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Transcriptional changes in response to X chromosome dosage in the mouse: implications for X inactivation and the molecular basis of Turner Syndrome.

ABSTRACT: X monosomic mice (39,XO) have a remarkably mild phenotype when compared to women with Turner syndrome (45,XO). The generally accepted hypothesis to explain this discrepancy is that the number of genes on the mouse X chromosome which escape X inactivation, and thus are expressed at higher levels in females, is very small. However this hypothesis has never been tested and only a small number of genes have been assayed for their X-inactivation status in the mouse. We performed a global expression analysis in four somatic tissues (brain, liver, kidney and muscle) of adult 40,XX and 39,XO mice using the Illumina Mouse WG-6 v1_1 Expression BeadChip and an extensive validation by quantitative real time PCR, in order to identify which genes are expressed from both X chromosomes.We identified several genes on the X chromosome which are overexpressed in XX females, including those previously reported as escaping X inactivation, as well as new candidates. However, the results obtained by microarray and qPCR were not fully concordant, illustrating the difficulty in ascertaining modest fold changes, such as those expected for genes escaping X inactivation. Remarkably, considerable variation was observed between tissues, suggesting that inactivation patterns may be tissue-dependent. Our analysis also exposed several autosomal genes involved in mitochondrial metabolism and in protein translation which are differentially expressed between XX and XO mice, revealing secondary transcriptional changes to the alteration in X chromosome dosage.Our results support the prediction that the mouse inactive X chromosome is largely silent, while providing a list of the genes potentially escaping X inactivation in rodents. Although the lower expression of X-linked genes in XO mice may not be relevant in the particular tissues/systems which are affected in human X chromosome monosomy, genes deregulated in XO mice are good candidates for further study in an involvement in Turner Syndrome phenotype.

SUBMITTER: Lopes AM

PROVIDER: S-EPMC2837040 | biostudies-literature | 2010 Feb

REPOSITORIES: biostudies-literature

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Transcriptional changes in response to X chromosome dosage in the mouse: implications for X inactivation and the molecular basis of Turner Syndrome.

Lopes Alexandra M AM Burgoyne Paul S PS Ojarikre Andrew A Bauer Julien J Sargent Carole A CA Amorim António A Affara Nabeel A NA

BMC genomics 20100201

<h4>Background</h4>X monosomic mice (39,XO) have a remarkably mild phenotype when compared to women with Turner syndrome (45,XO). The generally accepted hypothesis to explain this discrepancy is that the number of genes on the mouse X chromosome which escape X inactivation, and thus are expressed at higher levels in females, is very small. However this hypothesis has never been tested and only a small number of genes have been assayed for their X-inactivation status in the mouse. We performed a ...[more]

PMID: 20122165

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Project description:What is the burden of X chromosome mosaicism in the occurrence of spontaneous menarche (SM) in Turner syndrome (TS)?SM was significantly associated with X chromosome mosaicism in the TS patients; a mosaicism with around 10% euploid cell line may predict spontaneous pubertal development when determined by molecular-cytogenetic techniques on uncultivated tissues.Spontaneous puberty can be observed in a minority of patients with TS, more frequently, but not exclusively, in those with a high level of 46,XX/45,X mosaicism at standard karyotype. The genetic mechanisms contributing to ovarian function in TS patients are still not determined. However, submicroscopic X-linked and autosomal copy number variations (CNVs) have recently emerged as an important genetic risk category for premature ovarian insufficiency and may be involved in modulating the TS ovarian phenotype.A group of 40 patients with a diagnosis of TS at conventional karyotyping participated in the study; 6 patients had SM and 34 patients had primary amenorrhoea (PA). All clinical data and the patients' DNA samples were collected over the years at a single paediatric clinic.The patients' samples were used to perform both genetic (Copy Number Assay) and molecular-cytogenetic (array-CGH and iFISH, interphase-FISH) analyses in order to evaluate the X chromosome mosaicism rate and to detect possible rare CNVs of genes with a known or predicted role in female fertility.All TS patients showed variable percentages of the 46,XX lineage, but these percentages were higher in the SM group (P < 0.01). A mosaicism around 10% for the euploid cell line may predict spontaneous pubertal development when determined by molecular-cytogenetic techniques performed in uncultivated tissues. A few CNVs involving autosomal and X-linked ovary-related loci were identified by array-CGH analysis and confirmed by real-time quantitative PCR, including a BMP15 gene duplication at Xp11.22, a deletion interrupting the PAPPA gene at 9q33.1, and an intragenic duplication involving the PDE8A gene at 15q25.3.This is a pilot study on a relatively small sample size and confirmation in larger TS cohorts may be required. The ovarian tissue could not be studied in any patients and in a subgroup of patients, the mosaicism was estimated in tissues of different embryonic origin.The combined determination of X chromosome mosaicism by molecular and molecular-cytogenetic techniques may become useful for the prediction of SM in TS. The detection of CNVs in both X-linked and autosomal ovary-related genes further suggests gene dosage as a relevant mechanism contributing to the ovarian phenotype of TS patients. These CNVs may pinpoint novel candidates relevant to female fertility and generate further insights into the mechanisms contributing to ovarian function.This study was funded by Telethon Foundation (grant no: GGP09126 to L.P.), the Italian Ministry of the University and Research (grant number: 2006065999 to P.F.) and a Ministry of Health grant 'Ricerca Corrente' to IRCCS Istituto Auxologico Italiano (grant number: 08C704-2006). The authors have no conflict of interest to declare.

Project description:Background: In both Turner syndrome (TS) and Klinefelter syndrome (KS) copy number aberrations of the X chromosome lead to various developmental symptoms. To date there has not been a comprehensive and directly comparative analysis of TS vs. KS regarding the changes on the molecular level Methods: We analyzed gene expression patterns with RNA-Seq and DNA methylation patterns with the CpGiant assay in lymphocytes, and chromatin conformation with in situ Hi-C in lymphoblastoid cell lines, from TS and KS patients together with their same gender controls. Results: In TS, differentially expressed escape genes were downregulated but differentially expressed inactive genes were upregulated. In KS, differentially expressed escape genes were upregulated while inactive genes appeared unchanged. Interestingly, 81 differentially expressed genes (DEGs) were associated with both TS and KS, and uniformly displayed expression changes into opposite directions. DEGs on the X chromosome and the autosomes were coexpressed in both TS and KS, indicating that there are molecular ripple effects of the changes in X chromosome dosage that extend to autosomes. Four potentially candidate genes (RPS4X, SEPT6, NKRF and CX0rf57) for KS were identified on Xq. Broad hypomethylation of the X chromosome is observed in TS whereas hypermethylation of chromosome X is present in KS. Only promoters of inactive genes were differentially methylated in both TS and KS while escape genes remained unchanged. The intrachromosomal contact map of the X chromosome in TS was partitioned into two superdomains and exhibited the structure of an active X chromosome. Conclusions: Components of the molecular basis of TS and KS were identified on the levels of the transcriptome and the epigenome, with candidate central genes on Xp for TS and on Xq for KS. The discovery of shared DEGs indicates the existence of common molecular mechanisms for gene regulation in TS and KS that are transmitting the gene dosage changes to the transcriptome.

Dataset Information

Transcriptional changes in response to X chromosome dosage in the mouse: implications for X inactivation and the molecular basis of Turner Syndrome.

Publications

Transcriptional changes in response to X chromosome dosage in the mouse: implications for X inactivation and the molecular basis of Turner Syndrome.

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