Imprinted X chromosome inactivation: evolution of mechanisms in distantly related mammals

Shafagh A. Waters; Paul D. Waters; Shafagh A. Waters; Paul D. Waters

doi:10.3934/genet.2015.2.110

AIMS Genetics

2015, Volume 2, Issue 2: 110-126. doi: 10.3934/genet.2015.2.110

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Review Special Issues

Imprinted X chromosome inactivation: evolution of mechanisms in distantly related mammals

Shafagh A. Waters ^,,
Paul D. Waters

School of Biotechnology & Biomolecular Sciences, Faculty of Science, UNSW Australia, Sydney, NSW 2052, Australia

Received: 03 November 2014 Accepted: 01 March 2015 Published: 04 March 2015

In females, X chromosome inactivation (XCI) ensures transcriptional silencing of one of the two Xs (either in a random or imprinted fashion) in somatic cells. Comparing this silencing between species has offered insight into different mechanisms of X inactivation, providing clues into the evolution of this epigenetic process in mammals. Long-noncoding RNAs have emerged as a common theme in XCI of therian mammals (eutherian and marsupial). Eutherian X inactivation is regulated by the noncoding RNA product of XIST, within a cis-acting master control region called the X inactivation center (XIC). Marsupials XCI is XIST independent. Instead, XCI is controlled by the long-noncoding RNA Rsx, which appears to be a functional analog of the eutherian XIST gene, insofar that its transcript coats the inactive X and represses activity of genes in cis. In this review we discuss XCI in eutherians, and contrast imprinted X inactivation in mouse and marsupials. We provide particular focus on the evolution of genomic elements that confer the unique epigenetic features that characterize the inactive X chromosome.
- X chromosome,
- XCI,
- imprinting,
- noncoding RNA,
- epigenetic regulation,
- marsupial,
- XIST,
- RSX,
- X inactivation center,
- evolution
Citation: Shafagh A. Waters, Paul D. Waters. Imprinted X chromosome inactivation: evolution of mechanisms in distantly related mammals[J]. AIMS Genetics, 2015, 2(2): 110-126. doi: 10.3934/genet.2015.2.110

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Abstract

In females, X chromosome inactivation (XCI) ensures transcriptional silencing of one of the two Xs (either in a random or imprinted fashion) in somatic cells. Comparing this silencing between species has offered insight into different mechanisms of X inactivation, providing clues into the evolution of this epigenetic process in mammals. Long-noncoding RNAs have emerged as a common theme in XCI of therian mammals (eutherian and marsupial). Eutherian X inactivation is regulated by the noncoding RNA product of XIST, within a cis-acting master control region called the X inactivation center (XIC). Marsupials XCI is XIST independent. Instead, XCI is controlled by the long-noncoding RNA Rsx, which appears to be a functional analog of the eutherian XIST gene, insofar that its transcript coats the inactive X and represses activity of genes in cis. In this review we discuss XCI in eutherians, and contrast imprinted X inactivation in mouse and marsupials. We provide particular focus on the evolution of genomic elements that confer the unique epigenetic features that characterize the inactive X chromosome.

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