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Gai Y, Cook B, Setru S, Stone HA, Petry S. Confinement size determines the architecture of Ran-induced microtubule networks. SOFT MATTER 2021; 17:5921-5931. [PMID: 34041514 PMCID: PMC8958645 DOI: 10.1039/d1sm00045d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The organization of microtubules (MTs) is critical for cells during interphase and mitosis. During mitotic spindle assembly, MTs are made and organized around chromosomes in a process regulated by RanGTP. The role of RanGTP has been explored in Xenopus egg extracts, which are not limited by a cell membrane. Here, we investigated whether cell-sized confinements affect the assembly of RanGTP-induced MT networks in Xenopus egg extracts. We used microfluidics to encapsulate extracts within monodisperse extract-in-oil droplets. Importantly, we find that the architecture of Ran-induced MT networks depends on the droplet diameter and the Ran concentration, and differs from structures formed in bulk extracts. Our results highlight that both MT nucleation and physical confinement play critical roles in determining the spatial organization of the MT cytoskeleton.
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Affiliation(s)
- Ya Gai
- Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, USA.
| | - Brian Cook
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA.
| | - Sagar Setru
- Lewis-Sigler Institute of Integrative Genomics, Princeton University, Princeton, NJ, USA
| | - Howard A Stone
- Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, USA.
| | - Sabine Petry
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA.
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2
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Abstract
A metaphase spindle is a complex structure consisting of microtubules and a myriad of different proteins that modulate microtubule dynamics together with chromatin and kinetochores. A decade ago, a full description of spindle formation and function seemed a lofty goal. Here, we describe how work in the last 10 years combining cataloging of spindle components, the characterization of their biochemical activities using single-molecule techniques, and theory have advanced our knowledge. Taken together, these advances suggest that a full understanding of spindle assembly and function may soon be possible.
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Affiliation(s)
- Simone Reber
- Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany Integrative Research Institute (IRI) for the Life Sciences, Humboldt-Universität zu Berlin, 10115 Berlin, Germany
| | - Anthony A Hyman
- Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany
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3
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Dubaissi E, Rousseau K, Lea R, Soto X, Nardeosingh S, Schweickert A, Amaya E, Thornton DJ, Papalopulu N. A secretory cell type develops alongside multiciliated cells, ionocytes and goblet cells, and provides a protective, anti-infective function in the frog embryonic mucociliary epidermis. Development 2014; 141:1514-25. [PMID: 24598166 PMCID: PMC3957375 DOI: 10.1242/dev.102426] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Accepted: 02/02/2014] [Indexed: 02/05/2023]
Abstract
The larval epidermis of Xenopus is a bilayered epithelium, which is an excellent model system for the study of the development and function of mucosal and mucociliary epithelia. Goblet cells develop in the outer layer while multiciliated cells and ionocytes sequentially intercalate from the inner to the outer layer. Here, we identify and characterise a fourth cell type, the small secretory cell (SSC). We show that the development of these cells is controlled by the transcription factor Foxa1 and that they intercalate into the outer layer of the epidermis relatively late, at the same time as embryonic hatching. Ultrastructural and molecular characterisation shows that these cells have an abundance of large apical secretory vesicles, which contain highly glycosylated material, positive for binding of the lectin, peanut agglutinin, and an antibody to the carbohydrate epitope, HNK-1. By specifically depleting SSCs, we show that these cells are crucial for protecting the embryo against bacterial infection. Mass spectrometry studies show that SSCs secrete a glycoprotein similar to Otogelin, which may form the structural component of a mucus-like protective layer, over the surface of the embryo, and several potential antimicrobial substances. Our study completes the characterisation of all the epidermal cell types in the early tadpole epidermis and reinforces the suitability of this system for the in vivo study of complex epithelia, including investigation of innate immune defences.
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Affiliation(s)
- Eamon Dubaissi
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Karine Rousseau
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
- Wellcome Trust Centre for Cell Matrix Research, University of Manchester, Manchester M13 9PT, UK
| | - Robert Lea
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
- The Healing Foundation Centre, University of Manchester, Manchester M13 9PT, UK
| | - Ximena Soto
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Siddarth Nardeosingh
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Axel Schweickert
- University of Hohenheim, Institute of Zoology, Garbenstrasse 30, D-70593 Stuttgart, Germany
| | - Enrique Amaya
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
- The Healing Foundation Centre, University of Manchester, Manchester M13 9PT, UK
| | - David J. Thornton
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
- Wellcome Trust Centre for Cell Matrix Research, University of Manchester, Manchester M13 9PT, UK
| | - Nancy Papalopulu
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
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4
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Walentek P, Bogusch S, Thumberger T, Vick P, Dubaissi E, Beyer T, Blum M, Schweickert A. A novel serotonin-secreting cell type regulates ciliary motility in the mucociliary epidermis of Xenopus tadpoles. Development 2014; 141:1526-33. [PMID: 24598162 DOI: 10.1242/dev.102343] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The embryonic skin of Xenopus tadpoles serves as an experimental model system for mucociliary epithelia (MCE) such as the human airway epithelium. MCEs are characterized by the presence of mucus-secreting goblet and multiciliated cells (MCCs). A third cell type, ion-secreting cells (ISCs), is present in the larval skin as well. Synchronized beating of MCC cilia is required for directional transport of mucus. Here we describe a novel cell type in the Xenopus laevis larval epidermis, characterized by serotonin synthesis and secretion. It is termed small secretory cell (SSC). SSCs are detectable at early tadpole stages, unlike MCCs and ISCs, which are specified at early neurulation. Subcellularly, serotonin was found in large, apically localized vesicle-like structures, which were entirely shed into the surrounding medium. Pharmacological inhibition of serotonin synthesis decreased the velocity of cilia-driven fluid flow across the skin epithelium. This effect was mediated by serotonin type 3 receptor (Htr3), which was expressed in ciliated cells. Knockdown of Htr3 compromised flow velocity by reducing the ciliary motility of MCCs. SSCs thus represent a distinct and novel entity of the frog tadpole MCE, required for ciliary beating and mucus transport across the larval skin. The identification and characterization of SSCs consolidates the value of the Xenopus embryonic skin as a model system for human MCEs, which have been known for serotonin-dependent regulation of ciliary beat frequency.
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Affiliation(s)
- Peter Walentek
- University of Hohenheim, Institute of Zoology, Garbenstrasse 30, D-70593 Stuttgart, Germany
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5
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Jevtić P, Levy DL. Mechanisms of nuclear size regulation in model systems and cancer. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 773:537-69. [PMID: 24563365 DOI: 10.1007/978-1-4899-8032-8_25] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Changes in nuclear size have long been used by cytopathologists as an important parameter to diagnose, stage, and prognose many cancers. Mechanisms underlying these changes and functional links between nuclear size and malignancy are largely unknown. Understanding mechanisms of nuclear size regulation and the physiological significance of proper nuclear size control will inform the interplay between altered nuclear size and oncogenesis. In this chapter we review what is known about molecular mechanisms of nuclear size control based on research in model experimental systems including yeast, Xenopus, Tetrahymena, Drosophila, plants, mice, and mammalian cell culture. We discuss how nuclear size is influenced by DNA ploidy, nuclear structural components, cytoplasmic factors and nucleocytoplasmic transport, the cytoskeleton, and the extracellular matrix. Based on these mechanistic insights, we speculate about how nuclear size might impact cell physiology and whether altered nuclear size could contribute to cancer development and progression. We end with some outstanding questions about mechanisms and functions of nuclear size regulation.
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Affiliation(s)
- Predrag Jevtić
- Department of Molecular Biology, University of Wyoming, 1000 E. University Avenue, Laramie, WY, 82071, USA,
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6
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Hazel J, Krutkramelis K, Mooney P, Tomschik M, Gerow K, Oakey J, Gatlin JC. Changes in cytoplasmic volume are sufficient to drive spindle scaling. Science 2013; 342:853-6. [PMID: 24233723 PMCID: PMC4004590 DOI: 10.1126/science.1243110] [Citation(s) in RCA: 147] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The mitotic spindle must function in cell types that vary greatly in size, and its dimensions scale with the rapid, reductive cell divisions that accompany early stages of development. The mechanism responsible for this scaling is unclear, because uncoupling cell size from a developmental or cellular context has proven experimentally challenging. We combined microfluidic technology with Xenopus egg extracts to characterize spindle assembly within discrete, geometrically defined volumes of cytoplasm. Reductions in cytoplasmic volume, rather than developmental cues or changes in cell shape, were sufficient to recapitulate spindle scaling observed in Xenopus embryos. Thus, mechanisms extrinsic to the spindle, specifically a limiting pool of cytoplasmic component(s), play a major role in determining spindle size.
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Affiliation(s)
- James Hazel
- Dept. of Molecular Biology, University of Wyoming, Laramie, WY 82071, USA
| | - Kaspars Krutkramelis
- Dept. of Chemical and Petroleum Engineering, University of Wyoming, Laramie, WY 82071, USA
| | - Paul Mooney
- Dept. of Molecular Biology, University of Wyoming, Laramie, WY 82071, USA
| | - Miroslav Tomschik
- Dept. of Molecular Biology, University of Wyoming, Laramie, WY 82071, USA
| | - Ken Gerow
- Dept. of Statistics, University of Wyoming, Laramie, WY 82071, USA
| | - John Oakey
- Dept. of Chemical and Petroleum Engineering, University of Wyoming, Laramie, WY 82071, USA
| | - J. C. Gatlin
- Dept. of Molecular Biology, University of Wyoming, Laramie, WY 82071, USA
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7
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Dubaissi E, Papalopulu N. Embryonic frog epidermis: a model for the study of cell-cell interactions in the development of mucociliary disease. Dis Model Mech 2010; 4:179-92. [PMID: 21183475 PMCID: PMC3046089 DOI: 10.1242/dmm.006494] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Specialised epithelia such as mucociliary, secretory and transporting epithelia line all major organs, including the lung, gut and kidney. Malfunction of these epithelia is associated with many human diseases. The frog embryonic epidermis possesses mucus-secreting and multiciliated cells, and has served as an excellent model system for the biogenesis of cilia. However, ionic regulation is important for the function of all specialised epithelia and it is not clear how this is achieved in the embryonic frog epidermis. Here, we show that a third cell type develops alongside ciliated and mucus-secreting cells in the tadpole skin. These cells express high levels of ion channels and transporters; therefore, we suggest that they are analogous to ionocytes found in transporting epithelia such as the mammalian kidney. We show that frog ionocytes express the transcription factor foxi1e, which is required for the development of these cells. Depletion of ionocytes by foxi1e knockdown has detrimental effects on the development of multiciliated cells, which show fewer and aberrantly beating cilia. These results reveal a newly identified role for ionocytes and suggest that the frog embryonic skin is a model system that is particularly suited to studying the interactions of different cell types in mucociliary, as well as in secretory and transporting, epithelia.
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Affiliation(s)
- Eamon Dubaissi
- Faculty of Life Sciences, University of Manchester, Manchester, UK
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Levy DL, Heald R. Nuclear size is regulated by importin α and Ntf2 in Xenopus. Cell 2010; 143:288-98. [PMID: 20946986 PMCID: PMC2966892 DOI: 10.1016/j.cell.2010.09.012] [Citation(s) in RCA: 182] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2010] [Revised: 07/06/2010] [Accepted: 09/07/2010] [Indexed: 01/14/2023]
Abstract
The size of the nucleus varies among different cell types, species, and disease states, but mechanisms of nuclear size regulation are poorly understood. We investigated nuclear scaling in the pseudotetraploid frog Xenopus laevis and its smaller diploid relative Xenopus tropicalis, which contains smaller cells and nuclei. Nuclear scaling was recapitulated in vitro using egg extracts, demonstrating that titratable cytoplasmic factors determine nuclear size to a greater extent than DNA content. Nuclear import rates correlated with nuclear size, and varying the concentrations of two transport factors, importin α and Ntf2, was sufficient to account for nuclear scaling between the two species. Both factors modulated lamin B3 import, with importin α increasing overall import rates and Ntf2 reducing import based on cargo size. Importin α also contributes to nuclear size changes during early X. laevis development. Thus, nuclear transport mechanisms are physiological regulators of both interspecies and developmental nuclear scaling.
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Affiliation(s)
- Daniel L Levy
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720-3200, USA
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Wühr M, Dumont S, Groen AC, Needleman DJ, Mitchison TJ. How does a millimeter-sized cell find its center? Cell Cycle 2009; 8:1115-21. [PMID: 19282671 PMCID: PMC2880816 DOI: 10.4161/cc.8.8.8150] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Microtubules play a central role in centering the nucleus or mitotic spindle in eukaryotic cells. However, despite common use of microtubules for centering, physical mechanisms can vary greatly, and depend on cell size and cell type. In the small fission yeast cells, the nucleus can be centered by pushing forces that are generated when growing microtubules hit the cell boundary. This mechanism may not be possible in larger cells, because the compressive force that microtubules can sustain are limited by buckling, so maximal force decreases with microtubule length. In a well-studied intermediate sized cell, the C. elegans fertilized egg, centrosomes are centered by cortex-attached motors that pull on microtubules. This mechanism is widely assumed to be general for larger cells. However, re-evaluation of classic experiments in a very large cell, the fertilized amphibian egg, argues against such generality. In these large eggs, movement of asters away from a part of the cell boundary that they are touching cannot be mediated by cortical pulling, because the astral microtubules are too short to reach the opposite cell boundary. Additionally, Herlant and Brachet discovered a century ago that multiple asters within a single egg center relative to the cell boundary, but also relative to each other. Here, we summarize current understanding of microtubule organization during the first cell cycle in a fertilized Xenopus egg, discuss how microtubule asters move towards the center of this very large cell, and how multiple asters shape and position themselves relative to each other.
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Affiliation(s)
- Martin Wühr
- Department of Systems Biology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115 USA.
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Wühr M, Chen Y, Dumont S, Groen AC, Needleman DJ, Salic A, Mitchison TJ. Evidence for an upper limit to mitotic spindle length. Curr Biol 2008; 18:1256-61. [PMID: 18718761 DOI: 10.1016/j.cub.2008.07.092] [Citation(s) in RCA: 165] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2008] [Revised: 07/13/2008] [Accepted: 07/15/2008] [Indexed: 12/18/2022]
Abstract
Size specification of macromolecular assemblies in the cytoplasm is poorly understood [1]. In principle, assemblies could scale with cell size or use intrinsic mechanisms. For the mitotic spindle, scaling with cell size is expected, because the function of this assembly is to physically move sister chromatids into the center of nascent daughter cells. Eggs of Xenopus laevis are among the largest cells known that cleave completely during cell division. Cell length in this organism changes by two orders of magnitude ( approximately 1200 microm to approximately 12 microm) while it develops from a fertilized egg into a tadpole [2]. We wondered whether, and how, mitotic spindle length and morphology adapt to function at these different length scales. Here, we show that spindle length increases with cell length in small cells, but in very large cells spindle length approaches an upper limit of approximately 60 microm. Further evidence for an upper limit to spindle length comes from an embryonic extract system that recapitulates mitotic spindle assembly in a test tube. We conclude that early mitotic spindle length in Xenopus laevis is uncoupled from cell length, reaching an upper bound determined by mechanisms that are intrinsic to the spindle.
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Affiliation(s)
- Martin Wühr
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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Hayes JM, Kim SK, Abitua PB, Park TJ, Herrington ER, Kitayama A, Grow MW, Ueno N, Wallingford JB. Identification of novel ciliogenesis factors using a new in vivo model for mucociliary epithelial development. Dev Biol 2007; 312:115-30. [PMID: 17961536 DOI: 10.1016/j.ydbio.2007.09.031] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2007] [Revised: 08/24/2007] [Accepted: 09/06/2007] [Indexed: 11/18/2022]
Abstract
Mucociliary epithelia are essential for homeostasis of many organs and consist of mucus-secreting goblet cells and ciliated cells. Here, we present the ciliated epidermis of Xenopus embryos as a facile model system for in vivo molecular studies of mucociliary epithelial development. Using an in situ hybridization-based approach, we identified numerous genes expressed differentially in mucus-secreting cells or in ciliated cells. Focusing on genes expressed in ciliated cells, we have identified new candidate ciliogenesis factors, including several not present in the current ciliome. We find that TTC25-GFP is localized to the base of cilia and to ciliary axonemes, and disruption of TTC25 function disrupts ciliogenesis. Mig12-GFP localizes very strongly to the base of cilia and confocal imaging of this construct allows for simple visualization of the planar polarity of basal bodies that underlies polarized ciliary beating. Knockdown of Mig12 disrupts ciliogenesis. Finally, we show that ciliogenesis factors identified in the Xenopus epidermis are required in the midline to facilitate neural tube closure. These results provide further evidence of a requirement for cilia in neural tube morphogenesis and suggest that genes identified in the Xenopus epidermis play broad roles in ciliogenesis. The suites of genes identified here will provide a foundation for future studies, and may also contribute to our understanding of pathological changes in mucociliary epithelia that accompany diseases such as asthma.
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Affiliation(s)
- Julie M Hayes
- Department of Molecular Cell and Developmental Biology, and Institute for Cellular and Molecular Biology, University Station C1000, University of Texas, Austin, TX 78712, USA
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