As phosphorus is one of the most limiting nutrients in many natural and agricultural ecosystems, plants have evolved strategies that cope with its scarcity. Genetic approaches have facilitated the identification of several molecular elements that regulate the phosphate (Pi) starvation response (PSR) of plants, including the master regulator of the transcriptional response to phosphate starvation PHOSPHATE STARVATION RESPONSE1 (PHR1). However, the chromatin modifications underlying the plant transcriptional response to phosphate scarcity remain largely unknown. Here, we present a detailed analysis of changes in chromatin accessibility during phosphate starvation in Arabidopsis thaliana root cells. Root cells undergo a genome-wide remodeling of chromatin accessibility in response to Pi starvation that is often associated with changes in the transcription of neighboring genes. Analysis of chromatin accessibility in the phr1 phl2 double mutant revealed that the transcription factors PHR1 and PHL2 play a key role in remodeling chromatin accessibility in response to Pi limitation. We also discovered that PHR1 and PHL2 play an important role in determining chromatin accessibility and the associated transcription of many genes under optimal Pi conditions, including genes involved in the PSR. We propose that a set of transcription factors directly activated by PHR1 in Pi-starved root cells trigger a second wave of epigenetic changes required for the transcriptional activation of the complete set of low-Pi–responsive genes. Significance Low phosphate (Pi) availability is a major constraint for plant productivity in both natural and agricultural environments. Over the course of evolution, plants acquired a complex cascade of transcriptional responses that enhance their capacity to survive and reproduce in phosphate-poor soils. However, it is unclear to what extent chromatin architecture is modified to activate or repress gene expression in response to Pi starvation. Here, we report the effects of Pi starvation on chromatin accessibility and its association with gene expression. We determined that major remodeling in chromatin accessibility takes place in response to Pi starvation and that this response is activated by the PHR1 family of transcription factors.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most intractable and devastating malignant tumors. Epigenetic modifications such as DNA methylation and histone modification regulate tumor initiation and progression. However, the contribution of histone variants in PDAC is unknown. Here, we demonstrated that the histone variant H2A.Z is highly expressed in PDAC cell lines and PDAC patients and that its overexpression correlates with poor prognosis. Moreover, all three H2A.Z isoforms (H2A.Z.1, H2A.Z.2.1, and H2A.Z.2.2) are highly expressed in PDAC cell lines and PDAC patients. Knockdown of these H2A.Z isoforms in PDAC cell lines induces a senescent phenotype, cell cycle arrest in phase G2/M, increased expression of cyclin-dependent kinase inhibitor CDKN2A/p16, SA-β-galactosidase activity and interleukin 8 production. Transcriptome analysis of H2A.Z-depleted PDAC cells showed altered gene expression in fatty acid biosynthesis pathways and those that regulate cell cycle and DNA damage repair. Importantly, depletion of H2A.Z isoforms reduces the tumor size in a mouse xenograft model in vivo and sensitizes PDAC cells to gemcitabine. Overexpression of H2A.Z.1 and H2A.Z.2.1 more than H2A.Z.2.2 partially restores the oncogenic phenotype. Therefore, our data suggest that overexpression of H2A.Z isoforms enables cells to overcome the oncoprotective barrier associated with senescence, favoring PDAC tumor grow and chemoresistance. These results make H2A.Z a potential candidate as a diagnostic biomarker and therapeutic target for PDAC.

Master hematopoietic transcription factors (TFs) and long noncoding RNAs (lncRNAs) coordinate shaping lineage-specific gene expression programs during hematopoietic differentiation. The architectural protein CCCTC-binding factor (CTCF) has emerged as a pivotal regulator of gene expression in cell differentiation. However, the relationship and its regulatory effect of CTCF on lncRNA genes in hematopoiesis remain elusive. We demonstrated that CTCF constrains the lncRNA DUBRtranscription throughout erythroid differentiation. DUBR is highly expressed in human hematopoietic stem and progenitor cells (HSPCs) but depleted in erythroblasts. DUBR perturbation dysregulates hematopoietic-erythroid cell differentiation genes and facilitates genome-wide activation of regulatory elements. A genomic map of RNA occupancy revealed that DUBR associates with a set of genes involved in regulating hematopoietic differentiation, including the erythroid repressor HES1, which targets a subset of regulatory elements of DUBR-dysregulated genes. Our results support the role of DUBR as a regulator of a hematopoietic differentiation gene program by coordinating the expression of genes and influencing their chromatin regulatory landscape.

Recent evidence suggests that human gene promoters display gene expression regulatory mechanisms beyond the typical single gene local transcription modulation. In mammalian genomes, genes with an associated bidirectional promoter are abundant; bidirectional promoter architecture serves as a regulatory hub for a gene pair expression. However, it has been suggested that its contribution to transcriptional regulation might exceed local transcription initiation modulation. Despite their abundance, the functional consequences of bidirectional promoter architecture remain largely unexplored. This work studies the long-range gene expression regulatory role of a long non-coding RNA gene promoter using chromosome conformation capture methods. We found that this particular bidirectional promoter contributes to distal gene expression regulation in a target-specific manner by establishing promoter–promoter interactions. In particular, we validated that the promoter–promoter interactions of this regulatory element with the promoter of distal gene BBX contribute to modulating the transcription rate of this gene; removing the bidirectional promoter from its genomic context leads to a rearrangement of BBX promoter–enhancer interactions and to increased gene expression. Moreover, long-range regulatory functionality is not directly dependent on its associated non-coding gene pair expression levels.

Polycomb domains safeguard cell identity by maintaining lineage-specific chromatin states enriched in repressive histone modifications, preserving the epigenetic memory of cell lineages. While Polycomb Repressive Complex 2 (PRC2) can re-establish its occupancy after perturbation, the mechanisms that guide de novo Polycomb recruitment remain unclear. To address this, we engineered an auxin-inducible degradation system to reversibly deplete and reintroduce the endogenous PRC2 core subunit Suz12 in mouse embryonic stem cells (mESCs). Genome-wide profiling at an early recovery time point revealed ∼1,100 PRC2 nucleation sites, characterized by rapid Suz12 and histone H3K27me3 re-accumulation with strong signal, with minimal impact on gene expression. These sites were significantly enriched at bivalent promoters, coinciding with unmethylated CpG islands and chromatin states associated with developmental regulation, and were largely conserved in differentiated cells. Motif analysis identified G/C-rich DNA sequences associated with E2F and zinc-finger proteins, alongside strong co-occupancy with MTF2 and JARID2, two PRC2 cofactors previously implicated in Polycomb targeting. Notably, a subset of nucleation sites overlapped with long-range chromatin interaction anchors in histone H3K27me3 HiChIP datasets. These findings reveal that PRC2 de novo nucleation sites are associated with a combination of chromatin states, DNA sequence features, cofactor co-occupancy and spatial genome organization, suggesting that epigenetic memory can be re-established through defined genomic and chromatin features. Author summary: Polycomb group proteins are key epigenetic regulators that silence gene expression by establishing and dispersing repressive chromatin domains marked by histone modifications such as histone H3K27me3 and H2AK119ub1 and are critical for defining cell identity. During differentiation, Polycomb domains are dynamically redistributed, implying a mechanism for de novo targeting to specific loci. How the Polycomb Repressive Complex 2 (PRC2) is initially recruited to these nucleation sites and which features stabilize its binding remain poorly understood. To explore this, we studied the characteristics of the de novo recruitment sites of PRC2 in mouse embryonic stem cells (mESCs) using an auxin-inducible degradation (AID) system targeting PRC2 to deplete and reintroduce the core subunit Suz12. We identified recruitment sites after complete clearance of the histone H3K27me3 through ChIP-seq at a very early time point after Suz12 reintroduction. Most nucleation sites were located at bivalent promoters of developmental genes and correlated with unmethylated CpG islands. Motif analysis revealed over-represented sequences and accessory partners such as MTF2 and JARID2, along with long-range chromatin interactions. These nucleation sites were also conserved in differentiated cells, highlighting their potential role in developmental regulation. Our study provides insight into how Polycomb domains are established and how epigenetic memory is maintained in stem cells.