Adenosine deaminases that act on RNA (ADARs) convert adenosine residues to inosine in double-stranded RNA. In vivo, ADAR1 is essential for the maintenance of hematopoietic stem/progenitors. Whether ...other hematopoietic cell types also require ADAR1 has not been assessed. Using erythroid- and myeloid-restricted deletion of Adar1 , we demonstrate that ADAR1 is dispensable for myelopoiesis but is essential for normal erythropoiesis. Adar1 -deficient erythroid cells display a profound activation of innate immune signaling and high levels of cell death. No changes in microRNA levels were found in ADAR1-deficient erythroid cells. Using an editing-deficient allele, we demonstrate that RNA editing is the essential function of ADAR1 during erythropoiesis. Mapping of adenosine-to-inosine editing in purified erythroid cells identified clusters of hyperedited adenosines located in long 3'-untranslated regions of erythroid-specific transcripts and these are ADAR1-specific editing events. ADAR1-mediated RNA editing is essential for normal erythropoiesis.
In proliferating cells, where most Polycomb repressive complex 2 (PRC2) studies have been performed, gene repression is associated with PRC2 trimethylation of H3K27 (H3K27me3). However, it is ...uncertain whether PRC2 writing of H3K27me3 is mechanistically required for gene silencing. Here, we studied PRC2 function in postnatal mouse cardiomyocytes, where the paucity of cell division obviates bulk H3K27me3 rewriting after each cell cycle. EED (embryonic ectoderm development) inactivation in the postnatal heart (Eed
) caused lethal dilated cardiomyopathy. Surprisingly, gene upregulation in Eed
was not coupled with loss of H3K27me3. Rather, the activating histone mark H3K27ac increased. EED interacted with histone deacetylases (HDACs) and enhanced their catalytic activity. HDAC overexpression normalized Eed
heart function and expression of derepressed genes. Our results uncovered a non-canonical, H3K27me3-independent EED repressive mechanism that is essential for normal heart function. Our results further illustrate that organ dysfunction due to epigenetic dysregulation can be corrected by epigenetic rewiring.
The study of human hematopoiesis is often limited by the inability to manipulate this process in vivo and differences that exist between humans and commonly employed model organisms. However, human ...genetics provides a way to gain insight into natural variation in a variety of hematologic phenotypes and creates an opportunity to better understand hematopoiesis. In this review, we discuss how genome-wide association studies are revealing common genetic variation that is associated with hematologic traits and diseases. We discuss how the resulting insight from these studies promises to increase our understanding of human hematopoiesis and outline the challenges that lay ahead in this field.
ERG, an ETS family transcription factor frequently overexpressed in human leukemia, has been implicated as a key regulator of hematopoietic stem cells. However, how ERG controls normal hematopoiesis, ...particularly at the stem and progenitor cell level, and how it contributes to leukemogenesis remain incompletely understood. Using homologous recombination, we generated an Erg knockdown allele (Erg
) in which Erg expression can be conditionally restored by Cre recombinase. Erg
animals die at E10.5-E11.5 due to defects in endothelial and hematopoietic cells, but can be completely rescued by Tie2-Cre-mediated restoration of Erg in these cells. In Erg
mice, ∼40% reduction in Erg dosage perturbs both fetal liver and bone marrow hematopoiesis by reducing the numbers of Lin
Sca-1
c-Kit
(LSK) hematopoietic stem and progenitor cells (HSPCs) and megakaryocytic progenitors. By genetic mosaic analysis, we find that Erg-restored HSPCs outcompete Erg
HSPCs for contribution to adult hematopoiesis in vivo. This defect is in part due to increased apoptosis of HSPCs with reduced Erg dosage, a phenotype that becomes more drastic during 5-FU-induced stress hematopoiesis. Expression analysis reveals that reduced Erg expression leads to changes in expression of a subset of ERG target genes involved in regulating survival of HSPCs, including increased expression of a pro-apoptotic regulator Bcl2l11 (Bim) and reduced expression of Jun. Collectively, our data demonstrate that ERG controls survival of HSPCs, a property that may be used by leukemic cells. Stem Cells 2017;35:1773-1785.
We have used a cDNA probe for mouse Gf-1 gene that encodes the erythroid cell transcription factor to identify genetic variation in genomic DNA between Mus species. The segregation of Gf-1 DNA ...variation was analyzed in Mus species crosses that have been previously typed for the segregation of more than 30 genes spanning 80 cM of the mouse X chromosome from the centromere to the border of the X-Y pairing region. We identified a single X chromosome locus in the mouse, Gf-1, and an analysis of recombinants from 203 backcross progeny mapped Gf-1 to the proximal portion of the chromosome, coincident with the Cybb locus and proximal to Otc gene locus. A gene order of centromere, DXWas70, Cybb/Gf-1, Otc, Timp was established for the mouse X chromosome, which is in agreement with the map position observed on the human X chromosome.
Activating mutations in the
ras oncogene are not considered sufficient to induce abnormal cellular proliferation in the absence of cooperating oncogenes. We demonstrate that the conditional ...expression of an endogenous
K-ras
G12D
allele in murine embryonic fibroblasts causes enhanced proliferation and partial transformation in the absence of further genetic abnormalities. Interestingly,
K-ras
G12D
-expressing fibroblasts demonstrate attenuation and altered regulation of canonical Ras effector signaling pathways. Widespread expression of endogenous
K-ras
G12D
is not tolerated during embryonic development, and directed expression in the lung and GI tract induces preneoplastic epithelial hyperplasias. Our results suggest that endogenous oncogenic
ras is sufficient to initiate transformation by stimulating proliferation, while further genetic lesions may be necessary for progression to frank malignancy.
Debate on the adaptive origins of primates has long focused on the functional ecology of the primate visual system. For example, it is hypothesized that variable expression of short- (SWS1) and ...middle-to-long-wavelength sensitive (M/LWS) opsins, which confer color vision, can be used to infer ancestral activity patterns and therefore selective ecological pressures. A problem with this approach is that opsin gene variation is incompletely known in the grandorder Euarchonta, that is, the orders Scandentia (treeshrews), Dermoptera (colugos), and Primates. The ancestral state of primate color vision is therefore uncertain. Here, we report on the genes (OPN1SW and OPN1LW) that encode SWS1 and M/LWS opsins in seven species of treeshrew, including the sole nocturnal scandentian Ptilocercus lowii. In addition, we examined the opsin genes of the Central American woolly opossum (Caluromys derbianus), an enduring ecological analogue in the debate on primate origins. Our results indicate: 1) retention of ultraviolet (UV) visual sensitivity in C. derbianus and a shift from UV to blue spectral sensitivities at the base of Euarchonta; 2) ancient pseudogenization of OPN1SW in the ancestors of P. lowii, but a signature of purifying selection in those of C. derbianus; and, 3) the absence of OPN1LW polymorphism among diurnal treeshrews. These findings suggest functional variation in the color vision of nocturnal mammals and a distinctive visual ecology of early primates, perhaps one that demanded greater spatial resolution under light levels that could support cone-mediated color discrimination.
Acute myeloid leukemia with KMT2A (MLL) rearrangements is characterized by specific patterns of gene expression and enhancer architecture, implying unique core transcriptional regulatory circuitry. ...Here, we identified the transcription factors MEF2D and IRF8 as selective transcriptional dependencies of KMT2A-rearranged AML, where MEF2D displays partially redundant functions with its paralog, MEF2C. Rapid transcription factor degradation followed by measurements of genome-wide transcription rates and superresolution microscopy revealed that MEF2D and IRF8 form a distinct core regulatory module with a narrow direct transcriptional program that includes activation of the key oncogenes MYC, HOXA9, and BCL2. Our study illustrates a mechanism of context-specific transcriptional addiction whereby a specific AML subclass depends on a highly specialized core regulatory module to directly enforce expression of common leukemia oncogenes.
Master transcriptional regulators of development often function through dispersed cis elements at endogenous target genes. While cis-elements are routinely studied in transfection and transgenic ...reporter assays, it is challenging to ascertain how they function in vivo. To address this problem in the context of the locus encoding the critical hematopoietic transcription factor Gata2, we engineered mice lacking a cluster of GATA motifs 2.8 kb upstream of the Gata2 transcriptional start site. We demonstrate that the −2.8 kb site confers maximal Gata2 expression in hematopoietic stem cells and specific hematopoietic progenitors. By contrast to our previous demonstration that a palindromic GATA motif at the neighboring −1.8 kb site maintains Gata2 repression in terminally differentiating erythroid cells, the −2.8 kb site was not required to initiate or maintain repression. These analyses reveal qualitatively distinct functions of 2 GATA motif-containing regions in vivo.
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