A Two-Step Mechanism for Creating Stable, Condensed Chromatin with the Polycomb Complex PRC1.

The PRC1 complex regulates gene expression by modifying histone proteins and chromatin architecture. Two PRC1 subunits, PSC and Ph, are most implicated in chromatin architecture. In vitro, PRC1 compacts chromatin and inhibits transcription and nucleosome remodeling.

How a disordered linker in the Polycomb protein Polyhomeotic tunes phase separation and oligomerization.

The Polycomb Group (PcG) complex PRC1 represses transcription, forms condensates in cells, and modifies chromatin architecture. These processes are connected through the essential, polymerizing Sterile Alpha Motif (SAM) present in the PRC1 subunit Polyhomeotic (Ph). , Ph SAM drives formation of short oligomers and phase separation with DNA or chromatin in the context of a Ph truncation ("mini-Ph").

Regulation of Polyhomeotic Condensates by Intrinsically Disordered Sequences That Affect Chromatin Binding.

The Polycomb group (PcG) complex PRC1 localizes in the nucleus in condensed structures called Polycomb bodies. The PRC1 subunit Polyhomeotic (Ph) contains an oligomerizing sterile alpha motif (SAM) that is implicated in both PcG body formation and chromatin organization in and mammalian cells. A truncated version of Ph containing the SAM (mini-Ph) forms phase-separated condensates with DNA or chromatin in vitro, suggesting that PcG bodies may form through SAM-driven phase separation.

Identification of R-loop-forming Sequences in Embryos and Tissue Culture Cells Using DRIP-seq.

R-loops are non-canonical nucleic structures composed of an RNA-DNA hybrid and a displaced ssDNA. Originally identified as a source of genomic instability, R-loops have been shown over the last decade to be involved in the targeting of proteins and to be associated with different histone modifications, suggesting a regulatory function. In addition, R-loops have been demonstrated to form differentially during the development of different tissues in plants and to be associated with diseases in mammals.

High throughput screening identifies SOX2 as a super pioneer factor that inhibits DNA methylation maintenance at its binding sites.

Binding of mammalian transcription factors (TFs) to regulatory regions is hindered by chromatin compaction and DNA methylation of their binding sites. Nevertheless, pioneer transcription factors (PFs), a distinct class of TFs, have the ability to access nucleosomal DNA, leading to nucleosome remodelling and enhanced chromatin accessibility. Whether PFs can bind to methylated sites and induce DNA demethylation is largely unknown.

Phase separation by the polyhomeotic sterile alpha motif compartmentalizes Polycomb Group proteins and enhances their activity.

Polycomb Group (PcG) proteins organize chromatin at multiple scales to regulate gene expression. A conserved Sterile Alpha Motif (SAM) in the Polycomb Repressive Complex 1 (PRC1) subunit Polyhomeotic (Ph) has been shown to play an important role in chromatin compaction and large-scale chromatin organization. Ph SAM forms helical head to tail polymers, and SAM-SAM interactions between chromatin-bound Ph/PRC1 are believed to compact chromatin and mediate long-range interactions.

Inheritance of Histone (H3/H4): A Binary Choice?

Histones carry information in the form of post-translational modifications (PTMs). For this information to be propagated through cell cycles, parental histones and their PTMs need to be maintained at the same genomic locations. Yet, during DNA replication, every nucleosome in the genome is disrupted to allow passage of the replisome.

DNA Binding Reorganizes the Intrinsically Disordered C-Terminal Region of PSC in Drosophila PRC1.

Polycomb Group proteins regulate gene expression by modifying chromatin. Polycomb Repressive Complex 1 (PRC1) has two activities: a ubiquitin ligase activity for histone H2A and a chromatin compacting activity. In Drosophila, the Posterior Sex Combs (PSC) subunit of PRC1 is central to both activities.

RNA-DNA strand exchange by the Drosophila Polycomb complex PRC2.

Polycomb Group (PcG) proteins form memory of transient transcriptional repression that is necessary for development. In Drosophila, DNA elements termed Polycomb Response Elements (PREs) recruit PcG proteins. How PcG activities are targeted to PREs to maintain repressed states only in appropriate developmental contexts has been difficult to elucidate.

Antibiotic prescribing for acute uncomplicated cystitis in Lebanese community pharmacies using a simulated patient.

Background: Urinary tract infections are considered as one of the most frequent bacterial infections in the community and hospital settings. In this era of increasing antimicrobial resistance, antimicrobial stewardship has become highly important in the struggle to preserve the effectiveness of available drugs. One the main causes of antibiotic resistance is the inappropriate prescribing of antibiotics; which evidence show that community pharmacists contribute to.

Early exposure to antibiotics in the neonatal intensive care unit alters the taxonomic and functional infant gut microbiome.

Introduction: The infant gut microbiome is thought to play a key role in developing metabolic and immunologic pathways. Antibiotics have been shown to disrupt the human microbiome, but the impact they have on infants during this key window of development remains poorly understood. Through this study, we further characterize the effect antibiotics have on the gut microbiome of infants by looking at metagenomic sequencing data over time.

Antibiotic Prescribing Rate in Lebanese Community Pharmacies: A Nationwide Patient-Simulated Study of Acute Bacterial Rhinosinusitis.

This study aims to evaluate the antibiotic prescribing rate for acute bacterial rhinosinusitis in community pharmacies and to study the corresponding attitude and behavior of participants. A cross-sectional, nationwide study was conducted using a patient-simulated case of bacterial rhinosinusitis. Descriptive data were reported for the medications prescribed, questions asked, and recommendations made.

Expression and Purification of Recombinant Proteins Using the Baculovirus System.

This article describes how to analyze protein expression in cells infected with recombinant baculovirus on a small scale for optimizing protein production, how to maximize and scale up recombinant protein production, and how to purify recombinant proteins. © 2018 by John Wiley & Sons, Inc.

Inheritance of Histones H3 and H4 during DNA Replication In Vitro.

Nucleosomes are believed to carry epigenetic information through the cell cycle, including through DNA replication. It has been known for decades that parental histones are reassembled on newly replicated chromatin, but the mechanisms underlying histone inheritance and dispersal during DNA replication are not fully understood. We monitored the fate of histones H3 or H4 from a single nucleosome through DNA replication in two in vitro systems.

Recent Advances in Understanding Cholangiocarcinoma.

Cholangiocarcinoma (CCA) is an aggressive malignancy that arises from damaged epithelial cells, cholangiocytes, and possibly de-differentiated hepatocytes. CCA has a poor overall survival rate and limited therapeutic options. Based on this data, it is imperative that new diagnostic and therapeutic interventions be developed.

Glioblastoma Multiforme, Diagnosis and Treatment; Recent Literature Review.

Background: Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor, with an incidence of 3.19 cases per 100,000 person years and remarkably poor prognosis showing a 5-year survival rate of 4-5%, and only a 26-33% survival rate at 2 years in clinical trials.

Objective: In this paper, we review the different types of treatment modalities based on the relevant databases.

Chromatin: Polycomb Group SAMs Unite.

Polycomb Group (PcG) proteins assemble a chromatin state that maintains developmental gene repression. A new study combining structure and in vivo analysis details a molecular network from DNA recognition to PcG recruitment, highlighting the essential role of Sterile Alpha Motifs.

Chromatin topology is coupled to Polycomb group protein subnuclear organization.

The genomes of metazoa are organized at multiple scales. Many proteins that regulate genome architecture, including Polycomb group (PcG) proteins, form subnuclear structures. Deciphering mechanistic links between protein organization and chromatin architecture requires precise description and mechanistic perturbations of both.

A polycomb group protein is retained at specific sites on chromatin in mitosis.

Epigenetic regulation of gene expression, including by Polycomb Group (PcG) proteins, may depend on heritable chromatin states, but how these states can be propagated through mitosis is unclear. Using immunofluorescence and biochemical fractionation, we find PcG proteins associated with mitotic chromosomes in Drosophila S2 cells. Genome-wide sequencing of chromatin immunoprecipitations (ChIP-SEQ) from mitotic cells indicates that Posterior Sex Combs (PSC) is not present at well-characterized PcG targets including Hox genes in mitosis, but does remain at a subset of interphase sites.

Chromatin modification by PSC occurs at one PSC per nucleosome and does not require the acidic patch of histone H2A.

Chromatin architecture is regulated through both enzymatic and non-enzymatic activities. For example, the Polycomb Group (PcG) proteins maintain developmental gene silencing using an array of chromatin-based mechanisms. The essential Drosophila PcG protein, Posterior Sex Combs (PSC), compacts chromatin and inhibits chromatin remodeling and transcription through a non-enzymatic mechanism involving nucleosome bridging.

A Polycomb complex remains bound through DNA replication in the absence of other eukaryotic proteins.

Propagation of chromatin states through DNA replication is central to epigenetic regulation and can involve recruitment of chromatin proteins to replicating chromatin through interactions with replication fork components. Here we show using a fully reconstituted T7 bacteriophage system that eukaryotic proteins are not required to tether the Polycomb complex PRC1 to templates during DNA replication. Instead, DNA binding by PRC1 can withstand passage of a simple replication fork.

Preparation of Drosophila tissue culture cells from different stages of the cell cycle for chromatin immunoprecipitation using centrifugal counterflow elutriation and fluorescence-activated cell sorting.

Many nuclear proteins alter their localization during the cell cycle. This includes proteins which regulate and execute cell cycle events and proteins involved in transcription and DNA repair. The core components of chromatin, the histone proteins, also change their modification state through the cell cycle.