In contrast to the fairly reliable and complete annotation of the protein coding genes in the human genome, comparable information is lacking for non-coding RNAs. We present a comparative screen of vertebrate genomes for structural non-coding RNAs, which evaluates sequence conservation, secondary structure conservation, and thermodynamic stability of putative RNA structures. We predict more than 30 000 structured RNA elements in the human genome, almost 1000 of which are conserved across all vertebrates. Roughly a third is found in introns of known genes, a sixth are potential regulatory elements in untranslated regions, about half are located far away of any known gene. Only a small fraction of these sequences has been described previously. EST data demonstrate, however, that the majority of them is at least transcribed. The widespread conservation of secondary structure points to a large number of functional ncRNAs in the human genome, which we estimate to be comparable to the number of protein-coding genes. The recent finishing of the human genome sequence emphasizes the "need for reliable experimental and computational methods for comprehensive identification of non-coding RNAs" 1 . A variety of experimental techniques have been used to uncover the human and mouse transcriptomes, in particular tiling arrays 2-4 , cDNA sequencing 5,6 , and unbiased mapping of transcription factor binding sites 7 . All these studies agree that a substantial fraction of the genome is transcribed and that a large fraction of the transcriptome consists of non-coding RNAs. It is unclear, however, which fraction are functional non-coding RNAs (ncRNAs), and which constitutes "transcriptional noise" 8 .Genome-wide computational surveys of ncRNAs, on the other hand, have been impossible until recently, because ncRNAs do not share common signals that could be detected at the sequence level. A large class of ncRNAs, however, has characteristic structures that are functional and hence are well conserved over evolutionary timescales: most of the "classical" ncRNAs, including rRNAs, tRNAs, snRNAs, snoRNAs, as well as the RNA components of RNAse P and the signal recognition particle, are of this type. The stabilizing selection acting on the secondary structure causes characteristic substitution patterns in the underlying sequences: Consistent and compensatory mutations replace one type of base-pair by another one in the paired regions (helices) of the molecule. In addition, loop regions are more variable than helices. These patterns can be ex-1 ploited in comparative computational approaches 9-12 to discriminate functional RNAs from other types of conserved sequence. Recently, high levels of sequence conservation of non-coding DNA regions have been reported 13, 14 . Here we screen the complete collection of conserved non-coding DNA sequences from mammalian genomes and provide a first annotation of the complement of structurally conserved RNAs in the human genome. ResultsSelection of conserved sequences and screening for structural RNAs We s...
In chronic kidney disease (CKD), the decline in the glomerular filtration rate is associated with increased morbidity and mortality and thus poses a major challenge for healthcare systems. While the contribution of tissue-derived miRNAs and mRNAs to CKD progression has been extensively studied, little is known about the role of urinary exosomes and their association with CKD. Exosomes are small, membrane-derived endocytic vesicles that contribute to cell-to-cell communication and are present in various body fluids, such as blood or urine. Next-generation sequencing approaches have revealed that exosomes are enriched in noncoding RNAs and thus exhibit great potential for sensitive nucleic acid biomarkers in various human diseases. Therefore, in this study we aimed to identify urinary exosomal ncRNAs as novel biomarkers for diagnosis of CKD. Since up to now most approaches have focused on the class of miRNAs, we extended our analysis to several other noncoding RNA classes, such as tRNAs, tRNA fragments (tRFs), mitochondrial tRNAs, or lincRNAs. For their computational identification from RNA-seq data, we developed a novel computational pipeline, designated as ncRNASeqScan. By these analyses, in CKD patients we identified 30 differentially expressed ncRNAs, derived from urinary exosomes, as suitable biomarkers for early diagnosis. Thereby, miRNA-181a appeared as the most robust and stable potential biomarker, being significantly decreased by about 200-fold in exosomes of CKD patients compared to healthy controls. Using a cell culture system for CKD indicated that urinary exosomes might indeed originate from renal proximal tubular epithelial cells.
It is now clear that inflammation plays a key role in atherogenesis. As a matter of fact, signs of inflammation of atherosclerotic plaques have been observed for centuries and also constituted the basis for a fierce controversy in the 19th century between the prominent Austrian pathologist Carl von Rokitansky and his German counterpart, Rudolf Virchow. While the former attributed a secondary role to these inflammatory arterial changes, Virchow considered them to be of primary importance. We had the unique opportunity to address this controversy by investigating atherosclerotic specimens from autopsies performed by Carl von Rokitansky up to 178 years ago. Twelve atherosclerotic arteries originally collected between the years 1827 to 1885 were selected from the Collection Rokitansky of the Federal Museum of Pathological Anatomy, Vienna Medical University. Using modern sophisticated immunohistochemical and immunofluorescence techniques, it was shown that various cellular intralesional components, as well as extracellular matrix proteins, were preserved in the historic atherosclerotic specimens. Most importantly, CD3 positive cells were abundant in early lesions, thus, rather supporting Virchows's view, that inflammation is an initiating factor in atherogenesis. Furthermore, we hope to have opened a new and intriguing possibility to study various pathological conditions using valuable historical specimens.
Up to 450 000 non-coding RNAs (ncRNAs) have been predicted to be transcribed from the human genome. However, it still has to be elucidated which of these transcripts represent functional ncRNAs. Since all functional ncRNAs in Eukarya form ribonucleo-protein particles (RNPs), we generated specialized cDNA libraries from size-fractionated RNPs and validated the presence of selected ncRNAs within RNPs by glycerol gradient centrifugation. As a proof of concept, we applied the RNP method to human Hela cells or total mouse brain, and subjected cDNA libraries, generated from the two model systems, to deep-sequencing. Bioinformatical analysis of cDNA sequences revealed several hundred ncRNP candidates. Thereby, ncRNAs candidates were mainly located in intergenic as well as intronic regions of the genome, with a significant overrepresentation of intron-derived ncRNA sequences. Additionally, a number of ncRNAs mapped to repetitive sequences. Thus, our RNP approach provides an efficient way to identify new functional small ncRNA candidates, involved in RNP formation.
In the recent past, several thousand noncoding RNA (ncRNA) genes have been predicted within eukaryal genomes. However, for their functional analysis only a few high-throughput methods are currently available to knock down selected ncRNA species, such as microRNAs, which are targeted by antisense probes, termed antagomirs. We thus compared the efficiencies of four knockdown strategies, previously mainly employed for the analysis of protein-coding genes, to study the function of ncRNAs, in particular, small nucleolar RNAs (snoRNAs). Thereby, the class of snoRNAs represents one of the most abundant ncRNA species. The majority of snoRNAs has been shown to mediate nucleotide modifications by targeting ribosomal RNAs (rRNAs) through complementary antisense elements. However, some snoRNAs, termed ''orphan snoRNAs,'' lack telltale complementarities to rRNAs and thus their function remains elusive. We therefore applied RNA interference (RNAi), locked nucleic acid (LNA), or peptide nucleic acid antisense approaches, as well as a ribozyme-based strategy to knock down a snoRNA. As a proof of principle, we targeted the canonical U81 snoRNA, which has been shown to mediate modification of nucleotide A 391 within eukaryal 28S rRNA. Our results demonstrate that while RNAi is an unsuitable tool for snoRNA knockdown, a ribozyme-based strategy, as well as an LNA-antisense oligonucleotide approach, resulted in a decrease of U81 snoRNA expression levels up to 60%. However, no concomitant decrease in enzymatic activity of U81 snoRNA was observed, indicating that improvement of more efficient knockdown techniques for ncRNAs will be required in the future.
Chronic kidney disease (CKD) is a progressive pathological condition marked by a gradual loss of kidney function. Treatment of CKD is most effective when diagnosed at an early stage and patients are still asymptomatic. However, current diagnostic biomarkers (e.g., serum creatinine and urine albumin) are insufficient for prediction of the pathogenesis of the disease. To address this need, we applied a cell-SELEX (systematic evolution of ligands by exponential enrichment) approach and identified a series of DNA aptamers, which exhibit high affinity and selectivity for cytokine-stimulated cells, resembling some aspects of a CKD phenotype. The cell-SELEX approach was driven toward the enrichment of aptamers that internalize via the endosomal pathway by isolating the endosomal fractions in each selection cycle. Indeed, we demonstrated co-localization of selected aptamers with lysosomal-associated membrane protein 1 (LAMP-1), a late endosomal and lysosomal marker protein, by fluorescence in situ hybridization. These findings are consistent with binding and subsequent internalization of the aptamers into cytokine-stimulated cells. Thus, our study sets the stage for applying selected DNA aptamers as theragnostic reagents for the development of targeted therapies to combat CKD.
Systematic Evolution of Ligands by Exponential Enrichment (SELEX) is an in vitro process enabling selection of nucleic acid molecules binding to target ligands with high binding affinity and specificity. The selection process involves several rounds of two successive steps: (1) binding of the oligonucleotides to the target under stringent conditions and (2) amplification of the target-bound nucleic acids by polymerase chain reaction. Using this strategy, RNA or DNA aptamers are selected upon recognition and binding to specific surface structures of the target. Aptamers generated during the final rounds of selection can be notably used in applications dedicated to diagnosis of diseases or therapeutic approaches.
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