Nonmodular oscillator and switch based on RNA decay drive regeneration of multimodal gene expression

Periodic gene expression dynamics are key to cell and organism physiology. Studies of oscillatory expression have focused on networks with intuitive regulatory negative feedback loops, leaving unknown whether other common biochemical reactions can produce oscillations. Oscillation and noise have been proposed to support the capacity of mammalian progenitor cells to restore heterogenous, multimodal expression from extreme subpopulations, but underlying networks and specific roles of noise remained elusive. We use mass-action-based models to show that regulated RNA degradation involving as few as two RNA species, applicable to nearly half of human protein-coding genes, can generate sustained oscillations without imposed feedback. Diverging oscillation periods synergize with noise to robustly restore bimodal expression in cell populations. The global bifurcation organizing this divergence relies on an oscillator and bistable switch which cannot be decomposed into two structural modules. Our work reveals surprisingly rich dynamics of post-transcriptional reactions and a potentially widespread mechanism useful for development and regeneration.

TASOR epigenetic repressor cooperates with a CNOT1 RNA degradation pathway to repress HIV

The Human Silencing Hub (HUSH) complex constituted of TASOR, MPP8 and Periphilin recruits the histone methyl-transferase SETDB1 to spread H3K9me3 repressive marks across genes and transgenes in an integration site-dependent manner. The deposition of these repressive marks leads to heterochromatin formation and inhibits gene expression, but the underlying mechanism is not fully understood. Here, we show that TASOR silencing or HIV-2 Vpx expression, which induces TASOR degradation, increases the accumulation of transcripts derived from the HIV-1 LTR promoter at a post-transcriptional level. Furthermore, using a yeast 2-hybrid screen, we identify new TASOR partners involved in RNA metabolism including the RNA deadenylase CCR4-NOT complex scaffold CNOT1. TASOR and CNOT1 synergistically repress HIV expression from its LTR. Similar to the RNA-induced transcriptional silencing complex found in fission yeast, we show that TASOR interacts with the RNA exosome and RNA Polymerase II, predominantly under its elongating state. Finally, we show that TASOR facilitates the association of RNA degradation proteins with RNA polymerase II and is detected at transcriptional centers. Altogether, we propose that HUSH operates at the transcriptional and post-transcriptional levels to repress HIV proviral expression.

The Role of miRNA in Ovarian Cancer: an Overview

Ovarian cancer (OC) is a highly malignant disease that seriously threatens women’s health and poses challenges for clinicians. MicroRNAs (miRNAs) have recently been intensively studied in the field of oncology due to their regulatory roles in gene expressions through RNA degradation and/or translation inhibition. This review summarizes the current studies on miRNAs in OC and introduces the latest updates of miRNAs in the early screening, treatment, and prognostic prediction of OC, thereby demonstrating the clinical significance of miRNAs in OC. Further exploration on potential targets of miRNAs in OC may provide new insights on optimizing the diagnosis and treatment of OC. MiRNAs are important driving factors for the progression of OC and the dysregulation of miRNAs can serve as biomarkers in the diagnosis, treatment and prognosis of OC. Therefore, miRNAs are potential biological targets for early screening, targeted therapy, drug resistance monitoring, and prognosis improvement in malignancies such as OC.

Modeling SARS-CoV-2 RNA Degradation in Small and Large Sewersheds

Wastewater-based epidemiology has played a significant role in monitoring the COVID-19 pandemic, yet little is known about degradation of SARS-CoV-2 in sewer networks. Here, we used advanced sewershed modeling software...

CRISPR/CasRx Proof-of-Concept for RNA Degradation: A Future Tool against RNA Viruses?

Influenza viruses provide a great threat for the human population, causing highly contagious respiratory infections that can lead to serious clinical complications. There are a limited variety of influenza antivirals, and these antivirals are subjected to the constant emergence of resistances. Therefore, the development of new antiviral strategies to combat influenza viruses and other RNA viruses must be promoted. In this work, we design a proof-of-concept of a recently described CRISPR/Cas tool that has been proposed as a possible future RNA virus antiviral, named CRISPR/CasRx. For this, we verified the efficiency of the CasRx endonuclease in the degradation of the eGFP mRNA reporter gene and we established the best conditions for, and the efficient performance of, the CRISPR/CasRx system. The results were measured by fluorescence microscopy, flow cytometry, and qRT-PCR. The analyses demonstrated a reduction in fluorescence, regardless of the amount of eGFP reporter plasmid transfected. The analyses showed an 86–90% reduction in fluorescence by flow cytometry and a 51–80% reduction in mRNA expression by qRT-PCR. Our results demonstrate that the CasRx endonuclease is an efficient tool for eGFP mRNA knockdown. Therefore, subsequent experiments could be useful for the development of a new antiviral tool.

High-fidelity Cas13 variants for targeted RNA degradation with minimal collateral effect

CRISPR-Cas13 systems have recently been employed for targeted RNA degradation in various organisms. However, collateral degradation of bystander RNAs has imposed a major barrier for their in vivo applications. We designed a dual-fluorescent reporter system for detecting collateral effects and screening Cas13 variants in mammalian cells. Among over 200 engineered variants, several Cas13 variants (including Cas13d and Cas13X) exhibit efficient on-target activity but markedly reduced collateral activity. Furthermore, transcriptome-wide off-targets and cell growth arrest induced by Cas13 are absent for these variants. Importantly, high-fidelity Cas13 variants show comparable RNA knockdown activity with wild-type Cas13 but no detectable collateral damage in transgenic mice and adeno-associated virus-mediated somatic cell targeting. Thus, high-fidelity Cas13 variants with minimal collateral effect are now available for targeted degradation of RNAs in basic research and therapeutic applications.

Global SLAM-Seq for accurate mRNA decay determination and identification of NMD targets

Gene expression analysis requires accurate measurements of global RNA degradation rates, earlier problematic with methods disruptive to cell physiology. Recently, metabolic RNA labeling emerged as an efficient and minimally invasive technique applied in mammalian cells. Here, we have adapted SH-Linked Alkylation for the Metabolic Sequencing of RNA (SLAM-Seq) for a global mRNA stability study in yeast using 4-thiouracil pulse-chase labeling. We assign high-confidence half-life estimates for 67.5 % of expressed ORFs, and measure a median half-life of 9.4 min. For mRNAs where half-life estimates exist in the literature, their ranking order was in good agreement with previous data, indicating that SLAM-Seq efficiently classifies stable and unstable transcripts. We then leveraged our yeast protocol to identify targets of the Nonsense-mediated decay (NMD) pathway. There are currently no global reports of half-lives in both wild type and NMD defective yeast cells; instead steady-state RNA level changes are used as a proxy. With SLAM-Seq, we assign 580 transcripts as putative NMD targets, based on their measured half-lives in wild-type and upf3Δ mutants. We find 230 novel targets, and observe a strong agreement with previous reports of NMD targets, 60 % of our candidates being identified in previous studies. This indicates that SLAM-Seq is a simpler and more economic method for global quantification of mRNA half-lives. Our adaptation for yeast yielded global quantitative measures of the NMD effect on transcript half-lives, high correlation with RNA half-lives measured previously with more technically challenging protocols, and identification of novel NMD regulated transcripts that escaped prior detection.

Functional interaction between the RNA exosome and the sirtuin deacetylase Hst3 maintains transcriptional homeostasis

Eukaryotic cells maintain an optimal level of mRNAs through unknown mechanisms that balance RNA synthesis and degradation. We found that inactivation of the RNA exosome leads to global reduction of nascent mRNA transcripts, and that this defect is accentuated by loss of deposition of histone variant H2A.Z. We identify the mRNA for the sirtuin deacetylase Hst3 as a key target for the RNA exosome that mediates communication between RNA degradation and transcription machineries. These findings reveal how the RNA exosome and H2A.Z function together to control a deacetylase, ensuring proper levels of transcription in response to changes in RNA degradation.

Determination of Time of Death Based on Blood Ring Formation and RNA Degradation

Time of death (TOD) determination is crucial in criminal cases. The method used to determine the TOD so far is only based on the state of the corpse found, therefore a new method is needed to improve the accuracy of the TOD determination. This study aims to determine the TOD based on a new method, namely the formation of blood rings and RNA degradation. Blood is commonly found in crime scenes. Blood consists of liquid part that is plasma and cellular part consisting of erythrocytes, leukocyte, and thrombocytes. The composition of blood as a liquid that contains dissolved solids makes the drops of dried blood forming “coffee ring effect”, which is a ring-like form on the perimeter of a blood drop. Coffee ring effect is used as an indicator of time by looking at the thickness of the ring formed from the perimeter of the blood drop to the middle which increases with time. RNA degradation was observed using Peptidylprolyl isomerase A (PPIA) gene. The PPIA gene is found in leukocyte and is used to see the degradation of RNA per 30 minutes period using the RT-PCR and qPCR methods. Degradation was observed by comparing the cycle threshold (ct) value of the standard curve with the ct value of the samples per unit time. TOD could be determined by the percentage of the blood ring thickness up until 120th minutes, and by observing the degradation of RNA until the 60th minute, after that the RNA had completely degraded.

THO and TRAMP complexes prevent transcription-replication conflicts, DNA breaks, and CAG repeat contractions

Expansion of structure-forming CAG/CTG repetitive sequences is the cause of several neurodegenerative disorders and deletion of repeats is a potential therapeutic strategy. Transcription-associated mechanisms are known to cause CAG repeat instability. In this study, we discovered that Thp2, an RNA export factor and member of the THO complex, and Trf4, a key component of the TRAMP complex involved in nuclear RNA degradation, are necessary to prevent CAG fragility and repeat contractions in a S. cerevisiae model system. Depletion of both Thp2 and Trf4 proteins causes a highly synergistic increase in CAG repeat fragility, indicating a complementary role of the THO and TRAMP complexes in preventing genome instability. Loss of either Thp2 or Trf4 causes an increase in RNA polymerase stalling at the CAG repeats and genome-wide transcription-replication conflicts (TRCs), implicating impairment of transcription elongation as a cause of CAG fragility and instability in their absence. Analysis of the effect of RNase H1 overexpression on CAG fragility and TRCs suggests that co-transcriptional R-loops are the main cause of CAG fragility in the thp2Δ mutants. In contrast, CAG fragility and TRCs in the trf4Δ mutant can be compensated for by RPA overexpression, suggesting that excess unprocessed RNA in TRAMP4 mutants leads to reduced RPA availability and high levels of TRCs. Our results show the importance of RNA surveillance pathways in preventing RNAPII stalling, TRCs, and DNA breaks, and show that RNA export and RNA decay factors work collaboratively to maintain genome stability.