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Deshpande O, de-Carvalho J, Vieira DV, Telley IA. Astral microtubule cross-linking safeguards uniform nuclear distribution in the Drosophila syncytium. J Cell Biol 2022; 221:212810. [PMID: 34766978 PMCID: PMC8594625 DOI: 10.1083/jcb.202007209] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 09/24/2021] [Accepted: 10/20/2021] [Indexed: 12/16/2022] Open
Abstract
The early insect embryo develops as a multinucleated cell distributing the genome uniformly to the cell cortex. Mechanistic insight for nuclear positioning beyond cytoskeletal requirements is missing. Contemporary hypotheses propose actomyosin-driven cytoplasmic movement transporting nuclei or repulsion of neighbor nuclei driven by microtubule motors. Here, we show that microtubule cross-linking by Feo and Klp3A is essential for nuclear distribution and internuclear distance maintenance in Drosophila. Germline knockdown causes irregular, less-dense nuclear delivery to the cell cortex and smaller distribution in ex vivo embryo explants. A minimal internuclear distance is maintained in explants from control embryos but not from Feo-inhibited embryos, following micromanipulation-assisted repositioning. A dimerization-deficient Feo abolishes nuclear separation in embryo explants, while the full-length protein rescues the genetic knockdown. We conclude that Feo and Klp3A cross-linking of antiparallel microtubule overlap generates a length-regulated mechanical link between neighboring microtubule asters. Enabled by a novel experimental approach, our study illuminates an essential process of embryonic multicellularity.
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Affiliation(s)
- Ojas Deshpande
- Instituto Gulbenkian de Ciência, Fundação Calouste Gulbenkian, Oeiras, Portugal
| | - Jorge de-Carvalho
- Instituto Gulbenkian de Ciência, Fundação Calouste Gulbenkian, Oeiras, Portugal
| | - Diana V Vieira
- Instituto Gulbenkian de Ciência, Fundação Calouste Gulbenkian, Oeiras, Portugal
| | - Ivo A Telley
- Instituto Gulbenkian de Ciência, Fundação Calouste Gulbenkian, Oeiras, Portugal
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2
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Abstract
The purpose of this review is to explore self-organizing mechanisms that pattern microtubules (MTs) and spatially organize animal cell cytoplasm, inspired by recent experiments in frog egg extract. We start by reviewing conceptual distinctions between self-organizing and templating mechanisms for subcellular organization. We then discuss self-organizing mechanisms that generate radial MT arrays and cell centers in the absence of centrosomes. These include autocatalytic MT nucleation, transport of minus ends, and nucleation from organelles such as melanosomes and Golgi vesicles that are also dynein cargoes. We then discuss mechanisms that partition the cytoplasm in syncytia, in which multiple nuclei share a common cytoplasm, starting with cytokinesis, when all metazoan cells are transiently syncytial. The cytoplasm of frog eggs is partitioned prior to cytokinesis by two self-organizing modules, protein regulator of cytokinesis 1 (PRC1)-kinesin family member 4A (KIF4A) and chromosome passenger complex (CPC)-KIF20A. Similar modules may partition longer-lasting syncytia, such as early Drosophila embryos. We end by discussing shared mechanisms and principles for the MT-based self-organization of cellular units.
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Affiliation(s)
- Timothy J Mitchison
- Harvard Medical School, Boston, Massachusetts 02115, USA; ,
- Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA
| | - Christine M Field
- Harvard Medical School, Boston, Massachusetts 02115, USA; ,
- Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA
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3
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Baluška F, Reber AS. CBC-Clock Theory of Life - Integration of cellular circadian clocks and cellular sentience is essential for cognitive basis of life. Bioessays 2021; 43:e2100121. [PMID: 34382225 DOI: 10.1002/bies.202100121] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2021] [Revised: 07/16/2021] [Accepted: 07/19/2021] [Indexed: 12/20/2022]
Abstract
Cellular circadian clocks represent ancient anticipatory systems which co-evolved with the first cells to safeguard their survival. Cyanobacteria represent one of the most ancient cells, having essentially invented photosynthesis together with redox-based cellular circadian clocks some 2.7 billion years ago. Bioelectricity phenomena, based on redox homeostasis associated electron transfers in membranes and within protein complexes inserted in excitable membranes, play important roles, not only in the cellular circadian clocks and in anesthetics-sensitive cellular sentience (awareness of environment), but also in the coupling of single cells into tissues and organs of unitary multicellular organisms. This integration of cellular circadian clocks with cellular basis of sentience is an essential feature of the cognitive CBC-Clock basis of cellular life.
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Affiliation(s)
- František Baluška
- Institute of Cellular and Molecular Botany, University of Bonn, Bonn, Germany
| | - Arthur S Reber
- Department of Psychology, University of British Columbia, Vancouver, Canada
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4
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Khetan N, Pruliere G, Hebras C, Chenevert J, Athale CA. Self-organized optimal packing of kinesin-5-driven microtubule asters scales with cell size. J Cell Sci 2021; 134:jcs257543. [PMID: 34080632 DOI: 10.1242/jcs.257543] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2020] [Accepted: 04/18/2021] [Indexed: 12/18/2022] Open
Abstract
Radial microtubule (MT) arrays or asters determine cell geometry in animal cells. Multiple asters interacting with motors, such as those in syncytia, form intracellular patterns, but the mechanical principles behind this are not clear. Here, we report that oocytes of the marine ascidian Phallusia mammillata treated with the drug BI-D1870 spontaneously form cytoplasmic MT asters, or cytasters. These asters form steady state segregation patterns in a shell just under the membrane. Cytaster centers tessellate the oocyte cytoplasm, that is divide it into polygonal structures, dominated by hexagons, in a kinesin-5-dependent manner, while inter-aster MTs form 'mini-spindles'. A computational model of multiple asters interacting with kinesin-5 can reproduce both tessellation patterns and mini-spindles in a manner specific to the number of MTs per aster, MT lengths and kinesin-5 density. Simulations predict that the hexagonal tessellation patterns scale with increasing cell size, when the packing fraction of asters in cells is ∼1.6. This self-organized in vivo tessellation by cytasters is comparable to the 'circle packing problem', suggesting that there is an intrinsic mechanical pattern-forming module that is potentially relevant to understanding the role of collective mechanics of cytoskeletal elements in embryogenesis. This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Neha Khetan
- Division of Biology, IISER Pune, Dr. Homi Bhabha Road, Pashan, Pune 411008, India
| | - Gérard Pruliere
- LBDV, Sorbonne Universite/CNRS, 06230 Villefranche-sur-Mer, France
| | - Celine Hebras
- LBDV, Sorbonne Universite/CNRS, 06230 Villefranche-sur-Mer, France
| | - Janet Chenevert
- LBDV, Sorbonne Universite/CNRS, 06230 Villefranche-sur-Mer, France
| | - Chaitanya A Athale
- Division of Biology, IISER Pune, Dr. Homi Bhabha Road, Pashan, Pune 411008, India
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5
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Affiliation(s)
- Timothy J. Mitchison
- Harvard Medical School, Boston, MA, USA
- Marine Biological Laboratory, Woods Hole, MA, USA
| | - Christine M. Field
- Harvard Medical School, Boston, MA, USA
- Marine Biological Laboratory, Woods Hole, MA, USA
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6
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Field CM, Pelletier JF, Mitchison TJ. Disassembly of Actin and Keratin Networks by Aurora B Kinase at the Midplane of Cleaving Xenopus laevis Eggs. Curr Biol 2019; 29:1999-2008.e4. [PMID: 31178324 DOI: 10.1016/j.cub.2019.05.016] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2019] [Revised: 03/28/2019] [Accepted: 05/03/2019] [Indexed: 11/19/2022]
Abstract
The large length scale of Xenopus laevis eggs facilitates observation of bulk cytoplasm dynamics far from the cortex during cytokinesis. The first furrow ingresses through the egg midplane, which is demarcated by chromosomal passenger complex (CPC) localized on microtubule bundles at the boundary between asters. Using an extract system, we found that local kinase activity of the Aurora B kinase (AURKB) subunit of the CPC caused disassembly of F-actin and keratin between asters and local softening of the cytoplasm as assayed by flow patterns. Beads coated with active CPC mimicked aster boundaries and caused AURKB-dependent disassembly of F-actin and keratin that propagated ∼40 μm without microtubules and much farther with microtubules present. Consistent with extract observations, we observed disassembly of the keratin network between asters in zygotes fixed before and during 1st cytokinesis. We propose that active CPC at aster boundaries locally reduces cytoplasmic stiffness by disassembling actin and keratin networks. Possible functions of this local disassembly include helping sister centrosomes move apart after mitosis, preparing a soft path for furrow ingression, and releasing G-actin from internal networks to build cortical networks that support furrow ingression.
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Affiliation(s)
- Christine M Field
- Department of Systems Biology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02153, USA; Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543, USA.
| | - James F Pelletier
- Department of Systems Biology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02153, USA; Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543, USA
| | - Timothy J Mitchison
- Department of Systems Biology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02153, USA; Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543, USA
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7
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Bornens M. Cell polarity: having and making sense of direction-on the evolutionary significance of the primary cilium/centrosome organ in Metazoa. Open Biol 2018; 8:180052. [PMID: 30068565 PMCID: PMC6119866 DOI: 10.1098/rsob.180052] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2018] [Accepted: 07/05/2018] [Indexed: 12/13/2022] Open
Abstract
Cell-autonomous polarity in Metazoans is evolutionarily conserved. I assume that permanent polarity in unicellular eukaryotes is required for cell motion and sensory reception, integration of these two activities being an evolutionarily constrained function. Metazoans are unique in making cohesive multicellular organisms through complete cell divisions. They evolved a primary cilium/centrosome (PC/C) organ, ensuring similar functions to the basal body/flagellum of unicellular eukaryotes, but in different cells, or in the same cell at different moments. The possibility that this innovation contributed to the evolution of individuality, in being instrumental in the early specification of the germ line during development, is further discussed. Then, using the example of highly regenerative organisms like planarians, which have lost PC/C organ in dividing cells, I discuss the possibility that part of the remodelling necessary to reach a new higher-level unit of selection in multi-cellular organisms has been triggered by conflicts among individual cell polarities to reach an organismic polarity. Finally, I briefly consider organisms with a sensorimotor organ like the brain that requires exceedingly elongated polarized cells for its activity. I conclude that beyond critical consequences for embryo development, the conservation of cell-autonomous polarity in Metazoans had far-reaching implications for the evolution of individuality.
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Affiliation(s)
- Michel Bornens
- Institut Curie, PSL Research University, CNRS - UMR 144, 75005 Paris, France
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8
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Sandler JE, Stathopoulos A. Stepwise Progression of Embryonic Patterning. Trends Genet 2016; 32:432-443. [PMID: 27230753 DOI: 10.1016/j.tig.2016.04.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Revised: 04/20/2016] [Accepted: 04/21/2016] [Indexed: 01/23/2023]
Abstract
It is long established that the graded distribution of Dorsal transcription factor influences spatial domains of gene expression along the dorsoventral (DV) axis of Drosophila melanogaster embryos. However, the more recent realization that Dorsal levels also change with time raises the question of whether these dynamics are instructive. An overview of DV axis patterning is provided, focusing on new insights identified through quantitative analysis of temporal changes in Dorsal target gene expression from one nuclear cycle to the next ('steps'). Possible roles for the stepwise progression of this patterning program are discussed including (i) tight temporal regulation of signaling pathway activation, (ii) control of gene expression cohorts, and (iii) ensuring the irreversibility of the patterning and cell fate specification process.
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Affiliation(s)
- Jeremy E Sandler
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Angelike Stathopoulos
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
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9
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Cinquin A, Zheng L, Taylor PH, Paz A, Zhang L, Chiang M, Snow JJ, Nie Q, Cinquin O. Semi-permeable Diffusion Barriers Enhance Patterning Robustness in the C. elegans Germline. Dev Cell 2016; 35:405-17. [PMID: 26609956 DOI: 10.1016/j.devcel.2015.10.027] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Revised: 07/15/2015] [Accepted: 10/28/2015] [Indexed: 01/29/2023]
Abstract
Positional information derived from local morphogen concentration plays an important role in patterning. A key question is how morphogen diffusion and gene expression regulation shape positional information into an appropriate profile with suitably low noise. We address this question using a model system--the C. elegans germline--whose regulatory network has been well characterized genetically but whose spatiotemporal dynamics are poorly understood. We show that diffusion within the germline syncytium is a critical control of stem cell differentiation and that semi-permeable diffusion barriers present at key locations make it possible--in combination with a feedback loop in the germline regulatory network--for mitotic zone size to be robust against spatial noise in Notch signaling. Spatial averaging within compartments defined by diffusion barriers is an advantageous patterning strategy, which attenuates noise while still allowing for sharp transitions between compartments. This strategy could apply to other organs.
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Affiliation(s)
- Amanda Cinquin
- Department of Developmental and Cell Biology, University of California at Irvine, Irvine, CA 92697, USA; Center for Complex Biological Systems, University of California at Irvine, Irvine, CA 92697, USA
| | - Likun Zheng
- Department of Mathematics, University of California at Irvine, Irvine, CA 92697, USA; Center for Complex Biological Systems, University of California at Irvine, Irvine, CA 92697, USA
| | - Pete H Taylor
- Department of Developmental and Cell Biology, University of California at Irvine, Irvine, CA 92697, USA; Center for Complex Biological Systems, University of California at Irvine, Irvine, CA 92697, USA
| | - Adrian Paz
- Department of Developmental and Cell Biology, University of California at Irvine, Irvine, CA 92697, USA; Center for Complex Biological Systems, University of California at Irvine, Irvine, CA 92697, USA
| | - Lei Zhang
- Department of Mathematics, University of California at Irvine, Irvine, CA 92697, USA; Center for Complex Biological Systems, University of California at Irvine, Irvine, CA 92697, USA
| | - Michael Chiang
- Department of Developmental and Cell Biology, University of California at Irvine, Irvine, CA 92697, USA; Center for Complex Biological Systems, University of California at Irvine, Irvine, CA 92697, USA
| | - Joshua J Snow
- Department of Biochemistry, University of Wisconsin at Madison, Madison, WI 53706, USA
| | - Qing Nie
- Department of Mathematics, University of California at Irvine, Irvine, CA 92697, USA; Center for Complex Biological Systems, University of California at Irvine, Irvine, CA 92697, USA
| | - Olivier Cinquin
- Department of Developmental and Cell Biology, University of California at Irvine, Irvine, CA 92697, USA; Center for Complex Biological Systems, University of California at Irvine, Irvine, CA 92697, USA.
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10
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Tikhonenko I, Irizarry K, Khodjakov A, Koonce MP. Organization of microtubule assemblies in Dictyostelium syncytia depends on the microtubule crosslinker, Ase1. Cell Mol Life Sci 2016; 73:859-68. [PMID: 26298292 PMCID: PMC4738076 DOI: 10.1007/s00018-015-2026-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Revised: 07/27/2015] [Accepted: 08/18/2015] [Indexed: 11/30/2022]
Abstract
It has long been known that the interphase microtubule (MT) array is a key cellular scaffold that provides structural support and directs organelle trafficking in eukaryotic cells. Although in animal cells, a combination of centrosome nucleating properties and polymer dynamics at the distal microtubule ends is generally sufficient to establish a radial, polar array of MTs, little is known about how effector proteins (motors and crosslinkers) are coordinated to produce the diversity of interphase MT array morphologies found in nature. This diversity is particularly important in multinucleated environments where multiple MT arrays must coexist and function. We initiate here a study to address the higher ordered coordination of multiple, independent MT arrays in a common cytoplasm. Deletion of a MT crosslinker of the MAP65/Ase1/PRC1 family disrupts the spatial integrity of multiple arrays in Dictyostelium discoideum, reducing the distance between centrosomes and increasing the intermingling of MTs with opposite polarity. This result, coupled with previous dynein disruptions suggest a robust mechanism by which interphase MT arrays can utilize motors and crosslinkers to sense their position and minimize overlap in a common cytoplasm.
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Affiliation(s)
- Irina Tikhonenko
- Division of Translational Medicine, NYS Department of Health, Wadsworth Center, Empire State Plaza, PO Box 509, Albany, NY, 12201-0509, USA
| | - Karen Irizarry
- Division of Translational Medicine, NYS Department of Health, Wadsworth Center, Empire State Plaza, PO Box 509, Albany, NY, 12201-0509, USA
| | - Alexey Khodjakov
- Division of Translational Medicine, NYS Department of Health, Wadsworth Center, Empire State Plaza, PO Box 509, Albany, NY, 12201-0509, USA
| | - Michael P Koonce
- Division of Translational Medicine, NYS Department of Health, Wadsworth Center, Empire State Plaza, PO Box 509, Albany, NY, 12201-0509, USA.
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11
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Baum DA. A comparison of autogenous theories for the origin of eukaryotic cells. AMERICAN JOURNAL OF BOTANY 2015; 102:1954-1965. [PMID: 26643887 DOI: 10.3732/ajb.1500196] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2015] [Accepted: 10/21/2015] [Indexed: 06/05/2023]
Abstract
PREMISE Eukaryotic cells have many unique features that all evolved on the stem lineage of living eukaryotes, making it difficult to reconstruct the order in which they accumulated. Nuclear endosymbiotic theories hold that three prokaryotes (nucleus, cytoplasm, and mitochondrion) came together to form a eukaryotic cell, whereas autogenous models hold that the nucleus and cytoplasm formed through evolutionary changes in a single prokaryotic lineage. Given several problems with nuclear endosymbiotic theories, this review focuses on autogenous models. KEY INSIGHTS Until recently all autogenous models assumed an outside-in (OI) topology, proposing that the nuclear envelope was formed from membrane-bound vesicles within the original cell body. Buzz Baum and I recently proposed an inside-out (IO) alternative, suggesting that the nucleus corresponds to the original cell body, with the cytoplasmic compartment deriving from extracellular protrusions. In this review, I show that OI and IO models are compatible with both mitochondria early (ME) or mitochondria late (ML) formulations. Whereas ME models allow that the relationship between mitochondria and host was mutualistic from the outset, ML models imply that the association began with predation or parasitism, becoming mutualistic later. In either case, the mutualistic interaction that eventually formed was probably syntrophic. CONCLUSIONS Diverse features of eukaryotic cell biology align well with the IOME model, but it would be premature to rule out the OIME model. ML models require that phagocytosis, a complex and energy expensive process, evolved before mitochondria, which seems unlikely. Nonetheless, further research is needed, especially resolution of the phylogenetic affinities of mitochondria.
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Affiliation(s)
- David A Baum
- Department of Botany and Wisconsin Institute for Discovery, University of Wisconsin, 430 Lincoln Drive, Madison, Wisconsin 53706 USA
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12
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Baum DA, Baum B. An inside-out origin for the eukaryotic cell. BMC Biol 2014; 12:76. [PMID: 25350791 PMCID: PMC4210606 DOI: 10.1186/s12915-014-0076-2] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2014] [Accepted: 09/17/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Although the origin of the eukaryotic cell has long been recognized as the single most profound change in cellular organization during the evolution of life on earth, this transition remains poorly understood. Models have always assumed that the nucleus and endomembrane system evolved within the cytoplasm of a prokaryotic cell. RESULTS Drawing on diverse aspects of cell biology and phylogenetic data, we invert the traditional interpretation of eukaryotic cell evolution. We propose that an ancestral prokaryotic cell, homologous to the modern-day nucleus, extruded membrane-bound blebs beyond its cell wall. These blebs functioned to facilitate material exchange with ectosymbiotic proto-mitochondria. The cytoplasm was then formed through the expansion of blebs around proto-mitochondria, with continuous spaces between the blebs giving rise to the endoplasmic reticulum, which later evolved into the eukaryotic secretory system. Further bleb-fusion steps yielded a continuous plasma membrane, which served to isolate the endoplasmic reticulum from the environment. CONCLUSIONS The inside-out theory is consistent with diverse kinds of data and provides an alternative framework by which to explore and understand the dynamic organization of modern eukaryotic cells. It also helps to explain a number of previously enigmatic features of cell biology, including the autonomy of nuclei in syncytia and the subcellular localization of protein N-glycosylation, and makes many predictions, including a novel mechanism of interphase nuclear pore insertion.
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13
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Anderson CA, Eser U, Korndorf T, Borsuk ME, Skotheim JM, Gladfelter AS. Nuclear repulsion enables division autonomy in a single cytoplasm. Curr Biol 2013; 23:1999-2010. [PMID: 24094857 PMCID: PMC4085259 DOI: 10.1016/j.cub.2013.07.076] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Revised: 05/31/2013] [Accepted: 07/23/2013] [Indexed: 02/08/2023]
Abstract
BACKGROUND Current models of cell-cycle control, based on classic studies of fused cells, predict that nuclei in a shared cytoplasm respond to the same CDK activities to undergo synchronous cycling. However, synchrony is rarely observed in naturally occurring syncytia, such as the multinucleate fungus Ashbya gossypii. In this system, nuclei divide asynchronously, raising the question of how nuclear timing differences are maintained despite sharing a common milieu. RESULTS We observe that neighboring nuclei are highly variable in division-cycle duration and that neighbors repel one another to space apart and demarcate their own cytoplasmic territories. The size of these territories increases as a nucleus approaches mitosis and can influence cycling rates. This nonrandom nuclear spacing is regulated by microtubules and is required for nuclear asynchrony, as nuclei that transiently come in very close proximity will partially synchronize. Sister nuclei born of the same mitosis are generally not persistent neighbors over their lifetimes yet remarkably retain similar division cycle times. This indicates that nuclei carry a memory of their birth state that influences their division timing and supports that nuclei subdivide a common cytosol into functionally distinct yet mobile compartments. CONCLUSIONS These findings support that nuclei use cytoplasmic microtubules to establish "cells within cells." Individual compartments appear to push against one another to compete for cytoplasmic territory and insulate the division cycle. This provides a mechanism by which syncytial nuclei can spatially organize cell-cycle signaling and suggests size control can act in a system without physical boundaries.
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Affiliation(s)
- Cori A. Anderson
- Department of Biological Sciences Dartmouth College Hanover, NH 03755
| | - Umut Eser
- Department of Applied Physics Stanford University Stanford, CA 94305
| | - Therese Korndorf
- Department of Biological Sciences Dartmouth College Hanover, NH 03755
| | - Mark E. Borsuk
- Thayer School of Engineering Dartmouth College Hanover, NH 03755
| | - Jan M. Skotheim
- Department of Biology Stanford University Stanford, CA 94305
| | - Amy S. Gladfelter
- Department of Biological Sciences Dartmouth College Hanover, NH 03755
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14
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Lee C, Zhang H, Baker AE, Occhipinti P, Borsuk ME, Gladfelter AS. Protein aggregation behavior regulates cyclin transcript localization and cell-cycle control. Dev Cell 2013; 25:572-84. [PMID: 23769973 DOI: 10.1016/j.devcel.2013.05.007] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2012] [Revised: 01/28/2013] [Accepted: 05/07/2013] [Indexed: 12/26/2022]
Abstract
Little is known about the active positioning of transcripts outside of embryogenesis or highly polarized cells. We show here that a specific G1 cyclin transcript is highly clustered in the cytoplasm of large multinucleate cells. This heterogeneous cyclin transcript localization results from aggregation of an RNA-binding protein, and deletion of a polyglutamine stretch in this protein results in random transcript localization. These multinucleate cells are remarkable in that nuclei cycle asynchronously despite sharing a common cytoplasm. Notably, randomization of cyclin transcript localization significantly diminishes nucleus-to-nucleus differences in the number of mRNAs and synchronizes cell-cycle timing. Thus, nonrandom cyclin transcript localization is important for cell-cycle timing control and arises due to polyQ-dependent behavior of an RNA-binding protein. There is a widespread association between polyQ expansions and RNA-binding motifs, suggesting that this is a broadly exploited mechanism to produce spatially variable transcripts and heterogeneous cell behaviors. PAPERCLIP:
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Affiliation(s)
- Changhwan Lee
- Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA
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15
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Pittman KJ, Skop AR. Anterior PAR proteins function during cytokinesis and maintain DYN-1 at the cleavage furrow in Caenorhabditis elegans. Cytoskeleton (Hoboken) 2012; 69:826-39. [PMID: 22887994 DOI: 10.1002/cm.21053] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Revised: 07/16/2012] [Accepted: 07/17/2012] [Indexed: 12/25/2022]
Abstract
PAR proteins are key regulators of cellular polarity and have links to the endocytic machinery and the actin cytoskeleton. Our data suggest a unique role for PAR proteins in cytokinesis. We have found that at the onset of cytokinesis, anterior PAR-6 and posterior PAR-2 proteins are redistributed to the furrow membrane in a temporal and spatial manner. PAR-6 and PAR-2 localize to the furrow membrane during ingression but PAR-2-GFP is distinct in that it is excluded from the extreme tip of the furrow. Once the midbody has formed, PAR-2-GFP becomes restricted to the midbody region (the midbody plus the membrane flanking it). Depletion of both anterior PAR proteins, PAR-3 and PAR-6, led to an increase in multinucleate embryos, suggesting that the anterior PAR proteins are necessary during cytokinesis and that PAR-3 and PAR-6 function in cytokinesis may be partially redundant. Lastly, anterior PAR proteins play a role in the maintenance of DYN-1 in the cleavage furrow. Our data indicate that the PAR proteins are involved in the events that occur during cytokinesis and may play a role in promoting the membrane trafficking and remodeling events that occur during this time.
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Affiliation(s)
- Kelly J Pittman
- Laboratory of Genetics and Medical Genetics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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16
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Nair DR, D'Ausilio CA, Occhipinti P, Borsuk ME, Gladfelter AS. A conserved G₁ regulatory circuit promotes asynchronous behavior of nuclei sharing a common cytoplasm. Cell Cycle 2010; 9:3771-9. [PMID: 20930528 DOI: 10.4161/cc.9.18.12999] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Synthesis and accumulation of conserved cell cycle regulators such as cyclins are thought to promote G₁/S and G₂/M transitions in most eukaryotes. When cells at different stages of the cell cycle are fused to form heterokaryons, the shared complement of regulators in the cytoplasm induces the nuclei to become synchronized. However, multinucleate fungi often display asynchronous nuclear division cycles, even though the nuclei inhabit a shared cytoplasm. Similarly, checkpoints can induce nuclear asynchrony in multinucleate cells by arresting only the nucleus that receives damage. The cell biological basis for nuclear autonomy in a common cytoplasm is not known. Here we show that in the filamentous fungus Ashbya gossypii, sister nuclei born from one mitosis immediately lose synchrony in the subsequent G₁ interval. A conserved G₁ transcriptional regulatory circuit involving the Rb-analogue Whi5p promotes the asynchronous behavior yet Whi5 protein is uniformly distributed among nuclei throughout the cell cycle. The homologous Whi5p circuit in S. cerevisiae employs positive feedback to promote robust and coherent entry into the cell cycle. We propose that positive feedback in this same circuit generates timing variability in a multinucleate cell. These unexpected findings indicate that a regulatory program whose products (mRNA transcripts) are translated in a common cytoplasm can nevertheless promote variability in the individual behavior of sister nuclei.
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Reynolds A. The redoubtable cell. STUDIES IN HISTORY AND PHILOSOPHY OF BIOLOGICAL AND BIOMEDICAL SCIENCES 2010; 41:194-201. [PMID: 20934640 DOI: 10.1016/j.shpsc.2010.07.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The cell theory--the thesis that all life is made up of one or more cells, the fundamental structural and physiological unit-is one of the most celebrated achievements of modern biological science. And yet from its very inception in the nineteenth century it has faced repeated criticism from some biologists. Why do some continue to criticize the cell theory, and how has it managed nevertheless to keep burying its undertakers? The answers to these questions reveal the complex nature of the cell theory and the cell concept on which it is based. Like other scientific 'laws', the assertion that all living things are made of cells purchases its universality at the expense of abstraction. If, however, this law is regarded merely as a widely applicable empirical generalization with notable exceptions, it still remains too important to discard. Debate about whether the cell or the organism standpoint provides the more correct account of anatomical, physiological, and developmental facts illustrates the tension between our attempts to express the truth about reality in conceptual terms conducive to a unified human understanding.
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Affiliation(s)
- Andrew Reynolds
- Department of Philosophy and Religious Studies, Cape Breton University, 1250 Grand Lake Road, Sydney, NS B1P 6L2, Canada.
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Abstract
Morphogen gradients provide embryonic tissues with positional information by inducing target genes at different concentration thresholds and thus at different positions. The Bicoid morphogen gradient in Drosophila melanogaster embryos has recently been analysed quantitatively, yet how it forms remains a matter of controversy. Several biophysical models that rely on production, diffusion and degradation have been formulated to account for the observed dynamics of the Bicoid gradient, but no one model can account for all its characteristics. Here, we discuss how existing data on this gradient fit the various proposed models and what aspects of gradient formation these models fail to explain. We suggest that knowing a few additional parameters, such as the lifetime of Bicoid, would help to identify and develop better models of Bicoid gradient formation.
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Affiliation(s)
- Oliver Grimm
- Howard Hughes Medical Institute, Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - Mathieu Coppey
- Laboratoire Kastler Brossel, Ecole normale supérieure, 46, rue d'Ulm, 75005 Paris, France
| | - Eric Wieschaus
- Howard Hughes Medical Institute, Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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Deng J, Wang W, Lu LJ, Ma J. A two-dimensional simulation model of the bicoid gradient in Drosophila. PLoS One 2010; 5:e10275. [PMID: 20422054 PMCID: PMC2858077 DOI: 10.1371/journal.pone.0010275] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2010] [Accepted: 03/31/2010] [Indexed: 12/31/2022] Open
Abstract
Background Bicoid (Bcd) is a Drosophila morphogenetic protein responsible for patterning the anterior structures in embryos. Recent experimental studies have revealed important insights into the behavior of this morphogen gradient, making it necessary to develop a model that can recapitulate the biological features of the system, including its dynamic and scaling properties. Methodology/Principal Findings We present a biologically realistic 2-D model of the dynamics of the Bcd gradient in Drosophila embryos. This model is based on equilibrium binding of Bcd molecules to non-specific, low affinity DNA sites throughout the Drosophila genome. It considers both the diffusion media within which the Bcd gradient is formed and the dynamic and other relevant properties of bcd mRNA from which Bcd protein is produced. Our model recapitulates key features of the Bcd protein gradient observed experimentally, including its scaling properties and the stability of its nuclear concentrations during development. Our simulation model also allows us to evaluate the effects of other biological activities on Bcd gradient formation, including the dynamic redistribution of bcd mRNA in early embryos. Our simulation results suggest that, in our model, Bcd protein diffusion is important for the formation of an exponential gradient in embryos. Conclusions/Significance The 2-D model described in this report is a simple and versatile simulation procedure, providing a quantitative evaluation of the Bcd gradient system. Our results suggest an important role of Bcd binding to non-specific, low-affinity DNA sites in proper formation of the Bcd gradient in our model. They demonstrate that highly complex biological systems can be effectively modeled with relatively few parameters.
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Affiliation(s)
- Jingyuan Deng
- Division of Biomedical Informatics, Cincinnati Children's Hospital Research Foundation, Cincinnati, Ohio, United States of America
- Department of Biomedical Engineering, University of Cincinnati, Cincinnati, Ohio, United States of America
| | - Wei Wang
- Division of Biomedical Informatics, Cincinnati Children's Hospital Research Foundation, Cincinnati, Ohio, United States of America
- Department of Chemical Engineering, University of Cincinnati, Cincinnati, Ohio, United States of America
| | - Long Jason Lu
- Division of Biomedical Informatics, Cincinnati Children's Hospital Research Foundation, Cincinnati, Ohio, United States of America
- Department of Biomedical Engineering, University of Cincinnati, Cincinnati, Ohio, United States of America
| | - Jun Ma
- Division of Biomedical Informatics, Cincinnati Children's Hospital Research Foundation, Cincinnati, Ohio, United States of America
- Division of Developmental Biology, Cincinnati Children's Hospital Research Foundation, Cincinnati, Ohio, United States of America
- * E-mail:
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