1
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Álvarez-Nava F, Soto-Quintana M. The Hypothesis of the Prolonged Cell Cycle in Turner Syndrome. J Dev Biol 2022; 10:16. [PMID: 35645292 PMCID: PMC9149809 DOI: 10.3390/jdb10020016] [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: 02/28/2022] [Accepted: 03/13/2022] [Indexed: 01/27/2023] Open
Abstract
Turner syndrome (TS) is a chromosomal disorder that is caused by a missing or structurally abnormal second sex chromosome. Subjects with TS are at an increased risk of developing intrauterine growth retardation, low birth weight, short stature, congenital heart diseases, infertility, obesity, dyslipidemia, hypertension, insulin resistance, type 2 diabetes mellitus, metabolic syndrome, and cardiovascular diseases (stroke and myocardial infarction). The underlying pathogenetic mechanism of TS is unknown. The assumption that X chromosome-linked gene haploinsufficiency is associated with the TS phenotype is questioned since such genes have not been identified. Thus, other pathogenic mechanisms have been suggested to explain this phenotype. Morphogenesis encompasses a series of events that includes cell division, the production of migratory precursors and their progeny, differentiation, programmed cell death, and integration into organs and systems. The precise control of the growth and differentiation of cells is essential for normal development. The cell cycle frequency and the number of proliferating cells are essential in cell growth. 45,X cells have a failure to proliferate at a normal rate, leading to a decreased cell number in a given tissue during organogenesis. A convergence of data indicates an association between a prolonged cell cycle and the phenotypical features in Turner syndrome. This review aims to examine old and new findings concerning the relationship between a prolonged cell cycle and TS phenotype. These studies reveal a diversity of phenotypic features in TS that could be explained by reduced cell proliferation. The implications of this hypothesis for our understanding of the TS phenotype and its pathogenesis are discussed. It is not surprising that 45,X monosomy leads to cellular growth pathway dysregulation with profound deleterious effects on both embryonic and later stages of development. The prolonged cell cycle could represent the beginning of the pathogenesis of TS, leading to a series of phenotypic consequences in embryonic/fetal, neonatal, pediatric, adolescence, and adulthood life.
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Affiliation(s)
- Francisco Álvarez-Nava
- Biological Sciences School, Faculty of Biological Sciences, Central University of Ecuador, Quito 170113, Ecuador
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2
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Yamazaki W, Tan SL, Taketo T. Role of the X and Y Chromosomes in the Female Germ Cell Line Development in the Mouse (Mus musculus). Sex Dev 2022:1-10. [PMID: 35235936 DOI: 10.1159/000521151] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Accepted: 11/18/2021] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND In eutherian mammals, the sex chromosome complement, XX and XY, determines sexual differentiation of gonadal primordia into testes and ovaries, which in turn direct differentiation of germ cells into haploid sperm and oocytes, respectively. When gonadal sex is reversed, however, the germ cell sex becomes discordant with the chromosomal sex. XY females in humans are infertile, while XY females in the mouse (Mus musculus) are subfertile or infertile dependent on the cause of sex reversal and the genetic background. This article reviews publications to understand how the sex chromosome complement affects the fertility of XY oocytes by comparing with XX and monosomy X (XO) oocytes. SUMMARY The results highlight 2 folds disadvantage of XY oocytes over XX oocytes: (1) the X and Y chromosomes fail to pair during the meiotic prophase I, resulting in sex chromosome aneuploidy at the first meiotic division and (2) expression of the Y-linked genes during oocyte growth affects the transcriptome landscape and renders the ooplasmic component incompetent for embryonic development. Key Message: The XX chromosome complement gives the oocyte the highest competence for embryonic development.
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Affiliation(s)
- Wataru Yamazaki
- Department of Surgery, McGill University, Montreal, Québec, Canada.,Research Institute of McGill University Health Centre, Montreal, Québec, Canada
| | - Seang Lin Tan
- Department of Obstetrics and Gynecology, McGill University, Montreal, Québec, Canada.,Research Institute of McGill University Health Centre, Montreal, Québec, Canada.,OriginElle Fertility Clinic and Women's Health Centre, Montreal, Québec, Canada
| | - Teruko Taketo
- Department of Surgery, McGill University, Montreal, Québec, Canada.,Department of Obstetrics and Gynecology, McGill University, Montreal, Québec, Canada.,Department of Biology, McGill University, Montreal, Québec, Canada.,Research Institute of McGill University Health Centre, Montreal, Québec, Canada
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3
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Vaz B, El Mansouri F, Liu X, Taketo T. Premature ovarian insufficiency in the XO female mouse on the C57BL/6J genetic background. Mol Hum Reprod 2020; 26:678-688. [PMID: 32634219 PMCID: PMC7473787 DOI: 10.1093/molehr/gaaa049] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2020] [Revised: 06/17/2020] [Indexed: 12/15/2022] Open
Abstract
In humans, all but 1% of monosomy 45.X embryos die in utero and those who reach term suffer from congenital abnormalities and infertility termed Turner's syndrome (TS). By contrast, XO female mice on various genetic backgrounds show much milder physical defects and normal fertility, diminishing their value as an animal model for studying the infertility of TS patients. In this article, we report that XO mice on the C57BL/6J (B6) genetic background showed early oocyte loss, infertility or subfertility and high embryonic lethality, suggesting that the effect of monosomy X in the female germline may be shared between mice and humans. First, we generated XO mice on either a mixed N2(C3H.B6) or B6 genetic background and compared the number of oocytes in neonatal ovaries; N2.XO females retained 45% of the number of oocytes in N2.XX females, whereas B6.XO females retained only 15% of that in B6.XX females. Second, while N2.XO females were as fertile as N2.XX females, both the frequency of delivery and the total number of pups delivered by B6.XO females were significantly lower than those by B6.XX females. Third, after mating with B6 males, both N2.XO and B6.XO females rarely produced XO pups carrying paternal X chromosomes, although a larger percentage of embryos was found to be XO before implantation. Furthermore, B6.XO females delivered 20% XO pups among female progeny after mating with C3H males. We conclude that the impact of monosomy X on female mouse fertility depends on the genetic background.
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Affiliation(s)
- B Vaz
- Department of Biology, McGill University, Montreal, QC H3A 1B1, Canada
| | - F El Mansouri
- Department of Surgery, McGill University, Montreal, QC H4A3J1, Canada
- Research Institute of the McGill University Health Centre, Montreal, QC H4A3J1, Canada
| | - X Liu
- Department of Surgery, McGill University, Montreal, QC H4A3J1, Canada
- Research Institute of the McGill University Health Centre, Montreal, QC H4A3J1, Canada
| | - T Taketo
- Department of Biology, McGill University, Montreal, QC H3A 1B1, Canada
- Department of Surgery, McGill University, Montreal, QC H4A3J1, Canada
- Research Institute of the McGill University Health Centre, Montreal, QC H4A3J1, Canada
- Department of Obstetrics & Gynecology, McGill University, Montreal, QC H4A3J1, Canada
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4
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Abstract
Fundamental differences exist between males and females, encompassing anatomy, physiology, behaviour, and genetics. Such differences undoubtedly play a part in the well documented, yet poorly understood, disparity in disease susceptibility between the sexes. Although traditionally attributed to gonadal sex hormone effects, recent work has begun to shed more light on the contribution of genetics - and in particular the sex chromosomes - to these sexual dimorphisms. Here, we explore the accumulating evidence for a significant genetic component to mammalian sexual dimorphism through the paradigm of sex chromosome evolution. The differences between the extant X and Y chromosomes, at both a sequence and regulatory level, arose across 166 million years. A functional result of these differences is cell autonomous sexual dimorphism. By understanding the process that changed a pair of homologous ancestral autosomes into the extant mammalian X and Y, we believe it easier to consider the mechanisms that may contribute to hormone-independent male-female differences. We highlight key roles for genes with homologues present on both sex chromosomes, where the X-linked copy escapes X chromosome inactivation. Finally, we summarise current experimental paradigms and suggest areas for developments to further increase our understanding of cell autonomous sexual dimorphism in the context of health and disease.
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Affiliation(s)
- Daniel M Snell
- Sex Chromosome Biology Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - James M A Turner
- Sex Chromosome Biology Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK.
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5
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He N, Lim SJ, Moreira de Mello JC, Navarro I, Bialecka M, Salvatori DCF, van der Westerlaken LAJ, Pereira LV, Chuva de Sousa Lopes SM. At Term, XmO and XpO Mouse Placentas Show Differences in Glucose Metabolism in the Trophectoderm-Derived Outer Zone. Front Cell Dev Biol 2017; 5:63. [PMID: 28680878 PMCID: PMC5478694 DOI: 10.3389/fcell.2017.00063] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Accepted: 06/06/2017] [Indexed: 12/21/2022] Open
Abstract
Genetic mouse model (39,XO) for human Turner Syndrome (45,XO) harboring either a single maternally inherited (Xm) or paternally inherited (Xp) chromosome show a pronounced difference in survival rate at term. However, a detailed comparison of XmO and XpO placentas to explain this difference is lacking. We aimed to investigate the morphological and molecular differences between XmO and XpO term mouse placentas. We observed that XpO placentas at term contained a significantly larger area of glycogen cells (GCs) in their outer zone, compared to XmO, XX, and XY placentas. In addition, the outer zone of XpO placentas showed higher expression levels of lactate dehydrogenase (Ldha) than XmO, XX, and XY placentas, suggestive of increased anaerobic glycolysis. In the labyrinth, we detected significantly lower expression level of trophectoderm (TE)-marker keratin 19 (Krt19) in XpO placentas than in XX placentas. The expression of other TE-markers was comparable as well as the area of TE-derived cells between XO and wild-type labyrinths. XpO placentas exhibited specific defects in the amount of GCs and glucose metabolism in the outer zone, suggestive of increased anaerobic glycolysis, as a consequence of having inherited a single Xp chromosome. In conclusion, the XpO genotype results in a more severe placental phenotype at term, with distinct abnormalities regarding glucose metabolism in the outer zone.
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Affiliation(s)
- Nannan He
- Department of Anatomy and Embryology, Leiden University Medical CenterLeiden, Netherlands
| | - Shujing J Lim
- Department of Anatomy and Embryology, Leiden University Medical CenterLeiden, Netherlands
| | | | - Injerreau Navarro
- Department of Anatomy and Embryology, Leiden University Medical CenterLeiden, Netherlands
| | - Monika Bialecka
- Department of Anatomy and Embryology, Leiden University Medical CenterLeiden, Netherlands
| | - Daniela C F Salvatori
- Department of Anatomy and Embryology, Leiden University Medical CenterLeiden, Netherlands.,Central Laboratory Animal Facility, Leiden University Medical CenterLeiden, Netherlands
| | | | - Lygia V Pereira
- Department of Genetics and Evolutionary Biology, University of São PauloSão Paulo, Brazil
| | - Susana M Chuva de Sousa Lopes
- Department of Anatomy and Embryology, Leiden University Medical CenterLeiden, Netherlands.,Department for Reproductive Medicine, Ghent University HospitalGhent, Belgium
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6
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Burgoyne PS, Arnold AP. A primer on the use of mouse models for identifying direct sex chromosome effects that cause sex differences in non-gonadal tissues. Biol Sex Differ 2016; 7:68. [PMID: 27999654 PMCID: PMC5154145 DOI: 10.1186/s13293-016-0115-5] [Citation(s) in RCA: 91] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/13/2016] [Accepted: 11/08/2016] [Indexed: 12/15/2022] Open
Abstract
In animals with heteromorphic sex chromosomes, all sex differences originate from the sex chromosomes, which are the only factors that are consistently different in male and female zygotes. In mammals, the imbalance in Y gene expression, specifically the presence vs. absence of Sry, initiates the differentiation of testes in males, setting up lifelong sex differences in the level of gonadal hormones, which in turn cause many sex differences in the phenotype of non-gonadal tissues. The inherent imbalance in the expression of X and Y genes, or in the epigenetic impact of X and Y chromosomes, also has the potential to contribute directly to the sexual differentiation of non-gonadal cells. Here, we review the research strategies to identify the X and Y genes or chromosomal regions that cause direct, sexually differentiating effects on non-gonadal cells. Some mouse models are useful for separating the effects of sex chromosomes from those of gonadal hormones. Once direct “sex chromosome effects” are detected in these models, further studies are required to narrow down the list of candidate X and/or Y genes and then to identify the sexually differentiating genes themselves. Logical approaches to the search for these genes are reviewed here.
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Affiliation(s)
- Paul S Burgoyne
- Stem Cell Biology and Developmental Genetics, Mill Hill Laboratory, Francis Crick Institute, The Ridgeway, London, NW7 1AA UK
| | - Arthur P Arnold
- Department of Integrative Biology and Physiology, and Laboratory of Neuroendocrinology of the Brain Research Institute, University of California, Los Angeles, 610 Charles Young Drive South, Los Angeles, CA 90095-7239 USA
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7
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Taketo T. The role of sex chromosomes in mammalian germ cell differentiation: can the germ cells carrying X and Y chromosomes differentiate into fertile oocytes? Asian J Androl 2016; 17:360-6. [PMID: 25578929 PMCID: PMC4430933 DOI: 10.4103/1008-682x.143306] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The sexual differentiation of germ cells into spermatozoa or oocytes is strictly regulated by their gonadal environment, testis or ovary, which is determined by the presence or absence of the Y chromosome, respectively. Hence, in normal mammalian development, male germ cells differentiate in the presence of X and Y chromosomes, and female germ cells do so in the presence of two X chromosomes. However, gonadal sex reversal occurs in humans as well as in other mammalian species, and the resultant XX males and XY females can lead healthy lives, except for a complete or partial loss of fertility. Germ cells carrying an abnormal set of sex chromosomes are efficiently eliminated by multilayered surveillance mechanisms in the testis, and also, though more variably, in the ovary. Studying the molecular basis for sex-specific responses to a set of sex chromosomes during gametogenesis will promote our understanding of meiotic processes contributing to the evolution of sex determining mechanisms. This review discusses the fate of germ cells carrying various sex chromosomal compositions in mouse models, the limitation of which may be overcome by recent successes in the differentiation of functional germ cells from embryonic stem cells under experimental conditions.
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Affiliation(s)
- Teruko Taketo
- Department of Surgery, Research Institute of MUHC; Department of Biology; Department of Obstetrics and Gynecology, McGill University, Montreal, Quebec, Canada
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8
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Vernet N, Szot M, Mahadevaiah SK, Ellis PJI, Decarpentrie F, Ojarikre OA, Rattigan Á, Taketo T, Burgoyne PS. The expression of Y-linked Zfy2 in XY mouse oocytes leads to frequent meiosis 2 defects, a high incidence of subsequent early cleavage stage arrest and infertility. Development 2014; 141:855-66. [PMID: 24496622 PMCID: PMC3912830 DOI: 10.1242/dev.091165] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Outbred XYSry- female mice that lack Sry due to the 11 kb deletion Srydl1Rlb have very limited fertility. However, five lines of outbred XYd females with Y chromosome deletions YDel(Y)1Ct-YDel(Y)5Ct that deplete the Rbmy gene cluster and repress Sry transcription were found to be of good fertility. Here we tested our expectation that the difference in fertility between XO, XYd-1 and XYSry- females would be reflected in different degrees of oocyte depletion, but this was not the case. Transgenic addition of Yp genes to XO females implicated Zfy2 as being responsible for the deleterious Y chromosomal effect on fertility. Zfy2 transcript levels were reduced in ovaries of XYd-1 compared with XYSry- females in keeping with their differing fertility. In seeking the biological basis of the impaired fertility we found that XYSry-, XYd-1 and XO,Zfy2 females produce equivalent numbers of 2-cell embryos. However, in XYSry- and XO,Zfy2 females the majority of embryos arrested with 2-4 cells and almost no blastocysts were produced; by contrast, XYd-1 females produced substantially more blastocysts but fewer than XO controls. As previously documented for C57BL/6 inbred XY females, outbred XYSry- and XO,Zfy2 females showed frequent failure of the second meiotic division, although this did not prevent the first cleavage. Oocyte transcriptome analysis revealed major transcriptional changes resulting from the Zfy2 transgene addition. We conclude that Zfy2-induced transcriptional changes in oocytes are sufficient to explain the more severe fertility impairment of XY as compared with XO females.
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Affiliation(s)
- Nadège Vernet
- MRC National Institute for Medical Research, London NW7 1AA, UK
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9
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Abramowitz LK, Olivier-Van Stichelen S, Hanover JA. Chromosome imbalance as a driver of sex disparity in disease. J Genomics 2014; 2:77-88. [PMID: 25031659 PMCID: PMC4091450 DOI: 10.7150/jgen.8123] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
It has long been recognized that men and women exhibit different risks for diverse disorders ranging from metabolic to autoimmune diseases. However, the underlying causes of these disparities remain obscure. Analysis of patients with chromosomal abnormalities, including Turner syndrome (45X) and Klinefelter syndrome (47XXY), has highlighted the importance of X-linked gene dosage as a contributing factor for disease susceptibility. Escape from X-inactivation and X-linked imprinting can result in transcriptional differences between normal men and women as well as in patients with sex chromosome abnormalities. Animal models support a role for X-linked gene dosage in disease with O-linked N-acetylglucosamine transferase (OGT) emerging as a prime candidate for a pleiotropic effector. OGT encodes a highly regulated nutrient-sensing epigenetic modifier with established links to immunity, metabolism and development.
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Affiliation(s)
- Lara K Abramowitz
- Laboratory of Cell and Molecular Biology, NIDDK, National Institutes of Health, Bethesda, MD 20892-0851, USA
| | | | - John A Hanover
- Laboratory of Cell and Molecular Biology, NIDDK, National Institutes of Health, Bethesda, MD 20892-0851, USA
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10
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Schulz EG, Meisig J, Nakamura T, Okamoto I, Sieber A, Picard C, Borensztein M, Saitou M, Blüthgen N, Heard E. The two active X chromosomes in female ESCs block exit from the pluripotent state by modulating the ESC signaling network. Cell Stem Cell 2014; 14:203-16. [PMID: 24506884 DOI: 10.1016/j.stem.2013.11.022] [Citation(s) in RCA: 117] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2013] [Revised: 10/18/2013] [Accepted: 11/26/2013] [Indexed: 01/18/2023]
Abstract
During early development of female mouse embryos, both X chromosomes are transiently active. X gene dosage is then equalized between the sexes through the process of X chromosome inactivation (XCI). Whether the double dose of X-linked genes in females compared with males leads to sex-specific developmental differences has remained unclear. Using embryonic stem cells with distinct sex chromosome compositions as a model system, we show that two X chromosomes stabilize the naive pluripotent state by inhibiting MAPK and Gsk3 signaling and stimulating the Akt pathway. Since MAPK signaling is required to exit the pluripotent state, differentiation is paused in female cells as long as both X chromosomes are active. By preventing XCI or triggering it precociously, we demonstrate that this differentiation block is released once XX cells have undergone X inactivation. We propose that double X dosage interferes with differentiation, thus ensuring a tight coupling between X chromosome dosage compensation and development.
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Affiliation(s)
- Edda G Schulz
- Mammalian Developmental Epigenetics Group, Institut Curie, CNRS UMR 3215, INSERM U934, Paris 75248, France.
| | - Johannes Meisig
- Institute of Pathology, Charité-Universitätsmedizin, 10117 Berlin, Germany; Integrative Research Institute for the Life Sciences and Institute for Theoretical Biology, Humboldt Universität, 10115 Berlin, Germany
| | - Tomonori Nakamura
- Department of Anatomy and Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan; JST, ERATO, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Ikuhiro Okamoto
- Department of Anatomy and Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan; JST, ERATO, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Anja Sieber
- Institute of Pathology, Charité-Universitätsmedizin, 10117 Berlin, Germany; Integrative Research Institute for the Life Sciences and Institute for Theoretical Biology, Humboldt Universität, 10115 Berlin, Germany
| | - Christel Picard
- Mammalian Developmental Epigenetics Group, Institut Curie, CNRS UMR 3215, INSERM U934, Paris 75248, France
| | - Maud Borensztein
- Mammalian Developmental Epigenetics Group, Institut Curie, CNRS UMR 3215, INSERM U934, Paris 75248, France
| | - Mitinori Saitou
- Department of Anatomy and Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan; JST, ERATO, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan; Center for iPS Cell Research and Application, Kyoto University, 53 Kawahara-cho, Shogoin Yoshida, Sakyo-ku, Kyoto 606-8507, Japan; Institute for Integrated Cell-Material Sciences, Kyoto University, Yoshida-Ushinomiya-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Nils Blüthgen
- Institute of Pathology, Charité-Universitätsmedizin, 10117 Berlin, Germany; Integrative Research Institute for the Life Sciences and Institute for Theoretical Biology, Humboldt Universität, 10115 Berlin, Germany
| | - Edith Heard
- Mammalian Developmental Epigenetics Group, Institut Curie, CNRS UMR 3215, INSERM U934, Paris 75248, France.
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11
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Kobayashi S, Totoki Y, Soma M, Matsumoto K, Fujihara Y, Toyoda A, Sakaki Y, Okabe M, Ishino F. Identification of an imprinted gene cluster in the X-inactivation center. PLoS One 2013; 8:e71222. [PMID: 23940725 PMCID: PMC3735490 DOI: 10.1371/journal.pone.0071222] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2013] [Accepted: 06/27/2013] [Indexed: 11/18/2022] Open
Abstract
Mammalian development is strongly influenced by the epigenetic phenomenon called genomic imprinting, in which either the paternal or the maternal allele of imprinted genes is expressed. Paternally expressed Xist, an imprinted gene, has been considered as a single cis-acting factor to inactivate the paternally inherited X chromosome (Xp) in preimplantation mouse embryos. This means that X-chromosome inactivation also entails gene imprinting at a very early developmental stage. However, the precise mechanism of imprinted X-chromosome inactivation remains unknown and there is little information about imprinted genes on X chromosomes. In this study, we examined whether there are other imprinted genes than Xist expressed from the inactive paternal X chromosome and expressed in female embryos at the preimplantation stage. We focused on small RNAs and compared their expression patterns between sexes by tagging the female X chromosome with green fluorescent protein. As a result, we identified two micro (mi)RNAs–miR-374-5p and miR-421-3p–mapped adjacent to Xist that were predominantly expressed in female blastocysts. Allelic expression analysis revealed that these miRNAs were indeed imprinted and expressed from the Xp. Further analysis of the imprinting status of adjacent locus led to the discovery of a large cluster of imprinted genes expressed from the Xp: Jpx, Ftx and Zcchc13. To our knowledge, this is the first identified cluster of imprinted genes in the cis-acting regulatory region termed the X-inactivation center. This finding may help in understanding the molecular mechanisms regulating imprinted X-chromosome inactivation during early mammalian development.
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Affiliation(s)
- Shin Kobayashi
- Japan Science and Technology Agency, Precursory Research for Embryonic Science and Technology, Kawaguchi, Saitama, Japan.
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12
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Genomic imprinting leads to less selectively maintained polymorphism on X chromosomes. Genetics 2012; 192:1455-64. [PMID: 23023005 DOI: 10.1534/genetics.112.145607] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Population-genetic models are developed to investigate the consequences of viability selection at a diallelic X-linked locus subject to genomic imprinting. Under complete paternal-X inactivation, a stable polymorphism is possible under the same conditions as for paternal-autosome inactivation with differential selection on males and females. A necessary but not sufficient condition is that there is sexual conflict, with selection acting in opposite directions in males and females. In contrast, models of complete maternal-X inactivation never admit a stable polymorphism and alleles will either be fixed or lost from the population. Models of complete paternal-X inactivation are more complex than corresponding models of maternal-X inactivation, as inactivation of paternally derived X chromosomes in females screens these chromosomes from selection for a generation. We also demonstrate that polymorphism is possible for incomplete X inactivation, but that the parameter conditions are more restrictive than for complete paternal-X inactivation. Finally, we investigate the effects of recurrent mutation in our models and show that deleterious alleles in mutation-selection balance at imprinted X-linked loci are at frequencies rather similar to those with corresponding selection pressures and mutation rates at unimprinted loci. Overall, our results add to the reasons for expecting less selectively maintained allelic variation on X chromosomes.
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13
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Abstract
The development of genetic sex determination and cytologically distinct sex chromosomes leads to the potential problem of gene dosage imbalances between autosomes and sex chromosomes and also between males and females. To circumvent these imbalances, mammals have developed an elaborate system of dosage compensation that includes both upregulation and repression of the X chromosome. Recent advances have provided insights into the evolutionary history of how both the imprinted and random forms of X chromosome inactivation have come about. Furthermore, our understanding of the epigenetic switch at the X-inactivation center and the molecular aspects of chromosome-wide silencing has greatly improved recently. Here, we review various facets of the ever-expanding field of mammalian dosage compensation and discuss its evolutionary, developmental, and mechanistic components.
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Affiliation(s)
- Bernhard Payer
- Howard Hughes Medical Institute, Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
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14
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Wakisaka N, Inoue K, Ogonuki N, Miki H, Sekita Y, Hanaki K, Akatsuka A, Kaneko-Ishino T, Ishino F, Ogura A. Ultrastructure of placental hyperplasia in mice: comparison of placental phenotypes with three different etiologies. Placenta 2008; 29:753-9. [PMID: 18602690 DOI: 10.1016/j.placenta.2008.05.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2008] [Revised: 05/19/2008] [Accepted: 05/22/2008] [Indexed: 11/28/2022]
Abstract
Hyperplastic placentas have been reported in several experimental mouse models, including animals produced by somatic cell nuclear transfer, by inter(sub)species hybridization, and by somatic cytoplasm introduction to oocytes followed by intracytoplasmic sperm injection. Of great interest are the gross and histological features common to these placental phenotypes--despite their quite different etiologies--such as the enlargement of the spongiotrophoblast layers. To find morphological clues to the pathways leading to these similar placental phenotypes, we analyzed the ultrastructure of the three different types of hyperplastic placenta. Most cells affected were of trophoblast origin and their subcellular ultrastructural lesions were common to the three groups, e.g., a heavy accumulation of cytoplasmic vacuoles in the trophoblastic cells composing the labyrinthine wall and an increased volume of spongiotrophoblastic cells with extraordinarily dilatated rough endoplasmic reticulum. Although the numbers of trophoblastic glycogen cells were greatly increased, they maintained their normal ultrastructural morphology, including a heavy glycogen deposition throughout the cytoplasm. The fetal endothelium and small vessels were nearly intact. Our ultrastructural study suggests that these three types of placental hyperplasias, with different etiologies, may have common pathological pathways, which probably exclusively affect the development of certain cell types of the trophoblastic lineage during mouse placentation.
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Affiliation(s)
- N Wakisaka
- Bioresouce Center, RIKEN, Tsukuba, Ibaraki 305-0074, Japan
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15
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Mills W, Moore T. Evolution of mammalian X chromosome-linked imprinting. Cytogenet Genome Res 2006; 113:336-44. [PMID: 16575198 DOI: 10.1159/000090850] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2005] [Accepted: 08/18/2005] [Indexed: 11/19/2022] Open
Abstract
We analyse the evolution of X chromosome-linked imprinting by modifying our previous model of imprinting of autosomal genes that influence the trade-off between maternal fecundity and offspring viability through alterations in maternal investment (Mills and Moore, 2004). Unlike previous genetic models, we analyse X-linked imprinting in the context of populations at equilibrium for either autosomal or X-linked biallelically expressed alleles at loci that influence the fecundity/viability trade-off. We show that selection under parental conflict over maternal investment in offspring can parsimoniously explain the occurrence of sex-specific gene expression patterns, without a requirement to postulate direct selection for sexual dimorphism mediated through imprinting. We note that sex chromosome imprinting causes a small distortion of the post-weaning sex ratio, providing a possible selection pressure against the evolution of X-linked imprints. We discuss our conclusions in the context of recent reports of imprinting of mouse X-linked Xlr genes.
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Affiliation(s)
- W Mills
- Department of Biochemistry, Biosciences Institute, University College Cork, Cork, Ireland.
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16
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Pelka GJ, Watson CM, Radziewic T, Hayward M, Lahooti H, Christodoulou J, Tam PPL. Mecp2 deficiency is associated with learning and cognitive deficits and altered gene activity in the hippocampal region of mice. ACTA ACUST UNITED AC 2006; 129:887-98. [PMID: 16467389 DOI: 10.1093/brain/awl022] [Citation(s) in RCA: 155] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Rett syndrome (RTT) is a debilitating neurological condition associated with mutations in the X-linked MECP2 gene, where apparently normal development is seen prior to the onset of cognitive and motor deterioration at 6-18 months of life. A targeted deletion of the methyl-CpG-binding domain (MBD) coding region and disruption of mRNA splicing was introduced in the mouse, resulting in a complete loss of Mecp2 transcripts and protein. Postnatal comparison of XO and XY mutant Mecp2 allele-containing null mice revealed similar effects on mouse growth and viability, suggesting that phenotypic manifestations are not modulated by the Y-chromosome. Further assessment of Mecp2-null XY mice highlighted cerebellar and hippocampal/amygdala-based learning deficits in addition to reduced motor dexterity and decreased anxiety levels. Brain tissues containing the hippocampal formation of XY Mecp2-null mice also displayed significant changes in genetic activity, which are related to the severity of the mutant phenotype.
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Affiliation(s)
- Gregory J Pelka
- Embryology Unit, Children's Medical Research Institute,Wentworthville, NSW, Australia
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17
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Lightfoot DA, Kouznetsova A, Mahdy E, Wilbertz J, Höög C. The fate of mosaic aneuploid embryos during mouse development. Dev Biol 2006; 289:384-94. [PMID: 16337934 DOI: 10.1016/j.ydbio.2005.11.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2005] [Revised: 10/12/2005] [Accepted: 11/02/2005] [Indexed: 11/24/2022]
Abstract
More than any other species, humans have difficulty reproducing. As recent studies show that human infertility is ever increasing, much efforts are needed towards the understanding of our low fecundity. While aneuploidy is the leading cause of spontaneous pregnancy loss in humans, we still know surprisingly little about the developmental consequences of chromosomal abnormalities. We have here used a mouse model that spontaneously incites chromosomal primary aneuploidy in female haploid oocytes and find that after fertilization, these primary aneuploid cells become cytological unstable, generating diverse karyotypic mosaic embryos. The mosaic aneuploid embryos can develop and implant into the female uterine tissue and initiate the gastrulation process (E6.5) but quickly degrade and succumb by E8.0. We find that loss of embryo viability due to chromosomal mosaicism is caused by the activation of a spatially and temporally controlled p53-independent apoptotic mechanism and does not result from a failure to progress through mitosis. We conclude that an initial state of primary aneuploidy within an embryo results in a rapid evolution of mosaicism and early embryonic death. This gestational loss due to aneuploid mosaicism could account for the large proportion of human pregnancy loss prior to clinical recognition.
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Affiliation(s)
- Daniel A Lightfoot
- Department of Cell and Molecular Biology and Center for Genomics and Bioinformatics, Karolinska Institutet, S-171 77 Stockholm, Sweden
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18
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Kobayashi S, Isotani A, Mise N, Yamamoto M, Fujihara Y, Kaseda K, Nakanishi T, Ikawa M, Hamada H, Abe K, Okabe M. Comparison of Gene Expression in Male and Female Mouse Blastocysts Revealed Imprinting of the X-Linked Gene, Rhox5/Pem, at Preimplantation Stages. Curr Biol 2006; 16:166-72. [PMID: 16431368 DOI: 10.1016/j.cub.2005.11.071] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2005] [Revised: 11/07/2005] [Accepted: 11/25/2005] [Indexed: 01/20/2023]
Abstract
Mammalian male preimplantation embryos develop more quickly than females . Using enhanced green fluorescent protein (EGFP)-tagged X chromosomes to identify the sex of the embryos, we compared gene expression patterns between male and female mouse blastocysts by DNA microarray. We detected nearly 600 genes with statistically significant sex-linked expression; most differed by 2-fold or less. Of 11 genes showing greater than 2.5-fold differences, four were expressed exclusively or nearly exclusively sex dependently. Two genes (Dby and Eif2s3y) were mapped to the Y chromosome and were expressed in male blastocysts. The remaining two (Rhox5/Pem and Xist) were mapped to the X chromosome and were predominantly expressed in female blastocysts. Moreover, Rhox5/Pem was expressed predominantly from the paternally inherited X chromosome, indicating sex differences in early epigenetic gene regulation.
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Affiliation(s)
- Shin Kobayashi
- Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan
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19
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Huynh KD, Lee JT. A continuity of X-chromosome silence from gamete to zygote. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2005; 69:103-12. [PMID: 16117638 DOI: 10.1101/sqb.2004.69.103] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- K D Huynh
- Howard Hughes Medical Institute, Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
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20
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Raefski AS, O'Neill MJ. Identification of a cluster of X-linked imprinted genes in mice. Nat Genet 2005; 37:620-4. [PMID: 15908953 DOI: 10.1038/ng1567] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2004] [Accepted: 03/31/2005] [Indexed: 01/28/2023]
Abstract
Complete or partial monosomy with respect to the X chromosome is the genetic basis of Turner syndrome in human females. Individuals with Turner syndrome have a spectrum of anatomical, physiological and behavioral phenotypes with expressivity dependent on the extent of monosomy and the parental origin of the single X. Parent-of-origin influences on social cognition in Turner syndrome might be due to the presence of imprinted genes on the X. Imprinting of X-linked genes has also been implicated in the male prevalence of autistic spectrum disorders, in male sexual orientation and in the developmental delay of XO mouse embryos. The only molecular evidence for X-chromosome imprinting, however, concerns X-chromosome inactivation in specific circumstances and does not account for these phenotypes. Using a mouse model for Turner syndrome, we searched for locus-specific imprinting of X-linked genes in developing brain. We identified a cluster of X-linked genes containing at least three genes that show transcriptional repression of paternal alleles. Imprinting of these three genes, Xlr3b, Xlr4b and Xlr4c, is independent of X-chromosome inactivation and has a dynamic and complex pattern of tissue and stage specificity.
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Affiliation(s)
- Adam S Raefski
- Department of Molecular and Cell Biology, University of Connecticut, 354 Mansfield Rd., U-2131, Storrs, Connecticut 06269, USA
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21
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Davies W, Isles A, Smith R, Karunadasa D, Burrmann D, Humby T, Ojarikre O, Biggin C, Skuse D, Burgoyne P, Wilkinson L. Xlr3b is a new imprinted candidate for X-linked parent-of-origin effects on cognitive function in mice. Nat Genet 2005; 37:625-9. [PMID: 15908950 DOI: 10.1038/ng1577] [Citation(s) in RCA: 162] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2005] [Accepted: 04/27/2005] [Indexed: 12/23/2022]
Abstract
Imprinted genes show differential expression between maternal and paternal alleles as a consequence of epigenetic modification that can result in 'parent-of-origin' effects on phenotypic traits. There is increasing evidence from mouse and human studies that imprinted genes may influence behavior and cognitive functioning. Previous work in girls with Turner syndrome (45,XO) has suggested that there are X-linked parent-of-origin effects on brain development and cognitive functioning, although the interpretation of these data in terms of imprinted gene effects has been questioned. We used a 39,XO mouse model to examine the influence of the parental origin of the X chromosome on cognitive behaviors and expression of X-linked genes in brain. Our findings confirm the existence of X-linked imprinted effects on cognitive processes and identify a new maternally expressed imprinted gene candidate on the X chromosome, Xlr3b, which may be of importance in mediating the behavioral effects.
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Affiliation(s)
- William Davies
- Laboratories of Cognitive and Behavioral Neuroscience and Developmental Genetics and Imprinting, The Babraham Institute, The Babraham Research Campus, Cambridge, CB2 4AT, UK
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22
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Spencer HG, Feldman MW, Clark AG, Weisstein AE. The effect of genetic conflict on genomic imprinting and modification of expression at a sex-linked locus. Genetics 2004; 166:565-79. [PMID: 15020445 PMCID: PMC1470692 DOI: 10.1534/genetics.166.1.565] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We examine how genomic imprinting may have evolved at an X-linked locus, using six diallelic models of selection in which one allele is imprintable and the other is not. Selection pressures are generated by genetic conflict between mothers and their offspring. The various models describe cases of maternal and paternal inactivation, in which females may be monogamous or bigamous. When inactivation is maternal, we examine the situations in which only female offspring exhibit imprinting as well as when both sexes do. We compare our results to those previously obtained for an autosomal locus and to four models in which a dominant modifier of biallelic expression is subjected to the same selection pressures. We find that, in accord with verbal predictions, maternal inactivation of growth enhancers and paternal inactivation of growth inhibitors are more likely than imprinting in the respective opposite directions, although these latter outcomes are possible for certain parameter combinations. The expected outcomes are easier to evolve than the same outcomes for autosomal loci, contradicting the available evidence concerning the direction of imprinting on mammalian sex chromosomes. In most of our models stable polymorphism of imprinting status is possible, a behavior not predicted by verbal accounts.
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Affiliation(s)
- Hamish G Spencer
- Allan Wilson Centre for Molecular Ecology and Evolution, Department of Zoology, University of Otago, Dunedin, New Zealand.
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23
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Abstract
There are two forms of X chromosome inactivation (XCI) in the laboratory mouse, random XCI in the fetus and imprinted paternal XCI limited to the extraembryonic tissues supporting the fetal life in utero. Imprinted XCI has been studied extensively because it takes place first in embryogenesis and it may hold clues to the mechanism of control of XCI in general and to the evolution of random' XCI. Classical microscopic and biochemical studies of embryos in vivo provide a basis for interpreting the multifaceted information yielded by various inventive approaches and for planning further experiments.
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Affiliation(s)
- Nobuo Takagi
- Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan.
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24
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Hemberger M. The role of the X chromosome in mammalian extra embryonic development. Cytogenet Genome Res 2004; 99:210-7. [PMID: 12900566 DOI: 10.1159/000071595] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2002] [Accepted: 12/23/2002] [Indexed: 11/19/2022] Open
Abstract
Accumulating evidence points to the importance of the X chromosome for trophoblast development. In rodents, the extraembryonic cell lineage differs from somatic tissues in that X chromosome inactivation is imprinted, preferentially silencing the paternal X chromosome. As a consequence, trophoblast development is extremely susceptible to deviations from normal X inactivation and is impaired in situations of increased and reduced X-linked gene dosage. Mouse mutants have also shown that maintenance of X chromosome silencing in extraembryonic tissues requires a special set of heterochromatin proteins. Moreover, the X chromosome has been implicated in causing several malformations of the placenta. The observed importance of the X chromosome for placental development can be explained by the presence of many trophoblast-expressed genes, especially in the proximal and central regions. Given that the placenta represents a postzygotic barrier to reproduction, evolutionary constraints may be responsible for the presence of placental genes on the X chromosome that are often co-expressed in brain and testis.
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Affiliation(s)
- M Hemberger
- Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta, Canada.
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25
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Burgoyne PS, Ojarikre OA, Turner JMA. Evidence that postnatal growth retardation in XO mice is due to haploinsufficiency for a non-PAR X gene. Cytogenet Genome Res 2004; 99:252-6. [PMID: 12900572 DOI: 10.1159/000071601] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2002] [Accepted: 12/06/2002] [Indexed: 11/19/2022] Open
Abstract
XO Turner women, irrespective of the parental source of the X chromosome, are of short stature, and this is now thought to be largely a consequence of haploinsufficiency for the pseudoautosomal region (PAR) gene SHOX. X(p)O mice (with a paternal X) are developmentally retarded in fetal life, are underweight at birth, and show reduced weight gain in the first few weeks after birth. X(m)O mice, on the other hand, are more developmentally advanced than their XX siblings in fetal life; their postnatal growth has not hitherto been assessed. Here we show that X(m)O mice are not underweight at birth, but they nevertheless show reduced weight gain postnatally. The fact that postnatal growth is affected in X(p)O and X(m)O mice, means that this must be due to X dosage deficiency. In order to see if haploinsufficiency for a PAR gene was responsible for this growth deficit (cf SHOX deficiency in Turner women), X(m)Y*(X) females, in which the Y*(X) chromosome provides a second copy of the PAR, were compared with XX females. These X(m)Y*(X) females were also growth-retarded relative to their XX sibs, suggesting that it may be haploinsufficiency for a non-dosage-compensated X gene or genes outside the PAR that is responsible for the postnatal growth deficit in XO mice. The X genes known to escape X inactivation in the mouse have closely similar Y homologues. X(m)YSRY-negative females were therefore compared with XX females to see if the presence of the SRY-negative Y chromosome corrected the growth deficit; this proved to be the case. The postnatal growth deficit of XO mice is therefore probably due to haploinsufficiency for a non-dosage-compensated X gene that has a Y homologue that provides an equivalent function in the somatic tissues of males.
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Affiliation(s)
- P S Burgoyne
- Division of Developmental Genetics, MRC National Institute for Medical Research, London, UK.
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26
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Ishikawa H, Rattigan A, Fundele R, Burgoyne PS. Effects of sex chromosome dosage on placental size in mice. Biol Reprod 2003; 69:483-8. [PMID: 12700203 DOI: 10.1095/biolreprod.102.012641] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Mice of the XO genotype with a paternally derived X chromosome (XpO) have placental hyperplasia in late pregnancy, although in early pregnancy the ectoplacental cone, a placental precursor, is smaller in XpO mice than in their XX sibs. This early size deficiency of the ectoplacental cone is apparently a consequence of Xp imprinting, because XmO embryos (with a maternally derived X chromosome) are unaffected. In the present study we sought to establish whether XpO placental hyperplasia in late pregnancy is also a consequence of Xp imprinting. Placental weight data were first collected from litters that included XpO or XmO fetuses and XX controls. Comparison of XO placentae with XX placentae showed that XpO and XmO placentae are hyperplastic. This finding suggested that the hyperplasia might be an X dosage effect, and this hypothesis was supported by the finding that XY male fetuses from the same crosses also had larger placentae than their XX sibs. Further analysis of a range of sex-chromosome variant genotypes, including XmYSry-negative females and XXSry transgenic males, showed that mouse fetuses with one X chromosome consistently had larger placentae than littermates with two X chromosomes, independent of their gonadal/androgen status.
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Affiliation(s)
- Hitoshi Ishikawa
- National Institute for Medical Research, London NW7 1AA, United Kingdom
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27
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Huynh KD, Lee JT. Imprinted X inactivation in eutherians: a model of gametic execution and zygotic relaxation. Curr Opin Cell Biol 2001; 13:690-7. [PMID: 11698184 DOI: 10.1016/s0955-0674(00)00272-6] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In mammals, X-chromosome inactivation (XCI) ensures equal expression of X-linked genes in XX and XY individuals by transcriptionally silencing one X-chromosome in female cells. In this review, we discuss an imprinted form of X-inactivation in which the paternal X (Xp) is preferentially silenced. Believed to be the ancestral mechanism of dosage compensation in mammals, imprinted X-inactivation can still be observed in modern-day marsupials and in the extraembryonic tissues of some eutherians such as the mouse. Recent experiments have addressed the nature of the gametic imprint and focused on the regulatory interaction between the noncoding RNA gene, Xist, and its antisense partner, Tsix. Our review of the literature has inspired an unconventional view of imprinted XCI in mice. First, the evidence strongly argues that imprinted XCI is inabsolute, so that a stochastic number of extraembryonic cells escape imprinting. Second, contrary to conventional thinking, we would like to consider the possibility that the paternal X might actually be transmitted to the zygote as a pre-inactivated chromosome. In this model, the gamete initiates and establishes imprinted XCI, while the zygote maintains the pre-established pattern of gametic inactivation. Finally, we hypothesize that the inabsolute nature of imprinting is caused by imperfect zygotic maintenance. We propose that the mouse represents a transitional stage in the evolution of random XCI from an absolutely imprinted mechanism.
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Affiliation(s)
- K D Huynh
- Howard Hughes Medical Institute, Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02115, USA.
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28
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Sado T, Wang Z, Sasaki H, Li E. Regulation of imprinted X-chromosome inactivation in mice by Tsix. Development 2001; 128:1275-86. [PMID: 11262229 DOI: 10.1242/dev.128.8.1275] [Citation(s) in RCA: 214] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In mammals, X-chromosome inactivation is imprinted in the extra-embryonic lineages with paternal X chromosome being preferentially inactivated. In this study, we investigate the role of Tsix, the antisense transcript from the Xist locus, in regulation of Xist expression and X-inactivation. We show that Tsix is transcribed from two putative promoters and its transcripts are processed. Expression of Tsix is first detected in blastocysts and is imprinted with only the maternal allele transcribed. The imprinted expression of Tsix persists in the extra-embryonic tissues after implantation, but is erased in embryonic tissues. To investigate the function of Tsix in X-inactivation, we disrupted Tsix by insertion of an IRES(β)geo cassette in the second exon, which blocked transcripts from both promoters. While disruption of the paternal Tsix allele has no adverse effects on embryonic development, inheritance of a disrupted maternal allele results in ectopic Xist expression and early embryonic lethality, owing to inactivation of both X chromosomes in females and single X chromosome in males. Further, early developmental defects of female embryos with maternal transmission of Tsix mutation can be rescued by paternal inheritance of the Xist deletion. These results provide genetic evidence that Tsix plays a crucial role in maintaining Xist silencing in cis and in regulation of imprinted X-inactivation in the extra-embryonic tissues.
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Affiliation(s)
- T Sado
- Division of Human Genetics, National Institute of Genetics, Yata, Mishima, Japan.
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29
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Affiliation(s)
- David Haig
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138; e-mail:
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30
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Abstract
In marsupials and in extraembryonic tissues of placental mammals, X inactivation is imprinted to occur on the paternal chromosome. Here, we find that imprinting is controlled by the antisense Xist gene, Tsix. Tsix is maternally expressed and mice carrying a Tsix deletion show normal paternal but impaired maternal transmission. Maternal inheritance occurs infrequently, with surviving progeny showing intrauterine growth retardation and reduced fertility. Transmission ratio distortion results from disrupted imprinting and postimplantation loss of mutant embryos. In contrast to effects in embryonic stem cells, deleting Tsix causes ectopic X inactivation in early male embryos and inactivation of both X chromosomes in female embryos, indicating that X chromosome counting cannot override Tsix imprinting. These results highlight differences between imprinted and random X inactivation but show that Tsix regulates both. We propose that an imprinting center lies within Tsix.
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Affiliation(s)
- J T Lee
- Department of Molecular Biology, Massachusetts General Hospital, Boston 02114, USA.
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31
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Abstract
Somatic nuclear transfer has been performed with frogs since the early 1960s, yet it has proved impossible to generate an adult frog using an adult cell as nuclear donor. After some initial skepticism, the birth of sheep, cows, goats, and mice using this technique with fetal or adult cell donors is now established fact. The success with adult mammalian cell donors extends the historic work in frogs by attesting to the totipotency of nuclei in at least some adult, differentiated cell types. Because the technique offers a developmental read out of the totality of genetic and molecular lifetime changes accumulated by the nucleus of a single somatic cell, basic research applications are seen in the fields of ageing, cancer, X chromosome inactivation, and imprinting. The prospect of a method for gene targeting in livestock holds particular promise for commercial applications; whilst for humans, the use of nuclear transfer to provide diverse populations of customized stem cells for therapeutic purposes presents a tantalizing future goal.
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Affiliation(s)
- A Colman
- PPL Therapeutics, Roslin, Edinburgh EH25 9PP, Scotland.
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