Xist recruits the X chromosome to the nuclear lamina to enable chromosome-wide silencing. Mus musculus

Xist orchestrates X chromosome inactivation, a process that entails chromosome-wide silencing and remodeling of the 3-dimensional structure of the X chromosome. Yet, it remains unclear whether these changes in nuclear structure are mediated by Xist and whether they are required for silencing. Here we show that Xist directly interacts with the Lamin B Receptor (LBR), an integral component of the nuclear lamina, and that this interaction is required for Xist-mediated silencing. We show that this interaction recruits the inactive X to the nuclear lamina and by doing so enables Xist to spread to actively transcribed genes across the X. Our results demonstrate that lamina recruitment changes the accessibility of DNA thereby enabling Xist, and its silencing proteins, to spread across the X to silence transcription. Overall design: We examined the genomic localization of the Xist lncRNA using RNA Antisense Purification (RAP) in male mouse ES cells where the endogenous Xist promoter is replaced by a tet-inducible one (pSM33) containing 1) wild-type Xist (WT), 2) LBR binding site deletion Xist (dLBS), 3) dLBS-Xist rescued with LMNB1 (LMNB1Res), 4) LBR CRISPRi knock down (LBRKD), or 5) SHARP CRISPRi knock down (SHARPKD). A-repeat deletion Xist (dA) was obtained from Engreitz et al. (2013) (GSE46918).