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1
de Keijzer, Jeroen, Alejandra Freire Rios und Viola Willemsen. „Physcomitrium patens: A Single Model to Study Oriented Cell Divisions in 1D to 3D Patterning“. International Journal of Molecular Sciences 22, Nr. 5 (05.03.2021): 2626. http://dx.doi.org/10.3390/ijms22052626.
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Development in multicellular organisms relies on cell proliferation and specialization. In plants, both these processes critically depend on the spatial organization of cells within a tissue. Owing to an absence of significant cellular migration, the relative position of plant cells is virtually made permanent at the moment of division. Therefore, in numerous plant developmental contexts, the (divergent) developmental trajectories of daughter cells are dependent on division plane positioning in the parental cell. Prior to and throughout division, specific cellular processes inform, establish and execute division plane control. For studying these facets of division plane control, the moss Physcomitrium (Physcomitrella) patens has emerged as a suitable model system. Developmental progression in this organism starts out simple and transitions towards a body plan with a three-dimensional structure. The transition is accompanied by a series of divisions where cell fate transitions and division plane positioning go hand in hand. These divisions are experimentally highly tractable and accessible. In this review, we will highlight recently uncovered mechanisms, including polarity protein complexes and cytoskeletal structures, and transcriptional regulators, that are required for 1D to 3D body plan formation.
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Concha, M. L., und R. J. Adams. „Oriented cell divisions and cellular morphogenesis in the zebrafish gastrula and neurula: a time-lapse analysis“. Development 125, Nr. 6 (15.03.1998): 983–94. http://dx.doi.org/10.1242/dev.125.6.983.
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We have taken advantage of the optical transparency of zebrafish embryos to investigate the patterns of cell division, movement and shape during early stages of development of the central nervous system. The surface-most epiblast cells of gastrula and neurula stage embryos were imaged and analysed using a computer-based, time-lapse acquisition system attached to a differential interference contrast (DIC) microscope. We find that the onset of gastrulation is accompanied by major changes in cell behaviour. Cells collect into a cohesive sheet, apparently losing independent motility and integrating their behaviour to move coherently over the yolk in a direction that is the result of two influences: towards the vegetal pole in the movements of epiboly and towards the dorsal midline in convergent movements that strengthen throughout gastrulation. Coincidentally, the plane of cell division becomes aligned to the surface plane of the embryo and oriented in the anterior-posterior (AP) direction. These behaviours begin at the blastoderm margin and propagate in a gradient towards the animal pole. Later in gastrulation, cells undergo increasingly mediolateral-directed elongation and autonomous convergence movements towards the dorsal midline leading to an enormous extension of the neural axis. Around the equator and along the dorsal midline of the gastrula, persistent AP orientation of divisions suggests that a common mechanism may be involved but that neither oriented cell movements nor shape can account for this alignment. When the neural plate begins to differentiate, there is a gradual transition in the direction of cell division from AP to the mediolateral circumference (ML). ML divisions occur in both the ventral epidermis and dorsal neural plate. In the neural plate, ML becomes the predominant orientation of division during neural keel and nerve rod stages and, from late neural keel stage, divisions are concentrated at the dorsal midline and generate bilateral progeny (C. Papan and J. A. Campos-Ortega (1994) Roux's Arch. Dev. Biol. 203, 178–186). Coincidentally, cells on the ventral surface also orient their divisions in the ML direction, cleaving perpendicular to the direction in which they are elongated. The ML alignment of epidermal divisions is well correlated with cell shape but ML divisions within the neuroepithelium appear to be better correlated with changes in tissue morphology associated with neurulation.
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Hart, Kevin C., Jiongyi Tan, Kathleen A. Siemers, Joo Yong Sim, Beth L. Pruitt, W. James Nelson und Martijn Gloerich. „E-cadherin and LGN align epithelial cell divisions with tissue tension independently of cell shape“. Proceedings of the National Academy of Sciences 114, Nr. 29 (03.07.2017): E5845—E5853. http://dx.doi.org/10.1073/pnas.1701703114.
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Tissue morphogenesis requires the coordinated regulation of cellular behavior, which includes the orientation of cell division that defines the position of daughter cells in the tissue. Cell division orientation is instructed by biochemical and mechanical signals from the local tissue environment, but how those signals control mitotic spindle orientation is not fully understood. Here, we tested how mechanical tension across an epithelial monolayer is sensed to orient cell divisions. Tension across Madin–Darby canine kidney cell monolayers was increased by a low level of uniaxial stretch, which oriented cell divisions with the stretch axis irrespective of the orientation of the cell long axis. We demonstrate that stretch-induced division orientation required mechanotransduction through E-cadherin cell–cell adhesions. Increased tension on the E-cadherin complex promoted the junctional recruitment of the protein LGN, a core component of the spindle orientation machinery that binds the cytosolic tail of E-cadherin. Consequently, uniaxial stretch triggered a polarized cortical distribution of LGN. Selective disruption of trans engagement of E-cadherin in an otherwise cohesive cell monolayer, or loss of LGN expression, resulted in randomly oriented cell divisions in the presence of uniaxial stretch. Our findings indicate that E-cadherin plays a key role in sensing polarized tensile forces across the tissue and transducing this information to the spindle orientation machinery to align cell divisions.
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Kimmel, C. B., R. M. Warga und D. A. Kane. „Cell cycles and clonal strings during formation of the zebrafish central nervous system“. Development 120, Nr. 2 (01.02.1994): 265–76. http://dx.doi.org/10.1242/dev.120.2.265.
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Cell lineage analysis of central nervous system progenitors during gastrulation and early segmentation in the zebrafish reveals consistent coupling of specific morphogenetic behaviors with particular cell cycles. Cells in single clones divide very synchronously. Cell divisions become progressively oriented, and act synergistically with oriented intercalations during the interphases of zygotic cell cycles 15 and 16 to extend a single lineage into a long, discontinuous string of cells aligned with the nascent embryonic axis. Dorsalwards convergence brings the string to the midline and, once there, cells enter division 16. This division, or sometimes the next one, and the following cell movement reorient to separate siblings across the midline. This change converts the single string into a bilateral pair of strings, one forming a part of each side of the neural tube. The stereotyped cellular behaviors appear to account for the previously reported clonal restriction in cell fate and to underlie morphogenesis of a midline organ of proper length and bilateral shape. Regulation of cellular morphogenesis could be cell-cycle dependent.
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Torres-Ruiz, R. A., und G. Jurgens. „Mutations in the FASS gene uncouple pattern formation and morphogenesis in Arabidopsis development“. Development 120, Nr. 10 (01.10.1994): 2967–78. http://dx.doi.org/10.1242/dev.120.10.2967.
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The pattern of cell division is very regular in Arabidopsis embryogenesis, enabling seedling structures to be traced back to groups of cells in the early embryo. Recessive mutations in the FASS gene alter the pattern of cell division from the zygote, without interfering with embryonic pattern formation: although no primordia of seedling structures can be recognised by morphological criteria at the early-heart stage, all elements of the body pattern are differentiated in the seedling. fass seedlings are strongly compressed in the apical-basal axis and enlarged circumferentially, notably in the hypocotyl. Depending on the width of the hypocotyl, fass seedlings may have up to three supernumerary cotyledons. fass mutants can develop into tiny adult plants with all parts, including floral organs, strongly compressed in their longitudinal axis. At the cellular level, fass mutations affect cell elongation and orientation of cell walls but do not interfere with cell polarity as evidenced by the unequal division of the zygote. The results suggest that the FASS gene is required for morphogenesis, i.e., oriented cell divisions and position-dependent cell shape changes generating body shape, but not for cell polarity which seems essential for pattern formation.
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Kaucka, Marketa, Evgeny Ivashkin, Daniel Gyllborg, Tomas Zikmund, Marketa Tesarova, Jozef Kaiser, Meng Xie et al. „Analysis of neural crest–derived clones reveals novel aspects of facial development“. Science Advances 2, Nr. 8 (August 2016): e1600060. http://dx.doi.org/10.1126/sciadv.1600060.
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Cranial neural crest cells populate the future facial region and produce ectomesenchyme-derived tissues, such as cartilage, bone, dermis, smooth muscle, adipocytes, and many others. However, the contribution of individual neural crest cells to certain facial locations and the general spatial clonal organization of the ectomesenchyme have not been determined. We investigated how neural crest cells give rise to clonally organized ectomesenchyme and how this early ectomesenchyme behaves during the developmental processes that shape the face. Using a combination of mouse and zebrafish models, we analyzed individual migration, cell crowd movement, oriented cell division, clonal spatial overlapping, and multilineage differentiation. The early face appears to be built from multiple spatially defined overlapping ectomesenchymal clones. During early face development, these clones remain oligopotent and generate various tissues in a given location. By combining clonal analysis, computer simulations, mouse mutants, and live imaging, we show that facial shaping results from an array of local cellular activities in the ectomesenchyme. These activities mostly involve oriented divisions and crowd movements of cells during morphogenetic events. Cellular behavior that can be recognized as individual cell migration is very limited and short-ranged and likely results from cellular mixing due to the proliferation activity of the tissue. These cellular mechanisms resemble the strategy behind limb bud morphogenesis, suggesting the possibility of common principles and deep homology between facial and limb outgrowth.
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Wong, Margaret N., Timothy P. Nguyen, Ting-Hsuan Chen, Jeffrey J. Hsu, Xingjuan Zeng, Aman Saw, Eric M. Demer, Xin Zhao, Yin Tintut und Linda L. Demer. „Preferred mitotic orientation in pattern formation by vascular mesenchymal cells“. American Journal of Physiology-Heart and Circulatory Physiology 303, Nr. 12 (15.12.2012): H1411—H1417. http://dx.doi.org/10.1152/ajpheart.00625.2012.
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Cellular self-organization is essential to physiological tissue and organ development. We previously observed that vascular mesenchymal cells, a multipotent subpopulation of aortic smooth muscle cells, self-organize into macroscopic, periodic patterns in culture. The patterns are produced by cells gathering into raised aggregates in the shape of nodules or ridges. To determine whether these patterns are accounted for by an oriented pattern of cell divisions or postmitotic relocation of cells, we acquired time-lapse, videomicrographic phase-contrast, and fluorescence images during self-organization. Cell division events were analyzed for orientation of daughter cells in mitoses during separation and their angle relative to local cell alignment, and frequency distribution of the mitotic angles was analyzed by both histographic and bin-free statistical methods. Results showed a statistically significant preferential orientation of daughter cells along the axis of local cell alignment as early as day 8, just before aggregate formation. This alignment of mitotic axes was also statistically significant at the time of aggregate development ( day 11) and after aggregate formation was complete ( day 15). Treatment with the nonmuscle myosin II inhibitor, blebbistatin, attenuated alignment of mitotic orientation, whereas Rho kinase inhibition eliminated local cell alignment, suggesting a role for stress fiber orientation in this self-organization. Inhibition of cell division using mitomycin C reduced the macroscopic pattern formation. Time-lapse monitoring of individual cells expressing green fluorescent protein showed postmitotic movement of cells into neighboring aggregates. These findings suggest that polarization of mitoses and postmitotic migration of cells both contribute to self-organization into periodic, macroscopic patterns in vascular stem cells.
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Wick, S. M. „Microtubules in plant cell division“. Proceedings, annual meeting, Electron Microscopy Society of America 47 (06.08.1989): 758–59. http://dx.doi.org/10.1017/s0424820100155761.
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Immunofluorescence microscopy has proven to be a valuable accompaniment to electron microscopy for study of the cytoskeleton of plant cells. Whereas electron microscopy provides greater resolution and details of the spatial relationships of the cytoskeleton to other cellular components, fluorescence visualization makes it possible to see the three-dimensional organization of cytoskeletal elements without laborious reconstruction of views from serial sections. An area in which immunofluorescence microscopy has been useful is the investigation of how plant cells organize and position the various microtubule arrays that are utilized during mitosis, cytokinesis and cell expansion phases. One of the earliest indications of an impending division in a meristematic plant cell is the formation of a preprophase band of microtubules in the cell cortex, at the site where the new wall will be placed at the subsequent cytokinesis. At its later stages, the band is narrower than when first identifiable. In most cells, preprophase band microtubules have the same general orientation as the preceding interphase microtubules, and so preprophase band formation here could, in theory, be achieved by lateral bundling of microtubules.Cells in which the division site and the preprophase band that marks it are not oriented parallel to interphase microtubules are found in stomatal complexes of grass leaves . Fig. 1 illustrates the arrangement of two such cell types: the guard mother cell, which divides lengthwise to form two guard cells, side-by-side, and the subsidiary mother cell, which undergoes a very asymmetric division to produce one of the pair of lens-shaped subsidiary cells that flank the guard cells. Interphase and preprophase arrangements of microtubules for each cell type are diagrammed in Figs. 2-4. In order to examine how these cell types achieve the reorientation of microtubules that is necessary to progress from interphase to preprophase, sheets of epidermis containing actively dividing stomatal complex cells were examined with immunofluorescence microscopy using antibodies to tubulin. Thin epidermal slices of leaves were fixed and glued down to a slide, whereupon cell walls were enzymatically weakened so that unwanted cell layers could be removed . Because waves of division pass along grass leaves, cells of the same type in a given file tend to be at similar stages, which facilitates deduction of the developmental pattern.
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Ling, Ji, Maria Sckaff, Manisha Tiwari, Yifang Chen, Jingting Li, Jackson Jones und George L. Sen. „RAS-mediated suppression of PAR3 and its effects on SCC initiation and tissue architecture occur independently of hyperplasia“. Journal of Cell Science 133, Nr. 23 (10.11.2020): jcs249102. http://dx.doi.org/10.1242/jcs.249102.
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ABSTRACTProper epithelial development and homeostasis depends on strict control of oriented cell division. Current evidence shows that this process is regulated by intrinsic polarity factors and external spatial cues. Owing to the lack of an appropriate model system that can recapitulate the architecture of the skin, deregulation of spindle orientation in human epithelial carcinoma has never been investigated. Here, using an inducible model of human squamous cell carcinoma (SCC), we demonstrate that RAS-dependent suppression of PAR3 (encoded by PARD3) accelerates epithelial disorganization during early tumorigenesis. Diminished PAR3 led to loss of E-cadherin-mediated cell adhesion, which in turn contributed to misoriented cell division. Pharmacological inhibition of the MAPK pathway downstream of RAS activation reversed the defects in PAR3 expression, E-cadherin-mediated cell adhesion and mitotic spindle orientation. Thus, temporal analysis of human neoplasia provides a powerful approach to study cellular and molecular transformations during early oncogenesis, which allowed identification of PAR3 as a critical regulator of tissue architecture during initial human SCC development.
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Crittenden, Sarah L., Kimberly A. Leonhard, Dana T. Byrd und Judith Kimble. „Cellular Analyses of the Mitotic Region in the Caenorhabditis elegans Adult Germ Line“. Molecular Biology of the Cell 17, Nr. 7 (Juli 2006): 3051–61. http://dx.doi.org/10.1091/mbc.e06-03-0170.
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The Caenorhabditis elegans germ line provides a model for understanding how signaling from a stem cell niche promotes continued mitotic divisions at the expense of differentiation. Here we report cellular analyses designed to identify germline stem cells within the germline mitotic region of adult hermaphrodites. Our results support several conclusions. First, all germ cells within the mitotic region are actively cycling, as visualized by bromodeoxyuridine (BrdU) labeling. No quiescent cells were found. Second, germ cells in the mitotic region lose BrdU label uniformly, either by movement of labeled cells into the meiotic region or by dilution, probably due to replication. No label-retaining cells were found in the mitotic region. Third, the distal tip cell niche extends processes that nearly encircle adjacent germ cells, a phenomenon that is likely to anchor the distal-most germ cells within the niche. Fourth, germline mitoses are not oriented reproducibly, even within the immediate confines of the niche. We propose that germ cells in the distal-most rows of the mitotic region serve as stem cells and more proximal germ cells embark on the path to differentiation. We also propose that C. elegans adult germline stem cells are maintained by proximity to the niche rather than by programmed asymmetric divisions.
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Fanwoua, Julienne, Pieter de Visser, Ep Heuvelink, Gerco Angenent, Xinyou Yin, Leo Marcelis und Paul Struik. „Response of Cell Division and Cell Expansion to Local Fruit Heating in Tomato Fruit“. Journal of the American Society for Horticultural Science 137, Nr. 5 (September 2012): 294–301. http://dx.doi.org/10.21273/jashs.137.5.294.
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To improve our understanding of fruit growth responses to temperature, it is important to analyze temperature effects on underlying fruit cellular processes. This study aimed at analyzing the response of tomato (Solanum lycopersicum) fruit size to heating as affected by changes in cell number and cell expansion in different directions. Individual trusses were enclosed into cuvettes and heating was applied either only during the first 7 days after anthesis (DAA), from 7 DAA until fruit maturity (breaker stage), or both. Fruit size and histological characteristics in the pericarp were measured. Heating fruit shortened fruit growth period and reduced final fruit size. Reduction in final fruit size of early-heated fruit was mainly associated with reduction in final pericarp cell volume. Early heating increased the number of cell layers in the pericarp but did not affect the total number of pericarp cells. These results indicate that in the tomato pericarp, periclinal cell divisions respond differently to temperature than anticlinal or randomly oriented cell divisions. Late heating only decreased pericarp thickness significantly. Continuously heating fruit reduced anticlinal cell expansion (direction perpendicular to fruit skin) more than periclinal cell expansion (direction parallel to fruit skin). This study emphasizes the need to measure cell expansion in more than one dimension in histological studies of fruit.
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Mathias, Sonja, Igor Adameyko, Andreas Hellander und Jochen Kursawe. „Contributions of cell behavior to geometric order in embryonic cartilage“. PLOS Computational Biology 19, Nr. 11 (29.11.2023): e1011658. http://dx.doi.org/10.1371/journal.pcbi.1011658.
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During early development, cartilage provides shape and stability to the embryo while serving as a precursor for the skeleton. Correct formation of embryonic cartilage is hence essential for healthy development. In vertebrate cranial cartilage, it has been observed that a flat and laterally extended macroscopic geometry is linked to regular microscopic structure consisting of tightly packed, short, transversal clonar columns. However, it remains an ongoing challenge to identify how individual cells coordinate to successfully shape the tissue, and more precisely which mechanical interactions and cell behaviors contribute to the generation and maintenance of this columnar cartilage geometry during embryogenesis. Here, we apply a three-dimensional cell-based computational model to investigate mechanical principles contributing to column formation. The model accounts for clonal expansion, anisotropic proliferation and the geometrical arrangement of progenitor cells in space. We confirm that oriented cell divisions and repulsive mechanical interactions between cells are key drivers of column formation. In addition, the model suggests that column formation benefits from the spatial gaps created by the extracellular matrix in the initial configuration, and that column maintenance is facilitated by sequential proliferative phases. Our model thus correctly predicts the dependence of local order on division orientation and tissue thickness. The present study presents the first cell-based simulations of cell mechanics during cranial cartilage formation and we anticipate that it will be useful in future studies on the formation and growth of other cartilage geometries.
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Hoops, H. J. „Flagellar, cellular and organismal polarity in Volvox carteri“. Journal of Cell Science 104, Nr. 1 (01.01.1993): 105–17. http://dx.doi.org/10.1242/jcs.104.1.105.
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It has previously been shown that the flagellar apparatus of the mature Volvox carteri somatic cell lacks the 180° rotational symmetry typical of most unicellular green algae. This asymmetry has been postulated to be the result of rotation of each half of the flagellar apparatus. Here it is shown that V. carteri axonemes contain polarity markers that are similar to those found in Chlamydomonas, except that in V. carteri the number one doublets do not face each other as they do in Chlamydomonas but are oriented in parallel and at approximately right angles to the line that connects the flagella. Thus, the rotational orientations of the axonemes are consistent with the postulate that the flagella of V. carteri have rotated in opposite directions, as was predicted earlier from the positions of the basal fibers and microtubular rootlets. Moreover, high-speed cinephotomicrographic analysis shows that the V. carteri flagellar effective strokes are also oriented in approximately the same direction, and in parallel planes. These results suggest that the direction of the effective stroke in both Chlamydomonas and Volvox is fixed, and that rotation of the axoneme is the cause of the differences in flagellar motility observed between Chlamydomonas and Volvox. These differences are probably essential for effective organismal motility. Cellular polarity of V. carteri can be related to that of Chlamydomonas after taking into account the developmental reorientation of flagellar apparatus components. This reorientation also results in the movement of the eyespot from a position nearer one of the flagellar bases to a position approximately equidistant between them. By analogy to Chlamydomonas, the anti side of the V. carteri somatic cell faces the spheroid anterior, the syn side faces the spheroid posterior. The cis side of the cell is to the cell's left (the right to an outside observer), although it cannot be described solely on the basis of eyespot position as it can in Chlamydomonas, while the trans side is to the cell's right. It follows that if the direction of the effective flagellar stroke is specified by structural features, then effective organismal motility in V. carteri, will be accomplished only if the cells are held in the proper orientation with respect to one another. The simplest arrangement that will yield both progression and rotation in ovoid or spherical colonies composed of biflagellate isokont cells is one in which the cells are arranged with rotational symmetry about the anterior-posterior axis of the spheroid. Analysis of the polarity of somatic cells from throughout the spheroid shows that it is constructed with just such symmetry. This symmetry probably originates with the very first divisions.
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Jacobs, C. W., A. E. Adams, P. J. Szaniszlo und J. R. Pringle. „Functions of microtubules in the Saccharomyces cerevisiae cell cycle.“ Journal of Cell Biology 107, Nr. 4 (01.10.1988): 1409–26. http://dx.doi.org/10.1083/jcb.107.4.1409.
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We used the inhibitor nocodazole in conjunction with immunofluorescence and electron microscopy to investigate microtubule function in the yeast cell cycle. Under appropriate conditions, this drug produced a rapid and essentially complete disassembly of cytoplasmic and intranuclear microtubules, accompanied by a rapid and essentially complete block of cellular and nuclear division. These effects were similar to, but more profound than, the effects of the related drug methyl benzimidazole carbamate (MBC). In the nocodazole-treated cells, the selection of nonrandom budding sites, the formation of chitin rings and rings of 10-nm filaments at those sites, bud emergence, differential bud enlargement, and apical bud growth appeared to proceed normally, and the intracellular distribution of actin was not detectably perturbed. Thus, the cytoplasmic microtubules are apparently not essential for the establishment of cell polarity and the localization of cell-surface growth. In contrast, nocodazole profoundly affected the behavior of the nucleus. Although spindle-pole bodies (SPBs) could duplicate in the absence of microtubules, SPB separation was blocked. Moreover, complete spindles present at the beginning of drug treatment appeared to collapse, drawing the opposed SPBs and associated nuclear envelope close together. Nuclei did not migrate to the mother-bud necks in nocodazole-treated cells, although nuclei that had reached the necks before drug treatment remained there. Moreover, the double SPBs in arrested cells were often not oriented toward the budding sites, in contrast to the situation in normal cells. Thus, microtubules (cytoplasmic, intranuclear, or both) appear to be necessary for the migration and proper orientation of the nucleus, as well as for SPB separation, spindle function, and nuclear division.
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Burg, Max F., Santiago A. Cadena, George H. Denfield, Edgar Y. Walker, Andreas S. Tolias, Matthias Bethge und Alexander S. Ecker. „Learning divisive normalization in primary visual cortex“. PLOS Computational Biology 17, Nr. 6 (07.06.2021): e1009028. http://dx.doi.org/10.1371/journal.pcbi.1009028.
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Divisive normalization (DN) is a prominent computational building block in the brain that has been proposed as a canonical cortical operation. Numerous experimental studies have verified its importance for capturing nonlinear neural response properties to simple, artificial stimuli, and computational studies suggest that DN is also an important component for processing natural stimuli. However, we lack quantitative models of DN that are directly informed by measurements of spiking responses in the brain and applicable to arbitrary stimuli. Here, we propose a DN model that is applicable to arbitrary input images. We test its ability to predict how neurons in macaque primary visual cortex (V1) respond to natural images, with a focus on nonlinear response properties within the classical receptive field. Our model consists of one layer of subunits followed by learned orientation-specific DN. It outperforms linear-nonlinear and wavelet-based feature representations and makes a significant step towards the performance of state-of-the-art convolutional neural network (CNN) models. Unlike deep CNNs, our compact DN model offers a direct interpretation of the nature of normalization. By inspecting the learned normalization pool of our model, we gained insights into a long-standing question about the tuning properties of DN that update the current textbook description: we found that within the receptive field oriented features were normalized preferentially by features with similar orientation rather than non-specifically as currently assumed.
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Kubai, D. F. „Nonrandom chromosome arrangements in germ line nuclei of Sciara coprophila males: the basis for nonrandom chromosome segregation on the meiosis I spindle.“ Journal of Cell Biology 105, Nr. 6 (01.12.1987): 2433–46. http://dx.doi.org/10.1083/jcb.105.6.2433.
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Meiosis I in males of the Dipteran Sciara coprophila results in the nonrandom distribution of maternally and paternally derived chromosome sets to the two division products. Based on an earlier study (Kubai, D.F. 1982. J. Cell Biol. 93:655-669), I suggested that the meiosis I spindle does not play a direct role in the nonrandom sorting of chromosomes but that, instead, haploid sets are already separated in prophase nuclei well before the onset of spindle formation. Here I report more direct evidence that this hypothesis is true; this evidence was gained from ultrastructural reconstruction analyses of the arrangement of chromosomes in germ line nuclei (prophase nuclei in spermatogonia and spermatocytes) of males heterozygous for an X-autosome chromosome translocation. Because of this translocation, the maternal and paternal chromosome sets are distinguishable, so it is possible to demonstrate that (a) the two haploid chromosome sets occupy distinct maternal and paternal nuclear compartments and that (b) nuclei are oriented so that the two haploid chromosome sets have consistent relationships to a well-defined cellular axis. The consequences of such nonrandom aspects of nuclear structure for chromosome behavior on premeiotic and meiotic spindles are discussed.
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Cantarero Navarro, Rubén, Ana Rubio Ruiz, Javier Dorado Chaparro, Felix J. Villanueva Molina, Maria J. Santofimia Romero, David Villa Alises und Juan C. Lopez Lopez. „A Proposal for Modeling Indoor–Outdoor Spaces through IndoorGML, Open Location Code and OpenStreetMap“. ISPRS International Journal of Geo-Information 9, Nr. 3 (12.03.2020): 169. http://dx.doi.org/10.3390/ijgi9030169.
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Traditionally, the standards of spatial modeling are oriented to represent the quantitative information of space. However, in recent years an increasingly common challenge is appearing: flexibly and appropriately integrating quantitative information that goes beyond the purely geometric. This problem has been aggravated due to the success of new paradigms such as the Internet of Things. This adds an additional challenge to the representation of this information due to the need to represent characteristic information of the space from different points of view in a model, such as WiFi coverage, dangerous surroundings, etc. While this problem has already been addressed in indoor spaces with the IndoorGML standard, it remains to be solved in outdoor and indoor–outdoor spaces. We propose to take the advantages proposed in IndoorGML, such as cellular space or multi-layered space model representation, to outdoor spaces in order to create indoor–outdoor models that enable the integration of heterogeneous information that represents different aspects of space. We also propose an approach that gives more flexibility in spatial representation through the integration of standards such as OpenLocationCode for the division of space. Further, we suggest a procedure to enrich the resulting model through the information available in OpenStreetMap.
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Kim, Nam-Hyung, Seong Koo Cho, Seok Hwa Choi, Eun Young Kim, Se Pill Park und Jin Ho Lim. „The distribution and requirements of microtubules and microfilaments in bovine oocytes during in vitro maturation“. Zygote 8, Nr. 1 (Februar 2000): 25–32. http://dx.doi.org/10.1017/s0967199400000794.
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Microtubules and microfilaments are major cytoskeletal components and important modulators for chromosomal movement and cellular division in mammalian oocytes. In this study we observed microtubule and microfilament organisation in bovine oocytes by laser scanning confocal microscopy, and determined requirements of their assembly during in vitro maturation. After germinal vesicle breakdown, small microtubular asters were observed near the condensed chromatin. The asters appeared to elongate and encompass condensed chromatin particles. At the metaphase stage, microtubules were observed in the second meiotic spindle at the metaphase stage. The meiotic spindle was a symmetrical, barrel-shaped structure containing anastral broad poles, located peripherally and radially oriented. Treatment with nocodazole did not inhibit germinal vesicle breakdown. However, progression to metaphase failed to occur in oocytes treated with nocodazole. In contrast, microfilaments were observed as a relatively thick uniform area around the cell cortex and overlying chromatin following germinal vesicle breakdown. Treatment with cytochalasin B inhibited microfilament polymerisation but did not prevent either germinal vesicle breakdown or metaphase formation. However, movement of chromatin to the proper position was inhibited in oocytes treated with cytochalasin B. These results suggest that both microtubules and microfilaments are closely associated with reconstruction and proper positioning of chromatin during meiotic maturation in bovine oocytes.
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Zaidel, Benjamin M., Ori Shental und Shlomo Shamai (Shitz). „Beyond Equal-Power Sparse NOMA: Two User Classes and Closed-Form Bounds on the Achievable Region“. Entropy 24, Nr. 2 (31.01.2022): 227. http://dx.doi.org/10.3390/e24020227.
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Non-orthogonal multiple access (NOMA) is a promising technology for future beyond-5G wireless networks, whose fundamental information-theoretic limits are yet to be fully explored. Considering regular sparse code-domain NOMA (with a fixed and finite number of orthogonal resources allocated to any designated user and vice versa), this paper extends previous results by the authors to a setting comprising two classes of users with different power constraints. Explicit rigorous closed-form analytical inner and outer bounds on the achievable rate (total class throughput) region in the large-system limit are derived and comparatively investigated in extreme-SNR regimes. The inner bound is based on the conditional vector entropy power inequality (EPI), while the outer bound relies on a recent strengthened version of the EPI. Valuable insights are provided into the potential performance gains of regular sparse NOMA in practically oriented settings, comprising, e.g., a combination of low-complexity devices and broadband users with higher transmit power capabilities, or combinations of cell-edge and cell-center users. The conditions for superior performance over dense code-domain NOMA (taking the form of randomly spread code-division multiple access), as well as a relatively small gap to the ultimate performance limits, are identified. The proposed bounds are also applicable for the analysis of interference networks, e.g., Wyner-type cellular models.
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Benabdallah, Mohammed, Oualid Talhi, Fatiha Nouali, Nouredine Choukchou-Braham, Khaldoun Bachari und Artur M. S. Silva. „Advances in Spirocyclic Hybrids: Chemistry and Medicinal Actions“. Current Medicinal Chemistry 25, Nr. 31 (16.10.2018): 3748–67. http://dx.doi.org/10.2174/0929867325666180309124821.
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The present review deals with the progress in medicinal chemistry of spirocyclic compounds, a wider class of natural and synthetic organic molecules, defined as a hybrid of two molecular entities covalently linked via a unique tetrahedral carbon. This spiro central carbon confers to the molecules a tridimensional structurally oriented framework, which is found in many medicinally relevant compounds, a well-known example is the antihypertensive spironolactone. Various bioactive natural products possess the privileged spiro linkage and different chemo-types thereof become synthetically accessible since the 20th century. Actually, there has been a growing interest in the synthesis of heterocyclic hybrids gathered via a spiro carbon. Most of these combinations are two moieties in one scaffold being able to interfere with biological systems through sequential mechanisms. Spirocyclic hybrids containing indole or oxindole units are compounds exhibiting higher interaction with biological receptors by protein inhibition or enzymatic pathways and their recognition as promising anticancer agents in targeted chemotherapy is foreseen. These specific, low-weight and noncomplex spirocyclic hybrids are potent inhibitors of SIRT1, Mdm2–p53 and PLK4, showing affinity for anaplastic lymphoma kinase (ALK) receptor. They are also known as excellent DNA binders, acting on cellular division by arresting the cell cycle at different phases and inducing apoptotic cell death. A structural diversity of spirocyclic hybrids has proved neuroprotective effects, anti-HIV, antiviral and antibacterial activities. Hundred of papers are mentioned in this review underlying chemical issues and pharmacological potencies of spiro compounds, which render them impressive synthetic hits for innovative drug conception.
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Babayeva, Sima, Yulia Zilber und Elena Torban. „Planar cell polarity pathway regulates actin rearrangement, cell shape, motility, and nephrin distribution in podocytes“. American Journal of Physiology-Renal Physiology 300, Nr. 2 (Februar 2011): F549—F560. http://dx.doi.org/10.1152/ajprenal.00566.2009.
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Glomerular podocytes are highly polarized cells characterized by dynamic actin-based foot processes (FPs). Neighboring FPs form specialized junctions, slit diaphragms (SDs), which prevent passage of proteins into the ultrafiltrate. The SD protein complex is linked to cytoskeletal actin filaments and mutations in SD proteins lead to a dramatic change in cell morphology; proteinuria is accompanied by FP retraction and loss of SD structure. Thus, organization of the podocyte cytoskeleton is tightly linked to filtration barrier function. In a variety of cell systems, cytoskeleton arrangement is regulated by the planar cell polarity (PCP) pathway. PCP signals lead to the appearance of highly organized cellular structures that support directional cell movement and oriented cell division. Derangement of the PCP pathway causes neural tube defects and cystic kidney disease in mice. Here, we establish that the PCP pathway regulates the cytoskeleton of podocytes. We identify expression of core PCP proteins in mouse kidney sections and of PCP transcripts in murine and human cultured podocytes. The pathway is functional since Wnt5a causes redistribution of PCP proteins Dishevelled and Daam1. We also show that Wnt5a treatment changes podocyte morphology, alters nephrin distribution, increases the number of stress fibers, and increases cell motility. In reciprocal experiments, siRNA depletion of the core PCP gene Vangl2 reduced the number of cell projections and decreased stress fibers and cell motility. Finally, we demonstrate direct interactions between Vangl2 and the SD protein, MAGI-2. This suggests that the PCP pathway may be directly linked to organization of the SD as well as to regulation of podocyte cytoskeleton. Our observations indicate that PCP signaling may play an important role both in podocyte development and FP cytoskeleton dynamics.
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Vitrinel, Burcu, Christine Vogel und Lionel Christiaen. „Ring Finger 149-Related Is an FGF/MAPK-Independent Regulator of Pharyngeal Muscle Fate Specification“. International Journal of Molecular Sciences 24, Nr. 10 (16.05.2023): 8865. http://dx.doi.org/10.3390/ijms24108865.
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During embryonic development, cell-fate specification gives rise to dedicated lineages that underlie tissue formation. In olfactores, which comprise tunicates and vertebrates, the cardiopharyngeal field is formed by multipotent progenitors of both cardiac and branchiomeric muscles. The ascidian Ciona is a powerful model to study cardiopharyngeal fate specification with cellular resolution, as only two bilateral pairs of multipotent cardiopharyngeal progenitors give rise to the heart and to the pharyngeal muscles (also known as atrial siphon muscles, ASM). These progenitors are multilineage primed, in as much as they express a combination of early ASM- and heart-specific transcripts that become restricted to their corresponding precursors, following oriented and asymmetric divisions. Here, we identify the primed gene ring finger 149 related (Rnf149-r), which later becomes restricted to the heart progenitors, but appears to regulate pharyngeal muscle fate specification in the cardiopharyngeal lineage. CRISPR/Cas9-mediated loss of Rnf149-r function impairs atrial siphon muscle morphogenesis, and downregulates Tbx1/10 and Ebf, two key determinants of pharyngeal muscle fate, while upregulating heart-specific gene expression. These phenotypes are reminiscent of the loss of FGF/MAPK signaling in the cardiopharyngeal lineage, and an integrated analysis of lineage-specific bulk RNA-seq profiling of loss-of-function perturbations has identified a significant overlap between candidate FGF/MAPK and Rnf149-r target genes. However, functional interaction assays suggest that Rnf149-r does not directly modulate the activity of the FGF/MAPK/Ets1/2 pathway. Instead, we propose that Rnf149-r acts both in parallel to the FGF/MAPK signaling on shared targets, as well as on FGF/MAPK-independent targets through (a) separate pathway(s).
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Bilgin, Adem. „Elhik’s Metamathematics and the robot Philia: Internet Communication Protocol Modelling of Observeds according to Observers“. European Journal of Artificial Intelligence and Machine Learning 1, Nr. 2 (22.03.2022): 1–10. http://dx.doi.org/10.24018/ejai.2022.1.2.3.
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Like all robot and IoT oriented mathematical studies this study is also transdisciplinary however most of the study remains in the field of mathematics and philosophy of mathematics due to the aim of mathematical modelling of the observations: a) protein synthesis by the information encoded in DNA and b) communication protocols of hacking software with encryption of IP of computers c) the process of DNA duplication to offspring formation in asexual and sexual reproduction. The ultimate mathematical aim of this study is providing a metamathematical approach for different types of mathematics to be utilized in information sciences by forced or free choice of artificial intelligence driven technological beings and computational systems. This study is biomathematically inspired from protein synthesis, cellular reproduction, DNA duplication, bacterial simple cell division, bacterial sex and zygote formation in human and mammalian fertilization; and all are modelled as moving pieces of quantized information. The ultimate robotic aim is finding an algorithm for data off-springs, thus the formation of the data-offspring in the form of living being off-springs’ DNA is chosen to be mathematically described. For this purpose, a new mathematics with new mathematical operations and a definition to mathematics are postulated, together with twelve postulations about the real-life observations. The introduced Aydan operation is synthesizing fuzzy logic based mathematical existence possibilities into abstract formal logic based abstract mathematical categories to be analyzed with additional color codes for each object, whereas deAydan operation is doing the opposite by analyzing a given synthesis. There is a coexistence of mathematical objects and operators in the biological cells. The co-existence of objects and mathematical operations in a given mathematics M, are axiomatically chosen to be a satisfiability rule for M to be accepted as mathematics in the form of a universal set isolated from other universal sets. Aydan function can be used for hacking other AI by deviating its results by merging them with forced formal logic based analytic input by another hacking software, and deAydan function can be used as anti-hack in the opposite direction. The metamathematical existence degree of a given mathematics is shown to be between zero and infinite dimensions. ELHIK is an abbreviation of the words El Harizmi and Immanuel Kant.
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Tamplin, Owen J., Ellen M. Durand, Logan A. Carr, Sarah J. Childs, Elliott H. Hagedorn und Leonard I. Zon. „High Resolution Imaging Reveals Hematopoietic Stem Cells in the Perivascular Niche Are Anchored to Mesenchymal Stromal Cells That Orient Their Divisions“. Blood 124, Nr. 21 (06.12.2014): 770. http://dx.doi.org/10.1182/blood.v124.21.770.770.
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Abstract Hematopoietic stem cells (HSC) reside in a highly structured microenvironment called the niche. There is two-way communication between a stem cell and its niche that determines important cell fate decisions. HSC must remain quiescent to persist throughout life but also divide and contribute progenitors that will replenish the blood supply. Although there have been a number of elegant studies that have imaged the mammalian bone marrow, we still lack a high-resolution real-time view of endogenous HSC behaviors and interactions within the niche. To overcome these challenges, we developed a transgenic zebrafish line that expresses GFP or mCherry in HSC. We generated this line using the previously described mouse Runx1 +23 kb intronic enhancer. We confirmed the purity of these stem cells by adult-to-adult limiting dilution transplantation with as few as one cell. Based on long-term multi-lineage engraftment, we estimated a stem cell purity of approximately 1/35, which is similar to the KSL (Kit+Sca1+Lin-) population in mouse. Using a novel embryo-to-embryo transplantation assay that is unique to zebrafish, we estimated an even higher stem cell purity of 1/2. These experiments have defined the most pure HSC population in the zebrafish. Using this novel transgenic reporter we have tracked HSC as they migrate in the live zebrafish embryo. This allowed us to image HSC as they interact with other cell types in their microenvironment, including endothelial cells and mesenchymal stromal cells. We have shown that a small group of endothelial cells remodel around a single HSC soon after it lodges in the niche. Recently, we have also found that a single stromal cell can anchor an HSC as it divides. In most cases, we observed that an HSC divides perpendicular to the stromal cell, with one daughter cell remaining attached to the stromal cell and the other migrating away. To gain a much higher resolution view of these cellular events than is possible with confocal microscopy we looked for an alternative approach. A combined method is called “Correlative Light and Electron Microscopy” (CLEM), and involves identification of cells by confocal microscopy, followed by processing of the same sample for EM scanning. We have applied this method by: 1) tracking endogenous HSC in the live embryo; 2) fixing the same embryo for serial block-face scanning EM; 3) reconstructing 3D models from high resolution serial EM sections. We used easily visible blood vessels as anatomical markers that allowed us to pinpoint a single cell in a relatively large block of scanned tissue. As expected, the identified HSC was round, had a distinctive large nucleus, scant cytoplasm, and ruffled membrane. The HSC was surrounded by a small group of 5-6 endothelial cells, as predicted from our confocal live imaging. However at this very high resolution (10 nm/pixel), we could see that only part of the HSC surface was contacted and wrapped by an endothelial cell. Other regions of the HSC surface were contacted by small endothelial cell protrusions. Much of the HSC surface was surrounded by a narrow extracellular space with endothelial and stromal cells lying opposite. Strikingly, we were able to identify the firm anchored attachment between a single stromal cell and HSC that we showed previously oriented the plane of division. By combining confocal live imaging of a novel zebrafish HSC reporter, and serial block-face scanning EM, we have created the first high-resolution 3D model of an endogenous stem cell in its niche. Disclosures Tamplin: Boston Children's Hospital: Patents & Royalties. Zon:FATE Therapeutics, Inc: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other; Scholar Rock: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other; Stemgent: Equity Ownership, Membership on an entity's Board of Directors or advisory committees.
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Bradner, James, Yong-Son Kim, Angela Koehler, Masaoki Kawasumi, Xiaodong Li, Stuart L. Schreiber und Paul Nghiem. „Identification and Characterization of Novel Small-Molecule Inhibitors of the Replication Checkpoint.“ Blood 104, Nr. 11 (16.11.2004): 763. http://dx.doi.org/10.1182/blood.v104.11.763.763.
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Abstract Background The replication (G2/M) checkpoint is principally mediated by the serine/threonine protein kinase ATR (ataxia telangiectasia mutated and Rad3-related). ATR is a large (350 kD) member of the phosphatidylinositol kinase related kinase family. After exposure to genotoxic or replication stress, ATR halts cell cycle progression, allowing DNA repair complexes time enough to restore the fidelity of the genome prior to cell division. Previous experiments have demonstrated that cancer cells with p53 mutation are critically dependent on ATR-mediated arrest of the cell cycle. Industrial approaches to identify ATR inhibitors have failed likely as a result of protein insolubility. Methods We have undertaken a novel chemical genetic approach employing small molecule microarrays (SMMs) to identify molecules with high binding specificity for ATR. Three diversity-oriented combinatorial chemical libraries of more than 15,000 entities were generated by split-pool synthesis in solid phase on polystyrene macrobead supports. Compounds were robotically printed in microarray format on glass slides. Four analogs of FK506 were printed as positive controls. Extracts were prepared from mammalian cells transfected with over-expression constructs of FLAG-tagged ATR, FKBP12 and GFP. A protocol was developed and optimized for screening employing a primary anti-FLAG mouse monoclonal antibody and Cy5-fluorophore labeled anti-mouse antibody. Data analysis for small molecule binders was performed with GenePix software on an Axon Scanner. Biological activity of these molecules was analyzed in the context of mitotic spread and chromosomal fragility assays. Results Protein expression and antibody fidelity was verified by Western blot. The lysate-based SMM screening approach was optimized and validated by recognition of an interaction between over-expressed, epitope-tagged FKBP12 and analogs of FK506. Six small molecule hits suggesting ATR binding were identified and verified by triplicate microarray assays. Positive compounds were structurally similar members of a dihydropyrancarboxamide library suggesting recognition of a common target. Mitotic spread analysis of cells treated with two of these molecules and hydroxyurea demonstrated the premature chromatin condensation phenotype characteristic of replication checkpoint inhibition. Chromosomal fragility was notably augmented by these molecules as well. Chemosensitivity following replication stress was witnessed in p53-negative cells relative to an otherwise identical wild-type cell line. Conclusions Classical approaches to drug discovery are often limited by challenges in protein biochemistry such as protein size, solubility, activity and yield. We present compelling data that the small molecule microarray format can effectively be tailored for use with cellular lysates over-expressing a protein target of biological interest. Furthermore, we have used an optimized protocol to identify two novel, active small molecule inhibitors of the replication checkpoint (SMIRC-1 and SMIRC-2). The enhanced chemosensitivity in p53-negative cell lines supports a plausible role for ATR inhibitors as potentially useful chemotherapeutic agents.
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Donà, Federico, Susanna Eli und Marina Mapelli. „Insights Into Mechanisms of Oriented Division From Studies in 3D Cellular Models“. Frontiers in Cell and Developmental Biology 10 (09.03.2022). http://dx.doi.org/10.3389/fcell.2022.847801.
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In multicellular organisms, epithelial cells are key elements of tissue organization. In developing tissues, cellular proliferation and differentiation are under the tight regulation of morphogenetic programs, that ensure the correct organ formation and functioning. In these processes, mitotic rates and division orientation are crucial in regulating the velocity and the timing of the forming tissue. Division orientation, specified by mitotic spindle placement with respect to epithelial apico-basal polarity, controls not only the partitioning of cellular components but also the positioning of the daughter cells within the tissue, and hence the contacts that daughter cells retain with the surrounding microenvironment. Daughter cells positioning is important to determine signal sensing and fate, and therefore the final function of the developing organ. In this review, we will discuss recent discoveries regarding the mechanistics of planar divisions in mammalian epithelial cells, summarizing technologies and model systems used to study oriented cell divisions in vitro such as three-dimensional cysts of immortalized cells and intestinal organoids. We also highlight how misorientation is corrected in vivo and in vitro, and how it might contribute to the onset of pathological conditions.
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Li, Yuwei, Ang Li, Jason Junge und Marianne Bronner. „Planar cell polarity signaling coordinates oriented cell division and cell rearrangement in clonally expanding growth plate cartilage“. eLife 6 (10.10.2017). http://dx.doi.org/10.7554/elife.23279.
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Both oriented cell divisions and cell rearrangements are critical for proper embryogenesis and organogenesis. However, little is known about how these two cellular events are integrated. Here we examine the linkage between these processes in chick limb cartilage. By combining retroviral-based multicolor clonal analysis with live imaging, the results show that single chondrocyte precursors can generate both single-column and multi-column clones through oriented division followed by cell rearrangements. Focusing on single column formation, we show that this stereotypical tissue architecture is established by a pivot-like process between sister cells. After mediolateral cell division, N-cadherin is enriched in the post-cleavage furrow; then one cell pivots around the other, resulting in stacking into a column. Perturbation analyses demonstrate that planar cell polarity signaling enables cells to pivot in the direction of limb elongation via this N-cadherin-mediated coupling. Our work provides new insights into the mechanisms generating appropriate tissue architecture of limb skeleton.
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Cepeda, Rodrigo E., John B. Terraza, Renato V. Pardo, Valentina Núñez-Pascual, Marco Mundaca-Escobar und Andres F. Sarrazin. „Spatiotemporal variation in cell proliferation patterns during arthropod axial elongation“. Scientific Reports 11, Nr. 1 (11.01.2021). http://dx.doi.org/10.1038/s41598-020-79373-0.
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AbstractAn elongated and segmented body plan is a common morphological characteristic of all arthropods and is probably responsible for their high adaptation ability to diverse environments. Most arthropods form their bodies by progressively adding segments, resembling vertebrate somitogenesis. This sequential segmentation relies on a molecular clock that operates in the posterior region of the elongating embryo that combines dynamically with cellular behaviors and tissue rearrangements, allowing the extension of the developing body along its main embryonic axis. Even though the molecular mechanisms involved in elongation and segment formation have been found to be conserved in a considerable degree, cellular processes such as cell division are quite variable between different arthropods. In this study, we show that cell proliferation in the beetle Tribolium castaneum has a nonuniform spatiotemporal patterning during axial elongation. We found that dividing cells are preferentially oriented along the anterior–posterior axis, more abundant and posteriorly localized during thoracic segments formation and that this cell proliferation peak was triggered at the onset of axis elongation. This raise in cell divisions, in turn, was correlated with an increase in the elongation rate, but not with changes in cell density. When DNA synthesis was inhibited over this period, both the area and length of thoracic segments were significantly reduced but not of the first abdominal segment. We discuss the variable participation that different cell division patterns and cell movements may have on arthropod posterior growth and their evolutionary contribution.
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Popkova, Anna, Matteo Rauzi und Xiaobo Wang. „Cellular and Supracellular Planar Polarity: A Multiscale Cue to Elongate the Drosophila Egg Chamber“. Frontiers in Cell and Developmental Biology 9 (02.03.2021). http://dx.doi.org/10.3389/fcell.2021.645235.
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Tissue elongation is known to be controlled by oriented cell division, elongation, migration and rearrangement. While these cellular processes have been extensively studied, new emerging supracellular mechanisms driving tissue extension have recently been unveiled. Tissue rotation and actomyosin contractions have been shown to be key processes drivingDrosophilaegg chamber elongation. First, egg chamber rotation facilitates the dorsal-ventral alignment of the extracellular matrix and of the cell basal actin fibers. Both fiber-like structures form supracellular networks constraining the egg growth in a polarized fashion thus working as ‘molecular corsets’. Second, the supracellular actin fiber network, powered by myosin periodic oscillation, contracts anisotropically driving tissue extension along the egg anterior-posterior axis. During both processes, cellular and supracellular planar polarity provide a critical cue to controlDrosophilaegg chamber elongation. Here we review how different planar polarized networks are built, maintained and function at both cellular and supracellular levels in theDrosophilaovarian epithelium.
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Müller, Sabine. „Update: On selected ROP cell polarity mechanisms in plant cell morphogenesis“. Plant Physiology, 18.04.2023. http://dx.doi.org/10.1093/plphys/kiad229.
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Abstract The unequal (asymmetric) distribution of cell structures and proteins within a cell is designated as cell polarity. Cell polarity is a crucial prerequisite for morphogenetic processes such as oriented cell division and directed cell expansion. Rho-related plants (ROPs) are required for cellular morphogenesis through the reorganization of the cytoskeleton and vesicle transport in various tissues. Here, I review recent advances in ROP-dependent tip growth, vesicle transport, and tip architecture. I report on the regulatory mechanisms of ROP upstream regulators found in different cell types. It appears that these regulators assemble in nanodomains with specific lipid compositions and recruit ROPs for activation in a stimulus-dependent manner. Current models link mechanosensing/mechanotransduction to ROP polarity signaling involved in feedback mechanisms via the cytoskeleton. Finally, I discuss ROP signaling components that are upregulated by tissue-specific transcription factors and exhibit specific localization patterns during cell division, clearly suggesting ROP signaling in division plane alignment. Advances box: Progress has been made in the characterization of upstream regulators of ROPase signaling in diverse tissues, revealing a common theme of RopGEF phosphoregulation by diverse kinases initiating various ROP signaling cascadesNovel insights link mechanosensing/signal transduction pathways, ROP signaling, and cell wall-reinforcing feedback mechanismsIn response to different stimulants, ROP GTPases are recruited to distinct, pre-existing nanodomains composed of specific lipids and RopGEFs. Thus, one ROP GTPase may respond differently to different stimuliMaintenance of tip architecture in tip-growing cells requires secretory and endocytic trafficking, but the precise site of endocytosis may differ between cell types/speciesCell polarity signaling molecules locate at the cortical division site, or are particularly excluded from it; analysis of respective mutant phenotypes implicate the respective genes in division plane selection in different tissue contexts and diverse plant taxa, suggesting evolutionary conservation
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Luo, Yimin, Mengyang Gu, Minwook Park, Xinyi Fang, Younghoon Kwon, Juan Manuel Urueña, Javier Read de Alaniz, Matthew E. Helgeson, Cristina M. Marchetti und Megan T. Valentine. „Molecular-scale substrate anisotropy, crowding and division drive collective behaviours in cell monolayers“. Journal of The Royal Society Interface 20, Nr. 204 (Juli 2023). http://dx.doi.org/10.1098/rsif.2023.0160.
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The ability of cells to reorganize in response to external stimuli is important in areas ranging from morphogenesis to tissue engineering. While nematic order is common in biological tissues, it typically only extends to small regions of cells interacting via steric repulsion. On isotropic substrates, elongated cells can co-align due to steric effects, forming ordered but randomly oriented finite-size domains. However, we have discovered that flat substrates with nematic order can induce global nematic alignment of dense, spindle-like cells, thereby influencing cell organization and collective motion and driving alignment on the scale of the entire tissue. Remarkably, single cells are not sensitive to the substrate’s anisotropy. Rather, the emergence of global nematic order is a collective phenomenon that requires both steric effects and molecular-scale anisotropy of the substrate. To quantify the rich set of behaviours afforded by this system, we analyse velocity, positional and orientational correlations for several thousand cells over days. The establishment of global order is facilitated by enhanced cell division along the substrate’s nematic axis, and associated extensile stresses that restructure the cells’ actomyosin networks. Our work provides a new understanding of the dynamics of cellular remodelling and organization among weakly interacting cells.
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Pan, Xue, Patricio Pérez-Henríquez, Jaimie M. Van Norman und Zhenbiao Yang. „Membrane Nanodomains: Dynamic Nanobuilding Blocks of Polarized Cell Growth“. Plant Physiology, 17.05.2023. http://dx.doi.org/10.1093/plphys/kiad288.
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Abstract Cell polarity is intimately linked to numerous biological processes, such as oriented plant cell division, particular asymmetric division, cell differentiation, cell and tissue morphogenesis, and transport of hormones and nutrients. Cell polarity is typically initiated by a polarizing cue that regulates the spatiotemporal dynamic of polarity molecules, leading to the establishment and maintenance of polar domains at the plasma membrane (PM). Despite considerable progress in identifying key polarity regulators in plants, the molecular and cellular mechanisms underlying cell polarity formation have yet to be fully elucidated. Recent work suggests a critical role for membrane protein/lipid nanodomains in polarized morphogenesis in plants. One outstanding question is how the spatiotemporal dynamics of signaling nanodomains are controlled to achieve robust cell polarization. In this review, we first summarize the current state of knowledge on potential regulatory mechanisms of nanodomain dynamics, with a special focus on RHO GTPases of Plants (ROPs). We then discuss the pavement cell system as an example of how cells may integrate multiple signals and nanodomain-involved feedback mechanisms to achieve robust polarity. A mechanistic understanding of nanodomains’ roles in plant cell polarity is still in the early stages and will remain an exciting area for future investigations.
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Rudall, Paula J. „Stomatal development and orientation – a phylogenetic and ecophysiological perspective“. Annals of Botany, 08.06.2023. http://dx.doi.org/10.1093/aob/mcad071.
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Abstract Background Oriented patterning of epidermal cells is achieved primarily by transverse protodermal cell divisions perpendicular to the organ axis, followed by axial cell elongation. In linear leaves with parallel venation, most stomata are regularly aligned with the veins. This longitudinal patterning operates under a strong developmental constraint and has demonstrable physiological benefits, especially in grasses. However, transversely oriented stomata characterise a few groups, both among living angiosperms and extinct Mesozoic seed plants. Scope This review examines comparative and developmental data on stomatal patterning in a broad phylogenetic context, focusing on the evolutionary and ecophysiological significance of guard-cell orientation. It draws from a diverse range of literature to explore the pivotal roles of the plant growth hormone auxin in establishing polarity and chemical gradients that enable cellular differentiation. Conclusions Transverse stomata evolved iteratively in a few seed-plant groups during the Mesozoic era, especially among parasitic or xerophytic taxa, such as the hemiparasitic mistletoe genus Viscum and the xerophytic shrub Casuarina, indicating a possible link with ecological factors such as the Cretaceous CO2 decline and changing water availability. The discovery of this feature in some extinct seed-plant taxa known only from fossils could represent a useful phylogenetic marker.
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Fujiwara, Motohiro, Tatsuaki Goh, Satoru Tsugawa, Keiji Nakajima, Hidehiro Fukaki und Koichi Fujimoto. „Tissue growth constrains root organ outlines into an isometrically scalable shape“. Development 148, Nr. 4 (15.02.2021). http://dx.doi.org/10.1242/dev.196253.
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ABSTRACT Organ morphologies are diverse but also conserved under shared developmental constraints among species. Any geometrical similarities in the shape behind diversity and the underlying developmental constraints remain unclear. Plant root tip outlines commonly exhibit a dome shape, which likely performs physiological functions, despite the diversity in size and cellular organization among distinct root classes and/or species. We carried out morphometric analysis of the primary roots of ten angiosperm species and of the lateral roots (LRs) of Arabidopsis, and found that each root outline was isometrically scaled onto a parameter-free catenary curve, a stable structure adopted for arch bridges. Using the physical model for bridges, we analogized that localized and spatially uniform occurrence of oriented cell division and expansion force the LR primordia (LRP) tip to form a catenary curve. These growth rules for the catenary curve were verified by tissue growth simulation of developing LRP development based on time-lapse imaging. Consistently, LRP outlines of mutants compromised in these rules were found to deviate from catenary curves. Our analyses demonstrate that physics-inspired growth rules constrain plant root tips to form isometrically scalable catenary curves.
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Rudolf, Mark A., Anna Andreeva, Christina E. Kim, Anthony C. J. DeNovio, Antoan N. Koshar, Wendy Baker, Alexander X. Cartagena-Rivera und Jeffrey T. Corwin. „Stiffening of Circumferential F-Actin Bands Correlates With Regenerative Failure and May Act as a Biomechanical Brake in the Mammalian Inner Ear“. Frontiers in Cellular Neuroscience 16 (04.05.2022). http://dx.doi.org/10.3389/fncel.2022.859882.
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The loss of inner ear hair cells causes permanent hearing and balance deficits in humans and other mammals, but non-mammals recover after supporting cells (SCs) divide and replace hair cells. The proliferative capacity of mammalian SCs declines as exceptionally thick circumferential F-actin bands develop at their adherens junctions. We hypothesized that the reinforced junctions were limiting regenerative responses of mammalian SCs by impeding changes in cell shape and epithelial tension. Using micropipette aspiration and atomic force microscopy, we measured mechanical properties of utricles from mice and chickens. Our data show that the epithelial surface of the mouse utricle stiffens significantly during postnatal maturation. This stiffening correlates with and is dependent on the postnatal accumulation of F-actin and the cross-linker Alpha-Actinin-4 at SC-SC junctions. In chicken utricles, where SCs lack junctional reinforcement, the epithelial surface remains compliant. There, SCs undergo oriented cell divisions and their apical surfaces progressively elongate throughout development, consistent with anisotropic intraepithelial tension. In chicken utricles, inhibition of actomyosin contractility led to drastic SC shape change and epithelial buckling, but neither occurred in mouse utricles. These findings suggest that species differences in the capacity for hair cell regeneration may be attributable in part to the differences in the stiffness and contractility of the actin cytoskeletal elements that reinforce adherens junctions and participate in regulation of the cell cycle.
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Sun, Kai, Miao Yu, Jiayu Wang, Hu Zhao, Haochen Liu, Hailan Feng, Yang Liu und Dong Han. „A Wnt10a-Notch signaling axis controls Hertwig’s epithelial root sheath cell behaviors during root furcation patterning“. International Journal of Oral Science 16, Nr. 1 (13.03.2024). http://dx.doi.org/10.1038/s41368-024-00288-x.
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AbstractHuman with bi-allelic WNT10A mutations and epithelial Wnt10a knockout mice present enlarged pulp chamber and apical displacement of the root furcation of multi-rooted teeth, known as taurodontism; thus, indicating the critical role of Wnt10a in tooth root morphogenesis. However, the endogenous mechanism by which epithelial Wnt10a regulates Hertwig’s epithelial root sheath (HERS) cellular behaviors and contributes to root furcation patterning remains unclear. In this study, we found that HERS in the presumptive root furcating region failed to elongate at an appropriate horizontal level in K14-Cre;Wnt10afl/fl mice from post-natal day 0.5 (PN0.5) to PN4.5. EdU assays and immunofluorescent staining of cyclin D1 revealed significantly decreased proliferation activity of inner enamel epithelial (IEE) cells of HERS in K14-Cre;Wnt10afl/fl mice at PN2.5 and PN3.5. Immunofluorescent staining of E-Cadherin and acetyl-α-Tubulin demonstrated that the IEE cells of HERS tended to divide perpendicularly to the horizontal plane, which impaired the horizontal extension of HERS in the presumptive root furcating region of K14-Cre;Wnt10afl/fl mice. RNA-seq and immunofluorescence showed that the expressions of Jag1 and Notch2 were downregulated in IEE cells of HERS in K14-Cre;Wnt10afl/fl mice. Furthermore, after activation of Notch signaling in K14-Cre;Wnt10afl/fl molars by Notch2 adenovirus and kidney capsule grafts, the root furcation defect was partially rescued. Taken together, our study demonstrates that an epithelial Wnt10a-Notch signaling axis is crucial for modulating HERS cell proper proliferation and horizontal-oriented division during tooth root furcation morphogenesis.
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Hettinger, Zachary, Sophia Hu, Jianhua Xing und Fabrisia Ambrosio. „Processing body accumulation in aged muscle stem cells contributes to impaired self-renewal“. Physiology 38, S1 (Mai 2023). http://dx.doi.org/10.1152/physiol.2023.38.s1.5730160.
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Stem cell exhaustion is a pillar of aging hallmarks, mediated by an inability of the body’s stem cells to self-renew. In skeletal muscle, impaired self-renewal of muscle stem cells (MuSCs) manifests as a progressive decline in muscle regenerative capacities, leading to functional dependence in the aged. Self-renewal depends on preventing degradation of factors mediating pluripotency during division, thereby averting differentiation, however, mechanisms underlying the inability of MuSCs to self-renew in the aged are unknown. Here, we show processing bodies (p-bodies) accumulate in MuSCs isolated from old mice. As p-bodies canonically represent cellular depots for RNA degradation, our findings suggest age-related changes to RNA degradation may contribute to impaired self-renewal of old MuSCs. To investigate the consequence of p-body enrichment in old MuSCs on self-renewal, we utilized a computational-based lineage analysis termed Dynamo following single cell RNA-sequencing of MuSCs isolated from young and old mice. Dynamo incorporates the velocity of RNA to generate transcriptional vector fields, allowing for inference of lineage specification. Moreover, through characterization of each cell’s transcriptome, this framework also allows for investigation of changes to lineage specification as a result of genetic perturbation. We found that manipulation of scaffold proteins mediating p-body formation resulted in a pronounced effect on lineage specification. Specifically, our results showed that upregulation of LSM14a mRNA processing body assembly factor ( LSM14a) in young MuSCs resulted in a loss of cycling-related gene expression, and subsequently promoted differentiation. Moreover, we found that downregulation of LSM14a in old MuSCs oriented transcriptional vector fields towards a self-renewing phenotype and away from differentiation, mediated by increased expression of cycling-related genes and decreases in differentiation-related genes. Together, the accumulation of p-bodies in old MuSCs coupled with the ability of p-bodies to facilitate self-renewal, suggests that targeted interventions focusing on p-body assembly may be therapeutic in restoring old MuSC self-renewal, and thereby regenerative capacities in the aged. This study was supported by NIA R01 AG061005 (FA), NIA R01 AG052978 (FA), and NIEHS R01 ES025529 (FA). Postdoctoral fellowship funding provided by P30AG024827 (ZH). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.