1
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Dean DM, Deitcher DL, Paster CO, Xu M, Loehlin DW. "A fly appeared": sable, a classic Drosophila mutation, maps to Yippee, a gene affecting body color, wings, and bristles. G3 (BETHESDA, MD.) 2022; 12:jkac058. [PMID: 35266526 PMCID: PMC9073688 DOI: 10.1093/g3journal/jkac058] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Accepted: 03/04/2022] [Indexed: 11/12/2022]
Abstract
Insect body color is an easily assessed and visually engaging trait that is informative on a broad range of topics including speciation, biomaterial science, and ecdysis. Mutants of the fruit fly Drosophila melanogaster have been an integral part of body color research for more than a century. As a result of this long tenure, backlogs of body color mutations have remained unmapped to their genes, all while their strains have been dutifully maintained, used for recombination mapping, and part of genetics education. Stemming from a lesson plan in our undergraduate genetics class, we have mapped sable1, a dark body mutation originally described by Morgan and Bridges, to Yippee, a gene encoding a predicted member of the E3 ubiquitin ligase complex. Deficiency/duplication mapping, genetic rescue, DNA and cDNA sequencing, RT-qPCR, and 2 new CRISPR alleles indicated that sable1 is a hypomorphic Yippee mutation due to an mdg4 element insertion in the Yippee 5'-UTR. Further analysis revealed additional Yippee mutant phenotypes including curved wings, ectopic/missing bristles, delayed development, and failed adult emergence. RNAi of Yippee in the ectoderm phenocopied sable body color and most other Yippee phenotypes. Although Yippee remains functionally uncharacterized, the results presented here suggest possible connections between melanin biosynthesis, copper homeostasis, and Notch/Delta signaling; in addition, they provide insight into past studies of sable cell nonautonomy and of the genetic modifier suppressor of sable.
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Affiliation(s)
- Derek M Dean
- Department of Biology, Williams College, Williamstown, MA 01267, USA
| | - David L Deitcher
- Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA
| | - Caleigh O Paster
- Department of Biology, Williams College, Williamstown, MA 01267, USA
| | - Manting Xu
- Department of Biology, Williams College, Williamstown, MA 01267, USA
| | - David W Loehlin
- Department of Biology, Williams College, Williamstown, MA 01267, USA
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2
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Gualtieri CT. Genomic Variation, Evolvability, and the Paradox of Mental Illness. Front Psychiatry 2021; 11:593233. [PMID: 33551865 PMCID: PMC7859268 DOI: 10.3389/fpsyt.2020.593233] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Accepted: 11/27/2020] [Indexed: 12/30/2022] Open
Abstract
Twentieth-century genetics was hard put to explain the irregular behavior of neuropsychiatric disorders. Autism and schizophrenia defy a principle of natural selection; they are highly heritable but associated with low reproductive success. Nevertheless, they persist. The genetic origins of such conditions are confounded by the problem of variable expression, that is, when a given genetic aberration can lead to any one of several distinct disorders. Also, autism and schizophrenia occur on a spectrum of severity, from mild and subclinical cases to the overt and disabling. Such irregularities reflect the problem of missing heritability; although hundreds of genes may be associated with autism or schizophrenia, together they account for only a small proportion of cases. Techniques for higher resolution, genomewide analysis have begun to illuminate the irregular and unpredictable behavior of the human genome. Thus, the origins of neuropsychiatric disorders in particular and complex disease in general have been illuminated. The human genome is characterized by a high degree of structural and behavioral variability: DNA content variation, epistasis, stochasticity in gene expression, and epigenetic changes. These elements have grown more complex as evolution scaled the phylogenetic tree. They are especially pertinent to brain development and function. Genomic variability is a window on the origins of complex disease, neuropsychiatric disorders, and neurodevelopmental disorders in particular. Genomic variability, as it happens, is also the fuel of evolvability. The genomic events that presided over the evolution of the primate and hominid lineages are over-represented in patients with autism and schizophrenia, as well as intellectual disability and epilepsy. That the special qualities of the human genome that drove evolution might, in some way, contribute to neuropsychiatric disorders is a matter of no little interest.
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3
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Poyatos JF. Genetic buffering and potentiation in metabolism. PLoS Comput Biol 2020; 16:e1008185. [PMID: 32925942 PMCID: PMC7514045 DOI: 10.1371/journal.pcbi.1008185] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Revised: 09/24/2020] [Accepted: 07/23/2020] [Indexed: 01/12/2023] Open
Abstract
Cells adjust their metabolism in response to mutations, but how this reprogramming depends on the genetic context is not well known. Specifically, the absence of individual enzymes can affect reprogramming, and thus the impact of mutations in cell growth. Here, we examine this issue with an in silico model of Saccharomyces cerevisiae's metabolism. By quantifying the variability in the growth rate of 10000 different mutant metabolisms that accumulated changes in their reaction fluxes, in the presence, or absence, of a specific enzyme, we distinguish a subset of modifier genes serving as buffers or potentiators of variability. We notice that the most potent modifiers refer to the glycolysis pathway and that, more broadly, they show strong pleiotropy and epistasis. Moreover, the evidence that this subset depends on the specific growing condition strengthens its systemic underpinning, a feature only observed before in a toy model of a gene-regulatory network. Some of these enzymes also modulate the effect that biochemical noise and environmental fluctuations produce in growth. Thus, the reorganization of metabolism induced by mutations has not only direct physiological implications but also transforms the influence that other mutations have on growth. This is a general result with implications in the development of cancer therapies based on metabolic inhibitors.
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Affiliation(s)
- Juan F. Poyatos
- Logic of Genomic Systems Lab (CNB-CSIC), Madrid, Spain
- Center for Genomics and Systems Biology (NYU), New York, United States of America
- * E-mail:
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4
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Sato A. Chaperones, Canalization, and Evolution of Animal Forms. Int J Mol Sci 2018; 19:E3029. [PMID: 30287767 PMCID: PMC6213012 DOI: 10.3390/ijms19103029] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Revised: 10/02/2018] [Accepted: 10/03/2018] [Indexed: 12/18/2022] Open
Abstract
Over half a century ago, British developmental biologist Conrad Hal Waddington proposed the idea of canalization, that is, homeostasis in development. Since the breakthrough that was made by Rutherford and Lindquist (1998), who proposed a role of Hsp90 in developmental buffering, chaperones have gained much attention in the study of canalization. However, recent studies have revealed that a number of other molecules are also potentially involved in canalization. Here, I introduce the emerging role of DnaJ chaperones in canalization. I also discuss how the expression levels of such buffering molecules can be altered, thereby altering organismal development. Since developmental robustness is maternally inherited in various organisms, I propose that dynamic bet hedging, an increase in within-clutch variation in offspring phenotypes that is caused by unpredictable environmental challenges to the mothers, plays a key role in altering the expression levels of buffering molecules. Investigating dynamic bet hedging at the molecular level and how it impacts upon morphological phenotypes will help our understanding of the molecular mechanisms of canalization and evolutionary processes.
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Affiliation(s)
- Atsuko Sato
- Department of Biology, Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112-0012, Japan.
- Marine Biological Association of the UK, The Laboratory, Plymouth PL1 2PB, UK.
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5
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Takahashi KH, Ishimori M, Iwata H. HSP90 as a global genetic modifier for male genital morphology in Drosophila melanogaster. Evolution 2018; 72:2419-2434. [PMID: 30221481 DOI: 10.1111/evo.13598] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Accepted: 09/03/2018] [Indexed: 02/06/2023]
Abstract
The molecular chaperone protein HSP90 has been proposed to modulate genotype-phenotype relationship in a broad range of organisms. We explore the proposed genetic modifier effect of HSP90 through a genomewide analysis. Here, we show that HSP90 functions as a genetic modifier of genital morphology in Drosophila melanogaster. We identified a large number of single-nucleotide polymorphisms (SNPs) with an HSP90-dependent effect by using genome wide association analysis. We classified the SNPs into the ones under capacitance effect (smaller allelic effect under HSP90 inhibition) or the ones under potentiation effect (larger allelic effect under HSP90 inhibition). Although the majority of SNPs are under capacitance, there are a large number of SNPs under potentiation. This observation provides support for a model in which Hsp90 is not described exclusively as a "genetic capacitor," but is described more broadly as a "genetic modifier." Because the majority of the candidate genes estimated from SNPs with an HSP90-dependent effect in the current study has never been reported to interact with HSP90 directly, the global genetic modifier effect of HSP90 may be exhibited through epistatic interactions in gene regulatory networks.
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Affiliation(s)
- Kazuo H Takahashi
- Graduate School of Environmental and Life Science, Okayama University, 1-1-1 Tsushima-naka, Kita-ku, Okayama-si, Okayama-ken, 700-8530, Japan
| | - Motoyuki Ishimori
- Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-8657, Japan
| | - Hiroyoshi Iwata
- Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-8657, Japan
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6
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Chen B, Feder ME, Kang L. Evolution of heat-shock protein expression underlying adaptive responses to environmental stress. Mol Ecol 2018; 27:3040-3054. [PMID: 29920826 DOI: 10.1111/mec.14769] [Citation(s) in RCA: 110] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Revised: 06/03/2018] [Accepted: 06/07/2018] [Indexed: 12/27/2022]
Abstract
Heat-shock proteins (Hsps) and their cognates are primary mitigators of cell stress. With increasingly severe impacts of climate change and other human modifications of the biosphere, the ability of the heat-shock system to affect evolutionary fitness in environments outside the laboratory and to evolve in response is topic of growing importance. Since the last major reviews, several advances have occurred. First, demonstrations of the heat-shock response outside the laboratory now include many additional taxa and environments. Many of these demonstrations are only correlative, however. More importantly, technical advances in "omic" quantification of nucleic acids and proteins, genomewide association analysis, and manipulation of genes and their expression have enabled the field to move beyond correlation. Several consequent advances are already evident: The pathway from heat-shock gene expression to stress tolerance in nature can be extremely complex, mediated through multiple biological processes and systems, and even multiple species. The underlying genes are more numerous, diverse and variable than previously appreciated, especially with respect to their regulatory variation and epigenetic changes. The impacts and limitations (e.g., due to trade-offs) of natural selection on these genes have become more obvious and better established. At last, as evolutionary capacitors, Hsps may have distinctive impacts on the evolution of other genes and ecological consequences.
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Affiliation(s)
- Bing Chen
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
| | - Martin E Feder
- Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, Illinois
| | - Le Kang
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
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7
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Decanalizing thinking on genetic canalization. Semin Cell Dev Biol 2018; 88:54-66. [PMID: 29751086 DOI: 10.1016/j.semcdb.2018.05.008] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Revised: 05/07/2018] [Accepted: 05/07/2018] [Indexed: 02/01/2023]
Abstract
The concept of genetic canalization has had an abiding influence on views of complex-trait evolution. A genetically canalized system has evolved to become less sensitive to the effects of mutation. When a gene product that supports canalization is compromised, the phenotypic impacts of a mutation should be more pronounced. This expected increase in mutational effects not only has important consequences for evolution, but has also motivated strategies to treat disease. However, recent studies demonstrate that, when putative agents of genetic canalization are impaired, systems do not behave as expected. Here, we review the evidence that is used to infer whether particular gene products are agents of genetic canalization. Then we explain how such inferences often succumb to a converse error. We go on to show that several candidate agents of genetic canalization increase the phenotypic impacts of some mutations while decreasing the phenotypic impacts of others. These observations suggest that whether a gene product acts as a 'buffer' (lessening mutational effects) or a 'potentiator' (increasing mutational effects) is not a fixed property of the gene product but instead differs for the different mutations with which it interacts. To investigate features of genetic interactions that might predispose them toward buffering versus potentiation, we explore simulated gene-regulatory networks. Similarly to putative agents of genetic canalization, the gene products in simulated networks also modify the phenotypic effects of mutations in other genes without a strong overall tendency towards lessening or increasing these effects. In sum, these observations call into question whether complex traits have evolved to become less sensitive (i.e., are canalized) to genetic change, and the degree to which trends exist that predict how one genetic change might alter another's impact. We conclude by discussing approaches to address these and other open questions that are brought into focus by re-thinking genetic canalization.
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8
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Takahashi KH. Multiple modes of canalization: Links between genetic, environmental canalizations and developmental stability, and their trait-specificity. Semin Cell Dev Biol 2018; 88:14-20. [PMID: 29787862 DOI: 10.1016/j.semcdb.2018.05.018] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2017] [Revised: 03/14/2018] [Accepted: 05/15/2018] [Indexed: 10/16/2022]
Abstract
The robustness of biological systems against mutational and environmental perturbations is termed canalization. Because reducing phenotypic variability under environmental and genetic perturbations can be adaptive and facilitated by natural selection, it has been suggested that once canalization mechanisms have evolved to buffer the effects of environmental perturbations, they may act to buffer any and all sources of variation. Although whether canalization mechanisms are general or specific to the types of perturbation or phenotypic traits that they buffer is often addressed, the links between different canalization mechanisms remain unclear. In this review, three major sources of phenotypic variation, associated canalization concepts and indicators of the degree of canalization are first outlined. Then, the molecular bases of canalization mechanisms based on recent empirical studies are overviewed. Finally, the links between the underlying processes of different canalization mechanisms are explored.
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Affiliation(s)
- Kazuo H Takahashi
- Graduate School of Environmental and Life Science, Okayama University, 1-1-1 Tsushima-naka, Kita-ku, Okayama-si, Okayama-ken, 700-8530, Japan.
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9
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Katsanos D, Koneru SL, Mestek Boukhibar L, Gritti N, Ghose R, Appleford PJ, Doitsidou M, Woollard A, van Zon JS, Poole RJ, Barkoulas M. Stochastic loss and gain of symmetric divisions in the C. elegans epidermis perturbs robustness of stem cell number. PLoS Biol 2017; 15:e2002429. [PMID: 29108019 PMCID: PMC5690688 DOI: 10.1371/journal.pbio.2002429] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Revised: 11/16/2017] [Accepted: 10/20/2017] [Indexed: 11/19/2022] Open
Abstract
Biological systems are subject to inherent stochasticity. Nevertheless, development is remarkably robust, ensuring the consistency of key phenotypic traits such as correct cell numbers in a certain tissue. It is currently unclear which genes modulate phenotypic variability, what their relationship is to core components of developmental gene networks, and what is the developmental basis of variable phenotypes. Here, we start addressing these questions using the robust number of Caenorhabditis elegans epidermal stem cells, known as seam cells, as a readout. We employ genetics, cell lineage tracing, and single molecule imaging to show that mutations in lin-22, a Hes-related basic helix-loop-helix (bHLH) transcription factor, increase seam cell number variability. We show that the increase in phenotypic variability is due to stochastic conversion of normally symmetric cell divisions to asymmetric and vice versa during development, which affect the terminal seam cell number in opposing directions. We demonstrate that LIN-22 acts within the epidermal gene network to antagonise the Wnt signalling pathway. However, lin-22 mutants exhibit cell-to-cell variability in Wnt pathway activation, which correlates with and may drive phenotypic variability. Our study demonstrates the feasibility to study phenotypic trait variance in tractable model organisms using unbiased mutagenesis screens.
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Affiliation(s)
- Dimitris Katsanos
- Department of Life Sciences, Imperial College, London, United Kingdom
| | - Sneha L. Koneru
- Department of Life Sciences, Imperial College, London, United Kingdom
| | | | - Nicola Gritti
- Institute for Atomic and Molecular Physics (AMOLF), Amsterdam, The Netherlands
| | - Ritobrata Ghose
- Department of Life Sciences, Imperial College, London, United Kingdom
| | - Peter J. Appleford
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Maria Doitsidou
- Centre for Integrative Physiology, University of Edinburgh, Edinburgh, United Kingdom
| | - Alison Woollard
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Jeroen S. van Zon
- Institute for Atomic and Molecular Physics (AMOLF), Amsterdam, The Netherlands
| | - Richard J. Poole
- Department of Cell and Developmental Biology, University College London, London, United Kingdom
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10
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Takahashi KH. Little effect of HSP90 inhibition on the quantitative wing traits variation in Drosophila melanogaster. Genetica 2016; 145:9-18. [PMID: 27909948 DOI: 10.1007/s10709-016-9940-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Accepted: 11/21/2016] [Indexed: 11/29/2022]
Abstract
Drosophila wings have been a model system to study the effect of HSP90 on quantitative trait variation. The effect of HSP90 inhibition on environmental buffering of wing morphology varies among studies while the genetic buffering effect of it was examined in only one study and was not detected. Variable results so far might show that the genetic background influences the environmental and genetic buffering effect of HSP90. In the previous studies, the number of the genetic backgrounds used is limited. To examine the effect of HSP90 inhibition with a larger number of genetic backgrounds than the previous studies, 20 wild-type strains of Drosophila melanogaster were used in this study. Here I investigated the effect of HSP90 inhibition on the environmental buffering of wing shape and size by assessing within-individual and among-individual variations, and as a result, I found little or very weak effects on environmental and genetic buffering. The current results suggest that the role of HSP90 as a global regulator of environmental and genetic buffering is limited at least in quantitative traits.
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Affiliation(s)
- Kazuo H Takahashi
- Graduate School of Environmental and Life Science, Okayama University, 1-1-1 Tsushima-naka, Kita-ku, Okayama-si, Okayama-ken, 700-8530, Japan.
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11
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Geiler-Samerotte KA, Zhu YO, Goulet BE, Hall DW, Siegal ML. Selection Transforms the Landscape of Genetic Variation Interacting with Hsp90. PLoS Biol 2016; 14:e2000465. [PMID: 27768682 PMCID: PMC5074785 DOI: 10.1371/journal.pbio.2000465] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Accepted: 09/26/2016] [Indexed: 11/18/2022] Open
Abstract
The protein-folding chaperone Hsp90 has been proposed to buffer the phenotypic effects of mutations. The potential for Hsp90 and other putative buffers to increase robustness to mutation has had major impact on disease models, quantitative genetics, and evolutionary theory. But Hsp90 sometimes contradicts expectations for a buffer by potentiating rapid phenotypic changes that would otherwise not occur. Here, we quantify Hsp90’s ability to buffer or potentiate (i.e., diminish or enhance) the effects of genetic variation on single-cell morphological features in budding yeast. We corroborate reports that Hsp90 tends to buffer the effects of standing genetic variation in natural populations. However, we demonstrate that Hsp90 tends to have the opposite effect on genetic variation that has experienced reduced selection pressure. Specifically, Hsp90 tends to enhance, rather than diminish, the effects of spontaneous mutations and recombinations. This result implies that Hsp90 does not make phenotypes more robust to the effects of genetic perturbation. Instead, natural selection preferentially allows buffered alleles to persist and thereby creates the false impression that Hsp90 confers greater robustness. Most biologists appreciate that natural selection filters new mutations (e.g., by eliminating deleterious ones), such that genetic variation in nature is biased. The idea that selection also skews the types of genetic interactions that exist in nature is less appreciated. For example, studies spanning diverse species have shown that the protein Hsp90, which helps other proteins to fold properly, tends to diminish the observable effects of genetic variation. This observation has led to the assumption that Hsp90 also buffers the effects of new mutations. This untested assumption has served as a rationale for cancer-treatment strategies and shaped our understanding of variation in complex traits. We measured the effects of new mutations on the shapes and sizes of individual yeast cells and found that Hsp90 does not tend to buffer these effects. Instead, Hsp90 interacts with new mutations in diverse ways, sometimes buffering, but more often enhancing mutational effects on cell shape and size. We conclude that selection preferentially allows buffered mutations to persist in natural populations. This result alters common perceptions about why cryptic (i.e., buffered) genetic variation exists and casts doubt on cancer-treatment strategies aiming to target presumed buffers of mutational effects.
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Affiliation(s)
- Kerry A Geiler-Samerotte
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America.,Department of Biology, Stanford University, Stanford, California, United States of America
| | - Yuan O Zhu
- Department of Biology, Stanford University, Stanford, California, United States of America.,Department of Genetics, Stanford University, Stanford, California, United States of America
| | - Benjamin E Goulet
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
| | - David W Hall
- Department of Genetics, University of Georgia, Athens, Georgia, United States of America
| | - Mark L Siegal
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
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12
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Mossman JA, Biancani LM, Zhu CT, Rand DM. Mitonuclear Epistasis for Development Time and Its Modification by Diet in Drosophila. Genetics 2016; 203:463-84. [PMID: 26966258 PMCID: PMC4858792 DOI: 10.1534/genetics.116.187286] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2016] [Accepted: 03/04/2016] [Indexed: 11/18/2022] Open
Abstract
Mitochondrial (mtDNA) and nuclear genes have to operate in a coordinated manner to maintain organismal function, and the regulation of this homeostasis presents a substantial source of potential epistatic (G × G) interactions. How these interactions shape the fitness landscape is poorly understood. Here we developed a novel mitonuclear epistasis model, using selected strains of the Drosophila Genetic Reference Panel (DGRP) and mitochondrial genomes from within Drosophila melanogaster and D. simulans to test the hypothesis that mtDNA × nDNA interactions influence fitness. In total we built 72 genotypes (12 nuclear backgrounds × 6 mtDNA haplotypes, with 3 from each species) to dissect the relationship between genotype and phenotype. Each genotype was assayed on four food environments. We found considerable variation in several phenotypes, including development time and egg-to-adult viability, and this variation was partitioned into genetic (G), environmental (E), and higher-order (G × G, G × E, and G × G × E) components. Food type had a significant impact on development time and also modified mitonuclear epistases, evidencing a broad spectrum of G × G × E across these genotypes. Nuclear background effects were substantial, followed by mtDNA effects and their G × G interaction. The species of mtDNA haplotype had negligible effects on phenotypic variation and there was no evidence that mtDNA variation has different effects on male and female fitness traits. Our results demonstrate that mitonuclear epistases are context dependent, suggesting the selective pressure acting on mitonuclear genotypes may vary with food environment in a genotype-specific manner.
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Affiliation(s)
- Jim A Mossman
- Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912
| | - Leann M Biancani
- Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912
| | - Chen-Tseh Zhu
- Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912
| | - David M Rand
- Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912
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13
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Abstract
Genetic robustness refers to phenotypic invariance in the face of mutation and is a common characteristic of life, but its evolutionary origin is highly controversial. Genetic robustness could be an intrinsic property of biological systems, a result of direct natural selection, or a byproduct of selection for environmental robustness. To differentiate among these hypotheses, we analyze the metabolic network of Escherichia coli and comparable functional random networks. Treating the flux of each reaction as a trait and computationally predicting trait values upon mutations or environmental shifts, we discover that 1) genetic robustness is greater for the actual network than the random networks, 2) the genetic robustness of a trait increases with trait importance and this correlation is stronger in the actual network than in the random networks, and 3) the above result holds even after the control of environmental robustness. These findings demonstrate an adaptive origin of genetic robustness, consistent with the theoretical prediction that, under certain conditions, direct selection is sufficiently powerful to promote genetic robustness in cellular organisms.
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Affiliation(s)
- Wei-Chin Ho
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor
| | - Jianzhi Zhang
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor
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14
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Measurement error in geometric morphometrics. Dev Genes Evol 2016; 226:139-58. [DOI: 10.1007/s00427-016-0537-4] [Citation(s) in RCA: 104] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2015] [Accepted: 12/28/2015] [Indexed: 10/22/2022]
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15
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Mestek Boukhibar L, Barkoulas M. The developmental genetics of biological robustness. ANNALS OF BOTANY 2016; 117:699-707. [PMID: 26292993 PMCID: PMC4845795 DOI: 10.1093/aob/mcv128] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2015] [Revised: 05/07/2015] [Accepted: 06/29/2015] [Indexed: 05/10/2023]
Abstract
BACKGROUND Living organisms are continuously confronted with perturbations, such as environmental changes that include fluctuations in temperature and nutrient availability, or genetic changes such as mutations. While some developmental systems are affected by such challenges and display variation in phenotypic traits, others continue consistently to produce invariable phenotypes despite perturbation. This ability of a living system to maintain an invariable phenotype in the face of perturbations is termed developmental robustness. Biological robustness is a phenomenon observed across phyla, and studying its mechanisms is central to deciphering the genotype-phenotype relationship. Recent work in yeast, animals and plants has shown that robustness is genetically controlled and has started to reveal the underlying mechinisms behind it. SCOPE AND CONCLUSIONS Studying biological robustness involves focusing on an important property of developmental traits, which is the phenotypic distribution within a population. This is often neglected because the vast majority of developmental biology studies instead focus on population aggregates, such as trait averages. By drawing on findings in animals and yeast, this Viewpoint considers how studies on plant developmental robustness may benefit from strict definitions of what is the developmental system of choice and what is the relevant perturbation, and also from clear distinctions between gene effects on the trait mean and the trait variance. Recent advances in quantitative developmental biology and high-throughput phenotyping now allow the design of targeted genetic screens to identify genes that amplify or restrict developmental trait variance and to study how variation propagates across different phenotypic levels in biological systems. The molecular characterization of more quantitative trait loci affecting trait variance will provide further insights into the evolution of genes modulating developmental robustness. The study of robustness mechanisms in closely related species will address whether mechanisms of robustness are evolutionarily conserved.
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Affiliation(s)
- Lamia Mestek Boukhibar
- Imperial College London, Department of Life Sciences, Sir Alexander Fleming Building, South Kensington Campus, London SW7 2AZ, UK
| | - Michalis Barkoulas
- Imperial College London, Department of Life Sciences, Sir Alexander Fleming Building, South Kensington Campus, London SW7 2AZ, UK
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16
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Takahashi KH. Novel genetic capacitors and potentiators for the natural genetic variation of sensory bristles and their trait specificity in Drosophila melanogaster. Mol Ecol 2015; 24:5561-72. [PMID: 26441383 DOI: 10.1111/mec.13407] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2014] [Revised: 09/28/2015] [Accepted: 09/30/2015] [Indexed: 11/30/2022]
Abstract
Cryptic genetic variation (CGV) is defined as the genetic variation that has little effect on phenotypic variation under a normal condition, but contributes to heritable variation under environmental or genetic perturbations. Genetic buffering systems that suppress the expression of CGV and store it in a population are called genetic capacitors, and the opposite systems are called genetic potentiators. One of the best-known candidates for a genetic capacitor and potentiator is the molecular chaperone protein, HSP90, and one of its characteristics is that it affects the genetic variation in various morphological traits. However, it remains unclear whether the wide-ranging effects of HSP90 on a broad range of traits are a general feature of genetic capacitors and potentiators. In the current study, I searched for novel genetic capacitors and potentiators for quantitative bristle traits of Drosophila melanogaster and then investigated the trait specificity of their genetic buffering effect. Three bristle traits of D. melanogaster were used as the target traits, and the genomic regions with genetic buffering effects were screened using the 61 genomic deficiencies examined previously for genetic buffering effects in wing shape. As a result, four and six deficiencies with significant effects on increasing and decreasing the broad-sense heritability of the bristle traits were identified, respectively. Of the 18 deficiencies with significant effects detected in the current study and/or by the previous study, 14 showed trait-specific effects, and four affected the genetic buffering of both bristle traits and wing shape. This suggests that most genetic capacitors and potentiators exert trait-specific effects, but that general capacitors and potentiators with effects on multiple traits also exist.
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Affiliation(s)
- Kazuo H Takahashi
- Graduate School of Environmental and Life Science, Okayama University, 1-1-1 Tsushima-naka, Kita-ku, Okayama-si, Okayama-ken, 700-8530, Japan
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Abstract
Phenotypic capacitance refers to the ability of a genome to accumulate mutations that are conditionally hidden and only reveal phenotype-altering effects after certain environmental or genetic changes. Capacitance has important implications for the evolution of novel forms and functions, but experimentally studied mechanisms behind capacitance are mostly limited to complex, multicomponent systems often involving several interacting protein molecules. Here we demonstrate phenotypic capacitance within a much simpler system, an individual RNA molecule with catalytic activity (ribozyme). This naturally occurring RNA molecule has a modular structure, where a scaffold module acts as an intramolecular chaperone that facilitates folding of a second catalytic module. Previous studies have shown that the scaffold module is not absolutely required for activity, but dramatically decreases the concentration of magnesium ions required for the formation of an active site. Here, we use an experimental perturbation of magnesium ion concentration that disrupts the folding of certain genetic variants of this ribozyme and use in vitro selection followed by deep sequencing to identify genotypes with altered phenotypes (catalytic activity). We identify multiple conditional mutations that alter the wild-type ribozyme phenotype under a stressful environmental condition of low magnesium ion concentration, but preserve the phenotype under more relaxed conditions. This conditional buffering is confined to the scaffold module, but controls the catalytic phenotype, demonstrating how modularity can enable phenotypic capacitance within a single macromolecule. RNA's ancient role in life suggests that phenotypic capacitance may have influenced evolution since life's origins.
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Moczek AP, Sears KE, Stollewerk A, Wittkopp PJ, Diggle P, Dworkin I, Ledon-Rettig C, Matus DQ, Roth S, Abouheif E, Brown FD, Chiu CH, Cohen CS, Tomaso AWD, Gilbert SF, Hall B, Love AC, Lyons DC, Sanger TJ, Smith J, Specht C, Vallejo-Marin M, Extavour CG. The significance and scope of evolutionary developmental biology: a vision for the 21st century. Evol Dev 2015; 17:198-219. [PMID: 25963198 DOI: 10.1111/ede.12125] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Evolutionary developmental biology (evo-devo) has undergone dramatic transformations since its emergence as a distinct discipline. This paper aims to highlight the scope, power, and future promise of evo-devo to transform and unify diverse aspects of biology. We articulate key questions at the core of eleven biological disciplines-from Evolution, Development, Paleontology, and Neurobiology to Cellular and Molecular Biology, Quantitative Genetics, Human Diseases, Ecology, Agriculture and Science Education, and lastly, Evolutionary Developmental Biology itself-and discuss why evo-devo is uniquely situated to substantially improve our ability to find meaningful answers to these fundamental questions. We posit that the tools, concepts, and ways of thinking developed by evo-devo have profound potential to advance, integrate, and unify biological sciences as well as inform policy decisions and illuminate science education. We look to the next generation of evolutionary developmental biologists to help shape this process as we confront the scientific challenges of the 21st century.
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Affiliation(s)
- Armin P Moczek
- Department of Biology, Indiana University, 915 East 3rd Street, Bloomington, IN 47405, USA
| | - Karen E Sears
- School of Integrative Biology and Institute for Genomic Biology, University of Illinois, 505 South Goodwin Avenue, Urbana, IL, 61801, USA
| | - Angelika Stollewerk
- School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London, E1 4NS, UK
| | - Patricia J Wittkopp
- Department of Ecology and Evolutionary Biology, Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
| | - Pamela Diggle
- Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, 06269, USA
| | - Ian Dworkin
- Department of Biology, McMaster University, 1280 Main St. West Hamilton, Ontario, L8S 4K1, Canada
| | - Cristina Ledon-Rettig
- Department of Biology, Indiana University, 915 East 3rd Street, Bloomington, IN 47405, USA
| | - David Q Matus
- Department of Biochemistry and Cell Biology, Stony Brook University, 412 Life Sciences Building, Stony Brook, NY, 11794-5215, USA
| | - Siegfried Roth
- University of Cologne, Institute of Developmental Biology, Biocenter, Zülpicher Straße 47b, D-50674, Cologne, Germany
| | - Ehab Abouheif
- Department of Biology, McGill University, 1205 Avenue Docteur Penfield, Montréal Québec, H3A 1B1, Canada
| | - Federico D Brown
- Departamento de Zoologia, Instituto Biociências, Universidade de São Paulo, Rua do Matão, Travessa 14, no. 101, 05508-090, São Paulo, Brazil
| | - Chi-Hua Chiu
- Department of Biological Sciences, Kent State University, OH, USA
| | - C Sarah Cohen
- Biology Department, Romberg Tiburon Center for Environmental Studies, San Francisco State University, 3150 Paradise Drive, Tiburon, CA, 94920, USA
| | | | - Scott F Gilbert
- Department of Biology, Swarthmore College, Swarthmore, Pennsylvania 19081, USA and Biotechnology Institute, University of Helsinki, 00014, Helsinki, Finland
| | - Brian Hall
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, CA, B3H 4R2, USA
| | - Alan C Love
- Department of Philosophy, Minnesota Center for Philosophy of Science, University of Minnesota, USA
| | - Deirdre C Lyons
- Department of Biology, Duke University, Box 90338, Durham, NC, 27708, USA
| | - Thomas J Sanger
- Department of Molecular Genetics and Microbiology, University of Florida, P.O. Box 103610, Gainesville, FL, 32610, USA
| | - Joel Smith
- Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA, 02543, USA
| | - Chelsea Specht
- Plant and Microbial Biology, Department of Integrative Biology, University and Jepson Herbaria, University of California, Berkeley, CA, USA
| | - Mario Vallejo-Marin
- Biological and Environmental Sciences, University of Stirling, FK9 4LA, Scotland, UK
| | - Cassandra G Extavour
- Department of Organismic and Evolutionary Biology, Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, BioLabs 4103, Cambridge, MA, 02138, USA
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Harrisson KA, Pavlova A, Telonis-Scott M, Sunnucks P. Using genomics to characterize evolutionary potential for conservation of wild populations. Evol Appl 2014; 7:1008-25. [PMID: 25553064 PMCID: PMC4231592 DOI: 10.1111/eva.12149] [Citation(s) in RCA: 157] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2013] [Accepted: 02/10/2014] [Indexed: 12/16/2022] Open
Abstract
Genomics promises exciting advances towards the important conservation goal of maximizing evolutionary potential, notwithstanding associated challenges. Here, we explore some of the complexity of adaptation genetics and discuss the strengths and limitations of genomics as a tool for characterizing evolutionary potential in the context of conservation management. Many traits are polygenic and can be strongly influenced by minor differences in regulatory networks and by epigenetic variation not visible in DNA sequence. Much of this critical complexity is difficult to detect using methods commonly used to identify adaptive variation, and this needs appropriate consideration when planning genomic screens, and when basing management decisions on genomic data. When the genomic basis of adaptation and future threats are well understood, it may be appropriate to focus management on particular adaptive traits. For more typical conservations scenarios, we argue that screening genome-wide variation should be a sensible approach that may provide a generalized measure of evolutionary potential that accounts for the contributions of small-effect loci and cryptic variation and is robust to uncertainty about future change and required adaptive response(s). The best conservation outcomes should be achieved when genomic estimates of evolutionary potential are used within an adaptive management framework.
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Affiliation(s)
| | - Alexandra Pavlova
- School of Biological Sciences, Monash UniversityMelbourne, Vic., Australia
| | | | - Paul Sunnucks
- School of Biological Sciences, Monash UniversityMelbourne, Vic., Australia
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Siegal ML, Leu JY. On the Nature and Evolutionary Impact of Phenotypic Robustness Mechanisms. ANNUAL REVIEW OF ECOLOGY, EVOLUTION, AND SYSTEMATICS 2014; 45:496-517. [PMID: 26034410 PMCID: PMC4448758 DOI: 10.1146/annurev-ecolsys-120213-091705] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Biologists have long observed that physiological and developmental processes are insensitive, or robust, to many genetic and environmental perturbations. A complete understanding of the evolutionary causes and consequences of this robustness is lacking. Recent progress has been made in uncovering the regulatory mechanisms that underlie environmental robustness in particular. Less is known about robustness to the effects of mutations, and indeed the evolution of mutational robustness remains a controversial topic. The controversy has spread to related topics, in particular the evolutionary relevance of cryptic genetic variation. This review aims to synthesize current understanding of robustness mechanisms and to cut through the controversy by shedding light on what is and is not known about mutational robustness. Some studies have confused mutational robustness with non-additive interactions between mutations (epistasis). We conclude that a profitable way forward is to focus investigations (and rhetoric) less on mutational robustness and more on epistasis.
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Affiliation(s)
- Mark L Siegal
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York 10003;
| | - Jun-Yi Leu
- Institute of Molecular Biology, Academia Sinica, Nankang, Taipei, Taiwan 11529;
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Trotter MV, Weissman DB, Peterson GI, Peck KM, Masel J. Cryptic genetic variation can make "irreducible complexity" a common mode of adaptation in sexual populations. Evolution 2014; 68:3357-67. [PMID: 25178652 DOI: 10.1111/evo.12517] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2013] [Accepted: 08/25/2014] [Indexed: 12/15/2022]
Abstract
The existence of complex (multiple-step) genetic adaptations that are "irreducible" (i.e., all partial combinations are less fit than the original genotype) is one of the longest standing problems in evolutionary biology. In standard genetics parlance, these adaptations require the crossing of a wide adaptive valley of deleterious intermediate stages. Here, we demonstrate, using a simple model, that evolution can cross wide valleys to produce "irreducibly complex" adaptations by making use of previously cryptic mutations. When revealed by an evolutionary capacitor, previously cryptic mutants have higher initial frequencies than do new mutations, bringing them closer to a valley-crossing saddle in allele frequency space. Moreover, simple combinatorics implies an enormous number of candidate combinations exist within available cryptic genetic variation. We model the dynamics of crossing of a wide adaptive valley after a capacitance event using both numerical simulations and analytical approximations. Although individual valley crossing events become less likely as valleys widen, by taking the combinatorics of genotype space into account, we see that revealing cryptic variation can cause the frequent evolution of complex adaptations.
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Affiliation(s)
- Meredith V Trotter
- Department of Biology, Stanford University, Stanford, California, 95306; Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, 85721
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Abstract
Cryptic genetic variation (CGV) is invisible under normal conditions, but it can fuel evolution when circumstances change. In theory, CGV can represent a massive cache of adaptive potential or a pool of deleterious alleles that are in need of constant suppression. CGV emerges from both neutral and selective processes, and it may inform about how human populations respond to change. CGV facilitates adaptation in experimental settings, but does it have an important role in the real world? Here, we review the empirical support for widespread CGV in natural populations, including its potential role in emerging human diseases and the growing evidence of its contribution to evolution.
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Affiliation(s)
- Annalise B Paaby
- Department of Biology, and Center for Genomics and Systems Biology, New York University, 12 Waverly Place, New York 10003, USA
| | - Matthew V Rockman
- Department of Biology, and Center for Genomics and Systems Biology, New York University, 12 Waverly Place, New York 10003, USA
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Schlichting CD, Wund MA. Phenotypic plasticity and epigenetic marking: an assessment of evidence for genetic accommodation. Evolution 2014; 68:656-72. [PMID: 24410266 DOI: 10.1111/evo.12348] [Citation(s) in RCA: 183] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 12/22/2013] [Indexed: 12/16/2022]
Abstract
The relationship between genotype (which is inherited) and phenotype (the target of selection) is mediated by environmental inputs on gene expression, trait development, and phenotypic integration. Phenotypic plasticity or epigenetic modification might influence evolution in two general ways: (1) by stimulating evolutionary responses to environmental change via population persistence or by revealing cryptic genetic variation to selection, and (2) through the process of genetic accommodation, whereby natural selection acts to improve the form, regulation, and phenotypic integration of novel phenotypic variants. We provide an overview of models and mechanisms for how such evolutionary influences may be manifested both for plasticity and epigenetic marking. We point to promising avenues of research, identifying systems that can best be used to address the role of plasticity in evolution, as well as the need to apply our expanding knowledge of genetic and epigenetic mechanisms to our understanding of how genetic accommodation occurs in nature. Our review of a wide variety of studies finds widespread evidence for evolution by genetic accommodation.
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Affiliation(s)
- Carl D Schlichting
- Department of Ecology & Evolutionary Biology, U-3043, University of Connecticut, Storrs, Connecticut 06269.
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Wray GA. Genomics and the Evolution of Phenotypic Traits. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2013. [DOI: 10.1146/annurev-ecolsys-110512-135828] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Evolutionary genetics has entered an unprecedented era of discovery, catalyzed in large part by the development of technologies that provide information about genome sequence and function. An important benefit is the ability to move beyond a handful of model organisms in lab settings to identify the genetic basis for evolutionarily interesting traits in many organisms in natural settings. Other benefits are the abilities to identify causal mutations and validate their phenotypic consequences more readily and in many more species. Genomic technologies have reinvigorated interest in some of the most fundamental and persistent questions in evolutionary genetics, revealed previously unsuspected evolutionary phenomena, and opened the door to a wide range of new questions.
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Affiliation(s)
- Gregory A. Wray
- Department of Biology and Institute for Genome Sciences & Policy, Duke University, Durham, North Carolina 27701
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Affiliation(s)
- Joanna Masel
- Ecology and Evolutionary Biology, University of Arizona, 1041 E, Lowell St, Tucson, AZ 84721, USA.
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Siegal ML. Crouching variation revealed. Mol Ecol 2013; 22:1187-9. [PMID: 23437837 DOI: 10.1111/mec.12195] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2012] [Revised: 11/29/2012] [Accepted: 12/04/2012] [Indexed: 11/28/2022]
Abstract
The term 'phenotypic capacitance' was introduced nearly 15 years ago to describe the strain-specific effects of impairing Hsp90, a molecular chaperone, in the fly Drosophila melanogaster (Rutherford & Lindquist 1998). In one genetic background, Hsp90 depletion caused deformed eyes, whereas in other genetic backgrounds, the wings or abdomens or other aspects of morphology were affected. Hsp90 was therefore viewed as acting like a capacitor, allowing genetic differences to build up and to be released at a later time. In the years since, it has been debated whether capacitance is a laboratory curiosity or a major force in evolution. In this issue of Molecular Ecology, Takahashi (2013) presents evidence, from high-resolution morphometric analysis of fly wings, that a large number of other capacitors exist in D. melanogaster, and that the variation they reveal can be quite subtle. His results advance our understanding of capacitance and contribute to a new view of its role in evolutionary adaptation.
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Affiliation(s)
- Mark L Siegal
- Department of Biology, Center for Genomics and Systems Biology, New York University, New York, NY 10003, USA.
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Richardson JB, Uppendahl LD, Traficante MK, Levy SF, Siegal ML. Histone variant HTZ1 shows extensive epistasis with, but does not increase robustness to, new mutations. PLoS Genet 2013; 9:e1003733. [PMID: 23990806 PMCID: PMC3749942 DOI: 10.1371/journal.pgen.1003733] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Accepted: 07/05/2013] [Indexed: 12/18/2022] Open
Abstract
Biological systems produce phenotypes that appear to be robust to perturbation by mutations and environmental variation. Prior studies identified genes that, when impaired, reveal previously cryptic genetic variation. This result is typically interpreted as evidence that the disrupted gene normally increases robustness to mutations, as such robustness would allow cryptic variants to accumulate. However, revelation of cryptic genetic variation is not necessarily evidence that a mutationally robust state has been made less robust. Demonstrating a difference in robustness requires comparing the ability of each state (with the gene perturbed or intact) to suppress the effects of new mutations. Previous studies used strains in which the existing genetic variation had been filtered by selection. Here, we use mutation accumulation (MA) lines that have experienced minimal selection, to test the ability of histone H2A.Z (HTZ1) to increase robustness to mutations in the yeast Saccharomyces cerevisiae. HTZ1, a regulator of chromatin structure and gene expression, represents a class of genes implicated in mutational robustness. It had previously been shown to increase robustness of yeast cell morphology to fluctuations in the external or internal microenvironment. We measured morphological variation within and among 79 MA lines with and without HTZ1. Analysis of within-line variation confirms that HTZ1 increases microenvironmental robustness. Analysis of between-line variation shows the morphological effects of eliminating HTZ1 to be highly dependent on the line, which implies that HTZ1 interacts with mutations that have accumulated in the lines. However, lines without HTZ1 are, as a group, not more phenotypically diverse than lines with HTZ1 present. The presence of HTZ1, therefore, does not confer greater robustness to mutations than its absence. Our results provide experimental evidence that revelation of cryptic genetic variation cannot be assumed to be caused by loss of robustness, and therefore force reevaluation of prior claims based on that assumption.
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Affiliation(s)
- Joshua B. Richardson
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
| | - Locke D. Uppendahl
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
| | - Maria K. Traficante
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
| | - Sasha F. Levy
- Department of Genetics, Stanford University, Stanford, California, United States of America
| | - Mark L. Siegal
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, New York, United States of America
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Iwasaki WM, Tsuda ME, Kawata M. Genetic and environmental factors affecting cryptic variations in gene regulatory networks. BMC Evol Biol 2013; 13:91. [PMID: 23622056 PMCID: PMC3679780 DOI: 10.1186/1471-2148-13-91] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Accepted: 04/16/2013] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND Cryptic genetic variation (CGV) is considered to facilitate phenotypic evolution by producing visible variations in response to changes in the internal and/or external environment. Several mechanisms enabling the accumulation and release of CGVs have been proposed. In this study, we focused on gene regulatory networks (GRNs) as an important mechanism for producing CGVs, and examined how interactions between GRNs and the environment influence the number of CGVs by using individual-based simulations. RESULTS Populations of GRNs were allowed to evolve under various stabilizing selections, and we then measured the number of genetic and phenotypic variations that had arisen. Our results showed that CGVs were not depleted irrespective of the strength of the stabilizing selection for each phenotype, whereas the visible fraction of genetic variation in a population decreased with increasing strength of selection. On the other hand, increasing the number of different environments that individuals encountered within their lifetime (i.e., entailing plastic responses to multiple environments) suppressed the accumulation of CGVs, whereas the GRNs with more genes and interactions were favored in such heterogeneous environments. CONCLUSIONS Given the findings that the number of CGVs in a population was largely determined by the size (order) of GRNs, we propose that expansion of GRNs and adaptation to novel environments are mutually facilitating and sustainable sources of evolvability and hence the origins of biological diversity and complexity.
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Affiliation(s)
- Watal M Iwasaki
- Department of Ecology and Evolution, Graduate School of Life Sciences, Tohoku University, Sendai 980–8578, Japan
| | - Masaki E Tsuda
- , RIKEN Advanced Science Institute, 2-1 Wako, Saitama 351-0198, Japan
| | - Masakado Kawata
- Department of Ecology and Evolution, Graduate School of Life Sciences, Tohoku University, Sendai 980–8578, Japan
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