On the distribution of auxin concentrations in root horizontal layer cells
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Morphogen
Root hair
Root hair
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During development of multicellular organisms, morphogen is a kind of signaling molecules produced at a local region and transported into a development field, which acts as dose-dependent regulators of gene expression, directs and controls cellular differentiation. Some experiments showed that during embryo development, dynamical processes of morphogen transport always accompany the tissue growth. However, how tissue growth affects morphogen gradients remains to be explored. To answer this problem, we propose a reaction-diffusion-convection model for morphogen transport. For this model, we mainly investigate local accumulation times (LATs) of morphogen gradients, which are a measure for time of forming the steady state of morphogen gradients. In this paper, we simplify the method of calculating the LATs and use this method to obtain analytic expressions of the LATs for uniform and linear growth, respectively. Besides, for tissue nonuniform growth, we apply an approximation method of the LATs to study them. This paper shows that tissue growth can shorten the LATs of morphogen gradients.
Morphogen
Multicellular organism
Concentration gradient
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Successful biological development via spatial regulation of cell differentiation relies on action of multiple signaling molecules that are known as morphogens.It is now well established that signaling molecules create non-uniform concentration profiles, morphogen gradients, that activate different genes, leading to patterning in the developing embryos.The current view of the formation of morphogen gradients is that it is a result of complex reaction-diffusion processes that include the strongly localized production, diffusion and uniform degradation of signaling molecules.However, multiple experimental studies also suggest that the production of morphogen in many cases is delocalized.We develop a theoretical method that allows us to investigate the role of the delocalization in the formation of morphogen gradients.The approach is based on discrete-state stochastic models that can be solved exactly for arbitrary production lengths and production rates of morphogen molecules.Our analysis shows that the delocalization might have a strong effect on mechanisms of the morphogen gradient formation.The physical origin of this effect is discussed.
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MDR‐like ABC transporter AtPGP4 is involved in auxin‐mediated lateral root and root hair development
Here we show that related isoform AtPGP4 is expressed predominantly during early root development. AtPGP4 loss‐of‐function plants reveal enhanced lateral root initiation and root hair lengths both known to be under the control of auxin. Further, atpgp4 plants show altered sensitivities toward auxin and the auxin transport inhibitor, NPA. Finally, mutant roots reveal elevated free auxin levels and reduced auxin transport capacities. These results together with yeast growth assays suggest a direct involvement of AtPGP4 in auxin transport processes controlling lateral root and root hair development.
Root hair
Lateral root
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Naama Barkai1,2 and Ben-Zion Shilo1 Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel Correspondence: naama.barkai{at}weizmann.ac.il
Morphogen
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Root hair
Epidermis (zoology)
Elongation
Lateral root
Wild type
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Root hair
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Morphogen
Dynamics
Cell fate determination
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Cells at different positions in a developing tissue receive different concentrations of signaling molecules, called morphogens, and this influences their cell fate. Morphogen concentration gradients have been proposed to control patterning as well as growth in many developing tissues. Some outstanding questions about tissue patterning by morphogen gradients are the following: What are the mechanisms that regulate gradient formation and shape? Is the positional information encoded in the gradient sufficiently precise to determine the positions of target gene domain boundaries? What are the temporal dynamics of gradients and how do they relate to patterning and growth? These questions are inherently quantitative in nature and addressing them requires measuring morphogen concentrations in cells, levels of downstream signaling activity, and kinetics of morphogen transport. Here we first present methods for quantifying morphogen gradient shape in which the measurements can be calibrated to reflect actual morphogen concentrations. We then discuss using fluorescence recovery after photobleaching to study the kinetics of morphogen transport at the tissue level. Finally, we present particle tracking as a method to study morphogen intracellular trafficking.
Morphogen
Concentration gradient
Photobleaching
Developmental Biology
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Morphogens are long-range signaling molecules that pattern developing tissues in a concentration-dependent manner. The graded activity of morphogens within tissues exposes cells to different signal levels and leads to region-specific transcriptional responses and cell fates. In its simplest incarnation, a morphogen signal forms a gradient by diffusion from a local source and clearance in surrounding tissues. Responding cells often transduce morphogen levels in a linear fashion, which results in the graded activation of transcriptional effectors. The concentration-dependent expression of morphogen target genes is achieved by their different binding affinities for transcriptional effectors as well as inputs from other transcriptional regulators. Morphogen distribution and interpretation are the result of complex interactions between the morphogen and responding tissues. The response to a morphogen is dependent not simply on morphogen concentration but also on the duration of morphogen exposure and the state of the target cells. In this review, we describe the morphogen concept and discuss the mechanisms that underlie the generation, modulation, and interpretation of morphogen gradients.
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