DDR efficiency could increase the yield of induced pluripotent stem cells (iPSC) upon reprogramming from somatic cells. The epigenetic mechanisms governing DDR during iPSC reprogramming are not completely understood. The goal was to evaluate the splicing isoforms of histone variant macroH2A1, macroH2A1.1, and macroH2A1.2, as potential regulators of DDR during iPSC reprogramming.

Together with groups from Italy (Rome), United Kingdom (Liverpool), Estonia (Tallinn) and Czech Republic (Brno), researchers from the TRANSTEM team used GFP-Trap one-step isolation of mtagGFP-macroH2A1.1 or mtagGFP-macroH2A1.2 fusion proteins from overexpressing human cell lines, followed by liquid chromatography-tandem mass spectrometry analysis, to uncover macroH2A1.1 exclusive interaction with Poly-ADP Ribose Polymerase 1 (PARP1) and X-ray cross-complementing protein 1 (XRCC1). MacroH2A1.1 overexpression in U2OS-GFP reporter cells enhanced specifically nonhomologous end joining (NHEJ) repair pathway, while macroH2A1.1 knock-out (KO) mice showed an impaired DDR capacity. The exclusive interaction of macroH2A1.1, but not macroH2A1.2, with PARP1/XRCC1, was confirmed in human umbilical vein endothelial cells (HUVEC) undergoing reprogramming into iPSC through episomal vectors. In HUVEC, macroH2A1.1 overexpression activated transcriptional programs that enhanced DDR and reprogramming. Consistently, macroH2A1.1 but not macroH2A1.2 overexpression improved iPSC reprogramming.

MacroH2A1 splicing isoform macroH2A1.1 was proposed as a promising epigenetic target to improve iPSC genome stability and therapeutic potential.

Fulltext citation: Giallongo S, Reháková D, Biagini T, Lo Re O, Raina P, Lochmanová G, Zdráhal Z, Resnick I, Pata P, Pata I, Mistrík M, de Magalhães JP, Mazza T, Koutná I, Vinciguerra M. Histone Variant macroH2A1.1 Enhances Nonhomologous End Joining-dependent DNA Double-strand-break Repair and Reprogramming Efficiency of Human iPSCs. Stem Cells, Volume 40, Issue 1, January 2022, Pages 35–48, https://doi.org/10.1093/stmcls/sxab004

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