Project description:During development, cells make switch-like decisions to activate the expression of new gene programs leading to lineage specification1. The mechanisms underlying these decisive choices remain unclear2. Here we find that Myocardin (MYOCD), a cardiomyocyte and smooth muscle cell-specific transcriptional coactivator3-6, activates lineage-specific gene programs by concentration-dependent and switch-like formation of nuclear condensates. While compartmentalization of the transcriptional machinery by condensates has been associated with gene activation7,8, directly linking the two processes has been a major challenge for the field9,10. By modeling the natural changes in MYOCD concentration during development, coupled with quantitative fluorescence microscopy, single-cell resolution reporter assays, and cellular differentiation assays, we demonstrate that condensate formation is directly linked to transcriptional activation and lineage specification. During cardiomyocyte and smooth muscle cell differentiation, the formation of MYOCD condensates precedes activation of cell identity genes and these condensates are present at sites of cell identity gene transcription. MYOCD condensates form, activate gene expression, and specify cell state at critical concentration thresholds, dependent upon the C-terminal disordered region of MYOCD. Disrupting condensate formation by manipulating the sequence of this region impairs gene activation which can be rescued by replacing this region with condensate-forming disordered regions from functionally unrelated proteins. These results demonstrate that coactivator condensation at critical concentrations enables switch-like changes in gene expression programs crucial for lineage specification.
Project description:During development, cells make switch-like decisions to activate new gene programs specifying cell lineage. The mechanisms underlying these decisive choices remain unclear. Here we show that the cardiovascular transcriptional coactivator, Myocardin (MYOCD), activates cell identity genes by concentration-dependent and switch-like formation of transcriptional condensates. MYOCD forms such condensates and activates cell identity genes at critical concentration thresholds achieved during smooth muscle cell and cardiomyocyte differentiation. The C-terminal disordered region of MYOCD is necessary and sufficient for condensate formation. Disrupting this region’s ability to form condensates disrupts gene activation. Rescuing condensate formation by replacing this region with disordered regions from functionally unrelated proteins rescues gene activation. Our findings demonstrate that MYOCD condensate formation is required for gene activation during differentiation. We propose that the formation of transcriptional condensates at critical concentrations of cell type-specific regulators provides a molecular switch underlying the activation of key cell identity genes during cell lineage specification.
Project description:The coactivator p300/CBP regulates genes by facilitating the assembly of transcriptional machinery and by acetylating histones and other factors. However, it remains mostly unclear how both functions of p300 are dynamically coordinated during gene control. Here, we showed that p300 appears to orchestrate two functions through the formation of dynamic co-condensates with certain transcription factors (TFs), which is mediated by the interactions between the TF’s trans-activation domain (TAD) and the intrinsically disordered regions (IDRs) of p300. Co-condensation enables spatially defined, all-or-none activation of p300’s catalytic activity, priming the recruitment of other coactivators including Brd4. We further revealed that co-condensation modulates transcriptional initiation rate and burst duration of target genes, underlying nonlinear and cooperative gene regulatory functions. Intriguingly, such modulation is consistent with how p300 shapes transcriptional bursting kinetics globally. Together, complementary lines of evidence suggest a new p300-mediated gene control mechanism, where TF and p300 co-condensation contributes to transcriptional bursting regulation and cooperative gene control.
Project description:deBack2012 - Lineage Specification in Pancreas Development
This model of two neighbouring pancreas precursor cells, describes the exocrine versus endocrine lineage specification process. To account for the tissue scale patterns, this couplet model has been extended to hundreds of coupled cells.
This model is described in the article:
On the role of lateral stabilization during early patterning in the pancreas
de Back W., Zhou JX, Brusch L
J. R. Soc. Interface 6 February 2013 vol. 10 no. 79 20120766
Abstract:
The cell fate decision of multi-potent pancreatic progenitor cells between the exocrine and endocrine lineages is regulated by Notch signalling, mediated by cell–cell interactions. However, canonical models of Notch-mediated lateral inhibition cannot explain the scattered spatial distribution of endocrine cells and the cell-type ratio in the developing pancreas. Based on evidence from acinar-to-islet cell transdifferentiation in vitro, we propose that lateral stabilization, i.e. positive feedback between adjacent progenitor cells, acts in parallel with lateral inhibition to regulate pattern formation in the pancreas. A simple mathematical model of transcriptional regulation and cell–cell interaction reveals the existence of multi-stability of spatial patterns whose simultaneous occurrence causes scattering of endocrine cells in the presence of noise. The scattering pattern allows for control of the endocrine-to-exocrine cell-type ratio by modulation of lateral stabilization strength. These theoretical results suggest a previously unrecognized role for lateral stabilization in lineage specification, spatial patterning and cell-type ratio control in organ development.
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Project description:ZNF462 haploinsufficiency is linked to Weiss-Kruszka Syndrome, a genetic disorder characterized by neurodevelopmental defects including Autism. Though conserved in vertebrates and essential for embryonic development the molecular functions of ZNF462 remain unclear. We identified its murine homolog ZFP462 in a screen for mediators of epigenetic gene silencing. Here, we show that ZFP462 safeguards neural lineage specification of mouse embryonic stem cells (ESCs) by targeting the H3K9-specific histone methyltransferase complex G9A/GLP to silence mesoendodermal genes. ZFP462 binds to transposable elements (TEs) that are potential enhancers harboring ESC-specific transcription factor (TF) binding sites. Recruiting G9A/GLP, ZFP462 seeds heterochromatin, restricting TF binding. Loss of ZFP462 in ESCs results in increased chromatin accessibility at target sites and ectopic expression of mesoendodermal genes. Taken together, ZFP462 confers lineage- and locus-specificity to the broadly expressed epigenetic regulator G9A/GLP. Our results suggest that aberrant activation of lineage non-specific genes in the neuronal lineage underlies ZNF462-associated neurodevelopmental pathology.