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Lister NC, Milton AM, Patel HR, Waters SA, Hanrahan BJ, McIntyre KL, Livernois AM, Horspool WB, Wee LK, Ringel AR, Mundlos S, Robson MI, Shearwin-Whyatt L, Grützner F, Graves JAM, Ruiz-Herrera A, Waters PD. Incomplete transcriptional dosage compensation of chicken and platypus sex chromosomes is balanced by post-transcriptional compensation. Proc Natl Acad Sci U S A 2024; 121:e2322360121. [PMID: 39074288 PMCID: PMC11317591 DOI: 10.1073/pnas.2322360121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Accepted: 06/25/2024] [Indexed: 07/31/2024] Open
Abstract
Heteromorphic sex chromosomes (XY or ZW) present problems of gene dosage imbalance between sexes and with autosomes. A need for dosage compensation has long been thought to be critical in vertebrates. However, this was questioned by findings of unequal mRNA abundance measurements in monotreme mammals and birds. Here, we demonstrate unbalanced mRNA levels of X genes in platypus males and females and a correlation with differential loading of histone modifications. We also observed unbalanced transcripts of Z genes in chicken. Surprisingly, however, we found that protein abundance ratios were 1:1 between the sexes in both species, indicating a post-transcriptional layer of dosage compensation. We conclude that sex chromosome output is maintained in chicken and platypus (and perhaps many other non therian vertebrates) via a combination of transcriptional and post-transcriptional control, consistent with a critical importance of sex chromosome dosage compensation.
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Affiliation(s)
- Nicholas C. Lister
- School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales Sydney, Sydney, NSW2052, Australia
| | - Ashley M. Milton
- School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales Sydney, Sydney, NSW2052, Australia
| | - Hardip R. Patel
- John Curtin School of Medical Research, Australian National University, Canberra, ACT2600, Australia
- National Centre for Indigenous Genomics, Australian National University, Canberra, ACT2600, Australia
| | - Shafagh A. Waters
- School of Biomedical Sciences, Faculty of Medicine and Health, University of New South Wales, Sydney, NSW2052, Australia
| | - Benjamin J. Hanrahan
- School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales Sydney, Sydney, NSW2052, Australia
| | - Kim L. McIntyre
- School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales Sydney, Sydney, NSW2052, Australia
| | | | - William B. Horspool
- School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales Sydney, Sydney, NSW2052, Australia
| | - Lee Kian Wee
- School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales Sydney, Sydney, NSW2052, Australia
| | - Alessa R. Ringel
- Max Planck Institute for Molecular Genetics, Berlin14195, Germany
- Institute for Medical and Human Genetics, Charité Universitätsmedizin Berlin, Berlin10117, Germany
- Institute of Chemistry and Biochemistry, Freie Universität Berlin, Berlin14195, Germany
| | - Stefan Mundlos
- Max Planck Institute for Molecular Genetics, Berlin14195, Germany
- Institute for Medical and Human Genetics, Charité Universitätsmedizin Berlin, Berlin10117, Germany
- Charité-Universitätsmedizin Berlin, Berlin Institute of Health Center for Regenerative Therapies, Berlin13353, Germany
| | - Michael I. Robson
- Max Planck Institute for Molecular Genetics, Berlin14195, Germany
- Institute for Medical and Human Genetics, Charité Universitätsmedizin Berlin, Berlin10117, Germany
- Medical Research Council Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, EdinburghEH8 9YL, United Kingdom
| | | | - Frank Grützner
- School of Biological Sciences, University of Adelaide, Adelaide, SA5000, Australia
| | - Jennifer A. Marshall Graves
- Department of Environment and Genetics, La Trobe University, Melbourne, VIC3068, Australia
- Institute of Applied Ecology, University of Canberra, Canberra, ACT2601, Australia
| | - Aurora Ruiz-Herrera
- Departament de Biologia Cellular, Fisiologia I Immunologia, Universitat Autònoma de Barcelona, Cerdanyola del Vallès08193, Spain
- Genome Integrity and Instability Group, Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès08193, Spain
| | - Paul D. Waters
- School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales Sydney, Sydney, NSW2052, Australia
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Aharonoff A, Kim J, Washington A, Ercan S. SMC-mediated dosage compensation in C. elegans evolved in the presence of an ancestral nematode mechanism. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.21.595224. [PMID: 38826443 PMCID: PMC11142195 DOI: 10.1101/2024.05.21.595224] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2024]
Abstract
Mechanisms of X chromosome dosage compensation have been studied extensively in a few model species representing clades of shared sex chromosome ancestry. However, the diversity within each clade as a function of sex chromosome evolution is largely unknown. Here, we anchor ourselves to the nematode Caenorhabditis elegans, for which a well-studied mechanism of dosage compensation occurs through a specialized structural maintenance of chromosomes (SMC) complex, and explore the diversity of dosage compensation in the surrounding phylogeny of nematodes. Through phylogenetic analysis of the C. elegans dosage compensation complex and a survey of its epigenetic signatures, including X-specific topologically associating domains (TADs) and X-enrichment of H4K20me1, we found that the condensin-mediated mechanism evolved recently in the lineage leading to Caenorhabditis through an SMC-4 duplication. Intriguingly, an independent duplication of SMC-4 and the presence of X-specific TADs in Pristionchus pacificus suggest that condensin-mediated dosage compensation arose more than once. mRNA-seq analyses of gene expression in several nematode species indicate that dosage compensation itself is ancestral, as expected from the ancient XO sex determination system. Indicative of the ancestral mechanism, H4K20me1 is enriched on the X chromosomes in Oscheius tipulae, which does not contain X-specific TADs or SMC-4 paralogs. Together, our results indicate that the dosage compensation system in C. elegans is surprisingly new, and condensin may have been co-opted repeatedly in nematodes, suggesting that the process of evolving a chromosome-wide gene regulatory mechanism for dosage compensation is constrained. Significance statement X chromosome dosage compensation mechanisms evolved in response to Y chromosome degeneration during sex chromosome evolution. However, establishment of dosage compensation is not an endpoint. As sex chromosomes change, dosage compensation strategies may have also changed. In this study, we performed phylogenetic and epigenomic analyses surrounding Caenorhabditis elegans and found that the condensin-mediated dosage compensation mechanism in C. elegans is surprisingly new, and has evolved in the presence of an ancestral mechanism. Intriguingly, condensin-based dosage compensation may have evolved more than once in the nematode lineage, the other time in Pristionchus. Together, our work highlights a previously unappreciated diversity of dosage compensation mechanisms within a clade, and suggests constraints in evolving new mechanisms in the presence of an existing one.
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Affiliation(s)
- Avrami Aharonoff
- Department of Biology, Center for Genomics and Systems Biology, New York University, New York, NY 10003
| | - Jun Kim
- Department of Biology, Center for Genomics and Systems Biology, New York University, New York, NY 10003
| | - Aaliyah Washington
- Department of Biology, Center for Genomics and Systems Biology, New York University, New York, NY 10003
| | - Sevinç Ercan
- Department of Biology, Center for Genomics and Systems Biology, New York University, New York, NY 10003
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Metzger DCH, Porter I, Mobley B, Sandkam BA, Fong LJM, Anderson AP, Mank JE. Transposon wave remodeled the epigenomic landscape in the rapid evolution of X-Chromosome dosage compensation. Genome Res 2023; 33:1917-1931. [PMID: 37989601 PMCID: PMC10760456 DOI: 10.1101/gr.278127.123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Accepted: 10/20/2023] [Indexed: 11/23/2023]
Abstract
Sex chromosome dosage compensation is a model to understand the coordinated evolution of transcription; however, the advanced age of the sex chromosomes in model systems makes it difficult to study how the complex regulatory mechanisms underlying chromosome-wide dosage compensation can evolve. The sex chromosomes of Poecilia picta have undergone recent and rapid divergence, resulting in widespread gene loss on the male Y, coupled with complete X Chromosome dosage compensation, the first case reported in a fish. The recent de novo origin of dosage compensation presents a unique opportunity to understand the genetic and evolutionary basis of coordinated chromosomal gene regulation. By combining a new chromosome-level assembly of P. picta with whole-genome bisulfite sequencing and RNA-seq data, we determine that the YY1 transcription factor (YY1) DNA binding motif is associated with male-specific hypomethylated regions on the X, but not the autosomes. These YY1 motifs are the result of a recent and rapid repetitive element expansion on the P. picta X Chromosome, which is absent in closely related species that lack dosage compensation. Taken together, our results present compelling support that a disruptive wave of repetitive element insertions carrying YY1 motifs resulted in the remodeling of the X Chromosome epigenomic landscape and the rapid de novo origin of a dosage compensation system.
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Affiliation(s)
- David C H Metzger
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada;
| | - Imogen Porter
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
| | - Brendan Mobley
- Biology Department, Reed College, Portland, Oregon 97202, USA
| | - Benjamin A Sandkam
- Department of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853, USA
| | - Lydia J M Fong
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
| | | | - Judith E Mank
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
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Fong LJM, Darolti I, Metzger DCH, Morris J, Lin Y, Sandkam BA, Mank JE. Parsimony and Poeciliid Sex Chromosome Evolution. Genome Biol Evol 2023; 15:evad128. [PMID: 37670515 PMCID: PMC10480581 DOI: 10.1093/gbe/evad128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/01/2023] [Indexed: 09/07/2023] Open
Affiliation(s)
- Lydia J M Fong
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, Canada
| | - Iulia Darolti
- Department of Ecology and Evolution, University of Lausanne, Switzerland
| | - David C H Metzger
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, Canada
| | - Jake Morris
- School of Biological Sciences, University of Bristol, United Kingdom
| | - Yuying Lin
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, Canada
| | - Benjamin A Sandkam
- Department of Neurobiology and Behavior, Cornell University, Ithaca, New York, USA
| | - Judith E Mank
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, Canada
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5
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Darolti I, Fong LJM, Sandkam BA, Metzger DCH, Mank JE. Sex chromosome heteromorphism and the Fast-X effect in poeciliids. Mol Ecol 2023; 32:4599-4609. [PMID: 37309716 DOI: 10.1111/mec.17048] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Revised: 05/29/2023] [Accepted: 05/31/2023] [Indexed: 06/14/2023]
Abstract
Fast-X evolution has been observed in a range of heteromorphic sex chromosomes. However, it remains unclear how early in the process of sex chromosome differentiation the Fast-X effect becomes detectible. Recently, we uncovered an extreme variation in sex chromosome heteromorphism across poeciliid fish species. The common guppy, Poecilia reticulata, Endler's guppy, P. wingei, swamp guppy, P. picta and para guppy, P. parae, appear to share the same XY system and exhibit a remarkable range of heteromorphism. Species outside this group lack this sex chromosome system. We combined analyses of sequence divergence and polymorphism data across poeciliids to investigate X chromosome evolution as a function of hemizygosity and reveal the causes for Fast-X effects. Consistent with the extent of Y degeneration in each species, we detect higher rates of divergence on the X relative to autosomes, a signal of Fast-X evolution, in P. picta and P. parae, species with high levels of X hemizygosity in males. In P. reticulata, which exhibits largely homomorphic sex chromosomes and little evidence of hemizygosity, we observe no change in the rate of evolution of X-linked relative to autosomal genes. In P. wingei, the species with intermediate sex chromosome differentiation, we see an increase in the rate of nonsynonymous substitutions on the older stratum of divergence only. We also use our comparative approach to test for the time of origin of the sex chromosomes in this clade. Taken together, our study reveals an important role of hemizygosity in Fast-X evolution.
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Affiliation(s)
- Iulia Darolti
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - Lydia J M Fong
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
| | - Benjamin A Sandkam
- Department of Neurobiology and Behavior, Cornell University, Ithaca, New York, USA
| | - David C H Metzger
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
| | - Judith E Mank
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
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6
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Fong LJM, Darolti I, Metzger DCH, Morris J, Lin Y, Sandkam BA, Mank JE. Evolutionary History of the Poecilia picta Sex Chromosomes. Genome Biol Evol 2023; 15:evad030. [PMID: 36802329 PMCID: PMC10003743 DOI: 10.1093/gbe/evad030] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 01/27/2023] [Accepted: 02/03/2023] [Indexed: 02/23/2023] Open
Abstract
The degree of divergence between the sex chromosomes is not always proportional to their age. In poeciliids, four closely related species all exhibit a male heterogametic sex chromosome system on the same linkage group, yet show a remarkable diversity in X and Y divergence. In Poecilia reticulata and P. wingei, the sex chromosomes remain homomorphic, yet P. picta and P. parae have a highly degraded Y chromosome. To test alternative theories about the origin of their sex chromosomes, we used a combination of pedigrees and RNA-seq data from P. picta families in conjunction with DNA-seq data collected from P. reticulata, P. wingei, P. parae, and P. picta. Phylogenetic clustering analysis of X and Y orthologs, identified through segregation patterns, and their orthologous sequences in closely related species demonstrates a similar time of origin for both the P. picta and P. reticulata sex chromosomes. We next used k-mer analysis to identify shared ancestral Y sequence across all four species, suggesting a single origin to the sex chromosome system in this group. Together, our results provide key insights into the origin and evolution of the poeciliid Y chromosome and illustrate that the rate of sex chromosome divergence is often highly heterogenous, even over relatively short evolutionary time frames.
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Affiliation(s)
- Lydia J M Fong
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Canada
| | - Iulia Darolti
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Canada
| | - David C H Metzger
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Canada
| | - Jake Morris
- Department of Zoology, University of Cambridge, United Kingdom
| | - Yuying Lin
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Canada
| | | | - Judith E Mank
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Canada
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7
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Fast KM, Rakestraw AW, Sandel MW. Complete mitochondrial genome of a livebearing freshwater fish (Cyprinodontiformes: Poeciliidae): Poecilia parae. Mitochondrial DNA B Resour 2023; 8:215-219. [PMID: 36761101 PMCID: PMC9904314 DOI: 10.1080/23802359.2023.2171246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Members of the fish family Poeciliidae (livebearing 'tooth-carps') have historically been used as models in medical research, behavior ecology, and biological control. This group of primarily freshwater fishes is highly tolerant to environmental factors such as salinity and warm temperatures and includes some invasive species. Here, we present the mitochondrial genome of Poecilia parae. A representative of this species was obtained from Suriname. The complete mitochondrial genome was sequenced using Oxford Nanopore technology and is 16,559 bp long. The genome contains 13 protein-coding genes, two ribosomal RNAs (rRNAs), 22 transfer RNAs (tRNAs), and one control region (D-loop). Phylogenetic analysis yielded topologies similar to those previously published. The data generated here will be useful in future studies of comparative biology and those utilizing environmental DNA (eDNA).
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Affiliation(s)
- Kayla M. Fast
- Department of Biological and Environmental Sciences, The University of West Alabama, Livingston, AL, USA,CONTACT Kayla M. Fast Department of Biological and Environmental Sciences, The University of West Alabama, Livingston, AL, USA
| | - Alex W. Rakestraw
- Department of Biological and Environmental Sciences, The University of West Alabama, Livingston, AL, USA
| | - Michael W. Sandel
- Department of Wildlife, Fisheries, and Aquaculture, Mississippi State University, Mississippi State, MS, USA,Michael W. Sandel Department of Wildlife, Fisheries, and Aquaculture, Mississippi State University, Mississippi State, MS, USA
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8
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Mank JE. Are plant and animal sex chromosomes really all that different? Philos Trans R Soc Lond B Biol Sci 2022; 377:20210218. [PMID: 35306885 PMCID: PMC8935310 DOI: 10.1098/rstb.2021.0218] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Accepted: 10/12/2021] [Indexed: 12/19/2022] Open
Abstract
Sex chromosomes in plants have often been contrasted with those in animals with the goal of identifying key differences that can be used to elucidate fundamental evolutionary properties. For example, the often homomorphic sex chromosomes in plants have been compared to the highly divergent systems in some animal model systems, such as birds, Drosophila and therian mammals, with many hypotheses offered to explain the apparent dissimilarities, including the younger age of plant sex chromosomes, the lesser prevalence of sexual dimorphism, or the greater extent of haploid selection. Furthermore, many plant sex chromosomes lack complete sex chromosome dosage compensation observed in some animals, including therian mammals, Drosophila, some poeciliids, and Anolis, and plant dosage compensation, where it exists, appears to be incomplete. Even the canonical theoretical models of sex chromosome formation differ somewhat between plants and animals. However, the highly divergent sex chromosomes observed in some animal groups are actually the exception, not the norm, and many animal clades are far more similar to plants in their sex chromosome patterns. This begs the question of how different are plant and animal sex chromosomes, and which of the many unique properties of plants would be expected to affect sex chromosome evolution differently than animals? In fact, plant and animal sex chromosomes exhibit more similarities than differences, and it is not at all clear that they differ in terms of sexual conflict, dosage compensation, or even degree of divergence. Overall, the largest difference between these two groups is the greater potential for haploid selection in plants compared to animals. This may act to accelerate the expansion of the non-recombining region at the same time that it maintains gene function within it. This article is part of the theme issue 'Sex determination and sex chromosome evolution in land plants'.
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Affiliation(s)
- Judith E. Mank
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, Canada
- Centre for Ecology and Conservation, University of Exeter, Penryn, UK
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9
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Kirkpatrick M, Sardell JM, Pinto BJ, Dixon G, Peichel CL, Schartl M. Evolution of the canonical sex chromosomes of the guppy and its relatives. G3 (BETHESDA, MD.) 2022; 12:jkab435. [PMID: 35100353 PMCID: PMC9335935 DOI: 10.1093/g3journal/jkab435] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Accepted: 12/03/2021] [Indexed: 11/14/2022]
Abstract
The sex chromosomes of the guppy, Poecilia reticulata, and its close relatives are of particular interest: they are much younger than the highly degenerate sex chromosomes of model systems such as humans and Drosophila melanogaster, and they carry many of the genes responsible for the males' dramatic coloration. Over the last decade, several studies have analyzed these sex chromosomes using a variety of approaches including sequencing genomes and transcriptomes, cytology, and linkage mapping. Conflicting conclusions have emerged, in particular concerning the history of the sex chromosomes and the evolution of suppressed recombination between the X and Y. Here, we address these controversies by reviewing the evidence and reanalyzing data. We find no evidence of a nonrecombining sex-determining region or evolutionary strata in P. reticulata. Furthermore, we find that the data most strongly support the hypothesis that the sex-determining regions of 2 close relatives of the guppy, Poecilia wingei and Micropoecilia picta, evolved independently after their lineages diverged. We identify possible causes of conflicting results in previous studies and suggest best practices going forward.
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Affiliation(s)
- Mark Kirkpatrick
- Department of Integrative Biology, University of Texas, Austin, TX 78712, USA
| | - Jason M Sardell
- Department of Integrative Biology, University of Texas, Austin, TX 78712, USA
| | - Brendan J Pinto
- Department of Integrative Biology, University of Texas, Austin, TX 78712, USA
- Milwaukee Public Museum, Milwaukee, WI 53233, USA
| | - Groves Dixon
- Department of Integrative Biology, University of Texas, Austin, TX 78712, USA
| | - Catherine L Peichel
- Institute of Ecology and Evolution, University of Bern, Bern 3012, Switzerland
| | - Manfred Schartl
- Developmental Biochemistry, University of Würzburg, Würzburg97074, Germany
- Department of Chemistry and Biochemistry, The Xiphophorus Genetic Stock Center, Texas State University, San Marcos, TX 78666, USA
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Basilicata MF, Keller Valsecchi CI. The good, the bad, and the ugly: Evolutionary and pathological aspects of gene dosage alterations. PLoS Genet 2021; 17:e1009906. [PMID: 34882671 PMCID: PMC8659298 DOI: 10.1371/journal.pgen.1009906] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Diploid organisms contain a maternal and a paternal genome complement that is thought to provide robustness and allow developmental progression despite genetic perturbations that occur in heterozygosity. However, changes affecting gene dosage from the chromosome down to the individual gene level possess a significant pathological potential and can lead to developmental disorders (DDs). This indicates that expression from a balanced gene complement is highly relevant for proper cellular and organismal function in eukaryotes. Paradoxically, gene and whole chromosome duplications are a principal driver of evolution, while heteromorphic sex chromosomes (XY and ZW) are naturally occurring aneuploidies important for sex determination. Here, we provide an overview of the biology of gene dosage at the crossroads between evolutionary benefit and pathogenicity during disease. We describe the buffering mechanisms and cellular responses to alterations, which could provide a common ground for the understanding of DDs caused by copy number alterations.
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