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This paper summarises the outcome of an analysis of stablecoins undertaken by the ECB Crypto-Assets Task Force. At the time of writing, the stablecoin debate lacks a common taxonomy and unambiguous terminology. This paper applies a definition that distinguishes stablecoins from existing forms of currencies – regardless of the technology used – and characterises stablecoin arrangements based on the functions they fulfil. This approach emphasises the role of technology-neutral regulation in preventing arbitrage, as well as comprehensive Eurosystem oversight, irrespective of stablecoins’ regulatory status. Against this background, this paper assesses stablecoins’ implications for the euro area based on three scenarios for the uptake of stablecoins: (i) as a crypto-assets accessory function; (ii) as a new payment method; and (iii) as an alternative store of value. While the first scenario is merely the continuation of the current state of the market and, thus far, has not posed concerns for the financial sector and/or central bank tasks, stablecoins of the type envisaged in the second scenario may reach a scale such that financial stability risks can become material, and the safety and efficiency of the payment system may be affected. The third scenario is both the least plausible and the most relevant from a monetary policy perspective. The paper concludes that the Eurosystem relies on appropriate regulation, oversight, and supervision to manage the implications of stablecoins (and the risks that stem from them) on its mandate and tasks under plausible scenarios. The Eurosystem continues monitoring the evolution of the stablecoin market and stands ready to respond to rapid changes in all possible scenarios.

In multicellular organisms, duplicated genes can diverge through tissue-specific gene expression patterns, as exemplified by highly regulated expression of RUNX transcription factor paralogs with apparent functional redundancy. Here we asked what cell-type-specific biologies might be supported by the selective expression of RUNX paralogs during Langerhans cell and inducible regulatory T cell differentiation. We uncovered functional nonequivalence between RUNX paralogs. Selective expression of native paralogs allowed integration of transcription factor activity with extrinsic signals, while non-native paralogs enforced differentiation even in the absence of exogenous inducers. DNA binding affinity was controlled by divergent amino acids within the otherwise highly conserved RUNT domain and evolutionary reconstruction suggested convergence of RUNT domain residues toward submaximal strength. Hence, the selective expression of gene duplicates in specialized cell types can synergize with the acquisition of functional differences to enable appropriate gene expression, lineage choice and differentiation in the mammalian immune system. Protein transcription factor paralogs are not equivalent and serve distinct roles in immune cells. Merkenschlager and colleagues show that RUNX1 and RUNX3 differ in binding strength to motif sequences and how this leads to differential functional activities.

In multicellular organisms, duplicated genes can diverge through tissue-specific gene expression patterns, as exemplified by highly regulated expression of RUNX transcription factor paralogs with apparent functional redundancy. Here we asked what cell-type-specific biologies might be supported by the selective expression of RUNX paralogs during Langerhans cell and inducible regulatory T cell differentiation. We uncovered functional nonequivalence between RUNX paralogs. Selective expression of native paralogs allowed integration of transcription factor activity with extrinsic signals, while non-native paralogs enforced differentiation even in the absence of exogenous inducers. DNA binding affinity was controlled by divergent amino acids within the otherwise highly conserved RUNT domain and evolutionary reconstruction suggested convergence of RUNT domain residues toward submaximal strength. Hence, the selective expression of gene duplicates in specialized cell types can synergize with the acquisition of functional differences to enable appropriate gene expression, lineage choice and differentiation in the mammalian immune system.

Credit risk models are validated to check that they produce unbiased, “high-quality” estimates of credit risk. Credit risk models follow different rating philosophies, ranging from point-in-time (PIT) models that reflect all currently available information to through-the-cycle (TTC) models whose credit risk estimates are independent of cyclical changes in macroeconomic conditions. TTC models have been favoured in particular from a macro-prudential perspective because they produce more stable capital requirements for banks over the cycle, thus avoiding pro-cyclicality. This paper investigates different ways to validate TTC credit rating systems, including possibilities to separate the validation of a TTC system into the validation of its PIT component and the validation of its adjustment for the cycle. We conclude that the validation of TTC models is significantly more difficult than the validation of PIT models, which may make the regulatory promotion of TTC models questionable. We argue that the regulatory requirement of PIT models combined with a more extensive use of the counter-cyclical capital buffer as a macro-prudential policy tool could be a potentially superior alternative to address pro-cyclicality.

Polycomb Repressor Complexes (PRCs) are important regulators of embryogenesis. In embryonic stem (ES) cells many genes that regulate subsequent stages in development are enriched at their promoters for PRC1, PRC2 and Ser 5-phosphorylated RNA Polymerase II (RNAP), and contain domains of 'bivalent' chromatin (enriched for H3K4me3; histone H3 di- or trimethylated at Lys 4 and H3K27me3; histone H3 trimethylated at Lys 27). Loss of individual PRC components in ES cells can lead to gene de-repression and to unscheduled differentiation. Here we show that Jarid2 is a novel subunit of PRC2 that is required for the co-recruitment of PRC1 and RNAP to genes that regulate development in ES cells. Jarid2-deficient ES cells showed reduced H3K4me2/me3 and H3K27me3 marking and PRC1/PRC2 recruitment, and did not efficiently establish Ser 5-phosporylated RNAP at target genes. ES cells lacking Jarid2, in contrast to previously characterized PRC1 and PRC2 mutants, did not inappropriately express PRC2 target genes. Instead, they show a severely compromised capacity for successful differentiation towards neural or mesodermal fates and failed to correctly initiate lineage-specific gene expression in vitro. Collectively, these data indicate that transcriptional priming of bivalent genes in pluripotent ES cells is Jarid2-dependent, and suggests that priming is critical for subsequent multi-lineage differentiation.

Regulatory T (Treg) cells safeguard against autoimmunity and immune pathology. Because determinants of the Treg cell fate are not completely understood, we have delineated signaling events that control the de novo expression of Foxp3 in naive peripheral CD4 T cells and in thymocytes. We report that premature termination of TCR signaling and inibition of phosphatidyl inositol 3-kinase (PI3K) p110α, p110δ, protein kinase B (Akt), or mammalian target of rapamycin (mTOR) conferred Foxp3 expression and Treg-like gene expression profiles. Conversely, continued TCR signaling and constitutive PI3K/Akt/mTOR activity antagonised Foxp3 induction. At the chromatin level, di- and trimethylation of lysine 4 of histone H3 (H3K4me2 and -3) near the Foxp3 transcription start site (TSS) and within the 5′ untranslated region (UTR) preceded active Foxp3 expression and, like Foxp3 inducibility, was lost upon continued TCR stimulation. These data demonstrate that the PI3K/Akt/mTOR signaling network regulates Foxp3 expression.

Over the last decade, the simple instrument policy rule developed by Taylor has become a popular tool for evaluating the monetary policy of central banks. As an extensive empirical analysis of the European Central Bank’s (ECB) past behaviour still seems to be in its infancy, we estimate several instrument policy reaction functions for the ECB to shed some light on actual monetary policy in the euro area under the presidency of Wim Duisenberg and answer questions like whether the ECB has actually followed a stabilizing or a destabilizing rule so far. Looking at contemporaneous Taylor rules, the evidence presented suggests that the ECB is accommodating changes in inflation and hence follows a destabilizing policy. However, this impression seems to be largely due to the lack of a forward-looking perspective in such specifications. Either assuming rational expectations and using a forward-looking specification, or using expectations as derived from surveys result in Taylor rules that do imply a stabilizing role of the ECB. The use of real-time industrial production data does not seem to play such a significant role as in the case of the United States.

Epigenetic genome modifications are thought to be important for specifying the lineage and developmental stage of cells within a multicellular organism. Here, we show that the epigenetic profile of pluripotent embryonic stem cells (ES) is distinct from that of embryonic carcinoma cells, haematopoietic stem cells (HSC) and their differentiated progeny. Silent, lineage-specific genes replicated earlier in pluripotent cells than in tissue-specific stem cells or differentiated cells and had unexpectedly high levels of acetylated H3K9 and methylated H3K4. Unusually, in ES cells these markers of open chromatin were also combined with H3K27 trimethylation at some non-expressed genes. Thus, pluripotency of ES cells is characterized by a specific epigenetic profile where lineage-specific genes may be accessible but, if so, carry repressive H3K27 trimethylation modifications. H3K27 methylation is functionally important for preventing expression of these genes in ES cells as premature expression occurs in embryonic ectoderm development (Eed)-deficient ES cells. Our data suggest that lineage-specific genes are primed for expression in ES cells but are held in check by opposing chromatin modifications.

Constitutive heterochromatin was once thought to be remarkably stable in composition and transcriptionally inert, but has recently been shown to be surprisingly dynamic. Here, we show that terminal muscle differentiation results in a global reorganisation and spatial clustering of constitutive heterochromatin. This is accompanied by enhanced histone H3K9 and H4K20 tri-methylation across major satellite regions and increased levels of major and minor satellite-encoded transcripts. Histone deacetylase (HDAC) activity is known to be important for initiating muscle differentiation. However, here, we show that low doses of HDAC inhibitors applied after the onset of muscle differentiation prevent the spatial reorganisation of constitutive heterochromatin while allowing terminal differentiation to proceed. Under these conditions, HDAC inhibition interferes with histone methylation and blocks centromere clustering, but does not prevent the temporal expression of muscle regulatory factors or the accumulation of centromere-derived transcripts. The demonstration that HDAC activity is required for spatial relocation of centromeres in differentiating muscle provides a convenient system in which the molecular drivers of differentiation-induced chromosome repositioning can be dissected.

Post-translational modifications of histone amino termini are thought to convey epigenetic information that extends the coding potential of DNA. In particular, histone lysine methylation has been implicated in conveying transcriptional memory and maintaining lineage fidelity. Here an analysis of histone lysine methylation in quiescent (G(0)) and cycling lymphocytes showed that methylation of histone H3 at lysines 4 (H3K4), 9 (H3K9), 27 (H3K27) and histone H4 at lysine 20 is markedly reduced in resting B lymphocytes as compared with cycling cells. Quiescent B cells also lacked heterochromatin-associated HP1beta and Ikaros at pericentric chromatin and expressed low levels of Ezh2 and ESET histone methyl transferases (HMTases). Nuclei from resting B or T cells were approximately three times more efficiently reprogrammed in nuclear transfer assays than cells in which HMTase expression, histone methylation and HP1beta binding had been restored following mitotic stimulation. These results showing local and global changes in histone lysine methylation levels in vivo demonstrate that constitutive heterochromatin organization is modified in resting lymphocytes and suggest that histone hypomethylation is a useful indicator of epigenetic plasticity.

Auf 14 landwirtschaftlich genutzten tiefgrundigen Losstandorten in Mittelhessen wurden hohe Nitratkonzentrationen in der Tiefe von einem Meter unter Flur gemessen. Bei mehreren Tiefbohrungen traten in Tiefen groser als drei Meter jedoch nur geringe bis mittlere Nitratwerte auf. Fur vier bezuglich der Bodenverhaltnisse und der Fruchtarten reprasentative Flachen wurden in zwei aufeinander folgenden Jahren die maximalen Wasserentzugstiefen gemessen. Sie lagen stets tiefer als 200 cm unter Flur bei einem Maximum von 290 cm unter mehrjahriger Luzerne, so dass auch noch in dieser Bodentiefe von einer Stickstoffaufnahme durch die Pflanze auszugehen ist. Fur die effektive Durchwurzelungstiefe ergaben sich erheblich hohere Messwerte als die Schatzwerte nach Bodenkundlicher Kartieranleitung (AG Boden, 1994), DVWK-Regeln 129/1995 (DVWK, 1995) oder DIN 4220 (DIN, 1998). Die im Wurzelraum zeitweise vorhandenen hohen Nitratgehalte wurden bei Jahresniederschlagen von ≤ 600 mm bei einer mittleren Vordringgeschwindigkeit der Sickerwasserfront unterhalb des Wurzelraumes von 0,23 m a—1 nur zu einem geringen Teil in grosere Tiefen verlagert. Das heist, dass der Nmin-Gehalt in 120 cm oder gar nur 90 cm Bodentiefe die potenzielle Grundwassergefahrdung nicht anzeigen kann. Effective rooting depth, percolation water, and nitrate leaching in deeply developed loess soils of a water-shortage area In 14 deeply developed loess soils, high amounts of mineral nitrogen (N) were measured within the first meter, whereas several nitrate depth profiles up to more than three meters resulted in low and medium nitrate values. The maximum depth of water uptake was measured in two years on four representative sites with regard to soil and crop properties. The maximum depth of water uptake was always considerably deeper than 200 cm, with a maximum of 290 cm (alfalfa). It is assumed that roots take up nitrogen even in this depth. The calculation of the effective rooting depth resulted in noticeably higher values (for wheat between 160 cm and 185 cm) than those given by the ”German Instructions for Soil Mapping” (AG Boden, 1994), the ”Regulations of the German Organisation for Water Management and Land Improvement” (DVWK, 1995) or the ”German Institute for Standardization” (DIN, 1998). As a result of low annual precipitation (normally less than 600 mm), only a minor part of the high amounts of nitrate within the root zone was leached into deeper soil layers. We conclude that it is not possible to predict the potential groundwater pollution with nitrate on the basis of the mineral N content in the first meter of the soil profile.

The development of multi-cellular organisms is regulated by the ordered definition of gene expression programmes that govern cell proliferation and differentiation. Although differential gene activity is mainly controlled by transcription factors, it is also dependent upon the underlying chromatin structure, which can stabilize transcriptional "on" or "off" states. We have recently isolated human (SUV39H1) and mouse (Suv39h1) histone methyltransferases (HMTases) and shown that they are important regulators for the organization of repressive chromatin domains. To investigate whether a SUV39H1-induced modulation of heterochromatin would affect mammalian development, we generated transgenic mice that over-express the SUV39H1 HMTase early during embryogenesis. SUV39H1 transgenic mice are growth retarded, display a weak penetrance of skeletal transformations and are largely characterized by impaired erythroid differentiation, consistent with highest transgene expression in foetal liver. Ex vivo transgenic foetal liver cultures initially contain reduced numbers of cells in G1 but progress to immortalized erythroblasts that are compromised in executing an erythroid differentiation programme. The outgrowing SUV39H1-immortalized erythroblasts can maintain a diploid karyotype despite deregulation of several tumour suppressor proteins and dispersed distribution of the heterochromatin component HP1. Together, these data provide evidence for a role of the SUV39H1 HMTase during the mammalian development and indicate a possible function for higher-order chromatin in contributing to the balance between proliferation and differentiation potentials of progenitor cells.

According to Woodford (1999) and (2003) [Woodford, Michael, 1999. Commentary: how should monetary policy be conducted in an era of price stability? In: New challenges for monetary policy. Federal Reserve Bank of Kansas City, pp. 277–316; Woodford, Michael, 2003. Interest and prices: foundations of a theory of monetary policy. Princeton University Press, Princeton, NJ], optimal monetary policy in the New Keynesian model follows the timeless perspective rule. We show why an economy that is sufficiently far away from its steady-state suffers from a short-run cost associated with the timeless perspective. In this case, discretionary policy-making can be better than the timeless perspective policy rule.

T2S is the single and harmonised IT platform for securities settlement in central bank money developed by the Eurosystem to promote integration in the European post-trading industry, and will go live in 2015. CSDs joining T2S are thus faced with the decision problem of determining to which degree they should reshape, that is, adapt their own IT infrastructure, human resources and business strategy to T2S. A more complete reshaping entails higher immediate fixed costs, but allows to benefit the most from the cost-reduction allowed by T2S. In this article we use a game theoretic approach to model the strategic choice of the CSDs. We then derive several results from this model. In particular, we give closed-form solutions for the degree of optimal reshaping and the optimal prices set in the unique equilibrium if the time-horizon is finite. In case of an infinite horizon we give a sufficient and necessary condition for the existence of another subgame perfect Nash equilibrium in which CSDs continually delay the decision to reshape. We argue this equilibrium is not robust and provide a condition under which a given CSD will always reshape, whatever the other CSDs JEL Classification: G10, G20, L11

Sister chromatids contain identical DNA sequence but are chiral with respect to both their helical handedness and their replication history. Emerging evidence from various model organisms suggests that certain stem cells segregate sister chromatids nonrandomly to either maintain genome integrity or to bias cellular differentiation in asymmetric cell divisions. Conventional methods for tracing of old vs. newly synthesized DNA strands generally lack resolution for individual chromosomes and employ halogenated thymidine analogs with profound cytotoxic effects on rapidly dividing cells. Here, we present a modified chromosome orientation fluorescence in situ hybridization (CO-FISH) assay, where identification of individual chromosomes and their replication history is achieved in subsequent hybridization steps with chromosome-specific DNA probes and PNA telomere probes. Importantly, we tackle the issue of BrdU cytotoxicity and show that our method is compatible with normal mouse ES cell biology, unlike a recently published related protocol. Results from our CO-FISH assay show that mitotic segregation of mouse chromosome 7 is random in ES cells, which contrasts previously published results from our laboratory and settles a controversy. Our straightforward protocol represents a useful resource for future studies on chromatid segregation patterns of in vitro-cultured cells from distinct model organisms.

Auf drei Grunlandstandorten unterschiedlicher Wasserspeicherkapazitat wurde im Herbst 1993 ein Modellversuch zur Stickstoffdynamik unter Kot- und Harnflecken angelegt. Unter den Exkrementstellen wurde uber Saugkerzen Bodenwasser entnommen und auf verschiedene Stickstofffraktionen hin untersucht. Die Berechnung der Sickerwassermengen und Stickstotffrachten erfolgte mit einem Speicherzellenmodell. Der schnelle Anstieg der Ammoniumkonzentrationen unter den Urinflecken auf 30 bis 60 mg NH4−N/I war trotz, geringer Bodentemperaluren auf eine schnelle Hydrolyse des Harnstoffs zuruckzufuhren. Mit sinkenden Ammoniumwerten stiegen die Nitratkonzentrationen kontinuierlich auf 160 mg NO3−N/I an und fielen erst wieder mit einsetzendem Pflanzenwachstum im Fruhjahr. Unter den Kotflecken war nur eine geringe Nitratverlagerung zu verzeichnen. Fur die Hamflecken wurde ein N-Austrag von 150 bis 320 kg/ha, fur die Kotflecken von 3 bis 28 kg/ha berechnet. Der Nitratfraktion kam mit 83% die groste Bedeutung zu, gefolgt von Norg- (11%) und der Ammoniumfraktion (6%). Von einer geschatzten Besatzleistung (Spatbeweidung) ausgehend berechnete sich eine durch Urinflecken bedeckte Bodenoberflache von 1% bis 3%. Leaching of nitrogen from pastures at the end of the grazing season A trial was carried out to describe nitrogen dynamics under excrement patches. On three grassland sites differing in water capacity, soil water was extracted by porous ceramic cups placed under the patches. Soil water was analyzed for different nitrogen fractions. Infiltration water and the amount of leached nitrogen was calculated by a simulation model. The rapid rise in concentrations under the urine patches to 30–60 mg NH4−N/I was due to the rapid hydrolysis of urea in spite of low soil temperatures. While the rates of ammonium decreased, the concentration of nitrate increased continuously up to 160 mg NO3−N/I and did not fall until the beginning of plant growth in early spring. Under the dung patches almost no nitrogen was found. For the urine patches the calculated nitrogen leaching was between 150 and 320 kg/ha, for the dung patches between 3 and 28 kg/ha. From the total of leached nitrogen the nitrate fraction (83%) was the most significant, followed by the organic nitrogen fraction (11%) and ammonium (6%). Taking account of an estimated grazing pressure, the urine-affected soil surface was calculated between 1% and 3

Ever since cloning the classic iv (inversed viscerum) mutation identified the “left-right dynein” (lrd) gene in mice, most research on body laterality determination has focused on its function in motile cilia at the node embryonic organizer. This model is attractive, as it links chirality of cilia architecture to asymmetry development. However, lrd is also expressed in blastocysts and embryonic stem cells, where it was shown to bias the segregation of recombined sister chromatids away from each other in mitosis. These data suggested that lrd is part of a cellular mechanism that recognizes and selectively segregates sister chromatids based on their replication history: old “Watson” versus old “Crick” strands. We previously proposed that the mouse left-right axis is established via an asymmetric cell division prior to/or during gastrulation. In this model, left-right dynein selectively segregates epigenetically differentiated sister chromatids harboring a hypothetical “left-right axis development 1” (“lra1”) gene during the left-right axis establishing cell division. Here, asymmetry development would be ultimately governed by the chirality of the cytoskeleton and the DNA molecule. Our model predicts that randomization of chromatid segregation in lrd mutants should produce embryos with 25% situs solitus, 25% situs inversus, and 50% embryonic death due to heterotaxia and isomerism. Here we confirmed this prediction by using two distinct lrd mutant alleles. Other than lrd, thus far Nodal gene is the most upstream function implicated in visceral organs laterality determination. We next tested whether the Nodal gene constitutes the lra1 gene hypothesized in the model by testing mutant’s effect on 50% embryonic lethality observed in lrd mutants. Since Nodal mutation did not suppress lethality, we conclude that Nodal is not equivalent to the lra1 gene. In summary, we describe the origin of 50% lethality in lrd mutant mice not yet explained by any other laterality-generating hypothesis.

This paper provides a framework to analyse emergency liquidity assistance of central banks on financial markets in response to aggregate and idiosyncratic liquidity shocks. The model combines the microeconomic view of liquidity as the ability to sell assets quickly and at low costs and the macroeconomic view of liquidity as a medium of exchange that influences the aggregate price level of goods. The central bank faces a trade-off between limiting the negative output effects of dramatic asset price declines and more inflation. Furthermore, the anticipation of central bank intervention causes a moral hazard effect with investors. This gives rise to the possibility of an optimal monetary policy under commitment.

Discretionary monetary policy produces a dynamic loss in the New Keynesian model in the presence of cost-push shocks. The possibility to commit to a specific policy rule can increase welfare. A number of authors since Woodford (1999) have argued in favour of a timeless perspective rule as an optimal policy. The short-run costs associated with the timeless perspective are neglected in general, however. Rigid prices, relatively impatient households, a high preference of policy makers for output stabilisation and a deviation from the steady state all worsen the performance of the timeless perspective rule and can make it inferior to discretion. JEL Classification: E5

Determining how genes are epigenetically regulated to ensure their correct spatial and temporal expression during development is key to our understanding of cell lineage commitment. Here we examined epigenetic changes at an important proneural regulator gene Mash1 (Ascl1), as embryonic stem (ES) cells commit to the neural lineage. In ES cells where the Mash1 gene is transcriptionally repressed, the locus replicated late in S phase and was preferentially positioned at the nuclear periphery with other late-replicating genes (Neurod, Sprr2a). This peripheral location was coupled with low levels of histone H3K9 acetylation at the Mash1 promoter and enhanced H3K27 methylation but surprisingly location was not affected by removal of the Ezh2/Eed HMTase complex or several other chromatin-silencing candidates (G9a, SuV39h-1, Dnmt-1, Dnmt-3a and Dnmt-3b). Upon neural induction however, Mash1 transcription was upregulated (>100-fold), switched its time of replication from late to early in S phase and relocated towards the interior of the nucleus. This spatial repositioning was selective for neural commitment because Mash1 was peripheral in ES-derived mesoderm and other non-neural cell types. A bidirectional analysis of replication timing across a 2 Mb region flanking the Mash1 locus showed that chromatin changes were focused at Mash1. These results suggest that Mash1 is regulated by changes in chromatin structure and location and implicate the nuclear periphery as an important environment for maintaining the undifferentiated state of ES cells.

Over the last decade, the simple instrument policy rule developed by Taylor (1993) has become a popular tool for evaluating monetary policy of central banks. As an extensive empirical analysis of the ECB’s past behaviour still seems to be in its infancy, we estimate several instrument policy reaction functions for the ECB which might shed some light on actual monetary policy in the euro area in the recent past and answer questions like whether the ECB has actually followed a stabilising or a destabilising rule so far? Looking at contemporaneous Taylor rules, the presented evidence suggests that the ECB is accommodating changes in inflation and hence follows a destabilising policy. However, this impression seems to be largely due to the lack of a forward-looking perspective in such specifications. Either assuming rational expectations and using a forward-looking specification, or using expectations as derived from surveys result in Taylor rules which do imply a stabilising role of the ECB. The use of real-time industrial production data does not seem to play such a significant role as in the case of the U.S.

Histone H3 lysine 9 methylation has been proposed to provide a major "switch" for the functional organization of chromosomal subdomains. Here, we show that the murine Suv39h histone methyltransferases (HMTases) govern H3-K9 methylation at pericentric heterochromatin and induce a specialized histone methylation pattern that differs from the broad H3-K9 methylation present at other chromosomal regions. Suv39h -deficient mice display severely impaired viability and chromosomal instabilities that are associated with an increased tumor risk and perturbed chromosome interactions during male meiosis. These in vivo data assign a crucial role for pericentric H3-K9 methylation in protecting genome stability, and define the Suv39h HMTases as important epigenetic regulators for mammalian development.

SummaryEmbryonic stem cells (ESCs) are pluripotent, self-renewing, and have the ability to reprogram differentiated cell types to pluripotency upon cellular fusion. Polycomb-group (PcG) proteins are important for restraining the inappropriate expression of lineage-specifying factors in ESCs. To investigate whether PcG proteins are required for establishing, rather than maintaining, the pluripotent state, we compared the ability of wild-type, PRC1-, and PRC2-depleted ESCs to reprogram human lymphocytes. We show that ESCs lacking either PRC1 or PRC2 are unable to successfully reprogram B cells toward pluripotency. This defect is a direct consequence of the lack of PcG activity because it could be efficiently rescued by reconstituting PRC2 activity in PRC2-deficient ESCs. Surprisingly, the failure of PRC2-deficient ESCs to reprogram somatic cells is functionally dominant, demonstrating a critical requirement for PcG proteins in the chromatin-remodeling events required for the direct conversion of differentiated cells toward pluripotency.

Runx proteins are essential for hematopoiesis and play an important role in T cell development by regulating key target genes, such as CD4 and CD8 as well as lymphokine genes, during the specialization of naive CD4 T cells into distinct T helper subsets. In regulatory T (T reg) cells, the signature transcription factor Foxp3 interacts with and modulates the function of several other DNA binding proteins, including Runx family members, at the protein level. We show that Runx proteins also regulate the initiation and the maintenance of Foxp3 gene expression in CD4 T cells. Full-length Runx promoted the de novo expression of Foxp3 during inducible T reg cell differentiation, whereas the isolated dominant-negative Runt DNA binding domain antagonized de novo Foxp3 expression. Foxp3 expression in natural T reg cells remained dependent on Runx proteins and correlated with the binding of Runx/core-binding factor β to regulatory elements within the Foxp3 locus. Our data show that Runx and Foxp3 are components of a feed-forward loop in which Runx proteins contribute to the expression of Foxp3 and cooperate with Foxp3 proteins to regulate the expression of downstream target genes.

SummaryCohesins mediate sister chromatid cohesion, which is essential for chromosome segregation and postreplicative DNA repair. In addition, cohesins appear to regulate gene expression and enhancer-promoter interactions. These noncanonical functions remained unexplained because knowledge of cohesin-binding sites and functional interactors in metazoans was lacking. We show that the distribution of cohesins on mammalian chromosome arms is not driven by transcriptional activity, in contrast to S. cerevisiae. Instead, mammalian cohesins occupy a subset of DNase I hypersensitive sites, many of which contain sequence motifs resembling the consensus for CTCF, a DNA-binding protein with enhancer blocking function and boundary-element activity. We find cohesins at most CTCF sites and show that CTCF is required for cohesin localization to these sites. Recruitment by CTCF suggests a rationale for noncanonical cohesin functions and, because CTCF binding is sensitive to DNA methylation, allows cohesin positioning to integrate DNA sequence and epigenetic state.

International audience; Mammalian embryonic stem (ES) cells can either self-renew or generate progenitor cells that have a more restricted developmental potential. This provides an important model system to ask how pluripotency, cell commitment and differentiation are regulated at the level of chromatin-based changes that distinguish stem cells from their differentiated progeny. Here we show that the differentiation of ES cells to neural progenitors results in dynamic changes in the epigenetic status of multiple genes that encode transcription factors critical for early embryonic development or lineage specification. In particular, we demonstrate that DNA replication at a subset of neural-associated genes including Pax3, Pax6, Irx3, Nkx2.9 and Mash1 is advanced upon neural induction, consistent with increased locus accessibility. Conversely, many ES-associated genes including Oct4, Nanog, Utf1, Foxd3, Cripto and Rex1 that replicate early in ES cells switch their replication timing to later in S-phase in response to differentiation. Detailed analysis of the Rex1 locus reveals that delayed replication extends to a 2.8 Mb region surrounding the gene and is associated with substantial reductions in the level of histone H3K9 and H4 acetylation at the promoter. These results show that loss of pluripotency (and lineage choice) is associated with extensive and predictable changes in the replication timing of key regulator genes.