Stem Cell Signalling Networks in Plants

The essential nature of meristematic tissues is addressed with reference to conceptual frameworks that have been developed to explain the behaviour of animal stem cells. Comparisons are made between different types of plant meristems with the objective of highlighting common themes that might illuminate underlying mechanisms. A more in depth comparison of the root and shoot apical meristems is made which suggests a common mechanism for maintaining stem cells. The relevance of organogenesis to stem cell maintenance is discussed, along with the nature of underlying mechanisms which help ensure that stem cell production is balanced with the depletion of cells through differentiation. Mechanisms that integrate stem cell behaviour in the whole plant are considered, with a focus on the roles of auxin and cytokinin. The review concludes with a brief discussion of epigenetic mechanisms that act to stabilise and maintain stem cell populations.     

Interleukin-6 Delays Gastric Emptying in Humans with Direct Effects on Glycemic Control

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Clinical Impact of ATR Checkpoint Signalling Failure in Humans

No abstract available.     

Adult Stem Cell Specification by Wnt Signaling in Muscle Regeneration

Recently, we describe a biological role for endogenous CD45+ stem cells in maintaining muscle integrity by participating in regeneration. Our experiments further establish that Wnt-signaling is the mechanism by which resident CD45+ adult stem cells are induced to undergo myogenic specification during muscle regeneration. Importantly, our study suggests that targeting the Wnt-pathway represents a promising therapeutic approach for the treatment of neuromuscular degenerative diseases.     

The Mechanism of Spontaneous Oscillatory Contractions in Skeletal Muscle

Most striated muscles generate steady contractile tension when activated, but some preparations, notably cardiac myocytes and slow-twitch fibers, may show spontaneous oscillatory contractions (SPOC) at low levels of activation. We have provided what we believe is new evidence that SPOC is a property of the contractile system at low actin-myosin affinity, whether caused by a thin-filament regulatory system or by other means. We present a quantitative single-sarcomere model for isotonic SPOC in skeletal muscle with three basic ingredients: i), actin and myosin filaments initially in partial overlap, ii), stretch activation by length-dependent changes in the lattice spacing, and iii), viscoelastic passive tension. Modeling examples are given for slow-twitch and fast-twitch fibers, with periods of 10 s and 4 s respectively. Isotonic SPOC occurs in a narrow domain of parameter values, with small minimum and maximum values for actin-myosin affinity, a minimum amount of passive tension, and a maximum transient response rate that explains why SPOC is favored in slow-twitch fibers. The model also predicts the contractile, relaxed and SPOC phases as a function of phosphate and ADP levels. The single-sarcomere model can also be applied to a whole fiber under auxotonic and fixed-end conditions if the remaining sarcomeres are treated as a viscoelastic load. Here the model predicts an upper limit for the load stiffness that leads to SPOC; this limit lies above the equivalent loads expected from the rest of the fiber.     

Early Cell Fate Decisions of Human Embryonic Stem Cells and Mouse Epiblast Stem Cells Are Controlled by the Same Signalling Pathways

Human embryonic stem cells have unique value for regenerative medicine, as they are capable of differentiating into a broad variety of cell types. Therefore, defining the signalling pathways that control early cell fate decisions of pluripotent stem cells represents a major task. Moreover, modelling the early steps of embryonic development in vitro may provide the best approach to produce cell types with native properties. Here, we analysed the function of key developmental growth factors such as Activin, FGF and BMP in the control of early cell fate decisions of human pluripotent stem cells. This analysis resulted in the development and validation of chemically defined culture conditions for achieving specification of human embryonic stem cells into neuroectoderm, mesendoderm and into extra-embryonic tissues. Importantly, these defined culture conditions are devoid of factors that could obscure analysis of developmental mechanisms or render the resulting tissues incompatible with future clinical applications. Importantly, the growth factor roles defined using these culture conditions similarly drove differentiation of mouse epiblast stem cells derived from post implantation embryos, thereby reinforcing the hypothesis that epiblast stem cells share a common embryonic identity with human pluripotent stem cells. Therefore the defined growth factor conditions described here represent an essential step toward the production of mature cell types from pluripotent stem cells in conditions fully compatible with clinical use ant also provide a general approach for modelling the early steps of mammalian embryonic development.     

The Dystrophin Glycoprotein Complex Regulates the Epigenetic Activation of Muscle Stem Cell Commitment

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Muscle Carnosine Is Associated with Cardiometabolic Risk Factors in Humans

BackgroundCarnosine is a naturally present dipeptide abundant in skeletal muscle and an over-the counter food additive. Animal data suggest a role of carnosine supplementation in the prevention and treatment of obesity, insulin resistance, type 2 diabetes and cardiovascular disease but only limited human data exists.ConclusionOur data shows that higher carnosine content in human skeletal muscle is positively associated with insulin resistance and fasting metabolic preference for glucose. Moreover, it is negatively associated with HDL-cholesterol and basal energy expenditure. Intervention studies targeting insulin resistance, metabolic and cardiovascular disease risk factors are necessary to evaluate its putative role in the prevention and management of type 2 diabetes and cardiovascular disease.     

Classification of Cell Signalling in Tissue Development

Abstract

The traditional classification of signalling in biological systems is insufficient and outdated and novel efforts must take into account advances in systems theory, information theory and linguistics. We present some of the classification systems currently used both within and outside of the biological field and discuss some specific aspects of the nature of signalling in tissue development. The analytical methods used in understanding non-biological networks provide a valuable vocabulary, which requires integration and a system of classification to further facilitate development.     

Modeling of Cancer Stem Cell State Transitions Predicts Therapeutic Response

Cancer stem cells (CSCs) possess capacity to both self-renew and generate all cells within a tumor, and are thought to drive tumor recurrence. Targeting the stem cell niche to eradicate CSCs represents an important area of therapeutic development. The complex nature of many interacting elements of the stem cell niche, including both intracellular signals and microenvironmental growth factors and cytokines, creates a challenge in choosing which elements to target, alone or in combination. Stochastic stimulation techniques allow for the careful study of complex systems in biology and medicine and are ideal for the investigation of strategies aimed at CSC eradication. We present a mathematical model of the breast cancer stem cell (BCSC) niche to predict population dynamics during carcinogenesis and in response to treatment. Using data from cell line and mouse xenograft experiments, we estimate rates of interconversion between mesenchymal and epithelial states in BCSCs and find that EMT/MET transitions occur frequently. We examine bulk tumor growth dynamics in response to alterations in the rate of symmetric self-renewal of BCSCs and find that small changes in BCSC behavior can give rise to the Gompertzian growth pattern observed in breast tumors. Finally, we examine stochastic reaction kinetic simulations in which elements of the breast cancer stem cell niche are inhibited individually and in combination. We find that slowing self-renewal and disrupting the positive feedback loop between IL-6, Stat3 activation, and NF-κB signaling by simultaneous inhibition of IL-6 and HER2 is the most effective combination to eliminate both mesenchymal and epithelial populations of BCSCs. Predictions from our model and simulations show excellent agreement with experimental data showing the efficacy of combined HER2 and Il-6 blockade in reducing BCSC populations. Our findings will be directly examined in a planned clinical trial of combined HER2 and IL-6 targeted therapy in HER2-positive breast cancer.     

Donor-Derived Brain Tumor Following Neural Stem Cell Transplantation in an Ataxia Telangiectasia Patient

Background

Neural stem cells are currently being investigated as potential therapies for neurodegenerative diseases, stroke, and trauma. However, concerns have been raised over the safety of this experimental therapeutic approach, including, for example, whether there is the potential for tumors to develop from transplanted stem cells.

Methods and Findings

A boy with ataxia telangiectasia (AT) was treated with intracerebellar and intrathecal injection of human fetal neural stem cells. Four years after the first treatment he was diagnosed with a multifocal brain tumor. The biopsied tumor was diagnosed as a glioneuronal neoplasm. We compared the tumor cells and the patient''s peripheral blood cells by fluorescent in situ hybridization using X and Y chromosome probes, by PCR for the amelogenin gene X- and Y-specific alleles, by MassArray for the ATM patient specific mutation and for several SNPs, by PCR for polymorphic microsatellites, and by human leukocyte antigen (HLA) typing. Molecular and cytogenetic studies showed that the tumor was of nonhost origin suggesting it was derived from the transplanted neural stem cells. Microsatellite and HLA analysis demonstrated that the tumor is derived from at least two donors.

Conclusions

This is the first report of a human brain tumor complicating neural stem cell therapy. The findings here suggest that neuronal stem/progenitor cells may be involved in gliomagenesis and provide the first example of a donor-derived brain tumor. Further work is urgently needed to assess the safety of these therapies.     

RhoA Regulates Calcium-Independent Periodic Contractions of the Cell Cortex

When microtubules are depolymerized in spreading cells, they experience morphological oscillations characterized by a period of about a minute, indicating that normal interactions between the microfilament and microtubule systems have been significantly altered. This experimental system provides a test bed for the development of both fine- and coarse-grained models of complex motile processes, but such models need to be adequately informed by experiment. Using criteria based on Fourier transform analysis, we detect spontaneous oscillations in spreading cells. However, their amplitude and tendency to operate at a single frequency are greatly enhanced by microtubule depolymerization. Knockdown of RhoA and addition of various inhibitors of the downstream effector of RhoA, Rho kinase, block oscillatory behavior. Inhibiting calcium fluxes from endoplasmic reticulum stores and from the extracellular medium does not significantly affect the ability of cells to oscillate, indicating that calcium plays a subordinate regulatory role compared to Rho. We characterized the dynamic structure of the oscillating cell by light, fluorescence, and electron microscopy, showing how oscillating cells are dynamically polarized in terms of their overall morphology, f-actin and phosphorylated myosin light chain distribution, and nuclear position and shape. Not only will these studies guide future experiments, they will also provide a framework for the development of refined mathematical models of the oscillatory process.     

外胚间充质干细胞构建组织工程骨骼肌的应用研究

目的:探讨利用大鼠颌突外胚间充质干细胞构建组织工程骨骼肌的可行性,并观察对骨骼肌缺损的修复重建的促进效应。方法:取妊娠E 11.5胎鼠颌突外胚间充质干细胞,纯化后在含5ml/L体积浓度二甲基亚砜的DMEM/F12培养基中诱导分化为骨骼肌样细胞,将细胞种植于BAM膜上培养形成组织工程骨骼肌。将其移植入大鼠骨骼肌缺损模型,手术后14 d观察骨骼肌恢复情况,同期进行组织学及免疫组化染色鉴定。结果:经诱导后外胚间充质干细胞可向骨骼肌样细胞转化,构建的组织工程骨骼肌可加速缺损的修复重建,组织学染色显示外胚间充质干细胞具有正常骨骼肌的组织形态,可表达成肌相关蛋白MyOD。结论:诱导后的外胚间充质干细胞可作为种子细胞构建组织工程骨骼肌,本实验为临床肌肉的缺损修复奠定了理论基础。     

Receptor Tyrosine Kinase (RTK) Signalling in the Control of Neural Stem and Progenitor Cell (NSPC) Development

Important developmental responses are elicited in neural stem and progenitor cells (NSPC) by activation of the receptor tyrosine kinases (RTK), including the fibroblast growth factor receptors, epidermal growth factor receptor, platelet-derived growth factor receptors and insulin-like growth factor receptor (IGF1R). Signalling through these RTK is necessary and sufficient for driving a number of developmental processes in the central nervous system. Within each of the four RTK families discussed here, receptors are activated by sets of ligands that do not cross-activate receptors of the other three families, and therefore, their activation can be independently regulated by ligand availability. These RTK pathways converge on a conserved core of signalling molecules, but differences between the receptors in utilisation of signalling molecules and molecular adaptors for intracellular signal propagation become increasingly apparent. Intracellular inhibitors of RTK signalling are widely involved in the regulation of developmental signalling in NSPC and often determine developmental outcomes of RTK activation. In addition, cellular responses of NSPC to the activation of a given RTK may be significantly modulated by signal strength. Cellular propensity to respond also plays a role in developmental outcomes of RTK signalling. In combination, these mechanisms regulate the balance between NSPC maintenance and differentiation during development and in adulthood. Attribution of particular developmental responses of NSPC to specific pathways of RTK signalling becomes increasingly elucidated. Co-activation of several RTK in developing NSPC is common, and analysis of co-operation between their signalling pathways may advance knowledge of RTK role in NSPC development.     

Contribution of Herpesvirus Specific CD8 T Cells to Anti-Viral T Cell Response in Humans

Herpesviruses infect most humans. Their infections can be associated with pathological conditions and significant changes in T cell repertoire but evidences of symbiotic effects of herpesvirus latency have never been demonstrated. We tested the hypothesis that HCMV and EBV-specific CD8 T cells contribute to the heterologous anti-viral immune response. Volume of activated/proliferating virus-specific and total CD8 T cells was evaluated in 50 patients with acute viral infections: 20 with HBV, 12 with Dengue, 12 with Influenza, 3 with Adenovirus infection and 3 with fevers of unknown etiology. Virus-specific (EBV, HCMV, Influenza) pentamer+ and total CD8 T cells were analyzed for activation (CD38/HLA-DR), proliferation (Ki-67/Bcl-2_low) and cytokine production. We observed that all acute viral infections trigger an expansion of activated/proliferating CD8 T cells, which differs in size depending on the infection but is invariably inflated by CD8 T cells specific for persistent herpesviruses (HCMV/EBV). CD8 T cells specific for other non-related non persistent viral infection (i.e. Influenza) were not activated. IL-15, which is produced during acute viral infections, is the likely contributing mechanism driving the selective activation of herpesvirus specific CD8 T cells. In addition we were able to show that herpesvirus specific CD8 T cells displayed an increased ability to produce the anti-viral cytokine interferon-γ during the acute phase of heterologous viral infection. Taken together, these data demonstrated that activated herpesvirus specific CD8 T cells inflate the activated/proliferating CD8 T cells population present during acute viral infections in human and can contribute to the heterologous anti-viral T cell response.     

Successful Reconstruction of Damaged Ocular Outer Surface in Humans Using Limbal and Conjuctival Stem Cell Culture Methods

When the ocular outer surface is badly damaged, subsequent corneal transplantation fails due to the absence of basal cells that are needed to support the graft. With the realization that the limbus and the conjunctiva have adult stem cells that can be cultured, it has been possible for us to explant culture these on de-epithelized human amniotic membrane, and to graft the resulting viable and transparent epithelium to 125 needy human patients with success. Ultrastructural, histological, biochemical and immunological assays establish the identity of the cells and the tissue formed.     

PAX3 Confers Functional Heterogeneity in Skeletal Muscle Stem Cell Responses to Environmental Stress

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