The Lin28b-let-7-Hmga2 axis determines the higher self-renewal potential of fetal haematopoietic stem cells
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ABSTRACT: Mouse haematopoietic stem cells (HSCs) undergo a post-natal transition in several properties, including a marked reduction in their self-renewal activity. We now show that the developmentally timed change in this key function of HSCs is associated with their decreased expression of Lin28b and an accompanying increase in their let-7 microRNA levels. Lentivirus(LV)-mediated overexpression of Lin28 in adult HSCs elevates their self-renewal activity in transplanted irradiated hosts, as does overexpression of Hmga2, a well-established let-7 target that is upregulated in fetal HSCs. Conversely, HSCs from fetal Hmga2-/- mice do not display the heightened self-renewal activity that is characteristic of wild-type fetal HSCs. Interestingly, overexpression of Hmga2 in adult HSCs does not mimic the ability of elevated Lin28 to activate a fetal lymphoid differentiation program. Thus Lin28b may act as a master regulator of developmentally timed changes in HSC programs with Hmga2 serving as its specific downstream modulator of HSC self-renewal potential. Lin-Sca1+cKit+ cells were isolated from E14.5 fetal livers (of wild-type of Hmga2-/- embryos) or the bone marrow of 8-12 week old mice by fluorescence activated cell sorting. The RNA was extracted and hybridized on Affymetrix mpuse gene 1.0 ST microarrays.
Project description:Mouse haematopoietic stem cells (HSCs) undergo a post-natal transition in several properties, including a marked reduction in their self-renewal activity. We now show that the developmentally timed change in this key function of HSCs is associated with their decreased expression of Lin28b and an accompanying increase in their let-7 microRNA levels. Lentivirus(LV)-mediated overexpression of Lin28 in adult HSCs elevates their self-renewal activity in transplanted irradiated hosts, as does overexpression of Hmga2, a well-established let-7 target that is upregulated in fetal HSCs. Conversely, HSCs from fetal Hmga2-/- mice do not display the heightened self-renewal activity that is characteristic of wild-type fetal HSCs. Interestingly, overexpression of Hmga2 in adult HSCs does not mimic the ability of elevated Lin28 to activate a fetal lymphoid differentiation program. Thus Lin28b may act as a master regulator of developmentally timed changes in HSC programs with Hmga2 serving as its specific downstream modulator of HSC self-renewal potential.
Project description:Increasing evidence links metabolic activity and cell growth to decline in hematopoietic stem cell (HSC) function during aging. The Lin28b/Hmga2 pathway controls tissue development and in the hematopoietic system the postnatal downregulation of this pathway causes a decrease in self renewal of adult HSCs compared to fetal HSCs. Igf2bp2 is an RNA binding protein and a mediator of the Lin28b/Hmga2 pathway, which regulates metabolism and growth signaling by influencing RNA stability and translation of its target genes. It is currently unknown whether Lin28/Hmga2/Igf2bp2 signaling impacts on aging-associated impairments in HSC function and hematopoiesis. Here, we analyzed homozygous Igf2bp2 germline knockout mice and wildtype control animals to address this question. The study shows that Igf2bp2 deletion rescues aging phenotypes of the hematopoietic system, such as the expansion of HSC numbers in bone marrow and the biased increase of myeloid cells in peripheral blood. This rescue of hematopoietic aging coincides with reduced mitochondrial metabolism and glycolysis in Igf2bp2-/- HSCs compared to Igf2bp2+/+ HSCs. Conversely, Igf2bp2 overexpression activates protein synthesis pathways in HSCs and leads to a rapid loss of self renewal by enhancing myeloid skewed differentiation in an mTOR/PI3K-dependent manner. Together, these results show that Igf2bp2 regulates energy metabolism and growth signaling in HSCs and that the activity of this pathways influences self renewal, differentiation, and aging of HSCs.
Project description:The transcription factor SOX17 is expressed by fetal, but not adult hematoipoietic stem cells (HSCs), and is required for the maintenance of fetal and neonatal, but not adult, HSCs. In the current study we show that ectopic expression of Sox17 in adult HSCs and transiently reconstituting multipotent progenitors was sufficient to confer increased self-renewal potential and the expression of fetal HSC genes including fetal HSC surface markers. To assess the mechanisms by which ectopic Sox17 expression in adult hematopoietic progenitors increased self-renewal potential and conferred fetal HSC properties, we compared the gene expression profiles of E16.5 fetal liver HSCs, young adult bone marrow HSCs, young adult bone marrow CD48+LSK cells, and Sox17-expressing CD48+LSK cells isolated from mice that had been transplanted with MSCV-Sox17-infected bone marrow cells 12 weeks earlier. Total RNA (~5ng) was isolated from 3 independent, freshly isolated aliquots of 10,000 E16.5 fetal liver HSCs, 10,000 fetal liver CD48+LSK cells, 10,000 adult bone marrow HSCs, 10,000 adult bone marrow CD48+LSK cells, 10,000 Sox17-expressing CD48+LSK cells isolated from primary recipients 12 weeks after transplantation of MSCV-Sox17-infected bone marrow cells. Purified RNA was reverse transcribed and amplified using the WT-Ovation™ Pico RNA Amplification system (NuGEN Technologies) following the manufacturer’s instructions. Sense strand cDNA was generated using WT-Ovation™ Exon Module (NuGEN), then fragmented and labeled using the FL-Ovation™ cDNA Biotin Module V2 (NuGEN). 2.5µg of labeled cDNA were hybridized to Affymetrix Mouse Gene ST 1.0 microarrays.
Project description:In blood, the transcription factor C/EBPa is essential for myeloid differentiation and has been implicated in regulating self-renewal of fetal liver hematopoietic stem cells (HSCs). However, its function in adult HSCs is unknown. Here, using an inducible knockout model, we found that C/EBPa deficient adult HSCs underwent a pronounced expansion with enhanced proliferation, characteristics resembling fetal liver HSCs. Consistently, transcription profiling of C/EBPa deficient HSCs revealed a gene expression program similar to fetal liver HSCs. Moreover we observed that age-specific C/EBPa expression correlated with its inhibitory effect on the HSC cell cycle. Mechanistically, we identified N-Myc as a C/EBPa downstream target. C/EBPa upregulation during HSC transition from an active fetal state to a quiescent adult state was accompanied by down-regulation of N-Myc, and loss of C/EBPa resulted in de-repression of NMyc. Our data establish that C/EBPa acts as a molecular switch between fetal and adult states of HSC in part via transcriptional repression of the proto-oncogene N-Myc. HSCs of Pu.1 knock-in (PU.1ki/ki) mice were used for RNA extraction and hybridization on Affymetrix microarrays. We compared these microarray samples with the corresponding wild type.
Project description:The transcription factor SOX17 is expressed by fetal, but not adult hematoipoietic stem cells (HSCs), and is required for the maintenance of fetal and neonatal, but not adult, HSCs. In the current study we show that ectopic expression of Sox17 in adult HSCs and transiently reconstituting multipotent progenitors was sufficient to confer increased self-renewal potential and the expression of fetal HSC genes including fetal HSC surface markers. To assess the acute effects of ectopic Sox17 expression on global gene expression in adult HSCs, we performed microarray analysis to compare the gene expression profile of adult Sox17-trangenic and control HSCs after short induction of Sox17-transgene expression. Total RNA were isolated from 5 independent, freshly isolated aliquots of 10,000 HSCs isolated from 8-week old Sox17-transgenic ((tetO)7CMVSox17-IRES-NucEGFP;B6.Cg-Gt(ROSA)26Sortm1(rtTA*M2)Jae/J double transgenic) or littermate control mice that were treated with doxycycline for 5 days to induce transgene expression. Purified RNA was reverse transcribed and amplified using the WT-Ovation™ Pico RNA Amplification system (NuGEN Technologies) following the manufacturer’s instructions. Sense strand cDNA was generated using WT-Ovation™ Exon Module (NuGEN), then fragmented and labeled using the FL-Ovation™ cDNA Biotin Module V2 (NuGEN). 2.5µg of labeled cDNA were hybridized to Affymetrix Mouse Gene ST 1.0 microarrays.
Project description:The fetal to adult switch in mouse hematopoietic stem cell (HSC) behavior is characterized by entry into quiescence and alterations in lineage output. Here we identify the ability of HSCs to undergo emergency megakaryopoiesis following acute inflammatory insult as an outcome of this developmental switch. Single cell accessibility mapping of fetal and adult HSCs resolves a heterogeneous chromatin landscape consistent with a two-step megakaryocyte lineage priming process. Importantly, we demonstrate that the accumulation of megakaryocyte primed HSCs is under the control of the developmentally restricted Lin28b RNA binding protein. Persistent Lin28b protein expression in postnatal HSCs delays the formation of a primed HSC pool and limits emergency megakaryopoiesis. Taken together, we identify Lin28b as a negative regulator of a megakaryocyte primed HSC state that is enforced at the chromatin level during unperturbed organismal development. These findings highlight the ontogenically timed onset of inflammatory responsiveness, with important implications for the delicate balance between host protection and tissue damage during neonatal life.
Project description:The fetal to adult switch in mouse hematopoietic stem cell (HSC) behavior is characterized by entry into quiescence and alterations in lineage output. Here we identify the ability of HSCs to undergo emergency megakaryopoiesis following acute inflammatory insult as an outcome of this developmental switch. Single cell accessibility mapping of fetal and adult HSCs resolves a heterogeneous chromatin landscape consistent with a two-step megakaryocyte lineage priming process. Importantly, we demonstrate that the accumulation of megakaryocyte primed HSCs is under the control of the developmentally restricted Lin28b RNA binding protein. Persistent Lin28b protein expression in postnatal HSCs delays the formation of a primed HSC pool and limits emergency megakaryopoiesis. Taken together, we identify Lin28b as a negative regulator of a megakaryocyte primed HSC state that is enforced at the chromatin level during unperturbed organismal development. These findings highlight the ontogenically timed onset of inflammatory responsiveness, with important implications for the delicate balance between host protection and tissue damage during neonatal life.
Project description:We isolated RNA from sorted common myeloid progenitor cells from wild-type fetal liver, wild-type adult bone marrow, transgenic Lin28b bone marrow, let-7b/c knock-out bone marrow, and Lin28b-deficient fetal liver and compared mRNA expression profiles. Examination of mRNA expression in common myeloid progenitors from multiple developmental time points and genotypes. Please note that iLin28* samples represent Lin28-induced samples, while the iLin28_*_vavcre samples represent hematopoietic-specific induction of Lin28.
Project description:The presence of unspliced transcripts in hematopoietic stem cells (HSCs) and the proposed association of CREBBP with the constitutive production of unspliced RNA and with pre-mRNA processing prompted us to examine more closely an anomaly we had noted in microarray-based gene expression studies but had previously attributed to experimental noise. We noticed that more than half of the probe sets down-regulated in Crebbp+/- fetal liver HSCs (FLHSCs) relative to wild-type (WT) mapped entirely within introns, rather than detecting exonic or spliced sequences. We therefore set out to test whether this might be evidence that reduced CREBBP levels selectively alter the generation of full-length, unspliced pre-mRNA. We also asked whether this process might be associated with differentiation since self-renewal and lineage commitment are the both responses for which HSCs are primed. Total RNA from wild-type, Crebbp+/-, Ep300+/-, Cdkn1a-/- FLHSCs and from wild type and Crebbp+/- mouse embryonic fibroblasts (MEFs) was isolated and hybridized to Affymetrix Mouse 430 2.0 expression microarrays. Fetal liver HSC RNA was amplified using the Ovation kit prior to hybridization. cell type comparison