ABSTRACT
B lymphoid development is initiated by the differentiation of hematopoietic stem cells into lineage committed progenitors, ultimately generating mature B cells. This highly regulated process generates clonal immunological diversity via recombination of immunoglobulin V, D and J gene segments. While several transcription factors that control B cell development and V(D)J recombination have been defined, how these processes are initiated and coordinated into a precise regulatory network remains poorly understood. Here, we show that the transcription factor ETS Related Gene (Erg) is essential for early B lymphoid differentiation. Erg initiates a transcriptional network involving the B cell lineage defining genes, Ebf1 and Pax5, which directly promotes expression of key genes involved in V(D)J recombination and formation of the B cell receptor. Complementation of Erg deficiency with a productively rearranged immunoglobulin gene rescued B lineage development, demonstrating that Erg is an essential and stage-specific regulator of the gene regulatory network controlling B lymphopoiesis.
Subject(s)
B-Lymphocytes/metabolism , Cell Differentiation/genetics , Hematopoietic Stem Cells/metabolism , Lymphopoiesis/genetics , Oncogene Proteins/genetics , Transcription, Genetic , Transcriptional Regulator ERG/genetics , Animals , B-Lymphocytes/cytology , Cell Lineage/genetics , Cells, Cultured , Gene Regulatory Networks/genetics , Hematopoietic Stem Cells/cytology , Mice, Inbred C57BL , Mice, Knockout , Oncogene Proteins/metabolism , PAX5 Transcription Factor/genetics , PAX5 Transcription Factor/metabolism , Transcription Factors/genetics , Transcription Factors/metabolism , Transcriptional Regulator ERG/metabolism , V(D)J Recombination/geneticsABSTRACT
Down syndrome (DS), with trisomy of chromosome 21 (HSA21), is the commonest human aneuploidy. Pre-leukemic myeloproliferative changes in DS foetal livers precede the acquisition of GATA1 mutations, transient myeloproliferative disorder (DS-TMD) and acute megakaryocytic leukemia (DS-AMKL). Trisomy of the Erg gene is required for myeloproliferation in the Ts(1716)65Dn DS mouse model. We demonstrate here that genetic changes specifically attributable to trisomy of Erg lead to lineage priming of primitive and early multipotential progenitor cells in Ts(1716)65Dn mice, excess megakaryocyte-erythroid progenitors, and malignant myeloproliferation. Gene expression changes dependent on trisomy of Erg in Ts(1716)65Dn multilineage progenitor cells were correlated with those associated with trisomy of HSA21 in human DS hematopoietic stem and primitive progenitor cells. These data suggest a role for ERG as a regulator of hematopoietic lineage potential, and that trisomy of ERG in the context of DS foetal liver hemopoiesis drives the pre-leukemic changes that predispose to subsequent DS-TMD and DS-AMKL.
Subject(s)
Chromosomes, Human, Pair 21/genetics , Down Syndrome/genetics , Oncogene Proteins/genetics , Stem Cells/cytology , Trans-Activators/genetics , Transcription Factors/genetics , Trisomy , ADP-ribosyl Cyclase 1/metabolism , Alleles , Animals , Antigens, CD34/metabolism , Cell Lineage , Cell Proliferation , Disease Models, Animal , Erythroid Cells/metabolism , Gene Expression Profiling , Gene Expression Regulation , Genotype , Hematopoiesis/genetics , Hematopoietic System/cytology , Hematopoietic System/metabolism , Humans , Megakaryocytes/metabolism , Mice , Mice, Knockout , Microarray Analysis , Proto-Oncogene Proteins c-ets/genetics , Proto-Oncogene Proteins c-ets/metabolism , Sequence Analysis, RNA , Stem Cells/metabolism , Transcriptional Regulator ERG , TranscriptomeABSTRACT
A central issue in the regulation of apoptosis by the Bcl-2 family is whether its BH3-only members initiate apoptosis by directly binding to the essential cell-death mediators Bax and Bak, or whether they can act indirectly, by engaging their pro-survival Bcl-2-like relatives. Contrary to the direct-activation model, we show that Bax and Bak can mediate apoptosis without discernable association with the putative BH3-only activators (Bim, Bid, and Puma), even in cells with no Bim or Bid and reduced Puma. Our results indicate that BH3-only proteins induce apoptosis at least primarily by engaging the multiple pro-survival relatives guarding Bax and Bak.
