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Mrnjavac A, Khudiakova KA, Barton NH, Vicoso B. Slower-X: reduced efficiency of selection in the early stages of X chromosome evolution. Evol Lett 2023; 7:4-12. [PMID: 37065438 PMCID: PMC10091493 DOI: 10.1093/evlett/qrac004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 11/08/2022] [Accepted: 12/17/2022] [Indexed: 02/04/2023] Open
Abstract
Abstract
Differentiated X chromosomes are expected to have higher rates of adaptive divergence than autosomes, if new beneficial mutations are recessive (the “faster-X effect”), largely because these mutations are immediately exposed to selection in males. The evolution of X chromosomes after they stop recombining in males, but before they become hemizygous, has not been well explored theoretically. We use the diffusion approximation to infer substitution rates of beneficial and deleterious mutations under such a scenario. Our results show that selection is less efficient on diploid X loci than on autosomal and hemizygous X loci under a wide range of parameters. This “slower-X” effect is stronger for genes affecting primarily (or only) male fitness, and for sexually antagonistic genes. These unusual dynamics suggest that some of the peculiar features of X chromosomes, such as the differential accumulation of genes with sex-specific functions, may start arising earlier than previously appreciated.
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Affiliation(s)
- Andrea Mrnjavac
- Institute of Science and Technology Austria , Am Campus 1, 3400 Klosterneuburg , Austria
| | - Ksenia A Khudiakova
- Institute of Science and Technology Austria , Am Campus 1, 3400 Klosterneuburg , Austria
| | - Nicholas H Barton
- Institute of Science and Technology Austria , Am Campus 1, 3400 Klosterneuburg , Austria
| | - Beatriz Vicoso
- Institute of Science and Technology Austria , Am Campus 1, 3400 Klosterneuburg , Austria
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Sex Chromosomes and Master Sex-Determining Genes in Turtles and Other Reptiles. Genes (Basel) 2021; 12:genes12111822. [PMID: 34828428 PMCID: PMC8622242 DOI: 10.3390/genes12111822] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 11/12/2021] [Accepted: 11/16/2021] [Indexed: 11/24/2022] Open
Abstract
Among tetrapods, the well differentiated heteromorphic sex chromosomes of birds and mammals have been highly investigated and their master sex-determining (MSD) gene, Dmrt1 and SRY, respectively, have been identified. The homomorphic sex chromosomes of reptiles have been the least studied, but the gap with birds and mammals has begun to fill. This review describes our current knowledge of reptilian sex chromosomes at the cytogenetic and molecular level. Most of it arose recently from various studies comparing male to female gene content. This includes restriction site-associated DNA sequencing (RAD-Seq) experiments in several male and female samples, RNA sequencing and identification of Z- or X-linked genes by male/female comparative transcriptome coverage, and male/female transcriptomic or transcriptome/genome substraction approaches allowing the identification of Y- or W-linked transcripts. A few putative master sex-determining (MSD) genes have been proposed, but none has been demonstrated yet. Lastly, future directions in the field of reptilian sex chromosomes and their MSD gene studies are considered.
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Stöck M, Kratochvíl L, Kuhl H, Rovatsos M, Evans BJ, Suh A, Valenzuela N, Veyrunes F, Zhou Q, Gamble T, Capel B, Schartl M, Guiguen Y. A brief review of vertebrate sex evolution with a pledge for integrative research: towards ' sexomics'. Philos Trans R Soc Lond B Biol Sci 2021; 376:20200426. [PMID: 34247497 PMCID: PMC8293304 DOI: 10.1098/rstb.2020.0426] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/08/2021] [Indexed: 02/07/2023] Open
Abstract
Triggers and biological processes controlling male or female gonadal differentiation vary in vertebrates, with sex determination (SD) governed by environmental factors or simple to complex genetic mechanisms that evolved repeatedly and independently in various groups. Here, we review sex evolution across major clades of vertebrates with information on SD, sexual development and reproductive modes. We offer an up-to-date review of divergence times, species diversity, genomic resources, genome size, occurrence and nature of polyploids, SD systems, sex chromosomes, SD genes, dosage compensation and sex-biased gene expression. Advances in sequencing technologies now enable us to study the evolution of SD at broader evolutionary scales, and we now hope to pursue a sexomics integrative research initiative across vertebrates. The vertebrate sexome comprises interdisciplinary and integrated information on sexual differentiation, development and reproduction at all biological levels, from genomes, transcriptomes and proteomes, to the organs involved in sexual and sex-specific processes, including gonads, secondary sex organs and those with transcriptional sex-bias. The sexome also includes ontogenetic and behavioural aspects of sexual differentiation, including malfunction and impairment of SD, sexual differentiation and fertility. Starting from data generated by high-throughput approaches, we encourage others to contribute expertise to building understanding of the sexomes of many key vertebrate species. This article is part of the theme issue 'Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part I)'.
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Affiliation(s)
- Matthias Stöck
- Leibniz-Institute of Freshwater Ecology and Inland Fisheries—IGB (Forschungsverbund Berlin), Müggelseedamm 301, 12587 Berlin, Germany
- Amphibian Research Center, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
| | - Lukáš Kratochvíl
- Department of Ecology, Faculty of Science, Charles University, Viničná 7, 12844 Prague, Czech Republic
| | - Heiner Kuhl
- Leibniz-Institute of Freshwater Ecology and Inland Fisheries—IGB (Forschungsverbund Berlin), Müggelseedamm 301, 12587 Berlin, Germany
| | - Michail Rovatsos
- Amphibian Research Center, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
| | - Ben J. Evans
- Department of Biology, McMaster University, Life Sciences Building Room 328, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1
| | - Alexander Suh
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TU, UK
- Department of Organismal Biology—Systematic Biology, Evolutionary Biology Centre, Science for Life Laboratory, Uppsala University, Norbyvägen 18D, 75236 Uppsala, Sweden
| | - Nicole Valenzuela
- Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA
| | - Frédéric Veyrunes
- Institut des Sciences de l'Evolution de Montpellier, ISEM UMR 5554 (CNRS/Université de Montpellier/IRD/EPHE), Montpellier, France
| | - Qi Zhou
- MOE Laboratory of Biosystems Homeostasis and Protection and Zhejiang Provincial Key Laboratory for Cancer Molecular Cell Biology, Life Sciences Institute, Zhejiang University, Hangzhou, Zhejiang 310058, People's Republic of China
- Department of Neuroscience and Developmental Biology, University of Vienna, A-1090 Vienna, Austria
| | - Tony Gamble
- Department of Biological Sciences, Marquette University, Milwaukee, WI 53201, USA
| | - Blanche Capel
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA
| | - Manfred Schartl
- Developmental Biochemistry, Biocenter, University of Würzburg, 97074 Würzburg, Germany
- The Xiphophorus Genetic Stock Center, Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
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Karyotypic Evolution of Sauropsid Vertebrates Illuminated by Optical and Physical Mapping of the Painted Turtle and Slider Turtle Genomes. Genes (Basel) 2020; 11:genes11080928. [PMID: 32806747 PMCID: PMC7464131 DOI: 10.3390/genes11080928] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 07/25/2020] [Accepted: 07/31/2020] [Indexed: 02/07/2023] Open
Abstract
Recent sequencing and software enhancements have advanced our understanding of the evolution of genomic structure and function, especially addressing novel evolutionary biology questions. Yet fragmentary turtle genome assemblies remain a challenge to fully decipher the genetic architecture of adaptive evolution. Here, we use optical mapping to improve the contiguity of the painted turtle (Chrysemys picta) genome assembly and use de novo fluorescent in situ hybridization (FISH) of bacterial artificial chromosome (BAC) clones, BAC-FISH, to physically map the genomes of the painted and slider turtles (Trachemys scripta elegans). Optical mapping increased C. picta's N50 by ~242% compared to the previous assembly. Physical mapping permitted anchoring ~45% of the genome assembly, spanning 5544 genes (including 20 genes related to the sex determination network of turtles and vertebrates). BAC-FISH data revealed assembly errors in C. picta and T. s. elegans assemblies, highlighting the importance of molecular cytogenetic data to complement bioinformatic approaches. We also compared C. picta's anchored scaffolds to the genomes of other chelonians, chicken, lizards, and snake. Results revealed a mostly one-to-one correspondence between chromosomes of painted and slider turtles, and high homology among large syntenic blocks shared with other turtles and sauropsids. Yet, numerous chromosomal rearrangements were also evident across chelonians, between turtles and squamates, and between avian and non-avian reptiles.
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Turtle Insights into the Evolution of the Reptilian Karyotype and the Genomic Architecture of Sex Determination. Genes (Basel) 2020; 11:genes11040416. [PMID: 32290488 PMCID: PMC7231036 DOI: 10.3390/genes11040416] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Revised: 04/06/2020] [Accepted: 04/08/2020] [Indexed: 01/01/2023] Open
Abstract
Sex chromosome evolution remains an evolutionary puzzle despite its importance in understanding sexual development and genome evolution. The seemingly random distribution of sex-determining systems in reptiles offers a unique opportunity to study sex chromosome evolution not afforded by mammals or birds. These reptilian systems derive from multiple transitions in sex determination, some independent, some convergent, that lead to the birth and death of sex chromosomes in various lineages. Here we focus on turtles, an emerging model group with growing genomic resources. We review karyotypic changes that accompanied the evolution of chromosomal systems of genotypic sex determination (GSD) in chelonians from systems under the control of environmental temperature (TSD). These transitions gave rise to 31 GSD species identified thus far (out of 101 turtles with known sex determination), 27 with a characterized sex chromosome system (13 of those karyotypically). These sex chromosomes are varied in terms of the ancestral autosome they co-opted and thus in their homology, as well as in their size (some are macro-, some are micro-chromosomes), heterogamety (some are XX/XY, some ZZ/ZW), dimorphism (some are virtually homomorphic, some heteromorphic with larger-X, larger W, or smaller-Y), age (the oldest system could be ~195 My old and the youngest < 25 My old). Combined, all data indicate that turtles follow some tenets of classic theoretical models of sex chromosome evolution while countering others. Finally, although the study of dosage compensation and molecular divergence of turtle sex chromosomes has lagged behind research on other aspects of their evolution, this gap is rapidly decreasing with the acceleration of ongoing research and growing genomic resources in this group.
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