Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Sp1/Sp3 transcription factors regulate hallmarks of megakaryocyte maturation, and platelet formation and function

ABSTRACT: Sp1 and Sp3 belong to the Specificity proteins (Sp)/Krüppel-like transcription factor family. They are closely related, ubiquitously expressed and recognize G-rich DNA motifs. They are thought to regulate generic processes such as cell cycle and growth control, metabolic pathways and apoptosis. Ablation of Sp1 or Sp3 in mice is lethal, and combined haploinsufficiency results in hematopoietic defects during the fetal stages. Here, we show that in adult mice conditional ablation of either Sp1 or Sp3 has minimal impact on hematopoiesis, while the simultaneous loss of Sp1 and Sp3 results in severe macrothrombocytopenia and platelet dysfunction. We employed flow cytometry, cell culture and electron microscopy and show that although megakaryocyte numbers are normal in bone marrow and spleen, they display a less compact demarcation membrane system and a striking inability to form proplatelets. Through megakaryocyte transcriptomics and platelet proteomics we identified several cytoskeleton-related proteins and downstream effector kinases, including Mylk, that were downregulated upon Sp1/Sp3 depletion, providing an explanation for the observed defects in megakaryopoiesis. We show that Mylk is required for proplatelet formation and stabilization and for ITAM-receptor mediated platelet aggregation. Our data highlights the specific vs generic role of these ubiquitous transcription factors in the highly specialized megakaryocytic lineage. Megakaryocyte mRNA profiles of Sp1fl/fl::Sp3fl/fl (WTlox) and Pf4-Cre::Sp1fl/fl::Sp3fl/fl (dKO) mice were generated by deep sequencing, in triplicate.

ORGANISM(S): Mus musculus

SUBMITTER: Harmen van de Werken

PROVIDER: E-GEOD-58707 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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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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Sp1/Sp3 transcription factors regulate hallmarks of megakaryocyte maturation, and platelet formation and function

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