Project description:Transcription profiling by array of primary megakaryocytes (MEG) and erythroblasts (ERY) developed from murine fetal liver hematopoietic stem cells
Project description:Enforced expression of the homeobox transcription factor HOXB4 has been shown to enhance hematopoietic stem cell (HSC) self-renewal and expansion ex vivo and in vivo. In order to investigate the largely unknown downstream targets of HOXB4 in hematopoietic progenitor cells, HOXB4 was constitutively overexpressed in the primitive hematopoietic progenitor cell line, EML. Gene expression differences were compared between KLS (c-Kit+, Lin-, Sca-1+)-EML cells that overexpressed HOXB4 (KLS-EML-HOXB4) to control KLS-EML cells that were transduced with vector alone. ChIP-chip was used to identify promoter regions bound by HOXB4.
Project description:HOXB4 mediates expansion of adult and embryo-derived hematopoietic stem cells (HSCs) when expressed ectopically. To define the underlying molecular mechanisms, we performed gene expression profiling in combination with subsequent functional analysis using enriched adult HSCs expressing inducible HOXB4. A substantial number of the identified HOXB4 target genes are involved in signaling pathways important for controlling self-renewal, maintenance and differentiation of stem cells. Functional assays performed on selected pathways confirmed the biological coherence of the array results. HOXB4 activity protected adult HSCs from the detrimental effects mediated by the proinflammatory cytokine TNF-alpha. Furthermore, we demonstrate that HOXB4 activity and FGF-signaling are intertwined. HOXB4-mediated expansion of adult HSCs was enhanced by specific and complete inhibition of FGF-receptors. Based on our results we propose that HOXB4 governs pivotal cell-intrinsic pathways involved in the regulation of cell cycle, differentiation and apoptosis. Our results strongly suggest that HOXB4 modulates the response of HSCs to multiple extrinsic signals in a concerted manner, thereby shifting the balance towards stem cell self-renewal. Experiment Overall Design: To understand the mechanisms of HOXB4 activity, we wished to identify target genes of HOXB4 in adult hematopoietic stem and progenitor cells (HSC/HPCs). We thus transduced murine HSC/HPCs with a retroviral vector that co-expresses EGFP and a tamoxifen-inducible form of HOXB4 (HOXB4-ER). Upon addition of 4-hydroxytamoxifen (TMX), the HOXB4-ER fusion protein translocates from the cytoplasm to the nucleus, consequently being capable of modulating gene expression. Transduced cell populations were expanded for 14 days in the presence of TMX. Thereafter, HOXB4-ER+LSK (GFP+ , lineage negative, Sca1+, ckit+) cells were flow cytometrically isolated and cultivated either with or without TMX for 1 or 4 hours. Inactivation of HOXB4 activity by TMX withdrawal was intended to mimic the naturally occurring down-regulation of HOXB4 in differentiating stem cells. RNA was prepared after the aforementioned times and the transcriptional profiles of HOXB4-ER+LSK +/- TMX analyzed using the Affymetrix⢠platform. As a control, profiling was also performed with LSK cells expressing unmodified constitutively active HOXB4 (HOXB4const) ± TMX, to exclude changes in gene expression due to unknown effects of tamoxifen itself. RNAs from adult LSK cells were processed for use on Affymetrix GeneChips Mouse Genome 430 2.0. All quality parameters for the arrays were confirmed to be in the recommended range.
Project description:Transcription profiling by high throughput sequencing of murine bone marrow endothelial cells and bone marrow stroma, in vitro and in vivo, with and without hematopoietic stem cells co-culture
Project description:Enforced expression of the homeobox transcription factor HOXB4 has been shown to enhance hematopoietic stem cell (HSC) self-renewal and expansion ex vivo and in vivo. In order to investigate the largely unknown downstream targets of HOXB4 in hematopoietic progenitor cells, HOXB4 was constitutively overexpressed in the primitive hematopoietic progenitor cell line, EML. Gene expression differences were compared between KLS (c-Kit+, Lin-, Sca-1+)-EML cells that overexpressed HOXB4 (KLS-EML-HOXB4) to control KLS-EML cells that were transduced with vector alone. ChIP-chip was used to identify promoter regions bound by HOXB4. We overexpressed HOXB4 in EML cells. We isolated 3 separate single cell clones as assessed by Southern Blot Analysis (3 clones for EML-HOXB4 and 3 clones for control EML-GFP cells). RNA was isolated from the KLS (c-Kit+, Lin-, Sca-1+) fraction of each single cell clone population and processed for hybridization to array chips using established lab protocols. Chip-Chip analysis of the three HOXB4 overexpressing clones was performed to identify HOXB4 bound promoters.