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Schweickert A, Ott T, Kurz S, Tingler M, Maerker M, Fuhl F, Blum M. Vertebrate Left-Right Asymmetry: What Can Nodal Cascade Gene Expression Patterns Tell Us? J Cardiovasc Dev Dis 2017; 5:jcdd5010001. [PMID: 29367579 PMCID: PMC5872349 DOI: 10.3390/jcdd5010001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Revised: 12/25/2017] [Accepted: 12/25/2017] [Indexed: 11/16/2022] Open
Abstract
Laterality of inner organs is a wide-spread characteristic of vertebrates and beyond. It is ultimately controlled by the left-asymmetric activation of the Nodal signaling cascade in the lateral plate mesoderm of the neurula stage embryo, which results from a cilia-driven leftward flow of extracellular fluids at the left-right organizer. This scenario is widely accepted for laterality determination in wildtype specimens. Deviations from this norm come in different flavors. At the level of organ morphogenesis, laterality may be inverted (situs inversus) or non-concordant with respect to the main body axis (situs ambiguus or heterotaxia). At the level of Nodal cascade gene activation, expression may be inverted, bilaterally induced, or absent. In a given genetic situation, patterns may be randomized or predominantly lacking laterality (absence or bilateral activation). We propose that the distributions of patterns observed may be indicative of the underlying molecular defects, with randomizations being primarily caused by defects in the flow-generating ciliary set-up, and symmetrical patterns being the result of impaired flow sensing, on the left, the right, or both sides. This prediction, the reasoning of which is detailed in this review, pinpoints functions of genes whose role in laterality determination have remained obscure.
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Affiliation(s)
- Axel Schweickert
- Institute of Zoology, University of Hohenheim, 70593 Stuttgart, Germany.
| | - Tim Ott
- Institute of Zoology, University of Hohenheim, 70593 Stuttgart, Germany.
| | - Sabrina Kurz
- Institute of Zoology, University of Hohenheim, 70593 Stuttgart, Germany.
| | - Melanie Tingler
- Institute of Zoology, University of Hohenheim, 70593 Stuttgart, Germany.
| | - Markus Maerker
- Institute of Zoology, University of Hohenheim, 70593 Stuttgart, Germany.
| | - Franziska Fuhl
- Institute of Zoology, University of Hohenheim, 70593 Stuttgart, Germany.
| | - Martin Blum
- Institute of Zoology, University of Hohenheim, 70593 Stuttgart, Germany.
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Tisler M, Schweickert A, Blum M. Xenopus, an ideal model organism to study laterality in conjoined twins. Genesis 2017; 55. [PMID: 28132423 DOI: 10.1002/dvg.22993] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Revised: 11/02/2016] [Accepted: 11/04/2016] [Indexed: 11/11/2022]
Abstract
Conjoined twins occur at low frequency in all vertebrates including humans. Many twins fused at the chest or abdomen display a very peculiar laterality defect: while the left twin is normal with respect to asymmetric organ morphogenesis and placement (situs solitus), the organ situs is randomized in right twins. Although this phenomenon has fascinated already some of the founders of experimental embryology in the 19th and early 20th century, such as Dareste, Fol, Warynsky and Spemann, its embryological basis has remained enigmatic. Here we summarize historical experiments and interpretations as well as current models, argue that the frog Xenopus is the only vertebrate model organism to tackle the issue, and outline suitable experiments to address the question of twin laterality in the context of cilia-based symmetry breakage.
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Affiliation(s)
- Matthias Tisler
- University of Hohenheim, Institute of Zoology, Stuttgart, D-70593, Germany
| | | | - Martin Blum
- University of Hohenheim, Institute of Zoology, Stuttgart, D-70593, Germany
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Tisler M, Thumberger T, Schneider I, Schweickert A, Blum M. Leftward Flow Determines Laterality in Conjoined Twins. Curr Biol 2017; 27:543-548. [PMID: 28190730 DOI: 10.1016/j.cub.2016.12.049] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Revised: 12/21/2016] [Accepted: 12/22/2016] [Indexed: 02/02/2023]
Abstract
Conjoined twins fused at the thorax display an enigmatic left-right defect: although left twins are normal, laterality is disturbed in one-half of right twins [1-3]. Molecularly, this randomization corresponds to a lack of asymmetric Nodal cascade induction in right twins [4]. We studied leftward flow [5, 6] at the left-right organizer (LRO) [7, 8] in thoracopagus twins in Xenopus, which displayed a duplicated, fused, and ciliated LRO. Cilia were motile and produced a leftward flow from the right LRO margin of the right to the left margin of the left twin. Motility was required for correct laterality in left twins, as knockdown of dynein motor dnah9 prevented Nodal cascade induction. Nodal was rescued by parallel knockdown of the inhibitor dand5 [9, 10] on the left side of the left twin. Lack of Nodal induction in the right twin, despite the presence of flow, was due to insufficient suppression of dand5. Knockdown of dand5 at the center of the fused LRO resulted in asymmetric Nodal cascade induction in the right twin as well. Manipulation of leftward flow and dand5 in a targeted and sided manner induced the Nodal cascade in a predictable manner, in the left twin, the right one, both, or neither. Laterality in conjoined twins thus was determined by cilia-driven leftward fluid flow like in single embryos, which solves a century-old riddle, as the phenomenon was already studied by some of the founders of experimental embryology, including Dareste [11], Fol and Warynsky [12], and Spemann and Falkenberg [13] (reviewed in [14]).
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Affiliation(s)
- Matthias Tisler
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Thomas Thumberger
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Isabelle Schneider
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Axel Schweickert
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Martin Blum
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany.
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Tosenberger A, Bessonov N, Levin M, Reinberg N, Volpert V, Morozova N. A conceptual model of morphogenesis and regeneration. Acta Biotheor 2015; 63:283-94. [PMID: 25822060 DOI: 10.1007/s10441-015-9249-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Accepted: 03/18/2015] [Indexed: 12/11/2022]
Abstract
This paper is devoted to computer modelling of the development and regeneration of multicellular biological structures. Some species (e.g. planaria and salamanders) are able to regenerate parts of their body after amputation damage, but the global rules governing cooperative cell behaviour during morphogenesis are not known. Here, we consider a simplified model organism, which consists of tissues formed around special cells that can be interpreted as stem cells. We assume that stem cells communicate with each other by a set of signals, and that the values of these signals depend on the distance between cells. Thus the signal distribution characterizes location of stem cells. If the signal distribution is changed, then the difference between the initial and the current signal distribution affects the behaviour of stem cells-e.g. as a result of an amputation of a part of tissue the signal distribution changes which stimulates stem cells to migrate to new locations, appropriate for regeneration of the proper pattern. Moreover, as stem cells divide and form tissues around them, they control the form and the size of regenerating tissues. This two-level organization of the model organism, with global regulation of stem cells and local regulation of tissues, allows its reproducible development and regeneration.
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Affiliation(s)
- A Tosenberger
- Institut des Hautes Études Scientifiques, 91440, Bures-sur-Yvette, France,
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5
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Blum M, Schweickert A, Vick P, Wright CVE, Danilchik MV. Symmetry breakage in the vertebrate embryo: when does it happen and how does it work? Dev Biol 2014; 393:109-23. [PMID: 24972089 PMCID: PMC4481729 DOI: 10.1016/j.ydbio.2014.06.014] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 06/08/2014] [Accepted: 06/17/2014] [Indexed: 10/25/2022]
Abstract
Asymmetric development of the vertebrate embryo has fascinated embryologists for over a century. Much has been learned since the asymmetric Nodal signaling cascade in the left lateral plate mesoderm was detected, and began to be unraveled over the past decade or two. When and how symmetry is initially broken, however, has remained a matter of debate. Two essentially mutually exclusive models prevail. Cilia-driven leftward flow of extracellular fluids occurs in mammalian, fish and amphibian embryos. A great deal of experimental evidence indicates that this flow is indeed required for symmetry breaking. An alternative model has argued, however, that flow simply acts as an amplification step for early asymmetric cues generated by ion flux during the first cleavage divisions. In this review we critically evaluate the experimental basis of both models. Although a number of open questions persist, the available evidence is best compatible with flow-based symmetry breakage as the archetypical mode of symmetry breakage.
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Affiliation(s)
- Martin Blum
- University of Hohenheim, Institute of Zoology (220), Garbenstrasse 30, D-70593 Stuttgart, Germany.
| | - Axel Schweickert
- University of Hohenheim, Institute of Zoology (220), Garbenstrasse 30, D-70593 Stuttgart, Germany
| | - Philipp Vick
- University of Hohenheim, Institute of Zoology (220), Garbenstrasse 30, D-70593 Stuttgart, Germany
| | - Christopher V E Wright
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37232-0494, USA
| | - Michael V Danilchik
- Department of Integrative Biosciences, Oregon Health & Science University, Portland, OR 97239-3098, USA
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VANDENBERG LAURAN, BLACKISTON DOUGLASJ, REA ADAMC, DORE TIMOTHYM, LEVIN MICHAEL. Left-right patterning in Xenopus conjoined twin embryos requires serotonin signaling and gap junctions. THE INTERNATIONAL JOURNAL OF DEVELOPMENTAL BIOLOGY 2014; 58:799-809. [PMID: 25896280 PMCID: PMC10471180 DOI: 10.1387/ijdb.140215ml] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
A number of processes operating during the first cell cleavages enable the left-right (LR) axis to be consistently oriented during Xenopus laevis development. Prior work showed that secondary organizers induced in frog embryos after cleavage stages (i.e. conjoined twins arising from ectopic induced primary axes) correctly pattern their own LR axis only when a primary (early) organizer is also present. This instructive effect confirms the unique LR patterning functions that occur during early embryogenesis, but leaves open the question: which mechanisms that operate during early stages are also involved in the orientation of later-induced organizers? We sought to distinguish the two phases of LR patterning in secondary organizers (LR patterning of the primary twin and the later transfer of this information to the secondary twin) by perturbing only the latter process. Here, we used reagents that do not affect primary LR patterning at the time secondary organizers form to inhibit each of 4 mechanisms in the induced twin. Using pharmacological, molecular-genetic, and photo-chemical tools, we show that serotonergic and gap-junctional signaling, but not proton or potassium flows, are required for the secondary organizer to appropriately pattern its LR axis in a multicellular context. We also show that consistently-asymmetric gene expression begins prior to ciliary flow. Together, our data highlight the importance of physiological signaling in the propagation of cleavage-derived LR orientation to multicellular cell fields.
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Affiliation(s)
- LAURA N. VANDENBERG
- Biology Department, Center for Regenerative and Developmental Biology, Tufts University, Medford, MA, USA
- Department of Public Health, Division of Environmental Health Sciences, University of Massachusetts – Amherst, Amherst, MA, USA
| | - DOUGLAS J. BLACKISTON
- Biology Department, Center for Regenerative and Developmental Biology, Tufts University, Medford, MA, USA
| | - ADAM C. REA
- Department of Chemistry, University of Georgia, Athens, GA, USA and
| | - TIMOTHY M. DORE
- Department of Chemistry, University of Georgia, Athens, GA, USA and
- New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
| | - MICHAEL LEVIN
- Biology Department, Center for Regenerative and Developmental Biology, Tufts University, Medford, MA, USA
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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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Ma K. Embryonic left-right separation mechanism allows confinement of mutation-induced phenotypes to one lateral body half of bilaterians. Am J Med Genet A 2013; 161A:3095-114. [PMID: 24254848 DOI: 10.1002/ajmg.a.36188] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 07/16/2013] [Indexed: 11/08/2022]
Abstract
A fundamental question in developmental biology is how a chimeric animal such as a bilateral gynandromorphic animal can have different phenotypes confined to different lateral body halves, and how mutation-induced phenotypes, such as genetic diseases, can be confined to one lateral body half in patients. Here, I propose that embryos of many, if not all, bilaterian animals are divided into left and right halves at a very early stage (which may vary among different types of animals), after which the descendants of the left-sided and right-sided cells will almost exclusively remain on their original sides, respectively, throughout the remaining development. This embryonic left-right separation mechanism allows (1) mutations and the mutation-induced phenotypes to be strictly confined to one lateral body half in animals and humans; (2) mothers with bilateral hereditary primary breast cancer to transmit their disease to their offspring at twofold of the rate compared to mothers with unilateral hereditary breast cancer; and (3) a mosaic embryo carrying genetic or epigenetic mutations to develop into either an individual with the mutation-induced phenotype confined unilaterally, or a pair of twins displaying complete, partial, or mirror-image discordance for the phenotype. Further, this left-right separation mechanism predicts that the two lateral halves of a patient carrying a unilateral genetic disease can each serve as a case and an internal control, respectively, for genetic and epigenetic comparative studies to identify the disease causations.
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9
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Blackiston DJ, Levin M. Ectopic eyes outside the head in Xenopus tadpoles provide sensory data for light-mediated learning. ACTA ACUST UNITED AC 2013; 216:1031-40. [PMID: 23447666 DOI: 10.1242/jeb.074963] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
A major roadblock in the biomedical treatment of human sensory disorders, including blindness, has been an incomplete understanding of the nervous system and its ability to adapt to changes in sensory modality. Likewise, fundamental insight into the evolvability of complex functional anatomies requires understanding brain plasticity and the interaction between the nervous system and body architecture. While advances have been made in the generation of artificial and biological replacement components, the brain's ability to interpret sensory information arising from ectopic locations is not well understood. We report the use of eye primordia grafts to create ectopic eyes along the body axis of Xenopus tadpoles. These eyes are morphologically identical to native eyes and can be induced at caudal locations. Cell labeling studies reveal that eyes created in the tail send projections to the stomach and trunk. To assess function we performed light-mediated learning assays using an automated machine vision and environmental control system. The results demonstrate that ectopic eyes in the tail of Xenopus tadpoles could confer vision to the host. Thus ectopic visual organs were functional even when present at posterior locations. These data and protocols demonstrate the ability of vertebrate brains to interpret sensory input from ectopic structures and incorporate them into adaptive behavioral programs. This tractable new model for understanding the robust plasticity of the central nervous system has significant implications for regenerative medicine and sensory augmentation technology.
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Affiliation(s)
- Douglas J Blackiston
- Center for Regenerative and Developmental Biology and Department of Biology, Tufts University, 200 Boston Avenue, Suite 4600, Medford, MA 02155, USA
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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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Röttinger E, Dahlin P, Martindale MQ. A framework for the establishment of a cnidarian gene regulatory network for "endomesoderm" specification: the inputs of ß-catenin/TCF signaling. PLoS Genet 2012; 8:e1003164. [PMID: 23300467 PMCID: PMC3531958 DOI: 10.1371/journal.pgen.1003164] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Accepted: 10/27/2012] [Indexed: 12/03/2022] Open
Abstract
Understanding the functional relationship between intracellular factors and
extracellular signals is required for reconstructing gene regulatory networks
(GRN) involved in complex biological processes. One of the best-studied
bilaterian GRNs describes endomesoderm specification and predicts that both
mesoderm and endoderm arose from a common GRN early in animal evolution.
Compelling molecular, genomic, developmental, and evolutionary evidence supports
the hypothesis that the bifunctional gastrodermis of the cnidarian-bilaterian
ancestor is derived from the same evolutionary precursor of both endodermal and
mesodermal germ layers in all other triploblastic bilaterian animals. We have
begun to establish the framework of a provisional cnidarian
“endomesodermal” gene regulatory network in the sea anemone,
Nematostella vectensis, by using a genome-wide microarray
analysis on embryos in which the canonical Wnt/ß-catenin pathway was
ectopically targeted for activation by two distinct pharmaceutical agents
(lithium chloride and 1-azakenpaullone) to identify potential targets of
endomesoderm specification. We characterized 51 endomesodermally expressed
transcription factors and signaling molecule genes (including 18 newly
identified) with fine-scale temporal (qPCR) and spatial (in
situ) analysis to define distinct co-expression domains within the
animal plate of the embryo and clustered genes based on their earliest zygotic
expression. Finally, we determined the input of the canonical
Wnt/ß-catenin pathway into the cnidarian endomesodermal GRN using
morpholino and mRNA overexpression experiments to show that NvTcf/canonical Wnt
signaling is required to pattern both the future endomesodermal and ectodermal
domains prior to gastrulation, and that both BMP and FGF (but not Notch)
pathways play important roles in germ layer specification in this animal. We
show both evolutionary conserved as well as profound differences in
endomesodermal GRN structure compared to bilaterians that may provide
fundamental insight into how GRN subcircuits have been adopted, rewired, or
co-opted in various animal lineages that give rise to specialized endomesodermal
cell types. Cnidarians (anemones, corals, and “jellyfish”) are an animal group
whose adults possess derivatives of only two germ layers: ectoderm and a
bifunctional (absorptive and contractile) gastrodermal (gut) layer. Cnidarians
are the closest living relatives to bilaterally symmetrical animals that possess
all three germ layers (ecto, meso, and endoderm); and compelling molecular,
genomic, developmental, and evolutionary evidence exists to demonstrate that the
cnidarian gastrodermis is evolutionarily related to both endodermal and
mesodermal germ layers in all other triploblastic bilaterian animals. Little is
known about endomesoderm specification in cnidarians. In this study, we
constructed the framework of a cnidarian endomesodermal gene regulatory network
in the sea anemone, Nematostella vectensis, using a combination
of experimental approaches. We identified and characterized by both qPCR and
in situ hybridization 51 genes expressed in defined domains
within the presumptive endomesoderm. In addition, we functionally demonstrate
that Wnt/Tcf signaling is crucial for regionalized expression of a defined
subset of these genes prior to gut formation and endomesoderm maintenance. Our
results support the idea of an ancient gene regulatory network underlying
endomesoderm specification that involves inputs from multiple signaling pathways
(Wnt, FGF, BMP, but not Notch) early in development, that are temporarily
uncoupled in bilaterian animals.
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Affiliation(s)
- Eric Röttinger
- Kewalo Marine Laboratory, Pacific Biosciences Research Center,
University of Hawai'i, Honolulu, Hawai'i, United States of
America
| | - Paul Dahlin
- Kewalo Marine Laboratory, Pacific Biosciences Research Center,
University of Hawai'i, Honolulu, Hawai'i, United States of
America
| | - Mark Q. Martindale
- Kewalo Marine Laboratory, Pacific Biosciences Research Center,
University of Hawai'i, Honolulu, Hawai'i, United States of
America
- * E-mail:
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Maurer B, Geyer SH, Weninger WJ. A chick embryo with a yet unclassified type of cephalothoracopagus malformation and a hypothesis for explaining its genesis. Anat Histol Embryol 2012; 42:191-200. [PMID: 22971166 DOI: 10.1111/ahe.12002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Accepted: 08/06/2012] [Indexed: 12/12/2022]
Abstract
Cephalothoracopagus embryos are conjoined twins, who share parts of their heads, necks and bodies. Our study aims at presenting a detailed morphological analysis of a cephalothoracopagus chick embryo of developmental stage 31. Because none of the existing theories can explain the genesis of the phenotype of this embryo, we also suggest a hypothesis, which explains it. Beside the cephalothoracopagus embryo, we investigated five control embryos. With the aid of the high-resolution episcopic microscopy (HREM) technique, we created digital volume data and three-dimensional (3D) computer models of the organs and arteries of the embryos. We used the 3D models for topological analysis and for measuring the diameters of the great intrathoracic arteries. The malformed embryo showed two body backs, each containing a notochord, spinal cord and dorsal aorta. The body backs continued into separated lower bodies. The embryo had a single, four-chambered heart, single respiratory tract and single upper alimentary tract. The topology of the pharyngeal arch arteries was normal, and the diameters of these arteries were similar to that of the control embryos. We classified the embryo we investigated as a yet unknown malformation and suggest a hypothesis explaining its genesis.
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Affiliation(s)
- B Maurer
- Integrative Morphology Group, Centre for Anatomy and Cell Biology, Medical University of Vienna, Vienna, Austria
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Vandenberg LN, Levin M. Polarity proteins are required for left-right axis orientation and twin-twin instruction. Genesis 2012; 50:219-34. [PMID: 22086838 PMCID: PMC3294047 DOI: 10.1002/dvg.20825] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2011] [Revised: 11/08/2011] [Accepted: 11/09/2011] [Indexed: 01/31/2023]
Abstract
Two main classes of models address the earliest steps of left-right patterning: those postulating that asymmetry is initiated via cilia-driven fluid flow in a multicellular tissue at gastrulation, and those postulating that asymmetry is amplified from intrinsic chirality of individual cells at very early embryonic stages. A recent study revealed that cultured human cells have consistent left-right (LR) biases that are dependent on apical-basal polarity machinery. The ability of single cells to set up asymmetry suggests that cellular chirality could be converted to embryonic laterality by cilia-independent polarity mechanisms in cell fields. To examine the link between cellular polarity and LR patterning in a vertebrate model organism, we probed the roles of apical-basal and planar polarity proteins in the orientation of the LR axis in Xenopus. Molecular loss-of-function targeting these polarity pathways specifically randomizes organ situs independently of contribution to the ciliated organ. Alterations in cell polarity also disrupt tight junction integrity, localization of the LR signaling molecule serotonin, the normally left-sided expression of Xnr-1, and the LR instruction occurring between native and ectopic organizers. We propose that well-conserved polarity complexes are required for LR asymmetry and that cell polarity signals establish the flow of laterality information across the early blastoderm independently of later ciliary functions. genesis 50:219-234, 2012. © 2011 Wiley Periodicals, Inc.
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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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Vandenberg LN. Laterality defects are influenced by timing of treatments and animal model. Differentiation 2012; 83:26-37. [PMID: 22099174 PMCID: PMC3222854 DOI: 10.1016/j.diff.2011.08.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2011] [Revised: 07/13/2011] [Accepted: 08/11/2011] [Indexed: 10/17/2022]
Abstract
The timing of when the embryonic left-right (LR) axis is first established and the mechanisms driving this process are subjects of strong debate. While groups have focused on the role of cilia in establishing the LR axis during gastrula and neurula stages, many animals appear to orient the LR axis prior to the appearance of, or without the benefit of, motile cilia. Because of the large amount of data available in the published literature and the similarities in the type of data collected across laboratories, I have examined relationships between the studies that do and do not implicate cilia, the choice of animal model, the kinds of LR patterning defects observed, and the penetrance of LR phenotypes. I found that treatments affecting cilia structure and motility had a higher penetrance for both altered gene expression and improper organ placement compared to treatments that affect processes in early cleavage stage embryos. I also found differences in penetrance that could be attributed to the animal models used; the mouse is highly prone to LR randomization. Additionally, the data were examined to address whether gene expression can be used to predict randomized organ placement. Using regression analysis, gene expression was found to be predictive of organ placement in frogs, but much less so in the other animals examined. Together, these results challenge previous ideas about the conservation of LR mechanisms, with the mouse model being significantly different from fish, frogs, and chick in almost every aspect examined. Additionally, this analysis indicates that there may be missing pieces in the molecular pathways that dictate how genetic information becomes organ positional information in vertebrates; these gaps will be important for future studies to identify, as LR asymmetry is not only a fundamentally fascinating aspect of development but also of considerable biomedical importance.
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Affiliation(s)
- Laura N. Vandenberg
- Tufts University, Center for Regenerative & Developmental Biology and Department of Biology, Medford MA 02155
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15
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Linking early determinants and cilia-driven leftward flow in left-right axis specification of Xenopus laevis: a theoretical approach. Differentiation 2011; 83:S67-77. [PMID: 22136958 DOI: 10.1016/j.diff.2011.11.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2011] [Revised: 11/10/2011] [Accepted: 11/13/2011] [Indexed: 11/23/2022]
Abstract
In vertebrates, laterality - the asymmetric placement of the viscera including organs of the gastrointestinal system, heart and lungs - is under the genetic control of a conserved signaling pathway in the left lateral plate mesoderm (LPM). A key feature of this pathway, shared by embryos of all non-avian vertebrate classes analyzed to date (e.g. fish, amphibia and mammals) is the formation of a transitory midline epithelial structure. Remarkably, the motility of cilia projecting from this epithelium produce a leftward-directed movement of extracellular liquid. This leftward flow precedes any sign of asymmetry in gene expression. Numerous analyses have shown that this leftward flow is not only necessary, but indeed sufficient to direct laterality. Interestingly, however, cilia-independent mechanisms acting much earlier in development in the frog Xenopus have been reported during the earliest cleavage stages, a period before any major zygotic gene transcription. The relationship between these two distinct mechanisms is not understood. In this review we present the conserved and critical steps of Xenopus LR axis formation. Next, we address the basic question of how an early asymmetric activity might contribute to, feed into, or regulate the conserved cilia-dependent pathway. Finally, we discuss the possibility that Spemann's organizer is itself polarized in the left-right dimension. In attempting to reconcile the sufficiency of the cilia-dependent pathway with potential earlier-acting asymmetries, we offer a general practical experimental checklist for the Xenopus community working on the process of left-right determination. This approach indicates areas where work still needs to be done to clarify the relationship between early determinants and cilia-driven leftward flow.
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16
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Vandenberg LN, Pennarola BW, Levin M. Low frequency vibrations disrupt left-right patterning in the Xenopus embryo. PLoS One 2011; 6:e23306. [PMID: 21826245 PMCID: PMC3149648 DOI: 10.1371/journal.pone.0023306] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Accepted: 07/15/2011] [Indexed: 11/19/2022] Open
Abstract
The development of consistent left-right (LR) asymmetry across phyla is a fascinating question in biology. While many pharmacological and molecular approaches have been used to explore molecular mechanisms, it has proven difficult to exert precise temporal control over functional perturbations. Here, we took advantage of acoustical vibration to disrupt LR patterning in Xenopus embryos during tightly-circumscribed periods of development. Exposure to several low frequencies induced specific randomization of three internal organs (heterotaxia). Investigating one frequency (7 Hz), we found two discrete periods of sensitivity to vibration; during the first period, vibration affected the same LR pathway as nocodazole, while during the second period, vibration affected the integrity of the epithelial barrier; both are required for normal LR patterning. Our results indicate that low frequency vibrations disrupt two steps in the early LR pathway: the orientation of the LR axis with the other two axes, and the amplification/restriction of downstream LR signals to asymmetric organs.
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Affiliation(s)
- Laura N. Vandenberg
- Center for Regenerative and Developmental Biology, Tufts University, Medford, Massachusetts, United States of America
- Biology Department, Tufts University, Medford, Massachusetts, United States of America
| | - Brian W. Pennarola
- Biology Department, Tufts University, Medford, Massachusetts, United States of America
| | - Michael Levin
- Center for Regenerative and Developmental Biology, Tufts University, Medford, Massachusetts, United States of America
- Biology Department, Tufts University, Medford, Massachusetts, United States of America
- * E-mail:
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17
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Kato Y. The multiple roles of Notch signaling during left-right patterning. Cell Mol Life Sci 2011; 68:2555-67. [PMID: 21544546 PMCID: PMC11114802 DOI: 10.1007/s00018-011-0695-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2010] [Revised: 03/28/2011] [Accepted: 04/19/2011] [Indexed: 10/18/2022]
Abstract
The establishment of left-right (LR) asymmetry is regulated by intricate signaling mechanisms during embryogenesis and this asymmetry is critical for morphogenesis as well as the positioning of internal organs within the organism. Recent progress including elucidation of ion transporters, leftward nodal flow, and regulation of asymmetric gene expression contributes to our understanding of how the breaking of the symmetry is initiated and how this laterality information is subsequently transmitted to the organ primordium. A number of developmental signaling pathways have been implicated in this complex process. In this review, we will focus on the roles of the Notch signaling pathway during development of LR asymmetry. The Notch signaling pathway is a short-range communication system between neighboring cells. While Notch signaling plays essential roles in regulating the morphogenesis of the node and left-specific expression of Nodal in the lateral plate mesoderm, a hallmark gene in LR patterning, Notch signaling also suppresses the expression of Pitx2 that is a direct downstream target of Nodal during later stages of development. This negative activity of Notch signaling towards left-specific activity was recently shown to be inhibited by the B cell lymphoma 6 (BCL6)/BCL6 co-repressor (BcoR) transcriptional repressor complex in a target-specific manner. The complex regulation of Notch-dependent gene expression for LR asymmetry will be highlighted in this review.
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Affiliation(s)
- Yoichi Kato
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL 32306, USA.
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18
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Utsuno H, Asami T, Van Dooren TJM, Gittenberger E. INTERNAL SELECTION AGAINST THE EVOLUTION OF LEFT-RIGHT REVERSAL. Evolution 2011; 65:2399-411. [DOI: 10.1111/j.1558-5646.2011.01293.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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19
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Blackiston D, Shomrat T, Nicolas CL, Granata C, Levin M. A second-generation device for automated training and quantitative behavior analyses of molecularly-tractable model organisms. PLoS One 2010; 5:e14370. [PMID: 21179424 PMCID: PMC3003703 DOI: 10.1371/journal.pone.0014370] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2010] [Accepted: 11/23/2010] [Indexed: 11/18/2022] Open
Abstract
A deep understanding of cognitive processes requires functional, quantitative analyses of the steps leading from genetics and the development of nervous system structure to behavior. Molecularly-tractable model systems such as Xenopus laevis and planaria offer an unprecedented opportunity to dissect the mechanisms determining the complex structure of the brain and CNS. A standardized platform that facilitated quantitative analysis of behavior would make a significant impact on evolutionary ethology, neuropharmacology, and cognitive science. While some animal tracking systems exist, the available systems do not allow automated training (feedback to individual subjects in real time, which is necessary for operant conditioning assays). The lack of standardization in the field, and the numerous technical challenges that face the development of a versatile system with the necessary capabilities, comprise a significant barrier keeping molecular developmental biology labs from integrating behavior analysis endpoints into their pharmacological and genetic perturbations. Here we report the development of a second-generation system that is a highly flexible, powerful machine vision and environmental control platform. In order to enable multidisciplinary studies aimed at understanding the roles of genes in brain function and behavior, and aid other laboratories that do not have the facilities to undergo complex engineering development, we describe the device and the problems that it overcomes. We also present sample data using frog tadpoles and flatworms to illustrate its use. Having solved significant engineering challenges in its construction, the resulting design is a relatively inexpensive instrument of wide relevance for several fields, and will accelerate interdisciplinary discovery in pharmacology, neurobiology, regenerative medicine, and cognitive science.
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Affiliation(s)
- Douglas Blackiston
- Biology Department and Center for Regenerative and Developmental Biology, Tufts University, Medford, Massachusetts, United States of America
- Department of Regenerative and Developmental Biology, Forsyth Institute, Boston, Massachusetts, United States of America
| | - Tal Shomrat
- Biology Department and Center for Regenerative and Developmental Biology, Tufts University, Medford, Massachusetts, United States of America
| | - Cindy L. Nicolas
- Biology Department and Center for Regenerative and Developmental Biology, Tufts University, Medford, Massachusetts, United States of America
| | - Christopher Granata
- Boston Engineering Corporation, Waltham, Massachusetts, United States of America
| | - Michael Levin
- Biology Department and Center for Regenerative and Developmental Biology, Tufts University, Medford, Massachusetts, United States of America
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Vandenberg LN, Levin M. Far from solved: a perspective on what we know about early mechanisms of left-right asymmetry. Dev Dyn 2010; 239:3131-46. [PMID: 21031419 PMCID: PMC10468760 DOI: 10.1002/dvdy.22450] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/31/2023] Open
Abstract
Consistent laterality is a crucial aspect of embryonic development, physiology, and behavior. While strides have been made in understanding unilaterally expressed genes and the asymmetries of organogenesis, early mechanisms are still poorly understood. One popular model centers on the structure and function of motile cilia and subsequent chiral extracellular fluid flow during gastrulation. Alternative models focus on intracellular roles of the cytoskeleton in driving asymmetries of physiological signals or asymmetric chromatid segregation, at much earlier stages. All three models trace the origin of asymmetry back to the chirality of cytoskeletal organizing centers, but significant controversy exists about how this intracellular chirality is amplified onto cell fields. Analysis of specific predictions of each model and crucial recent data on new mutants suggest that ciliary function may not be a broadly conserved, initiating event in left-right patterning. Many questions about embryonic left-right asymmetry remain open, offering fascinating avenues for further research in cell, developmental, and evolutionary biology.
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Affiliation(s)
- Laura N. Vandenberg
- Biology Department, and Tufts Center for Regenerative and Developmental Biology, Tufts University, Medford, Massachusetts
| | - Michael Levin
- Biology Department, and Tufts Center for Regenerative and Developmental Biology, Tufts University, Medford, Massachusetts
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