Xist RNA repeat E is essential for ASH2L recruitment to the inactive X and regulates histone modifications and escape gene expression

Long non-coding RNAs as promising targets for controlling disease vector mosquitoes

Hematophagous female mosquitoes are important vectors of numerous devastating human diseases, posing a major public health threat. Effective prevention and control of mosquito-borne diseases rely considerably on progress in understanding the molecular mechanisms of various life activities, and accordingly, the molecules that regulate the various life activities of mosquitoes are potential targets for implementing future vector control strategies. Many long non-coding RNAs (lncRNAs) have been identified in mosquitoes and significant progress has been made in determining their functions. Here, we present a comprehensive overview of the research advances on mosquito lncRNAs, including their molecular identification, function, and interaction with other non-coding RNAs, as well as their synergistic regulatory roles in mosquito life activities. We also highlight the potential roles of competitive endogenous RNAs in mosquito growth and development, as well as in insecticide resistance and virus-host interactions. Insights into the biological functions and mechanisms of lncRNAs in mosquito life activities, viral replication, pathogenesis, and transmission will contribute to the development of novel drugs and safe vaccines.

Developmental impacts and toxicological hallmarks of silver nanoparticles across diverse biological models

Silver nanoparticles (AgNPs), revered for their antimicrobial prowess, have become ubiquitous in a range of products, from biomedical equipment to food packaging. However, amidst their rising popularity, concerns loom over their possible detrimental effects on fetal development and subsequent adult life. This review delves into the developmental toxicity of AgNPs across diverse models, from aquatic species like zebrafish and catfish to mammalian rodents and in vitro embryonic stem cells. Our focus encompasses the fate of AgNPs in different contexts, elucidating associated hazardous results such as embryotoxicity and adverse pregnancy outcomes. Furthermore, we scrutinize the enduring adverse impacts on offspring, spanning impaired neurobehavior function, reproductive disorders, cardiopulmonary lesions, and hepatotoxicity. Key hallmarks of developmental harm are identified, encompassing redox imbalances, inflammatory cascades, DNA damage, and mitochondrial stress. Notably, we explore potential explanations, linking immunoregulatory dysfunction and disrupted epigenetic modifications to AgNPs-induced developmental failures. Despite substantial progress, our understanding of the developmental risks posed by AgNPs remains incomplete, underscoring the urgency of further research in this critical area.

Unraveling the role of Xist in X chromosome inactivation: insights from rabbit model and deletion analysis of exons and repeat A

X chromosome inactivation (XCI) is a process that equalizes the expression of X-linked genes between males and females. It relies on Xist, continuously expressed in somatic cells during XCI maintenance. However, how Xist impacts XCI maintenance and its functional motifs remain unclear. In this study, we conducted a comprehensive analysis of Xist, using rabbits as an ideal non-primate model. Homozygous knockout of exon 1, exon 6, and repeat A in female rabbits resulted in embryonic lethality. However, X∆ReAX females, with intact X chromosome expressing Xist, showed no abnormalities. Interestingly, there were no significant differences between females with homozygous knockout of exons 2-5 and wild-type rabbits, suggesting that exons 2, 3, 4, and 5 are less important for XCI. These findings provide evolutionary insights into Xist function.

Improved functions for non-linear sequence comparison using SEEKR

SEquence Evaluation through k -mer Representation (SEEKR) is a method of sequence comparison that utilizes sequence substrings called k -mers to quantify non-linear similarity between nucleic acid species. We describe the development of new functions within SEEKR that enable end-users to estimate p-values that ascribe statistical significance to SEEKR-derived similarities as well as visualize different aspects of k -mer similarity. We apply the new functions to identify chromatin-enriched long noncoding RNAs (lncRNAs) that harbor XIST -like sequence fragments and show that several of these fragments are bound by XIST -associated proteins. We also highlight the best practice of using RNA-Seq data to evaluate support for lncRNA annotations prior to their in-depth study in cell types of interest.

Isl1 promotes gene transcription through physical interaction with Set1/Mll complexes

Histone H3 lysine 4 (H3K4) methylation is generally recognized as a prominent marker of gene activation. While Set1/Mll complexes are major methyltransferases that are responsible for H3K4 methylation, the mechanism of how these complexes are recruited into the target gene promotor is still unclear. Here, starting with an affinity purification-mass spectrometry approach, we have found that Isl1, a highly tissue-specific expressed LIM/homeodomain transcription factor, is physically associated with Set1/Mll complexes. We then show that Wdr5 directly binds to Isl1. And this binding is likely mediated by the homeodomain of Isl1. Functionally, using mouse β-cell and human neuroblastoma tumor cell lines, we show that both Wdr5 binding and H3K4 methylation level at promoters of some Isl1 target genes are significantly reduced upon depletion of Isl1, suggesting Isl1 is required for efficient locus-specific H3K4 methylation. Taken together, our results establish a critical role of Set1/Mll complexes in regulating the target gene expression of Isl1.

Long noncoding RNA XIST: Mechanisms for X chromosome inactivation, roles in sex-biased diseases, and therapeutic opportunities

Sexual dimorphism has been reported in various human diseases including autoimmune diseases, neurological diseases, pulmonary arterial hypertension, and some types of cancers, although the underlying mechanisms remain poorly understood. The long noncoding RNA (lncRNA) X-inactive specific transcript (XIST) is involved in X chromosome inactivation (XCI) in female placental mammals, a process that ensures the balanced expression dosage of X-linked genes between sexes. XIST is abnormally expressed in many sex-biased diseases. In addition, escape from XIST-mediated XCI and skewed XCI also contribute to sex-biased diseases. Therefore, its expression or modification can be regarded as a biomarker for the diagnosis and prognosis of many sex-biased diseases. Genetic manipulation of XIST expression can inhibit the progression of some of these diseases in animal models, and therefore XIST has been proposed as a potential therapeutic target. In this manuscript, we summarize the current knowledge about the mechanisms for XIST-mediated XCI and the roles of XIST in sex-biased diseases, and discuss potential therapeutic strategies targeting XIST.

Lnc5926 is essential for early embryonic development in goats through regulation of ZSCAN4 and EIF1AX

Long noncoding RNAs (lncRNAs) are abundant in mammalian genomes and have been found to play important roles in many biological events. However, the mechanism by which lncRNAs regulate embryonic development remains to be fully elucidated. Here, we investigated the function of the lncRNA, TCONS_00135926 (referred to as lnc5926), through knockdown and overexpression experiments in goat early embryos. Lnc5926 expression at the eight-cell embryonic stage was significantly higher than that at other stages, which was consistent with the pattern of embryonic genome activation (EGA) gene expression. The blastocyst rate after lnc5926 knockdown in eight-cell embryos was significantly lower than that in the control group (0.2% vs. 17.1%, p < 0.05), whereas the cleavage rate was not affected (71.9% vs. 75.1%, p ˃ 0.05). After knockdown or overexpression of lnc5926 in embryos, we measured expression levels of the potential target genes, STAM, HACD1, UBL5, MIOX, ELF1, and the key EGA genes, ZSCAN4 and EIF1AX. Only ZSCAN4 and EIF1AX were significantly downregulated after lnc5926 knockdown, and this effect was reversed by lnc5926 overexpression. We conclude that lnc5926 plays an essential role in early embryonic development in goats by regulating expression of EGA-associated genes.

The tandem repeat modules of Xist lncRNA: a swiss army knife for the control of X-chromosome inactivation

X-inactive-specific transcript (Xist) is a long non-coding RNA (lncRNA) essential for X-chromosome inactivation (XCI) in female placental mammals. Thirty years after its discovery, it is still puzzling how this lncRNA triggers major structural and transcriptional changes leading to the stable silencing of an entire chromosome. Recently, a series of studies in mouse cells have uncovered domains of functional specialization within Xist mapping to conserved tandem repeat regions, known as Repeats A-to-F. These functional domains interact with various RNA binding proteins (RBPs) and fold into distinct RNA structures to execute specific tasks in a synergistic and coordinated manner during the inactivation process. This modular organization of Xist is mostly conserved in humans, but recent data point towards differences regarding functional specialization of the tandem repeats between the two species. In this review, we summarize the recent progress on understanding the role of Xist repetitive blocks and their involvement in the molecular mechanisms underlying XCI. We also discuss these findings in the light of the similarities and differences between mouse and human Xist.

Xist nucleates local protein gradients to propagate silencing across the X chromosome

The lncRNA Xist forms ∼50 diffraction-limited foci to transcriptionally silence one X chromosome. How this small number of RNA foci and interacting proteins regulate a much larger number of X-linked genes is unknown. We show that Xist foci are locally confined, contain ∼2 RNA molecules, and nucleate supramolecular complexes (SMACs) that include many copies of the critical silencing protein SPEN. Aggregation and exchange of SMAC proteins generate local protein gradients that regulate broad, proximal chromatin regions. Partitioning of numerous SPEN molecules into SMACs is mediated by their intrinsically disordered regions and essential for transcriptional repression. Polycomb deposition via SMACs induces chromatin compaction and the increase in SMACs density around genes, which propagates silencing across the X chromosome. Our findings introduce a mechanism for functional nuclear compartmentalization whereby crowding of transcriptional and architectural regulators enables the silencing of many target genes by few RNA molecules.

Sex as an important factor in nanomedicine

Nanomedicine has demonstrated substantial potential to improve the quality and efficacy of healthcare systems. Although the promise of nanomedicine to transform conventional medicine is evident, significant numbers of therapeutic nanomedicine products have failed in clinical trials. Most studies in nanomedicine have overlooked several important factors, including the significance of sex differences at various physiological levels. This report attempts to highlight the importance of sex in nanomedicine at cellular and molecular level. A more thorough consideration of sex physiology, among other critical variations (e.g., health status of individuals), would enable researchers to design and develop safer and more-efficient sex-specific diagnostic and therapeutic nanomedicine products.

Systematics for types and effects of RNA variations

Systematics is described for annotation of variations in RNA molecules. The conceptual framework is part of Variation Ontology (VariO) and facilitates depiction of types of variations, their functional and structural effects and other consequences in any RNA molecule in any organism. There are more than 150 RNA related VariO terms in seven levels, which can be further combined to generate even more complicated and detailed annotations. The terms are described together with examples, usually for variations and effects in human and in diseases. RNA variation type has two subcategories: variation classification and origin with subterms. Altogether six terms are available for function description. Several terms are available for affected RNA properties. The ontology contains also terms for structural description for affected RNA type, post-transcriptional RNA modifications, secondary and tertiary structure effects and RNA sugar variations. Together with the DNA and protein concepts and annotations, RNA terms allow comprehensive description of variations of genetic and non-genetic origin at all possible levels. The VariO annotations are readable both for humans and computer programs for advanced data integration and mining.

The complex activities of the SET1/MLL complex core subunits in development and disease

In mammalian cells, the SET1/MLL complexes are the main writers of the H3K4 methyl mark that is associated with active gene expression. The activities of these complexes are critically dependent on the association of the catalytic subunit with their shared core subunits, WDR5, RBBP5, ASH2L, and DPY30, collectively referred as WRAD. In addition, some of these core subunits can bind to proteins other than the SET1/MLL complex components. This review starts with discussion of the molecular activities of these core subunits, with an emphasis on DPY30 in organizing the assembly of the SET1/MLL complexes with other associated factors. This review then focuses on the roles of the core subunits in stem cells and development, as well as in diseased cell states, mainly cancer, and ends with discussion on dissecting the responsible activities of the core subunits and how we may target them for potential disease treatment. This article is part of a Special Issue entitled: The MLL family of proteins in normal development and disease edited by Thomas A Milne.

The B-side of Xist

Female mammals express the long noncoding X inactivation-specific transcript ( Xist) RNA to initiate X chromosome inactivation (XCI) that eventually results in the formation of the Barr body. Xist encompasses half a dozen repeated sequence stretches containing motifs for RNA-binding proteins that recruit effector complexes with functions for silencing genes and establishing a repressive chromatin configuration. Functional characterization of these effector proteins unveils the cooperation of a number of pathways to repress genes on the inactive X chromosome. Mechanistic insights can be extended to other noncoding RNAs with similar structure and open avenues for the design of new therapies to switch off gene expression. Here we review recent advances in the understanding of Xist and on this basis try to synthesize a model for the initiation of XCI.

LncRNA FOXD1-AS1 acts as a potential oncogenic biomarker in glioma

AIMS

Altered activities of long noncoding RNAs (lncRNAs) have been associated with cancer development, and lncRNA FOXD1-AS1 (FOXD1-AS1) is the antisense transcript of the gene encoding for FOXD1, known for its role as an oncogene in several tumor types including glioma. However, the role of FOXD1-AS1 in the differentiation and progression of glioma is not well known.

METHODS

Expression profile chip and qPCR were used to screen and identify FOXD1-AS1. Glioma cells were transfected with siRNA or eukaryotic expression vector to observe FOXD1-AS1 function in vitro and in vivo. Dual luciferase reporter gene analysis, Western blot, and ChIRP-MS were used to detect microRNAs and protein that combine with FOXD1-AS1.

RESULTS

FOXD1-AS1 was upregulated and directly correlated with the glioma grade, and it was localized in both the nucleus and the cytoplasm of the glioma cell. FOXD1-AS1 silencing caused tumor suppressive effects via inhibiting cell proliferation, migration, and apoptosis, while FOXD1-AS1 overexpression resulted in opposite effects. Additionally, in vivo experiments showed that FOXD1-AS1 knockdown reduced tumor volume and weight. More importantly, mechanical studies revealed that FOXD1-AS1 targeted both miR339-5p and miR342-3p (miR339/342). Furthermore, protein eukaryotic translation initiation factor 5 subunit A (eIF5a) resulted a direct target of FOXD1-AS1.

CONCLUSIONS

These data indicated that FOXD1-AS1, a miR339/342 target, affected biological processes via protein eIF5a; thus, it might be considered as a new therapeutic target for glioblastoma.

X Inactivation and Escape: Epigenetic and Structural Features

X inactivation represents a complex multi-layer epigenetic mechanism that profoundly modifies chromatin composition and structure of one X chromosome in females. The heterochromatic inactive X chromosome adopts a unique 3D bipartite structure and a location close to the nuclear periphery or the nucleolus. X-linked lncRNA loci and their transcripts play important roles in the recruitment of proteins that catalyze chromatin and DNA modifications for silencing, as well as in the control of chromatin condensation and location of the inactive X chromosome. A subset of genes escapes X inactivation, raising questions about mechanisms that preserve their expression despite being embedded within heterochromatin. Escape gene expression differs between males and females, which can lead to physiological sex differences. We review recent studies that emphasize challenges in understanding the role of lncRNAs in the control of epigenetic modifications, structural features and nuclear positioning of the inactive X chromosome. Second, we highlight new findings about the distribution of genes that escape X inactivation based on single cell studies, and discuss the roles of escape genes in eliciting sex differences in health and disease.

CRISPR/Cas9-mediated modulation of splicing efficiency reveals short splicing isoform of Xist RNA is sufficient to induce X-chromosome inactivation

Alternative splicing of mRNA precursors results in multiple protein variants from a single gene and is critical for diverse cellular processes and development. Xist encodes a long noncoding RNA which is a central player to induce X-chromosome inactivation in female mammals and has two major splicing variants: long and short isoforms of Xist RNA. Although a differentiation-specific and a female-specific expression of Xist isoforms have been reported, the functional role of each Xist RNA isoform is largely unexplored. Using CRISPR/Cas9-mediated targeted modification of the 5' splice site in Xist intron 7, we create mutant female ES cell lines which dominantly express the long- or short-splicing isoform of Xist RNA from the inactive X-chromosome (Xi) upon differentiation. Successful execution of CRISPR/Cas-based splicing modulation indicates that our CRISPR/Cas-based targeted modification of splicing sites is a useful approach to study specific isoforms of a transcript generated by alternative splicing. Upon differentiation of splicing-mutant Xist female ES cells, we find that both long and short Xist isoforms can induce X-chromosome inactivation normally during ES cell differentiation, suggesting that the short splicing isoform of Xist RNA is sufficient to induce X-chromosome inactivation.

En bloc and segmental deletions of human XIST reveal X chromosome inactivation-involving RNA elements

The XIST RNA is a non-coding RNA that induces X chromosome inactivation (XCI). Unlike the mouse Xist RNA, how the human XIST RNA controls XCI in female cells is less well characterized, and its functional motifs remain unclear. To systematically decipher the XCI-involving elements of XIST RNA, 11 smaller XIST segments, including repeats A, D and E; human-specific repeat elements; the promoter; and non-repetitive exons, as well as the entire XIST gene, were homozygously deleted in K562 cells using the Cas9 nuclease and paired guide RNAs at high efficiencies, followed by high-throughput RNA sequencing and RNA fluorescence in situ hybridization experiments. Clones containing en bloc and promoter deletions that consistently displayed no XIST RNAs and a global up-regulation of X-linked genes confirmed that the deletion of XIST reactivates the inactive X chromosome. Systematic analyses of segmental deletions delineated that exon 5 harboring the non-repeat element is important for X-inactivation maintenance, whereas exons 2, 3 and 4 as well as the other repeats in exon 1 are less important, a different situation from that of mouse Xist. This Cas9-assisted dissection of XIST allowed us to understand the unique functional domains within the human XIST RNA.

Xist Deletional Analysis Reveals an Interdependency between Xist RNA and Polycomb Complexes for Spreading along the Inactive X

During X-inactivation, Xist RNA spreads along an entire chromosome to establish silencing. However, the mechanism and functional RNA elements involved in spreading remain undefined. By performing a comprehensive endogenous Xist deletion screen, we identify Repeat B as crucial for spreading Xist and maintaining Polycomb repressive complexes 1 and 2 (PRC1/PRC2) along the inactive X (Xi). Unexpectedly, spreading of these three factors is inextricably linked. Deleting Repeat B or its direct binding partner, HNRNPK, compromises recruitment of PRC1 and PRC2. In turn, ablating PRC1 or PRC2 impairs Xist spreading. Therefore, Xist and Polycomb complexes require each other to propagate along the Xi, suggesting a positive feedback mechanism between RNA initiator and protein effectors. Perturbing Xist/Polycomb spreading causes failure of de novo Xi silencing, with partial compensatory downregulation of the active X, and also disrupts topological Xi reconfiguration. Thus, Repeat B is a multifunctional element that integrates interdependent Xist/Polycomb spreading, silencing, and changes in chromosome architecture.

Silver Nanoparticles Compromise Female Embryonic Stem Cell Differentiation through Disturbing X Chromosome Inactivation

The widespread use of silver nanoparticles (AgNPs) has raised substantial health risks to human beings. Despite a wealth of progress on toxicity studies, the understanding of the adverse effects on fetuses, embryos, and early stage cells is still rather limited, particularly under low-dose exposure settings. Moreover, nearly all previous studies ascribed AgNP-induced toxic effects to oxidative stress. Differently, we here unearthed a mechanism, namely, interruption of X chromosome inactivation (XCI) in female mouse embryonic stem cells (mESCs). Albeit with no observable cytotoxicity, significant differentiation retardation was found in female mESCs upon low-dose AgNP exposure. Mechanistic investigations uncovered expedited inactivation for the inactive X chromosome (Xi) and attenuated maintenance of the active X chromosome (Xa) state during mESC differentiation upon the challenge of low-dose AgNPs, indicative of disordered XCI. Thereby, a few X-linked genes (which are closely involved in orchestrating ESC differentiation) were found to be repressed, partially attributable to reinforced enrichment of histone modification ( e. g., histone 3 lysine 27 trimethylation, H3K27me3) on their promoter regions, as the result of disordered XCI. In stark contrast to female mESCs, no impairment of differentiation was observed in male mESCs under low-dose AgNP exposure. All considered, our data unearthed that AgNPs at low concentrations compromised the differentiation program of female mESCs through disturbing XCI. Thus, this work would provide a model for the type of studies necessary to advance the understandings on AgNP-induced developmental toxicity.

Long non-coding RNA XIST promotes osteoporosis through inhibiting bone marrow mesenchymal stem cell differentiation

The purpose of the present study was to identify the key long non-coding (lnc)RNAs in the occurrence and development of osteoporosis (OP) and to explore the associated molecular mechanism. First, the Gene Expression Omnibus (GEO) datasets, with key words ‘osteoporosis’ and ‘HG-133A’, were screened. RankProd R package was used to calculate the dysregulated lncRNAs in OP. Following this, bone marrow mesenchymal stem cells (BM-MSCs) harvested from 3-week-old Sprague Dawley rats were employed for detection of osteoblast differentiation. Following overexpression or interference with X-inactive specific transcript (XIST), osteogenesis-associated genes and proteins in BM-MSCs were detected using reverse transcription-quantitative polymerase chain reaction and western blot analysis. Alkaline phosphatase (ALP) and Alizarin Red S staining were also performed to measure the osteogenic ability of BM-MSCs. Results from the two datasets indicated that 6 lncRNAs were dysregulated in OP. Notably, XIST is key lncRNA in diverse diseases, and was subsequently selected for analysis. It was revealed that XIST was significantly upregulated in plasma and monocytes from patients with OP compared with the normal controls. Furthermore, results indicated that overexpression of XIST significantly inhibited osteoblast differentiation in BM-MSCs, as evidenced by the decreased expression of ALP, bone γ-carboxyglutamic acid-containing protein and runt related transcription factor 2, reduced ALP activity and a decreased number of calcium deposits. However, interference of XIST exhibited the opposite biological effects in BM-MSCs. Taken together, XIST was highly expressed in the serum and monocytes of patients with OP. In addition, the findings suggested that XIST could inhibit osteogenic differentiation of BM-MSCs.

Function by Structure: Spotlights on Xist Long Non-coding RNA

Recent experimental evidence indicates that lncRNAs can act as regulatory molecules in the context of development and disease. Xist, the master regulator of X chromosome inactivation, is a classic example of how lncRNAs can exert multi-layered and fine-tuned regulatory functions, by acting as a molecular scaffold for recruitment of distinct protein factors. In this review, we discuss the methodologies employed to define Xist RNA structures and the tight interplay between structural clues and functionality of lncRNAs. This model of modular function dictated by structure, can be also generalized to other lncRNAs, beyond the field of X chromosome inactivation, to explain common features of similarly folded RNAs.

Repeat E anchors Xist RNA to the inactive X chromosomal compartment through CDKN1A-interacting protein (CIZ1)

X chromosome inactivation is an epigenetic dosage compensation mechanism in female mammals driven by the long noncoding RNA, Xist. Although recent genomic and proteomic approaches have provided a more global view of Xist's function, how Xist RNA localizes to the inactive X chromosome (Xi) and spreads in cis remains unclear. Here, we report that the CDKN1-interacting zinc finger protein CIZ1 is critical for localization of Xist RNA to the Xi chromosome territory. Stochastic optical reconstruction microscopy (STORM) shows a tight association of CIZ1 with Xist RNA at the single-molecule level. CIZ1 interacts with a specific region within Xist exon 7-namely, the highly repetitive Repeat E motif. Using genetic analysis, we show that loss of CIZ1 or deletion of Repeat E in female cells phenocopies one another in causing Xist RNA to delocalize from the Xi and disperse into the nucleoplasm. Interestingly, this interaction is exquisitely sensitive to CIZ1 levels, as overexpression of CIZ1 likewise results in Xist delocalization. As a consequence, this delocalization is accompanied by a decrease in H3K27me3 on the Xi. Our data reveal that CIZ1 plays a major role in ensuring stable association of Xist RNA within the Xi territory.