1
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Courret C, Larracuente AM. High levels of intra-strain structural variation in Drosophila simulans X pericentric heterochromatin. Genetics 2023; 225:iyad176. [PMID: 37768175 PMCID: PMC10697818 DOI: 10.1093/genetics/iyad176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2023] [Revised: 08/12/2023] [Accepted: 09/14/2023] [Indexed: 09/29/2023] Open
Abstract
Large genome structural variations can impact genome regulation and integrity. Repeat-rich regions like pericentric heterochromatin are vulnerable to structural rearrangements although we know little about how often these rearrangements occur over evolutionary time. Repetitive genome regions are particularly difficult to study with genomic approaches, as they are missing from most genome assemblies. However, cytogenetic approaches offer a direct way to detect large rearrangements involving pericentric heterochromatin. Here, we use a cytogenetic approach to reveal large structural rearrangements associated with the X pericentromeric region of Drosophila simulans. These rearrangements involve large blocks of satellite DNA-the 500-bp and Rsp-like satellites-which colocalize in the X pericentromeric heterochromatin. We find that this region is polymorphic not only among different strains, but between isolates of the same strain from different labs, and even within individual isolates. On the one hand, our observations raise questions regarding the potential impact of such variation at the phenotypic level and our ability to control for such genetic variability. On the other hand, this highlights the very rapid turnover of the pericentric heterochromatin most likely associated with genomic instability of the X pericentromere. It represents a unique opportunity to study the dynamics of pericentric heterochromatin, the evolution of associated satellites on a very short time scale, and to better understand how structural variation arises.
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Affiliation(s)
- Cécile Courret
- Department of Biology, University of Rochester, Rochester, NY 14627, USA
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2
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Chang CH, Gregory LE, Gordon KE, Meiklejohn CD, Larracuente AM. Unique structure and positive selection promote the rapid divergence of Drosophila Y chromosomes. eLife 2022; 11:e75795. [PMID: 34989337 PMCID: PMC8794474 DOI: 10.7554/elife.75795] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Accepted: 12/18/2021] [Indexed: 02/06/2023] Open
Abstract
Y chromosomes across diverse species convergently evolve a gene-poor, heterochromatic organization enriched for duplicated genes, LTR retrotransposons, and satellite DNA. Sexual antagonism and a loss of recombination play major roles in the degeneration of young Y chromosomes. However, the processes shaping the evolution of mature, already degenerated Y chromosomes are less well-understood. Because Y chromosomes evolve rapidly, comparisons between closely related species are particularly useful. We generated de novo long-read assemblies complemented with cytological validation to reveal Y chromosome organization in three closely related species of the Drosophila simulans complex, which diverged only 250,000 years ago and share >98% sequence identity. We find these Y chromosomes are divergent in their organization and repetitive DNA composition and discover new Y-linked gene families whose evolution is driven by both positive selection and gene conversion. These Y chromosomes are also enriched for large deletions, suggesting that the repair of double-strand breaks on Y chromosomes may be biased toward microhomology-mediated end joining over canonical non-homologous end-joining. We propose that this repair mechanism contributes to the convergent evolution of Y chromosome organization across organisms.
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Affiliation(s)
- Ching-Ho Chang
- Department of Biology, University of RochesterRochesterUnited States
| | - Lauren E Gregory
- Department of Biology, University of RochesterRochesterUnited States
| | - Kathleen E Gordon
- School of Biological Sciences, University of Nebraska-LincolnLincolnUnited States
| | - Colin D Meiklejohn
- School of Biological Sciences, University of Nebraska-LincolnLincolnUnited States
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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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The Y chromosome may contribute to sex-specific ageing in Drosophila. Nat Ecol Evol 2020; 4:853-862. [PMID: 32313175 PMCID: PMC7274899 DOI: 10.1038/s41559-020-1179-5] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Accepted: 03/16/2020] [Indexed: 12/03/2022]
Abstract
Heterochromatin suppresses repetitive DNA, and a loss of heterochromatin has been observed in aged cells of several species, including humans and Drosophila. Males often contain substantially more heterochromatic DNA than females, due to the presence of a large, repeat-rich Y chromosome, and male flies generally have shorter average life spans than females. Here we show that repetitive DNA becomes de-repressed more rapidly in old male flies relative to females, and repeats on the Y chromosome are disproportionally mis-expressed during aging. This is associated with a loss of heterochromatin at repetitive elements during aging in male flies, and a general loss of repressive chromatin in aged males away from pericentromeric regions and the Y. By generating flies with different sex chromosome karyotypes (XXY females; X0 and XYY males), we show that repeat de-repression and average lifespan is correlated with the number of Y chromosomes. This suggests that sex-specific chromatin differences may contribute to sex-specific aging in flies.
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5
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Lindsay WR, Andersson S, Bererhi B, Höglund J, Johnsen A, Kvarnemo C, Leder EH, Lifjeld JT, Ninnes CE, Olsson M, Parker GA, Pizzari T, Qvarnström A, Safran RJ, Svensson O, Edwards SV. Endless forms of sexual selection. PeerJ 2019; 7:e7988. [PMID: 31720113 PMCID: PMC6839514 DOI: 10.7717/peerj.7988] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Accepted: 10/04/2019] [Indexed: 12/11/2022] Open
Abstract
In recent years, the field of sexual selection has exploded, with advances in theoretical and empirical research complementing each other in exciting ways. This perspective piece is the product of a “stock-taking” workshop on sexual selection and sexual conflict. Our aim is to identify and deliberate on outstanding questions and to stimulate discussion rather than provide a comprehensive overview of the entire field. These questions are organized into four thematic sections we deem essential to the field. First we focus on the evolution of mate choice and mating systems. Variation in mate quality can generate both competition and choice in the opposite sex, with implications for the evolution of mating systems. Limitations on mate choice may dictate the importance of direct vs. indirect benefits in mating decisions and consequently, mating systems, especially with regard to polyandry. Second, we focus on how sender and receiver mechanisms shape signal design. Mediation of honest signal content likely depends on integration of temporally variable social and physiological costs that are challenging to measure. We view the neuroethology of sensory and cognitive receiver biases as the main key to signal form and the ‘aesthetic sense’ proposed by Darwin. Since a receiver bias is sufficient to both initiate and drive ornament or armament exaggeration, without a genetically correlated or even coevolving receiver, this may be the appropriate ‘null model’ of sexual selection. Thirdly, we focus on the genetic architecture of sexually selected traits. Despite advances in modern molecular techniques, the number and identity of genes underlying performance, display and secondary sexual traits remains largely unknown. In-depth investigations into the genetic basis of sexual dimorphism in the context of long-term field studies will reveal constraints and trajectories of sexually selected trait evolution. Finally, we focus on sexual selection and conflict as drivers of speciation. Population divergence and speciation are often influenced by an interplay between sexual and natural selection. The extent to which sexual selection promotes or counteracts population divergence may vary depending on the genetic architecture of traits as well as the covariance between mating competition and local adaptation. Additionally, post-copulatory processes, such as selection against heterospecific sperm, may influence the importance of sexual selection in speciation. We propose that efforts to resolve these four themes can catalyze conceptual progress in the field of sexual selection, and we offer potential avenues of research to advance this progress.
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Affiliation(s)
- Willow R Lindsay
- Department of Biological and Environmental Sciences, University of Gothenburg, Göteborg, Sweden
| | - Staffan Andersson
- Department of Biological and Environmental Sciences, University of Gothenburg, Göteborg, Sweden
| | - Badreddine Bererhi
- Department of Biological and Environmental Sciences, University of Gothenburg, Göteborg, Sweden
| | - Jacob Höglund
- Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden
| | - Arild Johnsen
- Natural History Museum, University of Oslo, Oslo, Norway
| | - Charlotta Kvarnemo
- Department of Biological and Environmental Sciences, University of Gothenburg, Göteborg, Sweden
| | - Erica H Leder
- Natural History Museum, University of Oslo, Oslo, Norway
| | - Jan T Lifjeld
- Natural History Museum, University of Oslo, Oslo, Norway
| | - Calum E Ninnes
- Department of Biological and Environmental Sciences, University of Gothenburg, Göteborg, Sweden.,Department of Entomology and Nematology, University of Florida, Gainesville, FL, United States of America
| | - Mats Olsson
- Department of Biological and Environmental Sciences, University of Gothenburg, Göteborg, Sweden
| | - Geoff A Parker
- Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Tommaso Pizzari
- Department of Zoology, Edward Grey Institute, University of Oxford, Oxford, United Kingdom
| | - Anna Qvarnström
- Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden
| | - Rebecca J Safran
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, United States of America
| | - Ola Svensson
- School of Natural Sciences, Technology and Environmental Studies, Södertörn University, Huddinge, Sweden
| | - Scott V Edwards
- Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, Harvard University, Cambridge, MA, United States of America.,Gothenburg Centre for Advanced Studies in Science and Technology, Chalmers University of Technology, Göteborg, Sweden
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6
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Buchman A, Akbari OS. Site-specific transgenesis of the Drosophila melanogaster Y-chromosome using CRISPR/Cas9. INSECT MOLECULAR BIOLOGY 2019; 28:65-73. [PMID: 30079589 PMCID: PMC8459378 DOI: 10.1111/imb.12528] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Despite the importance of Y-chromosomes in evolution and sex determination, their heterochromatic, repeat-rich nature makes them difficult to sequence (due, in part, to ambiguities in sequence alignment and assembly) and to genetically manipulate. Therefore, they generally remain poorly understood. For example, the Drosophila melanogaster Y-chromosome, one of the most extensively studied Y-chromosomes, is widely heterochromatic and composed mainly of highly repetitive sequences, with only a handful of expressed genes scattered throughout its length. Efforts to insert transgenes on this chromosome have thus far relied on either random insertion of transposons (sometimes harbouring 'landing sites' for subsequent integrations) with limited success or on chromosomal translocations, thereby limiting the types of Y-chromosome-related questions that could be explored. Here, we describe a versatile approach to site-specifically insert transgenes on the Y-chromosome in D. melanogaster via CRISPR/Cas9-mediated homology-directed repair. We demonstrate the ability to insert, and detect expression from, fluorescently marked transgenes at two specific locations on the Y-chromosome, and we utilize these marked Y-chromosomes to detect and quantify rare chromosomal nondisjunction effects. Finally, we discuss how this Y-docking technique could be adapted to other insects to aid in the development of genetic control technologies for the management of insect disease vectors and pests.
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Affiliation(s)
- Anna Buchman
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, 92093, United States of America
| | - Omar S. Akbari
- Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California, 92093, United States of America
- Tata Institute for Genetics and Society, University of California, San Diego, La Jolla, CA 92093, United States of America
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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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Support for the Dominance Theory in Drosophila Transcriptomes. Genetics 2018; 210:703-718. [PMID: 30131345 PMCID: PMC6216581 DOI: 10.1534/genetics.118.301229] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Accepted: 08/10/2018] [Indexed: 12/14/2022] Open
Abstract
Interactions among divergent elements of transcriptional networks from different species can lead to misexpression in hybrids through regulatory incompatibilities, some with the potential to generate sterility. While the possible contribution of faster-male evolution to this misexpression has been explored, the role of the hemizygous X chromosome (i.e., the dominance theory for transcriptomes) remains yet to be determined. Here, we study genome-wide patterns of gene expression in females and males of Drosophila yakuba, Drosophila santomea and their hybrids. We used attached-X stocks to specifically test the dominance theory, and we uncovered a significant contribution of recessive alleles on the X chromosome to hybrid misexpression. Our analyses also suggest a contribution of weakly deleterious regulatory mutations to gene expression divergence in genes with sex-biased expression, but only in the sex toward which the expression is biased (e.g., genes with female-biased expression when analyzed in females). In the opposite sex, we found stronger selective constraints on gene expression divergence. Although genes with a high degree of male-biased expression show a clear signal of faster-X evolution of gene expression, we also detected slower-X evolution in other gene classes (e.g., female-biased genes). This slower-X effect is mediated by significant decreases in cis- and trans-regulatory divergence. The distinct behavior of X-linked genes with a high degree of male-biased expression is consistent with these genes experiencing a higher incidence of positively selected regulatory mutations than their autosomal counterparts.
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9
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The Y Chromosome Modulates Splicing and Sex-Biased Intron Retention Rates in Drosophila. Genetics 2017; 208:1057-1067. [PMID: 29263027 DOI: 10.1534/genetics.117.300637] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Accepted: 12/18/2017] [Indexed: 01/01/2023] Open
Abstract
The Drosophila Y chromosome is a 40-Mb segment of mostly repetitive DNA; it harbors a handful of protein-coding genes and a disproportionate amount of satellite repeats, transposable elements, and multicopy DNA arrays. Intron retention (IR) is a type of alternative splicing (AS) event by which one or more introns remain within the mature transcript. IR recently emerged as a deliberate cellular mechanism to modulate gene expression levels and has been implicated in multiple biological processes. However, the extent of sex differences in IR and the contribution of the Y chromosome to the modulation of AS and IR rates has not been addressed. Here we showed pervasive IR in the fruit fly Drosophila melanogaster with thousands of novel IR events, hundreds of which displayed extensive sex bias. The data also revealed an unsuspected role for the Y chromosome in the modulation of AS and IR. The majority of sex-biased IR events introduced premature termination codons and the magnitude of sex bias was associated with gene expression differences between the sexes. Surprisingly, an extra Y chromosome in males (X^YY genotype) or the presence of a Y chromosome in females (X^XY genotype) significantly modulated IR and recapitulated natural differences in IR between the sexes. Our results highlight the significance of sex-biased IR in tuning sex differences and the role of the Y chromosome as a source of variable IR rates between the sexes. Modulation of splicing and IR rates across the genome represent new and unexpected outcomes of the Drosophila Y chromosome.
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10
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Hua X. The impact of seasonality on niche breadth, distribution range and species richness: a theoretical exploration of Janzen's hypothesis. Proc Biol Sci 2017; 283:rspb.2016.0349. [PMID: 27466445 DOI: 10.1098/rspb.2016.0349] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 07/04/2016] [Indexed: 12/18/2022] Open
Abstract
Being invoked as one of the candidate mechanisms for the latitudinal patterns in biodiversity, Janzen's hypothesis states that the limited seasonal temperature variation in the tropics generates greater temperature stratification across elevations, which makes tropical species adapted to narrower ranges of temperatures and have lower effective dispersal across elevations than species in temperate regions. Numerous empirical studies have documented latitudinal patterns in species elevational ranges and thermal niche breadths that are consistent with the hypothesis, but the theoretical underpinnings remain unclear. This study presents the first mathematical model to examine the evolutionary processes that could back up Janzen's hypothesis and assess the effectiveness of limited seasonal temperature variation to promote speciation along elevation in the tropics. Results suggest that trade-offs in thermal tolerances provide a mechanism for Janzen's hypothesis. Limited seasonal temperature variation promotes gradient speciation not due to the reduction in gene flow that is associated with narrow thermal niche, but due to the pleiotropic effects of more stable divergent selection of thermal tolerance on the evolution of reproductive incompatibility. The proposed modelling approach also provides a potential way to test a speciation model against genetic data.
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Affiliation(s)
- Xia Hua
- Division of Evolution, Ecology, and Genetics, Research School of Biology, The Australian National University, Acton, Australian Capital Territory, 0200, Australia
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11
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Bernardini F, Galizi R, Wunderlich M, Taxiarchi C, Kranjc N, Kyrou K, Hammond A, Nolan T, Lawniczak MNK, Papathanos PA, Crisanti A, Windbichler N. Cross-Species Y Chromosome Function Between Malaria Vectors of the Anopheles gambiae Species Complex. Genetics 2017; 207:729-740. [PMID: 28860320 PMCID: PMC5629335 DOI: 10.1534/genetics.117.300221] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Accepted: 08/21/2017] [Indexed: 02/03/2023] Open
Abstract
Y chromosome function, structure and evolution is poorly understood in many species, including the Anopheles genus of mosquitoes-an emerging model system for studying speciation that also represents the major vectors of malaria. While the Anopheline Y had previously been implicated in male mating behavior, recent data from the Anopheles gambiae complex suggests that, apart from the putative primary sex-determiner, no other genes are conserved on the Y. Studying the functional basis of the evolutionary divergence of the Y chromosome in the gambiae complex is complicated by complete F1 male hybrid sterility. Here, we used an F1 × F0 crossing scheme to overcome a severe bottleneck of male hybrid incompatibilities that enabled us to experimentally purify a genetically labeled A. gambiae Y chromosome in an A. arabiensis background. Whole genome sequencing (WGS) confirmed that the A. gambiae Y retained its original sequence content in the A. arabiensis genomic background. In contrast to comparable experiments in Drosophila, we find that the presence of a heterospecific Y chromosome has no significant effect on the expression of A. arabiensis genes, and transcriptional differences can be explained almost exclusively as a direct consequence of transcripts arising from sequence elements present on the A. gambiae Y chromosome itself. We find that Y hybrids show no obvious fertility defects, and no substantial reduction in male competitiveness. Our results demonstrate that, despite their radically different structure, Y chromosomes of these two species of the gambiae complex that diverged an estimated 1.85 MYA function interchangeably, thus indicating that the Y chromosome does not harbor loci contributing to hybrid incompatibility. Therefore, Y chromosome gene flow between members of the gambiae complex is possible even at their current level of divergence. Importantly, this also suggests that malaria control interventions based on sex-distorting Y drive would be transferable, whether intentionally or contingent, between the major malaria vector species.
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Affiliation(s)
- Federica Bernardini
- Department of Life Sciences, Imperial College London, South Kensington Campus, SW7 2AZ, United Kingdom
| | - Roberto Galizi
- Department of Life Sciences, Imperial College London, South Kensington Campus, SW7 2AZ, United Kingdom
| | - Mariana Wunderlich
- Department of Life Sciences, Imperial College London, South Kensington Campus, SW7 2AZ, United Kingdom
| | - Chrysanthi Taxiarchi
- Department of Life Sciences, Imperial College London, South Kensington Campus, SW7 2AZ, United Kingdom
| | - Nace Kranjc
- Department of Life Sciences, Imperial College London, South Kensington Campus, SW7 2AZ, United Kingdom
| | - Kyros Kyrou
- Department of Life Sciences, Imperial College London, South Kensington Campus, SW7 2AZ, United Kingdom
| | - Andrew Hammond
- Department of Life Sciences, Imperial College London, South Kensington Campus, SW7 2AZ, United Kingdom
| | - Tony Nolan
- Department of Life Sciences, Imperial College London, South Kensington Campus, SW7 2AZ, United Kingdom
| | - Mara N K Lawniczak
- Malaria Programme, Wellcome Trust Sanger Institute, Hinxton, CB10 1SA Cambridge, United Kingdom
| | - Philippos Aris Papathanos
- Section of Genomics and Genetics, Department of Experimental Medicine, University of Perugia, 06132, Italy
| | - Andrea Crisanti
- Department of Life Sciences, Imperial College London, South Kensington Campus, SW7 2AZ, United Kingdom
| | - Nikolai Windbichler
- Department of Life Sciences, Imperial College London, South Kensington Campus, SW7 2AZ, United Kingdom
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12
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Archer CR, Stephens RM, Sharma MD, Hosken DJ. The Drosophila simulans Y chromosome interacts with the autosomes to influence male fitness. J Evol Biol 2017; 30:1821-1825. [PMID: 28703322 DOI: 10.1111/jeb.13141] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Revised: 06/09/2017] [Accepted: 07/08/2017] [Indexed: 01/03/2023]
Abstract
The Y chromosome should degenerate because it cannot recombine. However, male-limited transmission increases selection efficiency for male-benefit alleles on the Y, and therefore, Y chromosomes should contribute significantly to variation in male fitness. This means that although the Drosophila Y chromosome is small and gene-poor, Y-linked genes are vital for male fertility in Drosophila melanogaster and the Y chromosome has large male fitness effects. It is unclear whether the same pattern is seen in the closely related Drosophila simulans. We backcrossed Y chromosomes from three geographic locations into five genetic backgrounds and found strong Y and genetic background effects on male fertility. There was a significant Y-background interaction, indicating substantial epistasis between the Y and autosomal genes affecting male fertility. This supports accumulating evidence that interactions between the Y chromosome and the autosomes are key determinants of male fitness.
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Affiliation(s)
- C R Archer
- Science and Engineering Research Support Facility Centre for Ecology & Conservation, School of Biosciences, University of Exeter, Penryn, UK
| | - R M Stephens
- Science and Engineering Research Support Facility Centre for Ecology & Conservation, School of Biosciences, University of Exeter, Penryn, UK
| | - M D Sharma
- Science and Engineering Research Support Facility Centre for Ecology & Conservation, School of Biosciences, University of Exeter, Penryn, UK
| | - D J Hosken
- Science and Engineering Research Support Facility Centre for Ecology & Conservation, School of Biosciences, University of Exeter, Penryn, UK
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13
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Brekke TD, Henry LA, Good JM. Genomic imprinting, disrupted placental expression, and speciation. Evolution 2016; 70:2690-2703. [PMID: 27714796 PMCID: PMC5123974 DOI: 10.1111/evo.13085] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Revised: 09/27/2016] [Accepted: 09/28/2016] [Indexed: 12/22/2022]
Abstract
The importance of regulatory incompatibilities to the early stages of speciation remains unclear. Hybrid mammals often show extreme parent-of-origin growth effects that are thought to be a consequence of disrupted genetic imprinting (parent-specific epigenetic gene silencing) during early development. Here, we test the long-standing hypothesis that abnormal hybrid growth reflects disrupted gene expression due to loss of imprinting (LOI) in hybrid placentas, resulting in dosage imbalances between paternal growth factors and maternal growth repressors. We analyzed placental gene expression in reciprocal dwarf hamster hybrids that show extreme parent-of-origin growth effects relative to their parental species. In massively enlarged hybrid placentas, we observed both extensive transgressive expression of growth-related genes and biallelic expression of many genes that were paternally silenced in normal sized hybrids. However, the apparent widespread disruption of paternal silencing was coupled with reduced gene expression levels overall. These patterns are contrary to the predictions of the LOI model and indicate that hybrid misexpression of dosage-sensitive genes is caused by other regulatory mechanisms in this system. Collectively, our results support a central role for disrupted gene expression and imprinting in the evolution of mammalian hybrid inviability, but call into question the generality of the widely invoked LOI model.
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Affiliation(s)
- Thomas D. Brekke
- Division of Biological Sciences, University of Montana, Missoula, Montana 59812
| | - Lindy A. Henry
- Division of Biological Sciences, University of Montana, Missoula, Montana 59812
| | - Jeffrey M. Good
- Division of Biological Sciences, University of Montana, Missoula, Montana 59812
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14
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Hall AB, Papathanos PA, Sharma A, Cheng C, Akbari OS, Assour L, Bergman NH, Cagnetti A, Crisanti A, Dottorini T, Fiorentini E, Galizi R, Hnath J, Jiang X, Koren S, Nolan T, Radune D, Sharakhova MV, Steele A, Timoshevskiy VA, Windbichler N, Zhang S, Hahn MW, Phillippy AM, Emrich SJ, Sharakhov IV, Tu ZJ, Besansky NJ. Radical remodeling of the Y chromosome in a recent radiation of malaria mosquitoes. Proc Natl Acad Sci U S A 2016; 113:E2114-23. [PMID: 27035980 PMCID: PMC4839409 DOI: 10.1073/pnas.1525164113] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Y chromosomes control essential male functions in many species, including sex determination and fertility. However, because of obstacles posed by repeat-rich heterochromatin, knowledge of Y chromosome sequences is limited to a handful of model organisms, constraining our understanding of Y biology across the tree of life. Here, we leverage long single-molecule sequencing to determine the content and structure of the nonrecombining Y chromosome of the primary African malaria mosquito, Anopheles gambiae We find that the An. gambiae Y consists almost entirely of a few massively amplified, tandemly arrayed repeats, some of which can recombine with similar repeats on the X chromosome. Sex-specific genome resequencing in a recent species radiation, the An. gambiae complex, revealed rapid sequence turnover within An. gambiae and among species. Exploiting 52 sex-specific An. gambiae RNA-Seq datasets representing all developmental stages, we identified a small repertoire of Y-linked genes that lack X gametologs and are not Y-linked in any other species except An. gambiae, with the notable exception of YG2, a candidate male-determining gene. YG2 is the only gene conserved and exclusive to the Y in all species examined, yet sequence similarity to YG2 is not detectable in the genome of a more distant mosquito relative, suggesting rapid evolution of Y chromosome genes in this highly dynamic genus of malaria vectors. The extensive characterization of the An. gambiae Y provides a long-awaited foundation for studying male mosquito biology, and will inform novel mosquito control strategies based on the manipulation of Y chromosomes.
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Affiliation(s)
- Andrew Brantley Hall
- The Interdisciplinary PhD Program in Genetics, Bioinformatics, and Computational Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
| | - Philippos-Aris Papathanos
- Section of Genomics and Genetics, Department of Experimental Medicine, University of Perugia, 06132 Perugia, Italy; Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Atashi Sharma
- Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
| | - Changde Cheng
- Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN 46556; Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556
| | - Omar S Akbari
- Department of Entomology, Riverside Center for Disease Vector Research, Institute for Integrative Genome Biology, University of California, Riverside, CA 92521
| | - Lauren Assour
- Department of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN 46556
| | - Nicholas H Bergman
- National Biodefense Analysis and Countermeasures Center, Frederick, MD 21702
| | - Alessia Cagnetti
- Section of Genomics and Genetics, Department of Experimental Medicine, University of Perugia, 06132 Perugia, Italy
| | - Andrea Crisanti
- Section of Genomics and Genetics, Department of Experimental Medicine, University of Perugia, 06132 Perugia, Italy; Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Tania Dottorini
- Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Elisa Fiorentini
- Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Roberto Galizi
- Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Jonathan Hnath
- National Biodefense Analysis and Countermeasures Center, Frederick, MD 21702
| | - Xiaofang Jiang
- The Interdisciplinary PhD Program in Genetics, Bioinformatics, and Computational Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
| | - Sergey Koren
- Genome Informatics Section, Computational and Statistical Genomics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892
| | - Tony Nolan
- Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Diane Radune
- National Biodefense Analysis and Countermeasures Center, Frederick, MD 21702
| | - Maria V Sharakhova
- Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061; Laboratory of Evolutionary Cytogenetics, Tomsk State University, Tomsk 634050, Russia
| | - Aaron Steele
- Department of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN 46556
| | - Vladimir A Timoshevskiy
- Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
| | - Nikolai Windbichler
- Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Simo Zhang
- School of Informatics and Computing, Indiana University, Bloomington, IN 47405
| | - Matthew W Hahn
- School of Informatics and Computing, Indiana University, Bloomington, IN 47405; Department of Biology, Indiana University, Bloomington, IN 47405
| | - Adam M Phillippy
- Genome Informatics Section, Computational and Statistical Genomics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892
| | - Scott J Emrich
- Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN 46556; Department of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN 46556
| | - Igor V Sharakhov
- The Interdisciplinary PhD Program in Genetics, Bioinformatics, and Computational Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061; Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061; Laboratory of Evolutionary Cytogenetics, Tomsk State University, Tomsk 634050, Russia;
| | - Zhijian Jake Tu
- The Interdisciplinary PhD Program in Genetics, Bioinformatics, and Computational Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061; Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
| | - Nora J Besansky
- Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN 46556; Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556;
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15
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Araripe LO, Tao Y, Lemos B. Interspecific Y chromosome variation is sufficient to rescue hybrid male sterility and is influenced by the grandparental origin of the chromosomes. Heredity (Edinb) 2016; 116:516-22. [PMID: 26980343 DOI: 10.1038/hdy.2016.11] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Revised: 11/25/2015] [Accepted: 12/29/2015] [Indexed: 12/15/2022] Open
Abstract
Y chromosomes display population variation within and between species. Co-evolution within populations is expected to produce adaptive interactions between Y chromosomes and the rest of the genome. One consequence is that Y chromosomes from disparate populations could disrupt harmonious interactions between co-evolved genetic elements and result in reduced male fertility, sterility or inviability. Here we address the contribution of 'heterospecific Y chromosomes' to fertility in hybrid males carrying a homozygous region of Drosophila mauritiana introgressed in the Drosophila simulans background. In order to detect Y chromosome-autosome interactions, which may go unnoticed in a single-species background of autosomes, we constructed hybrid genotypes involving three sister species: Drosophila simulans, D. mauritiana, and D. sechellia. These engineered strains varied due to: (i) species origin of the Y chromosome (D. simulans or D. sechellia); (ii) location of the introgressed D. mauritiana segment on the D. simulans third chromosome, and (iii) grandparental genomic background (three genotypes of D. simulans). We find complex interactions between the species origin of the Y chromosome, the identity of the D. mauritiana segment and the grandparental genetic background donating the chromosomes. Unexpectedly, the interaction of the Y chromosome and one segment of D. mauritiana drastically reduced fertility in the presence of Ysim, whereas the fertility is partially rescued by the Y chromosome of D. sechellia when it descends from a specific grandparental genotype. The restoration of fertility occurs in spite of an autosomal and X-linked genome that is mostly of D. simulans origin. These results illustrate the multifactorial basis of genetic interactions involving the Y chromosome. Our study supports the hypothesis that the Y chromosome can contribute significantly to the evolution of reproductive isolation and highlights the conditional manifestation of infertility in specific genotypic combinations.
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Affiliation(s)
- L O Araripe
- Laboratório de Biologia Molecular de Insetos, Fundação Oswaldo Cruz, IOC, Rio de Janeiro, Brasil
| | - Y Tao
- Department of Mathematics and Statistics, Georgia State University, Atlanta, GA, USA
| | - B Lemos
- Program in Molecular and Integrative Physiological Sciences, Department of Environmental Health, Harvard T. H. Chan School of Public Health, Boston, MA, USA
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16
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Immonen E, Rönn J, Watson C, Berger D, Arnqvist G. Complex mitonuclear interactions and metabolic costs of mating in male seed beetles. J Evol Biol 2015; 29:360-70. [PMID: 26548644 DOI: 10.1111/jeb.12789] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Accepted: 11/03/2015] [Indexed: 02/02/2023]
Abstract
The lack of evolutionary response to selection on mitochondrial genes through males predicts the evolution of nuclear genetic influence on male-specific mitochondrial function, for example by gene duplication and evolution of sex-specific expression of paralogs involved in metabolic pathways. Intergenomic epistasis may therefore be a prevalent feature of the genetic architecture of male-specific organismal function. Here, we assess the role of mitonuclear genetic variation for male metabolic phenotypes [metabolic rate and respiratory quotient (RQ)] associated with ejaculate renewal, in the seed beetle Callosobruchus maculatus, by assaying lines with crossed combinations of distinct mitochondrial haplotypes and nuclear lineages. We found a significant increase in metabolic rate following mating relative to virgin males. Moreover, processes associated with ejaculate renewal showed variation in metabolic rate that was affected by mitonuclear interactions. Mitochondrial haplotype influenced mating-related changes in RQ, but this pattern varied over time. Mitonuclear genotype and the energy spent during ejaculate production affected the weight of the ejaculate, but the strength of this effect varied across mitochondrial haplotypes showing that the genetic architecture of male-specific reproductive function is complex. Our findings unveil hitherto underappreciated metabolic costs of mating and ejaculate renewal, and provide the first empirical demonstration of mitonuclear epistasis on male reproductive metabolic processes.
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Affiliation(s)
- E Immonen
- Evolutionary Biology Centre, Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden
| | - J Rönn
- Evolutionary Biology Centre, Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden
| | - C Watson
- Evolutionary Biology Centre, Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden
| | - D Berger
- Evolutionary Biology Centre, Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden
| | - G Arnqvist
- Evolutionary Biology Centre, Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden
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17
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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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18
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Meisel RP, Scott JG, Clark AG. Transcriptome Differences between Alternative Sex Determining Genotypes in the House Fly, Musca domestica. Genome Biol Evol 2015; 7:2051-61. [PMID: 26142430 PMCID: PMC4524491 DOI: 10.1093/gbe/evv128] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Sex determination evolves rapidly, often because of turnover of the genes at the top of the pathway. The house fly, Musca domestica, has a multifactorial sex determination system, allowing us to identify the selective forces responsible for the evolutionary turnover of sex determination in action. There is a male determining factor, M, on the Y chromosome (YM), which is probably the ancestral state. An M factor on the third chromosome (IIIM) has reached high frequencies in multiple populations across the world, but the evolutionary forces responsible for the invasion of IIIM are not resolved. To test whether the IIIM chromosome invaded because of sex-specific selection pressures, we used mRNA sequencing to determine whether isogenic males that differ only in the presence of the YM or IIIM chromosome have different gene expression profiles. We find that more genes are differentially expressed between YM and IIIM males in testis than head, and that genes with male-biased expression are most likely to be differentially expressed between YM and IIIM males. We additionally find that IIIM males have a “masculinized” gene expression profile, suggesting that the IIIM chromosome has accumulated an excess of male-beneficial alleles because of its male-limited transmission. These results are consistent with the hypothesis that sex-specific selection acts on alleles linked to the male-determining locus driving evolutionary turnover in the sex determination pathway.
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Affiliation(s)
| | | | - Andrew G Clark
- Department of Molecular Biology and Genetics, Cornell University
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19
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Aldrich JC, Maggert KA. Transgenerational inheritance of diet-induced genome rearrangements in Drosophila. PLoS Genet 2015; 11:e1005148. [PMID: 25885886 PMCID: PMC4401788 DOI: 10.1371/journal.pgen.1005148] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Accepted: 03/17/2015] [Indexed: 12/17/2022] Open
Abstract
Ribosomal RNA gene (rDNA) copy number variation modulates heterochromatin formation and influences the expression of a large fraction of the Drosophila genome. This discovery, along with the link between rDNA, aging, and disease, high-lights the importance of understanding how natural rDNA copy number variation arises. Pursuing the relationship between rDNA expression and stability, we have discovered that increased dietary yeast concentration, emulating periods of dietary excess during life, results in somatic rDNA instability and copy number reduction. Modulation of Insulin/TOR signaling produces similar results, indicating a role for known nutrient sensing signaling pathways in this process. Furthermore, adults fed elevated dietary yeast concentrations produce offspring with fewer rDNA copies demonstrating that these effects also occur in the germline, and are transgenerationally heritable. This finding explains one source of natural rDNA copy number variation revealing a clear long-term consequence of diet.
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Affiliation(s)
- John C. Aldrich
- Department of Biology, College of Science, Texas A&M University, College Station, Texas, United States of America
| | - Keith A. Maggert
- Department of Biology, College of Science, Texas A&M University, College Station, Texas, United States of America
- Department of Cellular and Molecular Medicine, College of Medicine, University of Arizona, Tucson, Arizona, United States of America
- * E-mail:
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20
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Abstract
Sex chromosome drivers are selfish elements that subvert Mendel's first law of segregation and therefore are overrepresented among the products of meiosis. The sex-biased progeny produced then fuels an extended genetic conflict between the driver and the rest of the genome. Many examples of sex chromosome drive are known, but the occurrence of this phenomenon is probably largely underestimated because of the difficulty to detect it. Remarkably, nearly all sex chromosome drivers are found in two clades, Rodentia and Diptera. Although very little is known about the molecular and cellular mechanisms of drive, epigenetic processes such as chromatin regulation could be involved in many instances. Yet, its evolutionary consequences are far-reaching, from the evolution of mating systems and sex determination to the emergence of new species.
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Affiliation(s)
- Quentin Helleu
- Laboratoire Évolution Génomes et Spéciation, CNRS UPR9034, Gif-sur-Yvette, France and Université Paris-Sud, Orsay, France
| | - Pierre R Gérard
- Laboratoire Évolution Génomes et Spéciation, CNRS UPR9034, Gif-sur-Yvette, France and Université Paris-Sud, Orsay, France
| | - Catherine Montchamp-Moreau
- Laboratoire Évolution Génomes et Spéciation, CNRS UPR9034, Gif-sur-Yvette, France and Université Paris-Sud, Orsay, France
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21
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Rettie EC, Dorus S. Drosophila sperm proteome evolution: Insights from comparative genomic approaches. SPERMATOGENESIS 2014; 2:213-223. [PMID: 23087838 PMCID: PMC3469443 DOI: 10.4161/spmg.21748] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Despite their conserved functional role in sexually reproducing organisms, spermatozoa are a diverse and rapidly evolving cell type. This phenomenon is largely attributed to sexual selection in polygamous species where sperm from multiple males compete to fertilize a limited number of oocytes. Drosophila have proven to be a particularly informative model system for the study of spermatogenesis and in this review we discuss how the characterization of the Drosophila melanogaster sperm proteome has advanced our understanding of the evolutionary genomics of sperm form and function. We summarize the molecular evolutionary characteristics of sperm genes and highlight recent evidence demonstrating the importance of novel gene creation in the evolution of sperm function and competitive ability. Comparative proteomic evidence is also provided, supporting an overall functional conservation between the Drosophila and mouse sperm proteomes. This analysis reveals a diverse repertoire of proteins functioning in proteolytic pathways, as well as the presence of proteins of the complement and innate immunity systems. We propose that these pathways may have functional relevance to post-mating female immunological responses as well as coevolved interactions with pathways expressed in the female reproductive tract, including those involved in sperm-oocyte recognition and fertilization.
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Affiliation(s)
- Elaine C Rettie
- Department of Biology and Biochemistry; University of Bath; Bath, UK
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22
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Mank JE, Hosken DJ, Wedell N. Conflict on the sex chromosomes: cause, effect, and complexity. Cold Spring Harb Perspect Biol 2014; 6:a017715. [PMID: 25280765 DOI: 10.1101/cshperspect.a017715] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Intralocus sexual conflict and intragenomic conflict both affect sex chromosome evolution and can in extreme cases even cause the complete turnover of sex chromosomes. Additionally, established sex chromosomes often become the focus of heightened conflict. This creates a tangled relationship between sex chromosomes and conflict with respect to cause and effect. To further complicate matters, sexual and intragenomic conflict may exacerbate one another and thereby further fuel sex chromosome change. Different magnitudes and foci of conflict offer potential explanations for lineage-specific variation in sex chromosome evolution and answer long-standing questions as to why some sex chromosomes are remarkably stable, whereas others show rapid rates of evolutionary change.
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Affiliation(s)
- Judith E Mank
- Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, United Kingdom
| | - David J Hosken
- Centre for Ecology & Conservation, University of Exeter, Cornwall, Tremough, Penryn TR10 9EZ, United Kingdom
| | - Nina Wedell
- Centre for Ecology & Conservation, University of Exeter, Cornwall, Tremough, Penryn TR10 9EZ, United Kingdom
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23
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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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24
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Swain Lenz D, Riles L, Fay JC. Heterochronic meiotic misexpression in an interspecific yeast hybrid. Mol Biol Evol 2014; 31:1333-42. [PMID: 24608322 DOI: 10.1093/molbev/msu098] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Regulatory changes rapidly accumulate between species, and interspecific hybrids often misexpress genes. Hybrid misexpression, expression levels outside the range of both parental species, can result from cis- and trans-acting regulatory changes that interact abnormally in hybrids. Thus, misexpressed genes may contribute to hybrid sterility. However, in the context of a whole organism, misexpression may not result directly from cis-trans interactions but rather indirectly from differences between hybrid and parental abundance of cell types. Here we eliminate the confounding effects of cell types by examining gene expression in a sterile interspecific yeast hybrid during meiosis. We investigated gene expression of the yeasts Saccharomyces cerevisiae, S. paradoxus, and their hybrid at multiple meiotic stages. Although the hybrid and parents exhibit similar changes in expression levels across meiosis, the hybrid meiotic program occurs earlier than either parent. The timing change produces a heterochronic pattern of misexpression during midmeiosis. Coincident with the timing of misexpression, we find a transition from predominantly trans-acting to cis-acting expression divergence and an increase in the number of opposing cis-trans changes. However, we find no direct relationship between opposing cis-trans changes and misexpression. Contrary to the notion that cis-trans interactions cause misexpression, a heterochronic shift in the normal meiotic gene expression program produces patterns of misexpression in an yeast hybrid. Our results imply that temporal dynamics of single cell types is important to understanding hybrid misexpression and its relationship to cis-trans interactions.
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Affiliation(s)
| | - Linda Riles
- Department of Genetics, Washington University
| | - Justin C Fay
- Department of Genetics, Washington UniversityCenter for Genome Sciences and Systems Biology, Washington University
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25
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Genome-wide gene expression effects of sex chromosome imprinting in Drosophila. G3-GENES GENOMES GENETICS 2014; 4:1-10. [PMID: 24318925 PMCID: PMC3887524 DOI: 10.1534/g3.113.008029] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Imprinting is well-documented in both plant and animal species. In Drosophila, the Y chromosome is differently modified when transmitted through the male and female germlines. Here, we report genome-wide gene expression effects resulting from reversed parent-of-origin of the X and Y chromosomes. We found that hundreds of genes are differentially expressed between adult male Drosophila melanogaster that differ in the maternal and paternal origin of the sex chromosomes. Many of the differentially regulated genes are expressed specifically in testis and midgut cells, suggesting that sex chromosome imprinting might globally impact gene expression in these tissues. In contrast, we observed much fewer Y-linked parent-of-origin effects on genome-wide gene expression in females carrying a Y chromosome, indicating that gene expression in females is less sensitive to sex chromosome parent-of-origin. Genes whose expression differs between females inheriting a maternal or paternal Y chromosome also show sex chromosome parent-of-origin effects in males, but the direction of the effects on gene expression (overexpression or underexpression) differ between the sexes. We suggest that passage of sex chromosome chromatin through male meiosis may be required for wild-type function in F1 progeny, whereas disruption of Y-chromosome function through passage in the female germline likely arises because the chromosome is not adapted to the female germline environment.
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26
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Rice WR. Nothing in Genetics Makes Sense Except in Light of Genomic Conflict. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2013. [DOI: 10.1146/annurev-ecolsys-110411-160242] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- William R. Rice
- Department of Ecology, Evolution & Marine Biology, University of California, Santa Barbara, California 93106-9610;
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27
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Herrig DK, Modrick AJ, Brud E, Llopart A. Introgression in the Drosophila subobscura--D. Madeirensis sister species: evidence of gene flow in nuclear genes despite mitochondrial differentiation. Evolution 2013; 68:705-19. [PMID: 24152112 PMCID: PMC4255303 DOI: 10.1111/evo.12295] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2013] [Accepted: 10/15/2013] [Indexed: 12/19/2022]
Abstract
Species hybridization, and thus the potential for gene flow, was once viewed as reproductive mistake. However, recent analysis based on large datasets and newly developed models suggest that gene exchange is not as rare as originally suspected. To investigate the history and speciation of the closely related species Drosophila subobscura, D. madeirensis, and D. guanche, we obtained polymorphism and divergence data for 26 regions throughout the genome, including the Y chromosome and mitochondrial DNA. We found that the D. subobscura X/autosome ratio of silent nucleotide diversity is significantly smaller than the 0.75 expected under neutrality. This pattern, if held genomewide, may reflect a faster accumulation of beneficial mutations on the X chromosome than on autosomes. We also detected evidence of gene flow in autosomal regions, while sex chromosomes remain distinct. This is consistent with the large X effect on hybrid male sterility seen in this system and the presence of two X chromosome inversions fixed between species. Overall, our data conform to chromosomal speciation models in which rearrangements are proposed to serve as gene flow barriers. Contrary to other observations in Drosophila, the mitochondrial genome appears resilient to gene flow in the presence of nuclear exchange.
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Affiliation(s)
- Danielle K Herrig
- Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA, 52242
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28
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Sackton TB, Hartl DL. Meta-analysis reveals that genes regulated by the Y chromosome in Drosophila melanogaster are preferentially localized to repressive chromatin. Genome Biol Evol 2013; 5:255-66. [PMID: 23315381 PMCID: PMC3595022 DOI: 10.1093/gbe/evt005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The Drosophila Y chromosome is a degenerated, heterochromatic chromosome with few functional genes. Despite this, natural variation on the Y chromosome in D. melanogaster has substantial trans-acting effects on the regulation of X-linked and autosomal genes. It is not clear, however, whether these genes simply represent a random subset of the genome or whether specific functional properties are associated with susceptibility to regulation by Y-linked variation. Here, we present a meta-analysis of four previously published microarray studies of Y-linked regulatory variation (YRV) in D. melanogaster. We show that YRV genes are far from a random subset of the genome: They are more likely to be in repressive chromatin contexts, be expressed tissue specifically, and vary in expression within and between species than non-YRV genes. Furthermore, YRV genes are more likely to be associated with the nuclear lamina than non-YRV genes and are generally more likely to be close to each other in the nucleus (although not along chromosomes). Taken together, these results suggest that variation on the Y chromosome plays a role in modifying how the genome is distributed across chromatin compartments, either via changes in the distribution of DNA-binding proteins or via changes in the spatial arrangement of the genome in the nucleus.
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Affiliation(s)
- Timothy B Sackton
- Department of Organismic and Evolutionary Biology, Harvard University, MA, USA
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29
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Branco AT, Tao Y, Hartl DL, Lemos B. Natural variation of the Y chromosome suppresses sex ratio distortion and modulates testis-specific gene expression in Drosophila simulans. Heredity (Edinb) 2013; 111:8-15. [PMID: 23591516 DOI: 10.1038/hdy.2013.5] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
X-linked sex-ratio distorters that disrupt spermatogenesis can cause a deficiency in functional Y-bearing sperm and a female-biased sex ratio. Y-linked modifiers that restore a normal sex ratio might be abundant and favored when a X-linked distorter is present. Here we investigated natural variation of Y-linked suppressors of sex-ratio in the Winters systems and the ability of these chromosomes to modulate gene expression in Drosophila simulans. Seventy-eight Y chromosomes of worldwide origin were assayed for their resistance to the X-linked sex-ratio distorter gene Dox. Y chromosome diversity caused males to sire ∼63% to ∼98% female progeny. Genome-wide gene expression analysis revealed hundreds of genes differentially expressed between isogenic males with sensitive (high sex ratio) and resistant (low sex ratio) Y chromosomes from the same population. Although the expression of about 75% of all testis-specific genes remained unchanged across Y chromosomes, a subset of post-meiotic genes was upregulated by resistant Y chromosomes. Conversely, a set of accessory gland-specific genes and mitochondrial genes were downregulated in males with resistant Y chromosomes. The D. simulans Y chromosome also modulated gene expression in XXY females in which the Y-linked protein-coding genes are not transcribed. The data suggest that the Y chromosome might exert its regulatory functions through epigenetic mechanisms that do not require the expression of protein-coding genes. The gene network that modulates sex ratio distortion by the Y chromosome is poorly understood, other than that it might include interactions with mitochondria and enriched for genes expressed in post-meiotic stages of spermatogenesis.
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Affiliation(s)
- A T Branco
- Molecular and Integrative Physiological Sciences, Environmental Health, Harvard School of Public Health, Boston, MA, USA
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Albrechtová J, Albrecht T, Baird SJE, Macholán M, Rudolfsen G, Munclinger P, Tucker PK, Piálek J. Sperm-related phenotypes implicated in both maintenance and breakdown of a natural species barrier in the house mouse. Proc Biol Sci 2012; 279:4803-10. [PMID: 23055063 PMCID: PMC3497091 DOI: 10.1098/rspb.2012.1802] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2012] [Accepted: 09/19/2012] [Indexed: 11/12/2022] Open
Abstract
The house mouse hybrid zone (HMHZ) is a species barrier thought to be maintained by a balance between dispersal and natural selection against hybrids. While the HMHZ is characterized by frequency discontinuities for some sex chromosome markers, there is an unexpected large-scale regional introgression of a Y chromosome across the barrier, in defiance of Haldane's rule. Recent work suggests that a major force maintaining the species barrier acts through sperm traits. Here, we test whether the Y chromosome penetration of the species barrier acts through sperm traits by assessing sperm characteristics of wild-caught males directly in a field laboratory set up in a Y introgression region of the HMHZ, later calculating the hybrid index of each male using 1401 diagnostic single nucleotide polymorphisms (SNPs). We found that both sperm count (SC) and sperm velocity were significantly reduced across the natural spectrum of hybrids. However, SC was more than rescued in the presence of the invading Y. Our results imply an asymmetric advantage for Y chromosome introgression consistent with the observed large-scale introgression. We suggest that selection on sperm-related traits probably explains a large component of patterns observed in the natural hybrid zone, including the Y chromosome penetration.
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Affiliation(s)
- Jana Albrechtová
- Department of Population Biology, Institute of Vertebrate Biology, Academy of Sciences of the Czech Republic, Brno and Studenec, Czech Republic
- Department of Zoology, Faculty of Science, Charles University in Prague, Prague, Czech Republic
| | - Tomáš Albrecht
- Department of Population Biology, Institute of Vertebrate Biology, Academy of Sciences of the Czech Republic, Brno and Studenec, Czech Republic
- Department of Zoology, Faculty of Science, Charles University in Prague, Prague, Czech Republic
| | | | - Miloš Macholán
- Laboratory of Mammalian Evolutionary Genetics, Institute of Animal Physiology and Genetics, ASCR, Brno, Czech Republic
| | - Geir Rudolfsen
- Department for Environmental Radioactivity, Norwegian Radiation Protection Authority, Framcenter, Tromsø, Norway
| | - Pavel Munclinger
- Department of Zoology, Faculty of Science, Charles University in Prague, Prague, Czech Republic
| | - Priscilla K. Tucker
- Department of Ecology and Evolutionary Biology and Museum of Zoology, University of Michigan, Ann Arbor, MI, USA
| | - Jaroslav Piálek
- Department of Population Biology, Institute of Vertebrate Biology, Academy of Sciences of the Czech Republic, Brno and Studenec, Czech Republic
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Conflictual speciation: species formation via genomic conflict. Trends Ecol Evol 2012; 28:48-57. [PMID: 22995895 DOI: 10.1016/j.tree.2012.08.015] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Revised: 08/14/2012] [Accepted: 08/15/2012] [Indexed: 11/23/2022]
Abstract
A remarkable suite of forms of genomic conflict has recently been implicated in speciation. We propose that these diverse roles of genomic conflict in speciation processes can be unified using the concept of 'conflictual speciation'. Conflictual speciation centers on the evolution of reproductive isolation as a byproduct of antagonistic selection among genomic elements with divergent fitness interests. Intragenomic conflicts are expected to readily generate Dobzhansky-Muller incompatibilities, due to population-specific interactions between opposing elements, and thus they could be especially important in speciation. Moreover, selection from genomic conflicts should be relatively unrelenting across ecological and evolutionary time scales. We explain how intragenomic conflicts can promote, or sometimes constrain, speciation, and describe evidence relating conflicts to the evolution of reproductive isolation.
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Campbell P, Good JM, Dean MD, Tucker PK, Nachman MW. The contribution of the Y chromosome to hybrid male sterility in house mice. Genetics 2012; 191:1271-81. [PMID: 22595240 PMCID: PMC3416006 DOI: 10.1534/genetics.112.141804] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2012] [Accepted: 05/10/2012] [Indexed: 12/18/2022] Open
Abstract
Hybrid sterility in the heterogametic sex is a common feature of speciation in animals. In house mice, the contribution of the Mus musculus musculus X chromosome to hybrid male sterility is large. It is not known, however, whether F1 male sterility is caused by X-Y or X-autosome incompatibilities or a combination of both. We investigated the contribution of the M. musculus domesticus Y chromosome to hybrid male sterility in a cross between wild-derived strains in which males with a M. m. musculus X chromosome and M. m. domesticus Y chromosome are partially sterile, while males from the reciprocal cross are reproductively normal. We used eight X introgression lines to combine different X chromosome genotypes with different Y chromosomes on an F1 autosomal background, and we measured a suite of male reproductive traits. Reproductive deficits were observed in most F1 males, regardless of Y chromosome genotype. Nonetheless, we found evidence for a negative interaction between the M. m. domesticus Y and an interval on the M. m. musculus X that resulted in abnormal sperm morphology. Therefore, although F1 male sterility appears to be caused mainly by X-autosome incompatibilities, X-Y incompatibilities contribute to some aspects of sterility.
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Affiliation(s)
- Polly Campbell
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USA.
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Why chromosome palindromes? INTERNATIONAL JOURNAL OF EVOLUTIONARY BIOLOGY 2012; 2012:207958. [PMID: 22844637 PMCID: PMC3403216 DOI: 10.1155/2012/207958] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/31/2012] [Accepted: 05/09/2012] [Indexed: 11/25/2022]
Abstract
We look at sex-limited chromosome (Y or W) evolution with particular emphasis on the importance of palindromes. Y chromosome palindromes consist of inverted duplicates that allow for local recombination in an otherwise nonrecombining chromosome. Since palindromes enable intrachromosomal gene conversion that can help eliminate deleterious mutations, they are often highlighted as mechanisms to protect against Y degeneration. However, the adaptive significance of recombination resides in its ability to decouple the evolutionary fates of linked mutations, leading to both a decrease in degeneration rate and an increase in adaptation rate. Our paper emphasizes the latter, that palindromes may exist to accelerate adaptation by increasing the potential targets and fixation rates of incoming beneficial mutations. This hypothesis helps reconcile two enigmatic features of the “palindromes as protectors” view: (1) genes that are not located in palindromes have been retained under purifying selection for tens of millions of years, and (2) under models that only consider deleterious mutations, gene conversion benefits duplicate gene maintenance but not initial fixation. We conclude by looking at ways to test the hypothesis that palindromes enhance the rate of adaptive evolution of Y-linked genes and whether this effect can be extended to palindromes on other chromosomes.
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Y chromosome mediates ribosomal DNA silencing and modulates the chromatin state in Drosophila. Proc Natl Acad Sci U S A 2012; 109:9941-6. [PMID: 22665801 DOI: 10.1073/pnas.1207367109] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Although the Drosophila Y chromosome is degenerated, heterochromatic, and contains few genes, increasing evidence suggests that it plays an important role in regulating the expression of numerous autosomal and X-linked genes. Here we use 15 Y chromosomes originating from a single founder 550 generations ago to study the role of the Y chromosome in regulating rRNA gene transcription, position-effect variegation (PEV), and the link among rDNA copy number, global gene expression, and chromatin regulation. Based on patterns of rRNA gene transcription indicated by transcription of the retrotransposon R2 that specifically inserts into the 28S rRNA gene, we show that X-linked rDNA is silenced in males. The silencing of X-linked rDNA expression by the Y chromosome is consistent across populations and independent of genetic background. These Y chromosomes also vary more than threefold in rDNA locus size and cause dramatically different levels of PEV suppression. The degree of suppression is negatively associated with the number and fraction of rDNA units without transposon insertions, but not with total rDNA locus size. Gene expression profiling revealed hundreds of differentially expressed genes among these Y chromosome introgression lines, as well as a divergent global gene expression pattern between the low-PEV and high-PEV flies. Our findings suggest that the Y chromosome is involved in diverse phenomena related to transcriptional regulation including X-linked rDNA silencing and suppression of PEV phenotype. These results further expand our understanding of the role of the Y chromosome in modulating global gene expression, and suggest a link with modifications of the chromatin state.
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Johnson NA, Lachance J. The genetics of sex chromosomes: evolution and implications for hybrid incompatibility. Ann N Y Acad Sci 2012; 1256:E1-22. [PMID: 23025408 PMCID: PMC3509754 DOI: 10.1111/j.1749-6632.2012.06748.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Heteromorphic sex chromosomes, where one sex has two different types of sex chromosomes, face very different evolutionary consequences than do autosomes. Two important features of sex chromosomes arise from being present in only one copy in one of the sexes: dosage compensation and the meiotic silencing of sex chromosomes. Other differences arise because sex chromosomes spend unequal amounts of time in each sex. Thus, the impact of evolutionary processes (mutation, selection, genetic drift, and meiotic drive) differs substantially between each sex chromosome, and between the sex chromosomes and the autosomes. Sex chromosomes also play a disproportionate role in Haldane's rule and other important patterns related to hybrid incompatibility, and thus speciation. We review the consequences of sex chromosomes on hybrid incompatibility. A theme running through this review is that epigenetic processes, notably those related to chromatin, may be more important to the evolution of sex chromosomes and the evolution of hybrid incompatibility than previously recognized.
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Affiliation(s)
- Norman A Johnson
- Department of Plant, Soil, and Insect Sciences, and Graduate Program in Organismic and Evolutionary Biology, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, USA.
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Hall DW, Goodisman MAD. The effects of kin selection on rates of molecular evolution in social insects. Evolution 2012; 66:2080-93. [PMID: 22759286 DOI: 10.1111/j.1558-5646.2012.01602.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The evolution of sociality represented a major transition point in biological history. The most advanced societies, such as those displayed by social insects, consist of reproductive and nonreproductive castes. The caste system fundamentally affects the way natural selection operates. Specifically, selection acts directly on reproductive castes, such as queens, but only indirectly through the process of kin selection on nonreproductive castes, such as workers. In this study, we present theoretical analyses to determine the rate of substitution at loci expressed exclusively in the queen or worker castes. We show that the rate of substitution is the same for queen- and worker-selected loci when the queen is singly mated. In contrast, when a queen is multiply mated, queen-selected loci show higher rates of substitution for adaptive alleles and lower rates of substitution for deleterious alleles than worker-selected loci. We compare our theoretical expectations to previously obtained genomic data from the honeybee, Apis mellifera, where queens mate multiply and the fire ant, Solenopsis invicta, where queens mate singly and find that rates of evolution of queen- and worker-selected loci are consistent with our predictions. Overall, our research tests theoretical expectations using empirically obtained genomic data to better understand the evolution of advanced societies.
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Affiliation(s)
- David W Hall
- Department of Genetics, University of Georgia, Athens, Georgia 30602, USA.
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Abstract
Although sex chromosomes have been the focus of a great deal of scientific scrutiny, most interest has centred on understanding the evolution and relative importance of X and Z chromosomes. By contrast, the sex-limited W and Y chromosomes have received far less attention, both because of their generally degenerate nature and the difficulty in studying non-recombining and often highly heterochromatic genomic regions. However, recent theory and empirical evidence suggest that the W and Y chromosomes play a far more important role in sex-specific fitness traits than would be expected based on their size alone, and this importance may explain the persistence of some Y and W chromosomes in the face of powerful degradative forces. In addition to their role in fertility and fecundity, the sex-limited nature of these genomic regions results in unique evolutionary forces acting on Y and W chromosomes, implicating them as potentially major contributors to sexual selection and speciation. Recent empirical studies have borne out these predictions and revealed that some W and Y chromosomes play a vital role in key sex-specific evolutionary processes.
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Affiliation(s)
- Judith E Mank
- Department of Zoology, Edward Grey Institute, University of Oxford, South Parks Road, Oxford, UK.
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