Ordered chromatin changes and human X chromosome reactivation by cell fusion-mediated pluripotent reprogramming

• Published in: Nature communications Vol. 7; no. 1; pp. 12354 - 12
• Main Authors: Cantone, Irene, Bagci, Hakan, Dormann, Dirk, Dharmalingam, Gopuraja, Nesterova, Tatyana, Brockdorff, Neil, Rougeulle, Claire, Vallot, Celine, Heard, Edith, Chaligne, Ronan, Merkenschlager, Matthias, Fisher, Amanda G.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 10.08.2016; Nature Publishing Group; Nature Portfolio
• Subjects: 13/31; 14/1; 14/32; 38/77; 38/90; 38/91; 42/100; 631/532/2435; 631/532/2442; 631/80/103; Animals; Cell division; Cell Fusion - methods; Cell Line; Cell Nucleus - genetics; Cell Nucleus - metabolism; Cellular Reprogramming - genetics; Chromatin - genetics; Chromosomes, Human, X - genetics; DNA methylation; Epigenesis, Genetic; Epigenetics; Female; Females; Fibroblasts; Genes; Histones - genetics; Humanities and Social Sciences; Humans; Induced Pluripotent Stem Cells - metabolism; Life Sciences; Male; Mice; Mitosis; Mouse Embryonic Stem Cells - metabolism; multidisciplinary; RNA polymerase; RNA, Long Noncoding - genetics; Science; Science (multidisciplinary); Stem cells; X Chromosome Inactivation - genetics; X chromosomes; United Kingdom > UK; France; Paris France
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms12354

Erasure of epigenetic memory is required to convert somatic cells towards pluripotency. Reactivation of the inactive X chromosome (Xi) has been used to model epigenetic reprogramming in mouse, but human studies are hampered by Xi epigenetic instability and difficulties in tracking partially reprogrammed iPSCs. Here we use cell fusion to examine the earliest events in the reprogramming-induced Xi reactivation of human female fibroblasts. We show that a rapid and widespread loss of Xi-associated H3K27me3 and XIST occurs in fused cells and precedes the bi-allelic expression of selected Xi-genes by many heterokaryons (30–50%). After cell division, RNA-FISH and RNA-seq analyses confirm that Xi reactivation remains partial and that induction of human pluripotency-specific XACT transcripts is rare (1%). These data effectively separate pre- and post-mitotic events in reprogramming-induced Xi reactivation and reveal a complex hierarchy of epigenetic changes that are required to reactivate the genes on the human Xi chromosome. Reactivation of the inactive X chromosome (Xi) has modelled epigenetic reprogramming in mouse. Here, by using cell fusion between human female fibroblasts and mouse embryonic stem cells, the authors show a complex hierarchy of epigenetic changes that are required to reactivate the genes on the human Xi chromosome.