Project description:X-inactivation is a paradigm of epigenetic transcriptional regulation. Human embryonic stem cells (hESCs) that harbor an inactivated X-chromosome often undergo erosion of X-inactivation upon prolonged culture. Here, we investigate the sources of X-inactivation instability by deriving new primed pluripotent hESC lines. We find that the composition of culture media dramatically influenced the expression of XIST lncRNA, a key regulator of X-inactivation. hESCs cultured in a defined medium stably maintained XIST RNA coating, whereas hESCs cultured in the widely-used mTeSR1 medium lost XIST RNA expression. We pinpointed lithium chloride in mTeSR1 as a cause of XIST RNA loss. The addition of LiCl or inhibitors of glycogen synthase kinase 3 (GSK-3) proteins, which are inhibited by lithium, to the defined hESC culture medium impeded XIST expression. Together, these data may reconcile the observed variations in X-inactivation in hESCs and inform the culture of pluripotent stem cells for disease modeling and regenerative medicine.
Project description:Naïve human embryonic stem cells (hESCs) can be derived from primed hESCs or directly from blastocysts, but their X-chromosome state has remained unresolved. We found that the inactive X-chromosome (Xi) of primed hESCs was reactivated in naïve culture conditions. Similar to cells of the blastocyst, resulting naive cells exhibited two active X-chromosomes with XIST expression and chromosome-wide transcriptional dampening, and initiated XIST-mediated X-inactivation upon differentiation. Both establishment and exit from the naïve state (differentiation) happened via an XIST-negative XaXa intermediate. Together, these findings identify a cell culture system for functionally exploring the two X-chromosome dosage compensation processes in early human development: X-dampening and X-inactivation. Furthermore, the naïve state reset Xi abnormalities of primed hESCs, providing cells better suited for downstream applications. However, naïve hESCs displayed differences to the embryo because XIST expression was predominantly mono-allelic instead of bi-allelic, and X-inactivation was non-random, indicating the need for further culture improvement.
Project description:Two major genetic pathways leading to colorectal carcinoma can well be distinguished; the ‘suppressor pathway’, which is characterized by inactivation of tumor-suppressor genes and the ‘mutator pathway’, which is characterized by microsatellite instability. The purpose of this study is to explore a third putative pathway; microsatellite and chromosome stable colorectal cancer where an alternative cancer-causative mechanism might play a role.
Project description:Naïve human embryonic stem cells (hESCs) can be derived from primed hESCs or directly from blastocysts, but their X-chromosome state has remained unresolved. We found that the inactive X-chromosome (Xi) of primed hESCs was reactivated in naïve culture conditions. Similar to cells of the blastocyst, resulting naive cells exhibited two active X-chromosomes with XIST expression and chromosome-wide transcriptional dampening, and initiated XIST-mediated X-inactivation upon differentiation. Both establishment and exit from the naïve state (differentiation) happened via an XIST-negative XaXa intermediate. Together, these findings identify a cell culture system for functionally exploring the two X-chromosome dosage compensation processes in early human development: X-dampening and X-inactivation. Furthermore, the naïve state reset Xi abnormalities of primed hESCs, providing cells better suited for downstream applications. However, naïve hESCs displayed differences to the embryo because XIST expression was predominantly mono-allelic instead of bi-allelic, and X-inactivation was non-random, indicating the need for further culture improvement.
Project description:Naïve human embryonic stem cells (hESCs) can be derived from primed hESCs or directly from blastocysts, but their X-chromosome state has remained unresolved. We found that the inactive X-chromosome (Xi) of primed hESCs was reactivated in naïve culture conditions. Similar to cells of the blastocyst, resulting naive cells exhibited two active X-chromosomes with XIST expression and chromosome-wide transcriptional dampening, and initiated XIST-mediated X-inactivation upon differentiation. Both establishment and exit from the naïve state (differentiation) happened via an XIST-negative XaXa intermediate. Together, these findings identify a cell culture system for functionally exploring the two X-chromosome dosage compensation processes in early human development: X-dampening and X-inactivation. Furthermore, the naïve state reset Xi abnormalities of primed hESCs, providing cells better suited for downstream applications. However, naïve hESCs displayed differences to the embryo because XIST expression was predominantly mono-allelic instead of bi-allelic, and X-inactivation was non-random, indicating the need for further culture improvement.
Project description:During development, transcriptional and chromatin modification changes co-occur but the order and causality of events often remain unclear. We explore the interrelationship of these processes using the paradigm of X-chromosome inactivation (XCI). We initiate XCI in female, mouse embryonic stem cells by inducing Xist expression and monitor changes in transcription and chromatin by allele-specific TT-seq and ChIP-seq respectively. An unprecedented temporal resolution enabled identification of the earliest chromatin alterations during XCI. We demonstrate that HDAC3 interacts with both NCOR1 and NCOR2 and is pre-bound on the X chromosome where it deacetylates histones to promote efficient gene silencing. We also reveal the choreography of polycomb accumulation following Xist RNA coating, with PRC1-associated H2AK119Ub preceding PRC2-associated H3K27me3. Furthermore, polycomb-associated marks accumulate initially at large, intergenic domains and then spreads into genes but only in the context of gene silencing. Our results provide the hierarchy of chromatin events during XCI and demonstrate that some chromatin changes play key roles in mediating transcriptional silencing.
Project description:In mice, imprinted X-chromosome inactivation (iXCI) of the paternal X in the pre-implantation embryo and extra-embryonic tissues is followed by X-reactivation in the epiblast precursors of the inner cell mass (ICM) of the blastocyst, to facilitate initiation of random XCI (rXCI) in all embryonic tissues. RNF12 is an E3 ubiquitin-ligase that plays a key role in XCI. RNF12 targets pluripotency protein REX1 for degradation to initiate rXCI in embryonic stem cells (ESCs) and loss of the maternal copy of Rnf12 leads to embryonic lethality due to iXCI failure. Here, we show that loss of Rex1 rescues the rXCI phenotype observed in Rnf12-/- ESCs, and that REX1 is the prime target of RNF12 in ESCs. Genetic ablation of Rex1 in Rnf12-/- mice rescues the Rnf12-/- iXCI phenotype, and results in viable and fertile Rnf12-/-:Rex1-/- female mice displaying normal iXCI and rXCI. Our results show that REX1 is the critical target of RNF12 in XCI.