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Open Access Research article

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

Alexandra M Lopes12*, Paul S Burgoyne3, Andrew Ojarikre3, Julien Bauer2, Carole A Sargent2, António Amorim14 and Nabeel A Affara2

Author affiliations

1 IPATIMUP, Instituto de Patologia e Imunologia Molecular da Universidade do Porto, R Dr Roberto Frias S/N, 4200-465 Porto, Portugal

2 Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK

3 Division of Stem Cell Biology and Developmental Genetics, MRC National Institute for Medical Research, London, NW7 1AA, UK

4 Faculdade de Ciências, Universidade do Porto, 4099-002 Porto, Portugal

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Citation and License

BMC Genomics 2010, 11:82  doi:10.1186/1471-2164-11-82

Published: 1 February 2010

Abstract

Background

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.

Results

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.

Conclusions

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.