EpoR stimulates rapid cycling and larger red cells during mouse and human erythropoiesis.

The erythroid terminal differentiation program couples sequential cell divisions with progressive reductions in cell size. The erythropoietin receptor (EpoR) is essential for erythroblast survival, but its other functions are not well characterized. Here we use Epor-/- mouse erythroblasts endowed with survival signaling to identify novel non-redundant EpoR functions. We find that, paradoxically, EpoR signaling increases red cell size while also increasing the number and speed of erythroblast cell cycles. EpoR-regulation of cell size is independent of established red cell size regulation by iron. High erythropoietin (Epo) increases red cell size in wild-type mice and in human volunteers. The increase in mean corpuscular volume (MCV) outlasts the duration of Epo treatment and is not the result of increased reticulocyte number. Our work shows that EpoR signaling alters the relationship between cycling and cell size. Further, diagnostic interpretations of increased MCV should now include high Epo levels and hypoxic stress.

A therapeutic convection-enhanced macroencapsulation device for enhancing ß cell viability and insulin secretion.

Islet transplantation for type 1 diabetes treatment has been limited by the need for lifelong immunosuppression regimens. This challenge has prompted the development of macroencapsulation devices (MEDs) to immunoprotect the transplanted islets. While promising, conventional MEDs are faced with insufficient transport of oxygen, glucose, and insulin because of the reliance on passive diffusion. Hence, these devices are constrained to two-dimensional, wafer-like geometries with limited loading capacity to maintain cells within a distance of passive diffusion. We hypothesized that convective nutrient transport could extend the loading capacity while also promoting cell viability, rapid glucose equilibration, and the physiological levels of insulin secretion. Here, we showed that convective transport improves nutrient delivery throughout the device and affords a three-dimensional capsule geometry that encapsulates 9.7-fold-more cells than conventional MEDs. Transplantation of a convection-enhanced MED (ceMED) containing insulin-secreting ß cells into immunocompetent, hyperglycemic rats demonstrated a rapid, vascular-independent, and glucose-stimulated insulin response, resulting in early amelioration of hyperglycemia, improved glucose tolerance, and reduced fibrosis. Finally, to address potential translational barriers, we outlined future steps necessary to optimize the ceMED design for long-term efficacy and clinical utility.

A 3D culture platform enables development of zinc-binding prodrugs for targeted proliferation of ß cells.

Advances in treating ß cell loss include islet replacement therapies or increasing cell proliferation rate in type 1 and type 2 diabetes, respectively. We propose developing multiple proliferation-inducing prodrugs that target high concentration of zinc ions in ß cells. Unfortunately, typical two-dimensional (2D) cell cultures do not mimic in vivo conditions, displaying a markedly lowered zinc content, while 3D culture systems are laborious and expensive. Therefore, we developed the Disque Platform (DP)-a high-fidelity culture system where stem cell-derived ß cells are reaggregated into thin, 3D discs within 2D 96-well plates. We validated the DP against standard 2D and 3D cultures and interrogated our zinc-activated prodrugs, which release their cargo upon zinc chelation-so preferentially in ß cells. Through developing a reliable screening platform that bridges the advantages of 2D and 3D culture systems, we identified an effective hit that exhibits 2.4-fold increase in ß cell proliferation compared to harmine.

Targets and genomic constraints of ectopic Dnmt3b expression.

DNA methylation plays an essential role in mammalian genomes and expression of the responsible enzymes is tightly controlled. Deregulation of the de novo DNA methyltransferase DNMT3B is frequently observed across cancer types, yet little is known about its ectopic genomic targets. Here, we used an inducible transgenic mouse model to delineate rules for abnormal DNMT3B targeting, as well as the constraints of its activity across different cell types. Our results explain the preferential susceptibility of certain CpG islands to aberrant methylation and point to transcriptional state and the associated chromatin landscape as the strongest predictors. Although DNA methylation and H3K27me3 are usually non-overlapping at CpG islands, H3K27me3 can transiently co-occur with DNMT3B-induced DNA methylation. Our genome-wide data combined with ultra-deep locus-specific bisulfite sequencing suggest a distributive activity of ectopically expressed Dnmt3b that leads to discordant CpG island hypermethylation and provides new insights for interpreting the cancer methylome.

Author Correction: Global delay in nascent strand DNA methylation.

Following online publication of this article, the Gene Expression Omnibus records corresponding to accession codes GSM2406773, MN-d6, and GSM2406772, MN-d14, listed in the data availability statement were deleted. The data are now available under accession codes GSM3039355, WGBS_hESC_WT_D6_R4 (MN day 6), and GSM3039351, WGBS_hESC_WT_D14_R4 (MN day 14), and the data availability statement has been updated with the new accession codes in the HTML and PDF versions of the article.

Global delay in nascent strand DNA methylation.

Cytosine methylation is widespread among organisms and essential for mammalian development. In line with early postulations of an epigenetic role in gene regulation, symmetric CpG methylation can be mitotically propagated over many generations with extraordinarily high fidelity. Here, we combine BrdU labeling and immunoprecipitation with genome-wide bisulfite sequencing to explore the inheritance of cytosine methylation onto newly replicated DNA in human cells. Globally, we observe a pronounced lag between the copying of genetic and epigenetic information in embryonic stem cells that is reconsolidated within hours to accomplish faithful mitotic transmission. Populations of arrested cells show a global reduction of lag-induced intermediate CpG methylation when compared to proliferating cells, whereas sites of transcription factor engagement appear cell-cycle invariant. Alternatively, the cancer cell line HCT116 preserves global epigenetic heterogeneity independently of cell-cycle arrest. Taken together, our data suggest that heterogeneous methylation largely reflects asynchronous proliferation, but is intrinsic to actively engaged cis-regulatory elements and cancer.

Dissecting the Functional Consequences of De Novo DNA Methylation Dynamics in Human Motor Neuron Differentiation and Physiology.

The somatic DNA methylation (DNAme) landscape is established early in development but remains highly dynamic within focal regions that overlap with gene regulatory elements. The significance of these dynamic changes, particularly in the central nervous system, remains unresolved. Here, we utilize a powerful human embryonic stem cell differentiation model for the generation of motor neurons (MNs) in combination with genetic mutations in the de novo DNAme machinery. We quantitatively dissect the role of DNAme in directing somatic cell fate with high-resolution genome-wide bisulfite-, bulk-, and single-cell-RNA sequencing. We find defects in neuralization and MN differentiation in DNMT3A knockouts (KO) that can be rescued by the targeting of DNAme to key developmental loci using catalytically inactive dCas9. We also find decreased dendritic arborization and altered electrophysiological properties in DNMT3A KO MNs. Our work provides a list of DNMT3A-regulated targets and a mechanistic link between de novo DNAme, cellular differentiation, and human MN function.

Genetic determinants and epigenetic effects of pioneer-factor occupancy.

Transcription factors (TFs) direct developmental transitions by binding to target DNA sequences, influencing gene expression and establishing complex gene-regultory networks. To systematically determine the molecular components that enable or constrain TF activity, we investigated the genomic occupancy of FOXA2, GATA4 and OCT4 in several cell types. Despite their classification as pioneer factors, all three TFs exhibit cell-type-specific binding, even when supraphysiologically and ectopically expressed. However, FOXA2 and GATA4 can be distinguished by low enrichment at loci that are highly occupied by these factors in alternative cell types. We find that expression of additional cofactors increases enrichment at a subset of these sites. Finally, FOXA2 occupancy and changes to DNA accessibility can occur in G1-arrested cells, but subsequent loss of DNA methylation requires DNA replication.

Global increase in replication fork speed during a p57KIP2-regulated erythroid cell fate switch.

Cell cycle regulators are increasingly implicated in cell fate decisions, such as the acquisition or loss of pluripotency and self-renewal potential. The cell cycle mechanisms that regulate these cell fate decisions are largely unknown. We studied an S phase-dependent cell fate switch, in which murine early erythroid progenitors transition in vivo from a self-renewal state into a phase of active erythroid gene transcription and concurrent maturational cell divisions. We found that progenitors are dependent on p57KIP2-mediated slowing of replication forks for self-renewal, a novel function for cyclin-dependent kinase inhibitors. The switch to differentiation entails rapid down-regulation of p57KIP2 with a consequent global increase in replication fork speed and an abruptly shorter S phase. Our work suggests that cell cycles with specialized global DNA replication dynamics are integral to the maintenance of specific cell states and to cell fate decisions.

A mutation creating an upstream initiation codon in the SOX9 5' UTR causes acampomelic campomelic dysplasia.

BACKGROUND: Campomelic dysplasia (CD) is a semilethal developmental disorder caused by mutations in and around SOX9. CD is characterized by multiple skeletal malformations including bending (campomelia) of long bones. Surviving patients frequently have the acampomelic form of CD (ACD). METHODS: This is a single case report on a patient with clinical and radiological features of ACD who has no mutation in the SOX9 protein-coding sequence nor a translocation with breakpoint in the SOX9 regulatory domain. We include functional studies of the novel mutant protein in vitro and in cultured cells. RESULTS: The patient was found to have a de novo heterozygous mutation c.-185G>A in the SOX9 5'UTR. The mutation creates an upstream translation start codon, uAUG, with a much better fit of its flanking sequence to the Kozak consensus than the wild-type AUG. By in vitro transcription-translation and transient transfection into COS-7 cells, we show that the uAUG leads to translation of a short peptide from a reading frame that terminates just after the wild-type AUG start codon. This results in reduced translation of the wild-type protein, compatible with the milder phenotype of the patient. CONCLUSION: Findings support the notion that more mildly affected, surviving CD/ACD patients carry mutant SOX9 alleles with residual expression of SOX9 wild-type protein. Although rarely described in human genetic disease and for the first time here for CD, mutations creating upstream AUG codons may be more common than generally assumed.

Transcriptional and Chromatin Dynamics of Muscle Regeneration after Severe Trauma.

Following injury, adult skeletal muscle undergoes a well-coordinated sequence of molecular and physiological events to promote repair and regeneration. However, a thorough understanding of the in vivo epigenomic and transcriptional mechanisms that control these reparative events is lacking. To address this, we monitored the in vivo dynamics of three histone modifications and coding and noncoding RNA expression throughout the regenerative process in a mouse model of traumatic muscle injury. We first illustrate how both coding and noncoding RNAs in tissues and sorted satellite cells are modified and regulated during various stages after trauma. Next, we use chromatin immunoprecipitation followed by sequencing to evaluate the chromatin state of cis-regulatory elements (promoters and enhancers) and view how these elements evolve and influence various muscle repair and regeneration transcriptional programs. These results provide a comprehensive view of the central factors that regulate muscle regeneration and underscore the multiple levels through which both transcriptional and epigenetic patterns are regulated to enact appropriate repair and regeneration.

A comparison of genetically matched cell lines reveals the equivalence of human iPSCs and ESCs.

The equivalence of human induced pluripotent stem cells (hiPSCs) and human embryonic stem cells (hESCs) remains controversial. Here we use genetically matched hESC and hiPSC lines to assess the contribution of cellular origin (hESC vs. hiPSC), the Sendai virus (SeV) reprogramming method and genetic background to transcriptional and DNA methylation patterns while controlling for cell line clonality and sex. We find that transcriptional and epigenetic variation originating from genetic background dominates over variation due to cellular origin or SeV infection. Moreover, the 49 differentially expressed genes we detect between genetically matched hESCs and hiPSCs neither predict functional outcome nor distinguish an independently derived, larger set of unmatched hESC and hiPSC lines. We conclude that hESCs and hiPSCs are molecularly and functionally equivalent and cannot be distinguished by a consistent gene expression signature. Our data further imply that genetic background variation is a major confounding factor for transcriptional and epigenetic comparisons of pluripotent cell lines, explaining some of the previously observed differences between genetically unmatched hESCs and hiPSCs.

A qPCR ScoreCard quantifies the differentiation potential of human pluripotent stem cells.

Research on human pluripotent stem cells has been hampered by the lack of a standardized, quantitative, scalable assay of pluripotency. We previously described an assay called ScoreCard that used gene expression signatures to quantify differentiation efficiency. Here we report an improved version of the assay based on qPCR that enables faster, more quantitative assessment of functional pluripotency. We provide an in-depth characterization of the revised signature panel (commercially available as the TaqMan hPSC Scorecard Assay) through embryoid body and directed differentiation experiments as well as a detailed comparison to the teratoma assay. We further show that the improved ScoreCard enables a wider range of applications, such as screening of small molecules, genetic perturbations and assessment of culture conditions. Our approach can be extended beyond stem cell applications to characterize and assess the utility of other cell types and lineages.

In vivo Monitoring of Transcriptional Dynamics After Lower-Limb Muscle Injury Enables Quantitative Classification of Healing.

Traumatic lower-limb musculoskeletal injuries are pervasive amongst athletes and the military and typically an individual returns to activity prior to fully healing, increasing a predisposition for additional injuries and chronic pain. Monitoring healing progression after a musculoskeletal injury typically involves different types of imaging but these approaches suffer from several disadvantages. Isolating and profiling transcripts from the injured site would abrogate these shortcomings and provide enumerative insights into the regenerative potential of an individual's muscle after injury. In this study, a traumatic injury was administered to a mouse model and healing progression was examined from 3 hours to 1 month using high-throughput RNA-Sequencing (RNA-Seq). Comprehensive dissection of the genome-wide datasets revealed the injured site to be a dynamic, heterogeneous environment composed of multiple cell types and thousands of genes undergoing significant expression changes in highly regulated networks. Four independent approaches were used to determine the set of genes, isoforms, and genetic pathways most characteristic of different time points post-injury and two novel approaches were developed to classify injured tissues at different time points. These results highlight the possibility to quantitatively track healing progression in situ via transcript profiling using high- throughput sequencing.

Targeted disruption of DNMT1, DNMT3A and DNMT3B in human embryonic stem cells.

DNA methylation is a key epigenetic modification involved in regulating gene expression and maintaining genomic integrity. Here we inactivated all three catalytically active DNA methyltransferases (DNMTs) in human embryonic stem cells (ESCs) using CRISPR/Cas9 genome editing to further investigate the roles and genomic targets of these enzymes. Disruption of DNMT3A or DNMT3B individually as well as of both enzymes in tandem results in viable, pluripotent cell lines with distinct effects on the DNA methylation landscape, as assessed by whole-genome bisulfite sequencing. Surprisingly, in contrast to findings in mouse, deletion of DNMT1 resulted in rapid cell death in human ESCs. To overcome this immediate lethality, we generated a doxycycline-responsive tTA-DNMT1* rescue line and readily obtained homozygous DNMT1-mutant lines. However, doxycycline-mediated repression of exogenous DNMT1* initiates rapid, global loss of DNA methylation, followed by extensive cell death. Our data provide a comprehensive characterization of DNMT-mutant ESCs, including single-base genome-wide maps of the targets of these enzymes.

Dissecting neural differentiation regulatory networks through epigenetic footprinting.

Models derived from human pluripotent stem cells that accurately recapitulate neural development in vitro and allow for the generation of specific neuronal subtypes are of major interest to the stem cell and biomedical community. Notch signalling, particularly through the Notch effector HES5, is a major pathway critical for the onset and maintenance of neural progenitor cells in the embryonic and adult nervous system. Here we report the transcriptional and epigenomic analysis of six consecutive neural progenitor cell stages derived from a HES5::eGFP reporter human embryonic stem cell line. Using this system, we aimed to model cell-fate decisions including specification, expansion and patterning during the ontogeny of cortical neural stem and progenitor cells. In order to dissect regulatory mechanisms that orchestrate the stage-specific differentiation process, we developed a computational framework to infer key regulators of each cell-state transition based on the progressive remodelling of the epigenetic landscape and then validated these through a pooled short hairpin RNA screen. We were also able to refine our previous observations on epigenetic priming at transcription factor binding sites and suggest here that they are mediated by combinations of core and stage-specific factors. Taken together, we demonstrate the utility of our system and outline a general framework, not limited to the context of the neural lineage, to dissect regulatory circuits of differentiation.

Global DNA demethylation during mouse erythropoiesis in vivo.

In the mammalian genome, 5'-CpG-3' dinucleotides are frequently methylated, correlating with transcriptional silencing. Genome-wide demethylation is thought to occur only twice during development, in primordial germ cells and in the pre-implantation embryo. These demethylation events are followed by de novo methylation, setting up a pattern inherited throughout development and modified only at tissue-specific loci. We studied DNA methylation in differentiating mouse erythroblasts in vivo by using genomic-scale reduced representation bisulfite sequencing (RRBS). Demethylation at the erythroid-specific ß-globin locus was coincident with global DNA demethylation at most genomic elements. Global demethylation was continuous throughout differentiation and required rapid DNA replication. Hence, DNA demethylation can occur globally during somatic cell differentiation, providing an experimental model for its study in development and disease.

Identification and analysis of mouse erythroid progenitors using the CD71/TER119 flow-cytometric assay.

The study of erythropoiesis aims to understand how red cells are formed from earlier hematopoietic and erythroid progenitors. Specifically, the rate of red cell formation is regulated by the hormone erythropoietin (Epo), whose synthesis is triggered by tissue hypoxia. A threat to adequate tissue oxygenation results in a rapid increase in Epo, driving an increase in erythropoietic rate, a process known as the erythropoietic stress response. The resulting increase in the number of circulating red cells improves tissue oxygen delivery. An efficient erythropoietic stress response is therefore critical to the survival and recovery from physiological and pathological conditions such as high altitude, anemia, hemorrhage, chemotherapy or stem cell transplantation. The mouse is a key model for the study of erythropoiesis and its stress response. Mouse definitive (adult-type) erythropoiesis takes place in the fetal liver between embryonic days 12.5 and 15.5, in the neonatal spleen, and in adult spleen and bone marrow. Classical methods of identifying erythroid progenitors in tissue rely on the ability of these cells to give rise to red cell colonies when plated in Epo-containing semi-solid media. Their erythroid precursor progeny are identified based on morphological criteria. Neither of these classical methods allow access to large numbers of differentiation-stage-specific erythroid cells for molecular study. Here we present a flow-cytometric method of identifying and studying differentiation-stage-specific erythroid progenitors and precursors, directly in the context of freshly isolated mouse tissue. The assay relies on the cell-surface markers CD71, Ter119, and on the flow-cytometric 'forward-scatter' parameter, which is a function of cell size. The CD71/Ter119 assay can be used to study erythroid progenitors during their response to erythropoietic stress in vivo, for example, in anemic mice or mice housed in low oxygen conditions. It may also be used to study erythroid progenitors directly in the tissues of genetically modified adult mice or embryos, in order to assess the specific role of the modified molecular pathway in erythropoiesis.

Developmental control of apoptosis by the immunophilin aryl hydrocarbon receptor-interacting protein (AIP) involves mitochondrial import of the survivin protein.

Survivin is a multifunctional protein with essential roles in cell division and inhibition of apoptosis, but the molecular underpinnings of its cytoprotective properties are poorly understood. Here we show that homozygous deletion of the aryl hydrocarbon receptor-interacting protein (AIP), a survivin-associated immunophilin, causes embryonic lethality in mice by embryonic day 13.5-14, increased apoptosis of Ter119(-)/CD71(-) early erythropoietic progenitors, and loss of survivin expression in its cytosolic and mitochondrial compartments in vivo. In import assays using recombinant proteins, AIP directly mediated the import of survivin to mitochondria, thus enabling its anti-apoptotic function, whereas a survivin 1-141 mutant that does not bind AIP was not imported to mitochondria and failed to inhibit apoptosis. AIP-directed mitochondrial import of survivin did not affect cell division, was independent of the organelle transmembrane potential, did not require the chaperone Heat Shock Protein 90 (Hsp90), and was inhibited by cytosolic factor(s) present in normal cells. shRNA knockdown of the mitochondrial import receptor Tom20 abolished mitochondrial import of survivin and sensitized tumor cells to apoptosis, whereas silencing of Tom70 had no effect. Therefore, an AIP-Tom20 recognition contributes to cell survival in development and cancer by mediating the mitochondrial import of survivin.

A key commitment step in erythropoiesis is synchronized with the cell cycle clock through mutual inhibition between PU.1 and S-phase progression.

Hematopoietic progenitors undergo differentiation while navigating several cell division cycles, but it is unknown whether these two processes are coupled. We addressed this question by studying erythropoiesis in mouse fetal liver in vivo. We found that the initial upregulation of cell surface CD71 identifies developmentally matched erythroblasts that are tightly synchronized in S-phase. We show that DNA replication within this but not subsequent cycles is required for a differentiation switch comprising rapid and simultaneous committal transitions whose precise timing was previously unknown. These include the onset of erythropoietin dependence, activation of the erythroid master transcriptional regulator GATA-1, and a switch to an active chromatin conformation at the ß-globin locus. Specifically, S-phase progression is required for the formation of DNase I hypersensitive sites and for DNA demethylation at this locus. Mechanistically, we show that S-phase progression during this key committal step is dependent on downregulation of the cyclin-dependent kinase p57(KIP2) and in turn causes the downregulation of PU.1, an antagonist of GATA-1 function. These findings therefore highlight a novel role for a cyclin-dependent kinase inhibitor in differentiation, distinct to their known function in cell cycle exit. Furthermore, we show that a novel, mutual inhibition between PU.1 expression and S-phase progression provides a "synchromesh" mechanism that "locks" the erythroid differentiation program to the cell cycle clock, ensuring precise coordination of critical differentiation events.