Project description:Alternative pre-mRNA splicing is a prevalent mechanism in mammals that promotes proteomic diversity, including expression of cell-type specific protein isoforms. We characterized a role for RBM38 (RNPC1) in regulation of alternative splicing during late erythroid differentiation. We used an affymetrix human exon junction (HJAY) splicing microarray to identify a panel of RBM38-regulated alternatively spliced transcripts. Using microarray databases, we noted high RBM38 expression levels in CD71+ erythroid cells and thus chose to examine RBM38 expression during erythroid differentiation of human hematopoietic stem cells, detecting enhanced RBM38 expression during late erythroid differentiation. In differentiated erythroid cells, we validated a subset of RBM38-regulated splicing events and determined that RBM38 regulates activation of Protein 4.1R (EPB41) exon 16 during late erythroid differentiation. Using Epb41 minigenes, Rbm38 was found to be a robust activator of exon 16 splicing. To further address the mechanism of RBM38-regulated alternative splicing, a novel mammalian protein expression system, followed by SELEX-Seq, was used to identify a GU-rich RBM38 binding motif. Lastly, using a tethering assay, we determined that RBM38 can directly activate splicing when recruited to a downstream intron. Together, our data support the role of RBM38 in regulating alternative splicing during erythroid differentiation. siRNA knockdown of RBM38 was perfomed in human MCF-7 breast cancer cells. The efficiency of RBM38 knockdown was monitored by western blot using an RBM38 antibody (Santa Cruz Biotechnology, SC-85873). We conducted HJAY exon and exon junction array profiling on RNAs from four siRBM38 treated MCF-7 samples vs. four sicontrol treated MCF-7 samples Control / knockdown comparison.
Project description:Alternative pre-mRNA splicing is a prevalent mechanism in mammals that promotes proteomic diversity, including expression of cell-type specific protein isoforms. We characterized a role for RBM38 (RNPC1) in regulation of alternative splicing during late erythroid differentiation. We used an affymetrix human exon junction (HJAY) splicing microarray to identify a panel of RBM38-regulated alternatively spliced transcripts. Using microarray databases, we noted high RBM38 expression levels in CD71+ erythroid cells and thus chose to examine RBM38 expression during erythroid differentiation of human hematopoietic stem cells, detecting enhanced RBM38 expression during late erythroid differentiation. In differentiated erythroid cells, we validated a subset of RBM38-regulated splicing events and determined that RBM38 regulates activation of Protein 4.1R (EPB41) exon 16 during late erythroid differentiation. Using Epb41 minigenes, Rbm38 was found to be a robust activator of exon 16 splicing. To further address the mechanism of RBM38-regulated alternative splicing, a novel mammalian protein expression system, followed by SELEX-Seq, was used to identify a GU-rich RBM38 binding motif. Lastly, using a tethering assay, we determined that RBM38 can directly activate splicing when recruited to a downstream intron. Together, our data support the role of RBM38 in regulating alternative splicing during erythroid differentiation.
Project description:Differentiating erythroid cells execute a unique gene expression program that insures synthesis of the appropriate proteome at each stage of maturation. Standard expression microarrays provide important insight into erythroid gene expression, but cannot detect qualitative changes in transcript structure, mediated by RNA processing, that alter structure and function of encoded proteins. We analyzed stage-specific changes in the late erythroid transcriptome via use of high resolution microarrays that detect altered expression of individual exons. Ten differentiation-associated changes in erythroblast splicing patterns were identified, including the previously known activation of protein 4.1R exon 16 splicing. Six new alternative splicing switches involving enhanced inclusion of internal cassette exons were discovered, as well as three changes in use of alternative first exons. All of these erythroid stage-specific splicing events represent activated inclusion of authentic annotated exons, suggesting they represent an active regulatory process rather than a general loss of splicing fidelity. The observation that three of the regulated transcripts encode RNA binding proteins (SNRP70, HNRPLL, MBNL2) may indicate significant changes in the RNA processing machinery of late erythroblasts. Together these results support the existence of a regulated alternative pre-mRNA splicing program that is critical for late erythroid differentiation. Keywords: Time course; Splicing-sensitive microarray
Project description:Differentiating erythroid cells execute a unique gene expression program that insures synthesis of the appropriate proteome at each stage of maturation. Standard expression microarrays provide important insight into erythroid gene expression, but cannot detect qualitative changes in transcript structure, mediated by RNA processing, that alter structure and function of encoded proteins. We analyzed stage-specific changes in the late erythroid transcriptome via use of high resolution microarrays that detect altered expression of individual exons. Ten differentiation-associated changes in erythroblast splicing patterns were identified, including the previously known activation of protein 4.1R exon 16 splicing. Six new alternative splicing switches involving enhanced inclusion of internal cassette exons were discovered, as well as three changes in use of alternative first exons. All of these erythroid stage-specific splicing events represent activated inclusion of authentic annotated exons, suggesting they represent an active regulatory process rather than a general loss of splicing fidelity. The observation that three of the regulated transcripts encode RNA binding proteins (SNRP70, HNRPLL, MBNL2) may indicate significant changes in the RNA processing machinery of late erythroblasts. Together these results support the existence of a regulated alternative pre-mRNA splicing program that is critical for late erythroid differentiation. Keywords: Time course; Splicing-sensitive microarray For Exon array hybridizations: 3 biological replicates of day 7, 2 biological replicates of day 10, 3 biological replicates of day 14; For HJAY array hybridizations: 5 biological replicates each were analyzed from day 7 and day 14. One day 14 replicate was deemed an outlier and removed from subsequent analyses.
Project description:It is unclear how epigenetic changes regulate the induction of erythroid-specific genes during terminal erythropoiesis. Here we use global mRNA sequencing (mRNA-seq) and chromatin immunoprecipitation coupled to high-throughput sequencing (CHIP-seq) to investigate the changes that occur in mRNA levels, RNA Polymerase II (Pol II) occupancy and multiple post-translational histone modifications when erythroid progenitors differentiate into late erythroblasts. Among genes induced during this developmental transition, there was an increase in the occupancy of Pol II, the activation marks H3K4me2, H3K4me3, H3K9Ac and H4K16Ac, and the elongation methylation mark H3K79me2. In contrast, genes that were repressed during differentiation showed relative decreases in H3K79me2 levels yet had levels of Pol II binding and active histone marks similar to those in erythroid progenitors. We also found that relative changes in histone modification levels-in particular, H3K79me2 and H4K16ac-were most predictive of gene expression patterns. Our results suggest that in terminal erythropoiesis both promoter and elongation-associated marks contribute to the induction of erythroid genes, while gene repression is marked by changes in histone modifications mediating Pol II elongation. Our data maps the epigenetic landscape of terminal erythropoiesis and suggests that control of transcription elongation regulates gene expression during terminal erythroid differentiation. Mouse fetal liver cells are double-labeled for erythroid-specific TER119 and non erythroid-specific transferrin receptor (CD71) and then sorted by flow-cytometry. E14.5 fetal livers contain at least five distinct populations of cells (R1 through R5); as they progressively differentiate they gain TER119 and then gain and subsequently lose CD71. CFU-E cells and proerythroblasts make up the R1 population; R2 consists of proerythroblasts and early basophilic erythroblasts; R3 includes early and late basophilic erythroblasts; R4 is mostly polychromatophilic and orthochromatophilic erythroblasts; and R5 is comprised of late orthochromatophilic erythroblasts and reticulocytes. We have sorted for R2-R5 cells for RNA-seq experiment.
Project description:Terminal differentiation of mammalian erythroid progenitors involves 4-5 cell divisions and induction of many erythroid important genes, followed by chromatin and nuclear condensation and enucleation. The protein levels of c-myc (Myc) are reduced dramatically during late stage erythroid maturation, coinciding with cell cycle arrest in G1-phase and enucleation, suggesting possible roles for c-myc in either or both of these processes. Here we demonstrate that ectopic Myc expression affects terminal erythroid maturation in a dose-dependent manner. Expression of Myc at physiological levels did not affect erythroid differentiation or cell cycle shutdown, but specifically blocked erythroid nuclear condensation and enucleation. Myc prevented deacetylation of several lysine residues in histones H3 and H4 that are normally deacetylated during erythroid maturation. When over-expressed at levels higher than the physiological range, Myc blocked erythroid differentiation and the cells continued to proliferate in cytokine-free, serum-containing culture medium with an early erythroblast morphology. These studies reveal an important dose-dependent function of Myc in regulating terminal maturation in mammalian erythroid cells. Our findings further support the emerging notion that Myc regulates chromatin structure by regulating global histone acetylation states. Five groups with three biological replicates in each.
Project description:Ribosomopathies constitute a range of disabling conditions associated with defective protein synthesis mainly affecting hematopoietic stem cells (HSCs) and erythroid development. Here we demonstrate that deletion of Polypyrimidine Tract Binding Protein 1 (PTBP1) in the hematopoietic compartment led to the development of a ribosomopathy-like condition. Specifically, loss of PTBP1 was associated with a decrease in HSC self-renewal, erythroid differentiation and protein synthesis. Consistent with its function as a splicing regulator, PTBP1 deficiency led to splicing defects in hundreds of genes and we demonstrate that the up-regulation of a specific isoform of CDC42 could partly mimic the protein synthesis defect associated with loss of PTBP1. Furthermore, PTBP1 deficiency was associated with a marked defect in ribosome biogenesis and a selective reduction in the translation of mRNAs encoding ribosomal proteins. Collectively, this work identifies PTBP1 as a key integrator of ribosomal functions and highlights the broad functional repertoire of RNA binding proteins.
Project description:Terminal differentiation of mammalian erythroid progenitors involves 4-5 cell divisions and induction of many erythroid important genes, followed by chromatin and nuclear condensation and enucleation. The protein levels of c-myc (Myc) are reduced dramatically during late stage erythroid maturation, coinciding with cell cycle arrest in G1-phase and enucleation, suggesting possible roles for c-myc in either or both of these processes. Here we demonstrate that ectopic Myc expression affects terminal erythroid maturation in a dose-dependent manner. Expression of Myc at physiological levels did not affect erythroid differentiation or cell cycle shutdown, but specifically blocked erythroid nuclear condensation and enucleation. Myc prevented deacetylation of several lysine residues in histones H3 and H4 that are normally deacetylated during erythroid maturation. When over-expressed at levels higher than the physiological range, Myc blocked erythroid differentiation and the cells continued to proliferate in cytokine-free, serum-containing culture medium with an early erythroblast morphology. These studies reveal an important dose-dependent function of Myc in regulating terminal maturation in mammalian erythroid cells. Our findings further support the emerging notion that Myc regulates chromatin structure by regulating global histone acetylation states.