LncRNA Jpx induces Xist expression in mice using both trans and cis mechanisms.

Sarah Carmona,Benjamin Lin,Sha Sun,Tristan Chou,Katti Arroyo,Gregory S Barsh

doi:10.1371/journal.pgen.1007378

Abstract

Mammalian X chromosome dosage compensation balances X-linked gene products between sexes and is coordinated by the long noncoding RNA (lncRNA) Xist. Multiple cis and trans-acting factors modulate Xist expression; however, the primary competence factor responsible for activating Xist remains a subject of dispute. The lncRNA Jpx is a proposed competence factor, yet it remains unknown if Jpx is sufficient to activate Xist expression in mice. Here, we utilize a novel transgenic mouse system to demonstrate a dose-dependent relationship between Jpx copy number and ensuing Jpx and Xist expression. By localizing transcripts of Jpx and Xist using RNA Fluorescence in situ Hybridization (FISH) in mouse embryonic cells, we provide evidence of Jpx acting in both trans and cis to activate Xist. Our data contribute functional and mechanistic insight for lncRNA activity in mice, and argue that Jpx is a competence factor for Xist activation in vivo.

Highlights

Mammalian gender is determined by a pair of sex chromosomes, leading to an inherent imbalance of X-linked gene products between the sexes
We developed a novel transgenic mouse system to demonstrate the regulatory mechanisms of long noncoding RNA (lncRNA) Jpx
X-Chromosome Inactivation (XCI) is primarily carried out by a cluster of long noncoding RNA located on the X chromosome in a region known as the X-inactivation center (Xic) [2,3]

Summary

Introduction

Mammalian gender is determined by a pair of sex chromosomes (females are XX while males are XY), leading to an inherent imbalance of X-linked gene products between the sexes. Gene dosage is compensated by X-Chromosome Inactivation (XCI), a process which transcriptionally silences one X chromosome in females during early embryonic development [1]. The master regulator of XCI is the lncRNA Xist, which coordinates X-linked gene silencing by spreading across the future inactive X (Xi) [4,5]. To determine the number of XCI events, the cell counts the number of X chromosomes relative to autosomes–the X:A ratio [9]. When the X:A ratio is disturbed, for example in genetic aneuploidies such as a male XXY (X:A = 2:2), the male cell initiates an XCI event to maintain proper X chromosome dosage [9]. A SelfEnhanced Transport (SET) model has been proposed to describe XCI activation, in which Xist exhibits an ultrasensitive (switch-like) response to a competence factor followed by a selfenhanced positive feedback mechanism to maintain Xist expression at the initiation of XCI [11]

Methods

Results

Conclusion