Stepwise activation of enhancer and promoter regions of the B cell commitment gene Pax5 in early lymphopoiesis.
ABSTRACT Pax5 is an essential regulator of B cell identity and function. Here, we used transgenesis and deletion mapping to identify a potent enhancer in intron 5 of the Pax5 locus. This enhancer in combination with the promoter region was sufficient to recapitulate the B lymphoid expression of Pax5. The enhancer was silenced by DNA methylation in embryonic stem cells, but became activated in multipotent hematopoietic progenitors. It contained functional binding sites for the transcription factors PU.1, IRF4, IRF8, and NF-kappaB, suggesting that these regulators contribute to sequential enhancer activation in hematopoietic progenitors and during B cell development. In contrast, the promoter region was repressed by Polycomb group proteins in non-B cells and was activated only at the onset of pro-B cell development through induction of chromatin remodeling by the transcription factor EBF1. These experiments demonstrate a stepwise activation of Pax5 in early lymphopoiesis and provide mechanistic insights into the process of B cell commitment.
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ABSTRACT: E2A proteins are essential for the development of B cells beyond the progenitor cell stage. Here we have isolated E2A-deficient bone marrow-derived cells that have the ability to grow long-term in vitro and coexpress, at low levels, regulators of different hematopoietic cell lineages. When transferred into lethally irradiated hosts, E2A-deficient hematopoietic progenitor cells reconstitute the T, NK, myeloid, dendritic, and erythroid lineages but fail to develop into mature B lineage cells. Enforced expression of E47 in E2A-deficient hematopoietic progenitor cells directly activates the transcription of a subset of B lineage-specific genes, including lambda5, mb-1, and Pax5. In contrast, E47 inhibits the expression of regulators of other hematopoietic lineages, including TCF-1 and GATA-1. These observations indicate that E2A-deficient hematopoietic progenitor cells remain pluripotent after long-term culture in vitro and that E2A proteins play a critical role in B cell commitment.Immunity 04/2004; 20(3):349-60. · 19.80 Impact Factor
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ABSTRACT: The transcription factor PU.1 is a hematopoietic-specific member of the ets family. Mice carrying a mutation in the PU.1 locus were generated by gene targeting. Homozygous mutant embryos died at a late gestational stage. Mutant embryos produced normal numbers of megakaryocytes and erythroid progenitors, but some showed an impairment of erythroblast maturation. An invariant consequence of the mutation was a multilineage defect in the generation of progenitors for B and T lymphocytes, monocytes, and granulocytes. Thus, the developmental programs of lymphoid and myeloid lineages require a common genetic function likely acting at the level of a multipotential progenitor.Science 10/1994; 265(5178):1573-7. · 31.03 Impact Factor
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ABSTRACT: Analyses of the human PAX-5 locus and of the 5' region of the mouse Pax-5 gene revealed that transcription from two distinct promoters results in splicing of two alternative 5' exons to the common coding sequences of exons 2-10. Transcription from the upstream promoter initiates downstream of a TATA box and occurs predominantly in B-lymphocytes, whereas the TATA-less downstream promoter is active in all Pax-5-expressing tissues. The human PAX-5 gene is located on chromosome 9 in region p13, which is involved in t(9;14)(pl3;q32) translocations recurring in small lymphocytic lymphomas of the plasmacytoid subtype and in derived large-cell lymphomas. A previous molecular analysis of a t(9;14) breakpoint from a diffuse large-cell lymphoma (KIS-1) demonstrated that the immunoglobulin heavy-chain (IgH) locus on 14q32 was juxtaposed to chromosome 9p13 sequences of unknown function [Ohno, H., Furukawa, T., Fukuhara, S., Zong, S. Q., Kamesaki, H., Shows, T. B., Le Beau, M. M., McKeithan, T. W., Kawakami, T. & Honjo, T. (1990) Proc. Natl. Acad. Sci. USA 87,628-632]. Here we show that the KIS-1 translocation breakpoint is located 1807 base pairs upstream of exon 1A of PAX-5, thus bringing the potent Emu enhancer of the IgH gene into close proximity of the PAX-5 promoters. These data suggest that deregulation of PAX-5 gene transcription by the t(9;14)(pl3;q32) translocation contributes to the pathogenesis of small lymphocytic lymphomas with plasmacytoid differentiation.Proceedings of the National Academy of Sciences 06/1996; 93(12):6129-34. · 9.74 Impact Factor