Project description:A stochastic differentiation programme shows stepwise separation of cell fate, with initiation of cell-type specific gene expression coupled to global transcriptome changes shared by all cells.
Project description:Stochastic activation of clustered Protocadherin (Pcdh) α, β, and γ genes generates a cell-surface identity code in individual neurons that functions in neural circuit assembly. Here, we show that Pcdhα gene choice involves the activation of an antisense promoter located in the first exon of each Pcdhα alternate gene. Transcription of an antisense long noncoding RNA (lncRNA) from this antisense promoter extends through the sense promoter, leading to DNA demethylation of the CTCF binding sites proximal to each promoter. Demethylation-dependent CTCF binding to both promoters facilitates cohesin-mediated DNA looping with a distal enhancer (HS5-1), locking in the transcriptional state of the chosen Pcdhα gene. Uncoupling DNA demethylation from antisense transcription by Tet3 overexpression in mouse olfactory neurons promotes CTCF binding to all Pcdhα promoters, resulting in proximity-biased DNA looping of the HS5-1 enhancer. Thus, antisense transcription-mediated promoter demethylation functions as a mechanism for distance-independent enhancer/promoter DNA looping to ensure stochastic Pcdhα promoter choice.
Project description:Antigen encounter directs CD4+ T cells to differentiate into T-helper or -regulatory cells. This process focuses the immune response on the invading pathogen and limits tissue damage. Mechanisms that govern -helper versus -regulatory fate remain poorly understood. Here, we show that the E3 ubiquitin ligase Cul5 determines fate selection in CD4+ T cells by regulating IL-4 receptor signaling. Mice lacking Cul5 in T cells developed enhanced Th2 and Th9 inflammation and pathophysiological features of atopic asthma upon allergen exposure. Following T cell activation, Cul5 formed a complex with CIS and pJak1. Loss of Cul5 function resulted in reduced ubiquitylation and increased stability of pJak1, elevated STAT6 activity, and a reduced threshold for IL-4 receptor signaling. In keeping with this, Cul5-deficient T cells deviated from Treg to Th9 differentiation in low IL-4 conditions. These data support that Cul5 promotes a tolerogenic T cell fate choice and reduces susceptibility to allergic asthma.
Project description:The spinal cord and mesodermal tissues of the trunk such as the vertebral column and skeletal musculature derive from neuro-mesodermal progenitors (NMPs). Sox2, Brachyury (T) and Tbx6 have been correlated with NMP potency and lineage choice, however, their exact role and interaction in these processes have not been revealed yet. Here we present a global analysis of NMPs and their descending lineages performed on purified cells from E8.5 wild-type and mutant embryos. We show that T, cooperatively with WNT signaling, controls the progenitor state and the switch towards the mesodermal fate. Sox2 acts antagonistically and promotes neural development. Tbx6 reinforces the mesodermal fate choice, represses the progenitor state and confers paraxial fate commitment. Our findings refine previous models and establish new concepts of the molecular principles of mammalian trunk development comprising NMP maintenance, lineage choice and mesoderm formation.
Project description:During commitment of a multipotent stem or progenitor cell to a particular lineage, a large number of genes alter their expression in a coordinated manner orchestrated by the gene regulatory network (GRN). The constraints imposed by the GRN govern how cells move in the high-dimensional gene expression state space and can be understood as a dynamical system in which phenotypic cell states (cell types) are attractors that stabilize the cell-type characteristic gene expression pattern against molecular noise. Despite insights from various theoretical models, it remains elusive how multipotent cells, when committing to a specific lineage, exit their attractor and enter a new distinct attractor. Here we show, using single-cell resolution monitoring of transcript patterns by qPCR that commitment of multipotent blood progenitor cells to either the erythroid or the myeloid lineage is preceded by a destabilization of the progenitorsâ?? attractor state and a slowing-down of relaxation of cells from outlier states, indicating a critical state transition (â??tipping pointâ??). The high-dimensionality of the system (many genes) and availability of individual trajectories of a large ensemble of systems (many cells) affords a novel signature for critical transition which can be predicted from theory: Decrease of correlation between cells and concomitant increase of correlation between genes as the cell population approaches the tipping point. Consistent with a destabilizing bifurcation that simultaneously opens access to the erythroid and myeloid attractors, differentiation signal for either lineage caused some cells to commit to the â??wrongâ?? fate; moreover providing conflicting signals resulted in a delayed decision at the bifurcation point that however was ultimately resolved by commitment to one fate. These results suggest that the theoretical framework of â??early-warning signsâ?? and critical transitions can be applied to ensembles of high-dimensional systems, offering a formal tool for analyzing single-cell omics data beyond current descriptive computational pattern recognition. Mouse blood progenitor cells (EML cell line) was exposed to EPO, IL-3/GM-CSF or a mixture of both cytokines and gene expression change was measured in sorted subpopulations wrt Sca1 progenitor surface marker expression. In total, there was 4 conditions (including control), three time points (including d0) and 20 samples (10 samples in duplicates) were analyzed. Two independent experiments were performed for each condition. The untreated progenitor cell population was used as control.
Project description:The exit from pluripotency or pluripotent-somatic transition (PST) landmarks an event of mammalian development, and is also a representative cell-fate transition model, but remains largely unresolved. Recently, we reported construction of robust JUN-induced PST completed in one cell cycle and whose dominant regulator SS18/BAFs (Brg1/Brahma-associated factors). However, the transition process in the chromatin architecture and the roles played by BAF are still unknown. Here we report the dynamic changes of chromatin accessibility during JUN-induced PST. Meanwhile, SS18/BAFs mediates PST process by relocating from pluripotent loci to AP-1 associated ones and once compromised, JUN fails to open chromatin and PST will be delayed. Furthermore, we show that the relocation of SS18/BAF partially relays on histone modification H3K27ac, instead of JUN-centric protein-protein interaction. These results reveal the orchestration of master transcription factor, epigenetic machine, and histone modification in the cell fate transition.
Project description:Olfactory sensory neurons (OSNs) transform the stochastic choice of one out of >1000 olfactory receptor (OR) genes into precise and stereotyped axon targeting of OR-specific glomeruli in the olfactory bulb. Here, we show that the PERK arm of the unfolded protein response (UPR) regulates both the glomerular coalescence of like axons, and the specificity of their projections. Subtle differences in OR protein sequences lead to distinct patterns of endoplasmic reticulum (ER) stress during OSN development, converting OR identity into distinct gene expression signatures. We identify the transcription factor Ddit3 as a key effector of PERK signaling that maps OR-dependent ER signaling patterns to the transcriptional regulation of axon guidance and cell adhesion genes, instructing targeting precision. Our results extend the known functions of the UPR from a quality control pathway that protects cells from misfolded proteins, to a sensor of cellular identity that interprets physiological states to direct axon wiring.
Project description:During commitment of a multipotent stem or progenitor cell to a particular lineage, a large number of genes alter their expression in a coordinated manner orchestrated by the gene regulatory network (GRN). The constraints imposed by the GRN govern how cells move in the high-dimensional gene expression state space and can be understood as a dynamical system in which phenotypic cell states (cell types) are attractors that stabilize the cell-type characteristic gene expression pattern against molecular noise. Despite insights from various theoretical models, it remains elusive how multipotent cells, when committing to a specific lineage, exit their attractor and enter a new distinct attractor. Here we show, using single-cell resolution monitoring of transcript patterns by qPCR that commitment of multipotent blood progenitor cells to either the erythroid or the myeloid lineage is preceded by a destabilization of the progenitors’ attractor state and a slowing-down of relaxation of cells from outlier states, indicating a critical state transition (“tipping point”). The high-dimensionality of the system (many genes) and availability of individual trajectories of a large ensemble of systems (many cells) affords a novel signature for critical transition which can be predicted from theory: Decrease of correlation between cells and concomitant increase of correlation between genes as the cell population approaches the tipping point. Consistent with a destabilizing bifurcation that simultaneously opens access to the erythroid and myeloid attractors, differentiation signal for either lineage caused some cells to commit to the “wrong” fate; moreover providing conflicting signals resulted in a delayed decision at the bifurcation point that however was ultimately resolved by commitment to one fate. These results suggest that the theoretical framework of “early-warning signs” and critical transitions can be applied to ensembles of high-dimensional systems, offering a formal tool for analyzing single-cell omics data beyond current descriptive computational pattern recognition.