcription factor myocyte enhancer factor 2 C (Mef2C) from Sclfl/fl fetal liver progenitor cell lines. Analysis of Mef2C-/- embryos showed that Mef2C, in contrast to Scl, is not essential for specification into primitive or definitive hematopoietic lineages. However, adult VavCre+Mef2Cfl/fl mice exhibited platelet defects similar to those observed in Scl deficient mice. The platelet counts were reduced, while platelet size was increased and the platelet shape and granularity was altered. Furthermore, megakaryopoiesis was severely impaired in vitro. ChIP-on-chip analysis revealed that Mef2C is directly regulated by Scl in megakaryocytic cells, but not in erythroid cells. In addition, an Scl independent requirement for Mef2C in B-lymphoid homeostasis was observed in Mef2C-deficient mice, characterized as severe age-dependent reduction of specific B cell progenitor populations reminiscent of premature aging. In summary, this work identifies Mef2C as an integral member of hematopoietic transcription factors with distinct upstream regulatory mechanisms and functional requirements in megakaryocyte and B-lymphoid lineages. Experiment Overall Design: Sclfl/fl hematopoietic progenitor lines were generated from fetal liver progenitors from E12.5 Sclfl/fl embryos9 by immortalization with Hox11 retrovirus.17 Sclfl/fl progenitor cells were cultured with IL3, and a clonal line containing cells with megakaryocyte morphology and acetylcholinesterase (AchE) activity was selected. The Sclfl/fl cell line was transduced with Cre- GFP retrovirus to generate the Scl Experiment Overall Design: Î?/Î? cell line, and the Scl Î?/Î? cell line was transduced with Scl retrovirus to re-introduce Scl expression (Scl Î?/Î? +Scl cell line). Megakaryocyte differentiation was enhanced by adding Tpo for 5 days before harvesting the cells. RNA was extracted with Trizol (Gibco BRL) and RNEasy (Qiagen) kits. Differential gene expression between Sclfl/fl, Scl Î?/Î? and Scl Î?/Î? +Scl cell lines was analyzed by Affymetrix MOE430_2 microarray in the microarray core facility at the Dana-Farber Cancer Institute.

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Genome -wide identification of SCL's target genes in Megakaryocyte progenitors

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