Abnormal dosage of ultraconserved elements is highly disfavored in healthy cells but not cancer cells

A first comprehensive analysis of Transcribed Ultra Conserved Regions uncovers important regulatory functions of novel non-coding transcripts in gliomas

Transcribed Ultra-Conserved Regions (TUCRs) represent a severely understudied class of putative non-coding RNAs (ncRNAs) that are 100% conserved across multiple species. We performed the first-ever analysis of TUCRs in glioblastoma (GBM) and low-grade gliomas (LGG). We leveraged large human datasets to identify the genomic locations, chromatin accessibility, transcription, differential expression, correlation with survival, and predicted functions of all 481 TUCRs, and identified TUCRs that are relevant to glioma biology. Of these, we investigated the expression, function, and mechanism of action of the most highly upregulated intergenic TUCR, uc.110, identifying it as a new oncogene. Uc.110 was highly overexpressed in GBM and LGG, where it promoted malignancy and tumor growth. Uc.110 activated the WNT pathway by upregulating the expression of membrane frizzled-related protein (MFRP), by sponging the tumor suppressor microRNA miR-544. This pioneering study shows important roles for TUCRs in gliomas and provides an extensive database and novel methods for future TUCR research.

Functional associations of evolutionarily recent human genes exhibit sensitivity to the 3D genome landscape and disease

Genome organization is intricately tied to regulating genes and associated cell fate decisions. In this study, we examine the positioning and functional significance of human genes, grouped by their evolutionary age, within the 3D organization of the genome. We reveal that genes of different evolutionary origin have distinct positioning relationships with both domains and loop anchors, and remarkably consistent relationships with boundaries across cell types. While the functional associations of each group of genes are primarily cell type-specific, such associations of conserved genes maintain greater stability across 3D genomic features and disease than recently evolved genes. Furthermore, the expression of these genes across various tissues follows an evolutionary progression, such that RNA levels increase from young genes to ancient genes. Thus, the distinct relationships of gene evolutionary age, function, and positioning within 3D genomic features contribute to tissue-specific gene regulation in development and disease.

Transcribed Ultraconserved Regions in Cancer

Transcribed ultraconserved regions are putative lncRNA molecules that are transcribed from DNA that is 100% conserved in human, mouse, and rat genomes. This is notable, as lncRNAs are typically poorly conserved. TUCRs remain very understudied in many diseases, including cancer. In this review, we summarize the current literature on TUCRs in cancer with respect to expression deregulation, functional roles, mechanisms of action, and clinical perspectives.

Non-coding RNAs transcribed from ultra-conserved regions (T-UCRs) are differentially expressed in dental follicle tissues of impacted mandibular third molars

INTRODUCTION

Transcribed ultra-conserved regions (T-UCRs) are a new class of long non-coding RNA molecules transcribed from ultra-conserved regions (UCRs) of the human genome. T-UCRs are extremely conserved in the human, rat, and mouse genomes. Deletions of genomic areas containing UCRs resulted in live mice that developed without discernible phenotypes, implying that T-UCRs are involved in developmental processes. In addition, there is increasing evidence that dental follicle tissues exhibit various cellular alterations involving deregulation of protein-coding genes and non-coding RNAs. Accordingly, the main objective of the present study was to determine the clinical significance and distinct expression signatures of non-coding RNA molecules transcribed from ultra-conserved regions in dental follicle samples.

MATERIALS AND METHODS

From March 2021 to December 2022, a total 42 patients who referred to clinic of oral and maxillofacial surgery department with the indications of impacted mandibular third molar extraction from 38^th and 48^th positions were enrolled for the study. For the analysis of T-UCR expression levels, real-time quantitative reverse transcription PCR method was used.

RESULTS

Findings of the present study indicated that T-UCRs are distinctly expressed in dental follicle tissues of impacted mandibular third molars. The expression of uc.38, uc.112, and uc.338 was found to be significantly increased in the dental follicles of impacted mandibular third molars, indicating a clinical significance of these molecules. In addition, no differences in T-UCR expression were found as a function of demographic factors.

CONCLUSIONS

Collectively, transcribed ultra-conserved elements, such as uc.38, uc.112, and uc.338, are considerably deregulated in the dental follicle tissues of impacted mandibular third molars and might be responsible for the molecular changes acquired by dental follicle tissues of impacted mandibular third molars.

Perfect and imperfect views of ultraconserved sequences

Across the human genome, there are nearly 500 'ultraconserved' elements: regions of at least 200 contiguous nucleotides that are perfectly conserved in both the mouse and rat genomes. Remarkably, the majority of these sequences are non-coding, and many can function as enhancers that activate tissue-specific gene expression during embryonic development. From their first description more than 15 years ago, their extreme conservation has both fascinated and perplexed researchers in genomics and evolutionary biology. The intrigue around ultraconserved elements only grew with the observation that they are dispensable for viability. Here, we review recent progress towards understanding the general importance and the specific functions of ultraconserved sequences in mammalian development and human disease and discuss possible explanations for their extreme conservation.

The dark matter of the human genome and its role in human cancers

The transcribed ultra-conserved regions (T-UCRs) are a novel family of non-coding RNAs which are absolutely conserved (100%) across orthologous regions of the human, mouse, and rat genomes. T-UCRs represent a small portion of the human genome that is likely to be functional but does not code for proteins and is referred to as the "dark matter" of the human genome. Although T-UCRs are ubiquitously expressed, tissue- and disease-specific expression of T-UCRs have also been observed. Accumulating evidence suggests that T-UCRs are differentially expressed and involved in the malignant transformation of human tumors through various genetic and epigenetic regulatory mechanisms. Therefore, T-UCRs are novel candidate predisposing biomarkers for cancer development. T-UCRs have shown to drive malignant transformation of human cancers through regulating non-coding RNAs and/or protein coding genes. However, the functions and fate of most T-UCRs remain mysterious. Here, we review and highlight the current knowledge on these ultra-conserved elements in the formation and progression of human cancers.

Subcellular Localization of uc.8+ as a Prognostic Biomarker in Bladder Cancer Tissue

Simple Summary

DNA regions having high sequence similarity among human, rat and mouse genomes are defined as Ultraconserved Regions. Non-coding RNA transcripts originating by these regions may play relevant roles in the onset and progression of multiple cancer types. We recently found that ultra-conserved-transcript-8+ (uc.8+) levels correlate with the grading and staging of bladder cancer. The aim of this study is to systematically evaluate the expression of ultra-conserved-transcript-8+ (uc.8+) in biopsies and assess its intracellular localization. Furthermore, we aimed to correlate uc.8+ levels with clinical parameters and patient survival. Our analysis indicates that uc.8+ can localize both in the cytoplasm and nucleus of bladder cells at early stages of tumorigenesis, while in tumors at advanced stages, uc.8+ has a prevalent cytoplasmic localization. These data provide relevant information about uc.8+ localization as a hallmark of tumor stage. Finally, using advanced computer-based techniques, we predicted the binding of uc.8+ to RNA-binding proteins. Our study overall suggests that uc.8+ localization can be used as a prognostic biomarker for bladder cancer.

Abstract

Non-coding RNA transcripts originating from Ultraconserved Regions (UCRs) have tissue-specific expression and play relevant roles in the pathophysiology of multiple cancer types. Among them, we recently identified and characterized the ultra-conserved-transcript-8+ (uc.8+), whose levels correlate with grading and staging of bladder cancer. Here, to validate uc.8+ as a potential biomarker in bladder cancer, we assessed its expression and subcellular localization by using tissue microarray on 73 human bladder cancer specimens. We quantified uc.8+ by in-situ hybridization and correlated its expression levels with clinical characteristics and patient survival. The analysis of subcellular localization indicated the simultaneous presence of uc.8+ in the cytoplasm and nucleus of cells from the Low-Grade group, whereas a prevalent cytoplasmic localization was observed in samples from the High-Grade group, supporting the hypothesis of uc.8+ nuclear-to-cytoplasmic translocation in most malignant tumor forms. Moreover, analysis of uc.8+ expression and subcellular localization in tumor-surrounding stroma revealed a marked down-regulation of uc.8+ levels compared to the paired (adjacent) tumor region. Finally, deep machine-learning approaches identified nucleotide sequences associated with uc.8+ localization in nucleus and/or cytoplasm, allowing to predict possible RNA binding proteins associated with uc.8+, recognizing also sequences involved in mRNA cytoplasm-translocation. Our model suggests uc.8+ subcellular localization as a potential prognostic biomarker for bladder cancer.

Genomic Characterization and Curation of UCEs Improves Species Tree Reconstruction

Ultraconserved genomic elements (UCEs) are generally treated as independent loci in phylogenetic analyses. The identification pipeline for UCE probes does not require prior knowledge of genetic identity, only selecting loci that are highly conserved, single copy, without repeats, and of a particular length. Here, we characterized UCEs from 11 phylogenomic studies across the animal tree of life, from birds to marine invertebrates. We found that within vertebrate lineages, UCEs are mostly intronic and intergenic, while in invertebrates, the majority are in exons. We then curated four different sets of UCE markers by genomic category from five different studies including: birds, mammals, fish, Hymenoptera (ants, wasps, and bees), and Coleoptera (beetles). Of genes captured by UCEs, we find that many are represented by two or more UCEs, corresponding to nonoverlapping segments of a single gene. We considered these UCEs to be nonindependent, merged all UCEs that belonged to a particular gene, constructed gene and species trees, and then evaluated the subsequent effect of merging cogenic UCEs on gene and species tree reconstruction. Average bootstrap support for merged UCE gene trees was significantly improved across all data sets apparently driven by the increase in loci length. Additionally, we conducted simulations and found that gene trees generated from merged UCEs were more accurate than those generated by unmerged UCEs. As loci length improves gene tree accuracy, this modest degree of UCE characterization and curation impacts downstream analyses and demonstrates the advantages of incorporating basic genomic characterizations into phylogenomic analyses. [Anchored hybrid enrichment; ants; ASTRAL; bait capture; carangimorph; Coleoptera; conserved nonexonic elements; exon capture; gene tree; Hymenoptera; mammal; phylogenomic markers; songbird; species tree; ultraconserved elements; weevils.]

Ultraconserved Elements Occupy Specific Arenas of Three-Dimensional Mammalian Genome Organization

This study explores the relationship between three-dimensional genome organization and ultraconserved elements (UCEs), an enigmatic set of DNA elements that are perfectly conserved between the reference genomes of distantly related species. Examining both human and mouse genomes, we interrogate the relationship of UCEs to three features of chromosome organization derived from Hi-C studies. We find that UCEs are enriched within contact domains and, further, that the subset of UCEs within domains shared across diverse cell types are linked to kidney-related and neuronal processes. In boundaries, UCEs are generally depleted, with those that do overlap boundaries being overrepresented in exonic UCEs. Regarding loop anchors, UCEs are neither overrepresented nor underrepresented, but those present in loop anchors are enriched for splice sites. Finally, as the relationships between UCEs and human Hi-C features are conserved in mouse, our findings suggest that UCEs contribute to interspecies conservation of genome organization and, thus, genome stability.

Genome-wide de novo L1 Retrotransposition Connects Endonuclease Activity with Replication

L1 retrotransposon-derived sequences comprise approximately 17% of the human genome. Darwinian selective pressures alter L1 genomic distributions during evolution, confounding the ability to determine initial L1 integration preferences. Here, we generated high-confidence datasets of greater than 88,000 engineered L1 insertions in human cell lines that act as proxies for cells that accommodate retrotransposition in vivo. Comparing these insertions to a null model, in which L1 endonuclease activity is the sole determinant dictating L1 integration preferences, demonstrated that L1 insertions are not significantly enriched in genes, transcribed regions, or open chromatin. By comparison, we provide compelling evidence that the L1 endonuclease disproportionately cleaves predominant lagging strand DNA replication templates, while lagging strand 3'-hydroxyl groups may prime endonuclease-independent L1 retrotransposition in a Fanconi anemia cell line. Thus, acquisition of an endonuclease domain, in conjunction with the ability to integrate into replicating DNA, allowed L1 to become an autonomous, interspersed retrotransposon.

Ultraconserved element uc.372 drives hepatic lipid accumulation by suppressing miR-195/miR4668 maturation

Ultraconserved (uc) RNAs, a class of long non-coding RNAs (lncRNAs), are conserved across humans, mice, and rats, but the physiological significance and pathological role of ucRNAs is largely unknown. Here we show that uc.372 is upregulated in the livers of db/db mice, HFD-fed mice, and NAFLD patients. Gain-of-function and loss-of-function studies indicate that uc.372 drives hepatic lipid accumulation in mice by promoting lipogenesis. We further demonstrate that uc.372 binds to pri-miR-195/pri-miR-4668 and suppresses maturation of miR-195/miR-4668 to regulate expression of genes related to lipid synthesis and uptake, including ACC, FAS, SCD1, and CD36. Finally, we identify that uc.372 is located downstream of the insulinoma-associated 2 (INSM2) gene that is transcriptionally activated by upstream transcription factor 1 (USF1). Our findings reveal a novel mechanism by which uc.372 drives hepatic steatosis through inhibition of miR-195/miR-4668 maturation to relieve miR-195/miR-4668-mediated suppression of functional target gene expression.

Ultraconserved RNAs are a class of long non-coding RNAs whose functions are yet to be identified. Here Guo and colleagues show that an ultraconserved RNA uc.372 promotes lipogenesis and lipid accumulation within the hepatocytes by suppressing the maturation of miR-195/miR-4668 that inhibits lipogenic gene expression.

Evolutionary conservation of DNA methylation in CpG sites within ultraconserved noncoding elements

Ultraconserved noncoding elements (UCNEs) constitute less than 1 Mb of vertebrate genomes and are impervious to accumulating mutations. About 4000 UCNEs exist in vertebrate genomes, each at least 200 nucleotides in length, sharing greater than 95% sequence identity between human and chicken. Despite extreme sequence conservation over 400 million years of vertebrate evolution, we show both ordered interspecies and within-species interindividual variation in DNA methylation in these regions. Here, we surveyed UCNEs with high CpG density in 56 species finding half to be intermediately methylated and the remaining near 0% or 100%. Intermediately methylated UCNEs displayed a greater range of methylation between mouse tissues. In a human population, most UCNEs showed greater variation than the LINE1 transposon, a frequently used epigenetic biomarker. Global methylation was found to be inversely correlated to hydroxymethylation across 60 vertebrates. Within UCNEs, DNA methylation is flexible, conserved between related species, and relaxed from the underlying sequence selection pressure, while remaining heritable through speciation.

The systematic analysis of ultraconserved genomic regions in the budding yeast

Motivation

In the evolution of species, a kind of special sequences, termed ultraconserved sequences (UCSs), have been inherited without any change, which strongly suggests those sequences should be crucial for the species to survive or adapt to the environment. However, the UCSs are still regarded as mysterious genetic sequences so far. Here, we present a systematic study of ultraconserved genomic regions in the budding yeast based on the publicly available genome sequences, in order to reveal their relationship with the adaptability or fitness advantages of the budding yeast.

Results

Our results indicate that, in addition to some fundamental biological functions, the UCSs play an important role in the adaptation of Saccharomyces cerevisiae to the acidic environment, which is backed up by the previous observation. Besides that, we also find the highly unchanged genes are enriched in some other pathways, such as the nutrient-sensitive signaling pathway. To facilitate the investigation of unique UCSs, the UCSC Genome Browser was utilized to visualize the chromosomal position and related annotations of UCSs in S.cerevisiae genome.

Availability and implementation

For more details on UCSs, please refer to the Supplementary information online, and the custom code is available on request.

Contact

fgao@tju.edu.cn.

Supplementary information

Supplementary data are available at Bioinformatics online.

Role of Non-Coding RNAs in the Etiology of Bladder Cancer

According to data of the International Agency for Research on Cancer and the World Health Organization (Cancer Incidence in Five Continents, GLOBOCAN, and the World Health Organization Mortality), bladder is among the top ten body locations of cancer globally, with the highest incidence rates reported in Southern and Western Europe, North America, Northern Africa and Western Asia. Males (M) are more vulnerable to this disease than females (F), despite ample frequency variations in different countries, with a M:F ratio of 4.1:1 for incidence and 3.6:1 for mortality, worldwide. For a long time, bladder cancer was genetically classified through mutations of two genes, fibroblast growth factor receptor 3 (FGFR3, for low-grade, non-invasive papillary tumors) and tumor protein P53 (TP53, for high-grade, muscle-invasive tumors). However, more recently scientists have shown that this disease is far more complex, since genes directly involved are more than 150; so far, it has been described that altered gene expression (up- or down-regulation) may be present for up to 500 coding sequences in low-grade and up to 2300 in high-grade tumors. Non-coding RNAs are essential to explain, at least partially, this ample dysregulation. In this review, we summarize the present knowledge about long and short non-coding RNAs that have been linked to bladder cancer etiology.

Pairing and anti-pairing: a balancing act in the diploid genome

The presence of maternal and paternal homologs appears to be much more than just a doubling of genetic material. We know this because genomes have evolved elaborate mechanisms that permit homologous regions to sense and then respond to each other. One way in which homologs communicate is to come into contact and, in fact, Dipteran insects such as Drosophila excel at this task, aligning all pairs of maternal and paternal chromosomes, end-to-end, in essentially all somatic tissues throughout development. Here, we reexamine the widely held tenet that extensive somatic pairing of homologous sequences cannot occur in mammals and suggest, instead, that pairing may be a widespread and significant potential that has gone unnoticed in mammals because they expend considerable effort to prevent it. We then extend this discussion to interchromosomal interactions, in general, and speculate about the potential of nuclear organization and pairing to impact inheritance.