Understanding the molecular regulation of hematopoietic stem and progenitor cell (HSPC) engraftment is paramount to improving transplant outcomes. To discover novel regulators of HSPC repopulation, ...we transplanted >1,300 mice with shRNA-transduced HSPCs within 24 h of isolation and transduction to focus on detecting genes regulating repopulation. We identified 17 regulators of HSPC repopulation: Arhgef5, Armcx1, Cadps2, Crispld1, Emcn, Foxa3, Fstl1, Glis2, Gprasp2, Gpr56, Myct1, Nbea, P2ry14, Smarca2, Sox4, Stat4, and Zfp251. Knockdown of each of these genes yielded a loss of function, except in the cases of Armcx1 and Gprasp2, whose loss enhanced hematopoietic stem cell (HSC) repopulation. The discovery of multiple genes regulating vesicular trafficking, cell surface receptor turnover, and secretion of extracellular matrix components suggests active cross talk between HSCs and the niche and that HSCs may actively condition the niche to promote engraftment. We validated that Foxa3 is required for HSC repopulating activity, as Foxa3(-/-) HSC fails to repopulate ablated hosts efficiently, implicating for the first time Foxa genes as regulators of HSPCs. We further show that Foxa3 likely regulates the HSC response to hematologic stress. Each gene discovered here offers a window into the novel processes that regulate stable HSPC engraftment into an ablated host.
How transcription factors (TFs) cooperate within large protein complexes to allow rapid modulation of gene expression during development is still largely unknown. Here we show that the key ...haematopoietic LIM-domain-binding protein-1 (LDB1) TF complex contains several activator and repressor components that together maintain an erythroid-specific gene expression programme primed for rapid activation until differentiation is induced. A combination of proteomics, functional genomics and in vivo studies presented here identifies known and novel co-repressors, most notably the ETO2 and IRF2BP2 proteins, involved in maintaining this primed state. The ETO2-IRF2BP2 axis, interacting with the NCOR1/SMRT co-repressor complex, suppresses the expression of the vast majority of archetypical erythroid genes and pathways until its decommissioning at the onset of terminal erythroid differentiation. Our experiments demonstrate that multimeric regulatory complexes feature a dynamic interplay between activating and repressing components that determines lineage-specific gene expression and cellular differentiation.
Progress in sample preparation for scRNA-seq is reported based on RevGel-seq, a reversible-hydrogel technology optimized for samples of fresh cells. Complexes of one cell paired with one barcoded ...bead are stabilized by a chemical linker and dispersed in a hydrogel in the liquid state. Upon gelation on ice the complexes are immobilized and physically separated without requiring nanowells or droplets. Cell lysis is triggered by detergent diffusion, and RNA molecules are captured on the adjacent barcoded beads for further processing with reverse transcription and preparation for cDNA sequencing. As a proof of concept, analysis of PBMC using RevGel-seq achieves results similar to microfluidic-based technologies when using the same original sample and the same data analysis software. In addition, a clinically relevant application of RevGel-seq is presented for pancreatic islet cells. Furthermore, characterizations carried out on cardiomyocytes demonstrate that the hydrogel technology readily accommodates very large cells. Standard analyses are in the 10,000-input cell range with the current gelation device, in order to satisfy common requirements for single-cell research. A convenient stopping point after two hours has been established by freezing at the cell lysis step, with full preservation of gene expression profiles. Overall, our results show that RevGel-seq represents an accessible and efficient instrument-free alternative, enabling flexibility in terms of experimental design and timing of sample processing, while providing broad coverage of cell types.
Cellular differentiation requires precisely regulated tissue‐specific and developmental stage‐specific gene expression patterns. Numerous studies have highlighted the predictive power of enhancers on ...lineage‐specific gene expression programs and have started to unravel their mechanisms of action. We review here the dynamics of the enhancer landscape during hematopoietic differentiation and how enhancers function in the context of the 3D organization of the genome. We further discuss the involvement of aberrant enhancer activity in human diseases and emerging strategies aiming at controlling enhancer activity and chromosome topology for therapeutic purposes.
Loss of hematopoietic stem cell (HSC) function and increased risk of developing hematopoietic malignancies are severe and concerning complications of anticancer radiotherapy and chemotherapy. We have ...previously shown that thrombopoietin (TPO), a critical HSC regulator, ensures HSC chromosomal integrity and function in response to γ-irradiation by regulating their DNA-damage response. TPO directly affects the double-strand break (DSB) repair machinery through increased DNA-protein kinase (DNA-PK) phosphorylation and nonhomologous end-joining (NHEJ) repair efficiency and fidelity. This effect is not shared by other HSC growth factors, suggesting that TPO triggers a specific signal in HSCs facilitating DNA-PK activation upon DNA damage. The discovery of these unique signaling pathways will provide a means of enhancing TPO-desirable effects on HSCs and improving the safety of anticancer DNA agents. We show here that TPO specifically triggers Erk and nuclear factor κB (NF-κB) pathways in mouse hematopoietic stem and progenitor cells (HSPCs). Both of these pathways are required for a TPO-mediated increase in DSB repair. They cooperate to induce and activate the early stress-response gene, Iex-1 (ier3), upon DNA damage. Iex-1 forms a complex with pERK and the catalytic subunit of DNA-PK, which is necessary and sufficient to promote TPO-increased DNA-PK activation and NHEJ DSB repair in both mouse and human HSPCs.
•TPO specifically activates Erk and NF-κB pathways in hematopoietic stem and progenitor cells.•Erk and NF-κB cooperate to trigger their common target, Iex-1, and DNA-PK-dependent NHEJ activation in HSPCs upon irradiation.
Un être humain adulte produit environ deux millions d’érythrocytes par seconde, à travers un processus connu sous le nom d’érythropoïèse. L’érythropoïèse est contrôlée par une balance entre ...prolifération et différenciation finement régulée. L’expression des gènes impliqués dans ces deux processus distincts, est régulée extrinsèquement (cytokines) et intrinsèquement (microenvirennement métabolique, facteurs de transcription). Les facteurs de transcription, fonctionnent sous forme de complexes multiprotéiques et contrôlent l’activité transcriptionnelle des cellules. Parmi eux, le complexe LDB1 joue un rôle clé dans la régulation de la balance prolifération/différenciation pendant l’érythropoïèse, puisqu’il contrôle l’expression des gènes impliquées dans ces deux processus. Au cours de mon doctorat, nous avons d’abord caractérisé les mécanismes moléculaires de la “pré-activation” des gènes de différenciation, également nommés marqueurs erythroides, dans les progéniteurs erythroides immatures. La pré-activation, est un état dans lequel, les gènes sont exprimés à un niveau basal très bas, permissif pour une activation significative pendant la différenciation. Nous avons ainsi montré que les répresseurs : ETO2, IRF2BP2 et NCOR1, interagissent avec le complexe LDB1, et lient ensemble les gènes des marqueurs erythroides et les répriment. Au cours de l’érythropoïèse, ces corépresseurs sont déstabilisés et LDB1 agit alors comme un activateur. En ce qui concerne les gènes de prolifération, nous avons observé que le complexe LDB1 est déstabilisé au niveau de ces loci pendant l’érythropoïèse. Afin d’étudier les mécanismes moléculaires de la répression génique des gènes de prolifération au cours de l’érythropoïèse, nous avons choisi d’étudier Myb, une cible du complexe LDB1, étudié auparavant dans le laboratoire. Nous avons testé trois facteurs : ZEB1, OGT et RNF12, en tant que candidats dans la répression de Myb. Nous avons montré que RNF12 est le seul facteur intervenant dans la transcription de Myb. RNF12 régule Myb probablement par une modification de complexes épigénétiques.
Every second about 2 million erythrocytes are produced in the adult human body, through a process called erythropoiesis. Erythropoiesis is controlled by a highly regulated balance between proliferation and differentiation. Expression of genes responsible for cell proliferation and differentiation is controlled external (such as cytokines) and internal (such as metabolic microenvironment and transcription factors). Transcription factors bind DNA and recruit co-factors generating transcriptional complexes. The LDB1 complex has a key role in the balance between erythroid proliferation vs. differentiation, since it regulates genes involved in both processes. During my Ph.D., we investigated the molecular mechanisms that LDB1 employs to regulate genes with divergent function. We first showed that in erythroid progenitors, differentiating genes, also known as erythroid markers, are primed. Gene priming consists of genes expressed in low basal but significant levels in progenitors, which can rapidly be activated during differentiation. We showed that in progenitors, ETO2, IRF2BP2 and NCOR1, bind the LDB1 complex therefore generating a priming complex. During differentiation, binding of the repressive (ETO2-IRF2BP2-NCOR1) co-factors to the LDB1 complex, is destabilized and genes become active. In genes involved in erythroid proliferation, we observed that LDB1 is destabilized, a feature leading to gene silencing. We used Myb, as a model of gene silencing in the context of regulation by the LDB1 complex. We tested three transcription factors: ZEB1, OGT and RNF12, as candidates in gene silencing. Among these factors, only RNF12 regulates Myb expression, probably through modifications of epigenetic silencers (Polycomb/MLL).
PDF
