Transcriptional interference--a crash course

Biophysical modeling reveals the transcriptional regulatory mechanism of Spo0A, the master regulator in starving Bacillus subtilis

In starving Bacillus subtilis bacteria, the initiation of two survival programs-biofilm formation and sporulation-is controlled by the same phosphorylated master regulator, Spo0A~P. Its gene, spo0A, is transcribed from two promoters, Pv and Ps, that are, respectively, regulated by RNA polymerase (RNAP) holoenzymes bearing σA and σH. Notably, transcription is directly autoregulated by Spo0A~P binding sites known as 0A1, 0A2, and 0A3 box, located in between the two promoters. It remains unclear whether, at the onset of starvation, these boxes activate or repress spo0A expression, and whether the Spo0A~P transcriptional feedback plays a role in the increase in spo0A expression. Based on the experimental data of the promoter activities under systematic perturbation of the promoter architecture, we developed a biophysical model of transcriptional regulation of spo0A by Spo0A~P binding to each of the 0A boxes. The model predicts that Spo0A~P binding to its boxes does not affect the RNAP recruitment to the promoters but instead affects the transcriptional initiation rate. Moreover, the effects of Spo0A~P binding to 0A boxes are mainly repressive and saturated early at the onset of starvation. Therefore, the increase in spo0A expression is mainly driven by the increase in RNAP holoenzyme levels. Additionally, we reveal that Spo0A~P affinity to 0A boxes is strongest at 0A3 and weakest at 0A2 and that there are attractive forces between the occupied 0A boxes. Our findings, in addition to clarifying how the sporulation master regulator is controlled, offer a framework to predict regulatory outcomes of complex gene-regulatory mechanisms.

IMPORTANCE

Cell differentiation is often critical for survival. In bacteria, differentiation decisions are controlled by transcriptional master regulators under transcriptional feedback control. Therefore, understanding how master regulators are transcriptionally regulated is required to understand differentiation. However, in many cases, the underlying regulation is complex, with multiple transcription factor binding sites and multiple promoters, making it challenging to dissect the exact mechanisms. Here, we address this problem for the Bacillus subtilis master regulator Spo0A. Using a biophysical model, we quantitatively characterize the effect of individual transcription factor binding sites on each spo0A promoter. Furthermore, the model allows us to identify the specific transcription step that is affected by transcription factor binding. Such a model is promising for the quantitative study of a wide range of master regulators involved in transcriptional feedback.

Evolutionary Process Underlying Receptor Gene Expansion and Cellular Divergence of Olfactory Sensory Neurons in Honeybees

Olfaction is crucial for animals' survival and adaptation. Unlike the strict singular expression of odorant receptor (OR) genes in vertebrate olfactory sensory neurons (OSNs), insects exhibit complex OR gene expression patterns. In honeybees (Apis mellifera), a significant expansion of OR genes implies a selection preference for the olfactory demands of social insects. However, the mechanisms underlying receptor expression specificity and their contribution to OSN divergence remain unclear. In this study, we used single-nucleus multiomics profiling to investigate the transcriptional regulation of OR genes and the cellular identity of OSNs in A. mellifera. We identified three distinct OR expression patterns, singular OR expression, co-expression of multiple OR genes with a single active promoter, and co-expression of multiple OR genes with multiple active promoters. Notably, ∼50% of OSNs co-expressed multiple OR genes, driven by polycistronic transcription of tandemly duplicated OR genes via a single active promoter. In these OSNs, their identity was determined by the first transcribed receptor. The divergent activation of the promoter for duplicated OR genes ensures the coordinated increased divergence of OSN population. By integrating multiomics data with genomic architecture, we illustrate how fundamental genetic mechanisms drive OR gene expansion and influence flanking regulatory elements, ultimately contributing to the cellular divergence of OSNs. Our findings highlight the interplay between gene duplication and regulatory evolution in shaping OSN diversity, providing new insights into the evolution and adaptation of olfaction in social insects. This study also sheds light on how genetic innovations contribute to the evolution of complex traits.

Mechanism of expression regulation of head-to-head overlapping protein-coding genes INO80E and HIRIP3

Although the existence of overlapping protein-coding genes in eukaryotic genomes is known for decades, their role in regulating expression remains far from fully understood. Here, the mechanism regulating the expression of head-to-head overlapping genes, a pair of INO80E and HIRIP3 genes is presented. Based on a series of experiments, we show that the expression of these genes is strongly dependent on sense/antisense interactions. The overlapping transcripts form an RNA:RNA duplex that has a stabilizing effect on the mRNAs involved, and this stabilization may be mediated by the ELAVL1 protein. We also show that the transcription factor RARG is important for the transcription of both genes studied. In addition, we demonstrate that the overlapping isoform of INO80E forms an R-loop that may positively regulate HIRIP3 isoforms. We propose that both structures, dsRNA and R-loops, help to keep the DNA loop open to allow the transcription of the remaining variants of both genes. However, experiments suggest that RNA:RNA duplex formation plays a major role, while R-loops play only a complementary one. The absence of this dsRNA structure leads to the loss of a stable DNA opening and consequently to transcriptional interference.

A transcription factor from the cryptic Escherichia coli Rac prophage controls both phage and host operons

Bacterial genomes are shaped by cryptic prophages, which are viral genomes integrated into the bacterial chromosome. Escherichia coli genomes have 10 prophages on average. Though usually inactive, prophage genes can profoundly impact host cell physiology. Among the phage genes in the E. coli chromosome, there are several putative transcription factors (TFs). These prophage TFs are predicted to control only phage promoters; however, their regulatory functions are not well characterized. The cohabitation of prophages and bacteria has led to conditions under which the majority of prophage genes are unexpressed, at least under normal growth conditions. We characterized a Rac prophage TF, YdaT, expression of which is normally inhibited by Rac TFs and, surprisingly, by the host global regulator OxyR. YdaT, when expressed, leads to a toxic phenotype manifested by drastic cell filamentation and cell death. We determined the binding sites and regulatory action for YdaT, finding two sites within the Rac locus, and one upstream of the host rcsA gene, which codes for the global regulator RcsA. The resulting increase in RcsA strongly impacts the bacterial RcsA/B regulon, which includes operons related to motility, capsule biosynthesis, colanic acid production, biofilm formation, and cell division. Our results provide novel insights into the host's genetic network, which appears to integrate YdaT in a complex manner, favoring its maintenance in the silenced state. The fact that the potentially toxic YdaT locus remains unmutated suggests its importance and potential benefits for the host, which may appear under stress conditions that are not yet known.

Gene syntax defines supercoiling-mediated transcriptional feedback

Gene syntax-the order and arrangement of genes and their regulatory elements-shapes the dynamic coordination of both natural and synthetic gene circuits. Transcription at one locus profoundly impacts the transcription of nearby adjacent genes, but the molecular basis of this effect remains poorly understood. Here, using integrated reporter circuits in human cells, we show that supercoiling-mediated feedback regulates expression of adjacent genes in a syntax-specific manner. Using Region Capture Micro-C, we measure induction-dependent formation of supercoiled plectonemes and syntax-specific chromatin structures in human induced pluripotent stem cells. Using syntax as a design parameter, we built compact gene circuits, tuning the mean, variance, and stoichiometries of expression across diverse delivery methods and cell types. Integrating supercoiling-mediated feedback into models of gene regulation will expand our understanding of native systems and enhance the design of synthetic gene circuits.

Gene regulation by convergent promoters

Convergent transcription, that is, the collision of sense and antisense transcription, is ubiquitous in mammalian genomes and believed to diminish RNA expression. Recently, antisense transcription downstream of promoters was found to be surprisingly prevalent. However, functional characteristics of affected promoters are poorly investigated. Here we show that convergent transcription marks an unexpected positively co-regulated promoter constellation. By assessing transcriptional dynamic systems, we identified co-regulated constituent promoters connected through a distinct chromatin structure. Within these cis-regulatory domains, transcription factors can regulate both constituting promoters by binding to only one of them. Convergent promoters comprise about a quarter of all active transcript start sites and initiate 5'-overlapping antisense RNAs-an RNA class believed previously to be rare. Visualization of nascent RNA molecules reveals convergent cotranscription at these loci. Together, our results demonstrate that co-regulated convergent promoters substantially expand the cis-regulatory repertoire, reveal limitations of the transcription interference model and call for adjusting the promoter concept.

Sen1: The Varied Virtues of a Multifaceted Helicase

Several machineries concurrently work on the DNA, but among them RNA Polymerases (RNAPs) are the most widespread and active users. The homeostasis of such a busy genomic environment relies on the existence of mechanisms that allow limiting transcription to a functional level, both in terms of extent and rate. Sen1 is a central player in this sense: using its translocase activity this protein has evolved the specific function of dislodging RNAPs from the DNA template, thus ending the transcription cycle. Over the years, studies have shown that Sen1 uses this same mechanism in a multitude of situations, allowing termination of all three eukaryotic RNAPs in different contexts. In virtue of its helicase activity, Sen1 has also been proposed to have a prominent function in the resolution of co-transcriptional genotoxic R-loops, which can cause the stalling of replication forks. In this review, we provide a synopsis of past and recent findings on the functions of Sen1 in yeast and of its human homologue Senataxin (SETX).

The Proteomics of T-Cell and Early T-Cell Precursor (ETP) Acute Lymphocytic Leukemia: Prognostic Patterns in Adult and Pediatric-ETP ALL

BACKGROUND

The 5-year overall survival (OS) rates of T-cell lymphocytic leukemia (T-ALL) are better for children (>90%) compared to adults (~57%). The early T-cell precursor (ETP) T-ALL subtype is prognostically unfavorable in adults, but less significant in pediatric T-ALL, and the diagnosis and prognosis of "near"-ETP is controversial. We compared protein and RNA expression patterns in pediatric and adult T-ALL to identify prognostic subgroups, and to further characterize ETP and near-ETP T-ALL in both age groups.

METHODS

Protein expression was assessed using RPPA methodology for 321 target proteins in 361 T-ALL patient samples from 292 pediatrics and 69 adults, including 103 ETP-ALL. RNA-sequencing was performed on 81 pediatric T-ALL samples.

RESULTS

We identified recurrent protein expression patterns that classified patients into ten protein expression signatures using the "MetaGalaxy" analysis. In adults, Cox regression analysis identified two risk-groups associated with OS (p = 0.0002) and complete remission duration (p < 0.001). Cluster analysis of adults and pediatric-ETP patients identified three ETP-clusters strongly associated with age. Pediatric ETP-patients with a pediatric-dominant expression profile were associated with a shorter OS (p = 0.04) and event-free survival (p = 0.05) compared to pediatric ETP-patients with an ETP expression profile that was also identified in adults.

CONCLUSION

Our study demonstrates that proteomics are predictive of outcome in adult T-ALL and that we can identify a small subset of pediatric ETP with an inferior outcome. The observation that there are age-specific patterns supports the idea that the origin of T-ALL in most pediatric and adult patients is different, while overlapping patterns suggests that there are some with a common pathophysiology. Proteomics could enhance risk stratification in both pediatric and adults with T-ALL.

Physics of collective transport and traffic phenomena in biology: Progress in 20 years

Enormous progress has been made in the last 20 years since the publication of our review [1] in this journal on transport and traffic phenomena in biology. In this brief article we present a glimpse of the major advances during this period. First, we present similarities and differences between collective intracellular transport of a single micron-size cargo by multiple molecular motors and that of a cargo particle by a team of ants on the basis of the common principle of load-sharing. Second, we sketch several models all of which are biologically motivated extensions of the Asymmetric Simple Exclusion Process (ASEP); some of these models represent the traffic of molecular machines, like RNA polymerase (RNAP) and ribosome, that catalyze template-directed polymerization of RNA and proteins, respectively, whereas few other models capture the key features of the traffic of ants on trails. More specifically, using the ASEP-based models we demonstrate the effects of traffic of RNAPs and ribosomes on random and 'programmed' errors in gene expression as well as on some other subcellular processes. We recall a puzzling empirical result on the single-lane traffic of predatory ants Leptogenys processionalis as well as recent attempts to account for this puzzle. We also mention some surprising effects of lane-changing rules observed in a ASEP-based model for 3-lane traffic of army ants. Finally, we explain the conceptual similarities between the pheromone-mediated indirect communication, called stigmergy, between ants on a trail and the floor-field-mediated interaction between humans in a pedestrian traffic. For the floor-field model of human pedestrian traffic we present a major theoretical result that is relevant from the perspective of all types of traffic phenomena.

The Salmonella enterica EnvE is an Outer Membrane Lipoprotein and Its Gene Expression Leads to Transcriptional Repression of the Virulence Gene msgA

The envE gene of Salmonella enterica serovar Typhimurium is encoded within Salmonella Pathogenicity Island-11 (SPI-11) and is located immediately upstream of the virulence gene msgA (macrophage survival gene A) in the same transcriptional orientation. To date, the characteristics and roles of envE remain largely unexplored. In this study, we show that EnvE, a predicted lipoprotein, is localized on the outer membrane using sucrose gradient ultracentrifugation. Under oxidative stress conditions, envE transcription is suppressed, while msgA transcription is induced, indicating an inverse correlation between the mRNA levels of the two neighboring genes. Importantly, inactivation of envE leads to constitutive transcription of msgA regardless of the presence of oxidative stress. Moreover, trans-complementation of the envE mutant with a plasmid-borne envE fails to prevent the induction of msgA transcription, suggesting that envE functions as a cis-regulatory element rather than a trans-acting factor. We further show that both inactivation and complementation of envE confer wild-type levels of resistance to oxidative stress by ensuring the expression of msgA. Our data suggest that the S. enterica envE gene encodes an outer membrane lipoprotein, and its transcription represses msgA expression in a cis-acting manner, probably by transcriptional interference, although the exact molecular details are yet unclear.

Impacts of the feedback loop between sense-antisense RNAs in regulating circadian rhythms

Antisense transcripts are a unique group of non-coding RNAs and play regulatory roles in a variety of biological processes, including circadian rhythms. Per2AS is an antisense transcript to the sense core clock gene Period2 (Per2) in mouse and its expression is rhythmic and antiphasic to Per2. To understand the impact of Per2AS-Per2 interaction, we developed a new mathematical model that mechanistically described the mutually repressive relationship between Per2 and Per2AS. This mutual repression can regulate both amplitude and period of circadian oscillation by affecting a negative feedback regulation of Per2. Simulations from this model also fit with experimental observations that could not be fully explained by our previous model. Our revised model can not only serve as a foundation to build more detailed models to better understand the impact of Per2AS-Per2 interaction in the future, but also be used to analyze other sense-antisense RNA pairs that mutually repress each other.

Natural antisense transcripts as versatile regulators of gene expression

Long non-coding RNAs (lncRNAs) are emerging as a major class of gene products that have central roles in cell and developmental biology. Natural antisense transcripts (NATs) are an important subset of lncRNAs that are expressed from the opposite strand of protein-coding and non-coding genes and are a genome-wide phenomenon in both eukaryotes and prokaryotes. In eukaryotes, a myriad of NATs participate in regulatory pathways that affect expression of their cognate sense genes. Recent developments in the study of NATs and lncRNAs and large-scale sequencing and bioinformatics projects suggest that whether NATs regulate expression, splicing, stability or translation of the sense transcript is influenced by the pattern and degrees of overlap between the sense-antisense pair. Moreover, epigenetic gene regulatory mechanisms prevail in somatic cells whereas mechanisms dependent on the formation of double-stranded RNA intermediates are prevalent in germ cells. The modulating effects of NATs on sense transcript expression make NATs rational targets for therapeutic interventions.

Exploring the transcription start sites and other genomic features facilitates the accurate identification and annotation of small RNAs across multiple stress conditions in Mycobacterium tuberculosis

Mycobacterium tuberculosis (MTB) is a pathogen that is known for its ability to persist in harsh environments and cause chronic infections. Understanding the regulatory networks of MTB is crucial for developing effective treatments. Small regulatory RNAs (sRNAs) play important roles in gene expression regulation in all kingdoms of life, and their classification based solely on genomic location can be imprecise due to the computational-based prediction of protein-coding genes in bacteria, which often neglects segments of mRNA such as 5'UTRs, 3'UTRs, and intercistronic regions of operons. To address this issue, our study simultaneously discovered genomic features such as TSSs, UTRs, and operons together with sRNAs in the M. tuberculosis H37Rv strain (ATCC 27294) across multiple stress conditions. Our analysis identified 1,376 sRNA candidates and 8,173 TSSs in MTB, providing valuable insights into its complex regulatory landscape. TSS mapping enabled us to classify these sRNAs into more specific categories, including promoter-associated sRNAs, 5'UTR-derived sRNAs, 3'UTR-derived sRNAs, true intergenic sRNAs, and antisense sRNAs. Three of these sRNA candidates were experimentally validated using 3'-RACE-PCR: predictedRNA_0240, predictedRNA_0325, and predictedRNA_0578. Future characterization and validation are necessary to fully elucidate the functions and roles of these sRNAs in MTB. Our study is the first to simultaneously unravel TSSs and sRNAs in MTB and demonstrate that the identification of other genomic features, such as TSSs, UTRs, and operons, allows for more accurate and specific classification of sRNAs.

TTF1 control of LncRNA synthesis delineates a tumor suppressor pathway directly regulating the ribosomal RNA genes

The tumor suppressor p14/19ARF regulates ribosomal RNA (rRNA) synthesis by controlling the nucleolar localization of Transcription Termination Factor 1 (TTF1). However, the role played by TTF1 in regulating the rRNA genes and in potentially controlling growth has remained unclear. We now show that TTF1 expression regulates cell growth by determining the cellular complement of ribosomes. Unexpectedly, it achieves this by acting as a "roadblock" to synthesis of the noncoding LncRNA and pRNA that we show are generated from the "Spacer Promoter" duplications present upstream of the 47S pre-rRNA promoter on the mouse and human ribosomal RNA genes. Unexpectedly, the endogenous generation of these noncoding RNAs does not induce CpG methylation or gene silencing. Rather, it acts in cis to suppress 47S preinitiation complex formation and hence de novo pre-rRNA synthesis by a mechanism reminiscent of promoter interference or occlusion. Taken together, our data delineate a pathway from p19ARF to cell growth suppression via the regulation of ribosome biogenesis by noncoding RNAs and validate a key cellular growth law in mammalian cells.

RNAi-based Boolean gates in the yeast Saccharomyces cerevisiae

Boolean gates, the fundamental components of digital circuits, have been widely investigated in synthetic biology because they permit the fabrication of biosensors and facilitate biocomputing. This study was conducted to design and construct Boolean gates in the yeast Saccharomyces cerevisiae, the main component of which was the RNA interference pathway (RNAi) that is naturally absent from the budding yeast cells. We tested different expression cassettes for the siRNA precursor (a giant hairpin sequence, a DNA fragment-flanked by one or two introns-between convergent promoters or transcribed separately in the sense and antisense directions) and placed different components under the control of the circuit inputs (i.e., the siRNA precursor or proteins such as the Dicer and the Argonaute). We found that RNAi-based logic gates are highly sensitive to promoter leakage and, for this reason, challenging to implement in vivo. Convergent-promoter architecture turned out to be the most reliable solution, even though the overall best performance was achieved with the most difficult design based on the siRNA precursor as a giant hairpin.

Systematic decoding of cis gene regulation defines context-dependent control of the multi-gene costimulatory receptor locus in human T cells

Cis-regulatory elements (CREs) interact with trans regulators to orchestrate gene expression, but how transcriptional regulation is coordinated in multi-gene loci has not been experimentally defined. We sought to characterize the CREs controlling dynamic expression of the adjacent costimulatory genes CD28, CTLA4 and ICOS, encoding regulators of T cell-mediated immunity. Tiling CRISPR interference (CRISPRi) screens in primary human T cells, both conventional and regulatory subsets, uncovered gene-, cell subset- and stimulation-specific CREs. Integration with CRISPR knockout screens and assay for transposase-accessible chromatin with sequencing (ATAC-seq) profiling identified trans regulators influencing chromatin states at specific CRISPRi-responsive elements to control costimulatory gene expression. We then discovered a critical CCCTC-binding factor (CTCF) boundary that reinforces CRE interaction with CTLA4 while also preventing promiscuous activation of CD28. By systematically mapping CREs and associated trans regulators directly in primary human T cell subsets, this work overcomes longstanding experimental limitations to decode context-dependent gene regulatory programs in a complex, multi-gene locus critical to immune homeostasis.

Genome-wide nucleosome and transcription factor responses to genetic perturbations reveal chromatin-mediated mechanisms of transcriptional regulation

Epigenetic mechanisms contribute to gene regulation by altering chromatin accessibility through changes in transcription factor (TF) and nucleosome occupancy throughout the genome. Despite numerous studies focusing on changes in gene expression, the intricate chromatin-mediated regulatory code remains largely unexplored on a comprehensive scale. We address this by employing a factor-agnostic, reverse-genetics approach that uses MNase-seq to capture genome-wide TF and nucleosome occupancies in response to the individual deletion of 201 transcriptional regulators in Saccharomyces cerevisiae, thereby assaying nearly one million mutant-gene interactions. We develop a principled approach to identify and quantify chromatin changes genome-wide, observing differences in TF and nucleosome occupancy that recapitulate well-established pathways identified by gene expression data. We also discover distinct chromatin signatures associated with the up- and downregulation of genes, and use these signatures to reveal regulatory mechanisms previously unexplored in expression-based studies. Finally, we demonstrate that chromatin features are predictive of transcriptional activity and leverage these features to reconstruct chromatin-based transcriptional regulatory networks. Overall, these results illustrate the power of an approach combining genetic perturbation with high-resolution epigenomic profiling; the latter enables a close examination of the interplay between TFs and nucleosomes genome-wide, providing a deeper, more mechanistic understanding of the complex relationship between chromatin organization and transcription.

DDX21 mediates co-transcriptional RNA m6A modification to promote transcription termination and genome stability

N6-methyladenosine (m6A) is a crucial RNA modification that regulates diverse biological processes in human cells, but its co-transcriptional deposition and functions remain poorly understood. Here, we identified the RNA helicase DDX21 with a previously unrecognized role in directing m6A modification on nascent RNA for co-transcriptional regulation. DDX21 interacts with METTL3 for co-recruitment to chromatin through its recognition of R-loops, which can be formed co-transcriptionally as nascent transcripts hybridize onto the template DNA strand. Moreover, DDX21's helicase activity is needed for METTL3-mediated m6A deposition onto nascent RNA following recruitment. At transcription termination regions, this nexus of actions promotes XRN2-mediated termination of RNAPII transcription. Disruption of any of these steps, including the loss of DDX21, METTL3, or their enzymatic activities, leads to defective termination that can induce DNA damage. Therefore, we propose that the R-loop-DDX21-METTL3 nexus forges the missing link for co-transcriptional modification of m6A, coordinating transcription termination and genome stability.

Impacts of the feedback loop between sense-antisense RNAs in regulating circadian rhythms

Antisense transcripts are a unique group of non-coding RNAs that are transcribed from the opposite strand of a sense coding gene in an antisense orientation. Even though they do not encode a protein, these transcripts play a regulatory role in a variety of biological processes, including circadian rhythms. We and others found an antisense transcript, Per2AS , that is transcribed from the strand opposite the sense transcript Period2 ( Per2 ) and exhibits a rhythmic and antiphasic expression pattern compared to Per2 in mouse. By assuming that Per2AS and Per2 mutually repress each other, our previous mathematical model predicted that Per2AS regulates the robustness and the amplitude of circadian rhythms. In this study, we revised our previous model and developed a new mathematical model that mechanistically described the mutually repressive relationship between Per2 and Per2AS via transcriptional interference. We found that the simulation results are largely consistent with experimental observations including the counterintuitive ones that could not be fully explained by our previous model. These results indicate that our revised model serves as a foundation to build more detailed models in the future to better understand the impact of Per2AS-Per2 interaction in the mammalian circadian clock. Our mechanistic description of Per2AS-Per2 interaction can also be extended to other mathematical models that involve sense-antisense RNA pairs that mutually repress each other.

Mitigating transcription noise via protein sharing in syncytial cells

Bursty transcription allows nuclei to concentrate the work of transcribing mRNA into short, intermittent intervals, potentially reducing transcriptional interference. However, bursts of mRNA production can increase noise in protein abundances. Here, we formulate models for gene expression in syncytia, or multinucleate cells, showing that protein abundance noise may be mitigated locally via spatial averaging of diffuse proteins. Our modeling shows a universal reduction in protein noise, which increases with the average number of nuclei per cell and persists even when the number of nuclei is itself a random variable. Experimental data comparing distributions of a cyclin mRNA that is conserved between brewer's yeast and a closely related filamentous fungus Ashbya gossypii confirm that syncytism is permissive of greater levels of transcriptional noise. Our findings suggest that division of transcriptional labor between nuclei allows syncytia to sidestep tradeoffs between efficiency and precision of gene expression.

Identification of promoter activity in gene-less cassettes from Vibrionaceae superintegrons

Integrons are genetic platforms that acquire new genes encoded in integron cassettes (ICs), building arrays of adaptive functions. ICs generally encode promoterless genes, whose expression relies on the platform-associated Pc promoter, with the cassette array functioning as an operon-like structure regulated by the distance to the Pc. This is relevant in large sedentary chromosomal integrons (SCIs) carrying hundreds of ICs, like those in Vibrio species. We selected 29 gene-less cassettes in four Vibrio SCIs, and explored whether their function could be related to the transcription regulation of adjacent ICs. We show that most gene-less cassettes have promoter activity on the sense strand, enhancing the expression of downstream cassettes. Additionally, we identified the transcription start sites of gene-less ICs through 5'-RACE. Accordingly, we found that most of the superintegron in Vibrio cholerae is not silent. These promoter cassettes can trigger the expression of a silent dfrB9 cassette downstream, increasing trimethoprim resistance >512-fold in V. cholerae and Escherichia coli. Furthermore, one cassette with an antisense promoter can reduce trimethoprim resistance when cloned downstream. Our findings highlight the regulatory role of gene-less cassettes in the expression of adjacent cassettes, emphasizing their significance in SCIs and their clinical importance if captured by mobile integrons.

MetJ-Based Mutually Interfering SAM-ON/SAM-OFF Biosensors

SAM (S-adenosylmethionine) is an important metabolite that operates as a major donor of methyl groups and is a controller of various physiological processes. Its availability is also believed to be a major bottleneck in the biological production of numerous high-value metabolites. Here, we constructed SAM-sensing systems using MetJ, an SAM-dependent transcriptional regulator, as a core component. SAM is a corepressor of MetJ, which suppresses the MetJ promoter with an increasing cellular concentration of SAM (SAM-OFF sensor). The application of transcriptional interference and evolutionary tuning effectively inverted its response, yielding a SAM-ON sensor (signal increases with increasing SAM concentration). By linking two genes encoding fluorescent protein reporters in such a way that their transcription events interfere with each other's and by placing one of them under the control of MetJ, we could increase the effective signal-to-noise ratio of the SAM sensor while decreasing the batch-to-batch deviation in signal output, likely by canceling out the growth-associated fluctuation in translational resources. By taking the ratio of SAM-ON/SAM-OFF signals and by resetting the default pool size of SAM, we could rapidly identify SAM synthetase (MetK) mutants with increased cellular activity from a random library. The strategy described herein should be widely applicable for identifying activity mutants, which would be otherwise overlooked because of the strong homeostasis of metabolic networks.

Recent insights into the functions and mechanisms of antisense RNA: emerging applications in cancer therapy and precision medicine

The antisense RNA molecule is a unique DNA transcript consisting of 19-23 nucleotides, characterized by its complementary nature to mRNA. These antisense RNAs play a crucial role in regulating gene expression at various stages, including replication, transcription, and translation. Additionally, artificial antisense RNAs have demonstrated their ability to effectively modulate gene expression in host cells. Consequently, there has been a substantial increase in research dedicated to investigating the roles of antisense RNAs. These molecules have been found to be influential in various cellular processes, such as X-chromosome inactivation and imprinted silencing in healthy cells. However, it is important to recognize that in cancer cells; aberrantly expressed antisense RNAs can trigger the epigenetic silencing of tumor suppressor genes. Moreover, the presence of deletion-induced aberrant antisense RNAs can lead to the development of diseases through epigenetic silencing. One area of drug development worth mentioning is antisense oligonucleotides (ASOs), and a prime example of an oncogenic trans-acting long noncoding RNA (lncRNA) is HOTAIR (HOX transcript antisense RNA). NATs (noncoding antisense transcripts) are dysregulated in many cancers, and researchers are just beginning to unravel their roles as crucial regulators of cancer's hallmarks, as well as their potential for cancer therapy. In this review, we summarize the emerging roles and mechanisms of antisense RNA and explore their application in cancer therapy.

Syncytial Assembly Lines: Consequences of Multinucleate Cellular Compartments for Fungal Protein Synthesis

Fast growth and prodigious cellular outputs make fungi powerful tools in biotechnology. Recent modeling work has exposed efficiency gains associated with dividing the labor of transcription over multiple nuclei, and experimental innovations are opening new windows on the capacities and adaptations that allow nuclei to behave autonomously or in coordination while sharing a single, common cytoplasm. Although the motivation of our review is to motivate and connect recent work toward a greater understanding of fungal factories, we use the analogy of the assembly line as an organizing idea for studying coordinated gene expression, generally.

Assessing in vivo the impact of gene context on transcription through DNA supercoiling

Gene context can have significant impact on gene expression but is currently not integrated in quantitative models of gene regulation despite known biophysical principles and quantitative in vitro measurements. Conceptually, the simplest gene context consists of a single gene framed by two topological barriers, known as the twin transcriptional-loop model, which illustrates the interplay between transcription and DNA supercoiling. In vivo, DNA supercoiling is additionally modulated by topoisomerases, whose modus operandi remains to be quantified. Here, we bridge the gap between theory and in vivo properties by realizing in Escherichia coli the twin transcriptional-loop model and by measuring how gene expression varies with promoters and distances to the topological barriers. We find that gene expression depends on the distance to the upstream barrier but not to the downstream barrier, with a promoter-dependent intensity. We rationalize these findings with a first-principle biophysical model of DNA transcription. Our results are explained if TopoI and gyrase both act specifically, respectively upstream and downstream of the gene, with antagonistic effects of TopoI, which can repress initiation while facilitating elongation. Altogether, our work sets the foundations for a systematic and quantitative description of the impact of gene context on gene regulation.

Elongation roadblocks mediated by dCas9 across human genes modulate transcription and nascent RNA processing

Non-cleaving Cas9 (dCas9) is widely employed to manipulate specific gene loci, often with scant regard for unintended transcriptional effects. We demonstrate here that dCas9 mediates precise RNA polymerase II transcriptional pausing followed by transcription termination and potential alternative polyadenylation. By contrast, alternative splicing is unaffected, likely requiring more sustained alteration to elongation speed. The effect on transcription is orientation specific, with pausing only being induced when dCas9-associated guide RNA anneals to the non-template strand. Targeting the template strand induces minimal effects on transcription elongation and thus provides a neutral approach to recruit dCas9-linked effector domains to specific gene regions. In essence, we evaluate molecular effects of targeting dCas9 to mammalian transcription units. In so doing, we also provide new information on elongation by RNA polymerase II and coupled pre-mRNA processing.

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The interaction of nucleic acids with proteins plays an important role in many fundamental biological processes in living cells, including replication, transcription, and translation. Therefore, understanding nucleic acid-protein interaction is of high relevance in many areas of biology, medicine and technology. During almost four decades of its existence atomic force microscopy (AFM) accumulated a significant experience in investigation of biological molecules at a single-molecule level. AFM has become a powerful tool of molecular biology and biophysics providing unique information about properties, structure, and functioning of biomolecules. Despite a great variety of nucleic acid-protein systems under AFM investigations, there are a number of typical approaches for such studies. This review is devoted to the analysis of the typical AFM-based approaches of investigation of DNA (RNA)-protein complexes with a major focus on transcription studies. The basic strategies of AFM analysis of nucleic acid-protein complexes including investigation of the products of DNA-protein reactions and real-time dynamics of DNA-protein interaction are categorized and described by the example of the most relevant research studies. The described approaches and protocols have many universal features and, therefore, are applicable for future AFM studies of various nucleic acid-protein systems.

Refactoring the architecture of a polyketide gene cluster enhances docosahexaenoic acid production in Yarrowia lipolytica through improved expression and genetic stability

BACKGROUND

Long-chain polyunsaturated fatty acids (LC-PUFAs), such as docosahexaenoic acid (DHA), are essential for human health and have been widely used in the food and pharmaceutical industries. However, the limited availability of natural sources, such as oily fish, has led to the pursuit of microbial production as a promising alternative. Yarrowia lipolytica can produce various PUFAs via genetic modification. A recent study upgraded Y. lipolytica for DHA production by expressing a four-gene cluster encoding a myxobacterial PKS-like PUFA synthase, reducing the demand for redox power. However, the genetic architecture of gene expression in Y. lipolytica is complex and involves various control elements, offering space for additional improvement of DHA production. This study was designed to optimize the expression of the PUFA cluster using a modular cloning approach.

RESULTS

Expression of the monocistronic cluster with each gene under the control of the constitutive TEF promoter led to low-level DHA production. By using the minLEU2 promoter instead and incorporating additional upstream activating UAS1B4 sequences, 5' promoter introns, and intergenic spacers, DHA production was increased by 16-fold. The producers remained stable over 185 h of cultivation. Beneficially, the different genetic control elements acted synergistically: UAS1B elements generally increased expression, while the intron caused gene-specific effects. Mutants with UAS1B16 sequences within 2-8 kb distance, however, were found to be genetically unstable, which limited production performance over time, suggesting the avoidance of long repetitive sequence blocks in synthetic multigene clusters and careful monitoring of genetic stability in producing strains.

CONCLUSIONS

Overall, the results demonstrate the effectiveness of synthetic heterologous gene clusters to drive DHA production in Y. lipolytica. The combinatorial exploration of different genetic control elements allowed the optimization of DHA production. These findings have important implications for developing Y. lipolytica strains for the industrial-scale production of valuable polyunsaturated fatty acids.

Use of the mCherry fluorescent protein to optimize the expression of class I lanthipeptides in Escherichia coli

BACKGROUND

Lanthipeptides are a rapidly expanding family of ribosomally synthesized and post-translationally modified natural compounds with diverse biological functions. Lanthipeptide structural and biosynthetic genes can readily be identified in genomic datasets, which provides a substantial repository for unique peptides with a wide range of potentially novel bioactivities. To realize this potential efficiently optimized heterologous production systems are required. However, only a few class I lanthipeptides have been successfully expressed using Escherichia coli as heterologous producer. This may be attributed to difficulties experienced in the co-expression of structural genes and multiple processing genes as well as complex optimization experiments.

RESULTS

Here, an optimized modular plasmid system is presented for the complete biosynthesis for each of the class I lanthipeptides nisin and clausin, in E. coli. Genes encoding precursor lanthipeptides were fused to the gene encoding the mCherry red fluorescent protein and co-expressed along with the required synthetases from the respective operons. Antimicrobially active nisin and clausin were proteolytically liberated from the expressed mCherry fusions. The mCherry-NisA expression system combined with in vivo fluorescence monitoring was used to elucidate the effect of culture media composition, promoter arrangement, and culture conditions including choice of growth media and inducer agents on the heterologous expression of the class I lanthipeptides. To evaluate the promiscuity of the clausin biosynthetic enzymes, the optimized clausin expression system was used for the heterologous expression of epidermin.

CONCLUSION

We succeeded in developing novel mCherry-fusion based plug and play heterologous expression systems to produce two different subgroups of class I lanthipeptides. Fully modified Pre-NisA, Pre-ClausA and Pre-EpiA fused to the mCherry fluorescence gene was purified from the Gram-negative host E. coli BL21 (DE3). Our study demonstrates the potential of using in vivo fluorescence as a platform to evaluate the expression of mCherry-fused lanthipeptides in E. coli. This allowed a substantial reduction in optimization time, since expression could be monitored in real-time, without the need for extensive and laborious purification steps or the use of in vitro activity assays. The optimized heterologous expression systems developed in this study may be employed in future studies for the scalable expression of novel NisA derivatives, or novel genome mined derivatives of ClausA and other class I lanthipeptides in E. coli.

Improved RNA stability estimation indicates that transcriptional interference is frequent in diverse bacteria

We used stochastic simulations and experimental data from E. coli, K. aerogenes, Synechococcus PCC 7002 and Synechocystis PCC 6803 to provide evidence that transcriptional interference via the collision mechanism is likely a prevalent mechanism for bacterial gene regulation. Rifampicin time-series data can be used to globally monitor and quantify collision between sense and antisense transcription-complexes. Our findings also highlight that transcriptional events, such as differential RNA decay, partial termination, and internal transcriptional start sites often deviate from gene annotations. Consequently, within a single gene annotation, there exist transcript segments with varying half-lives and transcriptional properties. To address these complexities, we introduce 'rifi', an R-package that analyzes transcriptomic data from rifampicin time series. 'rifi' employs a dynamic programming-based segmentation approach to identify individual transcripts, enabling accurate assessment of RNA stability and detection of diverse transcriptional events.

When push comes to shove - RNA polymerase and DNA-bound protein roadblocks

In recent years, transcriptional roadblocking has emerged as a crucial regulatory mechanism in gene expression, whereby other DNA-bound obstacles can block the progression of transcribing RNA polymerase (RNAP), leading to RNAP pausing and ultimately dissociation from the DNA template. In this review, we discuss the mechanisms by which transcriptional roadblocks can impede RNAP progression, as well as how RNAP can overcome these obstacles to continue transcription. We examine different DNA-binding proteins involved in transcriptional roadblocking and their biophysical properties that determine their effectiveness in blocking RNAP progression. The catalytically dead CRISPR-Cas (dCas) protein is used as an example of an engineered programmable roadblock, and the current literature in understanding the polarity of dCas roadblocking is also discussed. Finally, we delve into a stochastic model of transcriptional roadblocking and highlight the importance of transcription factor binding kinetics and its resistance to dislodgement by an elongating RNAP in determining the strength of a roadblock.

Natural antisense transcript of MYOG regulates development and regeneration in skeletal muscle by shielding the binding sites of MicroRNAs of MYOG mRNA 3'UTR

Natural antisense transcripts (NATs) are endogenous RNAs opposite to sense transcripts, and they can significantly contribute to regulating various biological processes through multiple epigenetic mechanisms. NATs can affect their sense transcripts to regulate the growth and development of skeletal muscle. Our analysis of third-generation full-length transcriptome sequencing data revealed that NATs represented a significant portion of the lncRNA, accounting for up to 30.19%-33.35%. The expression of NATs correlated with myoblast differentiation, and genes expressing NATs were mainly involved in RNA synthesis, protein transport, and cell cycle. We found a NAT of MYOG (MYOG-NAT) in the data. We found that the MYOG-NAT could promote the differentiation of myoblasts in vitro. Additionally, knockdown of MYOG-NAT in vivo led to muscle fiber atrophy and muscle regeneration retardation. Molecular biology experiments demonstrated that MYOG-NAT enhances the stability of MYOG mRNA by competing with miR-128-2-5p, miR-19a-5p, and miR-19b-5p for binding to MYOG mRNA 3'UTR. These findings suggest that MYOG-NAT plays a critical role in skeletal muscle development and provides insights into the post-transcriptional regulation of NATs.

Head-on and co-directional RNA polymerase collisions orchestrate bidirectional transcription termination

Genomic DNA is a crowded track where motor proteins frequently collide. It remains underexplored whether these collisions carry physiological function. In this work, we develop a single-molecule assay to visualize the trafficking of individual E. coli RNA polymerases (RNAPs) on DNA. Based on transcriptomic data, we hypothesize that RNAP collisions drive bidirectional transcription termination of convergent gene pairs. Single-molecule results show that the head-on collision between two converging RNAPs is necessary to prevent transcriptional readthrough but insufficient to release the RNAPs from the DNA. Remarkably, co-directional collision of a trailing RNAP into the head-on collided complex dramatically increases the termination efficiency. Furthermore, stem-loop structures formed in the nascent RNA are required for collisions to occur at well-defined positions between convergent genes. These findings suggest that physical collisions between RNAPs furnish a mechanism for transcription termination and that programmed genomic conflicts can be exploited to co-regulate the expression of multiple genes.

Transgene insertion into the plastid genome alters expression of adjacent native chloroplast genes at the transcriptional and translational levels

In plant biotechnology and basic research, chloroplasts have been used as chassis for the expression of various transgenes. However, potential unintended side effects of transgene insertion and high-level transgene expression on the expression of native chloroplast genes are often ignored and have not been studied comprehensively. Here, we examined expression of the chloroplast genome at both the transcriptional and translational levels in five transplastomic tobacco (Nicotiana tabacum) lines carrying the identical aadA resistance marker cassette in diverse genomic positions. Although none of the lines exhibits a pronounced visible phenotype, the analysis of three lines that contain the aadA insertion in different locations within the petL-petG-psaJ-rpl33-rps18 transcription unit demonstrates that transcriptional read-through from the aadA resistance marker is unavoidable, and regularly causes overexpression of downstream sense-oriented chloroplast genes at the transcriptional and translational levels. Investigation of additional lines that harbour the aadA intergenically and outside of chloroplast transcription units revealed that expression of the resistance marker can also cause antisense effects by interference with transcription/transcript accumulation and/or translation of downstream antisense-oriented genes. In addition, we provide evidence for a previously suggested role of genomically encoded tRNAs in chloroplast transcription termination and/or transcript processing. Together, our data uncover principles of neighbouring effects of chloroplast transgenes and suggest general strategies for the choice of transgene insertion sites and expression elements to minimize unintended consequences of transgene expression on the transcription and translation of native chloroplast genes.

Promoter-pervasive transcription causes RNA polymerase II pausing to boost DOG1 expression in response to salt

Eukaryotic genomes are pervasively transcribed by RNA polymerase II. Yet, the molecular and biological implications of such a phenomenon are still largely puzzling. Here, we describe noncoding RNA transcription upstream of the Arabidopsis thaliana DOG1 gene, which governs salt stress responses and is a key regulator of seed dormancy. We find that expression of the DOG1 gene is induced by salt stress, thereby causing a delay in seed germination. We uncover extensive transcriptional activity on the promoter of the DOG1 gene, which produces a variety of lncRNAs. These lncRNAs, named PUPPIES, are co-directionally transcribed and extend into the DOG1 coding region. We show that PUPPIES RNAs respond to salt stress and boost DOG1 expression, resulting in delayed germination. This positive role of pervasive PUPPIES transcription on DOG1 gene expression is associated with augmented pausing of RNA polymerase II, slower transcription and higher transcriptional burst size. These findings highlight the positive role of upstream co-directional transcription in controlling transcriptional dynamics of downstream genes.

Therapeutic strategies for autism: targeting three levels of the central dogma of molecular biology

The past decade has yielded much success in the identification of risk genes for Autism Spectrum Disorder (ASD), with many studies implicating loss-of-function (LoF) mutations within these genes. Despite this, no significant clinical advances have been made so far in the development of therapeutics for ASD. Given the role of LoF mutations in ASD etiology, many of the therapeutics in development are designed to rescue the haploinsufficient effect of genes at the transcriptional, translational, and protein levels. This review will discuss the various therapeutic techniques being developed from each level of the central dogma with examples including: CRISPR activation (CRISPRa) and gene replacement at the DNA level, antisense oligonucleotides (ASOs) at the mRNA level, and small-molecule drugs at the protein level, followed by a review of current delivery methods for these therapeutics. Since central nervous system (CNS) penetrance is of utmost importance for ASD therapeutics, it is especially necessary to evaluate delivery methods that have higher efficiency in crossing the blood-brain barrier (BBB).

The Functional Meaning of 5'UTR in Protein-Coding Genes

As it is well known, messenger RNA has many regulatory regions along its sequence length. One of them is the 5' untranslated region (5'UTR), which itself contains many regulatory elements such as upstream ORFs (uORFs), internal ribosome entry sites (IRESs), microRNA binding sites, and structural components involved in the regulation of mRNA stability, pre-mRNA splicing, and translation initiation. Activation of the alternative, more upstream transcription start site leads to an extension of 5'UTR. One of the consequences of 5'UTRs extension may be head-to-head gene overlap. This review describes elements in 5'UTR of protein-coding transcripts and the functional significance of protein-coding genes 5' overlap with implications for transcription, translation, and disease.

Knowing when to stop: Transcription termination on protein-coding genes by eukaryotic RNAPII

Gene expression is controlled in a dynamic and regulated manner to allow for the consistent and steady expression of some proteins as well as the rapidly changing production of other proteins. Transcription initiation has been a major focus of study because it is highly regulated. However, termination of transcription also plays an important role in controlling gene expression. Transcription termination on protein-coding genes is intimately linked with 3' end cleavage and polyadenylation of transcripts, and it generally results in the production of a mature mRNA that is exported from the nucleus. Termination on many non-coding genes can also result in the production of a mature transcript. Termination is dynamically regulated-premature termination and transcription readthrough occur in response to a number of cellular signals, and these can have varied consequences on gene expression. Here, we review eukaryotic transcription termination by RNA polymerase II (RNAPII), focusing on protein-coding genes.

Design of Gene Boolean Gates and Circuits with Convergent Promoters

Gene digital circuits are the subject of many research works due to their various potential applications, from hazard detection to medical diagnostic. Moreover, a remarkable number of techniques, developed in electronics, can be used for the construction of biological digital systems. In our previous works, we showed how to automatize the design and modeling of gene digital circuits whose gates were based on transcription and translation regulation. In this chapter, we illustrate how Boolean gates could be implemented by following a particular architecture, the convergent promoter one, rather diffuse in nature but seldom adopted in Synthetic Biology. Beside gate design, we also explain how to extend our previous modeling approach, based on composable parts and pools of molecules, to quantitatively describe and simulate this particular kind of digital biological devices.

Genetic and environmental perturbations alter the rhythmic expression pattern of a circadian long non-coding RNA, Per2AS, in mouse liver

Background: Long non-coding RNAs (lncRNAs) play a wide variety of biological roles without encoding a protein. Although the functions of many lncRNAs have been uncovered in recent years, the regulatory mechanism of lncRNA expression is still poorly understood despite that the expression patterns of lncRNAs are much more specific compared to mRNAs. Here, we investigated the rhythmic expression of Per2AS, a novel lncRNA that regulates circadian rhythms. Given that Per2AS expression is antiphasic to Period2 ( Per2), a core circadian clock gene, and transcribed from the antisense strand of Per2, we hypothesized that the rhythmic Per2AS expression is driven either by its own promoter or by the rhythmic Per2 transcription via transcriptional interference. Methods: We leveraged existing circadian RNA-seq datasets and analyzed the expression patterns of Per2AS and Per2 in response to the genetic or environmental disruption of the circadian rhythm in mouse liver. We tested our hypotheses by comparing the changes in the expression patterns of Per2AS and Per2. Conclusions: We found that, in some cases, Per2AS expression is independently controlled by other circadian transcription factors. In other cases, the pattern of expression change is consistent with both transcriptional interference and independent regulation hypotheses. Although additional experiments will be necessary to distinguish these possibilities, findings from this work contribute to a deeper understanding of the mechanism of how the expression of lncRNA is regulated.

Navigating the Multiverse of Antisense RNAs: The Transcription- and RNA-Dependent Dimension

Evidence accumulated over the past decades shows that the number of identified antisense transcripts is continuously increasing, promoting them from transcriptional noise to real genes with specific functions. Indeed, recent studies have begun to unravel the complexity of the antisense RNA (asRNA) world, starting from the multidimensional mechanisms that they can exert in physiological and pathological conditions. In this review, we discuss the multiverse of the molecular functions of asRNAs, describing their action through transcription-dependent and RNA-dependent mechanisms. Then, we report the workflow and methodologies to study and functionally characterize single asRNA candidates.

Forging a Functional Cure for HIV: Transcription Regulators and Inhibitors

Current antiretroviral therapy (ART) increases the survival of HIV-infected individuals, yet it is not curative. The major barrier to finding a definitive cure for HIV is our inability to identify and eliminate long-lived cells containing the dormant provirus, termed viral reservoir. When ART is interrupted, the viral reservoir ensures heterogenous and stochastic HIV viral gene expression, which can reseed infection back to pre-ART levels. While strategies to permanently eradicate the virus have not yet provided significant success, recent work has focused on the management of this residual viral reservoir to effectively limit comorbidities associated with the ongoing viral transcription still observed during suppressive ART, as well as limit the need for daily ART. Our group has been at the forefront of exploring the viability of the block-and-lock remission approach, focused on the long-lasting epigenetic block of viral transcription such that without daily ART, there is no risk of viral rebound, transmission, or progression to AIDS. Numerous studies have reported inhibitors of both viral and host factors required for HIV transcriptional activation. Here, we highlight and review some of the latest HIV transcriptional inhibitor discoveries that may be leveraged for the clinical exploration of block-and-lock and revolutionize the way we treat HIV infections.

Automated model-predictive design of synthetic promoters to control transcriptional profiles in bacteria

Transcription rates are regulated by the interactions between RNA polymerase, sigma factor, and promoter DNA sequences in bacteria. However, it remains unclear how non-canonical sequence motifs collectively control transcription rates. Here, we combine massively parallel assays, biophysics, and machine learning to develop a 346-parameter model that predicts site-specific transcription initiation rates for any σ70 promoter sequence, validated across 22132 bacterial promoters with diverse sequences. We apply the model to predict genetic context effects, design σ70 promoters with desired transcription rates, and identify undesired promoters inside engineered genetic systems. The model provides a biophysical basis for understanding gene regulation in natural genetic systems and precise transcriptional control for engineering synthetic genetic systems.

A Novel ATM Antisense Transcript ATM-AS Positively Regulates ATM Expression in Normal and Breast Cancer Cells

Objective

The ataxia telangiectasia mutated (ATM) gene is a master regulator in cellular DNA damage response. The dysregulation of ATM expression is frequent in breast cancer, and is known to be involved in the carcinogenesis and prognosis of cancer. However, the underlying mechanism remains unclear. The bioinformatic analysis predicted a potential antisense transcript ATM-antisense (AS) from the opposite strand of the ATM gene. The purpose of this study was to identify ATM-AS and investigate the possible effect of ATM-AS on the ATM gene regulation.

Methods

Single strand-specific RT-PCR was performed to verify the predicted antisense transcript ATM-AS within the ATM gene locus. qRT-PCR and Western blotting were used to detect the expression levels of ATM-AS and ATM in normal and breast cancer cell lines as well as in tissue samples. Luciferase reporter gene assays, biological mass spectrometry, ChIP-qPCR and RIP were used to explore the function of ATM-AS in regulating the ATM expression. Immunofluorescence and host-cell reactivation (HCR) assay were performed to evaluate the biological significance of ATM-AS in ATM-mediated DNA damage repair. Breast cancer tissue samples were used for evaluating the correlation of the ATM-AS level with the ATM expression as well as prognosis of the patients.

Results

The ATM-AS significantly upregulated the ATM gene activity by recruiting KAT5 histone acetyltransferase to the gene promoter. The reduced ATM-AS level led to the abnormal downregulation of ATM expression, and impaired the ATM-mediated DNA damage repair in normal breast cells in vitro. The ATM-AS level was positively correlated with the ATM expression in the examined breast cancer tissue samples, and the patient prognosis.

Conclusion

The present study demonstrated that ATM-AS, an antisense transcript located within the ATM gene body, is an essential positive regulator of ATM expression, and functions by mediating the binding of KAT5 to the ATM promoter. These findings uncover the novel mechanism underlying the dysregulation of the ATM gene in breast cancer, and enrich our understanding of how an antisense transcript regulates its host gene.

Potential multi-modal effects of provirus integration on HIV-1 persistence: lessons from other viruses

Despite antiretroviral therapy (ART), HIV-1 persists as proviruses integrated into the genomic DNA of CD4⁺ T cells. The mechanisms underlying the persistence and clonal expansion of these cells remain incompletely understood. Cases have been described in which proviral integration can alter host gene expression to drive cellular proliferation. Here, we review observations from other genome-integrating human viruses to propose additional putative modalities by which HIV-1 integration may alter cellular function to favor persistence, such as by altering susceptibility to cytotoxicity in virus-expressing cells. We propose that signals implicating such mechanisms may have been masked thus far by the preponderance of defective and/or nonreactivatable HIV-1 proviruses, but could be revealed by focusing on the integration sites of intact proviruses with expression potential.

Mpe1 senses the binding of pre-mRNA and controls 3' end processing by CPF

Most eukaryotic messenger RNAs (mRNAs) are processed at their 3' end by the cleavage and polyadenylation specificity factor (CPF/CPSF). CPF mediates the endonucleolytic cleavage of the pre-mRNA and addition of a polyadenosine (poly(A)) tail, which together define the 3' end of the mature transcript. The activation of CPF is highly regulated to maintain the fidelity of RNA processing. Here, using cryo-EM of yeast CPF, we show that the Mpe1 subunit directly contacts the polyadenylation signal sequence in nascent pre-mRNA. The region of Mpe1 that contacts RNA also promotes the activation of CPF endonuclease activity and controls polyadenylation. The Cft2 subunit of CPF antagonizes the RNA-stabilized configuration of Mpe1. In vivo, the depletion or mutation of Mpe1 leads to widespread defects in transcription termination by RNA polymerase II, resulting in transcription interference on neighboring genes. Together, our data suggest that Mpe1 plays a major role in accurate 3' end processing, activating CPF, and ensuring timely transcription termination.

Dynamic spreading of chromatin-mediated gene silencing and reactivation between neighboring genes in single cells

In mammalian cells genes that are in close proximity can be transcriptionally coupled: silencing or activating one gene can affect its neighbors. Understanding these dynamics is important for natural processes, such as heterochromatin spreading during development and aging, and when designing synthetic gene regulation circuits. Here, we systematically dissect this process in single cells by recruiting and releasing repressive chromatin regulators at dual-gene synthetic reporters, and measuring how fast gene silencing and reactivation spread as a function of intergenic distance and configuration of insulator elements. We find that silencing by KRAB, associated with histone methylation, spreads between two genes within hours, with a time delay that increases with distance. This fast KRAB-mediated spreading is not blocked by the classical cHS4 insulators. Silencing by histone deacetylase HDAC4 of the upstream gene can also facilitate background silencing of the downstream gene by PRC2, but with a days-long delay that does not change with distance. This slower silencing can sometimes be stopped by insulators. Gene reactivation of neighboring genes is also coupled, with strong promoters and insulators determining the order of reactivation. Our data can be described by a model of multi-gene regulation that builds upon previous knowledge of heterochromatin spreading, where both gene silencing and gene reactivation can act at a distance, allowing for coordinated dynamics via chromatin regulator recruitment.

Pervasive transcription: a controlled risk

Transcriptome-wide interrogation of eukaryotic genomes has unveiled the pervasive nature of RNA polymerase II transcription. Virtually, any DNA region with an accessible chromatin structure can be transcribed, resulting in a mass production of noncoding RNAs (ncRNAs) with the potential of interfering with gene expression programs. Budding yeast has proved to be a powerful model organism to understand the mechanisms at play to control pervasive transcription and overcome the risks of hazardous disruption of cellular functions. In this review, we focus on the actors and strategies yeasts employ to govern ncRNA production, and we discuss recent findings highlighting the dangers of losing control over pervasive transcription.

Emerging Functions of lncRNA Loci beyond the Transcript Itself

Thousands of long noncoding RNAs (lncRNAs) are actively transcribed in mammalian genomes. This class of RNAs has important regulatory functions in a broad range of cellular processes and diseases. Numerous lncRNAs have been demonstrated to mediate gene regulation through RNA-based mechanisms. Simultaneously, non-functional lncRNA transcripts derived from the activity of lncRNA loci have been identified, which underpin the notion that a considerable fraction of lncRNA loci exert regulatory functions through mechanisms associated with the production or the activity of lncRNA loci beyond the synthesized transcripts. We particularly distinguish two main RNA-independent components associated with regulatory effects; the act of transcription and the activity of DNA regulatory elements. We describe the experimental approaches to distinguish and understand the functional mechanisms derived from lncRNA loci. These scenarios reveal emerging mechanisms important to understanding the lncRNA implications in genome biology.

It's a DoG-eat-DoG world-altered transcriptional mechanisms drive downstream-of-gene (DoG) transcript production

The past decade has revolutionized our understanding of regulatory noncoding RNAs (ncRNAs). Among the most recently identified ncRNAs are downstream-of-gene (DoG)-containing transcripts that are produced by widespread transcriptional readthrough. The discovery of DoGs has set the stage for future studies to address many unanswered questions regarding the mechanisms that promote readthrough transcription, RNA processing, and the cellular functions of the unique transcripts. In this review, we summarize current findings regarding the biogenesis, function, and mechanisms regulating this exciting new class of RNA molecules.