Variant PRC1 Complex-Dependent H2A Ubiquitylation Drives PRC2 Recruitment and Polycomb Domain Formation

Chromatin modifying activities inherent to polycomb repressive complexes PRC1 and PRC2 play an essential role in gene regulation, cellular differentiation, and development. However, the mechanisms by which these complexes recognize their target sites and function together to form repressive chromatin domains remain poorly understood. Recruitment of PRC1 to target sites has been proposed to occur through a hierarchical process, dependent on prior nucleation of PRC2 and placement of H3K27me3. Here, using a de novo targeting assay in mouse embryonic stem cells we unexpectedly discover that PRC1-dependent H2AK119ub1 leads to recruitment of PRC2 and H3K27me3 to effectively initiate a polycomb domain. This activity is restricted to variant PRC1 complexes, and genetic ablation experiments reveal that targeting of the variant PCGF1/PRC1 complex by KDM2B to CpG islands is required for normal polycomb domain formation and mouse development. These observations provide a surprising PRC1-dependent logic for PRC2 occupancy at target sites in vivo.This study was funded by the Wellcome Trust (WT0834922 and WT081385), CRUK (C28585/A10839), NIHR, EMBO, Lister Institute of Preventative Medicine, RIKEN, MEXT, and JST CRES

Results of the COVID-19 mental health international for the general population (COMET-G) study.

INTRODUCTION: There are few published empirical data on the effects of COVID-19 on mental health, and until now, there is no large international study. MATERIAL AND METHODS: During the COVID-19 pandemic, an online questionnaire gathered data from 55,589 participants from 40 countries (64.85% females aged 35.80 ± 13.61; 34.05% males aged 34.90±13.29 and 1.10% other aged 31.64±13.15). Distress and probable depression were identified with the use of a previously developed cut-off and algorithm respectively. STATISTICAL ANALYSIS: Descriptive statistics were calculated. Chi-square tests, multiple forward stepwise linear regression analyses and Factorial Analysis of Variance (ANOVA) tested relations among variables. RESULTS: Probable depression was detected in 17.80% and distress in 16.71%. A significant percentage reported a deterioration in mental state, family dynamics and everyday lifestyle. Persons with a history of mental disorders had higher rates of current depression (31.82% vs. 13.07%). At least half of participants were accepting (at least to a moderate degree) a non-bizarre conspiracy. The highest Relative Risk (RR) to develop depression was associated with history of Bipolar disorder and self-harm/attempts (RR = 5.88). Suicidality was not increased in persons without a history of any mental disorder. Based on these results a model was developed. CONCLUSIONS: The final model revealed multiple vulnerabilities and an interplay leading from simple anxiety to probable depression and suicidality through distress. This could be of practical utility since many of these factors are modifiable. Future research and interventions should specifically focus on them

Genome-Wide Estrogen Receptor Activity in Breast Cancer.

The largest subtype of breast cancer is characterized by the expression and activity of the estrogen receptor alpha (ERalpha/ER). Although several effective therapies have significantly improved survival, the adaptability of cancer cells means that patients frequently stop responding or develop resistance to endocrine treatment. ER does not function in isolation and multiple associating factors have been reported to play a role in regulating the estrogen-driven transcriptional program. This review focuses on the dynamic interplay between some of these factors which co-occupy ER-bound regulatory elements, their contribution to estrogen signaling, and their possible therapeutic applications. Furthermore, the review illustrates how some ER association partners can influence and reprogram the genomic distribution of the estrogen receptor. As this dynamic ER activity enables cancer cell adaptability and impacts the clinical outcome, defining how this plasticity is determined is fundamental to our understanding of the mechanisms of disease progression

A simplified representation of the responsive model emphasizing that it has properties of a classical bistable switch.

<p>A schematic of the proposed bistable switch (center panel). The ground state at CpG island chromatin, PcG occupancy (left panel), is the default that is overcome only when TF-mediated gene activation reaches a critical threshold. Positive feedback mechanisms between PRC1 and PRC2 reinforce PcG occupancy and antagonize the TrxG state. Beyond the activation threshold, the system switches to the TrxG state (right panel) that is in turn reinforced by positive feedback mechanisms between RNAPII and TrxG factors. This, together with TrxG-mediated antagonism of PcG activities, ensures stability of the TrxG state such that stochastic fluctuations in gene activation signal would not trigger a switch back to the PcG state. However, when gene activation signals drop below a critical threshold, the CpG island will switch back to the default PcG state.</p

Core components of the major PcG complexes in vertebrate cells overlap with CpG islands.

<p>(A) PRC1 complexes catalyze monoubiquitylation of histone H2A lysine 119 (H2AK119ub1). The catalytic subunits are RING1A/B and one of six PCGF protein homologues, PCGF1–6. PRC1 exists in canonical and noncanonical forms. Canonical PRC1 complexes comprise RING1A/B, PCGF2/4, the CBX protein subunit that has a chromodomain (CD) that binds specifically to PRC2-mediated H3K27me3, and the PH subunit. In noncanonical PRC1, CBX proteins are substituted by the RYBP/YAF2 subunit and the PH subunit is absent. Association of additional subunits with noncanonical PRC1 occurs in a manner dependent on the associated PCGF protein. Thus, PCGF1 complexes, discussed extensively herein, include the additional subunits BCOR and KDM2B. KDM2B has a zinc finger CxxC domain (CXXC) that mediates binding to unmethylated CpG dinucleotides. PRC2 complexes methylate histone H3 lysine 27 (H3K27me1/2/3) and comprise the catalytic EZH2 protein and the core subunits EED, SUZ12, and RBAP48. JARID2 is a substoichiometric subunit that has been implicated in PRC2 targeting. (B) PcG complexes occupy CpG islands at target gene promoters: an example from genome-wide ChIP-seq analysis of mouse embryonic stem cells illustrating a PcG target gene, Lhx4. The Bio-CAP procedure provides a molecular readout of the density of unmethylated CpG dinucleotides with peaks corresponding to CpG islands. ChIP-seq for PRC1 (RING1B) and PRC2 (EZH2) subunits illustrates that PcG protein occupancy closely mirrors unmethylated CpG density.</p

CpG Islands Recruit a Histone H3 Lysine 36 Demethylase

In higher eukaryotes, up to 70% of genes have high levels of nonmethylated cytosine/guanine base pairs (CpGs) surrounding promoters and gene regulatory units. These features, called CpG islands, were identified over 20 years ago, but there remains little mechanistic evidence to suggest how these enigmatic elements contribute to promoter function, except that they are refractory to epigenetic silencing by DNA methylation. Here we show that CpG islands directly recruit the H3K36-specific lysine demethylase enzyme KDM2A. Nucleation of KDM2A at these elements results in removal of H3K36 methylation, creating CpG island chromatin that is uniquely depleted of this modification. KDM2A utilizes a zinc finger CxxC (ZF-CxxC) domain that preferentially recognizes nonmethylated CpG DNA, and binding is blocked when the CpG DNA is methylated, thus constraining KDM2A to nonmethylated CpG islands. These data expose a straightforward mechanism through which KDM2A delineates a unique architecture that differentiates CpG island chromatin from bulk chromatin

The effect of different degrees of lockdown and self-identified gender on anxiety, depression and suicidality during the COVID-19 pandemic: Data from the international COMET-G study.

INTRODUCTION: During the COVID-19 pandemic various degrees of lockdown were applied by countries around the world. It is considered that such measures have an adverse effect on mental health but the relationship of measure intensity with the mental health effect has not been thoroughly studied. Here we report data from the larger COMET-G study pertaining to this question. MATERIAL AND METHODS: During the COVID-19 pandemic, data were gathered with an online questionnaire from 55,589 participants from 40 countries (64.85% females aged 35.80 ± 13.61; 34.05% males aged 34.90±13.29 and 1.10% other aged 31.64±13.15). Anxiety was measured with the STAI, depression with the CES-D and suicidality with the RASS. Distress and probable depression were identified with the use of a previously developed cut-off and algorithm respectively. STATISTICAL ANALYSIS: It included the calculation of Relative Risk (RR), Factorial ANOVA and Multiple backwards stepwise linear regression analysis RESULTS: Approximately two-thirds were currently living under significant restrictions due to lockdown. For both males and females the risk to develop clinical depression correlated significantly with each and every level of increasing lockdown degree (RR 1.72 and 1.90 respectively). The combined lockdown and psychiatric history increased RR to 6.88 The overall relationship of lockdown with severity of depression, though significant was small. CONCLUSIONS: The current study is the first which reports an almost linear relationship between lockdown degree and effect in mental health. Our findings, support previous suggestions concerning the need for a proactive targeted intervention to protect mental health more specifically in vulnerable groups