Mediator Condensates Localize Signaling Factors to Key Cell Identity Genes

The gene expression programs that define the identity of each cell are controlled by master transcription factors (TFs) that bind cell-type-specific enhancers, as well as signaling factors, which bring extracellular stimuli to these enhancers. Recent studies have revealed that master TFs form phase-separated condensates with the Mediator coactivator at super-enhancers. Here, we present evidence that signaling factors for the WNT, TGF-β, and JAK/STAT pathways use their intrinsically disordered regions (IDRs) to enter and concentrate in Mediator condensates at super-enhancers. We show that the WNT coactivator β-catenin interacts both with components of condensates and DNA-binding factors to selectively occupy super-enhancer-associated genes. We propose that the cell-type specificity of the response to signaling is mediated in part by the IDRs of the signaling factors, which cause these factors to partition into condensates established by the master TFs and Mediator at genes with prominent roles in cell identity

Linking Biomolecular Condensates to Disease and Therapeutic Development

The cell is compartmentalized into membrane-bound and membraneless organelles that organize and regulate key cellular functions. Over the past decade, growing evidence supports the notion that membraneless organelles, called biomolecular condensates, compartmentalize biomolecules – proteins and nucleic acids – involved in shared cellular processes through a biophysical process called phase separation. Biomolecular condensates have distinct physicochemical properties dependent on the molecular features and interactions of constituent biomolecules. Diseaseassociated mutations in individual biomolecules that compose condensates can alter condensate physicochemical properties. In addition, key drug targets have been identified as components of condensates. This thesis examines biomolecular condensates in disease and therapeutic development. We find that condensate-promoting features in condensate-forming proteins can be mapped and leveraged to build a resource cataloging mutations that likely contribute to condensate dysregulation in human diseases (Banani et al., 2022). Pathogenic mutations in condensate-promoting features span diverse disease classes across both Mendelian diseases and cancers. FDA-approved small molecule therapeutics interact with condensates, selectively partitioning into some condensates and not others (Klein et al., 2020). Selective partitioning of small molecules has broad implications for drug therapeutic activity and resistance. These findings demonstrate the need to integrate condensate-based models in our study of disease and therapeutic development – an effort which will generate novel pathogenic mechanistic hypotheses and improved drug design for human diseases.Ph.D

Mediator Condensates Localize Signaling Factors to Key Cell Identity Genes

The gene expression programs that define the identity of each cell are controlled by master transcription factors (TFs) that bind cell-type-specific enhancers, as well as signaling factors, which bring extracellular stimuli to these enhancers. Recent studies have revealed that master TFs form phase-separated condensates with the Mediator coactivator at super-enhancers. Here, we present evidence that signaling factors for the WNT, TGF-β, and JAK/STAT pathways use their intrinsically disordered regions (IDRs) to enter and concentrate in Mediator condensates at super-enhancers. We show that the WNT coactivator β-catenin interacts both with components of condensates and DNA-binding factors to selectively occupy super-enhancer-associated genes. We propose that the cell-type specificity of the response to signaling is mediated in part by the IDRs of the signaling factors, which cause these factors to partition into condensates established by the master TFs and Mediator at genes with prominent roles in cell identity.National Science Foundation (U.S.). (Grant PHY1743900)National Institutes of Health (U.S.) (Grants GM123511, GM117370 and T32CA009172)German Research Foundation Research Fellowship (DE 3069/1-1