Repression Of Gene Expression Research Articles

MYT1L deficiency impairs excitatory neuron trajectory during cortical development

Mutations reducing the function of MYT1L, a neuron-specific transcription factor, are associated with a syndromic neurodevelopmental disorder. MYT1L is used as a pro-neural factor in fibroblast-to-neuron transdifferentiation and is hypothesized to influence neuronal specification and maturation, but it is not clear which neuron types are most impacted by MYT1L loss. In this study, we profile 412,132 nuclei from the forebrains of wild-type and MYT1L-deficient mice at three developmental stages: E14 at the peak of neurogenesis, P1 when cortical neurons have been born, and P21 when neurons are maturing, to examine the role of MYT1L levels on neuronal development. MYT1L deficiency disrupts cortical neuron proportions and gene expression, primarily affecting neuronal maturation programs. Effects are mostly cell autonomous and persistent through development. While MYT1L can both activate and repress gene expression, the repressive effects are most sensitive to haploinsufficiency, likely mediating MYT1L syndrome. These findings illuminate MYT1L’s role in orchestrating gene expression during neuronal development, providing insights into the molecular underpinnings of MYT1L syndrome.

The H3K27me3 histone mark correlates with repression of colour and aroma development post-harvest in strawberry fruit.

Strawberry ripening is non-climacteric, and post-harvest fruit enter senescence and deteriorate rapidly. Chilled storage induces transcriptome wide changes in gene expression, including the down-regulation of aroma related genes. Histone marks are associated with transcriptional activation or repression; the H3K27me3 mark is mainly associated with repression of gene expression. Here genes associated with H3K27me3 were identified through ChIP-seq in ripe red strawberry fruit at harvest and after 5 days of chilled storage in the dark. The number of ChIP peaks increased with storage time, indicating an increased role for this mark in regulation of gene expression following chilled dark storage. Comparing ChIP-seq data to RNA-seq data from the same material identified 440 genes whose expression correlates with H3K27me3 repression. Abiotic stress genes, especially cold stress response genes, were down-regulated during storage. Increased association with the H3K27me3 mark indicates that they may be repressed via this epigenetic mark. Other functional groups included cell wall and carbohydrate metabolism. The association with the H3K27me3 mark of two transcription factors (FaHY5 and FaTRAB1) and FaADH, involved in ester biosynthesis, was validated by ChIP-PCR. These three genes are all down-regulated during storage and indicate a network of H3K27me3 gene repression affecting both anthocyanin and ester biosynthesis.

The role of histone post-translational modifications in cancer and cancer immunity: functions, mechanisms and therapeutic implications.

Histones play crucial roles in both promoting and repressing gene expression, primarily regulated through post-translational modifications (PTMs) at specific amino acid residues. Histone PTMs, including methylation, acetylation, ubiquitination, phosphorylation, lactylation, butyrylation, and propionylation, act as important epigenetic markers. These modifications influence not only chromatin compaction but also gene expression. Their importance extends to the treatment and prevention of various human diseases, particularly cancer, due to their involvement in key cellular processes. Abnormal histone modifications and the enzymes responsible for these alterations often serve as critical drivers in tumor cell proliferation, invasion, apoptosis, and stemness. This review introduces key histone PTMs and the enzymes responsible for these modifications, examining their impact on tumorigenesis and cancer progression. Furthermore, it explores therapeutic strategies targeting histone PTMs and offers recommendations for identifying new potential therapeutic targets.

Optogenetic Control of Phosphate-Responsive Genes Using Single-Component Fusion Proteins in Saccharomyces cerevisiae.

Blue light illumination can be detected by light-oxygen-voltage (LOV) photosensing proteins and translated into a range of biochemical responses, facilitating the generation of novel optogenetic tools to control cellular function. Here, we develop new variants of our previously described VP-EL222 light-dependent transcription factor and apply them to study the phosphate-responsive signaling (PHO) pathway in the budding yeast Saccharomyces cerevisiae, exemplifying the utilities of these new tools. Focusing first on the VP-EL222 protein itself, we quantified the tunability of gene expression as a function of light intensity and duration and demonstrated that this system can tolerate the addition of substantially larger effector domains without impacting function. We further demonstrated the utility of several EL222-driven transcriptional controllers in both plasmid and genomic settings, using the PHO5 and PHO84 promoters in their native chromosomal contexts as examples. These studies highlight the utility of light-controlled gene activation using EL222 tethered to either artificial transcription domains or yeast activator proteins (Pho4). Similarly, we demonstrate the ability to optogenetically repress gene expression with EL222 fused to the yeast Ume6 protein. We finally investigated the effects of moving EL222 recruitment sites to different locations within the PHO5 and PHO84 promoters, as well as determining how this artificial light-controlled regulation could be integrated with the native controls dependent on inorganic phosphate (Pi) availability. Taken together, our work expands the applicability of these versatile optogenetic tools in the types of functionalities that they can deliver and the biological questions that can be probed.

BvgR is important for virulence-related phenotypes in Bordetella bronchiseptica.

Bordetella bronchiseptica is a pathogenic bacterium that causes respiratory infections in mammals. Adhesins, toxins, and secretion systems necessary for infection are regulated by the two-component system BvgAS. When the BvgAS system is inactive, there is no transcription of virulence-activated genes, and virulence-repressed genes (vrg) are expressed. The regulation of some vrgs in B. bronchiseptica is dependent upon the virulence-activated gene bvgR. Although having a regulatory role, no DNA-binding domain is described for BvgR. Instead, it contains an EAL domain, usually found in cyclic-di-GMP (c-di-GMP)-specific phosphodiesterases. c-di-GMP is a bacterial second messenger that regulates multiple phenotypes in bacteria, including B. bronchiseptica. The current study aimed to deepen our knowledge about BvgR. We employed RNA-seq analysis to define the BvgR regulon, and then we investigated the phenotypes in which BvgR regulation might be involved such as biofilm formation, cytotoxicity, and virulence. Our result revealed that BvgR inhibits biofilm formation and flagellin expression in virulent phase. Although BvgR has long been considered a repressor protein, our results show that it also upregulates almost 100 genes. This regulation is likely indirect, as BvgR lacks a DNA-binding domain. Notably, among the upregulated genes, we identified 15 associated with the type three secretion system. Consistent with these findings, a B. bronchiseptica strain deficient in bvgR was less cytotoxic than the wild-type strain, elicited a milder immune response, and was less able to persist in the lower respiratory tract of mice.IMPORTANCEBordetella bronchiseptica is a harmful bacterium responsible for respiratory infections in mammals. Its ability to cause disease is tightly regulated by a system called BvgAS. In this study, we focused on understanding the role of a specific gene called bvgR in regulating B. bronchiseptica's virulence factors. Our findings revealed that BvgR, previously thought to primarily repress gene expression, actually plays a complex role in both activating and inhibiting various genes involved in bacterial virulence. This newfound understanding sheds light on the intricate mechanisms underlying B. bronchiseptica's ability to cause infections, providing valuable insights for developing strategies to combat these infections in humans and animals.

Development of compact transcriptional effectors using high-throughput measurements in diverse contexts.

Transcriptional effectors are protein domains known to activate or repress gene expression; however, a systematic understanding of which effector domains regulate transcription across genomic, cell type and DNA-binding domain (DBD) contexts is lacking. Here we develop dCas9-mediated high-throughput recruitment (HT-recruit), a pooled screening method for quantifying effector function at endogenous target genes and test effector function for a library containing 5,092 nuclear protein Pfam domains across varied contexts. We also map context dependencies of effectors drawn from unannotated protein regions using a larger library tiling chromatin regulators and transcription factors. We find that many effectors depend on target and DBD contexts, such as HLH domains that can act as either activators or repressors. To enable efficient perturbations, we select context-robust domains, including ZNF705 KRAB, that improve CRISPRi tools to silence promoters and enhancers. We engineer a compact human activator called NFZ, by combining NCOA3, FOXO3 and ZNF473 domains, which enables efficient CRISPRa with better viral delivery and inducible control of chimeric antigen receptor T cells.

Global loss of promoter–enhancer connectivity and rebalancing of gene expression during early colorectal cancer carcinogenesis

Although three-dimensional (3D) genome architecture is crucial for gene regulation, its role in disease remains elusive. We traced the evolution and malignant transformation of colorectal cancer (CRC) by generating high-resolution chromatin conformation maps of 33 colon samples spanning different stages of early neoplastic growth in persons with familial adenomatous polyposis (FAP). Our analysis revealed a substantial progressive loss of genome-wide cis-regulatory connectivity at early malignancy stages, correlating with nonlinear gene regulation effects. Genes with high promoter–enhancer (P–E) connectivity in unaffected mucosa were not linked to elevated baseline expression but tended to be upregulated in advanced stages. Inhibiting highly connected promoters preferentially represses gene expression in CRC cells compared to normal colonic epithelial cells. Our results suggest a two-phase model whereby neoplastic transformation reduces P–E connectivity from a redundant state to a rate-limiting one for transcriptional levels, highlighting the intricate interplay between 3D genome architecture and gene regulation during early CRC progression.

Mrc1Claspin is essential for heterochromatin maintenance in Schizosaccharomyces pombe.

In eukaryotes, maintenance of heterochromatin structure that represses gene expression during cell proliferation is essential for guaranteeing cell identity. However, how heterochromatin is maintained and transmitted to the daughter cells remains elusive. In this study, we constructed a reporter system to study the maintenance of heterochromatin in the subtelomeric region of the fission yeast, Schizosaccharomyces pombe. We demonstrated that once subtelomeric heterochromatin was established, it tended to be maintained as a metastable structure through cell proliferation. Using this system, we screened an S. pombe genome-wide gene deletion library for subtelomeric heterochromatin maintenance factors and identified 57 genes related to various cellular processes, in addition to well-characterized heterochromatin factors. We focused on Mrc1Claspin, a mediator of DNA replication checkpoint. We found that Mrc1 maintains heterochromatin structure not only at the subtelomeres but also at the pericentromeres and mating-type regions. Furthermore, we showed that Mrc1 is required for the localization of Snf2/Hdac-containing Repressor Complex (SHREC) and the maintenance of hypoacetylation state of histone H3K14. This study complements the recent discoveries that Mrc1 functions as a histone H3-H4 chaperone in heterochromatin maintenance.

Optogenetic control of phosphate-responsive genes using single component fusion proteins in Saccharomyces cerevisiae.

Blue light illumination can be detected by Light-Oxygen-Voltage (LOV) photosensing proteins and translated into a range of biochemical responses, facilitating the generation of novel optogenetic tools to control cellular function. Here, we develop new variants of our previously described VP-EL222 light-dependent transcription factor and apply them to study the phosphate-responsive signaling ( PHO ) pathway in the budding yeast Saccharomyces cerevisiae , exemplifying the utilities of these new tools. Focusing first on the VP-EL222 protein itself, we quantified the tunability of gene expression as a function of light intensity and duration, and demonstrated that this system can tolerate the addition of substantially larger effector domains without impacting function. We further demonstrated the utility of several EL222-driven transcriptional controllers in both plasmid and genomic settings, using the PHO5 and PHO84 promoters in their native chromosomal contexts as examples. These studies highlight the utility of light-controlled gene activation using EL222 tethered to either artificial transcription domains or yeast activator proteins (Pho4). Similarly, we demonstrate the ability to optogenetically repress gene expression with EL222 fused to the yeast Ume6 protein. We finally investigated the effects of moving EL222 recruitment sites to different locations within the PHO5 and PHO84 promoters, as well as determining how this artificial light-controlled regulation could be integrated with the native controls dependent on inorganic phosphate (P i ) availability. Taken together, our work expands the applicability of these versatile optogenetic tools in the types of functionalities they can deliver and biological questions that can be probed.

ZNF512B binds RBBP4 via a variant NuRD interaction motif and aggregates chromatin in a NuRD complex-independent manner.

The evolutionarily conserved histone variant H2A.Z plays a crucial role in various DNA-based processes, but the mechanisms underlying its activity are not completely understood. Recently, we identified the zinc finger (ZF) protein ZNF512B as a protein associated with H2A.Z, HMG20A and PWWP2A. Here, we report that high levels of ZNF512B expression lead to nuclear protein and chromatin aggregation foci that form in a manner that is dependent on the ZF domains of ZNF512B. Notably, we demonstrate ZNF512B binding to the nucleosome remodeling and deacetylase (NuRD) complex. We discover a conserved amino acid sequence within ZNF512B that resembles the NuRD-interaction motif (NIM) previously identified in FOG-1 and other transcriptional regulators. By solving the crystal structure of this motif bound to the NuRD component RBBP4 and by applying several biochemical and biophysical assays, we demonstrate that this internal NIM is both necessary and sufficient for robust and high-affinity NuRD binding. Transcriptome analyses and reporter assays identify ZNF512B as a repressor of gene expression that can act in both NuRD-dependent and -independent ways. Our study might have implications for diseases in which ZNF512B expression is deregulated, such as cancer and neurodegenerative diseases, and hints at the existence of more proteins as potential NuRD interactors.

Fpa (YlaN) is an iron(II) binding protein that functions to relieve Fur-mediated repression of gene expression in Staphylococcus aureus.

Iron (Fe) is a trace nutrient required by nearly all organisms. As a result of the demand for Fe and the toxicity of non-chelated cytosolic ionic Fe, regulatory systems have evolved to tightly balance Fe acquisition and usage while limiting overload. In most bacteria, including the mammalian pathogen Staphylococcus aureus, the ferric uptake regulator (Fur) is the primary transcriptional regulator controlling the transcription of genes that code for Fe uptake and utilization proteins. Fpa (formerly YlaN) was demonstrated to be essential in Bacillus subtilis unless excess Fe is added to the growth medium, suggesting a role in Fe homeostasis. Here, we demonstrate that Fpa is essential in S. aureus upon Fe deprivation. Null fur alleles bypassed the essentiality of Fpa. The absence of Fpa abolished the derepression of Fur-regulated genes during Fe limitation. Bioinformatic analyses suggest that fpa was recruited to Gram-positive bacteria and, once acquired, was maintained in the genome as it co-evolved with Fur. Consistent with a role for Fpa in alleviating Fur-dependent repression, Fpa and Fur interacted in vivo, and Fpa decreased the DNA-binding ability of Fur in vitro. Fpa bound Fe(II) in vitro using oxygen or nitrogen ligands with an association constant that is consistent with a physiological role in Fe homeostasis. These findings have led to a model wherein Fpa is an Fe(II) binding protein that influences Fur-dependent regulation through direct interaction.IMPORTANCEIron (Fe) is an essential nutrient for nearly all organisms. If Fe homeostasis is not maintained, Fe may accumulate in the cytosol, which can be toxic. Questions remain about how cells efficiently balance Fe uptake and usage to prevent overload. Iron uptake and proper metalation of proteins are essential processes in the mammalian bacterial pathogen Staphylococcus aureus. Understanding the gene products involved in the genetic regulation of Fe uptake and usage and the physiological adaptations that S. aureus uses to survive in Fe-depleted conditions provides insight into pathogenesis. Herein, we demonstrate that the DNA-binding activity of the ferric uptake regulator transcriptional repressor is alleviated under Fe limitation, but uniquely, in S. aureus, alleviation requires the presence of Fpa.

THE EPIGENETIC REGULATORY PROTEIN CBX2 AS A NOVEL THERAPEUTIC TARGET FOR GLIOBLASTOMA

Abstract AIMS Glioblastoma (GBM) is the deadliest and most common form of brain tumour. The average length of survival for GBM patients remains low, in part, due to a lack of targeted therapeutics. Identification and validation of novel therapeutic targets is therefore crucial. Chomobox 2 (CBX2; a component of polycomb repressive complex 1 (PRC1)), represses gene expression and has a pro-oncogenic role in several aggressive cancer subtypes. CBX2 expression is elevated in GBM, however, very little is known about its role in this deadly disease. We aim to assess the phenotypic and gene expression effects of preventing CBX2-chromatin interaction in patient-derived GBM cell models, and to determine the functional mechanisms by which CBX2 promotes GBM progression; thereby determining its potential as a novel therapeutic target. METHOD Crucial to impactful target validation is the use of translationally relevant models, this study utilises a 3D spheroid model, using patient-derived cells, which more closely recapitulates the in vivo tumour microenvironment. GBM cell monolayers and spheroids were treated with SW2_152F, a selective CBX2 inhibitor. The phenotypic effects of CBX2 inhibition were assessed by cell count, CellTiter-Glo viability assays, fluorescence microscopy, and flow cytometry. Genes and biological pathways differentially regulated following CBX2 inhibition were assessed by RNA-sequencing and Gene Set Enrichment Analysis (GSEA). RESULTS Inhibition of CBX2 induced cell death and reduced cell viability in both 2D and 3D GBM cultures. RNA-seq and GSEA of SW2_152F-treated cells identified dysregulation of gene signatures involved in pro-oncogenic MYC and E2F signalling pathways, and dysregulation of genes associated with G2/M cell cycle progression. CONCLUSION Preventing CBX2-chromatin interaction induces GBM cell death. Further research will identify CBX2- chromatin binding sites to characterise the activity and direct regulatory role of CBX2 in GBM. Furthermore, we will assess the phenotypic and gene expression effects of CBX2 inhibition and depletion on ex vivo maintained GBM tissue biopsies.

Cocaine taking and craving produce distinct transcriptional profiles in dopamine neurons.

Dopamine (DA) signaling plays an essential role in reward valence attribution and in encoding the reinforcing properties of natural and artificial rewards. The adaptive responses from midbrain dopamine neurons to artificial rewards such as drugs of abuse are therefore important for understanding the development of substance use disorders. Drug-induced changes in gene expression are one such adaptation that can determine the activity of dopamine signaling in projection regions of the brain reward system. One of the major challenges to obtaining this understanding involves the complex cellular makeup of the brain, where each neuron population can be defined by a distinct transcriptional profile. To bridge this gap, we have adapted a virus-based method for labeling and capture of dopamine nuclei, coupled with nuclear RNA-sequencing, to study the transcriptional adaptations, specifically, of dopamine neurons in the ventral tegmental area (VTA) during cocaine taking and cocaine craving, using a mouse model of cocaine intravenous self-administration (IVSA). Our results show significant changes in gene expression across non-drug operant training, cocaine taking, and cocaine craving, highlighted by an enrichment of repressive epigenetic modifying enzyme gene expression during cocaine craving. Immunohistochemical validation further revealed an increase of H3K9me3 deposition in DA neurons during cocaine craving. These results demonstrate that cocaine-induced transcriptional adaptations in dopamine neurons vary by phase of self-administration and underscore the utility of this approach for identifying relevant phase-specific molecular targets to study the behavioral course of substance use disorders.

Visualization of Type IV-A1 CRISPR-mediated repression of gene expression and plasmid replication.

Type IV CRISPR-Cas (clustered regularly interspaced short palindromic repeats and CRISPR-associated proteins) effector complexes are often encoded on plasmids and are proposed to prevent the replication of competing plasmids. The Type IV-A1 CRISPR-Cas system of Pseudomonas oleovorans additionally harbors a CRISPR RNA (crRNA) that tightly regulates the transcript levels of a chromosomal target and represents a natural CRISPR interference (CRISPRi) tool. This study investigates CRISPRi effects of this system using synthetic crRNAs against genome and plasmid sequences. Targeting of reporter genes revealed extended interference in P. oleovorans and Escherichia coli cells producing recombinant CRISPR ribonucleoprotein (crRNP) complexes. RNA sequencing (RNA-seq) analyses of Type IV-A1 CRISPRi-induced transcriptome alterations demonstrated highly effective long-range downregulation of histidine operon expression, whereas CRISPRi effects of dCas9 remained limited to the vicinity of its binding site. Single-molecule microscopy uncovered the localization dynamics of crRNP complexes. The tracks of fluorescently labeled crRNPs co-localized with regions of increased plasmid replication, supporting efficient plasmid targeting. These results identify mechanistic principles that facilitate the application of Type IV-A1 CRISPRi for the regulation of gene expression and plasmid replication.

The TOP-2/condensin II axis silences transcription during germline specification in C. elegans.

In C. elegans, the germline is specified via a preformation mechanism that relies on the PIE-1 protein's ability to globally silence mRNA transcription in germline precursor cells, also known as the P lineage. Recent work from our group has identified additional genome silencing events in C. elegans during oogenesis and in starved L1 larvae, and these require the condensin II complex, topoisomerase II (TOP-2), and components of the H3K9me/heterochromatin pathway. Interestingly, silencing in oocytes also requires PIE-1, but this is not the case in starved L1s. Here, we ask if additional genome silencing components besides PIE-1 are required to repress gene expression in the P lineage of early embryos, and we find that condensin II and TOP-2 are required and the H3K9me/heterochromatin pathway is not. We show that depletion of TOP-2/condensin II activates the normally suppressed RNA polymerase II to inappropriately transcribe somatic genes in the P lineage. We also present evidence that while both PIE-1 and TOP-2/condensin II are required for genome silencing in the P lineage, PIE-1 can silence transcription independently of TOP-2/condensin II when misexpressed in somatic cells. Thus, in oocytes, all three genome silencing systems (TOP-2/condensin II, H3K9me, and PIE-1) are operational while in both early embryos and starved L1s two of the three are active. Our data show that multiple, redundantly acting genome silencing mechanisms act in a mix and match manner to repress transcription at different developmental stages in the C. elegans germline.

Competing endogenous RNAs (ceRNAs) and drug resistance to cancer therapy.

Competing endogenous RNAs (ceRNAs) are transcripts that possess highly similar microRNA response elements (MREs). microRNAs (miRNAs) are short, endogenous, single-stranded non-coding RNAs (ncRNAs) that can repress gene expression by binding to MREs on the 3' untranslated regions (UTRs) of the target mRNA transcripts to suppress gene expression by promoting mRNA degradation and/or inhibiting protein translation. mRNA transcripts, circular RNAs (circRNAs), long non-coding RNAs (lncRNAs), and transcribed pseudogenes could share similar MREs, and they can compete for the same pool of miRNAs. These ceRNAs may affect the level of one another by competing for their shared miRNAs. This interplay between different RNAs constitutes a ceRNA network, which regulates many important biological processes. Cancer drug resistance is a major factor leading to treatment failure in patients receiving chemotherapy. It can be acquired through genetic, epigenetic, and various tumor microenvironment mechanisms. The involvement of ceRNA crosstalk and its disruption in chemotherapy resistance is attracting attention in the cancer research community. This review presents an updated summary of the latest research on ceRNA dysregulation causing drug resistance across different cancer types and chemotherapeutic drug classes. Interestingly, accumulating evidence suggests that ceRNAs may be used as prognostic biomarkers to predict clinical response to cancer chemotherapy. Nevertheless, detailed experimental investigations of the putative ceRNA networks generated by computational algorithms are needed to support their translation for therapeutic and prognostic applications.

Assessment of Sodium Butyrate’s Pharmacological Effects on Gentamicin-induced Nephrotic Disorders in a Rat Model

Background Sodium butyrate (SB) used to increase oxidative stress was reduced and the glutathione redox pathway was boosted. It inhibits proliferation, induction of differentiation, and induction or repression of gene expression and it has also anti-inflammatory action. This is endorsed for suppression of nephrotic symptoms. Objectives The present study was carried out to evaluate the nephroprotective activity of SB on gentamicin-induced nephrotoxicity in rats. Materials and Methods Present research work was designed to estimate pharmacological potential of SB in gentamicin-induced nephrotic disorder. The pharmacological prospective was estimated in gentamicin-induced rats through the oral administration of SB formulation 200 mg/kg and 300 mg/kg BW. Results The study observed that the SB significantly protects the kidneys from gentamicin-induced nephrotic disorders. Gentamicin 100 mg/kg for 7 days was used for induction of nephrotoxicity in Wistar rats by intraperitoneal administration. The administration of SB was observed to decrease the occurrence of glomerular congestion, vascular congestion, epithelial desquamation, inflammatory cell build-up, and kidney cell necrosis induced by gentamicin. The dose of SB maintained the gentamicin-induced increased creatinine (0.62±0.05), serum urea (18.10±0.79), uric acid (2.10±0.28), and blood urea nitrogen (BUN) (17.56±0.55) levels. This fact is further sustained by the histopathological examinations. Conclusion Sodium butyrate formulation with antinephrotic activity in maintaining uremic solutes such as urea, uric acid, creatinine, BUN, ketone, urobilinogen, glucose, specific gravity, and urine pH in Wistar rats with gentamicin-induced glomerulonephritis (GN). The SB was administered to the animals at doses of 200 and 300 mg/kg body weight. Pretreatment with the drug showed promising results in maintaining elevated parameters in nephritic rats within a short duration.

CyAbrB2 is a nucleoid-associated protein in Synechocystis controlling hydrogenase expression during fermentation.

The hox operon in Synechocystis sp. PCC 6803, encoding bidirectional hydrogenase responsible for H2 production, is transcriptionally upregulated under microoxic conditions. Although several regulators for hox transcription have been identified, their dynamics and higher-order DNA structure of hox region in microoxic conditions remain elusive. We focused on key regulators for the hox operon: cyAbrB2, a conserved regulator in cyanobacteria, and SigE, an alternative sigma factor. Chromatin immunoprecipitation sequencing revealed that cyAbrB2 binds to the hox promoter region under aerobic conditions, with its binding being flattened in microoxic conditions. Concurrently, SigE exhibited increased localization to the hox promoter under microoxic conditions. Genome-wide analysis revealed that cyAbrB2 binds broadly to AT-rich genome regions and represses gene expression. Moreover, we demonstrated the physical interactions of the hox promoter region with its distal genomic loci. Both the transition to microoxic conditions and the absence of cyAbrB2 influenced the chromosomal interaction. From these results, we propose that cyAbrB2 is a cyanobacterial nucleoid-associated protein (NAP), modulating chromosomal conformation, which blocks RNA polymerase from the hox promoter in aerobic conditions. We further infer that cyAbrB2, with altered localization pattern upon microoxic conditions, modifies chromosomal conformation in microoxic conditions, which allows SigE-containing RNA polymerase to access the hox promoter. The coordinated actions of this NAP and the alternative sigma factor are crucial for the proper hox expression in microoxic conditions. Our results highlight the impact of cyanobacterial chromosome conformation and NAPs on transcription, which have been insufficiently investigated.

CyAbrB2 is a nucleoid-associated protein in Synechocystis controlling hydrogenase expression during fermentation

The hox operon in Synechocystis sp. PCC 6803, encoding bidirectional hydrogenase responsible for H2 production, is transcriptionally upregulated under microoxic conditions. Although several regulators for hox transcription have been identified, their dynamics and higher-order DNA structure of hox region in microoxic conditions remain elusive. We focused on key regulators for the hox operon: cyAbrB2, a conserved regulator in cyanobacteria, and SigE, an alternative sigma factor. Chromatin immunoprecipitation sequencing revealed that cyAbrB2 binds to the hox promoter region under aerobic conditions, with its binding being flattened in microoxic conditions. Concurrently, SigE exhibited increased localization to the hox promoter under microoxic conditions. Genome-wide analysis revealed that cyAbrB2 binds broadly to AT-rich genome regions and represses gene expression. Moreover, we demonstrated the physical interactions of the hox promoter region with its distal genomic loci. Both the transition to microoxic conditions and the absence of cyAbrB2 influenced the chromosomal interaction. From these results, we propose that cyAbrB2 is a cyanobacterial nucleoid-associated protein (NAP), modulating chromosomal conformation, which blocks RNA polymerase from the hox promoter in aerobic conditions. We further infer that cyAbrB2, with altered localization pattern upon microoxic conditions, modifies chromosomal conformation in microoxic conditions, which allows SigE-containing RNA polymerase to access the hox promoter. The coordinated actions of this NAP and the alternative sigma factor are crucial for the proper hox expression in microoxic conditions. Our results highlight the impact of cyanobacterial chromosome conformation and NAPs on transcription, which have been insufficiently investigated.

Identification and characterization of archaeal-type FAD synthase as a novel tractable drug target from the parasitic protozoa Entamoeba histolytica.

Flavin adenine dinucleotide (FAD) is an essential cofactor for numerous flavoenzymes present in all living organisms. The biosynthesis of FAD from riboflavin involves two sequential reactions catalyzed by riboflavin kinase and flavin adenine dinucleotide synthase (FADS). Entamoeba histolytica, the protozoan parasite responsible for amebiasis, apparently lacks a gene encoding FADS that share similarity with bacterial and eukaryotic canonical FADS, yet it can synthesize FAD. In this study, we have identified the gene responsible for FADS and thoroughly characterized physiological and biochemical properties of FADS from E. histolytica. Phylogenetic analysis revealed that the gene was likely laterally transferred from archaea. The kinetic properties of recombinant EhFADS were consistent with the notion that EhFADS is of archaeal origin, exhibiting KM and kcat values similar to those of the arachaeal enzyme while significantly differing from the human counterpart. Repression of gene expression of EhFADS by epigenetic gene silencing caused substantial reduction in FAD levels and parasite growth, underscoring the importance of EhFADS for the parasite. Furthermore, we demonstrated that EhFADS gene silencing reduced thioredoxin reductase activity, which requires FAD as a cofactor and makes the ameba more susceptible to metronidazole. In summary, this study unveils unique evolutionary and biochemical features of EhFADS and underscores its significance as a promising drug target in combating human amebiasis.IMPORTANCEFAD is important for all forms of life, yet its role and metabolism are still poorly studied in E. histolytica, the protozoan parasite causing human amebiasis. Our study uncovers the evolutionary unique key enzyme, archaeal-type FADS for FAD biosynthesis from E. histolytica for the first time. Additionally, we showed the essentiality of this enzyme for parasite survival, highlighting its potential as target for drug development against E. histolytica infections.