Origin and evolution of the long non-coding genes in the X-inactivation center. Biochimie. 2011;93:1935-1942. [PMID: 21820484 DOI: 10.1016/j.biochi.2011.07.009]

Species-specific regulation of XIST by the JPX/FTX orthologs

X chromosome inactivation (XCI) is an essential process, yet it initiates with remarkable diversity in various mammalian species. XIST, the main trigger of XCI, is controlled in the mouse by an interplay of lncRNA genes (LRGs), some of which evolved concomitantly to XIST and have orthologues across all placental mammals. Here, we addressed the functional conservation of human orthologues of two such LRGs, FTX and JPX. By combining analysis of single-cell RNA-seq data from early human embryogenesis with various functional assays in matched human and mouse pluripotent stem- or differentiated post-XCI cells, we demonstrate major functional differences for these orthologues between species, independently of primary sequence conservation. While the function of FTX is not conserved in humans, JPX stands as a major regulator of XIST expression in both species. However, we show that different entities of JPX control the production of XIST at various steps depending on the species. Altogether, our study highlights the functional versatility of LRGs across evolution, and reveals that functional conservation of orthologous LRGs may involve diversified mechanisms of action. These findings represent a striking example of how the evolvability of LRGs can provide adaptative flexibility to constrained gene regulatory networks.

Using ncRNAs as Tools in Cancer Diagnosis and Treatment-The Way towards Personalized Medicine to Improve Patients' Health

Although the first discovery of a non-coding RNA (ncRNA) dates back to 1958, only in recent years has the complexity of the transcriptome started to be elucidated. However, its components are still under investigation and their identification is one of the challenges that scientists are presently facing. In addition, their function is still far from being fully understood. The non-coding portion of the genome is indeed the largest, both quantitatively and qualitatively. A large fraction of these ncRNAs have a regulatory role either in coding mRNAs or in other ncRNAs, creating an intracellular network of crossed interactions (competing endogenous RNA networks, or ceRNET) that fine-tune the gene expression in both health and disease. The alteration of the equilibrium among such interactions can be enough to cause a transition from health to disease, but the opposite is equally true, leading to the possibility of intervening based on these mechanisms to cure human conditions. In this review, we summarize the present knowledge on these mechanisms, illustrating how they can be used for disease treatment, the current challenges and pitfalls, and the roles of environmental and lifestyle-related contributing factors, in addition to the ethical, legal, and social issues arising from their (improper) use.

Long noncoding RNAs in hepatitis B virus replication and oncogenesis

Several diverse long noncoding RNAs (lncRNAs) have been identified to be involved in hepatitis B virus (HBV) replication and oncogenesis, especially those dysregulated in HBV-related hepatocellular carcinoma (HCC). Most of these dysregulated lncRNAs are modulated by the HBV X protein. The regulatory mechanisms of some lncRNAs in HBV replication and oncogenesis have been characterized. Genetic polymorphisms of several lncRNAs affecting HBV replication or oncogenesis have also been studied. The prognosis of HCC remains poor. It is important to identify novel tumor markers for early diagnosis and find more therapeutic targets for effective treatments of HCC. Some dysregulated lncRNAs in HBV-related HCC may become biomarkers for early diagnosis and/or the therapeutic targets of HCC. This mini-review summarizes these findings briefly, focusing on recent developments.

Diversity of Dysregulated Long Non-Coding RNAs in HBV-Related Hepatocellular Carcinoma

Infection with the hepatitis B virus (HBV) continues to pose a major threat to public health as approximately 292 million people worldwide are currently living with the chronic form of the disease, for which treatment is non-curative. Chronic HBV infections often progress to hepatocellular carcinoma (HCC) which is one of the world’s leading causes of cancer-related deaths. Although the process of hepatocarcinogenesis is multifaceted and has yet to be fully elucidated, several studies have implicated numerous long non-coding RNAs (lncRNAs) as contributors to the development of HCC. These host-derived lncRNAs, which are often dysregulated as a consequence of viral infection, have been shown to function as signals, decoys, guides, or scaffolds, to modulate gene expression at epigenetic, transcriptional, post-transcriptional and even post-translational levels. These lncRNAs mainly function to promote HBV replication and oncogene expression or downregulate tumor suppressors. Very few lncRNAs are known to suppress tumorigenesis and these are often downregulated in HCC. In this review, we describe the mechanisms by which lncRNA dysregulation in HBV-related HCC promotes tumorigenesis and cancer progression.

LncRNA FTX promotes the malignant progression of colorectal cancer by regulating the miR-214-5p-JAG1 axis

Background

Long non-coding RNAs (lncRNAs) have recently been found to be vital regulators of various cancers, including colorectal cancer (CRC). It has been previously reported that the dysregulated expression of lncRNA Five prime to Xist (FTX) is involved in carcinogenesis. However, the role of lncRNA FTX in the progression of CRC is still unclear.

Methods

Fluorescence in situ hybridization (FISH) was used to detect the expression of lncRNA FTX and miR-214-5p in CRC tissues. Cell Counting Kit-8 assay, transwell assay, wound-healing assay, and proliferation assay were used to explore the function of lncRNA FTX in CRC cells. Quantitative real-time polymerase chain reaction (qRT-PCR), western blotting, and luciferase reporter assay were used to confirm the relationship between lncRNA FTX and miR-214-5p-jagged canonical Notch ligand 1 (JAG1). We further explored the role of lncRNA FTX in vivo using xenograft tumor assay.

Results

lncRNA FTX was found to be upregulated in CRC tissues by FISH. The downregulation of endogenous lncRNA FTX expression inhibited CRC cell proliferation, migration, and invasion. Mechanistically, lncRNA FTX sequestered miR-214-5p and thus released its repression on JAG1, driving the malignant progression of CRC.

Conclusions

These findings give rise to a new perspective, the lncRNA FTX-miR-214-5p-JAG1 regulatory axis, in exploring the cancer-promoting mechanism of lncRNA FTX in CRC.

Exploring Evidence of Non-coding RNA Translation With Trips-Viz and GWIPS-Viz Browsers

Detection of translation in so-called non-coding RNA provides an opportunity for identification of novel bioactive peptides and microproteins. The main methods used for these purposes are ribosome profiling and mass spectrometry. A number of publicly available datasets already exist for a substantial number of different cell types grown under various conditions, and public data mining is an attractive strategy for identification of translation in non-coding RNAs. Since the analysis of publicly available data requires intensive data processing, several data resources have been created recently for exploring processed publicly available data, such as OpenProt, GWIPS-viz, and Trips-Viz. In this work we provide a detailed demonstration of how to use the latter two tools for exploring experimental evidence for translation of RNAs hitherto classified as non-coding. For this purpose, we use a set of transcripts with substantially different patterns of ribosome footprint distributions. We discuss how certain features of these patterns can be used as evidence for or against genuine translation. During our analysis we concluded that the MTLN mRNA, previously misannotated as lncRNA LINC00116, likely encodes only a short proteoform expressed from shorter RNA transcript variants.

LncRNA FTX activates FOXA2 expression to inhibit non-small-cell lung cancer proliferation and metastasis

Lung cancer leads to the highest mortality among all cancer types in the world, and non–small‐cell lung cancer (NSCLC) occupies over 80% of the lung cancer cases. Numerous studies have demonstrated that long non‐coding RNA (lncRNA) is involved in various human diseases including cancer. LncRNA FTX was firstly identified in Xist gene locus and was dysregulated in many human cancers. However, the function of FTX in NSCLC is still unclear. Here, we report that long non‐coding RNA FTX expression level is down‐regulated in NSCLC clinical tissue samples and cell lines. Ectopic expression of FTX inhibits proliferation and metastasis of lung cancer cells in vitro and in vivo. Furthermore, we find that FTX overexpression activates the expression of transcription factor FOXA2, an important regulator in lung cancer progression, and we reveal a novel FTX/miR‐200a‐3p/FOXA2 competing endogenous RNA regulatory axis in lung cancer cells. Our results provide new insights and directions for exploring the function of FTX in lung cancer progression.

The latest progress on miR-374 and its functional implications in physiological and pathological processes

Non‐coding RNAs (ncRNAs) have been emerging players in cell development, differentiation, proliferation and apoptosis. Based on their differences in length and structure, they are subdivided into several categories including long non‐coding RNAs (lncRNAs >200nt), stable non‐coding RNAs (60‐300nt), microRNAs (miRs or miRNAs, 18‐24nt), circular RNAs, piwi‐interacting RNAs (26‐31nt) and small interfering RNAs (about 21nt). Therein, miRNAs not only directly regulate gene expression through pairing of nucleotide bases between the miRNA sequence and a specific mRNA that leads to the translational repression or degradation of the target mRNA, but also indirectly affect the function of downstream genes through interactions with lncRNAs and circRNAs. The latest studies have highlighted their importance in physiological and pathological processes. MiR‐374 family member are located at the X‐chromosome inactivation center. In recent years, numerous researches have uncovered that miR‐374 family members play an indispensable regulatory role, such as in reproductive disorders, cell growth and differentiation, calcium handling in the kidney, various cancers and epilepsy. In this review, we mainly focus on the role of miR‐374 family members in multiple physiological and pathological processes. More specifically, we also summarize their promising potential as novel prognostic biomarkers and therapeutic targets from bench to bedside.

Single nucleotide polymorphism array analysis uncovers a large, novel duplication in Xq13.1 in a floppy infant syndrome patient

OBJECTIVE

To identify candidate genes for the clinical diagnosis of floppy infant syndrome (FIS) using single nucleotide polymorphism (SNP) array in a specific FIS family.

METHODS

SNP array analysis of the whole chromosome copy number was performed in the proband (III₁). Multiple polymerase chain reaction (PCR) combined with denaturing high-performance liquid chromatography (DHPLC) was used to validate the array data.

RESULTS

A large 5.818182 Mb duplication (Xq13.1: 67987646-73805828), which encompasses 66 known genes, was found in III₁. The start and end points of the duplication were confirmed with an SNP array. Duplicated genes with potential roles in central and/or peripheral nervous system development (HDAC8, PHKA1, TAF1, DLG3, KIF4A, IGBP1, PJA1, and SLC16A2) were confirmed by multiple PCR-DHPLC in III₁. The patient's mother and grandmother carry duplications in these eight genes, but only on one X chromosome, while the patient's aunt does not carry any of the duplications.

CONCLUSION

Based on the location of the eight candidate genes in Xq13.1, the large duplication found by SNP array does indeed exist and is predicted to be both novel and pathogenic. Moreover, we recommend SNP array as the first option for genetic diagnosis of both large-scale and rare/complicated diseases, such as FIS.

XIST Induced by JPX Suppresses Hepatocellular Carcinoma by Sponging miR-155-5p

PURPOSE

The influence of X-inactive specific transcript (XIST) and X-chromosome inactivation associated long non-coding RNAs (lncRNAs) just proximal to XIST (JPX) on hepatocellular carcinoma (HCC) remains controversial in light of previous reports, which the present study aimed to verify.

MATERIALS AND METHODS

The DIANA lncRNA-microRNA (miRNA) interaction database was used to explore miRNA interactions with JPX or XIST. JPX, XIST, and miR-155-5p expression levels in paired HCC specimens and adjacent normal tissue were analyzed by RT-qPCR. Interaction between XIST and miR-155-5p was verified by dual luciferase reporter assay. Expression levels of miR-155-5p and its known target genes, SOX6 and PTEN, were verified by RT-qPCR and Western blot in HepG2 cells with or without XIST knock-in. The potential suppressive role of XIST and JPX on HCC was verified by cell functional assays and tumor formation assay using a xenograft model.

RESULTS

JPX and XIST expression was significantly decreased in HCC pathologic specimens, compared to adjacent tissue, which correlated with HCC progression and increased miR-155-5p expression. Dual luciferase reporter assay revealed XIST as a direct target of miR-155-5p. XIST knock-in significantly reduced miR-155-5p expression level and increased that of SOX6 and PTEN, while significantly inhibiting HepG2 cell growth in vitro, which was partially reversed by miR-155-5p mimic transfection. JPX knock-in significantly increased XIST expression and inhibited HepG2 cell growth in vitro or tumor formation in vivo in a XIST dependent manner.

CONCLUSION

JPX and XIST play a suppressive role in HCC. JPX increases expression levels of XIST in HCC cells, which suppresses HCC development by sponging the cancer promoting miR-155-5p.

Genomic positional conservation identifies topological anchor point RNAs linked to developmental loci

BACKGROUND

The mammalian genome is transcribed into large numbers of long noncoding RNAs (lncRNAs), but the definition of functional lncRNA groups has proven difficult, partly due to their low sequence conservation and lack of identified shared properties. Here we consider promoter conservation and positional conservation as indicators of functional commonality.

RESULTS

We identify 665 conserved lncRNA promoters in mouse and human that are preserved in genomic position relative to orthologous coding genes. These positionally conserved lncRNA genes are primarily associated with developmental transcription factor loci with which they are coexpressed in a tissue-specific manner. Over half of positionally conserved RNAs in this set are linked to chromatin organization structures, overlapping binding sites for the CTCF chromatin organiser and located at chromatin loop anchor points and borders of topologically associating domains (TADs). We define these RNAs as topological anchor point RNAs (tapRNAs). Characterization of these noncoding RNAs and their associated coding genes shows that they are functionally connected: they regulate each other's expression and influence the metastatic phenotype of cancer cells in vitro in a similar fashion. Furthermore, we find that tapRNAs contain conserved sequence domains that are enriched in motifs for zinc finger domain-containing RNA-binding proteins and transcription factors, whose binding sites are found mutated in cancers.

CONCLUSIONS

This work leverages positional conservation to identify lncRNAs with potential importance in genome organization, development and disease. The evidence that many developmental transcription factors are physically and functionally connected to lncRNAs represents an exciting stepping-stone to further our understanding of genome regulation.

Ftx non coding RNA-derived miR-545 promotes cell proliferation by targeting RIG-I in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third cause of cancer-related death worldwide. Accumulating studies have demonstrated that aberrant expression of several lncRNAs was found to be involved in the hepatocarcinogenesis. In this study, a lncRNA Ftx was chosen to investigate its effects on HCC cells, and clarify the possible mechanism. We demonstrated that the lncRNA Ftx and Ftx-derived miR-545 were up-regulated in both HCC tissues and cells. MiR-545 was positively correlated with lncRNA Ftx expression. Notably, clinical association analysis revealed that the high expression of lncRNA Ftx and miR-545 was associated with poor prognostic features, and conferred a reduced 5-year overall survival (OS) and disease-free survival (DFS) of HCC patients. We found that miR-545 was a pivotal mediator in Ftx-induced promotion of HCC cell growth. Subsequently, we identified RIG-I as a direct target of miR-545. The expression of RIG-I was downregulated in HCC tissues and was inversely correlated with miR-545 expression. Our data revealed that ectopic expression of RIG-I abrogated the effects of lncRNA Ftx or miR-545 on HCC cells. LncRNA Ftx/miR-545-mediated downregulation of RIG-I led to increased Akt phosphorylation in vitro and in vivo. Inhibition of Akt phosphorylation abolished the effects of lncRNA Ftx/miR-545 on HCC cells. In conclusion, our study demonstrates that the novel pathway lncRNA Ftx/miR-545/RIG-I promotes HCC development by activating PI3K/Akt signaling, and it may serve as a novel prognostic biomarker and therapeutic target for HCC.

A subset of conserved mammalian long non-coding RNAs are fossils of ancestral protein-coding genes

Background

Only a small portion of human long non-coding RNAs (lncRNAs) appear to be conserved outside of mammals, but the events underlying the birth of new lncRNAs in mammals remain largely unknown. One potential source is remnants of protein-coding genes that transitioned into lncRNAs.

Results

We systematically compare lncRNA and protein-coding loci across vertebrates, and estimate that up to 5% of conserved mammalian lncRNAs are derived from lost protein-coding genes. These lncRNAs have specific characteristics, such as broader expression domains, that set them apart from other lncRNAs. Fourteen lncRNAs have sequence similarity with the loci of the contemporary homologs of the lost protein-coding genes. We propose that selection acting on enhancer sequences is mostly responsible for retention of these regions. As an example of an RNA element from a protein-coding ancestor that was retained in the lncRNA, we describe in detail a short translated ORF in the JPX lncRNA that was derived from an upstream ORF in a protein-coding gene and retains some of its functionality.

Conclusions

We estimate that ~ 55 annotated conserved human lncRNAs are derived from parts of ancestral protein-coding genes, and loss of coding potential is thus a non-negligible source of new lncRNAs. Some lncRNAs inherited regulatory elements influencing transcription and translation from their protein-coding ancestors and those elements can influence the expression breadth and functionality of these lncRNAs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-017-1293-0) contains supplementary material, which is available to authorized users.

Long non-coding RNAs in hepatocellular carcinoma: Potential roles and clinical implications

Long non-coding RNAs (lncRNAs) are a subgroup of non-coding RNA transcripts greater than 200 nucleotides in length with little or no protein-coding potential. Emerging evidence indicates that lncRNAs may play important regulatory roles in the pathogenesis and progression of human cancers, including hepatocellular carcinoma (HCC). Certain lncRNAs may be used as diagnostic or prognostic markers for HCC, a serious malignancy with increasing morbidity and high mortality rates worldwide. Therefore, elucidating the functional roles of lncRNAs in tumors can contribute to a better understanding of the molecular mechanisms of HCC and may help in developing novel therapeutic targets. In this review, we summarize the recent progress regarding the functional roles of lncRNAs in HCC and explore their clinical implications as diagnostic or prognostic biomarkers and molecular therapeutic targets for HCC.

Knockdown of Long Noncoding RNA FTX Inhibits Proliferation, Migration, and Invasion in Renal Cell Carcinoma Cells

Renal cell carcinoma (RCC) is one of the most common kidney cancers worldwide. Although great progressions have been made in the past decades, its morbidity and lethality remain increasing. Long noncoding RNAs (lncRNAs) are demonstrated to play significant roles in the tumorigenesis. This study aimed to investigate the detailed roles of lncRNA FTX in RCC cell proliferation and metastasis. Our results showed that the transcript levels of FTX in both clinical RCC tissues and the cultured RCC cells were significantly upregulated and associated with multiple clinical parameters of RCC patients, including familial status, tumor sizes, lymphatic metastasis, and TNM stages. With cell proliferation assays, colony formation assays, and cell cycle assays, we testified that knockdown of FTX in A498 and ACHIN cells with specific shRNAs inhibited cell proliferation rate, colony formation ability, and arrested cell cycle in the G₀/G₁ phase. FTX depletion also suppressed cell migration and invasion with Transwell assays and wound-healing assays. These data indicated the pro-oncogenic potential of FTX in RCC, which makes it a latent therapeutic target of RCC diagnosis and treatment in the clinic.

A Genomic Analysis of Factors Driving lincRNA Diversification: Lessons from Plants

Transcriptomic analyses from across eukaryotes indicate that most of the genome is transcribed at some point in the developmental trajectory of an organism. One class of these transcripts is termed long intergenic noncoding RNAs (lincRNAs). Recently, attention has focused on understanding the evolutionary dynamics of lincRNAs, particularly their conservation within genomes. Here, we take a comparative genomic and phylogenetic approach to uncover factors influencing lincRNA emergence and persistence in the plant family Brassicaceae, to which Arabidopsis thaliana belongs. We searched 10 genomes across the family for evidence of > 5000 lincRNA loci from A. thaliana. From loci conserved in the genomes of multiple species, we built alignments and inferred phylogeny. We then used gene tree/species tree reconciliation to examine the duplication history and timing of emergence of these loci. Emergence of lincRNA loci appears to be linked to local duplication events, but, surprisingly, not whole genome duplication events (WGD), or transposable elements. Interestingly, WGD events are associated with the loss of loci for species having undergone relatively recent polyploidy. Lastly, we identify 1180 loci of the 6480 previously annotated A. thaliana lincRNAs (18%) with elevated levels of conservation. These conserved lincRNAs show higher expression, and are enriched for stress-responsiveness and cis-regulatory motifs known as conserved noncoding sequences (CNSs). These data highlight potential functional pathways and suggest that CNSs may regulate neighboring genes at both the genomic and transcriptomic level. In sum, we provide insight into processes that may influence lincRNA diversification by providing an evolutionary context for previously annotated lincRNAs.

Antagonist Xist and Tsix co-transcription during mouse oogenesis and maternal Xist expression during pre-implantation development calls into question the nature of the maternal imprint on the X chromosome

During the first divisions of the female mouse embryo, the paternal X-chromosome is coated by Xist non-coding RNA and gradually silenced. This imprinted X-inactivation principally results from the apposition, during oocyte growth, of an imprint on the X-inactivation master control region: the X-inactivation center (Xic). This maternal imprint of yet unknown nature is thought to prevent Xist upregulation from the maternal X (X^M) during early female development. In order to provide further insight into the X^M imprinting mechanism, we applied single-cell approaches to oocytes and pre-implantation embryos at different stages of development to analyze the expression of candidate genes within the Xic. We show that, unlike the situation pertaining in most other cellular contexts, in early-growing oocytes, Xist and Tsix sense and antisense transcription occur simultaneously from the same chromosome. Additionally, during early development, Xist appears to be transiently transcribed from the X^M in some blastomeres of late 2-cell embryos concomitant with the general activation of the genome indicating that X^M imprinting does not completely suppress maternal Xist transcription during embryo cleavage stages. These unexpected transcriptional regulations of the Xist locus call for a re-evaluation of the early functioning of the maternal imprint on the X-chromosome and suggest that Xist/Tsix antagonist transcriptional activities may participate in imprinting the maternal locus as described at other loci subject to parental imprinting.

Function and evolution of the long noncoding RNA circuitry orchestrating X-chromosome inactivation in mammals

X-chromosome inactivation (XCI) is a chromosome-wide regulatory process that ensures dosage compensation for X-linked genes in Theria. XCI is established during early embryogenesis and is developmentally regulated. Different XCI strategies exist in mammalian infraclasses and the regulation of this process varies also among closely related species. In Eutheria, initiation of XCI is orchestrated by a cis-acting locus, the X-inactivation center (Xic), which is particularly enriched in genes producing long noncoding RNAs (lncRNAs). Among these, Xist generates a master transcript that coats and propagates along the future inactive X-chromosome in cis, establishing X-chromosome wide transcriptional repression through interaction with several protein partners. Other lncRNAs also participate to the regulation of X-inactivation but the extent to which their function has been maintained in evolution is still poorly understood. In Metatheria, Xist is not conserved, but another, evolutionary independent lncRNA with similar properties, Rsx, has been identified, suggesting that lncRNA-mediated XCI represents an evolutionary advantage. Here, we review current knowledge on the interplay of X chromosome-encoded lncRNAs in ensuring proper establishment and maintenance of chromosome-wide silencing, and discuss the evolutionary implications of the emergence of species-specific lncRNAs in the control of XCI within Theria. WIREs RNA 2016, 7:702-722. doi: 10.1002/wrna.1359 For further resources related to this article, please visit the WIREs website.

Enlightening the contribution of the dark matter to the X chromosome inactivation process in mammals

X-chromosome inactivation (XCI) in mammals represents an exceptional example of transcriptional co-regulation occurring at the level of an entire chromosome. XCI is considered as a means to compensate for gene dosage imbalance between sexes, yet the largest part of the chromosome is composed of repeated elements of different nature and origins. Here we consider XCI from a repeat point of view, interrogating the mechanisms for inactivating X chromosome-derived repeated sequences and discussing the contribution of repetitive elements to the silencing process itself and to its evolution.

Dosage compensation and nuclear organization: cluster to control chromosome-wide gene expression

In many species, male and female animals differ in the number of X chromosomes they possess. As a consequence, large scale differences in gene dosage exist between sexes; a phenomenon that is rarely tolerated by the organism for changes in autosome dosage. Several strategies have evolved independently to balance X-linked gene dosage between sexes, named dosage compensation (DC). The molecular basis of DC differs among the three best-studied examples: mammals, fruit fly and nematodes. In this short review, we summarize recent microscopic and chromosome conformation capture data that reveal key features of the compensated X chromosome and highlight the events leading to the establishment of a functional, specialized nuclear compartment, the X domain.

Evolution of vertebrate sex chromosomes and dosage compensation

Differentiated sex chromosomes in mammals and other vertebrates evolved independently but in strikingly similar ways. Vertebrates with differentiated sex chromosomes share the problems of the unequal expression of the genes borne on sex chromosomes, both between the sexes and with respect to autosomes. Dosage compensation of genes on sex chromosomes is surprisingly variable - and can even be absent - in different vertebrate groups. Systems that compensate for different gene dosages include a wide range of global, regional and gene-by-gene processes that differ in their extent and their molecular mechanisms. However, many elements of these control systems are similar across distant phylogenetic divisions and show parallels to other gene silencing systems. These dosage systems cannot be identical by descent but were probably constructed from elements of ancient silencing mechanisms that are ubiquitous among vertebrates and shared throughout eukaryotes.

Overexpression of OCT4A ortholog elevates endogenous XIST in porcine parthenogenic blastocysts

X-chromosome inactivation (XCI) is an epigenetic process that equalizes expression of X-borne genes between male and female eutherians. This process is observed in early eutherian embryo development in a species-specific manner. Until recently, various pluripotent factors have been suggested to regulate the process of XCI by repressing XIST expression, which is the master inducer for XCI. Recent insights into the process and its regulation have been restricted in mouse species despite the evolutionary diversity of the process and molecular mechanism among the species. OCT4A is one of the represented pluripotent factors, the gate-keeper for maintaining pluripotency, and an XIST repressor. Therefore, in here, we examined the relation between OCT4A and X-linked genes in porcine preimplantation embryos. Three X-linked genes, XIST, LOC102165544, and RLIM, were selected in present study because their orthologues have been known to regulate XCI in mice. Expression levels of OCT4A were positively correlated with XIST and LOC102165544 in female blastocysts. Furthermore, overexpression of exogenous human OCT4A in cleaved parthenotes generated blastocysts with increased XIST expression levels. However, increased XIST expression was not observed when exogenous OCT4A was obtained from early blastocysts. These results suggest the possibility that OCT4A would be directly or indirectly involved in XIST expression in earlier stage porcine embryos rather than blastocysts.

Long Intergenic Non-Coding RNAs: Novel Drivers of Human Lymphocyte Differentiation

Upon recognition of a foreign antigen, CD4(+) naïve T lymphocytes proliferate and differentiate into subsets with distinct functions. This process is fundamental for the effective immune system function, as CD4(+) T cells orchestrate both the innate and adaptive immune response. Traditionally, this differentiation event has been regarded as the acquisition of an irreversible cell fate so that memory and effector CD4(+) T subsets were considered terminally differentiated cells or lineages. Consequently, these lineages are conventionally defined thanks to their prototypical set of cytokines and transcription factors. However, recent findings suggest that CD4(+) T lymphocytes possess a remarkable phenotypic plasticity, as they can often re-direct their functional program depending on the milieu they encounter. Therefore, new questions are now compelling such as which are the molecular determinants underlying plasticity and stability and how the balance between these two opposite forces drives the cell fate. As already mentioned, in some cases, the mere expression of cytokines and master regulators could not fully explain lymphocytes plasticity. We should consider other layers of regulation, including epigenetic factors such as the modulation of chromatin state or the transcription of non-coding RNAs, whose high cell-specificity give a hint on their involvement in cell fate determination. In this review, we will focus on the recent advances in understanding CD4(+) T lymphocytes subsets specification from an epigenetic point of view. In particular, we will emphasize the emerging importance of non-coding RNAs as key players in these differentiation events. We will also present here new data from our laboratory highlighting the contribution of long non-coding RNAs in driving human CD4(+) T lymphocytes differentiation.

Pseudogene-derived lncRNAs: emerging regulators of gene expression

In the more than one decade since the completion of the Human Genome Project, the prevalence of non-protein-coding functional elements in the human genome has emerged as a key revelation in post-genomic biology. Highlighted by the ENCODE (Encyclopedia of DNA Elements) and FANTOM (Functional Annotation of Mammals) consortia, these elements include tens of thousands of pseudogenes, as well as comparably numerous long non-coding RNA (lncRNA) genes. Pseudogene transcription and function remain insufficiently understood. However, the field is of great importance for human disease due to the high sequence similarity between pseudogenes and their parental protein-coding genes, which generates the potential for sequence-specific regulation. Recent case studies have established essential and coordinated roles of both pseudogenes and lncRNAs in development and disease in metazoan systems, including functional impacts of lncRNA transcription at pseudogene loci on the regulation of the pseudogenes’ parental genes. This review synthesizes the nascent evidence for regulatory modalities jointly exerted by lncRNAs and pseudogenes in human disease, and for recent evolutionary origins of these systems.

The miR-545/374a cluster encoded in the Ftx lncRNA is overexpressed in HBV-related hepatocellular carcinoma and promotes tumorigenesis and tumor progression

Hepatitis B virus (HBV) infection is a major risk factor for hepatocellular carcinoma (HCC). Previous studies have shown several long noncoding RNAs (lncRNAs) play various roles in HCC progression, but no research has focused on the expression pattern of microRNA clusters encoded in lncRNAs. The Ftx gene encodes a lncRNA which harbors 2 clusters of microRNAs in its introns, the miR-374b/421 cluster and the miR-545/374a cluster. To date, no research has focused on the role of the miR-545/374a and miR-374b/421 clusters in HBV-related HCC. In this study, 66 pairs of HBV-related HCC tissue and matched non-cancerous liver tissue specimens were analyzed for the expression of the Ftx microRNA clusters. Our results showed that the miR-545/374a cluster was upregulated in HBV-HCC tissue and significantly correlated with prognosis-related clinical features, including histological grade, metastasis and tumor capsule. Transfection studies with microRNA mimics and inhibitors revealed that miR-545/374a expression promoted in vitro cell proliferation, cell migration and invasion. The wild-type HBV-genome-containing plasmid or full-length HBx protein encoding plasmid was transfected into the Bel-7402 cell line and observed for their influence on miR-545/374a expression. We found that transfection of the HBV genome or HBx alone resulted in an increase in miR-545/374a expression. Next, by monitoring the expression of sera miR-545/374a before and after surgical tumor excision, we found serum miR-545/374a was tumor-derived and exhibited a sharp decrease 25 days after tumor excision. We also examined the gender-based difference in miR-545/374a expression among HCC patients and utilized microRNA target prediction software to find the targets of miR-545/374a. One of these targets, namely estrogen-related receptor gamma (ESRRG) was inversely correlated with miR-545 expression. In conclusion, the overexpression of miR-545/374a cluster located in the Ftx lncRNA is partially responsible for a poor prognosis, and monitoring sera levels of miR-545/374a may be a useful diagnostic marker for HCC.

Regulation of histone methylation by noncoding RNAs

Cells can adapt to their environment and develop distinct identities by rewiring their transcriptional networks to regulate the output of key biological pathways without concomitant mutations to the underlying genes. These alterations, called epigenetic changes, persist stably through mitotic or, in some instances, meiotic cell divisions. In eukaryotes, heritable changes to chromatin structure are a prominent, but not exclusive, mechanism by which epigenetic changes are mediated. These changes are initiated by sequence-specific events, which trigger a cascade of molecular interactions resulting in feedback mechanisms, alterations in chromatin structure, histone posttranslational modifications (PTMs), and ultimately establishment of distinct transcriptional states. In recent years, advances in next generation sequencing have led to the discovery of several novel classes of noncoding RNAs (ncRNAs). In addition to their well-established cytoplasmic roles in posttranscriptional regulation of gene expression, ncRNAs have emerged as key regulators of epigenetic changes via chromatin-dependent mechanisms in organisms ranging from yeast to man. They function by affecting chromatin structure, histone PTMs, and the recruitment of transcriptional activating or repressing complexes. Among histone PTMs, lysine methylation serves as the binding substrate for the recruitment of key protein complexes involved in the regulation of genome architecture, stability, and gene expression. In this review, we will outline the known mechanisms by which ncRNAs of different origins regulate histone methylation, and in doing so contribute to a variety of genome regulatory functions in eukaryotes.

Evolutionary conservation of long non-coding RNAs; sequence, structure, function

BACKGROUND

Recent advances in genomewide studies have revealed the abundance of long non-coding RNAs (lncRNAs) in mammalian transcriptomes. The ENCODE Consortium has elucidated the prevalence of human lncRNA genes, which are as numerous as protein-coding genes. Surprisingly, many lncRNAs do not show the same pattern of high interspecies conservation as protein-coding genes. The absence of functional studies and the frequent lack of sequence conservation therefore make functional interpretation of these newly discovered transcripts challenging. Many investigators have suggested the presence and importance of secondary structural elements within lncRNAs, but mammalian lncRNA secondary structure remains poorly understood. It is intriguing to speculate that in this group of genes, RNA secondary structures might be preserved throughout evolution and that this might explain the lack of sequence conservation among many lncRNAs.

SCOPE OF REVIEW

Here, we review the extent of interspecies conservation among different lncRNAs, with a focus on a subset of lncRNAs that have been functionally investigated. The function of lncRNAs is widespread and we investigate whether different forms of functionalities may be conserved.

MAJOR CONCLUSIONS

Lack of conservation does not imbue a lack of function. We highlight several examples of lncRNAs where RNA structure appears to be the main functional unit and evolutionary constraint. We survey existing genomewide studies of mammalian lncRNA conservation and summarize their limitations. We further review specific human lncRNAs which lack evolutionary conservation beyond primates but have proven to be both functional and therapeutically relevant.

GENERAL SIGNIFICANCE

Pioneering studies highlight a role in lncRNAs for secondary structures, and possibly the presence of functional "modules", which are interspersed with longer and less conserved stretches of nucleotide sequences. Taken together, high-throughput analysis of conservation and functional composition of the still-mysterious lncRNA genes is only now becoming feasible.

Dosage compensation of the sex chromosomes

Differentiated sex chromosomes evolved because of suppressed recombination once sex became genetically controlled. In XX/XY and ZZ/ZW systems, the heterogametic sex became partially aneuploid after degeneration of the Y or W. Often, aneuploidy causes abnormal levels of gene expression throughout the entire genome. Dosage compensation mechanisms evolved to restore balanced expression of the genome. These mechanisms include upregulation of the heterogametic chromosome as well as repression in the homogametic sex. Remarkably, strategies for dosage compensation differ between species. In organisms where more is known about molecular mechanisms of dosage compensation, specific protein complexes containing noncoding RNAs are targeted to the X chromosome. In addition, the dosage-regulated chromosome often occupies a specific nuclear compartment. Some genes escape dosage compensation, potentially resulting in sex-specific differences in gene expression. This review focuses on dosage compensation in mammals, with comparisons to fruit flies, nematodes, and birds.

The origin and evolution of vertebrate sex chromosomes and dosage compensation

In mammals, birds, snakes and many lizards and fish, sex is determined genetically (either male XY heterogamy or female ZW heterogamy), whereas in alligators, and in many reptiles and turtles, the temperature at which eggs are incubated determines sex. Evidently, different sex-determining systems (and sex chromosome pairs) have evolved independently in different vertebrate lineages. Homology shared by Xs and Ys (and Zs and Ws) within species demonstrates that differentiated sex chromosomes were once homologous, and that the sex-specific non-recombining Y (or W) was progressively degraded. Consequently, genes are left in single copy in the heterogametic sex, which results in an imbalance of the dosage of genes on the sex chromosomes between the sexes, and also relative to the autosomes. Dosage compensation has evolved in diverse species to compensate for these dose differences, with the stringency of compensation apparently differing greatly between lineages, perhaps reflecting the concentration of genes on the original autosome pair that required dosage compensation. We discuss the organization and evolution of amniote sex chromosomes, and hypothesize that dosage insensitivity might predispose an autosome to evolving function as a sex chromosome.