biostudies-literatureGeneroso SFHHS | National Institutes of Healthspanish ministry of science and innovationHHS | NIH | Office of Extramural Research, National Institutes of HealthNIDDK NIH HHSNIMH NIH HHSNIGMS NIH HHSe2213810120https://www.ebi.ac.uk/biostudies/studies/S-EPMC9942853biostudies-literatureUnknown120(4)Reactivation of the inactive X chromosome is a hallmark epigenetic event during reprogramming of mouse female somatic cells to induced pluripotent stem cells (iPSCs). This involves global structural remodeling from a condensed, heterochromatic into an open, euchromatic state, thereby changing a transcriptionally inactive into an active chromosome. Despite recent advances, very little is currently known about the molecular players mediating this process and how this relates to iPSC-reprogramming in general. To gain more insight, here we perform a RNAi-based knockdown screen during iPSC-reprogramming of mouse fibroblasts. We discover factors important for X chromosome reactivation (XCR) and iPSC-reprogramming. Among those, we identify the cohesin complex member SMC1a as a key molecule with a specific function in XCR, as its knockdown greatly affects XCR without interfering with iPSC-reprogramming. Using super-resolution microscopy, we find SMC1a to be preferentially enriched on the active compared with the inactive X chromosome and that SMC1a is critical for the decompacted state of the active X. Specifically, depletion of SMC1a leads to contraction of the active X both in differentiated and in pluripotent cells, where it normally is in its most open state. In summary, we reveal cohesin as a key factor for remodeling of the X chromosome from an inactive to an active structure and that this is a critical step for XCR during iPSC-reprogramming.Proceedings of the National Academy of Sciences of the United States of AmericaCohesin controls X chromosome structure remodeling and X-reactivation during mouse iPSC-reprogramming.PMC9942853R01-GM58839BFU2014-55275-PR01 MH118351R01 GM058839R01-MH118351R35 GM137916P30 DK040561Cosma MPNeguembor MVSadreyev RIAudergon PPayer BYabuta YHochedlinger KRicci RBeliveau BJSaitou MBauer MLee JTHershberg EAGeneroso SFKurimoto KfalseCohesin controls X chromosome structure remodeling and X-reactivation during mouse iPSC-reprogramming.Reactivation of the inactive X chromosome is a hallmark epigenetic event during reprogramming of mouse female somatic cells to induced pluripotent stem cells (iPSCs). This involves global structural remodeling from a condensed, heterochromatic into an open, euchromatic state, thereby changing a transcriptionally inactive into an active chromosome. Despite recent advances, very little is currently known about the molecular players mediating this process and how this relates to iPSC-reprogramming in general. To gain more insight, here we perform a RNAi-based knockdown screen during iPSC-reprogramming of mouse fibroblasts. We discover factors important for X chromosome reactivation (XCR) and iPSC-reprogramming. Among those, we identify the cohesin complex member SMC1a as a key molecule with a specific function in XCR, as its knockdown greatly affects XCR without interfering with iPSC-reprogramming. Using super-resolution microscopy, we find SMC1a to be preferentially enriched on the active compared with the inactive X chromosome and that SMC1a is critical for the decompacted state of the active X. Specifically, depletion of SMC1a leads to contraction of the active X both in differentiated and in pluripotent cells, where it normally is in its most open state. In summary, we reveal cohesin as a key factor for remodeling of the X chromosome from an inactive to an active structure and that this is a critical step for XCR during iPSC-reprogramming.2023-01-01T00:00:00Z2023 Jan2025-05-18T12:58:01.214Z2025-05-18T12:58:01.214ZS-EPMC99428533666911310.1073/pnas.2213810120