Project description:RNA Polymerase II transcriptional recycling is an underappreciated mechanism for which the required factors and contributions to overall gene expression levels are poorly understood. We describe an in vitro methodology facilitating unbiased identification of novel RNA Pol II transcriptional recycling factors and quantitative measurement of transcriptional output from recycled transcriptional components. Proof-of-principle experiments identified PAF1 complex components among recycling factors and detected defective transcriptional output from RNA Pol II recycling following PAF1 depletion. Dynamic ChIP-seq confirmed in vivo PAF1 complex cycling through gene bodies with RNA Pol II and recycling back to the transcription start sites, while PAF1 silencing triggered defective RNA Pol II recycling. Prostate tumors exhibited enhanced transcriptional recycling, which was attenuated by antibody-based PAF1 depletion. These findings identify RNA Pol II recycling as a potential target in cancer and demonstrate the assay’s applicability to characterize RNA Pol II recycling in cells and tissues from other disease states.
Project description:Cis-encoded antisense RNAs (asRNAs) are widespread along bacterial transcriptomes. However, the role of the vast majority of these RNAs remains unknown, and there is an ongoing discussion as to what extent these transcripts are the result of transcriptional noise. We show, by comparative transcriptomics of 20 bacterial species and one chloroplast, that the number of asRNAs is exponentially dependent on the genomic AT content, and that expression of asRNA at low levels exerts little impact in terms of energy consumption. A transcription model simulating mRNA and asRNA production indicates that the asRNA regulatory effect is only observed above certain expression thresholds, substantially higher than physiological transcript levels. These predictions were verified experimentally by overexpressing 9 different asRNAs in M. pneumoniae. Our results suggest that most of the antisense transcripts found in bacteria are the consequence of transcriptional noise, arising at spurious promoters throughout the genome.
Project description:The NuA4 histone acetyltransferase (HAT) complex is required for gene specific regulation, cell cycle progression, and DNA repair. Dissection of the 13-subunit complex reveals that the Eaf7 subunit bridges Eaf5 with Eaf3, a H3K36me3-binding chromodomain protein, and this Eaf5/7/3 trimer is anchored to NuA4 through Eaf5. This subcomplex represents a functional module as deletions of these genes create similar phenotypes and a large portion of the trimer exists in a native form outside the NuA4 complex. Gene-specific and genome-wide location analyses indicate that the Eaf5/7/3 trimer correlates with transcription activity and is enriched over the coding region. In agreement with a role in transcription elongation, the Eaf5/7/3 trimer interacts with phosphorylated RNA polymerase II and helps its progression. In addition, loss of Eaf5/7/3 partially suppresses intragenic cryptic transcription arising in set2 mutant cells, suggesting a role in nucleosome destabilization. Such a function is supported by genetic interactions with the FACT histone chaperone. On the other hand, loss of the trimer leads to an increase of replication-independent histone exchange over the coding region of transcribed genes. Taken together, these results lead to a model where Eaf5/7/3 associates with elongating polymerase and is involved in the disassembly of nucleosomes in front of the polymerase, but also in their recycling in its wake.
Project description:The molecular mechanisms underlying the great differences in susceptibility to noise-induced hearing loss (NIHL) exhibited by both humans and laboratory animals are unknown. Using microarray technology, the present study demonstrates that the effects of noise overexposure on the expression of molecules likely to be important to the development of NIHL differ among inbred mice that have distinctive susceptibilities to NIHL including B6.CAST, 129X1/SvJ, and 129S1/SvImJ. The noise-exposure protocol produced, on average, a permanent loss of about 40 dB in sensitivity for auditory brainstem responses in susceptible B6.CAST mice, but no threshold elevations for the two resistant 129S1/SvImJ and 129X1/SvJ substrains. Measurements of noise-induced gene expression changes 6 h after the noise exposure revealed significant alterations in the expression levels of 48 genes in the resistant mice, while by these same criteria, there were seven differentially expressed genes in the susceptible B6.CAST mice. Differentially expressed genes in both groups of mice included subsets of transcription factors. However, only in the resistant mice was there a significant induction of proteins involved in cell-survival pathways such as HSP70, HSP40, p21, GADD45ï¢, Ier3, and Nfï«ï¢iïº. Moreover, increased expression of three of these factors after noise was confirmed at the protein level. Drastically enhanced HSP70, GADD45ï¢, and p21 immunostaining were detected 6 h after the noise exposure in subsets of cells of the lateral wall, spiral limbus, and organ of Corti as well as in cochlear nerve fibers. Upregulation of these proteins after noise exposure likely contributes to the prevalence of survival cellular pathways and thus to the resistance to NIHL that is characteristic of the 129X1/SvJ mice. Experiment Overall Design: Female 10-wk-old mice of the B6.CAST and 129X1/SvJ strains were divided randomly into non-noise control and noise-exposure groups. The non-noise mice served as controls in the gene-profiling experiments to control for the stress induced by experimenter handling and/or confinement of the mice in the noise-exposure chamber that was not directly related to the noise. This mice were in the noise chamber for a sham exposure. In contrast, the ânoiseâ groups were exposed to a 105-dB SPL, 10-kHz octave band of noise for 1 h and sacrificed 6 h after the exposure. Of each of these major groups, eight mice were used for each of three 129X1/SvJ control and three noise-exposed 129X1/SvJ arrays and two B6.CAST control and two noise-exposed B6.CAST arrays. Consequently within each subgroup the arrays are biological replicates.
Project description:Mammalian RNA polymerase II (Pol II) initiation, elongation, termination and reinitiation are well studied, but how Pol II dynamically recycles after the transcription cycle remains unclear. By establishing in vitro and in vivo transcription recycling systems, we find that human Mediator 1 (MED1), when phosphorylated at the mammal-specific threonine 1032 by cyclin-dependent kinase 9, dynamically travels with Pol II throughout the transcribed genes to drive Pol II recycling. Mechanistically, MED1 phosphorylation leads to an increase of recycled Pol II via the molecular bridge of MED31, enhancing mRNA output during the transcription recycling process. Importantly, MED1 phosphorylation increases during prostate cancer progression to the lethal phase, and pharmacological inhibition of CDK9 decreases prostate tumor growth through decreasing MED1 phosphorylation and Pol II recycling. Our findings reveal essential mechanisms underlying Pol II recycling and suggest a neglected, yet fundamental Pol II transcription process for therapeutic intervention.
Project description:Stochastic fluctuations in gene expression (‘noise’) are often considered detrimental but, in many disciplines, fluctuations are exploited for benefit (e.g., dither). We show here that DNA base-excision repair amplifies transcriptional noise to facilitate cellular reprogramming. Specifically, the DNA-repair protein Apex1, which recognizes both naturally occurring and unnatural base modifications, amplifies expression noise while homeostatically maintaining mean-expression levels. This amplified expression noise originates from shorter duration, higher intensity, transcriptional bursts generated by Apex1-mediated DNA supercoiling. The remodeling of DNA topology first impedes and then accelerates transcription to maintain mean levels and this mechanism, which we term Discordant Transcription through Repair (DiThR), potentiates cellular reprogramming and differentiation. Our study reveals a potential functional role for transcriptional fluctuations mediated by DNA base modifications in embryonic development and disease.
Project description:Cis-encoded antisense RNAs (asRNAs) are widespread along bacterial transcriptomes. However, the role of the vast majority of these RNAs remains unknown, and there is an ongoing discussion as to what extent these transcripts are the result of transcriptional noise. We show, by comparative transcriptomics of 20 bacterial species and one chloroplast, that the number of asRNAs is exponentially dependent on the genomic AT content, and that expression of asRNA at low levels exerts little impact in terms of energy consumption. A transcription model simulating mRNA and asRNA production indicates that the asRNA regulatory effect is only observed above certain expression thresholds, substantially higher than physiological transcript levels. These predictions were verified experimentally by overexpressing 9 different asRNAs in M. pneumoniae. Our results suggest that most of the antisense transcripts found in bacteria are the consequence of transcriptional noise, arising at spurious promoters throughout the genome.