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Yamada S, Tanaka Y, Imai KS, Saigou M, Onuma TA, Nishida H. Wavy movements of epidermis monocilia drive the neurula rotation that determines left-right asymmetry in ascidian embryos. Dev Biol 2019; 448:173-182. [PMID: 30059669 DOI: 10.1016/j.ydbio.2018.07.023] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 06/19/2018] [Accepted: 07/26/2018] [Indexed: 12/22/2022]
Abstract
Tadpole larvae of the ascidian, Halocynthia roretzi, show morphological left-right asymmetry in the brain structures and the orientation of tail bending within the vitelline membrane. Neurula embryos rotate along the anterior-posterior axis in a counterclockwise direction, and then this rotation stops when the left side of the embryo is oriented downwards. Contact of the left-side epidermis with the vitelline membrane promotes nodal gene expression in the left-side epidermis. This is a novel mechanism in which rotation of whole embryos provides the initial cue for breaking left-right symmetry. Here we show that epidermal monocilia, which appear at the neurula rotation stage, generate the driving force for rotation. A ciliary protein, Arl13b, fused with Venus YFP was used for live imaging of ciliary movements. Although overexpression of wild-type Arl13b fusion protein resulted in aberrant movements of the cilia and abrogation of neurula rotation, mutant Arl13b fusion protein, in which the GTPase and coiled-coil domains were removed, did not affect the normal ciliary movements and neurula rotation. Epidermis cilia moved in a wavy and serpentine way like sperm flagella but not in a rotational way or beating way with effective stroke and recovery stroke. They moved very slowly, at 1/7 Hz, consistent with the low angular velocity of neurula rotation (ca. 43°/min). The tips of most cilia pointed in the opposite direction of embryonic rotation. Similar motility was also observed in Ciona robusta embryos. When embryos were treated with a dynein inhibitor, Ciliobrevin D, both ciliary movements and neurula rotation were abrogated, showing that ciliary movements drive neurula rotation in Halocynthia. The drug also inhibited Ciona neurula rotation. Our observations suggest that the driving force of rotation is generated using the vitelline membrane as a substrate but not by making a water current around the embryo. It is of evolutionary interest that ascidians use ciliary movements to break embryonic left-right symmetry, like in many vertebrates. Meanwhile, ascidian embryos rotate as a whole, similar to embryos of non-vertebrate deuterostomes, such as echinoderm, hemichordate, and amphioxus, while swimming.
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Affiliation(s)
- Shiori Yamada
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Yuka Tanaka
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Kaoru S Imai
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Motohiko Saigou
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Takeshi A Onuma
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan.
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Tanaka Y, Yamada S, Connop SL, Hashii N, Sawada H, Shih Y, Nishida H. Vitelline membrane proteins promote left-sided nodal expression after neurula rotation in the ascidian, Halocynthia roretzi. Dev Biol 2019; 449:52-61. [PMID: 30710513 DOI: 10.1016/j.ydbio.2019.01.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2018] [Revised: 01/28/2019] [Accepted: 01/30/2019] [Indexed: 11/19/2022]
Abstract
Stereotyped left-right asymmetry both in external and internal organization is found in various animals. Left-right symmetry is broken by the neurula rotation in the ascidian, Halocynthia roretzi. Neurula embryos rotate along the anterior-posterior axis in a counterclockwise direction, and the rotation stops when the left side of the embryo is oriented downwards, resulting in contact of the left-side epidermis with the vitelline membrane at the bottom of perivitelline space. Then, such contact induces the expression of nodal and its downstream Pitx2 gene in the left-side epidermis. Vitelline membrane is required for the promotion of nodal expression. Here, we showed that a chemical signal from the vitelline membrane promotes nodal gene expression, but mechanical stimulus at the point of contact is unnecessary since the treatment of devitellinated neurulae with an extract of the vitelline membrane promoted nodal expression on both sides. The signal molecules are already present in the vitelline membranes of unfertilized eggs. These signal molecules are proteins but not sugars. Specific fractions in gel filtration chromatography had the nodal promoting activity. By mass spectrometry, we selected 48 candidate proteins. Proteins that contain both a zona pellucida (ZP) domain and epidermal growth factor (EGF) repeats were enriched in the candidates of the nodal inducing molecules. Six of the ZP proteins had multiple EGF repeats that are only found in ascidian ZP proteins. These were considered to be the most viable candidates of the nodal-inducing molecules. Signal molecules are anchored to the entire vitelline membrane, and contact sites of signal-receiving cells are spatially and mechanically controlled by the neurula rotation. In this context, ascidians are unusual with respect to mechanisms for specification of the left-right axis. By suppressing formation of epidermis monocilia, we also showed that epidermal cilia drive the neurula rotation but are dispensable for sensing the signal from the vitelline membrane.
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Affiliation(s)
- Yuka Tanaka
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Shiori Yamada
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Samantha L Connop
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Noritaka Hashii
- Division of Biological Chemistry and Biologicals, National Institute of Health Sciences, Kawasaki, Kanagawa 210-9501, Japan
| | - Hitoshi Sawada
- Sugashima Marine Biological Laboratory, Graduate School of Science, Nagoya University, Sugashima, Toba 517-0004, Japan
| | - Yu Shih
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Hiroki Nishida
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
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Tingler M, Kurz S, Maerker M, Ott T, Fuhl F, Schweickert A, LeBlanc-Straceski JM, Noselli S, Blum M. A Conserved Role of the Unconventional Myosin 1d in Laterality Determination. Curr Biol 2018; 28:810-816.e3. [PMID: 29478852 DOI: 10.1016/j.cub.2018.01.075] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2017] [Revised: 01/01/2018] [Accepted: 01/24/2018] [Indexed: 02/05/2023]
Abstract
Anatomical and functional asymmetries are widespread in the animal kingdom [1, 2]. In vertebrates, many visceral organs are asymmetrically placed [3]. In snails, shells and inner organs coil asymmetrically, and in Drosophila, genitalia and hindgut undergo a chiral rotation during development. The evolutionary origin of these asymmetries remains an open question [1]. Nodal signaling is widely used [4], and many, but not all, vertebrates use cilia for symmetry breaking [5]. In Drosophila, which lacks both cilia and Nodal, the unconventional myosin ID (myo1d) gene controls dextral rotation of chiral organs [6, 7]. Here, we studied the role of myo1d in left-right (LR) axis formation in Xenopus. Morpholino oligomer-mediated myo1d downregulation affected organ placement in >50% of morphant tadpoles. Induction of the left-asymmetric Nodal cascade was aberrant in >70% of cases. Expression of the flow-target gene dand5 was compromised, as was flow itself, due to shorter, fewer, and non-polarized cilia at the LR organizer. Additional phenotypes pinpointed Wnt/planar cell polarity signaling and suggested that myo1d, like in Drosophila [8], acted in the context of the planar cell polarity pathway. Indeed, convergent extension of gastrula explant cultures was inhibited in myo1d morphants, and the ATF2 reporter gene for non-canonical Wnt signaling was downregulated. Finally, genetic interference experiments demonstrated a functional interaction between the core planar cell polarity signaling gene vangl2 and myo1d in LR axis formation. Thus, our data identified myo1d as a common denominator of arthropod and chordate asymmetry, in agreement with a monophyletic origin of animal asymmetry.
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Affiliation(s)
- Melanie Tingler
- University of Hohenheim, Institute of Zoology, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Sabrina Kurz
- University of Hohenheim, Institute of Zoology, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Markus Maerker
- University of Hohenheim, Institute of Zoology, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Tim Ott
- University of Hohenheim, Institute of Zoology, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Franziska Fuhl
- University of Hohenheim, Institute of Zoology, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Axel Schweickert
- University of Hohenheim, Institute of Zoology, Garbenstrasse 30, 70593 Stuttgart, Germany
| | | | - Stéphane Noselli
- Université Côte d'Azur, CNRS, INSERM, Institut de Biologie Valrose, Parc Valrose, 06108 Nice, France
| | - Martin Blum
- University of Hohenheim, Institute of Zoology, Garbenstrasse 30, 70593 Stuttgart, Germany.
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Palmquist K, Davidson B. Establishment of lateral organ asymmetries in the invertebrate chordate, Ciona intestinalis. EvoDevo 2017; 8:12. [PMID: 28770040 PMCID: PMC5526266 DOI: 10.1186/s13227-017-0075-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Accepted: 07/17/2017] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND The evolutionary emergence and diversification of the chordates appear to involve dramatic changes in organ morphogenesis along the left/right axis. However, the ancestral chordate mechanism for establishing lateral asymmetry remains ambiguous. Additionally, links between the initial establishment of lateral asymmetry and subsequent asymmetries in organ morphogenesis are poorly characterized. RESULTS To explore asymmetric organ morphogenesis during chordate evolution, we have begun to characterize left/right patterning of the heart and endodermal organs in an invertebrate chordate, Ciona intestinalis. Here, we show that Ciona has a laterally asymmetric, right-sided heart. Our data indicate that cardiac lateral asymmetry requires H+/K+ ion flux, but is independent of Nodal signaling. Our pharmacological inhibitor studies show that ion flux is required for polarization of epidermal cilia and neurula rotation and suggest that ion flux functions synergistically with chorion contact to drive cardiac laterality. Live imaging analysis revealed that larval heart progenitor cells undergo a lateral shift without displaying any migratory behaviors. Furthermore, we find that this passive shift corresponds with the emergence of lateral asymmetry in the endoderm, which is also ion flux dependent. CONCLUSIONS Our data suggest that ion flux promotes laterally asymmetric morphogenesis of the larval endoderm rudiment leading to a passive, Nodal-independent shift in the position of associated heart progenitor cells. These findings help to refine hypotheses regarding ancestral chordate left/right patterning mechanisms and how they have diverged within invertebrate and vertebrate chordate lineages.
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Affiliation(s)
- Karl Palmquist
- Department of Biology, Swarthmore College, 500 College Ave., Swarthmore, PA 19081 USA
| | - Brad Davidson
- Department of Biology, Swarthmore College, 500 College Ave., Swarthmore, PA 19081 USA
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5
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Ryan K, Lu Z, Meinertzhagen IA. The CNS connectome of a tadpole larva of Ciona intestinalis (L.) highlights sidedness in the brain of a chordate sibling. eLife 2016; 5. [PMID: 27921996 PMCID: PMC5140270 DOI: 10.7554/elife.16962] [Citation(s) in RCA: 133] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Accepted: 10/17/2016] [Indexed: 12/12/2022] Open
Abstract
Left-right asymmetries in brains are usually minor or cryptic. We report brain asymmetries in the tiny, dorsal tubular nervous system of the ascidian tadpole larva, Ciona intestinalis. Chordate in body plan and development, the larva provides an outstanding example of brain asymmetry. Although early neural development is well studied, detailed cellular organization of the swimming larva's CNS remains unreported. Using serial-section EM we document the synaptic connectome of the larva's 177 CNS neurons. These formed 6618 synapses including 1772 neuromuscular junctions, augmented by 1206 gap junctions. Neurons are unipolar with at most a single dendrite, and few synapses. Some synapses are unpolarised, others form reciprocal or serial motifs; 922 were polyadic. Axo-axonal synapses predominate. Most neurons have ciliary organelles, and many features lack structural specialization. Despite equal cell numbers on both sides, neuron identities and pathways differ left/right. Brain vesicle asymmetries include a right ocellus and left coronet cells.
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Affiliation(s)
- Kerrianne Ryan
- Department of Biology, Life Sciences Centre, Dalhousie University, Halifax, Canada.,Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University, Halifax, Canada
| | - Zhiyuan Lu
- Department of Biology, Life Sciences Centre, Dalhousie University, Halifax, Canada.,Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University, Halifax, Canada
| | - Ian A Meinertzhagen
- Department of Biology, Life Sciences Centre, Dalhousie University, Halifax, Canada.,Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University, Halifax, Canada
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Negishi T, Miyazaki N, Murata K, Yasuo H, Ueno N. Physical association between a novel plasma-membrane structure and centrosome orients cell division. eLife 2016; 5:e16550. [PMID: 27502556 PMCID: PMC4978527 DOI: 10.7554/elife.16550] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 06/20/2016] [Indexed: 01/16/2023] Open
Abstract
In the last mitotic division of the epidermal lineage in the ascidian embryo, the cells divide stereotypically along the anterior-posterior axis. During interphase, we found that a unique membrane structure invaginates from the posterior to the centre of the cell, in a microtubule-dependent manner. The invagination projects toward centrioles on the apical side of the nucleus and associates with one of them. Further, a cilium forms on the posterior side of the cell and its basal body remains associated with the invagination. A laser ablation experiment suggests that the invagination is under tensile force and promotes the posterior positioning of the centrosome. Finally, we showed that the orientation of the invaginations is coupled with the polarized dynamics of centrosome movements and the orientation of cell division. Based on these findings, we propose a model whereby this novel membrane structure orchestrates centrosome positioning and thus the orientation of cell division axis.
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Affiliation(s)
- Takefumi Negishi
- Division of Morphogenesis, National Institute for Basic Biology, National Institutes of Natural Sciences, Okazaki, Japan
- Laboratoire de Biologie du Développement de Villefranche-sur-mer UMR7009, Observatoire Océanologique, Sorbonne Universités, UPMC Université Paris 06, CNRS, Villefranche-sur-Mer, France
| | - Naoyuki Miyazaki
- National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki, Japan
| | - Kazuyoshi Murata
- National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki, Japan
| | - Hitoyoshi Yasuo
- Laboratoire de Biologie du Développement de Villefranche-sur-mer UMR7009, Observatoire Océanologique, Sorbonne Universités, UPMC Université Paris 06, CNRS, Villefranche-sur-Mer, France
| | - Naoto Ueno
- Division of Morphogenesis, National Institute for Basic Biology, National Institutes of Natural Sciences, Okazaki, Japan
- Department of Basic Biology, School of Life Science, The Graduate University for Advanced Studies, Okazaki, Japan
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7
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Thompson H, Shimeld SM. Transmission and Scanning Electron Microscopy of the Accessory Cells and Chorion During Development of Ciona intestinalis Type B Embryos and the Impact of Their Removal on Cell Morphology. Zoolog Sci 2015; 32:217-22. [PMID: 26003975 DOI: 10.2108/zs140231] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Spawned ascidian oocytes are surrounded by a membrane called the chorion (or vitelline coat) and associated with two populations of maternally-supplied cells. Outside the chorion are follicle cells, which may affect the buoyancy of eggs. Inside the chorion are test cells, which during oogenesis provision the egg and which after fertilisation contribute to the larval tunic. The structure of maternal cells may vary between species. The model ascidian Ciona intestinalis has been recently split into two species, currently named type A and type B. The ultrastructure of extraembryonic cells and structures from type A embryos has been reported. Here we describe the ultrastructure of follicle and test cells from C. intestinalis type B embryos. Test cells are about 5 µm in diameter and line the inside of the chorion of developing embryos in a dense sheet. Follicle cells are large (> 100 µm long) and spike-shaped, with many large vesicles. Terminal electron dense granules are found towards the tips of spikes, adjacent to cytoplasm containing numerous small electron dense bodies connected by filaments. These are probably vesicles containing material for the terminal granules. Removal of maternal structures and cells just after fertilisation, as commonly used in many experiments manipulating C. intestinalis development, has been reported to affect embryonic patterning. We examined the impact of this on embryonic ectoderm cells by scanning electron microscopy. Cells of embryos that developed without maternal structures still developed cilia, but had indistinct cell boundaries and a more flattened appearance than those that developed within the chorion.
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Affiliation(s)
- Helen Thompson
- Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
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8
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Blum M, Feistel K, Thumberger T, Schweickert A. The evolution and conservation of left-right patterning mechanisms. Development 2014; 141:1603-13. [PMID: 24715452 DOI: 10.1242/dev.100560] [Citation(s) in RCA: 116] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Morphological asymmetry is a common feature of animal body plans, from shell coiling in snails to organ placement in humans. The signaling protein Nodal is key for determining this laterality. Many vertebrates, including humans, use cilia for breaking symmetry during embryonic development: rotating cilia produce a leftward flow of extracellular fluids that induces the asymmetric expression of Nodal. By contrast, Nodal asymmetry can be induced flow-independently in invertebrates. Here, we ask when and why flow evolved. We propose that flow was present at the base of the deuterostomes and that it is required to maintain organ asymmetry in otherwise perfectly bilaterally symmetrical vertebrates.
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Affiliation(s)
- Martin Blum
- Institute of Zoology, University of Hohenheim, 70593 Stuttgart, Germany
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9
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Namigai EK, Kenny NJ, Shimeld SM. Right across the tree of life: The evolution of left-right asymmetry in the Bilateria. Genesis 2014; 52:458-70. [DOI: 10.1002/dvg.22748] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 01/27/2014] [Accepted: 01/29/2014] [Indexed: 02/02/2023]
Affiliation(s)
- Erica K.O. Namigai
- Department of Zoology; University of Oxford; South Parks Road Oxford United Kingdom
| | - Nathan J. Kenny
- Department of Zoology; University of Oxford; South Parks Road Oxford United Kingdom
| | - Sebastian M. Shimeld
- Department of Zoology; University of Oxford; South Parks Road Oxford United Kingdom
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10
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Abstract
The satellite symposium on 'Making and breaking the left-right axis: implications of laterality in development and disease' was held in June 2013 in conjunction with the 17th International Society for Developmental Biology meeting in Cancún, Mexico. As we summarize here, leaders in the field gathered at the symposium to discuss recent advances in understanding how left-right asymmetry is generated and utilized across the animal kingdom.
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Affiliation(s)
- Rebecca D Burdine
- Department of Molecular Biology, Princeton University, Washington Road, Princeton, NJ 08544, USA
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11
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Vandenberg LN, Lemire JM, Levin M. It's never too early to get it Right: A conserved role for the cytoskeleton in left-right asymmetry. Commun Integr Biol 2013; 6:e27155. [PMID: 24505508 PMCID: PMC3912007 DOI: 10.4161/cib.27155] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Revised: 11/08/2013] [Accepted: 11/11/2013] [Indexed: 01/08/2023] Open
Abstract
For centuries, scientists and physicians have been captivated by the consistent left-right (LR) asymmetry of the heart, viscera, and brain. A recent study implicated tubulin proteins in establishing laterality in several experimental models, including asymmetric chemosensory receptor expression in C. elegans neurons, polarization of HL-60 human neutrophil-like cells in culture, and asymmetric organ placement in Xenopus. The same mutations that randomized asymmetry in these diverse systems also affect chirality in Arabidopsis, revealing a remarkable conservation of symmetry-breaking mechanisms among kingdoms. In Xenopus, tubulin mutants only affected LR patterning very early, suggesting that this axis is established shortly after fertilization. This addendum summarizes and extends the knowledge of the cytoskeleton's role in the patterning of the LR axis. Results from many species suggest a conserved role for the cytoskeleton as the initiator of asymmetry, and indicate that symmetry is first broken during early embryogenesis by an intracellular process.
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Affiliation(s)
- Laura N Vandenberg
- Biology Department; Center for Regenerative and Developmental Biology; Tufts University; Medford, MA USA ; Current affiliation: Department of Public Health; Division of Environmental Health Sciences; University of Massachusetts, Amherst; Amherst, MA USA
| | - Joan M Lemire
- Biology Department; Center for Regenerative and Developmental Biology; Tufts University; Medford, MA USA
| | - Michael Levin
- Biology Department; Center for Regenerative and Developmental Biology; Tufts University; Medford, MA USA
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12
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Roles of cilia, fluid flow, and Ca2+ signaling in breaking of left-right symmetry. Trends Genet 2013; 30:10-7. [PMID: 24091059 DOI: 10.1016/j.tig.2013.09.001] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Revised: 08/18/2013] [Accepted: 09/03/2013] [Indexed: 11/23/2022]
Abstract
The emergence of left-right (L-R) asymmetry during embryogenesis is a classic problem in developmental biology. It is only since the 1990s, however, that substantial insight into this problem has been achieved by molecular and genetic approaches. Various genes required for L-R asymmetric morphogenesis in vertebrates have now been identified, and many of these genes are required for the formation and motility of cilia. Breaking of L-R symmetry in the mouse embryo occurs in the ventral node, where two types of cilia are present. Whereas centrally located motile cilia generate a leftward fluid flow, peripherally located immotile cilia sense a flow-dependent signal, which is either chemical or mechanical in nature. Although Ca2+ signaling is implicated in flow sensing, the precise mechanism remains unknown. Here we summarize current knowledge of L-R symmetry breaking in vertebrates (focusing on the mouse), with a special emphasis on the roles of cilia, fluid flow, and Ca2+ signaling.
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13
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Katsumoto S, Hatta K, Nakagawa M. Brief hypo-osmotic shock causes test cell death, prevents neurula rotation, and disrupts left-right asymmetry in Ciona intestinalis. Zoolog Sci 2013; 30:352-9. [PMID: 23646939 DOI: 10.2108/zsj.30.352] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Ascidian Ciona intestinalis tadpole larvae exhibit left-right asymmetry. The photoreceptors are situated on the right side of the sensory vesicle, and the tail curls along the left side of the trunk within the chorion. In tailbud embryos, the Ci-pitx gene is expressed in the left-side epidermis. It was previously reported that embryos generated from naked eggs, which lack the chorionic membrane and accessory cells (follicle cells attached to the outside of the chorion and test cells covering the inner surface of the chorion), show bilateral expression of Ci-pitx. This suggested that the chorion or accessory cells are needed for generation of asymmetry. Here, we show that a brief treatment with 60% artificial seawater (ASW) before, but not after, the neurula stage results in bilateral expression of Ci-pitx in the chorion of tailbud embryos, loss of follicle cells, and randomization of both the direction of tail curling and the locations of photoreceptors in larvae. This treatment also impaired the transient counterclockwise rotation within the chorion at the neurula stage. Nearly all test cells in the chorion died following 60% ASW treatment. These results suggest that dead test cells blocked the neural rotation and impaired left-right asymmetry. We also showed that tailbud embryos and larvae generated from defolliculated eggs produced by 80% ASW treatment, in which the test cells were alive, showed normal left-right asymmetry, suggesting that the follicle cells were not essential for asymmetric morphogenesis.
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Affiliation(s)
- Shimpei Katsumoto
- Graduate School of Life Science, University of Hyogo, Koto 3-2-1, Kamigori, Akoh-gun, Japan
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14
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Vandenberg LN, Levin M. A unified model for left-right asymmetry? Comparison and synthesis of molecular models of embryonic laterality. Dev Biol 2013; 379:1-15. [PMID: 23583583 PMCID: PMC3698617 DOI: 10.1016/j.ydbio.2013.03.021] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Revised: 03/15/2013] [Accepted: 03/22/2013] [Indexed: 12/31/2022]
Abstract
Understanding how and when the left-right (LR) axis is first established is a fundamental question in developmental biology. A popular model is that the LR axis is established relatively late in embryogenesis, due to the movement of motile cilia and the resultant directed fluid flow during late gastrulation/early neurulation. Yet, a large body of evidence suggests that biophysical, molecular, and bioelectrical asymmetries exist much earlier in development, some as early as the first cell cleavage after fertilization. Alternative models of LR asymmetry have been proposed that accommodate these data, postulating that asymmetry is established due to a chiral cytoskeleton and/or the asymmetric segregation of chromatids. There are some similarities, and many differences, in how these various models postulate the origin and timing of symmetry breaking and amplification, and these events' linkage to the well-conserved subsequent asymmetric transcriptional cascades. This review examines experimental data that lend strong support to an early origin of LR asymmetry, yet are also consistent with later roles for cilia in the amplification of LR pathways. In this way, we propose that the various models of asymmetry can be unified: early events are needed to initiate LR asymmetry, and later events could be utilized by some species to maintain LR-biases. We also present an alternative hypothesis, which proposes that individual embryos stochastically choose one of several possible pathways with which to establish their LR axis. These two hypotheses are both tractable in appropriate model species; testing them to resolve open questions in the field of LR patterning will reveal interesting new biology of wide relevance to developmental, cell, and evolutionary biology.
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Affiliation(s)
- Laura N. Vandenberg
- Center for Regenerative and Developmental Biology, and Biology Department, Tufts University, Medford, MA 02155
| | - Michael Levin
- Center for Regenerative and Developmental Biology, and Biology Department, Tufts University, Medford, MA 02155
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