In this study, we describe the 3D chromosome regulatory landscape of human naive and primed embryonic stem cells. To devise this map, we identified transcriptional enhancers and insulators in these ...cells and placed them within the context of cohesin-associated CTCF-CTCF loops using cohesin ChIA-PET data. The CTCF-CTCF loops we identified form a chromosomal framework of insulated neighborhoods, which in turn form topologically associating domains (TADs) that are largely preserved during the transition between the naive and primed states. Regulatory changes in enhancer-promoter interactions occur within insulated neighborhoods during cell state transition. The CTCF anchor regions we identified are conserved across species, influence gene expression, and are a frequent site of mutations in cancer cells, underscoring their functional importance in cellular regulation. These 3D regulatory maps of human pluripotent cells therefore provide a foundation for future interrogation of the relationships between chromosome structure and gene control in development and disease.
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•ChIA-PET analysis maps enhancers and insulators into looped domains•Cohesin-associated loops organize topologically associating domains (TADs)•Regulatory changes during cell state transitions take place within TADs•The conserved anchors of CTCF-CTCF loops are frequently mutated in cancer
Ji et al. map the chromosome organizational structures that underlie gene regulation in human naive and primed pluripotent cells. Their framework of cohesin-associated CTCF loops, and the cohesin-associated enhancer-promoter loops within them, provides a reference map for future interrogation of regulatory interactions.
Embryonic stem cells (ESCs) of mice and humans have distinct molecular and biological characteristics, raising the question of whether an earlier, “naive” state of pluripotency may exist in humans. ...Here we took a systematic approach to identify small molecules that support self-renewal of naive human ESCs based on maintenance of endogenous OCT4 distal enhancer activity, a molecular signature of ground state pluripotency. Iterative chemical screening identified a combination of five kinase inhibitors that induces and maintains OCT4 distal enhancer activity when applied directly to conventional human ESCs. These inhibitors generate human pluripotent cells in which transcription factors associated with the ground state of pluripotency are highly upregulated and bivalent chromatin domains are depleted. Comparison with previously reported naive human ESCs indicates that our conditions capture a distinct pluripotent state in humans that closely resembles that of mouse ESCs. This study presents a framework for defining the culture requirements of naive human pluripotent cells.
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•TALEN-mediated engineering of a reporter system for naive human pluripotency•Chemical screen for maintenance of naive reporter activity in absence of transgenes•Optimized chemical conditions capture a distinct state of human pluripotency•Gene expression of naive human cells is highly similar to that of naive mouse cells
Through sequential chemical screening, Theunissen et al. identify a combination of kinase inhibitors that induces and maintains defining features of naive pluripotency in human embryonic stem cells.
Tet enzymes (Tet1/2/3) convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) and are dynamically expressed during development. Whereas loss of individual Tet enzymes or combined deficiency ...of Tet1/2 allows for embryogenesis, the effect of complete loss of Tet activity and 5hmC marks in development is not established. We have generated Tet1/2/3 triple-knockout (TKO) mouse embryonic stem cells (ESCs) and examined their developmental potential. Combined deficiency of all three Tets depleted 5hmC and impaired ESC differentiation, as seen in poorly differentiated TKO embryoid bodies (EBs) and teratomas. Consistent with impaired differentiation, TKO ESCs contributed poorly to chimeric embryos, a defect rescued by Tet1 reexpression, and could not support embryonic development. Global gene-expression and methylome analyses of TKO EBs revealed promoter hypermethylation and deregulation of genes implicated in embryonic development and differentiation. These findings suggest a requirement for Tet- and 5hmC-mediated DNA demethylation in proper regulation of gene expression during ESC differentiation and development.
•Combined loss of all three Tet enzymes restricts normal differentiation of ESCs•Tet null ESCs contribute poorly to developing embryos and cannot support development•Tet loss causes promoter hypermethylation and deregulation of developmental genes
Dawlaty et al. used Tet1/2/3 triple-knockout (TKO) embryonic stem cells (ESCs) to ablate Tet-mediated hydroxylation at methylated DNA. TKO ESCs hypermethylate and repress developmental genes and fail to differentiate properly in chimeric mouse embryos. Thus, a shared role for paralogous Tet enzymes is required for ESC differentiation and subsequent development.
Devices based on deep-blue emitting iridium(III) complexes with N-heterocyclic carbene (NHC) ligands have recently been shown to give excellent performance as phosphorescent organic light-emitting ...diodes (PHOLEDs). To facilitate the design of even better deep-blue phosphorescent emitters, we carried out density functional theory (DFT) calculations of the lowest triplet (T1) potential-energy surfaces upon lengthening the iridium–ligand (Ir–C) bonds. Relativistic time dependent DFT calculations demonstrate that this changes the nature of T1 from a highly emissive metal-to-ligand charge transfer (3MLCT) state to a metal centered (3MC) state where the radiative decay rate is orders of magnitude slower than that of the 3MLCT state. We identify the elongation of an Ir–C bond on the NHC group as the pathway with the lowest energy barrier between the 3MLCT and 3MC states for all complexes studied and show that the barrier height is correlated with the experimentally measured nonradiative decay rate. This suggests that the thermal population of 3MC states is the dominant nonradiative decay mechanism at room temperature. We show that the 3MLCT → 3MC transition is reversible, in marked contrast to deep-blue phosphors containing coordinating nitrogen atoms, where the population of 3MC states breaks Ir–N bonds. This suggests that, as well as improved efficiency, blue PHOLEDs containing phosphors where the metal is only coordinated by carbon atoms will have improved device lifetimes.
Tet enzymes (Tet1/2/3) convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) in various embryonic and adult tissues. Mice mutant for either Tet1 or Tet2 are viable, raising the question of ...whether these enzymes have overlapping roles in development. Here we have generated Tet1 and Tet2 double-knockout (DKO) embryonic stem cells (ESCs) and mice. DKO ESCs remained pluripotent but were depleted of 5hmC and caused developmental defects in chimeric embryos. While a fraction of double-mutant embryos exhibited midgestation abnormalities with perinatal lethality, viable and overtly normal Tet1/Tet2-deficient mice were also obtained. DKO mice had reduced 5hmC and increased 5mC levels and abnormal methylation at various imprinted loci. Nevertheless, animals of both sexes were fertile, with females having smaller ovaries and reduced fertility. Our data show that loss of both enzymes is compatible with development but promotes hypermethylation and compromises imprinting. The data also suggest a significant contribution of Tet3 to hydroxylation of 5mC during development.
► Tet1/Tet2 double-mutant ESCs are depleted of 5hmC and remain pluripotent ► Mice with combined loss of Tet1 and Tet2 are viable with reduced fertility ► Hypermethylation and partial perinatal lethality are associated with Tet1/Tet2 loss ► Deficiency of Tet1 and Tet2 compromises imprinting
Dawlaty et al. generated Tet1/Tet2 double-mutant mice, attenuating hydroxylation and demethylation of 5-methylcytosine in embryonic stem cells (ESCs) and germ cells. Tet/Tet2 deficiency is compatible with ESC pluripotency and embryonic development but promotes DNA hypermethylation, compromises imprinting and fertility, and causes diverse partially penetrant defects, including exencephaly and perinatal lethality.
The Tet family of enzymes (Tet1/2/3) converts 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). Mouse embryonic stem cells (mESCs) highly express Tet1 and have an elevated level of 5hmC. Tet1 ...has been implicated in ESC maintenance and lineage specification in vitro but its precise function in development is not well defined. To establish the role of Tet1 in pluripotency and development, we have generated Tet1 mutant mESCs and mice. Tet1−/− ESCs have reduced levels of 5hmC and subtle changes in global gene expression, and are pluripotent and support development of live-born mice in tetraploid complementation assay, but display skewed differentiation toward trophectoderm in vitro. Tet1 mutant mice are viable, fertile, and grossly normal, though some mutant mice have a slightly smaller body size at birth. Our data suggest that Tet1 loss leading to a partial reduction in 5hmC levels does not affect pluripotency in ESCs and is compatible with embryonic and postnatal development.
► Tet1−/− ESCs show a partial reduction in 5hmC and subtle changes in gene expression ► Loss of Tet1 is compatible with maintaining pluripotency ► Tet1−/− ESCs can drive normal embryo development in 4n complementation assays ► Tet1 mutant mice are viable and fertile with slight variation in body size
Entrepreneurial intentions and start-ups Shinnar, Rachel S; Hsu, Dan K; Powell, Benjamin C ...
International small business journal,
02/2018, Volume:
36, Issue:
1
Journal Article
Peer reviewed
Open access
While empirical data clearly show that women are underrepresented among entrepreneurs, the causes of this gap are entirely not clear. This article explores one potential cause: that women might be ...less likely to act on their entrepreneurial intentions. Building on Ajzen’s theory of planned behaviour, we propose that intentions predict start-up behaviours, that is, that there is an intention–behaviour link. We then apply social role theory to propose that the intention–behaviour link is moderated by sex. Analysing data drawn from a sample of US-based management students during their first session in an introductory entrepreneurship course, at the end of the course, on their graduation and at a point up to three years after graduation, we find support for the intention–behaviour link and moderation of this link by sex. We identify additional contributions from our study and implications of our findings for addressing the sex gap in entrepreneurship.
Spin-crossover (SCO) materials display many fascinating behaviors including collective phase transitions and spin-state switching controlled by external stimuli, e.g., light and electrical currents. ...As single-molecule switches, they have been fêted for numerous practical applications, but these remain largely unrealized–partly because of the difficulty of switching these materials at high temperatures. We introduce a semiempirical microscopic model of SCO materials combining crystal field theory with elastic intermolecular interactions. For realistic parameters, this model reproduces the key experimental results including thermally induced phase transitions, light-induced spin-state trapping (LIESST), and reverse-LIESST. Notably, we reproduce and explain the experimentally observed relationship between the critical temperature of the thermal transition, T 1/2, and the highest temperature for which the trapped state is stable, T LIESST, and explain why increasing the stiffness of the coordination sphere increases T LIESST. We propose strategies to design SCO materials with higher T LIESST: optimizing the spin–orbit coupling via heavier atoms (particularly in the inner coordination sphere) and minimizing the enthalpy difference between the high-spin (HS) and low-spin (LS) states. However, the most dramatic increases arise from increasing the cooperativity of the spin-state transition by increasing the rigidity of the crystal. Increased crystal rigidity can also stabilize the HS state to low temperatures on thermal cycling yet leave the LS state stable at high temperatures following, for example, reverse-LIESST. We show that such highly cooperative systems offer a realistic route to robust room-temperature switching, demonstrate this in silico, and discuss material design rationale to realize this.
Melanins are pigmentary macromolecules found throughout the biosphere that, in the 1970s, were discovered to conduct electricity and display bistable switching. Since then, it has been widely ...believed that melanins are naturally occurring amorphous organic semiconductors. Here, we report electrical conductivity, muon spin relaxation, and electron paramagnetic resonance measurements of melanin as the environmental humidity is varied. We show that hydration of melanin shifts the comproportionation equilibrium so as to dope electrons and protons into the system. This equilibrium defines the relative proportions of hydroxyquinone, semiquinone, and quinone species in the macromolecule. As such, the mechanism explains why melanin at neutral pH only conducts when "wet" and suggests that both carriers play a role in the conductivity. Understanding that melanin is an electronic-ionic hybrid conductor rather than an amorphous organic semiconductor opens exciting possibilities for bioelectronic applications such as ion-toelectron transduction given its biocompatibility.
Purpose
This paper focuses on the problem of knowledge that is difficult to share because it cannot be articulated: intractably tacit knowledge. It offers knowledge sharing between relatives or ...friends, a nepotistic practice, as a potential solution.
Design/methodology/approach
Analysis of a US Supreme Court decision in favor of a nepotistic hiring practice provides insights into how such a nepotistic approach can facilitate the sharing of intractably tacit knowledge. The paper builds on this analysis to articulate the conditions under which nepotistic selection can be useful to managers.
Findings
The US Supreme Court decided in favor of a nepotistic hiring practice based on its potential effectiveness in selecting and developing river pilots. Such a nepotistic approach is problematic, but it can be valuable in a very specific and narrow application, i.e., when organizations need to transfer intractably tacit knowledge. A nepotistic approach should thus be employed only if the benefit of sharing intractably tacit knowledge exceed the cost of nepotism. Organizations should enhance the benefit by ensuring effective knowledge transfer and reduce the cost by mitigating the discrimination and inequity that nepotism enhances.
Originality/value
While much has been written on tacit knowledge, the portion of tacit knowledge that cannot be articulated has been ignored in some studies and neglected in others. Managers responsible for the sharing of such knowledge need guidance. This paper explores an unusual solution: nepotistic selection.
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