Dataset Information

Escape from X chromosome inactivation is an intrinsic property of the Jarid1c locus.

ABSTRACT: Although most genes on one X chromosome in mammalian females are silenced by X inactivation, some "escape" X inactivation and are expressed from both active and inactive Xs. How these escape genes are transcribed from a largely inactivated chromosome is not fully understood, but underlying genomic sequences are likely involved. We developed a transgene approach to ask whether an escape locus is autonomous or is instead influenced by X chromosome location. Two BACs carrying the mouse Jarid1c gene and adjacent X-inactivated transcripts were randomly integrated into mouse XX embryonic stem cells. Four lines with single-copy, X-linked transgenes were identified, and each was inserted into regions that are normally X-inactivated. As expected for genes that are normally subject to X inactivation, transgene transcripts Tspyl2 and Iqsec2 were X-inactivated. However, allelic expression and RNA/DNA FISH indicate that transgenic Jarid1c escapes X inactivation. Therefore, transgenes at 4 different X locations recapitulate endogenous inactive X expression patterns. We conclude that escape from X inactivation is an intrinsic feature of the Jarid1c locus and functionally delimit this escape domain to the 112-kb maximum overlap of the BACs tested. Additionally, although extensive chromatin differences normally distinguish active and inactive loci, unmodified BACs direct proper inactive X expression patterns, establishing that primary DNA sequence alone, in a chromosome position-independent manner, is sufficient to determine X chromosome inactivation status. This transgene approach will enable further dissection of key elements of escape domains and allow rigorous testing of specific genomic sequences on inactive X expression.

SUBMITTER: Li N

PROVIDER: S-EPMC2579377 | biostudies-literature | 2008 Nov

REPOSITORIES: biostudies-literature

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Escape from X chromosome inactivation is an intrinsic property of the Jarid1c locus.

Li Nan N Carrel Laura L

Proceedings of the National Academy of Sciences of the United States of America 20081029 44

Although most genes on one X chromosome in mammalian females are silenced by X inactivation, some "escape" X inactivation and are expressed from both active and inactive Xs. How these escape genes are transcribed from a largely inactivated chromosome is not fully understood, but underlying genomic sequences are likely involved. We developed a transgene approach to ask whether an escape locus is autonomous or is instead influenced by X chromosome location. Two BACs carrying the mouse Jarid1c gene ...[more]

PMID: 18971342

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Project description:BackgroundX-chromosome inactivation (XCI) is the epigenetic inactivation of one of two X chromosomes in XX eutherian mammals. The inactive X chromosome is the result of multiple silencing pathways that act in concert to deposit chromatin changes, including DNA methylation and histone modifications. Yet over 15% of genes escape or variably escape from inactivation and continue to be expressed from the otherwise inactive X chromosome. To the extent that they have been studied, epigenetic marks correlate with this expression.ResultsUsing publicly available data, we compared XCI status calls with DNA methylation, H3K4me1, H3K4me3, H3K9me3, H3K27ac, H3K27me3 and H3K36me3. At genes subject to XCI we found heterochromatic marks enriched, and euchromatic marks depleted on the inactive X when compared to the active X. Genes escaping XCI were more similar between the active and inactive X. Using sample-specific XCI status calls, we found some marks differed significantly with variable XCI status, but which marks were significant was not consistent between genes. A model trained to predict XCI status from these epigenetic marks obtained over 75% accuracy for genes escaping and over 90% for genes subject to XCI. This model made novel XCI status calls for genes without allelic differences or CpG islands required for other methods. Examining these calls across a domain of variably escaping genes, we saw XCI status vary across individual genes rather than at the domain level. Lastly, we compared XCI status calls to genetic polymorphisms, finding multiple loci associated with XCI status changes at variably escaping genes, but none individually sufficient to induce an XCI status change.ConclusionThe control of expression from the inactive X chromosome is multifaceted, but ultimately regulated at the individual gene level with detectable but limited impact of distant polymorphisms. On the inactive X, at silenced genes euchromatic marks are depleted while heterochromatic marks are enriched. Genes escaping inactivation show a less significant enrichment of heterochromatic marks and depletion of H3K27ac. Combining all examined marks improved XCI status prediction, particularly for genes without CpG islands or polymorphisms, as no single feature is a consistent feature of silenced or expressed genes.

Dataset Information

Escape from X chromosome inactivation is an intrinsic property of the Jarid1c locus.

Publications

Escape from X chromosome inactivation is an intrinsic property of the Jarid1c locus.

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