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Female human primordial germ cells display X-chromosome dosage compensation despite the absence of X-inactivation.

ABSTRACT: X-chromosome dosage compensation in female placental mammals is achieved by X-chromosome inactivation (XCI). Human pre-implantation embryos are an exception, in which dosage compensation occurs by X-chromosome dampening (XCD). Here, we examined whether XCD extends to human prenatal germ cells given their similarities to naive pluripotent cells. We found that female human primordial germ cells (hPGCs) display reduced X-linked gene expression before entering meiosis. Moreover, in hPGCs, both X chromosomes are active and express the long non-coding RNAs X active coating transcript (XACT) and X inactive specific transcript (XIST)-the master regulator of XCI-which are silenced after entry into meiosis. We find that XACT is a hPGC marker, describe XCD associated with XIST expression in hPGCs and suggest that XCD evolved in humans to regulate X-linked genes in pre-implantation embryos and PGCs. Furthermore, we found a unique mechanism of X-chromosome regulation in human primordial oocytes. Therefore, future studies of human germline development must consider the sexually dimorphic X-chromosome dosage compensation mechanisms in the prenatal germline.

SUBMITTER: Chitiashvili T

PROVIDER: S-EPMC7717582 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Female human primordial germ cells display X-chromosome dosage compensation despite the absence of X-inactivation [Female]

Project description:This SuperSeries is composed of the SubSeries listed below.

2020-10-19 | GSE143381 | GEO

Female human primordial germ cells display X-chromosome dosage compensation despite the absence of X-inactivation [Female]

Project description:X chromosome dosage compensation is one of the most important epigenetic events in female mammalian development. Although the mouse has served as the primary model to study how genetic equality is established between male and female mammals, it is now appreciated that these mechanisms are not fully conserved in humans. Using human primordial germ cells (hPGCs) as a model together with single cell RNA-sequencing, in vitro differentiation of hPGC like cells and human embryo attachment culture, we show that X-linked gene expression in female hPGCs is compensated to levels found in female somatic cells though a mechanism related to X chromosome dampening rather than X chromosome inactivation. Loss of dampening and decompensation of both X chromosomes occurs when female hPGCs enter meiosis and is coincident with loss of the long non-coding RNAs XIST and XACT. In contrast, differentiation of male hPGCs results in no change in compensation despite loss of XACT. Taken together, future studies of X-linked gene regulation and function in human germ cell development and fertility must take into account the unique and sexually dimorphic dosage compensation occurring during in the prenatal human germline prior to birth.

2020-10-19 | GSE143380 | GEO

Female human primordial germ cells display X-chromosome dosage compensation despite the absence of X-inactivation [Male]

2020-10-19 | GSE143356 | GEO

Absence of X-chromosome dosage compensation in the primordial germ cells of Drosophila embryos.

Project description:Dosage compensation is a mechanism that equalizes sex chromosome gene expression between the sexes. In Drosophila, individuals with two X chromosomes (XX) become female, whereas males have one X chromosome (XY). In males, dosage compensation of the X chromosome in the soma is achieved by five proteins and two non-coding RNAs, which assemble into the male-specific lethal (MSL) complex to upregulate X-linked genes twofold. By contrast, it remains unclear whether dosage compensation occurs in the germline. To address this issue, we performed transcriptome analysis of male and female primordial germ cells (PGCs). We found that the expression levels of X-linked genes were approximately twofold higher in female PGCs than in male PGCs. Acetylation of lysine residue 16 on histone H4 (H4K16ac), which is catalyzed by the MSL complex, was undetectable in these cells. In male PGCs, hyperactivation of X-linked genes and H4K16ac were induced by overexpression of the essential components of the MSL complex, which were expressed at very low levels in PGCs. Together, these findings indicate that failure of MSL complex formation results in the absence of X-chromosome dosage compensation in male PGCs.

| S-EPMC7921590 | biostudies-literature

Female human primordial germ cells display X-chromosome dosage compensation despite the absence of X-inactivation [Female]

Project description:Female human primordial germ cells display X-chromosome dosage compensation despite the absence of X-inactivation [Female]

| PRJNA600258 | ENA

Female human primordial germ cells display X-chromosome dosage compensation despite the absence of X-inactivation [Female]

Project description:Female human primordial germ cells display X-chromosome dosage compensation despite the absence of X-inactivation [Female]

| PRJNA600254 | ENA

Female human primordial germ cells display X-chromosome dosage compensation despite the absence of X-inactivation [Male]

Project description:Female human primordial germ cells display X-chromosome dosage compensation despite the absence of X-inactivation [Male]

| PRJNA600212 | ENA

Mammalian X chromosome inactivation evolved as a dosage-compensation mechanism for dosage-sensitive genes on the X chromosome.

Project description:How and why female somatic X-chromosome inactivation (XCI) evolved in mammals remains poorly understood. It has been proposed that XCI is a dosage-compensation mechanism that evolved to equalize expression levels of X-linked genes in females (2X) and males (1X), with a prior twofold increase in expression of X-linked genes in both sexes ("Ohno's hypothesis"). Whereas the parity of X chromosome expression between the sexes has been clearly demonstrated, tests for the doubling of expression levels globally along the X chromosome have returned contradictory results. However, changes in gene dosage during sex-chromosome evolution are not expected to impact on all genes equally, and should have greater consequences for dosage-sensitive genes. We show that, for genes encoding components of large protein complexes (? 7 members)--a class of genes that is expected to be dosage-sensitive--expression of X-linked genes is similar to that of autosomal genes within the complex. These data support Ohno's hypothesis that XCI acts as a dosage-compensation mechanism, and allow us to refine Ohno's model of XCI evolution. We also explore the contribution of dosage-sensitive genes to X aneuploidy phenotypes in humans, such as Turner (X0) and Klinefelter (XXY) syndromes. X aneuploidy in humans is common and is known to have mild effects because most of the supernumerary X genes are inactivated and not affected by aneuploidy. Only genes escaping XCI experience dosage changes in X-aneuploidy patients. We combined data on dosage sensitivity and XCI to compute a list of candidate genes for X-aneuploidy syndromes.

| S-EPMC3325647 | biostudies-literature

Clinical Epigenetic Therapies Disrupt Sex Chromosome Dosage Compensation in Human Female Cells.

Project description:Sex chromosome gene dosage compensation is required to ensure equivalent levels of X-linked gene expression between males (46, XY) and females (46, XX). To achieve similar expression, X-chromosome inactivation (XCI) is initiated in female cells during early stages of embryogenesis. Within each cell, either the maternal or paternal X chromosome is selected for whole chromosome transcriptional silencing, which is initiated and maintained by epigenetic and chromatin conformation mechanisms. With the emergence of small-molecule epigenetic inhibitors for the treatment of disease, such as cancer, the epigenetic mechanism underlying XCI may be inadvertently targeted. Here, we test 2 small-molecule epigenetic inhibitors being used clinically, GSK126 (a histone H3 lysine 27 methyltransferase inhibitor) and suberoylanilide hydroxamic acid (a histone deacetylase inhibitor), on their effects of the inactive X (Xi) in healthy human female fibroblasts. The combination of these modifiers, at subcancer therapeutic levels, leads to the inability to detect the repressive H3K27me3 modification characteristic of XCI in the majority of the cells. Importantly, genes positioned near the X-inactivation center (Xic), where inactivation is initiated, exhibit robust expression with treatment of the inhibitors, while genes located near the distal ends of the X chromosome intriguingly exhibit significant downregulation. These results demonstrate that small-molecule epigenetic inhibitors can have profound consequences on XCI in human cells, and they underscore the importance of considering gender when developing and clinically testing small-molecule epigenetic inhibitors, in particular those that target the well-characterized mechanisms of X inactivation.

| S-EPMC6424500 | biostudies-literature

Global analysis of X-chromosome dosage compensation.

Project description:Drosophila melanogaster females have two X chromosomes and two autosome sets (XX;AA), while males have a single X chromosome and two autosome sets (X;AA). Drosophila male somatic cells compensate for a single copy of the X chromosome by deploying male-specific-lethal (MSL) complexes that increase transcription from the X chromosome. Male germ cells lack MSL complexes, indicating that either germline X-chromosome dosage compensation is MSL-independent, or that germ cells do not carry out dosage compensation.To investigate whether dosage compensation occurs in germ cells, we directly assayed X-chromosome transcripts using DNA microarrays and show equivalent expression in XX;AA and X;AA germline tissues. In X;AA germ cells, expression from the single X chromosome is about twice that of a single autosome. This mechanism ensures balanced X-chromosome expression between the sexes and, more importantly, it ensures balanced expression between the single X chromosome and the autosome set. Oddly, the inactivation of an X chromosome in mammalian females reduces the effective X-chromosome dose and means that females face the same X-chromosome transcript deficiency as males. Contrary to most current dosage-compensation models, we also show increased X-chromosome expression in X;AA and XX;AA somatic cells of Caenorhabditis elegans and mice.Drosophila germ cells compensate for X-chromosome dose. This occurs by equilibrating X-chromosome and autosome expression in X;AA cells. Increased expression of the X chromosome in X;AA individuals appears to be phylogenetically conserved.

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