The Implication of Early Chromatin Changes in X Chromosome Inactivation.

During development, the precise relationships between transcription and chromatin modifications often remain unclear. We use the X chromosome inactivation (XCI) paradigm to explore the implication of chromatin changes in gene silencing. Using female mouse embryonic stem cells, we initiate XCI by inducing Xist and then monitor the temporal changes in transcription and chromatin by allele-specific profiling. This reveals histone deacetylation and H2AK119 ubiquitination as the earliest chromatin alterations during XCI. We show that HDAC3 is pre-bound on the X chromosome and that, upon Xist coating, its activity is required for efficient gene silencing. We also reveal that first PRC1-associated H2AK119Ub and then PRC2-associated H3K27me3 accumulate initially at large intergenic domains that can then spread into genes only in the context of histone deacetylation and gene silencing. Our results reveal the hierarchy of chromatin events during the initiation of XCI and identify key roles for chromatin in the early steps of transcriptional silencing.

CDK7 kinase activity promotes RNA polymerase II promoter escape by facilitating initiation factor release.

Cyclin-dependent kinase 7 (CDK7), part of the general transcription factor TFIIH, promotes gene transcription by phosphorylating the C-terminal domain of RNA polymerase II (RNA Pol II). Here, we combine rapid CDK7 kinase inhibition with multi-omics analysis to unravel the direct functions of CDK7 in human cells. CDK7 inhibition causes RNA Pol II retention at promoters, leading to decreased RNA Pol II initiation and immediate global downregulation of transcript synthesis. Elongation, termination, and recruitment of co-transcriptional factors are not directly affected. Although RNA Pol II, initiation factors, and Mediator accumulate at promoters, RNA Pol II complexes can also proceed into gene bodies without promoter-proximal pausing while retaining initiation factors and Mediator. Further downstream, RNA Pol II phosphorylation increases and initiation factors and Mediator are released, allowing recruitment of elongation factors and an increase in RNA Pol II elongation velocity. Collectively, CDK7 kinase activity promotes the release of initiation factors and Mediator from RNA Pol II, facilitating RNA Pol II escape from the promoter.

The Cdk8 kinase module regulates interaction of the mediator complex with RNA polymerase II.

The Cdk8 kinase module (CKM) is a dissociable part of the coactivator complex mediator, which regulates gene transcription by RNA polymerase II. The CKM has both negative and positive functions in gene transcription that remain poorly understood at the mechanistic level. In order to reconstitute the role of the CKM in transcription initiation, we prepared recombinant CKM from the yeast Saccharomyces cerevisiae. We showed that CKM bound to the core mediator (cMed) complex, sterically inhibiting cMed from binding to the polymerase II preinitiation complex (PIC) in vitro. We further showed that the Cdk8 kinase activity of the CKM weakened CKM-cMed interaction, thereby facilitating dissociation of the CKM and enabling mediator to bind the PIC in order to stimulate transcription initiation. Finally, we report that the kinase activity of Cdk8 is required for gene activation during the stressful condition of heat shock in vivo but not under steady-state growth conditions. Based on these results, we propose a model in which the CKM negatively regulates mediator function at upstream-activating sequences by preventing mediator binding to the PIC at the gene promoter. However, during gene activation in response to stress, the Cdk8 kinase activity of the CKM may release mediator and allow its binding to the PIC, thereby accounting for the positive function of CKM. This may impart improved adaptability to stress by allowing a rapid transcriptional response to environmental changes, and we speculate that a similar mechanism in metazoans may allow the precise timing of developmental transcription programs.

CDK12 globally stimulates RNA polymerase II transcription elongation and carboxyl-terminal domain phosphorylation.

Cyclin-dependent kinase 12 (CDK12) phosphorylates the carboxyl-terminal domain (CTD) of RNA polymerase II (pol II) but its roles in transcription beyond the expression of DNA damage response genes remain unclear. Here, we have used TT-seq and mNET-seq to monitor the direct effects of rapid CDK12 inhibition on transcription activity and CTD phosphorylation in human cells. CDK12 inhibition causes a genome-wide defect in transcription elongation and a global reduction of CTD Ser2 and Ser5 phosphorylation. The elongation defect is explained by the loss of the elongation factors LEO1 and CDC73, part of PAF1 complex, and SPT6 from the newly-elongating pol II. Our results indicate that CDK12 is a general activator of pol II transcription elongation and indicate that it targets both Ser2 and Ser5 residues of the pol II CTD.

Aberration of the modulatory functions of intronic microRNA hsa-miR-933 on its host gene ATF2 results in type II diabetes mellitus and neurodegenerative disease development.

BACKGROUND: MicroRNAs are ~ 22-nucleotide-long biological modifiers that act as the post-transcriptional modulator of gene expression. Some of them are identified to be embedded within the introns of protein-coding genes, these miRNAs are called the intronic miRNAs. Previous findings state that these intronic miRNAs are co-expressed with their host genes. This co-expression is necessary to maintain the robustness of the biological system. Till to date, only a few experiments are performed discretely to elucidate the functional relationship between few co-expressed intronic miRNAs and their associated host genes. RESULTS: In this study, we have interpreted the underlying modulatory mechanisms of intronic miRNA hsa-miR-933 on its target host gene ATF2 and found that aberration can lead to several disease conditions. A protein-protein interaction network-based approach was adopted, and functional enrichment analysis was performed to elucidate the significantly over-represented biological functions and pathways of the common targets. Our approach delineated that hsa-miR-933 might control the hyperglycemic condition and hyperinsulinism by regulating ATF2 target genes MAP4K4, PRKCE, PEA15, BDNF, PRKACB, and GNAS which can otherwise lead to the development of type II diabetes mellitus. Moreover, we showed that hsa-miR-933 can regulate a target of ATF2, brain-derived neurotrophic factor (BDNF), to modulate the optimal expression of ATF2 in neuron cells to render neuroprotection for the inhibition of neurodegenerative diseases. CONCLUSIONS: Our in silico model provides interesting resources for experimentations in a model organism or cell line for further validation. These findings may extend the common perception of gene expression analysis with new regulatory functionality.