Trans- and cis-acting effects of Firre on epigenetic features of the inactive X chromosome

The Role of Ovarian Granulosa Cells Related-ncRNAs in Ovarian Dysfunctions: Mechanism Research and Clinical Exploration

Ovarian dysfunctions, encompassing conditions such as polycystic ovary syndrome (PCOS), premature ovarian failure (POF), premature ovarian insufficiency (POI), and diminished ovarian reserve (DOR), are closely linked to disruptions in follicular development, often tied to granulosa cell (GC) abnormalities. Despite ongoing research, the precise mechanisms underlying these dysfunctions remain elusive. Increasing evidence highlights the pivotal role of non-coding RNAs (ncRNAs) in the pathogenesis of ovarian dysfunctions. As transcripts that do not encode proteins, ncRNAs are capable of regulating gene expression at various levels. They influence GCs by modulating key biological processes including proliferation, apoptosis, autophagy, cell cycle progression, steroidogenesis, mitochondrial function, inflammatory responses, and aging. Disruptions in GC development and function can lead to impaired follicular development, consequently contributing to ovarian dysfunctions. Thus, ncRNAs are likely integral to the regulatory mechanisms underlying these pathologies, exhibiting distinct expression patterns in affected individuals. This review delves into the regulatory roles of ncRNAs in GCs and their implications for ovarian dysfunctions (PCOS, POF, POI, DOR), offering insights into potential biomarkers for ovarian function assessment and novel therapeutic approaches for treating these conditions.

CTCF-mediated insulation and chromatin environment modulate Car5b escape from X inactivation

BACKGROUND

Genes that escape X-chromosome inactivation (XCI) in female somatic cells vary in number and levels of escape among mammalian species and tissues, potentially contributing to species- and tissue-specific sex differences. CTCF, a master chromatin conformation regulator, is enriched at escape regions and may play an important role in regulating escape, but the molecular mechanisms remain elusive.

RESULTS

CTCF binding profiles and epigenetic features were systematically examined at escape genes (escapees) using mouse allelic systems with skewed XCI to distinguish the inactive X (Xi) and active X (Xa) chromosomes. We found that six constitutive and two facultative escapees are located inside 30-800 kb domains marked by convergent arrays of CTCF binding sites, consistent with the formation of chromatin loops. Facultative escapees show clear differences in CTCF binding depending on their XCI status in specific cell types/tissues. In addition, sets of strong and in some cases divergent CTCF binding sites located at the boundary between an escapee and its adjacent neighbors subject to XCI would also help insulate domains. Indeed, deletion but not inversion of a CTCF binding site at the boundary between the facultative escapee Car5b and its silent neighbor Siah1b results in a dramatic reduction of Car5b escape. This is associated with reduced CTCF and cohesin binding, which indicates loss of looping and insulation and is supported by 3C combined with Hi-C analysis. In addition, enrichment in the repressive mark H3K27me3 invades the Car5b domain in deleted cells, consistent with loss of expression from the Xi. In contrast, cells with an inversion of the CTCF binding site retain CTCF and cohesin binding, as well as looping, in line with persistence of escape. Interestingly, the levels of escape increase in cells with deletion of either Dxz4, which disrupts the Xi-specific compact 3D structure, or Firre, which results in lower H3K27me3 enrichment on the Xi, indicating that the structural and epigenetic features of the Xi constrain escape from XCI in wild type conditions.

CONCLUSIONS

Taken together, our findings support the idea that escape from XCI in female somatic cells is modulated by both the topological insulation of domains via CTCF binding and the surrounding heterochromatin environment.

KDM6A facilitates Xist upregulation at the onset of X inactivation

BACKGROUND

X chromosome inactivation (XCI) is a female-specific process in which one X chromosome is silenced to balance X-linked gene expression between the sexes. XCI is initiated in early development by upregulation of the lncRNA Xist on the future inactive X (Xi). A subset of X-linked genes escape silencing and thus have higher expression in females, suggesting female-specific functions. One of these genes is the highly conserved gene Kdm6a, which encodes a histone demethylase that removes methyl groups at H3K27 to facilitate gene expression. KDM6A mutations have been implicated in congenital disorders such as Kabuki Syndrome, as well as in sex differences in development and cancer.

METHODS

Kdm6a was knocked out (KO) using CRISPR/Cas9 gene editing in hybrid female mouse embryonic stem (ES) cells derived either from a 129 × Mus castaneus (cast) cross or a BL6 x cast cross. In one of the lines a transcriptional stop signal inserted in Tsix results in completely skewed X silencing upon differentiation. The effects of both homozygous and heterozygous Kdm6a KO on Xist expression during the onset of XCI were measured by RT-PCR and RNA-FISH. Changes in gene expression and in H3K27me3 enrichment were investigated using allele-specific RNA-seq and Cut&Run, respectively. KDM6A binding to the Xist gene was characterized by Cut&Run.

RESULTS

We observed impaired upregulation of Xist and reduced coating of the Xi during early stages of differentiation in Kdm6a KO cells, both homozygous and heterozygous, suggesting a threshold effect of KDM6A. This was associated with aberrant overexpression of genes from the Xi after differentiation, indicating loss of X inactivation potency. Consistent with KDM6A having a direct role in Xist regulation, we found that the histone demethylase binds to the Xist promoter and KO cells show an increase in H3K27me3 at Xist, consistent with reduced expression.

CONCLUSIONS

These results reveal a novel female-specific role for the X-linked histone demethylase, KDM6A in the initiation of XCI through histone demethylase-dependent activation of Xist during early differentiation. X chromosome inactivation is a female-specific mechanism that evolved to balance sex-linked gene dosage between females (XX) and males (XY) by silencing one X chromosome in females. X inactivation begins with the upregulation of the long noncoding RNA Xist on the future inactive X chromosome. While most genes become silenced on the inactive X chromosome some genes escape inactivation and thus have higher expression in females compared to males, suggesting that escape genes may have female-specific functions. One such gene encodes the histone demethylase KDM6A which function is to turn on gene expression by removing repressive histone modifications. In this study, we investigated the role of KDM6A in the regulation of Xist expression during the onset of X inactivation. We found that KDM6A binds to the Xist gene to remove repressive histone marks and facilitate its expression in early development. Indeed, depletion of KDM6A prevents upregulation of Xist due to abnormal persistence of repressive histone modifications. In turn, this results in aberrant overexpression of genes from the inactive X chromosome. Our findings point to a novel mechanism of Xist regulation during the initiation of X inactivation, which may lead to new avenues of treatment to alleviate congenital disorders such as Kabuki syndrome and sex-biased immune disorders where X-linked gene dosage is perturbed.

X-linked deletion of Crossfirre, Firre, and Dxz4 in vivo uncovers diverse phenotypes and combinatorial effects on autosomes

The lncRNA Crossfirre was identified as an imprinted X-linked gene, and is transcribed antisense to the trans-acting lncRNA Firre. The Firre locus forms an inactive-X-specific interaction with Dxz4, both loci providing the platform for the largest conserved chromatin structures. Here, we characterize the epigenetic profile of these loci, revealing them as the most female-specific accessible regions genome-wide. To address their in vivo role, we perform one of the largest X-linked knockout studies by deleting Crossfirre, Firre, and Dxz4 individually and in combination. Despite their distinct epigenetic features observed on the X chromosome, our allele-specific analysis uncovers these loci as dispensable for imprinted and random X chromosome inactivation. However, we provide evidence that Crossfirre affects autosomal gene regulation but only in combination with Firre. To shed light on the functional role of these sex-specific loci, we perform an extensive standardized phenotyping pipeline and uncover diverse knockout and sex-specific phenotypes. Collectively, our study provides the foundation for exploring the intricate interplay of conserved X-linked loci in vivo.

Stepwise de novo establishment of inactive X chromosome architecture in early development

X chromosome inactivation triggers a dramatic reprogramming of transcription and chromosome architecture. However, how the chromatin organization of inactive X chromosome is established de novo in vivo remains elusive. Here, we identified an Xist-separated megadomain structure (X-megadomains) on the inactive X chromosome in mouse extraembryonic lineages and extraembryonic endoderm (XEN) cell lines, and transiently in the embryonic lineages, before Dxz4-delineated megadomain formation at later stages in a strain-specific manner. X-megadomain boundary coincides with strong enhancer activities and cohesin binding in an Xist regulatory region required for proper Xist activation in early embryos. Xist regulatory region disruption or cohesin degradation impaired X-megadomains in extraembryonic endoderm cells and caused ectopic activation of regulatory elements and genes near Xist, indicating that cohesin loading at regulatory elements promotes X-megadomains and confines local gene activities. These data reveal stepwise X chromosome folding and transcriptional regulation to achieve both essential gene activation and global silencing during the early stages of X chromosome inactivation.

Multifaceted role of CTCF in X-chromosome inactivation

Therian female mammals compensate for the dosage of X-linked gene expression by inactivating one of the X-chromosomes. X-inactivation is facilitated by the master regulator Xist long non-coding RNA, which coats the inactive-X and facilitates heterochromatinization through recruiting different chromatin modifiers and changing the X-chromosome 3D conformation. However, many mechanistic aspects behind the X-inactivation process remain poorly understood. Among the many contributing players, CTCF has emerged as one of the key players in orchestrating various aspects related to X-chromosome inactivation by interacting with several other protein and RNA partners. In general, CTCF is a well-known architectural protein, which plays an important role in chromatin organization and transcriptional regulation. Here, we provide significant insight into the role of CTCF in orchestrating X-chromosome inactivation and highlight future perspectives.

The temporal dynamics of lncRNA Firre-mediated epigenetic and transcriptional regulation

Numerous studies have now demonstrated that lncRNAs can influence gene expression programs leading to cell and organismal phenotypes. Typically, lncRNA perturbations and concomitant changes in gene expression are measured on the timescale of many hours to days. Thus, we currently lack a temporally grounded understanding of the primary, secondary, and tertiary relationships of lncRNA-mediated transcriptional and epigenetic regulation-a prerequisite to elucidating lncRNA mechanisms. To begin to address when and where a lncRNA regulates gene expression, we genetically engineer cell lines to temporally induce the lncRNA Firre. Using this approach, we are able to monitor lncRNA transcriptional regulatory events from 15 min to four days. We observe that upon induction, Firre RNA regulates epigenetic and transcriptional states in trans within 30 min. These early regulatory events result in much larger transcriptional changes after 12 h, well before current studies monitor lncRNA regulation. Moreover, Firre-mediated gene expression changes are epigenetically remembered for days. Overall, this study suggests that lncRNAs can rapidly regulate gene expression by establishing persistent epigenetic and transcriptional states.

Chrom-seq identifies RNAs at chromatin marks

Chromatin marks are associated with transcriptional regulatory activities. However, very few lncRNAs have been characterized with the role in regulating epigenetic marks, largely due to the technical difficulty in identifying chromatin-associating RNA. Current methods are largely limited by the availability of ChIP-grade antibody and the crosslinking, which generates high noise. Here, we developed a method termed Chrom-seq to efficiently capture RNAs associated with various chromatin marks in living cells. Chrom-seq jointly applies highly specific chromatin mark reader with APEX2, which catalyzes the oxidation of biotin-aniline to label the adjacent RNAs for isolation by streptavidin-coated beads. Using the readers of mCBX7/dPC, mCBX1, and mTAF3, we detected RNA species significantly associated with H3K27me3, H3K9me3, and H3K4me3, respectively. We demonstrated that Chrom-seq outperformed other equivalent methods in terms of sensitivity, efficiency, and cost of practice. It provides an antibody-free approach to systematically map RNAs at chromatin marks with potential regulatory roles in epigenetic events.

Emerging roles of nuclear bodies in genome spatial organization

Nuclear bodies (NBs) are biomolecular condensates that participate in various cellular processes and respond to cellular stimuli in the nucleus. The assembly and function of these protein- and RNA-rich bodies, such as nucleoli, nuclear speckles, and promyelocytic leukemia (PML) NBs, contribute to the spatial organization of the nucleus, regulating chromatin activities locally and globally. Recent technological advancements, including spatial multiomics approaches, have revealed novel roles of nucleoli in modulating ribosomal DNA (rDNA) and adjacent non-rDNA chromatin activity, nuclear speckles in scaffolding active genome architecture, and PML NBs in maintaining genome stability during stress conditions. In this review, we summarize emerging functions of these important NBs in the spatial organization of the genome, aided by recently developed spatial multiomics approaches toward this direction.

Xist Deletion in B Cells Results in Systemic Lupus Erythematosus Phenotypes

Systemic lupus erythematosus (SLE) is an autoimmune disease preferentially observed in females. X-linked gene expression in XX females is normalized to that of XY males by X-Chromosome Inactivation (XCI). However, B cells from female SLE patients and mouse models of SLE exhibit mislocalization of Xist RNA, a critical regulator of XCI, and aberrant expression of X-linked genes, suggesting that impairment of XCI may contribute to disease. Here, we find that a subset of female mice harboring a conditional deletion of Xis t in B cells ("Xist cKO") spontaneously develop SLE phenotypes, including expanded activated B cell subsets, disease-specific autoantibodies, and glomerulonephritis. Moreover, pristane-induced SLE-like disease is more severe in Xist cKO mice. Activated B cells from Xist cKO mice with SLE phenotypes have increased expression of proinflammatory X-linked genes implicated in SLE. Together, this work indicates that impaired XCI maintenance in B cells directly contributes to the female-bias of SLE.

Potential roles of inter-chromosomal interactions in cell fate determination

Mammalian genomic DNA is packed in a small nucleus, and its folding and organization in the nucleus are critical for gene regulation and cell fate determination. In interphase, chromosomes are compartmentalized into certain nuclear spaces and territories that are considered incompatible with each other. The regulation of gene expression is influenced by the epigenetic characteristics of topologically associated domains and A/B compartments within chromosomes (intrachromosomal). Previously, interactions among chromosomes detected via chromosome conformation capture-based methods were considered noise or artificial errors. However, recent studies based on newly developed ligation-independent methods have shown that inter-chromosomal interactions play important roles in gene regulation. This review summarizes the recent understanding of spatial genomic organization in mammalian interphase nuclei and discusses the potential mechanisms that determine cell identity. In addition, this review highlights the potential role of inter-chromosomal interactions in early mouse development.

Microarray analysis identifies lncFirre as a potential regulator of obesity-related acute lung injury

AIMS

The inflammatory response in acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is heightened in obesity. The aim of this study was to investigate whether lncRNAs are involved in the effects of obesity on acute lung injury and to find possible effector lncRNAs.

MAIN METHODS

Microarray analysis was used to assess the transcriptional profiles of lncRNAs and mRNAs in lung tissues from normal (CON), high-fat diet induced obese (DIO), and obese ALI mice (DIO-ALI). GO and KEGG analyses were employed to explore the biological functions of differentially expressed genes. A lncRNA-mRNA co-expression network was constructed to identify specific lncRNA. Lung tissues and peripheral blood samples from patients with obesity and healthy lean donors were utilized to confirm the expression characteristics of lncFirre through qRT-PCR. lncFirre was knocked down in MH-S macrophages to explore its function. ELISA and Griess reagent kit were used to detect PGE2 and NO. Flow cytometry was used to detect macrophages polarization.

KEY FINDINGS

There were 475 lncRNAs and 404 mRNAs differentially expressed between DIO and CON, while 1348 lncRNAs and 1349 mRNAs between DIO-ALI and DIO. Obesity increased lncFirre expression in both mice and patients, and PA elevated lncFirre in MH-S. PA exacerbated the inflammation and proinflammatory polarization of MH-S induced by LPS. LncFirre knockdown inhibited the secretion of PGE2 and NO, M1 differentiation while promoted the M2 differentiation in PA and LPS co-challenged MH-S.

SIGNIFICANCE

Interfering with lncFirre effectively inhibit inflammation in MH-S, lncFirre can serve as a promising target for treating obesity-related ALI.

LncRNAs: the good, the bad, and the unknown

Long non-coding RNAs (lncRNAs) are significant contributors in maintaining genomic integrity through epigenetic regulation. LncRNAs can interact with chromatin-modifying complexes in both cis and trans pathways, drawing them to specific genomic loci and influencing gene expression via DNA methylation, histone modifications, and chromatin remodeling. They can also operate as building blocks to assemble different chromatin-modifying components, facilitating their interactions and gene regulatory functions. Deregulation of these molecules has been associated with various human diseases, including cancer, cardiovascular disease, and neurological disorders. Thus, lncRNAs are implicated as potential diagnostic indicators and therapeutic targets. This review discusses the current understanding of how lncRNAs mediate epigenetic control, genomic integrity, and their putative functions in disease pathogenesis.

Aging differentially alters the transcriptome and landscape of chromatin accessibility in the male and female mouse hippocampus

Aging-related memory impairment and pathological memory disorders such as Alzheimer's disease differ between males and females, and yet little is known about how aging-related changes in the transcriptome and chromatin environment differ between sexes in the hippocampus. To investigate this question, we compared the chromatin accessibility landscape and gene expression/alternative splicing pattern of young adult and aged mouse hippocampus in both males and females using ATAC-seq and RNA-seq. We detected significant aging-dependent changes in the expression of genes involved in immune response and synaptic function and aging-dependent changes in the alternative splicing of myelin sheath genes. We found significant sex-bias in the expression and alternative splicing of hundreds of genes, including aging-dependent female-biased expression of myelin sheath genes and aging-dependent male-biased expression of genes involved in synaptic function. Aging was associated with increased chromatin accessibility in both male and female hippocampus, especially in repetitive elements, and with an increase in LINE-1 transcription. We detected significant sex-bias in chromatin accessibility in both autosomes and the X chromosome, with male-biased accessibility enriched at promoters and CpG-rich regions. Sex differences in gene expression and chromatin accessibility were amplified with aging, findings that may shed light on sex differences in aging-related and pathological memory loss.

Heterochromatin organization and phase separation

The eukaryotic nucleus displays a variety of membraneless compartments with distinct biomolecular composition and specific cellular activities. Emerging evidence indicates that protein-based liquid-liquid phase separation (LLPS) plays an essential role in the formation and dynamic regulation of heterochromatin compartmentalization. This feature is especially conspicuous at the pericentric heterochromatin domains. In this review, we will describe our understanding of heterochromatin organization and LLPS. In addition, we will highlight the increasing importance of multivalent weak homo- and heteromolecular interactions in LLPS-mediated heterochromatin compartmentalization in the complex environment inside living cells.

Chromatin-mediated silencing on the inactive X chromosome

In mammals, the second X chromosome in females is silenced to enable dosage compensation between XX females and XY males. This essential process involves the formation of a dense chromatin state on the inactive X (Xi) chromosome. There is a wealth of information about the hallmarks of Xi chromatin and the contribution each makes to silencing, leaving the tantalising possibility of learning from this knowledge to potentially remove silencing to treat X-linked diseases in females. Here, we discuss the role of each chromatin feature in the establishment and maintenance of the silent state, which is of crucial relevance for such a goal.

KDM6A facilitates Xist upregulation at the onset of X inactivation

X chromosome inactivation (XCI) is a female-specific process in which one X chromosome is silenced to balance X-linked gene expression between the sexes. XCI is initiated in early development by upregulation of the lncRNA Xist on the future inactive X (Xi). A subset of X-linked genes escape silencing and thus have higher expression in females, suggesting female-specific functions. One of these genes is the highly conserved gene Kdm6a , which encodes a histone demethylase that removes methyl groups at H3K27 to facilitate gene expression. Here, we investigate the role of KDM6A in the regulation of Xist . We observed impaired upregulation of Xist during early stages of differentiation in hybrid mouse ES cells following CRISPR/Cas9 knockout of Kdm6a . This is associated with reduced Xist RNA coating of the Xi, suggesting diminished XCI potency. Indeed, Kdm6a knockout results in aberrant overexpression of genes from the Xi after differentiation. KDM6A binds to the Xist promoter and knockout cells show an increase in H3K27me3 at Xist . These results indicate that KDM6A plays a role in the initiation of XCI through histone demethylase-dependent activation of Xist during early differentiation.

The Talented LncRNAs: Meshing into Transcriptional Regulatory Networks in Cancer

As a group of diseases characterized by uncontrollable cell growth, cancer is highly multifaceted in how it overrides checkpoints controlling proliferation. Amongst the regulators of these checkpoints, long non-coding RNAs (lncRNAs) can have key roles in why natural biological processes go haywire. LncRNAs represent a large class of regulatory transcripts that can localize anywhere in cells. They were found to affect gene expression on many levels from transcription to mRNA translation and even protein stability. LncRNA participation in such control mechanisms can depend on cell context, with given transcripts sometimes acting as oncogenes or tumor suppressors. Importantly, the tissue-specificity and low expression levels of lncRNAs make them attractive therapeutic targets or biomarkers. Here, we review the various cellular processes affected by lncRNAs and outline molecular strategies they use to control gene expression, particularly in cancer and in relation to transcription factors.

A novel trans-acting lncRNA of ACTG1 that induces the remodeling of ovarian follicles

Previous studies have implicated the attractive role of long noncoding RNAs (lncRNAs) in the remodeling of mammalian tissues. The migration of granulosa cells (GCs), which are the main supporting cells in ovarian follicles, stimulates the follicular remodeling. Here, with the cultured GCs as the follicular model, the actin gamma 1 (ACTG1) was observed to significantly promote the migration and proliferation while inhibit the apoptosis of GCs, suggesting that ACTG1 was required for ovarian remodeling. Moreover, we identified the trans-regulatory lncRNA of ACTG1 (TRLA), which was epigenetically targeted by histone H3 lysine 4 acetylation (H3K4ac). Mechanistically, the 2-375 nt of TRLA bound to ACTG1's mRNA to increase the expression of ACTG1. Furthermore, TRLA facilitated the migration and proliferation while inhibited the apoptosis of GCs, thereby accelerating follicular remodeling. Besides, TRLA acted as a ceRNA for miR-26a to increase the expression of high-mobility group AT-hook 1 (HMGA1). Collectively, TRLA induces the remodeling of ovarian follicles via complementary to ACTG1's mRNA and regulating miR-26a/HMGA1 axis in GCs. These observations revealed a novel and promising trans-acting lncRNA mechanism mediated by H3K4ac, and TRLA might be a new target to restore follicular remodeling and development.

CTCF-mediated insulation and chromatin environment modulate Car5b escape from X inactivation

Background

The number and escape levels of genes that escape X chromosome inactivation (XCI) in female somatic cells vary among tissues and cell types, potentially contributing to specific sex differences. Here we investigate the role of CTCF, a master chromatin conformation regulator, in regulating escape from XCI. CTCF binding profiles and epigenetic features were systematically examined at constitutive and facultative escape genes using mouse allelic systems to distinguish the inactive X (Xi) and active X (Xa) chromosomes.

Results

We found that escape genes are located inside domains flanked by convergent arrays of CTCF binding sites, consistent with the formation of loops. In addition, strong and divergent CTCF binding sites often located at the boundaries between escape genes and adjacent neighbors subject to XCI would help insulate domains. Facultative escapees show clear differences in CTCF binding dependent on their XCI status in specific cell types/tissues. Concordantly, deletion but not inversion of a CTCF binding site at the boundary between the facultative escape gene Car5b and its silent neighbor Siah1b resulted in loss of Car5b escape. Reduced CTCF binding and enrichment of a repressive mark over Car5b in cells with a boundary deletion indicated loss of looping and insulation. In mutant lines in which either the Xi-specific compact structure or its H3K27me3 enrichment was disrupted, escape genes showed an increase in gene expression and associated active marks, supporting the roles of the 3D Xi structure and heterochromatic marks in constraining levels of escape.

Conclusion

Our findings indicate that escape from XCI is modulated both by looping and insulation of chromatin via convergent arrays of CTCF binding sites and by compaction and epigenetic features of the surrounding heterochromatin.

LncRNA-Smad7 mediates cross-talk between Nodal/TGF-β and BMP signaling to regulate cell fate determination of pluripotent and multipotent cells

Transforming growth factor β (TGF-β) superfamily proteins are potent regulators of cellular development and differentiation. Nodal/Activin/TGF-β and BMP ligands are both present in the intra- and extracellular milieu during early development, and cross-talk between these two branches of developmental signaling is currently the subject of intense research focus. Here, we show that the Nodal induced lncRNA-Smad7 regulates cell fate determination via repression of BMP signaling in mouse embryonic stem cells (mESCs). Depletion of lncRNA-Smad7 dramatically impairs cardiomyocyte differentiation in mESCs. Moreover, lncRNA-Smad7 represses Bmp2 expression through binding with the Bmp2 promoter region via (CA)12-repeats that forms an R-loop. Importantly, Bmp2 knockdown rescues defects in cardiomyocyte differentiation induced by lncRNA-Smad7 knockdown. Hence, lncRNA-Smad7 antagonizes BMP signaling in mESCs, and similarly regulates cell fate determination between osteocyte and myocyte formation in C2C12 mouse myoblasts. Moreover, lncRNA-Smad7 associates with hnRNPK in mESCs and hnRNPK binds at the Bmp2 promoter, potentially contributing to Bmp2 expression repression. The antagonistic effects between Nodal/TGF-β and BMP signaling via lncRNA-Smad7 described in this work provides a framework for understanding cell fate determination in early development.

DeepLoop robustly maps chromatin interactions from sparse allele-resolved or single-cell Hi-C data at kilobase resolution

Mapping chromatin loops from noisy Hi-C heatmaps remains a major challenge. Here we present DeepLoop, which performs rigorous bias correction followed by deep-learning-based signal enhancement for robust chromatin interaction mapping from low-depth Hi-C data. DeepLoop enables loop-resolution, single-cell Hi-C analysis. It also achieves a cross-platform convergence between different Hi-C protocols and micrococcal nuclease (micro-C). DeepLoop allowed us to map the genetic and epigenetic determinants of allele-specific chromatin interactions in the human genome. We nominate new loci with allele-specific interactions governed by imprinting or allelic DNA methylation. We also discovered that, in the inactivated X chromosome (X_i), local loops at the DXZ4 'megadomain' boundary escape X-inactivation but the FIRRE 'superloop' locus does not. Importantly, DeepLoop can pinpoint heterozygous single-nucleotide polymorphisms and large structure variants that cause allelic chromatin loops, many of which rewire enhancers with transcription consequences. Taken together, DeepLoop expands the use of Hi-C to provide loop-resolution insights into the genetics of the three-dimensional genome.

Evolutionary divergence of Firre localization and expression

Long noncoding RNAs (lncRNAs) are rapidly evolving and thus typically poorly conserved in their sequences. How these sequence differences affect the characteristics and potential functions of lncRNAs with shared synteny remains unclear. Here we show that the syntenically conserved lncRNA Firre displays distinct expression and localization patterns in human and mouse. Single molecule RNA FISH reveals that in a range of cell lines, mouse Firre (mFirre) is predominantly nuclear, while human FIRRE (hFIRRE) is distributed between the cytoplasm and nucleus. This localization pattern is maintained in human/mouse hybrid cells expressing both human and mouse Firre, implying that the localization of the lncRNA is species autonomous. We find that the majority of hFIRRE transcripts in the cytoplasm are comprised of isoforms that are enriched in RRD repeats. We furthermore determine that in various tissues, mFirre is more highly expressed than its human counterpart. Our data illustrate that the rapid evolution of syntenic lncRNAs can lead to variations in lncRNA localization and abundance, which in turn may result in disparate lncRNA functions even in closely related species.

Histone Modifications and Non-Coding RNAs: Mutual Epigenetic Regulation and Role in Pathogenesis

In the last few years, more and more scientists have suggested and confirmed that epigenetic regulators are tightly connected and form a comprehensive network of regulatory pathways and feedback loops. This is particularly interesting for a better understanding of processes that occur in the development and progression of various diseases. Appearing on the preclinical stages of diseases, epigenetic aberrations may be prominent biomarkers. Being dynamic and reversible, epigenetic modifications could become targets for a novel option for therapy. Therefore, in this review, we are focusing on histone modifications and ncRNAs, their mutual regulation, role in cellular processes and potential clinical application.

Identification and Characterization of a Novel Long Noncoding RNA that Regulates Osteogenesis in Diet-Induced Obesity Mice

As a precursor to type 2 diabetes mellitus (T2D), obesity adversely alters bone cell functions, causing decreased bone quality. Currently, the mechanisms leading to alterations in bone quality in obesity and subsequently T2D are largely unclear. Emerging evidence suggests that long noncoding RNAs (lncRNAs) participate in a vast repertoire of biological processes and play essential roles in gene expression and posttranscriptional processes. Mechanistically, the expression of lncRNAs is implicated in pathogenesis surrounding the aggregation or alleviation of human diseases. To investigate the functional link between specific lncRNA and obesity-associated poor bone quality and elucidate the molecular mechanisms underlying the interaction between the two, we first assessed the structure of the bones in a diet-induced obese (DIO) mouse model. We found that bone microarchitecture markedly deteriorated in the DIO mice, mainly because of aberrant remodeling in the bone structure. The results of in vitro mechanistic experiments supported these observations. We then screened mRNAs and lncRNAs from DIO bones and functionally identified a specific lncRNA, Gm15222. Further analyses demonstrated that Gm15222 promotes osteogenesis and inhibits the expression of adipogenesis-related genes in DIO via recruitment of lysine demethylases KDM6B and KDM4B, respectively. Through this epigenetic pathway, Gm15222 modulates histone methylation of osteogenic genes. In addition, Gm15222 showed a positive correlation with the expression of a neighboring gene, BMP4. Together, the results of this study identified and provided initial characterization of Gm15222 as a critical epigenetic modifier that regulates osteogenesis and has potential roles in targeting the pathophysiology of bone disease in obesity and potential T2D.

MILNP: Plant lncRNA-miRNA Interaction Prediction Based on Improved Linear Neighborhood Similarity and Label Propagation

Knowledge of the interactions between long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) is the basis of understanding various biological activities and designing new drugs. Previous computational methods for predicting lncRNA-miRNA interactions lacked for plants, and they suffer from various limitations that affect the prediction accuracy and their applicability. Research on plant lncRNA-miRNA interactions is still in its infancy. In this paper, we propose an accurate predictor, MILNP, for predicting plant lncRNA-miRNA interactions based on improved linear neighborhood similarity measurement and linear neighborhood propagation algorithm. Specifically, we propose a novel similarity measure based on linear neighborhood similarity from multiple similarity profiles of lncRNAs and miRNAs and derive more precise neighborhood ranges so as to escape the limits of the existing methods. We then simultaneously update the lncRNA-miRNA interactions predicted from both similarity matrices based on label propagation. We comprehensively evaluate MILNP on the latest plant lncRNA-miRNA interaction benchmark datasets. The results demonstrate the superior performance of MILNP than the most up-to-date methods. What's more, MILNP can be leveraged for isolated plant lncRNAs (or miRNAs). Case studies suggest that MILNP can identify novel plant lncRNA-miRNA interactions, which are confirmed by classical tools. The implementation is available on https://github.com/HerSwain/gra/tree/MILNP.

LncRNA-mediated DNA methylation: an emerging mechanism in cancer and beyond

DNA methylation is one of the most important epigenetic mechanisms to regulate gene expression, which is highly dynamic during development and specifically maintained in somatic cells. Aberrant DNA methylation patterns are strongly associated with human diseases including cancer. How are the cell-specific DNA methylation patterns established or disturbed is a pivotal question in developmental biology and cancer epigenetics. Currently, compelling evidence has emerged that long non-coding RNA (lncRNA) mediates DNA methylation in both physiological and pathological conditions. In this review, we provide an overview of the current understanding of lncRNA-mediated DNA methylation, with emphasis on the roles of this mechanism in cancer, which to the best of our knowledge, has not been systematically summarized. In addition, we also discuss the potential clinical applications of this mechanism in RNA-targeting drug development.

Long noncoding RNA LUCAT1 enhances the survival and therapeutic effects of mesenchymal stromal cells post-myocardial infarction

Mesenchymal stromal cell (MSC) transplantation has been a promising therapeutic strategy for repairing heart tissues post-myocardial infarction (MI). Nevertheless, its therapeutic efficacy remains low, which is mainly ascribed to the low viability of transplanted MSCs. Recently, long noncoding RNAs (lncRNAs) have been reported to participate in diverse physiological and pathological processes, but little is known about their role in MSC survival. Using unbiased transcriptome profiling of hypoxia-preconditioned MSCs (HP-MSCs) and normoxic MSCs (N-MSCs), we identified a lncRNA named lung cancer-associated transcript 1 (LUCAT1) under hypoxia. LUCAT1 knockdown reduced the survival of engrafted MSCs and decreased the MSC-based therapeutic potency, as shown by impaired cardiac function, reduced cardiomyocyte survival, and increased fibrosis post-MI. Conversely, LUCAT1 overexpression had the opposite results. Mechanistically, LUCAT1 bound with and recruited jumonji domain-containing 6 (JMJD6) to the promoter of forkhead box Q1 (FOXQ1), which demethylated FOXQ1 at H4R3me^2(s) and H3R2me^2(a), thus downregulating Bax expression and upregulating Bcl-2 expression to attenuate MSC apoptosis. Therefore, our findings revealed the protective effects of LUCAT1 on MSC apoptosis and demonstrated that the LUCAT1-mediated JMJD6-FOXQ1 pathway might represent a novel target to potentiate the therapeutic effect of MSC-based therapy for ischemic cardiovascular diseases.

Genome-wide analysis and functional annotation of chromatin-enriched noncoding RNAs in rice during somatic cell regeneration

BACKGROUND

Plants have the remarkable ability to generate callus, a pluripotent cell mass that acquires competence for subsequent tissue regeneration. Global chromatin remodeling is required for this cell fate transition, but how the process is regulated is not fully understood. Chromatin-enriched noncoding RNAs (cheRNAs) are thought to play important roles in maintaining chromatin state. However, whether cheRNAs participate in somatic cell regeneration in plants has not yet been clarified.

RESULTS

To uncover the characteristics and functions of cheRNAs during somatic cell reprogramming in plants, we systematically investigate cheRNAs during callus induction, proliferation and regeneration in rice. We identify 2284 cheRNAs, most of which are novel long non-coding RNAs or small nucleolar RNAs. These cheRNAs, which are highly conserved across plant species, shuttle between chromatin and the nucleoplasm during somatic cell regeneration. They positively regulate the expression of neighboring genes via specific RNA motifs, which may interact with DNA motifs around cheRNA loci. Large-scale mutant analysis shows that cheRNAs are associated with plant size and seed morphology. Further detailed functional investigation of two che-lncRNAs demonstrates that their loss of function impairs cell dedifferentiation and plant regeneration, highlighting the functions of cheRNAs in regulating the expression of neighboring genes via specific motifs. These findings support cis- regulatory roles of cheRNAs in influencing a variety of rice traits.

CONCLUSIONS

cheRNAs are a distinct subclass of regulatory non-coding RNAs that are required for somatic cell regeneration and regulate rice traits. Targeting cheRNAs has great potential for crop trait improvement and breeding in future.

Long RNA-Mediated Chromatin Regulation in Fission Yeast and Mammals

As part of a complex network of genome control, long regulatory RNAs exert significant influences on chromatin dynamics. Understanding how this occurs could illuminate new avenues for disease treatment and lead to new hypotheses that would advance gene regulatory research. Recent studies using the model fission yeast Schizosaccharomyces pombe (S. pombe) and powerful parallel sequencing technologies have provided many insights in this area. This review will give an overview of key findings in S. pombe that relate long RNAs to multiple levels of chromatin regulation: histone modifications, gene neighborhood regulation in cis and higher-order chromosomal ordering. Moreover, we discuss parallels recently found in mammals to help bridge the knowledge gap between the study systems.

Gene regulation in time and space during X-chromosome inactivation

X-chromosome inactivation (XCI) is the epigenetic mechanism that ensures X-linked dosage compensation between cells of females (XX karyotype) and males (XY). XCI is essential for female embryos to survive through development and requires the accurate spatiotemporal regulation of many different factors to achieve remarkable chromosome-wide gene silencing. As a result of XCI, the active and inactive X chromosomes are functionally and structurally different, with the inactive X chromosome undergoing a major conformational reorganization within the nucleus. In this Review, we discuss the multiple layers of genetic and epigenetic regulation that underlie initiation of XCI during development and then maintain it throughout life, in light of the most recent findings in this rapidly advancing field. We discuss exciting new insights into the regulation of X inactive-specific transcript (XIST), the trigger and master regulator of XCI, and into the mechanisms and dynamics that underlie the silencing of nearly all X-linked genes. Finally, given the increasing interest in understanding the impact of chromosome organization on gene regulation, we provide an overview of the factors that are thought to reshape the 3D structure of the inactive X chromosome and of the relevance of such structural changes for XCI establishment and maintenance.

Rapid Macrosatellite Evolution Promotes X-Linked Hybrid Male Sterility in a Feline Interspecies Cross

The sterility or inviability of hybrid offspring produced from an interspecific mating result from incompatibilities between parental genotypes that are thought to result from divergence of loci involved in epistatic interactions. However, attributes contributing to the rapid evolution of these regions also complicates their assembly, thus discovery of candidate hybrid sterility loci is difficult and has been restricted to a small number of model systems. Here we reported rapid interspecific divergence at the DXZ4 macrosatellite locus in an interspecific cross between two closely related mammalian species: the domestic cat (Felis silvestris catus) and the Jungle cat (Felis chaus). DXZ4 is an interesting candidate due to its structural complexity, copy number variability, and described role in the critical yet complex biological process of X-chromosome inactivation. However, the full structure of DXZ4 was absent or incomplete in nearly every available mammalian genome assembly given its repetitive complexity. We compared highly continuous genomes for three cat species, each containing a complete DXZ4 locus, and discovered that the felid DXZ4 locus differs substantially from the human ortholog, and that it varies in copy number between cat species. Additionally, we reported expression, methylation, and structural conformation profiles of DXZ4 and the X chromosome during stages of spermatogenesis that have been previously associated with hybrid male sterility. Collectively, these findings suggest a new role for DXZ4 in male meiosis and a mechanism for feline interspecific incompatibility through rapid satellite divergence.

Differential Allelic Expression among Long Non-Coding RNAs

Long non-coding RNAs (lncRNA) comprise a diverse group of non-protein-coding RNAs >200 bp in length that are involved in various normal cellular processes and disease states, and can affect coding gene expression through mechanisms in cis or in trans. Since the discovery of the first functional lncRNAs transcribed by RNA Polymerase II, H19 and Xist, many others have been identified and noted for their unusual transcriptional pattern, whereby expression from one chromosome homolog is strongly favored over the other, also known as mono-allelic or differential allelic expression. lncRNAs with differential allelic expression have been observed to play critical roles in developmental gene regulation, chromosome structure, and disease. Here, we will focus on known examples of differential allelic expression of lncRNAs and highlight recent research describing functional lncRNAs expressed from both imprinted and random mono-allelic expression domains.

Single-cell landscape of nuclear configuration and gene expression during stem cell differentiation and X inactivation

BACKGROUND

Mammalian development is associated with extensive changes in gene expression, chromatin accessibility, and nuclear structure. Here, we follow such changes associated with mouse embryonic stem cell differentiation and X inactivation by integrating, for the first time, allele-specific data from these three modalities obtained by high-throughput single-cell RNA-seq, ATAC-seq, and Hi-C.

RESULTS

Allele-specific contact decay profiles obtained by single-cell Hi-C clearly show that the inactive X chromosome has a unique profile in differentiated cells that have undergone X inactivation. Loss of this inactive X-specific structure at mitosis is followed by its reappearance during the cell cycle, suggesting a "bookmark" mechanism. Differentiation of embryonic stem cells to follow the onset of X inactivation is associated with changes in contact decay profiles that occur in parallel on both the X chromosomes and autosomes. Single-cell RNA-seq and ATAC-seq show evidence of a delay in female versus male cells, due to the presence of two active X chromosomes at early stages of differentiation. The onset of the inactive X-specific structure in single cells occurs later than gene silencing, consistent with the idea that chromatin compaction is a late event of X inactivation. Single-cell Hi-C highlights evidence of discrete changes in nuclear structure characterized by the acquisition of very long-range contacts throughout the nucleus. Novel computational approaches allow for the effective alignment of single-cell gene expression, chromatin accessibility, and 3D chromosome structure.

CONCLUSIONS

Based on trajectory analyses, three distinct nuclear structure states are detected reflecting discrete and profound simultaneous changes not only to the structure of the X chromosomes, but also to that of autosomes during differentiation. Our study reveals that long-range structural changes to chromosomes appear as discrete events, unlike progressive changes in gene expression and chromatin accessibility.

X-factors in human disease: Impact of gene content and dosage regulation

The gene content of the X and Y chromosomes has dramatically diverged during evolution. The ensuing dosage imbalance within the genome of males and females has led to unique chromosome-wide regulatory mechanisms with significant and sex-specific impacts on X-linked gene expression. X inactivation or silencing of most genes on one X chromosome chosen at random in females profoundly affects the manifestation of X-linked diseases, as males inherit a single maternal allele, while females express maternal and paternal alleles in a mosaic manner. An additional complication is the existence of genes that escape X inactivation and thus are ubiquitously expressed from both alleles in females. The mosaic nature of X-linked gene expression and the potential for escape can vary between individuals, tissues, cell types, and stages of life. Our understanding of the specialized nature of X-linked genes and of the multilayer epigenetic regulation that influence their expression throughout the organism has been helped by molecular studies conducted by tissue-specific and single-cell-specific approaches. In turn, the definition of molecular events that control X silencing has helped develop new approaches for the treatment of some X-linked disorders. This review focuses on the peculiarities of the X chromosome genetic content and epigenetic regulation in shaping the manifestation of congenital and acquired X-linked disorders in a sex-specific manner.

Identification and Roles of miR-29b-1-3p and miR29a-3p-Regulated and Non-Regulated lncRNAs in Endocrine-Sensitive and Resistant Breast Cancer Cells

Despite improvements in the treatment of endocrine-resistant metastatic disease using combination therapies in patients with estrogen receptor α (ERα) primary tumors, the mechanisms underlying endocrine resistance remain to be elucidated. Non-coding RNAs (ncRNAs), including microRNAs (miRNA) and long non-coding RNAs (lncRNA), are targets and regulators of cell signaling pathways and their exosomal transport may contribute to metastasis. Previous studies have shown that a low expression of miR-29a-3p and miR-29b-3p is associated with lower overall breast cancer survival before 150 mos. Transient, modest overexpression of miR-29b1-3p or miR-29a-3p inhibited MCF-7 tamoxifen-sensitive and LCC9 tamoxifen-resistant cell proliferation. Here, we identify miR-29b-1/a-regulated and non-regulated differentially expressed lncRNAs in MCF-7 and LCC9 cells using next-generation RNA seq. More lncRNAs were miR-29b-1/a-regulated in LCC9 cells than in MCF-7 cells, including DANCR, GAS5, DSCAM-AS1, SNHG5, and CRND. We examined the roles of miR-29-regulated and differentially expressed lncRNAs in endocrine-resistant breast cancer, including putative and proven targets and expression patterns in survival analysis using the KM Plotter and TCGA databases. This study provides new insights into lncRNAs in endocrine-resistant breast cancer.

Revisiting the consequences of deleting the X inactivation center

Mammalian cells equalize X-linked dosages between the male (XY) and female (XX) sexes by silencing one X chromosome in the female sex. This process, known as "X chromosome inactivation" (XCI), requires a master switch within the X inactivation center (Xic). The Xic spans several hundred kilobases in the mouse and includes a number of regulatory noncoding genes that produce functional transcripts. Over three decades, transgenic and deletional analyses have demonstrated both the necessity and sufficiency of the Xic to induce XCI, including the steps of X chromosome counting, choice, and initiation of whole-chromosome silencing. One recent study, however, reported that deleting the noncoding sequences of the Xic surprisingly had no effect for XCI and attributed a sufficiency to drive counting to the coding gene, Rnf12/Rlim Here, we revisit the question by creating independent Xic deletion cell lines. Multiple independent clones carrying heterozygous deletions of the Xic display an inability to up-regulate Xist expression, consistent with a counting defect. This defect is rescued by a second site mutation in Tsix occurring in trans, bypassing the defect in counting. These findings reaffirm the essential nature of noncoding Xic elements for the initiation of XCI.

Balancing cohesin eviction and retention prevents aberrant chromosomal interactions, Polycomb-mediated repression, and X-inactivation

Depletion of architectural factors globally alters chromatin structure but only modestly affects gene expression. We revisit the structure-function relationship using the inactive X chromosome (Xi) as a model. We investigate cohesin imbalances by forcing its depletion or retention using degron-tagged RAD21 (cohesin subunit) or WAPL (cohesin release factor). Cohesin loss disrupts the Xi superstructure, unveiling superloops between escapee genes with minimal effect on gene repression. By contrast, forced cohesin retention markedly affects Xi superstructure, compromises spreading of Xist RNA-Polycomb complexes, and attenuates Xi silencing. Effects are greatest at distal chromosomal ends, where looping contacts with the Xist locus are weakened. Surprisingly, cohesin loss creates an Xi superloop, and cohesin retention creates Xi megadomains on the active X chromosome. Across the genome, a proper cohesin balance protects against aberrant inter-chromosomal interactions and tempers Polycomb-mediated repression. We conclude that a balance of cohesin eviction and retention regulates X inactivation and inter-chromosomal interactions across the genome.

RNAs as Regulators of Cellular Matchmaking

RNA molecules are increasingly being identified as facilitating or impeding the interaction of proteins and nucleic acids, serving as so-called scaffolds or decoys. Long non-coding RNAs have been commonly implicated in such roles, particularly in the regulation of nuclear processes including chromosome topology, regulation of chromatin state and gene transcription, and assembly of nuclear biomolecular condensates such as paraspeckles. Recently, an increased awareness of cytoplasmic RNA scaffolds and decoys has begun to emerge, including the identification of non-coding regions of mRNAs that can also function in a scaffold-like manner to regulate interactions of nascently translated proteins. Collectively, cytoplasmic RNA scaffolds and decoys are now implicated in processes such as mRNA translation, decay, protein localization, protein degradation and assembly of cytoplasmic biomolecular condensates such as P-bodies. Here, we review examples of RNA scaffolds and decoys in both the nucleus and cytoplasm, illustrating common themes, the suitability of RNA to such roles, and future challenges in identifying and better understanding RNA scaffolding and decoy functions.