Xist Exon 7 Contributes to the Stable Localization of Xist RNA on the Inactive X-Chromosome.

Norishige Yamada,Minghui Yue,Yuko Hasegawa,Shinichi Nakagawa,Tomofumi Hamada,Yuya Ogawa,Jeannie T Lee

doi:10.1371/journal.pgen.1005430

Abstract

To equalize X-linked gene dosage between the sexes in mammalian females, Xist RNA inactivates one of the two X-chromosomes. Here, we report the crucial function of Xist exon 7 in X-inactivation. Xist exon 7 is the second-largest exon with a well-conserved repeat E in eutherian mammals, but its role is often overlooked in X-inactivation. Although female ES cells with a targeted truncation of the Xist exon 7 showed no significant differences in their Xist expression levels and RNA stability from control cells expressing wild-type Xist, compromised localization of Xist RNA and incomplete silencing of X-linked genes on the inactive X-chromosome (Xi) were observed in the exon 7-truncated mutant cells. Furthermore, the interaction between the mutant Xist RNA and hnRNP U required for localization of Xist RNA to the Xi was impaired in the Xist exon 7 truncation mutant cells. Our results suggest that exon 7 of Xist RNA plays an important role for stable Xist RNA localization and silencing of the X-linked genes on the Xi, possibly acting through an interaction with hnRNP U.

Highlights

In eukaryotes, an overwhelming majority of genomes are transcribed as non-protein-coding RNAs [1,2]
Mouse X inactive-specific transcript (Xist) RNA is commonly organized into 7 exons, with the extensively studied and known important domains of Xist residing within exon 1
Our objective was to clarify the role of this exon in X-inactivation through the use of Xist truncation mutant female ES cells

Summary

Introduction

An overwhelming majority of genomes are transcribed as non-protein-coding RNAs (ncRNAs) [1,2]. A recent paper has shown that the depletion of Xist in murine hematopoietic stem cells after the establishment of X-inactivation leads to a genome-wide aberration in gene expression, especially in the expression of X-linked genes, and an induction of highly aggressive myeloproliferative neoplasm and myelodysplastic syndrome in a female-specific manner [21]. This finding suggests a critical role of Xist in the maintenance phase of Xinactivation to prevent cancer transformation and progression. Proper regulation of Xist is critical in both the initiation and maintenance phases for cell survival, cellular differentiation and development, and the prevention of cancer pathogenesis in mammalian species

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