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Brashear WA, Bredemeyer KR, Murphy WJ. Genomic architecture constrained placental mammal X Chromosome evolution. Genome Res 2021; 31:1353-1365. [PMID: 34301625 PMCID: PMC8327908 DOI: 10.1101/gr.275274.121] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Accepted: 06/22/2021] [Indexed: 01/02/2023]
Abstract
Susumu Ohno proposed that the gene content of the mammalian X Chromosome should remain highly conserved due to dosage compensation. X Chromosome linkage (gene order) conservation is widespread in placental mammals but does not fall within the scope of Ohno's prediction and may be an indirect result of selection on gene content or selection against rearrangements that might disrupt X-Chromosome inactivation (XCI). Previous comparisons between the human and mouse X Chromosome sequences have suggested that although single-copy X Chromosome genes are conserved between species, most ampliconic genes were independently acquired. To better understand the evolutionary and functional constraints on X-linked gene content and linkage conservation in placental mammals, we aligned a new, high-quality, long-read X Chromosome reference assembly from the domestic cat (incorporating 19.3 Mb of targeted BAC clone sequence) to the pig, human, and mouse assemblies. A comprehensive analysis of annotated X-linked orthologs in public databases demonstrated that the majority of ampliconic gene families were present on the ancestral placental X Chromosome. We generated a domestic cat Hi-C contact map from an F1 domestic cat/Asian leopard cat hybrid and demonstrated the formation of the bipartite structure found in primate and rodent inactivated X Chromosomes. Conservation of gene order and recombination patterns is attributable to strong selective constraints on three-dimensional genomic architecture necessary for superloop formation. Species with rearranged X Chromosomes retain the ancestral order and relative spacing of loci critical for superloop formation during XCI, with compensatory inversions evolving to maintain these long-range physical interactions.
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Affiliation(s)
- Wesley A Brashear
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, Texas 77843, USA.,Interdisciplinary Program in Genetics, Texas A&M University, College Station, Texas 77843, USA
| | - Kevin R Bredemeyer
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, Texas 77843, USA.,Interdisciplinary Program in Genetics, Texas A&M University, College Station, Texas 77843, USA
| | - William J Murphy
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, Texas 77843, USA.,Interdisciplinary Program in Genetics, Texas A&M University, College Station, Texas 77843, USA
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Kawashima S, Hattori A, Suzuki E, Matsubara K, Toki M, Kosaki R, Hasegawa Y, Nakabayashi K, Fukami M, Kagami M. Methylation status of genes escaping from X-chromosome inactivation in patients with X-chromosome rearrangements. Clin Epigenetics 2021; 13:134. [PMID: 34193245 PMCID: PMC8244138 DOI: 10.1186/s13148-021-01121-6] [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: 03/11/2021] [Accepted: 06/22/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND X-chromosome inactivation (XCI) is a mechanism in which one of two X chromosomes in females is randomly inactivated in order to compensate for imbalance of gene dosage between sexes. However, about 15% of genes on the inactivated X chromosome (Xi) escape from XCI. The methylation level of the promoter region of the escape gene is lower than that of the inactivated genes. Dxz4 and/or Firre have critical roles for forming the three-dimensional (3D) structure of Xi. In mice, disrupting the 3D structure of Xi by deleting both Dxz4 and Firre genes led to changing of the escape genes list. To estimate the impact for escape genes by X-chromosome rearrangements, including DXZ4 and FIRRE, we examined the methylation status of escape gene promoters in patients with various X-chromosome rearrangements. RESULTS To detect the breakpoints, we first performed array-based comparative genomic hybridization and whole-genome sequencing in four patients with X-chromosome rearrangements. Subsequently, we conducted array-based methylation analysis and reduced representation bisulfite sequencing in the four patients with X-chromosome rearrangements and controls. Of genes reported as escape genes by gene expression analysis using human hybrid cells in a previous study, 32 genes showed hypomethylation of the promoter region in both male controls and female controls. Three patients with X-chromosome rearrangements had no escape genes with abnormal methylation of the promoter region. One of four patients with the most complicated rearrangements exhibited abnormal methylation in three escape genes. Furthermore, in the patient with the deletion of the FIRRE gene and the duplication of DXZ4, most escape genes remained hypomethylated. CONCLUSION X-chromosome rearrangements are unlikely to affect the methylation status of the promoter regions of escape genes, except for a specific case with highly complex rearrangements, including the deletion of the FIRRE gene and the duplication of DXZ4.
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Affiliation(s)
- Sayaka Kawashima
- Department of Molecular Endocrinology, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo, 157-8535, Japan.,Department of Pediatrics, Tohoku University School of Medicine, 1-1 Seiryomachi, Aobaku, Sendai, Miyagi, 980-8574, Japan
| | - Atsushi Hattori
- Department of Molecular Endocrinology, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo, 157-8535, Japan
| | - Erina Suzuki
- Department of Molecular Endocrinology, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo, 157-8535, Japan
| | - Keiko Matsubara
- Department of Molecular Endocrinology, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo, 157-8535, Japan
| | - Machiko Toki
- Department of Pediatrics, Hiratsuka City Hospital, 1-19-1 Minamihara, Hiratsuka, Kanagawa, 254-0065, Japan.,Department of Pediatrics, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan
| | - Rika Kosaki
- Division of Medical Genetics, National Center for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo, 157-8535, Japan
| | - Yukihiro Hasegawa
- Division of Endocrinology and Metabolism, Tokyo Metropolitan Children's Medical Center, 2-8-29 Musashidai, Fuchu, Tokyo, 183-8561, Japan
| | - Kazuhiko Nakabayashi
- Department of Maternal Fetal Biology, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo, 157-8535, Japan
| | - Maki Fukami
- Department of Molecular Endocrinology, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo, 157-8535, Japan
| | - Masayo Kagami
- Department of Molecular Endocrinology, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo, 157-8535, Japan.
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Bansal P, Kondaveeti Y, Pinter SF. Forged by DXZ4, FIRRE, and ICCE: How Tandem Repeats Shape the Active and Inactive X Chromosome. Front Cell Dev Biol 2020; 7:328. [PMID: 32076600 PMCID: PMC6985041 DOI: 10.3389/fcell.2019.00328] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Accepted: 11/26/2019] [Indexed: 12/11/2022] Open
Abstract
Recent efforts in mapping spatial genome organization have revealed three evocative and conserved structural features of the inactive X in female mammals. First, the chromosomal conformation of the inactive X reveals a loss of topologically associated domains (TADs) present on the active X. Second, the macrosatellite DXZ4 emerges as a singular boundary that suppresses physical interactions between two large TAD-depleted "megadomains." Third, DXZ4 reaches across several megabases to form "superloops" with two other X-linked tandem repeats, FIRRE and ICCE, which also loop to each other. Although all three structural features are conserved across rodents and primates, deletion of mouse and human orthologs of DXZ4 and FIRRE from the inactive X have revealed limited impact on X chromosome inactivation (XCI) and escape in vitro. In contrast, loss of Xist or SMCHD1 have been shown to impair TAD erasure and gene silencing on the inactive X. In this perspective, we summarize these results in the context of new research describing disruption of X-linked tandem repeats in vivo, and discuss their possible molecular roles through the lens of evolutionary conservation and clinical genetics. As a null hypothesis, we consider whether the conservation of some structural features on the inactive X may reflect selection for X-linked tandem repeats on account of necessary cis- and trans-regulatory roles they may play on the active X, rather than the inactive X. Additional hypotheses invoking a role for X-linked tandem repeats on X reactivation, for example in the germline or totipotency, remain to be assessed in multiple developmental models spanning mammalian evolution.
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Affiliation(s)
- Prakhar Bansal
- Department of Genetics and Genome Sciences, School of Medicine, UCONN Health, University of Connecticut, Farmington, CT, United States
- Institute for Systems Genomics, University of Connecticut, Farmington, CT, United States
| | - Yuvabharath Kondaveeti
- Department of Genetics and Genome Sciences, School of Medicine, UCONN Health, University of Connecticut, Farmington, CT, United States
- Institute for Systems Genomics, University of Connecticut, Farmington, CT, United States
| | - Stefan F. Pinter
- Department of Genetics and Genome Sciences, School of Medicine, UCONN Health, University of Connecticut, Farmington, CT, United States
- Institute for Systems Genomics, University of Connecticut, Farmington, CT, United States
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