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MED26-mediated phase separation regulates erythropoiesis by tuning transcription pausing

ABSTRACT: The Mediator complex plays a pivotal role in various aspects of transcription and development. However, it remains unclear whether individual Mediator subunits play differential roles during the progression of the developmental process. In this study, we found that the protein level of MED26, a subunit in the core Mediator complex, remained relatively abundant in terminal erythropoiesis, while that of most Mediator subunits drastically diminished. MED26 exhibits pronounced phase separation capability, which is essential for erythroid differentiation of primary human erythroblasts. Interestingly, we found that ~60% of chromatin sites with MED26 or MED1 occupancy did not co-localize. Moreover, MED26-enriched loci were associated with RNA polymerase II pausing, and MED26 preferentially interacted with transcription pausing factors, including PAF1, via its TFIIS domain. During erythropoiesis, both the relative abundance of MED26 and the Pausing Index (PI) increased. Erythroid differentiation was promoted by small molecule-induced PI elevation or overexpression of MED26—full-length or the IDR alone—indicating that MED26-associated pausing is necessary for erythropoiesis. In conclusion, this study revealed that MED26 tunes transcription pausing to facilitate erythroid development via a phase separation mechanism.

ORGANISM(S): Homo sapiens

PROVIDER: GSE212374 | GEO | 2025/08/26

REPOSITORIES: GEO

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MED26-mediated phase separation regulates erythropoiesis by tuning transcription pausing

Project description:MED26-mediated phase separation regulates erythropoiesis by tuning transcription pausing

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2011-08-31 | E-GEOD-28715 | biostudies-arrayexpress

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Project description:We investigated modulation of metazoan MED interaction with RNA polymerase II (Pol II) by antagonistic effects of the MED26 subunit and the Cdk8 kinase module (CKM), both of which associate dynamically with MED. Results from in vivo studies point to a general and important role of MED26 in transcription, connected to Pol II recruitment. Analysis of CKM-MED and MED26-MED complexes by cryo-EM and crosslinking-mass spectrometry showed that CKM and MED26 have opposite effects on mMED association with Pol II (blocking and facilitating it, respectively), and revealed that the structural basis for their antagonistic interaction with MED relates to extended intrinsically-disordered regions (IDRs) in MED26 and the CKM subunit MED13 competing for interaction with MED. We found CKM-MED to be the preferred target of nuclear receptors (NRs), whose binding can initiate rearrangements of the MED13 IDR that allow MED26-dependent interaction of CKM-MED with the Pol II carboxy-terminal domain (CTD). Our results suggest that activators might play a critical role independent of MED recruitment, instead “activating” CKM-MED for CTD interaction in a MED26-dependent manner and, thus, controlling the start of preinitiation complex assembly. The presence of an intermediate state in which MED26 and the CTD II can interact with CKM-MED suggests a mechanism for fast, recruitment-independent activation connected to promoter-proximal Pol II pausing, with an activator enabling interaction between the originally inactive CKM-MED and a paused Pol II poised to initiate transcription. We found that CTD interaction with CKM-MED influences the subunit composition of the Tail module and this allostery suggests that the mechanism we propose could apply to non-NR activators targeting Tail subunits.

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RNA Polymerase II pausing temporally coordinates cell cycle progression and erythroid differentiation [NET-seq]

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The role of Mediator and Little Elongation Complex in transcription termination

Project description:Mediator is a coregulatory complex involved in regulating the transcription of Pol II-dependent genes. Metazoan Mediator subunit MED26 functions as a docking site for the ELL/EAF-containing Super Elongation Complex (SEC) and L ittle Elongation Complex (LEC), which regulate the expression of distinct genes. MED26 helps to recruit SEC to protein-coding genes including c-Myc and LEC to small nuclear RNA (snRNA) genes. However, why MED26 takes advantage of SEC or LEC to regulate different claases of genes is unclear. Here, we present evidence that MED26 recruits LEC to support optimal transcription termination at non-polyadenylated genes including snRNA and replication-dependent histone (RDH) genes. Our findings indicate that LEC recruited by MED26 promotes efficient transcription termination by Pol II through interaction with CBC-ARS2 and NELF/DSIF, and then LEC promotes 3’-end processing through the recruitment of Integrator or Heat labile factor to snRNA or RDH genes, respectively.

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Transcription factors activate genes through the phase separation capacity of their activation domains [RNA-seq]

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2018-10-26 | GSE120474 | GEO

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