The Wnt and Notch signalling pathways represent two major channels of communication used by animal cells to control their identities and behaviour during development. A number of reports indicate ...that their activities are closely intertwined during embryonic development. Here, we review the evidence for this relationship and suggest that Wnt and Notch (`Wntch') signalling act as components of an integrated device that, rather than defining the fate of a cell, determines the probability that a cell will adopt that fate.
The mammalian embryo's caudal lateral epiblast (CLE) harbours bipotent progenitors, called neural mesodermal progenitors (NMPs), that contribute to the spinal cord and the paraxial mesoderm ...throughout axial elongation. Here, we performed a single cell analysis of different
NMP populations produced either from embryonic stem cells (ESCs) or epiblast stem cells (EpiSCs) and compared them with E8.25 CLE mouse embryos. In our analysis of this region, our findings challenge the notion that NMPs can be defined by the exclusive co-expression of
and
at mRNA level. We analyse the
NMP-like populations using a purpose-built support vector machine (SVM) based on the embryo CLE and use it as a classification model to compare the
and
populations. Our results show that NMP differentiation from ESCs leads to heterogeneous progenitor populations with few NMP-like cells, as defined by the SVM algorithm, whereas starting with EpiSCs yields a high proportion of cells with the embryo NMP signature. We find that the population from which the Epi-NMPs are derived in culture contains a node-like population, which suggests that this population probably maintains the expression of
and thereby a source of NMPs. In conclusion, differentiation of EpiSCs into NMPs reproduces events
and suggests a sequence of events for the emergence of the NMP population.
The development of the central nervous system is known to result from two sequential events. First, an inductive event of the mesoderm on the overlying ectoderm that generates a neural plate that, ...after rolling into a neural tube, acts as the main source of neural progenitors. Second, the axial regionalization of the neural plate that will result in the specification of neurons with different anteroposterior identities. Although this description of the process applies with ease to amphibians and fish, it is more difficult to confirm in amniote embryos. Here, a specialized population of cells emerges at the end of gastrulation that, under the influence of Wnt and FGF signalling, expands and generates the spinal cord and the paraxial mesoderm. This population is known as the long-term neuromesodermal precursor (NMp). Here, we show that controlled increases of Wnt/β-catenin and FGF signalling during adherent culture differentiation of mouse embryonic stem cells (mESCs) generates a population with many of the properties of the NMp. A single-cell analysis of gene expression within this population reveals signatures that are characteristic of stem cell populations. Furthermore, when this activation is triggered in three-dimensional aggregates of mESCs, the population self-organizes macroscopically and undergoes growth and axial elongation that mimics some of the features of the embryonic spinal cord and paraxial mesoderm. We use both adherent and three-dimensional cultures of mESCs to probe the establishment and maintenance of NMps and their differentiation.
There is evidence that pluripotency of mouse embryonic stem (ES) cells is associated with the activity of a network of transcription factors with Sox2, Oct4, and Nanog at the core. Using fluorescent ...reporters for the expression of Nanog, we observed that a population of ES cells is best described by a dynamic distribution of Nanog expression characterized by two peaks defined by high (HN) and low (LN) Nanog expression. Typically, the LN state is 5%-20% of the total population, depending on the culture conditions. Modelling of the activity of Nanog reveals that a simple network of Oct4/Sox2 and Nanog activity can account for the observed distribution and its properties as long as the transcriptional activity is tuned by transcriptional noise. The model also predicts that the LN state is unstable, something that is born out experimentally. While in this state, cells can differentiate. We suggest that transcriptional fluctuations in Nanog expression are an essential element of the pluripotent state and that the function of Sox2, Oct4, and Nanog is to act as a network that promotes and maintains transcriptional noise to interfere with the differentiation signals.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The assignation of cell fates during eukaryotic development relies on the coordinated and stable expression of cohorts of genes within cell populations. The precise and reproducible nature of this ...process is remarkable given that, at the single-cell level, the transcription of individual genes is associated with noise - random molecular fluctuations that create variability in the levels of gene expression within a cell population. Here we consider the implications of transcriptional noise for development and suggest the existence of molecular devices that are dedicated to filtering noise. On the basis of existing evidence, we propose that one such mechanism might depend on the Wnt signalling pathway.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
6.
Notch, a Universal Arbiter of Cell Fate Decisions Ehebauer, Matthias; Hayward, Penelope; Martinez Arias, Alfonso
Science (American Association for the Advancement of Science),
12/2006, Letnik:
314, Številka:
5804
Journal Article
Recenzirano
Members of the Notch family of receptors act as membrane-tethered transcription factors that are tightly associated with binary cell fate decisions. Notch signaling acts as a molecular gate that ...allows cells to adopt or forfeit a particular fate. Interaction of Notch with ligands triggers a sequence of proteolytic cleavages that release the intracellular domain to the nucleus; this mechanism is a target of therapies for leukemias associated with Notch activation. Although the molecular mechanism of Notch activation is well characterized, further analysis in an appropriate cellular context will provide new insight into Notch signaling.
Tankyrases (TNKSs), members of the PARP (Poly(ADP-ribose)polymerases) superfamily of enzymes, have gained interest as therapeutic drug targets, especially as they are involved in the regulation of ...Wnt signalling. A series of 2-arylquinazolin-4-ones with varying substituents at the 8-position was synthesised. An 8-methyl group (compared to 8-H, 8-OMe, 8-OH), together with a 4′-hydrophobic or electron-withdrawing group, provided the most potency and selectivity towards TNKSs. Co-crystal structures of selected compounds with TNKS-2 revealed that the protein around the 8-position is more hydrophobic in TNKS-2 compared to PARP-1/2, rationalising the selectivity. The NAD+-binding site contains a hydrophobic cavity which accommodates the 2-aryl group; in TNKS-2, this has a tunnel to the exterior but the cavity is closed in PARP-1. 8-Methyl-2-(4-trifluoromethylphenyl)quinazolin-4-one was identified as a potent and selective inhibitor of TNKSs and Wnt signalling. This compound and analogues could serve as molecular probes to study proliferative signalling and for development of inhibitors of TNKSs as drugs.
Display omitted
•Structure-Activity Relationship of 2-arylquinazolin-4-ones as tankyrase inhibitors.•8-Methyl group gives selectivity for tankyrases over PARP-1 and PARP-2.•Polar groups at the 8-position give poor isoform-selectivity.•Crystal structures rationalised the observed selectivity.•Reveal a novel, potent and selective tankyrase and Wnt signalling inhibitor.
Digital interventions deliver healthcare
the internet or smartphone application to support people's well-being and health. Yet uptake is relatively poor. Furthermore, several studies exploring ...attitudes towards digital interventions have found inconsistent attitudes. In addition to this, regional and cultural nuances may further influence attitudes to digital interventions.
This study aimed to understand New Zealand adults' attitudes towards digital interventions and their influences.
A mixed-method design consisting of a cross-sectional survey and semi-structured interviews found that New Zealand adults hold varied and complex attitudes towards digital interventions. Attitudes were found to be influenced by group membership and the scenarios in which digital interventions are made available. In addition, beliefs about the benefits and concerns surrounding digital interventions, knowledge, perceived views of others, and previous experience and confidence influenced these attitudes.
Findings indicated that digital interventions would be acceptable if offered as part of the healthcare service rather than a standalone intervention. Key modifiable factors that could positively influence attitudes were identified and could be leveraged to increase the perceived acceptability of digital interventions.
Indigenous communities often have poorer health outcomes and services under traditional models of care. In New Zealand, this holds true for Māori people who are tāngata whenua (the indigenous ...people). Several barriers exist that decrease the likelihood of indigenous communities often have poorer health outcomes and poor service fit under traditional models of care, including access issues, systemic and provider racism, and a lack of culturally safe and responsive services. Web-based interventions (WBIs) have been shown to be effective in supporting mental health and well-being and can overcome some of these barriers. Despite the large number of WBIs developed, more investigation is needed to know how well WBIs fit with an indigenous worldview and how they meet the needs of indigenous communities so that a digitally based future does not drive social and health inequities.
This study aims to explore the goodness-of-fit of WBIs of Māori individuals, the indigenous people of Aotearoa/New Zealand.
We used interviews (n=3) and focus groups (n=5) with 30 Māori participants to explore their views about WBIs. Interviews were analyzed using reflexive thematic analysis by members of the research team.
Overall, there was a perception that the design of WBIs did not align with the Māori worldview, which centers around people, relationships, spirituality, and holistic views of well-being. A total of 4 key themes and several subthemes emerged, indicating that WBIs were generally considered a poor fit for Māori. Specifically, the themes were as follows: (1) WBIs are disconnected from the core values of te ao Māori (the Māori worldview), (2) WBIs could be helpful in the right context, (3) there are significant barriers that may make it harder for Māori to use WBIs than other groups, and (4) ways to improve WBIs to help engagement with Māori.
While WBIs are often considered a way to reduce barriers to care, they may not meet the needs of Māori when used as a stand-alone intervention. If WBIs are continued to be offered, developers and researchers need to consider how to develop WBIs that are responsive and engaging to the needs of indigenous communities rather than driving inequities. Ideally, WBIs should be developed by the people they are intended for to fit with those populations' world views.
Pluripotency in embryonic stem cells is maintained through the activity of a small set of transcription factors centred around Oct4 and Nanog, which control the expression of ‘self‐renewal’ and ...‘differentiation’ genes. Here, we combine single‐cell quantitative immunofluorescence microscopy and gene expression analysis, together with theoretical modelling, to investigate how the activity of those factors is regulated. We uncover a key role for post‐translational regulation in the maintenance of pluripotency, which complements the well‐established transcriptional regulatory layer. Specifically, we find that the activity of a network of protein complexes involving Nanog, Oct4, Tcf3, and β‐catenin suffices to account for the behavior of ES cells under different conditions. Our results suggest that the function of the network is to buffer the transcriptional activity of Oct4, which appears to be the main determinant to exit pluripotency. The protein network explains the mechanisms underlying the gain and loss of function in different mutants, and brings us closer to a full understanding of the molecular basis of pluripotency.
The dynamic competition for complex formation between the pluripotency network components Oct4, Nanog, Tcf3, and β‐catenin prevents embryonic stem cell differentiation by controlling the levels of free Oct4.
Synopsis
The dynamic competition for complex formation between the pluripotency network components Oct4, Nanog, Tcf3, and β‐catenin prevents embryonic stem cell differentiation by controlling the levels of free Oct4.
Pluripotency is defined by the ratios between the levels of pluripotency factors rather than by their absolute levels.
Competition between different protein complexes involving Nanog, Oct4, Tcf3, and β‐catenin can account for the ratios associated with pluripotency.
The unstable pluripotency of Nanog mutant cells was shown to depend on the interactions between Oct4 and β‐catenin.
The function of the protein competition network is to control the levels of free Oct4, which are balanced by Nanog and β‐catenin in embryonic stem cells.
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