Project description:Mammalian primed pluripotent stem cells have been shown to be highly susceptible to cell death stimuli due to their low apoptotic threshold, but how this threshold is regulated remains largely unknown. Here we identify miRNA-mediated regulation as a key mechanism controlling apoptosis in the post-implantation epiblast. Moreover, we find that three miRNA families, miR-20, miR-92 and miR-302, control the mitochondrial apoptotic machinery by fine-tuning the levels of expression of the pro-apoptotic protein BIM. These families therefore represent an essential buffer needed to maintain cell survival in stem cells that are not only primed for differentiation but also for cell death. We used microarrays to compare the gene expression profiles of Dicer conditional Epiblast stem cells (Dicer fx/fx EpiSCs, used as control cells) and Dicer deleted epiblast stem cells (Dicer-/- EpiSCs) five days after the induction of Dicer deletion
Project description:Mammalian primed pluripotent stem cells have been shown to be highly susceptible to cell death stimuli due to their low apoptotic threshold, but how this threshold is regulated remains largely unknown. Here we identify miRNA-mediated regulation as a key mechanism controlling apoptosis in the post-implantation epiblast. Moreover, we find that three miRNA families, miR-20, miR-92 and miR-302, control the mitochondrial apoptotic machinery by fine-tuning the levels of expression of the pro-apoptotic protein BIM. These families therefore represent an essential buffer needed to maintain cell survival in stem cells that are not only primed for differentiation but also for cell death. We used microarrays to compare the gene expression profiles of Dicer conditional Epiblast stem cells (Dicer fx/fx EpiSCs, used as control cells) and Dicer deleted epiblast stem cells (Dicer-/- EpiSCs) five days after the induction of Dicer deletion Dicer fx/fx EpiSCs were left untreated (control cells) or treated with 0.3uM of 4-OH-Tamoxifen for three days and without Tamoxifen for two further days, until day 5 when RNA was extracted and used for microarray analysis. Three independent deletion experiments including a Dicer fx/fx sample and a Dicer -/- sample were analyzed as biological replicates.
Project description:Pluripotency is highly dynamic and progresses through a continuum of pluripotent stem-cell states. The two states that bookend the pluripotency continuum, naïve and primed, are well characterized, but our understanding of the intermediate states and transitions between them remain incomplete. Here, we dissect the dynamics of pluripotent state transitions underlying pre- to post-implantation epiblast differentiation. Through comprehensive mapping of the proteome, phosphoproteome, transcriptome, and epigenome of embryonic stem cells transitioning from naïve to primed pluripotency, we find that rapid, acute, and widespread changes to the phosphoproteome precede ordered changes to the epigenome, transcriptome, and proteome. Reconstruction of kinase-substrate networks reveals signaling cascades, dynamics, and crosstalk. Distinct waves of global proteomic changes mark discrete phases of pluripotency, with cell state-specific surface markers tracking pluripotent state transitions. Our data provide new insights into the multi-layered control of the phased progression of pluripotency and a foundation for modeling mechanisms regulating pluripotent state transitions (www.stemcellatlasorg).
Project description:Pluripotent stem cells are defined by their self-renewal capacity, which is the ability of the stem cells to proliferate indefinitely while maintaining the pluripotent identity essential for their ability to differentiate into any somatic cell lineage. However, understanding the mechanisms that control stem cell fitness versus the pluripotent cell identity is challenging. To investigate the interplay between these two aspects of pluripotency, we performed four parallel genome-scale CRISPR-Cas9 loss-of-function screens interrogating stem cell fitness in hPSC self-renewal conditions, and the dissolution of the primed pluripotency identity during early differentiation. Comparative analyses led to the discovery of genes with distinct roles in pluripotency regulation, including mitochondrial and metabolism regulators crucial for stem cell fitness, and chromatin regulators that control pluripotent identity during early differentiation. We further discovered a core set of factors that control both stem cell fitness and pluripotent identity, including a network of chromatin factors that safeguard pluripotency. Our unbiased and systematic screening and comparative analyses disentangle two interconnected aspects of pluripotency, provide rich datasets for exploring pluripotent cell identity versus cell fitness, and offer a valuable model for categorizing gene function in broad biological contexts.
Project description:T cells that encounter self-antigens after exiting the thymus avert autoimmunity through peripheral tolerance. Pathways for this include an unresponsive state known as anergy, clonal deletion, and T regulatory (Treg) cell induction. The transcription factor cues and kinetics that guide distinct peripheral tolerance outcomes remain unclear. Here, we found that anergic T cells are epigenetically primed for regulation by the non-classical AP-1 family member BATF. Tolerized BATF-deficient CD4+ T cells were resistant to anergy induction and instead underwent clonal deletion due to pro-apoptotic BIM (Bcl2l11) upregulation. During prolonged antigen exposure, BIM de-repression resulted in fewer PD-1+ conventional T cells as well as loss of peripherally-induced FOXP3+ Treg cells. Simultaneous Batf and Bcl2l11 knockdown meanwhile restored anergic T cell survival and Treg cell maintenance. The data identify the AP-1 nuclear factor BATF as a dominant driver of sustained T cell anergy and illustrate a mechanism for divergent peripheral tolerance fates.
Project description:T cells that encounter self-antigens after exiting the thymus avert autoimmunity through peripheral tolerance. Pathways for this include an unresponsive state known as anergy, clonal deletion, and T regulatory (Treg) cell induction. The transcription factor cues and kinetics that guide distinct peripheral tolerance outcomes remain unclear. Here, we found that anergic T cells are epigenetically primed for regulation by the non-classical AP-1 family member BATF. Tolerized BATF-deficient CD4+ T cells were resistant to anergy induction and instead underwent clonal deletion due to pro-apoptotic BIM (Bcl2l11) upregulation. During prolonged antigen exposure, BIM de-repression resulted in fewer PD-1+ conventional T cells as well as loss of peripherally-induced FOXP3+ Treg cells. Simultaneous Batf and Bcl2l11 knockdown meanwhile restored anergic T cell survival and Treg cell maintenance. The data identify the AP-1 nuclear factor BATF as a dominant driver of sustained T cell anergy and illustrate a mechanism for divergent peripheral tolerance fates.
Project description:Peripheral tolerance induction is critical for the maintenance of self-tolerance and can be mediated by immunoregulatory T cells or by direct induction of T cell anergy or deletion. While the molecular processes underlying anergy have been extensively studied, little is known about the molecular basis for peripheral T cell deletion. Here, we determined the gene expression signature of peripheral CD8+ T cells undergoing deletional tolerance, relative to those undergoing immunogenic priming or lymphopenia-induced proliferation. From these data, we report the first detailed molecular signature of cells undergoing deletion. Consistent with defective cytolysis, these cells exhibited deficiencies in granzyme up-regulation. Furthermore, they showed antigen-driven Bcl-2 down-regulation and early up-regulation of the pro-apoptotic protein Bim, consistent with the requirement of this BH3-only protein for peripheral T cell deletion. Bim up-regulation was paralleled by defective IL-7Ra chain re-expression, suggesting that Bim-dependent death may be triggered by loss of IL-7/IL-7R signaling. Finally, we observed parallels in molecular signatures between deletion and anergy suggesting that these tolerance pathways may not be as molecularly distinct as previously surmised. Naïve (CD44lo) OT-I T cells were CFSE labelled and transferred in a model of deletional tolerance (RIP-OVAhi mice), a model of immunity (mice primed with OVA coated splenocytes and LPS) or a model of lymphopenia induced proliferation (Rag-/- mice). 60 hrs (RIP-OVAhi and OVA coated splenocytes) or 5 days (Rag-/-) after transfer, OT-I cells that had undergone two or more divisions as determined by CFSE dilution were sorted, RNA extracted and samples were prepared for hybridisation to Affymetrix microarrays. As a control for naive cells, CFSE labelled OT-I cells were injected into antigen-free B6 mice and the undivided naive cells were sorted after 60 hrs and also used for microarray analysis. Two replicates were prepared for the naive cells, cells from RIP-OVAhi mice and cells from OVA coated splenocyte primed mice, while one replicate was prepared for the cells from Rag-/- mice.