Histone macroH2A1 is concentrated in the inactive X chromosome of female preimplantation mouse embryos

MacroH2As are core histone proteins with a hybrid structure consisting of a domain that closely resembles a full-length histone H2A followed by a large nonhistone domain. We recently showed that one of the macroH2A subtypes, macroH2A1.2, is concentrated in the inactive X chromosome in adult female mammals. Here we examine the timing of the association of macroH2A1.2 with the inactive X chromosome during preimplantation mouse development in order to assess the possibility that macroH2A1 participates in the initiation of X inactivation. The association of macroH2A1.2 with one of the X chromosomes was observed in 50% of blastocysts, occurring mostly, if not exclusively, in extraembryonic cells as was expected from previous studies, which indicated that X inactivation in embryonic lineages happens after implantation. Examination of earlier embryonic stages indicates that the association of macroH2A1 with the inactive X chromosome begins between the 8- and 16-cell stages. Of the changes that are known to happen during X inactivation in preimplantation embryos, the accumulation of macroH2A1 appears to be the earliest marker of the inactive X chromosome and is the only change that has been shown to occur during the period when transcriptional silencing is initiated.

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Genetic activity of sex chromosomes in somatic cells of mammals

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1970.0044 ◽

1970 ◽

Vol 259 (828) ◽

pp. 41-52 ◽

Cited By ~ 39

Keyword(s):

X Chromosome ◽

Germ Cells ◽

Chromosome Region ◽

Somatic Cells ◽

X Inactivation ◽

X Chromosomes ◽

Animal Group ◽

Inactive X Chromosome ◽

Genetic Activity ◽

Partial Inactivation

Mammals are thought to have a type of dosage compensation not so far known in any other animal group: however many X chromosomes are present, only one remains genetically active in somatic cells. Considerable evidence for this idea exists, in spite of criticism; the greatest difficulty is presented by the abnormalities in human individuals with X chromosome aberrations. Possible explanations for these abnormalities include: wrong X chromosome dosage in early development before X inactivation, reversal of inactivation, partial inactivation of both X chromosomes, activity of the X while in the condensed inactive state, and the presence of a homologous non-inactivated region of the human X and Y. In female germ cells X inactivation apparently does not occur, but the situation in male germ cells is less clear. The Y chromosome is probably also inactive in somatic cells of adults, but again its function in germ cells is not yet clear. Some species have a presumed doubly inactive X chromosome region, as well as the singly active one. The origins and functions of this region are unknown; it may have a role in female germ cells.

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The pattern of X-chromosome inactivation in the embryonic and extra-embryonic tissues of post-implantation digynic triploid LT/Sv strain mouse embryos

Genetics Research ◽

10.1017/s0016672300035175 ◽

1990 ◽

Vol 56 (2-3) ◽

pp. 107-114 ◽

Cited By ~ 7

Author(s):

S. Speirs ◽

J. M. Cross ◽

M. H. Kaufman

Keyword(s):

X Chromosome ◽

Sex Chromosome ◽

Yolk Sac ◽

X Inactivation ◽

Tissue Samples ◽

X Chromosomes ◽

Embryonic Tissues ◽

Inactive X Chromosome ◽

Distinct Cell ◽

Inactivation Pattern

SummarySpontaneously cycling LT/Sv strain female mice were mated to hemizygous Rb(X.2)2Ad males in order to facilitate the distinction of the paternal X chromosome, and the pregnant females were autopsied at about midday on the tenth day of gestation. Out of a total of 222 analysable embryos recovered, 165 (74·3%) were diploid and 57 (25·7%) were triploid. Of the triploids, 26 had an XXY and 31 an XXX sex chromosome constitution. Both embryonic and extra-embryonic tissue samples from the triploids were analysed cytogenetically by G-banding and by the Kanda technique to investigate their X-inactivation pattern. The yolk sac samples were separated enzymatically into their endodermally-derived and mesodermally-derived components, and these were similarly analysed, as were similar samples from a selection of control XmXp diploid embryos. In the case of the XmXmY digynic triploid embryos, a single darkly-staining Xm chromosome was observed in 485 (82·9%) out of 585, 304 (73·3%) out of 415, and 165 (44·7%) out of 369 metaphases from the embryonic, yolk sac mesodermally-derived and yolk sac endodermally-derived tissues, respectively. The absence of a darkly staining X-chromosome in the other metaphase spreads could either indicate that both X-chromosomes present were active, or that the Kanda technique had failed to differentially stain the inactive X-chromosome(s) present. In the case of the XmXmXp digynic triploid embryos, virtually all of the tissues analysed comprised two distinct cell lineages, namely those with two darkly-staining X-chromosomes, and those with a single darkly staining X-chromosome. Four X-inactivation patterns were consequently observed in this group, namely, (XmXp)Xm, (XmXm)Xp, (Xm)XmXp and XmXm(Xp) in which the inactive X is enclosed in parentheses. The incidence of these various classes varied among the tissues analysed. There was, however, a clear pattern of non-random selective paternal X-inactivation in yolk sac endodermally-derived samples which possessed two inactive X-chromosomes. This finding contrasts with the situation observed in the yolk sac mesodermally-derived and embryonic samples which possessed two inactive X-chromosomes, where the ratio of (XmXm)Xp:Xm(XmXp) was 1:1·20 and 1:1·03, respectively, being clear evidence that random X-inactivation had occurred in these tissues.

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An extra maternally derived X chromosome is deleterious to early mouse development

Development ◽

10.1242/dev.110.3.969 ◽

1990 ◽

Vol 110 (3) ◽

pp. 969-975 ◽

Cited By ~ 2

Author(s):

C. Shao ◽

N. Takagi

Keyword(s):

X Chromosome ◽

Early Death ◽

X Inactivation ◽

Mouse Development ◽

Extra Copy ◽

X Chromosomes ◽

Extraembryonic Membranes ◽

Early Mouse ◽

Ectoplacental Cone ◽

Embryonic Death

An extra copy of the X chromosome, unlike autosomes, exerts only minor effects on development in mammals including man and mice, because all X chromosomes except one are genetically inactivated. Contrary to this contention, we found that an additional maternally derived X (XM) chromosome, but probably not a paternally derived one (XP), consistently contributes to early death of 41,XXY and 41,XXX embryos in mice. Because of imprinted resistance to inactivation, two doses of XM remain active in the trophectoderm, and seem to be responsible for the failure in the development of the ectoplacental cone and extraembryonic ectoderm, and hence, from early embryonic death. Discordant observations in man indicating viability of XMXMXP and XMXMY individuals suggest that imprinting on the human X chromosome is either weak, unstable or erased before the initiation of X-inactivation in progenitors of extraembryonic membranes.

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Species-specific differences in X chromosome inactivation in mammals

Reproduction ◽

10.1530/rep-13-0173 ◽

2013 ◽

Vol 146 (4) ◽

pp. R131-R139 ◽

Cited By ~ 18

Author(s):

Takashi Sado ◽

Takehisa Sakaguchi

Keyword(s):

X Chromosome ◽

Molecular Basis ◽

Embryonic Stem ◽

X Chromosome Inactivation ◽

X Inactivation ◽

Chromosome Inactivation ◽

X Chromosomes ◽

Inactive X Chromosome ◽

Species Specific ◽

Genetically Manipulated

In female mammals, the dosage difference in X-linked genes between XX females and XY males is compensated for by inactivating one of the two X chromosomes during early development. Since the discovery of the X inactive-specific transcript (XIST) gene in humans and its subsequent isolation of the mouse homolog, Xist, in the early 1990s, the molecular basis of X chromosome inactivation (X-inactivation) has been more fully elucidated using genetically manipulated mouse embryos and embryonic stem cells. Studies on X-inactivation in other mammals, although limited when compared with those in the mice, have revealed that, while their inactive X chromosome shares many features with those in the mice, there are marked differences in not only some epigenetic modifications of the inactive X chromosome but also when and how X-inactivation is initiated during early embryonic development. Such differences raise the issue about what extent of the molecular basis of X-inactivation in the mice is commonly shared among others. Recognizing similarities and differences in X-inactivation among mammals may provide further insight into our understanding of not only the evolutionary but also the molecular aspects for the mechanism of X-inactivation. Here, we reviewed species-specific differences in X-inactivation and discussed what these differences may reveal.

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X-chromosome activity in preimplantation mouse embryos from XX and XO mothers

Development ◽

10.1242/dev.46.1.53 ◽

1978 ◽

Vol 46 (1) ◽

pp. 53-64

Author(s):

Marilyn Monk ◽

Mary Harper

Keyword(s):

X Chromosome ◽

Bimodal Distribution ◽

Mouse Embryos ◽

Activity Levels ◽

Cell Stage ◽

X Chromosomes ◽

Preimplantation Mouse Embryos ◽

Preimplantation Mouse ◽

Morula Stage ◽

The Mean

Embryos from XO female mice begin development with half the activity levels of an enzyme (HPRT) coded for by a gene on the X chromosome, compared with embryos from XX females. Groups of unfertilized eggs and individual embryos at the 8-cell, morula and blastocyst stages were assayed for HPRT activity. An autosomally coded enzyme (APRT) was assayed simultaneously in the same reaction mix as a control. There is a substantial increase in HPRT activity by the 8-cell stage. However, the mean activity of HPRT in embryos of XO mothers remains half that in embryos of XX mothers. This suggests a significant maternally inherited component of HPRT activity in 8-cell embryos. By the 9- to 16-cell morula stage the HPRT activities in the two groups of embryos become similar due, presumably, to a transition to embryo-coded activity; HPRT activities in individual morulae from XX mothers show a bimodal distribution consistent with the hypothesis that both X-chromosomes are active in XX embryos at this stage.

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Bipartite structure of the inactive mouse X chromosome

Genome Biology ◽

10.1186/s13059-015-0728-8 ◽

2015 ◽

Vol 16 (1) ◽

Cited By ~ 143

Author(s):

Xinxian Deng ◽

Wenxiu Ma ◽

Vijay Ramani ◽

Andrew Hill ◽

Fan Yang ◽

...

Keyword(s):

X Chromosome ◽

Structural Changes ◽

3D Structure ◽

Boundary Region ◽

X Inactivation ◽

Imprinted Genes ◽

X Chromosomes ◽

F1 Hybrid ◽

Inactive X Chromosome ◽

Single Allele

Abstract Background In mammals, one of the female X chromosomes and all imprinted genes are expressed exclusively from a single allele in somatic cells. To evaluate structural changes associated with allelic silencing, we have applied a recently developed Hi-C assay that uses DNase I for chromatin fragmentation to mouse F1 hybrid systems. Results We find radically different conformations for the two female mouse X chromosomes. The inactive X has two superdomains of frequent intrachromosomal contacts separated by a boundary region. Comparison with the recently reported two-superdomain structure of the human inactive X shows that the genomic content of the superdomains differs between species, but part of the boundary region is conserved and located near the Dxz4/DXZ4 locus. In mouse, the boundary region also contains a minisatellite, Ds-TR, and both Dxz4 and Ds-TR appear to be anchored to the nucleolus. Genes that escape X inactivation do not cluster but are located near the periphery of the 3D structure, as are regions enriched in CTCF or RNA polymerase. Fewer short-range intrachromosomal contacts are detected for the inactive alleles of genes subject to X inactivation compared with the active alleles and with genes that escape X inactivation. This pattern is also evident for imprinted genes, in which more chromatin contacts are detected for the expressed allele. Conclusions By applying a novel Hi-C method to map allelic chromatin contacts, we discover a specific bipartite organization of the mouse inactive X chromosome that probably plays an important role in maintenance of gene silencing.

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Escape from X Chromosome Inactivation and the Female Predominance in Autoimmune Diseases

International Journal of Molecular Sciences ◽

10.3390/ijms22031114 ◽

2021 ◽

Vol 22 (3) ◽

pp. 1114

Author(s):

Ali Youness ◽

Charles-Henry Miquel ◽

Jean-Charles Guéry

Keyword(s):

Autoimmune Diseases ◽

X Chromosome ◽

Gene Dosage ◽

X Chromosome Inactivation ◽

Chromosome Inactivation ◽

X Chromosomes ◽

Female Sex Hormones ◽

Inactive X Chromosome ◽

Immune Related Genes ◽

Female Specific

Women represent 80% of people affected by autoimmune diseases. Although, many studies have demonstrated a role for sex hormone receptor signaling, particularly estrogens, in the direct regulation of innate and adaptive components of the immune system, recent data suggest that female sex hormones are not the only cause of the female predisposition to autoimmunity. Besides sex steroid hormones, growing evidence points towards the role of X-linked genetic factors. In female mammals, one of the two X chromosomes is randomly inactivated during embryonic development, resulting in a cellular mosaicism, where about one-half of the cells in a given tissue express either the maternal X chromosome or the paternal one. X chromosome inactivation (XCI) is however not complete and 15 to 23% of genes from the inactive X chromosome (Xi) escape XCI, thereby contributing to the emergence of a female-specific heterogeneous population of cells with bi-allelic expression of some X-linked genes. Although the direct contribution of this genetic mechanism in the female susceptibility to autoimmunity still remains to be established, the cellular mosaicism resulting from XCI escape is likely to create a unique functional plasticity within female immune cells. Here, we review recent findings identifying key immune related genes that escape XCI and the relationship between gene dosage imbalance and functional responsiveness in female cells.

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Cell cycle–dependent localization of macroH2A in chromatin of the inactive X chromosome

The Journal of Cell Biology ◽

10.1083/jcb.200112074 ◽

2002 ◽

Vol 157 (7) ◽

pp. 1113-1123 ◽

Cited By ~ 74

Author(s):

Brian P. Chadwick ◽

Huntington F. Willard

Keyword(s):

Cell Cycle ◽

X Chromosome ◽

Degradation Pathway ◽

S Phase ◽

Histone H2a ◽

The Core ◽

Inactive X Chromosome ◽

Inactivation Center ◽

Chromatin Proteins ◽

Cycle Dependent

One of several features acquired by chromatin of the inactive X chromosome (Xi) is enrichment for the core histone H2A variant macroH2A within a distinct nuclear structure referred to as a macrochromatin body (MCB). In addition to localizing to the MCB, macroH2A accumulates at a perinuclear structure centered at the centrosome. To better understand the association of macroH2A1 with the centrosome and the formation of an MCB, we investigated the distribution of macroH2A1 throughout the somatic cell cycle. Unlike Xi-specific RNA, which associates with the Xi throughout interphase, the appearance of an MCB is predominantly a feature of S phase. Although the MCB dissipates during late S phase and G2 before reforming in late G1, macroH2A1 remains associated during mitosis with specific regions of the Xi, including at the X inactivation center. This association yields a distinct macroH2A banding pattern that overlaps with the site of histone H3 lysine-4 methylation centered at the DXZ4 locus in Xq24. The centrosomal pool of macroH2A1 accumulates in the presence of an inhibitor of the 20S proteasome. Therefore, targeting of macroH2A1 to the centrosome is likely part of a degradation pathway, a mechanism common to a variety of other chromatin proteins.

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Effects of embryo culture on global pattern of gene expression in preimplantation mouse embryos

Reproduction ◽

10.1530/rep.1.00297 ◽

2004 ◽

Vol 128 (3) ◽

pp. 301-311 ◽

Cited By ~ 193

Author(s):

Paolo Rinaudo ◽

Richard M Schultz

Keyword(s):

Gene Expression ◽

Preimplantation Embryos ◽

Expression Analysis Systematic Explorer ◽

Cell Stage ◽

Global Pattern ◽

Preimplantation Mouse Embryos ◽

Preimplantation Mouse ◽

Global Patterns ◽

The One

Culture of preimplantation embryos affects gene expression. The magnitude of the effect on the global pattern of gene expression, however, is not known. We compared global patterns of gene expression in blastocysts cultured from the one-cell stage in either Whitten’s medium or KSOM + amino acids (KSOM/AA) with that of blastocysts that developed in vivo, using the Affymetrix MOE430A chip. The analysis revealed that expression of 114 genes was affected after culture in Whitten’s medium, whereas only 29 genes were mis-expressed after culture in KSOM/AA. Expression Analysis Systematic Explorer was used to identify biological and molecular processes that are perturbed after culture and indicated that genes involved in protein synthesis, cell proliferation and transporter function were down-regulated after culture in Whitten’s medium. A common set of genes involved in transporter function was also down-regulated after culture in KSOM/AA. These results provide insights as to why embryos develop better in KSOM/AA than in Whitten’s medium, and highlight the power of microarray analysis to assess global patterns of gene expression.

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X-chromosome reactivation: a concise review

Biochemical Society Transactions ◽

10.1042/bst20210777 ◽

2021 ◽

Author(s):

Alessandra Spaziano ◽

Dr Irene Cantone

Keyword(s):

X Chromosome ◽

X Chromosome Inactivation ◽

Epigenetic Modifications ◽

X Chromosomes ◽

Cell Divisions ◽

Concise Review ◽

Inactive X Chromosome ◽

Silencing Pathways

Mammalian females (XX) silence transcription on one of the two X chromosomes to compensate the expression dosage with males (XY). This process — named X-chromosome inactivation — entails a variety of epigenetic modifications that act synergistically to maintain silencing and make it heritable through cell divisions. Genes along the inactive X chromosome are, indeed, refractory to reactivation. Nonetheless, X-chromosome reactivation can occur alongside with epigenome reprogramming or by perturbing multiple silencing pathways. Here we review the events associated with X-chromosome reactivation during in vivo and in vitro reprogramming and highlight recent efforts in inducing Xi reactivation by molecular perturbations. This provides us with a first understanding of the mechanisms underlying X-chromosome reactivation, which could be tackled for therapeutic purposes.

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