Early Progenitor Cells Research Articles

Targeted deletion of the Hoxa cluster affects B lymphopoiesis through depletion of early lymphoid progenitors.

It is well established that Hoxa genes play a critical role in the proliferative capacity of adult hematopoietic stem and progenitor cells, but the importance of Hoxa genes in later stages of hematopoietic differentiation is less clear. Previously, we observed that B-cell numbers were reduced in adult mice in which Hoxa deletion was induced. In the current study, we investigated the requirement of Hoxa genes at different stages of B-cell development. Using an MxCre-inducible conditional knock-out mouse model, we showed that immature B-cell fractions and early lymphoid progenitors were markedly reduced in the absence of Hoxa, whereas mature B-cell populations were found at levels comparable to controls. Deletion of Hoxa genes in B-cell lineage-committed cells, however, did not affect B-cell development despite sustained Hoxa gene expression in immature CD19+ B-cell subsets. Together, these results suggest that the effect of Hoxa on B-cell development originates in early lymphoid progenitor cells.

Top2b is involved in the formation of outer segment and synapse during late-stage photoreceptor differentiation by controlling key genes of photoreceptor transcriptional regulatory network.

Topoisomerase II beta (Top2b) is an enzyme that alters the topologic states of DNA during transcription. Top2b deletion in early retinal progenitor cells causes severe defects in neural differentiation and affects cell survival in all retinal cell types. However, it is unclear whether the observed severe phenotypes are the result of cell-autonomous/primary defects or non-cell-autonomous/secondary defects caused by alterations of other retinal cells. Using photoreceptor cells as a model, we first characterized the phenotypes in Top2b conditional knockout. Top2b deletion leads to malformation of photoreceptor outer segments (OSs) and synapses accompanied by dramatic cell loss at late-stage photoreceptor differentiation. Then, we performed mosaic analysis with shRNA-mediated Top2b knockdown in neonatal retina using in vivo electroportation to target rod photoreceptors in neonatal retina. Top2b knockdown causes defective OS without causing a dramatic cell loss, suggesting a Top2b cell-autonomous function. Furthermore, RNA-seq analysis reveals that Top2b controls the expression of key genes in the photoreceptor gene-regulatory network (e.g., Crx, Nr2e3, Opn1sw, Vsx2) and retinopathy-related genes (e.g., Abca4, Bbs7, Pde6b). Together, our data establish a combinatorial cell-autonomous and non-cell-autonomous role for Top2b in the late stage of photoreceptor differentiation and maturation. © 2017 The Authors Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Modeling Human Natural Killer Cell Development in the Era of Innate Lymphoid Cells

Decades after the discovery of natural killer (NK) cells, their developmental pathways in mice and humans have not yet been completely deciphered. Accumulating evidence indicates that NK cells can develop in multiple tissues throughout the body. Moreover, detailed and comprehensive models of NK cell development were proposed soon after the turn of the century. However, with the recent identification and characterization of other subtypes of innate lymphoid cells (ILCs), which show some overlapping functional and phenotypic features with NK cell developmental intermediates, the distinct stages through which human NK cells develop from early hematopoietic progenitor cells remain unclear. Thus, there is a need to reassess and refine older models of NK cell development in the context of new data and in the era of ILCs. Our group has focused on elucidating the developmental pathway of human NK cells in secondary lymphoid tissues (SLTs), including tonsils and lymph nodes. Here, we provide an update of recent progress that has been made with regard to human NK cell development in SLTs, and we discuss these new findings in the context of contemporary models of ILC development.

Discovering sparse transcription factor codes for cell states and state transitions during development.

Computational analysis of gene expression to determine both the sequence of lineage choices made by multipotent cells and to identify the genes influencing these decisions is challenging. Here we discover a pattern in the expression levels of a sparse subset of genes among cell types in B- and T-cell developmental lineages that correlates with developmental topologies. We develop a statistical framework using this pattern to simultaneously infer lineage transitions and the genes that determine these relationships. We use this technique to reconstruct the early hematopoietic and intestinal developmental trees. We extend this framework to analyze single-cell RNA-seq data from early human cortical development, inferring a neocortical-hindbrain split in early progenitor cells and the key genes that could control this lineage decision. Our work allows us to simultaneously infer both the identity and lineage of cell types as well as a small set of key genes whose expression patterns reflect these relationships.

Endothelial Colony Forming Cells (ECFCs) in murine AKI \u2013 implications for future cell-based therapies

BackgroundIn recent years, early Endothelial Progenitor Cells (eEPCs) have been proven as effective tool in murine ischemic AKI and in diabetic nephropathy. The mechanisms of eEPC-mediated vasoprotection have been elucidated in detail. Besides producing a diverse range of humoral factors, the cells also act by secreting vasomodulatory microvesicles. Only few data in contrast have been published about the role of so-called Endothelial Colony Forming Cells (ECFCs - late EPCs) in ischemic AKI. We thus aimed to investigate ECFC effects on postischemic kidney function over several weeks. Our special interest focused on endothelial-to-mesenchymal transition (EndoMT), peritubular capillary density (PTCD), endothelial alpha-Tubulin (aT - cytoskeletal integrity), and endothelial p62 (marker of autophagocytic flux).MethodsEight to twelve weeks old male C57Bl/6 N mice were subjected to bilateral renal pedicle clamping for 35 or 45 min, respectively. Donor-derived syngeneic ECFCs (0.5 × 106) were i.v. injected at the end of ischemia. Animals were analyzed 1, 4 and 6 weeks later.ResultsCell therapy improved kidney function exclusively at week 1 (35 and 45 min). Ischemia-induced fibrosis was diminished in all experimental groups by ECFCs, while PTCD loss remained unaffected. Significant EndoMT was detected in only two of 6 groups (35 min, week 4 and 45 min, week 6), ECFCs reduced EndoMT only in the latter. Endothelial aT declined under almost all experimental conditions and these effects were further aggravated by ECFCs. p62 was elevated in endothelial cells, more so after 45 than after 35 min of ischemia. Cell therapy did not modulate p62 abundances at any time point.ConclusionA single dose of ECFCs administered shortly post-ischemia is capable to reduce interstitial fibrosis in the mid- to long-term whereas excretory dysfunction is improved only in a transient manner. There are certain differences in renal outcome parameters between eEPCs and ECFC. The latter do not prevent animals from peritubular capillary loss and they also do not further elevate endothelial p62. We conclude that differences between eEPCs and ECFCs result from certain mechanisms by which the cells act around and within vessels. Overall, ECFC treatment was not as efficient as eEPC therapy in preventing mice from ischemia-induced mid- to long-term damage.

Loss of CD44dim Expression from Early Progenitor Cells Marks T-Cell Lineage Commitment in the Human Thymus.

Human T-cell development is less well studied than its murine counterpart due to the lack of genetic tools and the difficulty of obtaining cells and tissues. Here, we report the transcriptional landscape of 11 immature, consecutive human T-cell developmental stages. The changes in gene expression of cultured stem cells on OP9-DL1 match those of ex vivo isolated murine and human thymocytes. These analyses led us to define evolutionary conserved gene signatures that represent pre- and post-αβ T-cell commitment stages. We found that loss of dim expression of CD44 marks human T-cell commitment in early CD7+CD5+CD45dim cells, before the acquisition of CD1a surface expression. The CD44−CD1a− post-committed thymocytes have initiated in frame T-cell receptor rearrangements that are accompanied by loss of capacity to differentiate toward myeloid, B- and NK-lineages, unlike uncommitted CD44dimCD1a− thymocytes. Therefore, loss of CD44 represents a previously unrecognized human thymocyte stage that defines the earliest committed T-cell population in the thymus.

Zebrafish Pancreas Development and Regeneration: Fishing for Diabetes Therapies.

The zebrafish pancreas shares its basic organization and cell types with the mammalian pancreas. In addition, the developmental pathways that lead to the establishment of the pancreatic islets of Langherhans are generally conserved from fish to mammals. Zebrafish provides a powerful tool to probe the mechanisms controlling establishment of the pancreatic endocrine cell types from early embryonic progenitor cells, as well as the regeneration of endocrine cells after damage. This knowledge is, in turn, applicable to refining protocols to generate renewable sources of human pancreatic islet cells that are critical for regulation of blood sugar levels. Here, we review how previous and ongoing studies in zebrafish and beyond are influencing the understanding of molecular mechanisms underlying various forms of diabetes and efforts to develop cell-based approaches to cure this increasingly widespread disease.

GATA Factor Switching during Erythroid Differentiation Is Facilitated By FBW7 Mediated Clearance of GATA2

Erythroid differentiation is controlled by the dynamic exchange of GATA family transcription factors. During early erythroid maturation, high GATA2 levels activate progenitor genes such as c-kit-, c-myc, and GATA2 itself. In contrast, GATA1 levels are low in early progenitor cells, but rise during terminal maturation. During this process GATA1 turns off GATA2 controlled early progenitor genes and activates terminal maturation genes, such as globin genes, heme biosynthesis enzymes, and iron transporters. This involves the exchange of GATA1 for GATA2 at key chromatin sites, the so-called "GATA factor switch". GATA factor switching is facilitated by the much shorter half-life of GATA2 (~30-60 min) compared to GATA1 (>4-6 hrs). We and others recently demonstrated that the E3 ubiquitin ligase adaptor protein FBW7 contributes to GATA2’s relative instability. This prompted us to dissect the role of FBW7 during GATA switching and erythroid differentiation. We deleted the Fbw7 gene using CRISPR/Cas9 gene editing in the inducible G1-ER murine erythroid cell line. This resulted in the delayed clearance of GATA2 during differentiation. RNA-seq analysis at an early time points (7 hr) demonstrated impaired repression of GATA2 regulated genes and reduced activation of GATA1 target genes. Globally, altered gene expression was enriched for GATA factor switch genes. This ultimately resulted in delayed erythroid maturation. We also found that Fbw7 mRNA transcript levels increase during erythroid maturation in wild type cells. We identified a site ~40kb upstream of the Fbw7 gene transcriptional start site, which is itself a GATA factor switch site. We propose that FBW7 facilitates GATA factor switching by promoting the clearance of GATA2 from GATA factor switch sites. Moreover, we suggest that GATA factor switching at the Fbw7 locus itself reinforces the commitment of erythroid cells to terminal maturation, by enhancing the clearance of GATA2 and other Fbw7 progenitor target gene proteins such as c-Myc and c-Myb. As Fbw7 recognition of GATA2 requires phosphorylation of GATA2’s degron motif, this suggests that signaling pathways, acting through Fbw7, may modulate erythroid maturation kinetics. DisclosuresNo relevant conflicts of interest to declare.

Single-Cell Resolution of Human Pluripotent Stem Cell Derived Hemato-Endothelial Cells Reveals Distinct Transcriptional Signatures of Hemogenic Endothelium

Hemogenic endothelium is a rare and highly specialized subset of vascular endothelial cell that functions as a precursor cell population to definitive blood development. One of the mechanistic hallmarks of definitive hematopoiesis is the endothelial-to-hematopoietic transition (EHT), a process where hemogenic endothelial cells phenotypically switches to produce a detached and free-moving hematopoietic cell. While EHT has been visualized both in vitro and in vivo via lineage tracing studies, the regulation of this fate change at both a cellular and molecular level remains unclear. Human pluripotent stem cells, such as human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) can serve as a useful platform to characterize human hemogenic endothelium and to understand basic mechanisms underlying human EHT. We hypothesized that human hemogenic endothelium derived from hESCs is phenotypically and transcriptionally distinct from other vascular endothelial cells and hematopoietic progenitor cells. To identify human hemogenic endothelium, we used combined expression of endothelial cell surface antigens and RUNX1c expression via a fluorescent reporter previously validated in our lab. Specifically, we employed defined culture methods to differentiate hemogenic endothelial cells (HE) and vascular endothelial cells without hematopoietic potential (non-HE) from hESC harboring a RUNX1c-tdTomato reporter (hESC-RUNX1c-tdTomato). At Day 11 of differentiation, CD31+CD144+ endothelial cells were present, with approximately 40% of these cells tdTomato+. We next sorted HE (CD31+CD144+CD41-CD43-CD45-CD73-tdTomato+) and non-HE (CD31+CD144+CD41-CD43-CD45-CD73-tdTomato-) and cultured both populations in endothelial growth media (EGM) or hematopoietic growth media. HE retained characteristic cobblestone morphology and CD31 expression over the course of 5 days in EGM similar to control human umbilical vein endothelial cells. HE, but not non-HE, was able to generate non-adherent, tdTomato+ hematopoietic progenitor cells in hematopoietic growth media. Using these defined cell populations, we next performed single-cell RNASeq on HE, non-HE, and early hematopoietic progenitor cells (HP; CD34+CD43+tdTomato+). We captured a total of 55 HE, 47 non-HE, and 35 HP using the Fluidgm C1 single cell system and performed next generation sequencing of validated libraries. We analyzed single cell gene expression using Seurat, an R-based bioinformatics software package developed for the analysis of single cell NGS experiments. Populations were first validated based on expression of known genetic identifiers for vascular endothelium, hemogenic endothelium, and hematopoietic progenitor cells. HE and HP were both highly enriched for CDH5, ERG, ESAM, and FLI as compared to non-HE; these genes have been previously implicated in HE functionality. All single cell transcriptional profiles were similarly enriched for KDR, PECAM1, and LMO2, which are characteristic genes expressed in vascular endothelium. We next performed t-distributed stochastic neighbor embedding (t-SNE) using statistically significant principal components to distinguish groups of cells with similar transcriptional expression. Interestingly, we found overlap between individual HE and HP cells (Cluster 1); however, these cells were distinct from two, separate clusters of non-HE (Cluster 2 & 3; Figure 1). Further analysis of these clusters revealed novel biomarkers for HE/HP, such as TIMP3 (DGE: 2.06, Power: 0.91), ERG (DGE: 2.08, Power: 0.83), NOTCH4 (DGE: 2.35, Power: 0.78), and HEY1 (DGE: 2.47, Power: 0.74), Non-HE were found to cluster into two, distinct groups (Clusters 2 and 3), with Cluster 3 enriched for extracellular matrix genes (COL1A1 (DGE: 6.58, Power: 1.00), DCN (DGE: 6.09, Power: 1.00), VCAN (DGE: 3.55, Power: 1.00), FN1 (DGE: 2.19, Power: 0.96)). This profile suggests that some hESC-derived non-HE further differentiate into mesenchymal cells, in a process known as the endothelial-to mesenchymal transition (EndMT). Taken together, we demonstrate that hESC-derived HE and HP share a common developmental pathway, while non-HE is heterogeneous, but transcriptionally distinct. Our novel findings will be instrumental for testing new genetic targets to optimize the production of definitive hematopoietic cells. [Display omitted] DisclosuresKaufman:Fate Therapeutics: Consultancy.

Molecular and Immunophenotypic Characteristics of Adult Acute Leukemias of Ambiguous Lineage

Acute undifferentiated leukemia (AUL) and mixed phenotype acute leukemia (MPAL) are acute leukemias of ambiguous lineage representing less than 5% of all adult leukemias. Ontogenetically, they are thought to be caused by precursor lesions in early pluripotent hematopoietic progenitor cells having the ability to differentiate into both lymphoid and myeloid lineages. In contrast, common lymphoid and myeloid leukemias are likely derived from precursor lesions in committed progenitor cells. The molecular characteristics of the cell of origin of these leukemias have not been fully characterized.Given the ambiguous classification of these disorders, we used NGS to evaluate the molecular profiles of this unique subset of leukemias. Our panel tested for the 60 most commonly mutated genes in myeloid malignancies (MM), which can be used to further elucidate driver mutations that play a role in the pathogenesis of this unique entity. Molecular data was available for 18 of 35 patients (pts) (51%), of whom 8 were T/myeloid, 7 were B/myeloid, and 3 were AUL. 14 pts out of the 18 had samples at the time of initial diagnosis, 3 AUL cases harbored mutations commonly seen in MM, including one patient with DNMT3A and a germ line JAK3 mutation, another with U2AF1 and PHF6 mutations, and one pt with SF3B1 and MECOM mutations. Of the 5 B/myeloid cases, 4 had only one mutation detected by the sequencing panel, including TET2, PTPN11, KDM6A, and PHF6, and one had no mutations, but did have complex cytogenetics. Of interest, we identified four patients with T/myeloid MPAL that harbored a FLT3-ITD mutation. Notably, one of these cases had additional DNMT3A and TET2 mutations while another case had a WT1 mutation. We assert that the mutational data for MPAL supports that T-myeloid MPAL encompasses a borderland between early T precursor (ETP)-ALL/AML in addition to more typical cases of T-ALL/AML given its similar immunophenotype to ETP ALL (CD117, CD13 and CD33 positive). The overlap between these two entities is illustrated in the figure below. With this immunophenotyping and molecular profiling we propose a new provisional entity, ETP-myeloid MPAL in addition to already existing ETP ALL.Of 1250 pts with acute leukemia diagnosed from 1997-2016 at Cleveland Clinic, 35 had immunophenotypic characteristics of ambiguous leukemia based on WHO criteria. The median age at diagnosis was 50 years, and 22 (63%) were male. There were 31 MPAL (16 T/myeloid, 15 B/myeloid) and 4 AUL cases. Among the 31 MPAL patients, 2 were mixed lineage chimera (subclones), and 29 had true biphenotypic features. 48% of the cohort had normal cytogenetics at diagnosis, 23% had other cytogenetic abnormalities, 14% had complex karyotype, 9% had MLL gene rearrangement, and 6% had t(9;22). 62% of pts were treated with acute lymphoblastic leukemia (ALL) directed induction chemotherapy (IC), while 38% were treated with acute myelogenous leukemia (AML) directed IC. Rates of complete remission (CR) were significantly higher in pats treated with ALL-IC regimen (82%) versus AML-IC regimen (23%) (p=.003). In our study, two cases with the recurrent lymphoid mutations WT1 and KDM6A, that achieved CR with upfront ALL-IC, while one case with FLT3-ITD, DNMT3A, and TET2 mutations achieved CR with AML-IC treatment. Pts <40 yrs of age had significantly better median OS (41 months) than patients over 40 yrs old (16 months) (p=0.03). MPAL pts with normal cytogenetics had worse median OS (16 months) compared to any other cytogenetic group (25 months) (p=.05).In conclusion, clinical evaluations of ambiguous leukemias demonstrate that those with normal karyotype have the worst outcome of all pts diagnosed with MPAL. This can be partly explained by mutations that are detected at the time of diagnosis such as FLT3-ITD and DNMT3A, which have been associated with poor survival in AML with normal karyotype. Identification of actionable targets like FLT3-ITD can improve clinical outcomes for this subset of patients prior to BMT or for those ineligible for BMT. The existence of a unique subset of pts with immunophenotypic overlap between ETP-ALL/AML, that were classified in routine practice as T/myeloid leukemia, are important to recognize due to their unique actionable phenotype. Molecular profiling of these cases identified gene mutations more akin to MM. We propose that sequencing may play an important role in optimizing the therapeutic approach for patients with ambiguous lineage leukemia. [Display omitted] DisclosuresCarraway:Novartis: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Baxalta: Speakers Bureau; Celgene: Research Funding, Speakers Bureau.

Immunoprofiling of Normal Human Donor Blood Identified Potential Pharmacodynamic Markers for JNJ-63709178 (CD123xCD3) Duobody® Antibody Treatment

BackgroundJNJ-63709178 (CD123xCD3) is a promising new bispecific antibody currently being investigated for the treatment for acute myeloid leukemia (AML), a disorder of early hematopoietic progenitor cells characterized by the proliferation and accumulation of immature, clonal, myeloid cells. Constitutive overexpression of the α-subunit of the interleukin-3 receptor (ie, IL-3αR/CD123) is a hallmark of the early AML progenitor cell population (ie, leukemic stem cells [LSC]), as well as leukemic blasts. CD123 is unique to the IL-3 receptor and is responsible for the high specificity and low affinity binding of IL-3. Under physiological conditions, activation of the IL-3 receptor induces proliferative, anti-apoptotic, and differentiating signals. JNJ-63709178, a humanized IgG4 bispecific DuoBody® antibody with high affinity anti-CD123 and -CD3 arms, recognizes CD123 on myeloid cells and CD3 on T cells, leading to T-cell activation, with subsequent lysis of CD123+ AML blasts. JNJ-63709178 induces potent tumor cell killing in vitro, ex vivo, and in murine AML models, and is currently being evaluated in first-in-human clinical trials. Although CD123 is distinctively expressed on leukemic cells, some populations of normal myeloid cells have been reported to express CD123. The goals of this study were to determine CD123 receptor density on various leukocyte populations in normal human peripheral blood and evaluate the effects of JNJ-63709178 on those cells to identify potential pharmacodynamic markers.MethodsPeripheral blood samples from 6 normal human donors were analyzed ex vivo for CD123 expression on various leukocyte populations to determine receptor density. Receptor density on cells was quantified using Quantibrite PE enumeration kit. Subsequently, blood samples were treated with escalating concentrations of JNJ-63709178 (CD123xCD3) or the control compound CNTO 7008 (nullxCD3) DuoBody® antibodies and incubated at 37°C for 48 hours. After incubation, blood samples were stained and processed for analysis of T-cell activation (CD25 expression) and population persistence or depletion (frequencies within leukocytes). In the myeloid compartment, basophils, myeloid dendritic cells (mDCs), monocytes, neutrophils, and eosinophils were analyzed. In the lymphoid compartment, plasmacytoid dendritic cells (pDCs), B cells (naïve and memory), T cells (helper and cytotoxic), and natural killer (NK) cells (CD56bright and CD56dim) were analyzed.ResultsIn normal human peripheral blood samples, CD123 expression was highest on pDCs and basophils (above 10,000 receptors per cell). Intermediate expression (300-3,000 receptors per cell) was observed on mDCs, monocytes, eosinophils, and naïve B cells. Low expression (10-200 receptors per cell) was observed on neutrophils, memory B cells, T cells, and NK cells. These data are in agreement with previous studies (Busfield et al. ASH 2013 abs3598). Following incubation with JNJ-63709178, potent activation of CD4+ and CD8+ T cells was observed at sub-nanomolar levels, with EC50values of 0.07 nM and 0.1 nM, respectively. Higher CD123 expression and T-cell activation correlated strongly with profound depletion of basophils and pDCs, as well as partial depletion of eosinophils and monocytes. Consistent with low CD123 expression, T cells and NK cells did not show substantial dose-dependent depletion. In contrast to CD123 expression levels, B cells and neutrophils showed partial depletion, despite low CD123 expression, while mDCs did not show dose-dependent depletion, despite higher CD123 levels. The activation of T cells and cytotoxic effect on CD123-positive cells was observed only with JNJ-63709178. The control compound CNTO 7008 (nullxCD3) had no effect on T-cell activation or any of the investigated cell populations.ConclusionsThese findings highlight the potential pharmacodynamic markers of JNJ-63709178 (CD123xCD3) bispecific treatment and provide a better understanding of its mechanism of action and a rationale for receptor expression monitoring during ongoing clinical trials. DisclosuresBabich:Janssen: Employment. Li:Janssen: Employment. Gaudet:Janssen Pharmaceuticals R&D: Employment, Other: Stock options, Patents & Royalties: pending, not yet issued. Huang:Janssen Research & Development, LLC: Employment, Other: I am an employee of Janssen and a stock owner . Sasser:Johnson & Johnson: Equity Ownership; Janssen Pharmaceuticals R&D: Employment. Salvati:Janssen Pharmaceuticals R&D: Employment, Other: stock options, Patents & Royalties: patent. Kalota:Janssen Pharmaceuticals R&D: Employment, Other: stock.

Modeling Bone Marrow Failure and MDS in Shwachman Diamond Syndrome Using Induced Pluripotent Stem Cells

Myelodysplastic syndrome (MDS) caused by monosomy 7 or del(7q) is a frequent clonal abnormality that arises in the context of inherited bone marrow failure syndromes, such as Shwachman Diamond Syndrome (SDS). Monosomy 7/del(7q) also develops in a subset of patients with acquired aplastic anemia or de novo MDS in the general population. Monosomy 7/del(7q) is associated with high grade MDS and a high risk of malignant transformation, most frequently to acute myelogenous leukemia (AML). Bone marrow failure and clonal evolution to MDS and AML remain major causes of morbidity and mortality for individuals with SDS. Currently, the only curative therapy for these hematological complications is a hematopoietic stem cell transplant. Prognosis is extremely poor once SDS patients develop leukemia. The basis for this propensity to develop monosomy 7 clones remains unclear. The longterm aim of this study is to understand the molecular mechanisms underlying leukemia predisposition and develop more effective treatments.Whether monosomy 7/del(7q) functions as a driver of MDS, or is merely an associated marker of clonal progression in bone marrow failure remains a critical question. The lack of synteny between murine versus human chromosome 7 has posed a major barrier to the development of mouse models of monosomy 7/del(7q). To study the biological and molecular consequences of monosomy 7/del(7q) in SDS, induced pluripotent stem cells (iPSCs) were generated from bone marrow mononuclear cells of two patients with SDS. Each patient harbored homozygous c.258+2 T>C mutations in the canonical splice donor site of intron 2 in the SBDS gene. The SDS-iPSCs retained the pathogenic homozygous IVS2+2 T>C SBDS mutations, expressed stem cell markers, formed teratomas, and expressed reduced levels of SBDS protein similar to levels noted in the primary patient samples. Proliferation of 4 distinct SDS-iPSC clones derived from two different patients was reduced relative to wild type controls without an increase in cell death. SDS-iPSC formed smaller embryoid bodies with reduced production of CD34+ hematopoietic stem/progenitor cells. Hematopoietic differentiation from CD34+ to CD45+ cells was also impaired. Preliminary data suggest that SDS-iPSCs retain the capacity to give rise to hematopoietic stem/progenitor cells and early myeloid progenitor cells in vitro. These populations were also observed in primary SDS patient-derived bone marrow samples. Because the number of CD34+ cells derived from SDS-iPSCs are limiting, a previously reported 5 transcrition factor re-specification system was used to expand multilineage hematopietic progenitors for further characterization. SDS iPSCs were able to differentiate into an expandable CD34+ population in vitro. Further studies to characterize the hematopoietic impairment in SDS iPSC and primary marrow samples are ongoing.To model del(7q) in SDS iPSCs, a deletion of the MDS-associated long arm of chromosome 7 was genomically engineered using a previously published modified Cre-Lox approach. The deletion of 7q at locus (11.2) was confirmed by karyotyping and by qPCR across chromosome 7. The SDS (del7q) iPSCs retained the SBDS pathogenic mutations, expressed stem cell markers, and formed teratomas. Proliferation of the SDS del(7q) iPSC was markedly impaired compared to isogenic SDS iPSCs. No increase in cell death was observed in the SDS del7q iPSCs. Studies are in progress to determine the effects of del7q on hematopoiesis. Investigation is ongoing to determine the molecular consequences of deleting 7q. These isogenic SDS+/- del(7q) iPS models provide a platform to study the role of 7q loss in clonal evolution from bone marrow failure and to screen for novel therapeutic compounds or pathways to treat bone marrow failure and MDS. DisclosuresNo relevant conflicts of interest to declare.

Bone Marrow Stromal Cells Derived at Diagnosis and Remission Preferentially Support AML Cell Proliferation in Vitro

Introduction: Acute myeloid leukemia (AML) is a heterogeneous clonal disorder of hematopoietic progenitor cells characterized by excessive proliferation of early progenitor cells in the bone marrow (BM). The BM niche is a specialized type of microenvironment (ME) that actively supports growth, maturation and maintenance of hematopoietic stem and progenitor cells. They include a complex network of extracellular matrix proteins, soluble growth factors, and cytokines. The information regarding the clinical significance of leukemic microenvironment for AML initiation and propagation is scarce. The aim of the current study was to characterize the AML BM ME and its crosstalk with leukemic progenitor cells and define the role of BM stromal cells (SCs) in supporting leukemic cell growth in active disease as compared to the complete remission (CR) state.Methods: We developed a unique model of patient own stroma (POS) by growing SCs obtained at diagnosis, CR and relapse in a specific medium, including cytokines and proteins derived from human plasma solution. The growth rate and morphological changes of AML SCs were assessed and their ability to support AML cell expansion was studied by monitoring immunophenotyping alterations of CD34 and CD45 expression using FACS analysis. Levels of secreted MCP-1, IL6, GM-CSF, G-CSF and TNF in the co-culture medium were measured using the bead-based immunoassay CBA (BD Biosciences). In addition, real-time PCR (RT-PCR) amplification was performed in the co-culture to quantify changes aiming to assess the expression of specific genes associated with the maintenance of hematopoietic cells, self-renewal, quiescence regulation and mobilization. The following genes were amplified: CXCL12 (SDF1), transforming growth factor beta 1 (TGFβ), secreted phosphoprotein 1 (SPP1) and angiopoietin 1 (ANGP1).Results: The developed POS model allowed revealing high diversity in the morphological appearance of leukemic SCs obtained from different patients and at various disease stages. Patient SCs were found to grow slower than those of healthy volunteers (fig. 1A). Moreover, the growth rate differed between the patients and disease stages, being highest at relapse and lowest at diagnosis (fig. 1A). Levels of SDF-1, TGF-1 and SPP1 were elevated (X50, X50 and X 300 fold, respectively) in CR stroma compared to that of healthy volunteers. Of note, the level of MCP-1 was increased (2200 pg/ml) in the stroma derived at active disease stages (diagnosis and relapse) compared to CR or normal SCs (1050 pg/ml). Additionally, the expansion of CD34+ leukemic progenitor cells was higher in the presence of CR-derived stroma compared to healthy SCs (fig. 1B). In the co-culture, we observed selective ability of POS to support CD34+ leukemic cell expansion, as detected by flow cytometry (1.5 million cells more in POS than in healthy stroma), as well as differential expression of MCP-1 (x3000 pg/ml) and IL-6 (x9000 pg/ml) cytokines in co-cultures of AML cells and POS. These cytokines are known to be involved in the regulation of cell migration and inflammation.Conclusions: AML BM SCs are heterogeneous and differ from healthy BM SCs in their growth rate, morphology, immunophenotype features and the ability to support expansion of early progenitor CD34+ cells. Moreover, even an AML CR-derived stroma, which is considered "healthy", can provide an advantageous ME to leukemogenesis, as evident by increased proliferation of CD34+ leukemic cells in a co-culture with CR SCs compared to healthy SCs. Additionally, POS was found to selectively support the expansion of AML cells of the same patient. These findings, suggesting a cross-talk between leukemic progenitor cells and their specific POS, may lead to better understanding of the mechanisms underlying AML initiation and relapse. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Akirin2 is essential for the formation of the cerebral cortex.

BackgroundThe proper spatial and temporal regulation of dorsal telencephalic progenitor behavior is a prerequisite for the formation of the highly-organized, six-layered cerebral cortex. Premature differentiation of cells, disruption of cell cycle timing, excessive apoptosis, and/or incorrect neuronal migration signals can have devastating effects, resulting in a number of neurodevelopmental disorders involving microcephaly and/or lissencephaly. Though genes encoding many key players in cortical development have been identified, our understanding remains incomplete. We show that the gene encoding Akirin2, a small nuclear protein, is expressed in the embryonic telencephalon. Converging evidence indicates that Akirin2 acts as a bridge between transcription factors (including Twist and NF-κB proteins) and the BAF (SWI/SNF) chromatin remodeling machinery to regulate patterns of gene expression. Constitutive knockout of Akirin2 is early embryonic lethal in mice, while restricted loss in B cells led to disrupted proliferation and cell survival.MethodsWe generated cortex-restricted Akirin2 knockouts by crossing mice harboring a floxed Akirin2 allele with the Emx1-Cre transgenic line and assessed the resulting embryos using in situ hybridization, EdU labeling, and immunohistochemistry.ResultsThe vast majority of Akirin2 mutants do not survive past birth, and exhibit extreme microcephaly, with little dorsal telencephalic tissue and no recognizable cortex. This is primarily due to massive cell death of early cortical progenitors, which begins at embryonic day (E)10, shortly after Emx1-Cre is active. Immunostaining and cell cycle analysis using EdU labeling indicate that Akirin2-null progenitors fail to proliferate normally, produce fewer neurons, and undergo extensive apoptosis. All of the neurons that are generated in Akirin2 mutants also undergo apoptosis by E12. In situ hybridization for Wnt3a and Wnt-responsive genes suggest defective formation and/or function of the cortical hem in Akirin2 null mice. Furthermore, the apical ventricular surface becomes disrupted, and Sox2-positive progenitors are found to “spill” into the lateral ventricle.ConclusionsOur data demonstrate a previously-unsuspected role for Akirin2 in early cortical development and, given its known nuclear roles, suggest that it may act to regulate gene expression patterns critical for early progenitor cell behavior and cortical neuron production.Electronic supplementary materialThe online version of this article (doi:10.1186/s13064-016-0076-8) contains supplementary material, which is available to authorized users.

Study of corneal epithelial progenitor origin and the Yap1 requirement using keratin 12 lineage tracing transgenic mice.

Key issues in corneal epithelium biology are the mechanism for corneal epithelium stem cells to maintain the corneal epithelial homeostasis and wound healing responses, and what are the regulatory molecular pathways involved. There are apparent discrepancies about the locations of the progenitor populations responsible for corneal epithelial self-renewal. We have developed a genetic mouse model to trace the corneal epithelial progenitor lineages during adult corneal epithelial homeostasis and wound healing response. Our data revealed that the early corneal epithelial progenitor cells expressing keratin-12 originated from limbus, and gave rise to the transit amplifying cells that migrated centripetally to differentiate into corneal epithelial cells. Our results support a model that both corneal epithelial homeostasis and wound healing are mainly maintained by the activated limbal stem cells originating form limbus, but not from the corneal basal epithelial layer. In the present study, we further demonstrated the nuclear expression of transcriptional coactivator YAP1 in the limbal and corneal basal epithelial cells and its essential role for maintaining the high proliferative potential of those corneal epithelial progenitor cells in vivo.

Increased adult neurogenesis in mice with a permanent overexpression of the postsynaptic 5-HT1A receptor

Depression is among the leading causes of disability and disease burden. Recent studies point to an involvement of altered serotonin1A receptor (5-HT1AR) –mediated adult neurogenesis in depression. However, the exact underlying mechanisms remain unclear, mainly due to the complexity of the serotonergic system with its various receptors and their locations. Mice with permanent overexpression of postsynaptic 5-HT1ARs (OE mice) represent a unique tool for investigating the involvement of postsynaptic 5-HT1ARs in this context. Correct 5-HT1AR coupling and functioning has been demonstrated earlier, indicating that more postsynaptic 5-HT1ARs can be activated in these mice. Initially we examined morphometric parameters of the dentate gyrus (DG) and the prefrontal cortex as they are involved in adult hippocampal neurogenesis and/or depression. The volume of the DG in OE mice was increased in comparison to wildtype controls. We therefore investigated parameters of adult neurogenesis by the bromodeoxyuridine method. Proliferation and survival of newborn cells in the DG of OE mice were significantly increased. Significant increases in survived neurons were only detected in the female but not in the male subgroup. Additional staining for early precursor cells (Sox2) and progenitor cells of the neuronal lineage (doublecortin) showed an increase in type-1/2a as well as in type-2b/3 cells in OE mice. Our study suggests a leading role of the postsynaptic 5-HT1AR in adult hippocampal neurogenesis and might open an important link to depression.

Soluble Adenylyl Cyclase Is Required for Retinal Ganglion Cell and Photoreceptor Differentiation

PurposeWe have previously demonstrated that soluble adenylyl cyclase (sAC) is necessary for retinal ganglion cell (RGC) survival and axon growth. Here, we further investigate the role of sAC in neuronal differentiation during retinal development.MethodsChx10 or Math5 promoter-driven Cre-Lox recombination were used to conditionally delete sAC from early and intermediate retinal progenitor cells during retinal development. We examined cell type–specific markers expressed by retinal cells to estimate their relative numbers and characterize retinal laminar morphology by immunofluorescence in adult and newborn mice.ResultsRetinal ganglion cell and amacrine cell markers were significantly lower in the retinas of adult Math5cre/sACfl/fl and Chx10cre/sACfl/fl mice than in those of wild-type controls. The effect on RGC development was detectable as early as postnatal day 1 and deleting sAC in either Math5- or Chx10-expressing retinal progenitor cells also reduced nerve fiber layer thickness into adulthood. The thickness of the photoreceptor layer was slightly but statistically significantly decreased in both the newborn Chx10cre/sACfl/fl and Math5cre/sACfl/fl mice, but this reduction and abnormal morphology persisted in the adults in only the Chx10cre/sACfl/fl mice.ConclusionssAC plays an important role in the early retinal development of RGCs as well as in the development of amacrine cells and to a lesser degree photoreceptors.

Conditional Creation and Rescue of Nipbl-Deficiency in Mice Reveals Multiple Determinants of Risk for Congenital Heart Defects.

Elucidating the causes of congenital heart defects is made difficult by the complex morphogenesis of the mammalian heart, which takes place early in development, involves contributions from multiple germ layers, and is controlled by many genes. Here, we use a conditional/invertible genetic strategy to identify the cell lineage(s) responsible for the development of heart defects in a Nipbl-deficient mouse model of Cornelia de Lange Syndrome, in which global yet subtle transcriptional dysregulation leads to development of atrial septal defects (ASDs) at high frequency. Using an approach that allows for recombinase-mediated creation or rescue of Nipbl deficiency in different lineages, we uncover complex interactions between the cardiac mesoderm, endoderm, and the rest of the embryo, whereby the risk conferred by genetic abnormality in any one lineage is modified, in a surprisingly non-additive way, by the status of others. We argue that these results are best understood in the context of a model in which the risk of heart defects is associated with the adequacy of early progenitor cell populations relative to the sizes of the structures they must eventually form.

Noggin inactivation affects the number and differentiation potential of muscle progenitor cells in vivo.

Inactivation of Noggin, a secreted antagonist of Bone Morphogenetic Proteins (BMPs), in mice leads, among others, to severe malformations of the appendicular skeleton and defective skeletal muscle fibers. To determine the molecular basis of the phenotype, we carried out a histomorphological and molecular analysis of developing muscles Noggin−/− mice. We show that in 18.5 dpc embryos there is a marked reduction in muscle fiber size and a failure of nuclei migration towards the cell membrane. Molecularly, the absence of Noggin results in an increased BMP signaling in muscle tissue as shown by the increase in SMAD1/5/8 phosphorylation, concomitant with the induction of BMP target genes such as Id1, 2, 3 as well as Msx1. Finally, upon removal of Noggin, the number of mesenchymal Pax7+ muscle precursor cells is reduced and they are more prone to differentiate into adipocytes in vitro. Thus, our results highlight the importance of Noggin/BMP balance for myogenic commitment of early fetal progenitor cells.

Early Endothelial Progenitor Cells (eEPCs) in systemic sclerosis (SSc) - dynamics of cellular regeneration and mesenchymal transdifferentiation.

BackgroundPatients with systemic sclerosis (SSc) are endagered by tissue fibrosis and by microvasculopathy, with the latter caused by endothelial cell expansion/proliferation. SSc-associated fibrosis potentially results from mesenchymal transdifferentiation of endothelial cells. Early Endothelial Progenitor Cells (eEPCs) act proangiogenic under diverse conditions. Aim of the study was to analyze eEPC regeneration and mesenchymal transdifferentiation in patients with limited and diffuse SSs (lSSc and dSSc).MethodsPatients with both, lSSc and dSSc were included into the study. The following parameters were evaluated: eEPC numbers and regeneration, concentrations of vasomodulatory mediators, mesenchymal properties of blood-derived eEPC. Serum samples of healthy subjects and SS patients were used for stimulation of cultured human eEPC, subsequently followed by analysis of mesenchymal cell characteristics and mobility.ResultsTwenty-nine patients were included into the study. Regenerative activity of blood-derived eEPCs did not differ between Controls and patients. Circulating eEPC were significantly lower in all patients with SSc, and in limited and diffuse SSc (lSSc/dSSc). Serum concentrations of promesenchymal TGF-b was elevated in all patients with SSc. Cultured mononuclear cells from SS patients displayed higher abundances of CD31 and of CD31 and aSMA combined. Finally, serum from SSc patients inhibited migration of cultured eEPCs and the cells showed lower sensitivity towards the endothelin antagonist Bosentan.ConclusionsThe eEPC system, which represents an essential element of the endogenous vascular repair machinery is affected in SSc. The increased appearance of mesenchymal properties in eEPC may indicate that alterations of the cells potentially contribute to the accumulation of connective tissue and to vascular malfunction.Electronic supplementary materialThe online version of this article (doi:10.1186/s12891-016-1197-2) contains supplementary material, which is available to authorized users.