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  • 1
    Language: English
    In: SSRN Electronic Journal, 2015
    ISSN: SSRN Electronic Journal
    E-ISSN: 1556-5068
    Source: CrossRef
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  • 2
    Language: English
    In: Plant and soil, 2015, Vol.394(1), pp.109-126
    Description: AIMS: Stomata can close to avoid cavitation under decreased soil water availability. This closure can be triggered by hydraulic (‘H’) and/or chemical signals (‘C’, ‘H + C’). By combining plant hydraulic relations with a model for stomatal conductance, including chemical signalling, our aim was to derive direct relations that link soil water availability, expressed as fraction of roots in dry soil (fdᵣy), to transpiration reduction. METHODS: We used the mechanistic soil-root water flow model R-SWMS to verify this relation. Virtual split root experiments were simulated, comparing horizontal and vertical splits with varying fdᵣy and different strengths of stomatal regulation by chemical and hydraulic signals. RESULTS: Transpiration reduction predicted by the direct relations was in good agreement with numerical simulations. For small enough potential transpiration and large enough root hydraulic conductivity and stomatal sensitivity to chemical signalling isohydric plant behaviour originates from H + C control whereas anisohydric behaviour emerges from C control. For C control the relation between transpiration reduction and fdᵣy becomes independent of transpiration rate whereas H + C control results in stronger reduction for higher transpiration rates. CONCLUSION: Direct relations that link effective soil water potential and leaf water potential can describe different stomatal control resulting in contrasting behaviour. ; p. 109-126.
    Keywords: Plant Available Water ; Root Hydraulic Conductivity ; Stomata ; Leaf Water Potential ; Stomatal Conductance ; Roots ; Water Flow ; Mathematical Models ; Stomatal Movement ; Leaves ; Soil Water Potential
    ISSN: 0032-079X
    E-ISSN: 15735036
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  • 3
    Language: English
    In: Journal of European Public Policy, 01 August 2013, Vol.20(7), pp.1040-1055
    Description: This contribution considers the development of codecision over the last 20 years from a practitioner's point of view, from inside the European Parliament. It argues that the Parliament has adapted its behaviour and increased resources to ensure that the procedure works well and has used its...
    Keywords: Codecision ; Democracy ; European Parliament ; First Reading Agreements ; Lobbying ; Transparency ; Government ; Political Science
    ISSN: 1350-1763
    E-ISSN: 1466-4429
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  • 4
    Language: English
    In: Developmental Biology, 15 August 2013, Vol.380(2), pp.286-298
    Description: Islet-1 is a LIM-Homeodomain transcription factor with important functions for the development of distinct neuronal and non-neuronal cell populations. We show here that Islet-1 acts genetically downstream of Phox2B in cells of the sympathoadrenal cell lineage and that the development of sympathetic neurons and chromaffin cells is impaired in mouse embryos with a conditional deletion of Islet-1 controlled by the wnt1 promotor. Islet-1 is not essential for the initial differentiation of sympathoadrenal cells, as indicated by the correct expression of pan-neuronal and catecholaminergic subtype specific genes in primary sympathetic ganglia of Islet-1 deficient mouse embryos. However, our data indicate that the subsequent survival of sympathetic neuron precursors and their differentiation towards TrkA expressing neurons depends on Islet-1 function. In contrast to spinal sensory neurons, sympathetic neurons of Islet-1 deficient mice did not display ectopic expression of genes normally present in the CNS. In Islet-1 deficient mouse embryos the numbers of chromaffin cells were only mildly reduced, in contrast to that of sympathetic neurons, but the initiation of the adrenaline synthesizing enzyme PNMT was abrogated and the expression level of chromogranin A was diminished. Microarray analysis revealed that developing chromaffin cells of Islet-1 deficient mice displayed normal expression levels of TH, DBH and the transcription factors Phox2B, Mash-1, Hand2, Gata3 and Insm1, but the expression levels of the transcription factors Gata2 and Hand1, and AP-2ß were significantly reduced. Together our data indicate that Islet-1 is not essentially required for the initial differentiation of sympathoadrenal cells, but has an important function for the correct subsequent development of sympathetic neurons and chromaffin cells.
    Keywords: Islet-1 ; Sympathoadrenal Cell Lineage ; Sympathetic Neuron ; Chromaffin Cell ; Mouse ; Biology ; Zoology
    ISSN: 0012-1606
    E-ISSN: 1095-564X
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  • 5
    Language: English
    In: Plant and Soil, 2014, Vol.384(1), pp.93-112
    Description: Aims A simulation model to demonstrate that soil water potential can regulate transpiration, by influencing leaf water potential and/or inducing root production of chemical signals that are transported to the leaves. Methods Signalling impacts on the relationship between soil water potential and transpiration were simulated by coupling a 3D model for water flow in soil, into and through roots (Javaux et al. 2008) with a model for xylem transport of chemicals (produced as a function of local root water potential). Stomatal conductance was regulated by simulated leaf water potential (H) and/or foliar chemical signal concentrations (C; H+C). Split-root experiments were simulated by varying transpiration demands and irrigation placement. Results While regulation of stomatal conductance by chemical transport was unstable and oscillatory, simulated transpiration over time and root water uptake from the two soil compartments were similar for both H and H+C regulation. Increased stomatal sensitivity more strongly decreased transpiration, and decreased threshold root water potential (below which a chemical signal is produced) delayed transpiration reduction. Conclusions Although simulations with H+C regulation qualitatively reproduced transpiration of plants exposed to partial rootzone drying (PRD), long-term effects seemed negligible. Moreover, most transpiration responses to PRD could be explained by hydraulic signalling alone. Keywords Soil-root modeling * R-SWMS * Hormonal Signaling * Stomatal conductance * Partial rootzone drying
    Keywords: Soil-root modelling ; R-SWMS ; Hormonal signalling ; Stomatal conductance ; Partial rootzone drying
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 6
    Language: English
    In: European Security, 03 July 2015, Vol.24(3), pp.420-437
    Description: This contribution focuses on the European Parliament (EP) as an actor in European Union (EU) border policies. It situates the Parliament in the dynamics of the Schengen project and discusses the distinct role it plays therein, as well as its...
    Keywords: Schengen ; Eu Border Policy ; European Parliament ; Codecision ; Parliamentary Oversight ; Military & Naval Science
    ISSN: 0966-2839
    E-ISSN: 1746-1545
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  • 7
    Language: English
    In: Cell and Tissue Research, 2015, Vol.359(1), pp.333-341
    Description: Neuronal and neuroendocrine cells possess the capacity for Ca 2+ -regulated discharge of messenger molecules, which they release into synapses or the blood stream, respectively. The neural-crest-derived sympathoadrenal lineage gives rise to the sympathetic neurons of the autonomic nervous system and the neuroendocrine chromaffin cells of the adrenal medulla. These cells provide an excellent model system for studying common and distinct developmental mechanisms underlying the acquisition of neuroendocrine and neuronal properties. As catecholaminergic cells, they possess common markers related to noradrenaline synthesis, storage and release, but they also display diverging gene expression patterns and are morphologically and functionally different. The precise mechanisms that underlie the diversification of sympathoadrenal cells into neurons and neuroendocrine cells are not fully understood. However, in the past we could show that the establishment of a chromaffin phenotype does not depend on signals from the adrenal cortex and that chromaffin cells and sympathetic neurons apparently differ from the onset of their catecholaminergic differentiation. Nevertheless, the cues that specifically induce neuroendocrine features remain elusive. The early development of the progenitors of chromaffin cells and sympathetic neurons depends on a common set of transcription factors with overlapping but distinct influences on their development. In addition to the well-defined role of transcription factors as developmental regulators, our understanding of post-transcriptional gene regulation by microRNAs has substantially increased within the last few decades. This review highlights the major similarities and differences between chromaffin cells and sympathetic neurons, summarizes our current knowledge of the roles of selected transcription factors, microRNAs and environmental signals for the neuroendocrine differentiation of sympathoadrenal cells, and draws comparisons with the development of other endocrine and neuronal cells.
    Keywords: Neuroendocrine ; Chromaffin cells ; Sympathoadrenal cell lineage ; Transcription factors ; microRNAs
    ISSN: 0302-766X
    E-ISSN: 1432-0878
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  • 8
    Language: English
    In: Plant and Soil, 2017, Vol.415(1), pp.99-116
    Description: Background and aims The use of standard dynamic root architecture models to simulate root growth in soil containing macropores failed to reproduce experimentally observed root growth patterns. We thus developed a new, more mechanistic model approach for the simulation of root growth in structured soil. Methods In our alternative modelling approach, we distinguish between, firstly, the driving force for root growth, which is determined by the orientation of the previous root segment and the influence of gravitropism and, secondly, soil mechanical resistance to root growth. The latter is expressed by its inverse, soil mechanical conductance, and treated similarly to hydraulic conductivity in Darcy's law. At the presence of macropores, soil mechanical conductance is anisotropic, which leads to a difference between the direction of the driving force and the direction of the root tip movement. Results The model was tested using data from the literature, at pot scale, at macropore scale, and in a series of simulations where sensitivity to gravity and macropore orientation was evaluated. Conclusions Qualitative and quantitative comparisons between simulated and experimentally observed root systems showed good agreement, suggesting that the drawn analogy between soil water flow and root growth is a useful one.
    Keywords: Macropores ; Root architecture model ; Root growth direction ; R-SWMS
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 9
    Language: English
    In: Developmental Biology, 15 April 2015, Vol.400(2), pp.210-223
    Description: The development of sympathetic neurons and chromaffin cells is differentially controlled at distinct stages by various extrinsic and intrinsic signals. Here we use conditional deletion of in neural crest cells and noradrenergic neuroblasts to identify stage specific functions in sympathoadrenal lineages. Conditional Dicer1 knockout in neural crest cells of mice results in a rapid reduction in the size of developing sympathetic ganglia and adrenal medulla. In contrast, elimination in noradrenergic neuroblasts of animals affects sympathetic neuron survival starting at late embryonic stages and chromaffin cells persist at least until postnatal week 1. A differential function of signaling for the development of embryonic noradrenergic and cholinergic sympathetic neurons is demonstrated by the selective increase in the expression of Tlx3 and the cholinergic marker genes and at E16.5. The number of , and expressing noradrenergic neurons is strongly decreased in -deficient sympathetic ganglia at birth, whereas Tlx3 / Ret cholinergic neurons cells are spared from cell death. The postnatal death of chromaffin cells is preceded by the loss of and and an increase in the markers and , which suggests that is required for the maintenance of chromaffin cell differentiation and survival. Taken together, these findings demonstrate distinct stage and lineage specific functions of signaling in differentiation and survival of sympathetic neurons and adrenal chromaffin cells.
    Keywords: Sympathetic Neuron ; Chromaffin Cell ; Noradrenergic ; Cholinergic ; Survival ; Dicer1 ; Biology ; Zoology
    ISSN: 0012-1606
    E-ISSN: 1095-564X
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  • 10
    Language: English
    In: Developmental Biology, 2005, Vol.279(2), pp.501-508
    Description: Phox2B, a homeodomain transcription factor closely related to Phox2A, is expressed in peripheral and central noradrenergic neurons. In neural crest (NC) derivatives Phox2B is restricted to sympathetic and parasympathetic ganglia, enteric neurons, and adrenal and extraadrenal chromaffin cells. Similar to MASH-1, Phox2B has been implicated in synchronizing pan-neuronal and catecholaminergic phenotype-specific aspects of neurogenesis. The role of Phox2B for the differentiation of the neuroendocrine NC derivatives, the adrenal medullary chromaffin cells, has not been explored. We have previously reported that in MASH-1-deficient mice most chromaffin cells are arrested at the early neuroblast stage and lack catecholaminergic differentiation. We show now that in Phox2B knockout/lacZ knockin mice the maturation of presumptive chromaffin cells is arrested at an even earlier stage of development. The cells lack the catecholaminergic marker enzyme TH and fail to form a centrally located medulla. In contrast to MASH-1 (−/−) mice they do not express dHand, Phox2A, c-ret, neurofilament, neuron-specific tubulin, and NCAM and appear ultrastructurally more immature. Many of these cells die by apoptosis. Despite the complete lack of differentiation, few lacZ-positive adrenal cells can still be found at E16.5. We conclude that Phox2B regulates very early events in the differentiation of adrenal chromaffin cells distinct to steps, which essentially require MASH-1.
    Keywords: Sympathoadrenal Cell Lineage ; Adrenal Chromaffin Cells ; Phox2b ; Phox2a ; Dhand ; Mash-1 ; Biology ; Zoology
    ISSN: 0012-1606
    E-ISSN: 1095-564X
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