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Cīrulis A, Hansson B, Abbott JK. Sex-limited chromosomes and non-reproductive traits. BMC Biol 2022; 20:156. [PMID: 35794589 PMCID: PMC9261002 DOI: 10.1186/s12915-022-01357-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2021] [Accepted: 06/22/2022] [Indexed: 12/03/2022] Open
Abstract
Sex chromosomes are typically viewed as having originated from a pair of autosomes, and differentiated as the sex-limited chromosome (e.g. Y) has degenerated by losing most genes through cessation of recombination. While often thought that degenerated sex-limited chromosomes primarily affect traits involved in sex determination and sex cell production, accumulating evidence suggests they also influence traits not sex-limited or directly involved in reproduction. Here, we provide an overview of the effects of sex-limited chromosomes on non-reproductive traits in XY, ZW or UV sex determination systems, and discuss evolutionary processes maintaining variation at sex-limited chromosomes and molecular mechanisms affecting non-reproductive traits.
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Affiliation(s)
- Aivars Cīrulis
- Department of Biology, Lund University, 223 62, Lund, Sweden.
| | - Bengt Hansson
- Department of Biology, Lund University, 223 62, Lund, Sweden
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2
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Do Ty3/Gypsy Transposable Elements Play Preferential Roles in Sex Chromosome Differentiation? Life (Basel) 2022; 12:life12040522. [PMID: 35455013 PMCID: PMC9025612 DOI: 10.3390/life12040522] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Revised: 03/13/2022] [Accepted: 03/30/2022] [Indexed: 12/16/2022] Open
Abstract
Transposable elements (TEs) comprise a substantial portion of eukaryotic genomes. They have the unique ability to integrate into new locations and serve as the main source of genomic novelties by mediating chromosomal rearrangements and regulating portions of functional genes. Recent studies have revealed that TEs are abundant in sex chromosomes. In this review, we propose evolutionary relationships between specific TEs, such as Ty3/Gypsy, and sex chromosomes in different lineages based on the hypothesis that these elements contributed to sex chromosome differentiation processes. We highlight how TEs can drive the dynamics of sex-determining regions via suppression recombination under a selective force to affect the organization and structural evolution of sex chromosomes. The abundance of TEs in the sex-determining regions originates from TE-poor genomic regions, suggesting a link between TE accumulation and the emergence of the sex-determining regions. TEs are generally considered to be a hallmark of chromosome degeneration. Finally, we outline recent approaches to identify TEs and study their sex-related roles and effects in the differentiation and evolution of sex chromosomes.
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3
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Brown EJ, Nguyen AH, Bachtrog D. The Drosophila Y Chromosome Affects Heterochromatin Integrity Genome-Wide. Mol Biol Evol 2021; 37:2808-2824. [PMID: 32211857 PMCID: PMC7530609 DOI: 10.1093/molbev/msaa082] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The Drosophila Y chromosome is gene poor and mainly consists of silenced, repetitive DNA. Nonetheless, the Y influences expression of hundreds of genes genome-wide, possibly by sequestering key components of the heterochromatin machinery away from other positions in the genome. To test the influence of the Y chromosome on the genome-wide chromatin landscape, we assayed the genomic distribution of histone modifications associated with gene activation (H3K4me3) or heterochromatin (H3K9me2 and H3K9me3) in fruit flies with varying sex chromosome complements (X0, XY, and XYY males; XX and XXY females). Consistent with the general deficiency of active chromatin modifications on the Y, we find that Y gene dose has little influence on the genomic distribution of H3K4me3. In contrast, both the presence and the number of Y chromosomes strongly influence genome-wide enrichment patterns of repressive chromatin modifications. Highly repetitive regions such as the pericentromeres, the dot, and the Y chromosome (if present) are enriched for heterochromatic modifications in wildtype males and females, and even more strongly in X0 flies. In contrast, the additional Y chromosome in XYY males and XXY females diminishes the heterochromatic signal in these normally silenced, repeat-rich regions, which is accompanied by an increase in expression of Y-linked repeats. We find hundreds of genes that are expressed differentially between individuals with aberrant sex chromosome karyotypes, many of which also show sex-biased expression in wildtype Drosophila. Thus, Y chromosomes influence heterochromatin integrity genome-wide, and differences in the chromatin landscape of males and females may also contribute to sex-biased gene expression and sexual dimorphisms.
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Affiliation(s)
- Emily J Brown
- Department of Integrative Biology, University of California Berkeley, Berkeley, CA
| | - Alison H Nguyen
- Department of Integrative Biology, University of California Berkeley, Berkeley, CA
| | - Doris Bachtrog
- Department of Integrative Biology, University of California Berkeley, Berkeley, CA
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4
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Liu J, Ali M, Zhou Q. Establishment and evolution of heterochromatin. Ann N Y Acad Sci 2020; 1476:59-77. [PMID: 32017156 PMCID: PMC7586837 DOI: 10.1111/nyas.14303] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 10/31/2019] [Accepted: 01/02/2020] [Indexed: 12/12/2022]
Abstract
The eukaryotic genome is packaged into transcriptionally active euchromatin and silent heterochromatin, with most studies focused on the former encompassing the majority of protein-coding genes. The recent development of various sequencing techniques has refined this classic dichromatic partition and has better illuminated the composition, establishment, and evolution of this genomic and epigenomic "dark matter" in the context of topologically associated domains and phase-separated droplets. Heterochromatin includes genomic regions that can be densely stained by chemical dyes, which have been shown to be enriched for repetitive elements and epigenetic marks, including H3K9me2/3 and H3K27me3. Heterochromatin is usually replicated late, concentrated at the nuclear periphery or around nucleoli, and usually lacks highly expressed genes; and now it is considered to be as neither genetically inert nor developmentally static. Heterochromatin guards genome integrity against transposon activities and exerts important regulatory functions by targeting beyond its contained genes. Both its nucleotide sequences and regulatory proteins exhibit rapid coevolution between species. In addition, there are dynamic transitions between euchromatin and heterochromatin during developmental and evolutionary processes. We summarize here the ever-changing characteristics of heterochromatin and propose models and principles for the evolutionary transitions of heterochromatin that have been mainly learned from studies of Drosophila and yeast. Finally, we highlight the role of sex chromosomes in studying heterochromatin evolution.
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Affiliation(s)
- Jing Liu
- MOE Laboratory of Biosystems Homeostasis & Protection, Life Sciences InstituteZhejiang UniversityHangzhouChina
- Department of Molecular Evolution and DevelopmentUniversity of ViennaViennaAustria
| | - Mujahid Ali
- Department of Molecular Evolution and DevelopmentUniversity of ViennaViennaAustria
| | - Qi Zhou
- MOE Laboratory of Biosystems Homeostasis & Protection, Life Sciences InstituteZhejiang UniversityHangzhouChina
- Department of Molecular Evolution and DevelopmentUniversity of ViennaViennaAustria
- Center for Reproductive Medicine, The 2nd Affiliated Hospital, School of MedicineZhejiang UniversityHangzhouChina
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5
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Tahira AC, Barbosa AR, Feltrin AS, Gastaldi VD, de Toledo VHC, de Carvalho Pereira JG, Lisboa BCG, de Souza Reis VN, dos Santos ACF, Maschietto M, Brentani H. Putative contributions of the sex chromosome proteins SOX3 and SRY to neurodevelopmental disorders. Am J Med Genet B Neuropsychiatr Genet 2019; 180:390-414. [PMID: 30537354 PMCID: PMC6767407 DOI: 10.1002/ajmg.b.32704] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Revised: 11/08/2018] [Accepted: 11/12/2018] [Indexed: 12/12/2022]
Abstract
The male-biased prevalence of certain neurodevelopmental disorders and the sex-biased outcomes associated with stress exposure during gestation have been previously described. Here, we hypothesized that genes distinctively targeted by only one or both homologous proteins highly conserved across therian mammals, SOX3 and SRY, could induce sexual adaptive changes that result in a differential risk for neurodevelopmental disorders. ChIP-seq/chip data showed that SOX3/SRY gene targets were expressed in different brain cell types in mice. We used orthologous human genes in rodent genomes to extend the number of SOX3/SRY set (1,721). These genes were later found to be enriched in five modules of coexpressed genes during the early and mid-gestation periods (FDR < 0.05), independent of sexual hormones. Genes with differential expression (24, p < 0.0001) and methylation (40, p < 0.047) between sexes were overrepresented in this set. Exclusive SOX3 or SRY target genes were more associated with the late gestational and postnatal periods. Using autism as a model sex-biased disorder, the SOX3/SRY set was enriched in autism gene databases (FDR ≤ 0.05), and there were more de novo variations from the male autism spectrum disorder (ASD) samples under the SRY peaks compared to the random peaks (p < 0.024). The comparison of coexpressed networks of SOX3/SRY target genes between male autism and control samples revealed low preservation in gene modules related to stress response (99 genes) and neurogenesis (78 genes). This study provides evidence that while SOX3 is a regulatory mechanism for both sexes, the male-exclusive SRY also plays a role in gene regulation, suggesting a potential mechanism for sex bias in ASD.
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Affiliation(s)
- Ana Carolina Tahira
- LIM23, Instituto de Psiquiatria, Hospital das Clinicas HCFMUSP, Faculdade de Medicina, Universidade de Sao PauloSao PauloSPBrazil
| | - André Rocha Barbosa
- LIM23, Instituto de Psiquiatria, Hospital das Clinicas HCFMUSP, Faculdade de Medicina, Universidade de Sao PauloSao PauloSPBrazil
- Inter‐institutional Grad Program on BioinformaticsUniversity of São PauloSão PauloSPBrazil
| | | | - Vinicius Daguano Gastaldi
- LIM23, Instituto de Psiquiatria, Hospital das Clinicas HCFMUSP, Faculdade de Medicina, Universidade de Sao PauloSao PauloSPBrazil
| | - Victor Hugo Calegari de Toledo
- LIM23, Instituto de Psiquiatria, Hospital das Clinicas HCFMUSP, Faculdade de Medicina, Universidade de Sao PauloSao PauloSPBrazil
| | | | - Bianca Cristina Garcia Lisboa
- LIM23, Instituto de Psiquiatria, Hospital das Clinicas HCFMUSP, Faculdade de Medicina, Universidade de Sao PauloSao PauloSPBrazil
| | - Viviane Neri de Souza Reis
- LIM23, Instituto de Psiquiatria, Hospital das Clinicas HCFMUSP, Faculdade de Medicina, Universidade de Sao PauloSao PauloSPBrazil
| | - Ana Cecília Feio dos Santos
- LIM23, Instituto de Psiquiatria, Hospital das Clinicas HCFMUSP, Faculdade de Medicina, Universidade de Sao PauloSao PauloSPBrazil
- Laboratório de Pesquisas Básicas em Malária – EntomologiaSeção de Parasitologia – Instituto Evandro Chagas/SVS/MSAnanindeuaPABrazil
| | - Mariana Maschietto
- Brazilian Biosciences National Laboratory (LNBio)Brazilian Center for Research in Energy and Materials (CNPEM)CampinasSPBrazil
| | - Helena Brentani
- LIM23, Instituto de Psiquiatria, Hospital das Clinicas HCFMUSP, Faculdade de Medicina, Universidade de Sao PauloSao PauloSPBrazil
- Inter‐institutional Grad Program on BioinformaticsUniversity of São PauloSão PauloSPBrazil
- Instituto de Psiquiatria, Hospital das Clinicas HCFMUSP, Faculdade de Medicina, Universidade de Sao PauloSPBrazil
- National Institute of Developmental Psychiatry for Children and Adolescents (INPD)Sao PauloSPBrazil
- Faculdade de Medicina FMUSPUniversidade de Sao PauloSao PauloSPBrazil
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6
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Deakin JE, Potter S, O'Neill R, Ruiz-Herrera A, Cioffi MB, Eldridge MDB, Fukui K, Marshall Graves JA, Griffin D, Grutzner F, Kratochvíl L, Miura I, Rovatsos M, Srikulnath K, Wapstra E, Ezaz T. Chromosomics: Bridging the Gap between Genomes and Chromosomes. Genes (Basel) 2019; 10:genes10080627. [PMID: 31434289 PMCID: PMC6723020 DOI: 10.3390/genes10080627] [Citation(s) in RCA: 52] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 08/10/2019] [Accepted: 08/13/2019] [Indexed: 02/07/2023] Open
Abstract
The recent advances in DNA sequencing technology are enabling a rapid increase in the number of genomes being sequenced. However, many fundamental questions in genome biology remain unanswered, because sequence data alone is unable to provide insight into how the genome is organised into chromosomes, the position and interaction of those chromosomes in the cell, and how chromosomes and their interactions with each other change in response to environmental stimuli or over time. The intimate relationship between DNA sequence and chromosome structure and function highlights the need to integrate genomic and cytogenetic data to more comprehensively understand the role genome architecture plays in genome plasticity. We propose adoption of the term 'chromosomics' as an approach encompassing genome sequencing, cytogenetics and cell biology, and present examples of where chromosomics has already led to novel discoveries, such as the sex-determining gene in eutherian mammals. More importantly, we look to the future and the questions that could be answered as we enter into the chromosomics revolution, such as the role of chromosome rearrangements in speciation and the role more rapidly evolving regions of the genome, like centromeres, play in genome plasticity. However, for chromosomics to reach its full potential, we need to address several challenges, particularly the training of a new generation of cytogeneticists, and the commitment to a closer union among the research areas of genomics, cytogenetics, cell biology and bioinformatics. Overcoming these challenges will lead to ground-breaking discoveries in understanding genome evolution and function.
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Affiliation(s)
- Janine E Deakin
- Institute for Applied Ecology, University of Canberra, Canberra, ACT 2617, Australia.
| | - Sally Potter
- Research School of Biology, Australian National University, Acton, ACT 2601, Australia
- Australian Museum Research Institute, Australian Museum, 1 William St Sydney, NSW 2010, Australia
| | - Rachel O'Neill
- Institute for Systems Genomics and Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA
| | - Aurora Ruiz-Herrera
- Departament de Biologia Cel·lular, Fisiologia i Immunologia, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain
- Genome Integrity and Instability Group, Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain
| | - Marcelo B Cioffi
- Laboratório de Citogenética de Peixes, Departamento de Genética e Evolução, Universidade Federal de São Carlos, São Carlos, SP 13565-905, Brazil
| | - Mark D B Eldridge
- Australian Museum Research Institute, Australian Museum, 1 William St Sydney, NSW 2010, Australia
| | - Kichi Fukui
- Graduate School of Pharmaceutical Sciences, Osaka University, Suita 565-0871, Osaka, Japan
| | - Jennifer A Marshall Graves
- Institute for Applied Ecology, University of Canberra, Canberra, ACT 2617, Australia
- School of Life Sciences, LaTrobe University, Melbourne, VIC 3168, Australia
| | - Darren Griffin
- School of Biosciences, University of Kent, Canterbury CT2 7NJ, UK
| | - Frank Grutzner
- School of Biological Sciences, The University of Adelaide, Adelaide, SA 5005, Australia
| | - Lukáš Kratochvíl
- Department of Ecology, Faculty of Science, Charles University, Viničná 7, 128 44 Prague 2, Czech Republic
| | - Ikuo Miura
- Amphibian Research Center, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
| | - Michail Rovatsos
- School of Biological Sciences, The University of Adelaide, Adelaide, SA 5005, Australia
| | - Kornsorn Srikulnath
- Laboratory of Animal Cytogenetics & Comparative Genomics (ACCG), Department of Genetics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand
| | - Erik Wapstra
- School of Natural Sciences, University of Tasmania, Hobart 7000, Australia
| | - Tariq Ezaz
- Institute for Applied Ecology, University of Canberra, Canberra, ACT 2617, Australia.
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7
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Abstract
Levels and patterns of genetic diversity can provide insights into a population’s history. In species with sex chromosomes, differences between genomic regions with unique inheritance patterns can be used to distinguish between different sets of possible demographic and selective events. This review introduces the differences in population history for sex chromosomes and autosomes, provides the expectations for genetic diversity across the genome under different evolutionary scenarios, and gives an introductory description for how deviations in these expectations are calculated and can be interpreted. Predominantly, diversity on the sex chromosomes has been used to explore and address three research areas: 1) Mating patterns and sex-biased variance in reproductive success, 2) signatures of selection, and 3) evidence for modes of speciation and introgression. After introducing the theory, this review catalogs recent studies of genetic diversity on the sex chromosomes across species within the major research areas that sex chromosomes are typically applied to, arguing that there are broad similarities not only between male-heterogametic (XX/XY) and female-heterogametic (ZZ/ZW) sex determination systems but also any mating system with reduced recombination in a sex-determining region. Further, general patterns of reduced diversity in nonrecombining regions are shared across plants and animals. There are unique patterns across populations with vastly different patterns of mating and speciation, but these do not tend to cluster by taxa or sex determination system.
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Affiliation(s)
- Melissa A Wilson Sayres
- School of Life Sciences, Center for Evolution and Medicine, The Biodesign Institute, Arizona State University
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8
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Lakhotia SC. Non-coding RNAs demystify constitutive heterochromatin as essential modulator of epigenotype. THE NUCLEUS 2017. [DOI: 10.1007/s13237-017-0221-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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9
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Śliwińska EB, Martyka R, Tryjanowski P. Evolutionary interaction between W/Y chromosome and transposable elements. Genetica 2016; 144:267-78. [PMID: 27000053 PMCID: PMC4879163 DOI: 10.1007/s10709-016-9895-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2015] [Accepted: 03/13/2016] [Indexed: 11/28/2022]
Abstract
The W/Y chromosome is unique among chromosomes as it does not recombine in its mature form. The main side effect of cessation of recombination is evolutionary instability and degeneration of the W/Y chromosome, or frequent W/Y chromosome turnovers. Another important feature of W/Y chromosome degeneration is transposable element (TEs) accumulation. Transposon accumulation has been confirmed for all W/Y chromosomes that have been sequenced so far. Models of W/Y chromosome instability include the assemblage of deleterious mutations in protein coding genes, but do not include the influence of transposable elements that are accumulated gradually in the non-recombining genome. The multiple roles of genomic TEs, and the interactions between retrotransposons and genome defense proteins are currently being studied intensively. Small RNAs originating from retrotransposon transcripts appear to be, in some cases, the only mediators of W/Y chromosome function. Based on the review of the most recent publications, we present knowledge on W/Y evolution in relation to retrotransposable element accumulation.
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Affiliation(s)
- Ewa B Śliwińska
- Institute of Zoology, Poznań University of Life Sciences, Wojska Polskiego 71C, 60-625, Poznań, Poland.
- Institute of Nature Conservation, Polish Academy of Sciences, Mickiewicza 33, 31-120, Kraków, Poland.
| | - Rafał Martyka
- Institute of Nature Conservation, Polish Academy of Sciences, Mickiewicza 33, 31-120, Kraków, Poland
| | - Piotr Tryjanowski
- Institute of Zoology, Poznań University of Life Sciences, Wojska Polskiego 71C, 60-625, Poznań, Poland
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10
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Griffin RM, Le Gall D, Schielzeth H, Friberg U. Within-population Y-linked genetic variation for lifespan inDrosophila melanogaster. J Evol Biol 2015; 28:1940-7. [DOI: 10.1111/jeb.12708] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Revised: 07/24/2015] [Accepted: 07/24/2015] [Indexed: 12/12/2022]
Affiliation(s)
- R. M. Griffin
- Department of Evolutionary Biology; Uppsala University; Uppsala Sweden
| | - D. Le Gall
- Department of Evolutionary Biology; Uppsala University; Uppsala Sweden
- Department of Biology; Ecole Normale Supérieure de Cachan; Cachan France
| | - H. Schielzeth
- Department of Evolutionary Biology; Bielefeld University; Bielefeld Germany
| | - U. Friberg
- Department of Evolutionary Biology; Uppsala University; Uppsala Sweden
- IFM Biology; AVIAN Behavioural Genomics and Physiology Group; Linköping University; Linköping Sweden
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11
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Abstract
Dioecy (separate male and female individuals) ensures outcrossing and is more prevalent in animals than in plants. Although it is common in bryophytes and gymnosperms, only 5% of angiosperms are dioecious. In dioecious higher plants, flowers borne on male and female individuals are, respectively deficient in functional gynoecium and androecium. Dioecy is inherited via three sex chromosome systems: XX/XY, XX/X0 and WZ/ZZ, such that XX or WZ is female and XY, X0 or ZZ are males. The XX/XY system generates the rarer XX/X0 and WZ/ZZ systems. An autosome pair begets XY chromosomes. A recessive loss-of-androecium mutation (ana) creates X chromosome and a dominant gynoecium-suppressing (GYS) mutation creates Y chromosome. The ana/ANA and gys/GYS loci are in the sex-determining region (SDR) of the XY pair. Accumulation of inversions, deleterious mutations and repeat elements, especially transposons, in the SDR of Y suppresses recombination between X and Y in SDR, making Y labile and increasingly degenerate and heteromorphic from X. Continued recombination between X and Y in their pseudoautosomal region located at the ends of chromosomal arms allows survival of the degenerated Y and of the species. Dioecy is presumably a component of the evolutionary cycle for the origin of new species. Inbred hermaphrodite species assume dioecy. Later they suffer degenerate-Y-led population regression. Cross-hybridization between such extinguishing species and heterologous species, followed by genome duplication of segregants from hybrids, give rise to new species.
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12
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Díaz-Castillo C. Evidence for a sexual dimorphism in gene expression noise in metazoan species. PeerJ 2015; 3:e750. [PMID: 25649874 PMCID: PMC4314086 DOI: 10.7717/peerj.750] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Accepted: 01/15/2015] [Indexed: 11/20/2022] Open
Abstract
Many biological processes depend on very few copies of intervening elements, which makes such processes particularly susceptible to the stochastic fluctuations of these elements. The intrinsic stochasticity of certain processes is propagated across biological levels, causing genotype- and environment-independent biological variation which might permit populations to better cope with variable environments. Biological variations of stochastic nature might also allow the accumulation of variations at the genetic level that are hidden from natural selection, which might have a great potential for population diversification. The study of any mechanism that resulted in the modulation of stochastic variation is, therefore, of potentially wide interest. I propose that sex might be an important modulator of the stochastic variation in gene expression, i.e., gene expression noise. Based on known associations between different patterns of gene expression variation, I hypothesize that in metazoans the gene expression noise might be generally larger in heterogametic than in homogametic individuals. I directly tested this hypothesis by comparing putative genotype- and environment-independent variations in gene expression between females and males of Drosophila melanogaster strains. Also, considering the potential effect of the propagation of gene expression noise across biological levels, I indirectly tested the existence of a metazoan sexual dimorphism in gene expression noise by analyzing putative genotype- and environment-independent variation in phenotypes related to interaction with the environment in D. melanogaster strains and metazoan species. The results of these analyses are consistent with the hypothesis that gene expression is generally noisier in heterogametic than in homogametic individuals. Further analyses and discussion of existing literature permits the speculation that the sexual dimorphism in gene expression noise is ultimately based on the nuclear dynamics in gametogenesis and very early embryogenesis of sex-specific chromosomes, i.e., Y and W chromosomes.
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Affiliation(s)
- Carlos Díaz-Castillo
- Department of Developmental & Cell Biology, University of California, Irvine , CA , USA
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13
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Abstract
Sex chromosomes are the most dynamic entity in any genome having unique morphology, gene content, and evolution. They have evolved multiple times and independently throughout vertebrate evolution. One of the major genomic changes that pertain to sex chromosomes involves the amplification of common repeats. It is hypothesized that such amplification of repeats facilitates the suppression of recombination, leading to the evolution of heteromorphic sex chromosomes through genetic degradation of Y or W chromosomes. Although contrasting evidence is available, it is clear that amplification of simple repetitive sequences played a major role in the evolution of Y and W chromosomes in vertebrates. In this review, we present a brief overview of the repetitive DNA classes that accumulated during sex chromosome evolution, mainly focusing on vertebrates, and discuss their possible role and potential function in this process.
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