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McDowell G, Rajadurai S, Levin M. From cytoskeletal dynamics to organ asymmetry: a nonlinear, regulative pathway underlies left-right patterning. Philos Trans R Soc Lond B Biol Sci 2017; 371:rstb.2015.0409. [PMID: 27821521 DOI: 10.1098/rstb.2015.0409] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/15/2016] [Indexed: 12/25/2022] Open
Abstract
Consistent left-right (LR) asymmetry is a fundamental aspect of the bodyplan across phyla, and errors of laterality form an important class of human birth defects. Its molecular underpinning was first discovered as a sequential pathway of left- and right-sided gene expression that controlled positioning of the heart and visceral organs. Recent data have revised this picture in two important ways. First, the physical origin of chirality has been identified; cytoskeletal dynamics underlie the asymmetry of single-cell behaviour and patterning of the LR axis. Second, the pathway is not linear: early disruptions that alter the normal sidedness of upstream asymmetric genes do not necessarily induce defects in the laterality of the downstream genes or in organ situs Thus, the LR pathway is a unique example of two fascinating aspects of biology: the interplay of physics and genetics in establishing large-scale anatomy, and regulative (shape-homeostatic) pathways that correct molecular and anatomical errors over time. Here, we review aspects of asymmetry from its intracellular, cytoplasmic origins to the recently uncovered ability of the LR control circuitry to achieve correct gene expression and morphology despite reversals of key 'determinant' genes. We provide novel functional data, in Xenopus laevis, on conserved elements of the cytoskeleton that drive asymmetry, and comparatively analyse it together with previously published results in the field. Our new observations and meta-analysis demonstrate that despite aberrant expression of upstream regulatory genes, embryos can progressively normalize transcriptional cascades and anatomical outcomes. LR patterning can thus serve as a paradigm of how subcellular physics and gene expression cooperate to achieve developmental robustness of a body axis.This article is part of the themed issue 'Provocative questions in left-right asymmetry'.
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Affiliation(s)
- Gary McDowell
- Biology Department, Tufts University, 200 Boston Avenue, Suite 4600, Medford, MA 02155-4243, USA.,Allen Discovery Center, Tufts University, 200 Boston Avenue, Suite 4600, Medford, MA 02155-4243, USA
| | - Suvithan Rajadurai
- Biology Department, Tufts University, 200 Boston Avenue, Suite 4600, Medford, MA 02155-4243, USA.,Allen Discovery Center, Tufts University, 200 Boston Avenue, Suite 4600, Medford, MA 02155-4243, USA
| | - Michael Levin
- Biology Department, Tufts University, 200 Boston Avenue, Suite 4600, Medford, MA 02155-4243, USA .,Allen Discovery Center, Tufts University, 200 Boston Avenue, Suite 4600, Medford, MA 02155-4243, USA
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Inaki M, Liu J, Matsuno K. Cell chirality: its origin and roles in left-right asymmetric development. Philos Trans R Soc Lond B Biol Sci 2017; 371:rstb.2015.0403. [PMID: 27821533 PMCID: PMC5104503 DOI: 10.1098/rstb.2015.0403] [Citation(s) in RCA: 86] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/30/2016] [Indexed: 12/19/2022] Open
Abstract
An item is chiral if it cannot be superimposed on its mirror image. Most biological molecules are chiral. The homochirality of amino acids ensures that proteins are chiral, which is essential for their functions. Chirality also occurs at the whole-cell level, which was first studied mostly in ciliates, single-celled protozoans. Ciliates show chirality in their cortical structures, which is not determined by genetics, but by 'cortical inheritance'. These studies suggested that molecular chirality directs whole-cell chirality. Intriguingly, chirality in cellular structures and functions is also found in metazoans. In Drosophila, intrinsic cell chirality is observed in various left-right (LR) asymmetric tissues, and appears to be responsible for their LR asymmetric morphogenesis. In other invertebrates, such as snails and Caenorhabditis elegans, blastomere chirality is responsible for subsequent LR asymmetric development. Various cultured cells of vertebrates also show intrinsic chirality in their cellular behaviours and intracellular structural dynamics. Thus, cell chirality may be a general property of eukaryotic cells. In Drosophila, cell chirality drives the LR asymmetric development of individual organs, without establishing the LR axis of the whole embryo. Considering that organ-intrinsic LR asymmetry is also reported in vertebrates, this mechanism may contribute to LR asymmetric development across phyla.This article is part of the themed issue 'Provocative questions in left-right asymmetry'.
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Affiliation(s)
- Mikiko Inaki
- Department of Biological Sciences, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
| | - Jingyang Liu
- Department of Biological Sciences, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
| | - Kenji Matsuno
- Department of Biological Sciences, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
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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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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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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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Abstract
Most animal species exhibit left-right asymmetry in their body plans and show a strong bias for one handedness over the other. The mechanism of handedness choice, recognized as an intriguing problem over a century ago, is still a mystery. However, from recent advances in understanding when and how asymmetry arises in both invertebrates and vertebrates, developmental pathways for establishment and maintenance of left-right differences are beginning to take shape, and speculations can be made on the initial choice mechanism.
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Affiliation(s)
- W B Wood
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder 80309-0347, USA.
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Abstract
The early embryo orients to the antero-posterior axis and differentiates along this, and the dorso-ventral and lateral axes. From Drosophila melanogaster, detailed knowledge has accrued of how segmentation and dorso-ventral differentiation proceed, and of their genic control, mostly by selector and homeobox (Hox) genes. The study of the control of lateral differentiation, instead, has been largely neglected. Yet handed asymmetry (the "obvious" asymmetries of, for example, heart, lung, anatomical features of the nervous system, etc.) is basic and, possibly, universal. In the mouse, two genes control this: the iv gene which, when mutated, leads to random, in the place of biased, asymmetry and so to random situs inversus viscerum: and the inv mutation which, by contrast, results in 100% situs inversus. Both mutants act as autosomal recessives. Human situs inversus is heterogeneous and may be akin to that produced by the murine iv gene. In spite of situs inversus, there is no shift of hand preference; but there is no information on other lateralization, e.g. of language or of dermatoglyphic patterns. Handed asymmetry is known in Drosophila, but there is no information on its control. In the experimental nematode, Caenorhabditis elegans, asymmetry arises when differently programmed cells arrange themselves to the two body sides, and is present already at the six-cell stage; and even the major sensory neurons chains along the body axis are distributed unequally on the two sides of the worm. Experimentally, by embryonic micro-manipulation or the use of chemical mutagens, the normal and invariate direction of handed asymmetry can be reversed.
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Affiliation(s)
- P E Polani
- Division of Medical and Molecular Genetics, United Medical and Dental Schools of Guy's and St Thomas's Hospital, London, UK
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