bioRxiv preprint doi: https://doi.org/10.1101/545558; this version posted February 9, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. Dynamic Erasure of Random X-Chromosome Inactivation during iPSC Reprogramming Adrian Janiszewski1,*, Irene Talon1,*, Juan Song1, Natalie De Geest1, San Kit To1, Greet Bervoets2,3, Jean-Christophe Marine2,3, Florian Rambow2,3, Vincent Pasque1,✉. 1 KU Leuven - University of Leuven, Department of Development and Regeneration, Herestraat 49, B-3000 Leuven, Belgium. 2 Laboratory for Molecular Cancer Biology, VIB Center for Cancer Biology 3 Department of Oncology, KU Leuven, Belgium ✉ Correspondence to:
[email protected] (V.P.) * These authors contributed equally Format: Research paper ABSTRACT Background: Induction and reversal of chromatin silencing is critical for successful development, tissue homeostasis and the derivation of induced pluripotent stem cells (iPSCs). X-chromosome inactivation (XCI) and reactivation (XCR) in female cells represent chromosome-wide transitions between active and inactive chromatin states. While XCI has long been studied and provided important insights into gene regulation, the dynamics and mechanisms underlying the reversal of stable chromatin silencing of X-linked genes are much less understood. Here, we use allele- specific transcriptomic approaches to study XCR during mouse iPSC reprogramming in order to elucidate the timing and mechanisms of chromosome-wide reversal of gene silencing. Results: We show that XCR is hierarchical, with subsets of genes reactivating early, late and very late.