Junk DNA Research Articles

Junk DNA and Cancer: Why the Trash in Your Cells is Very Important

Junk DNA and Cancer: Why the Trash in Your Cells is Very Important

Alpha satellite DNA biology: finding function in the recesses of the genome.

Repetitive DNA, formerly referred to by the misnomer "junk DNA," comprises a majority of the human genome. One class of this DNA, alpha satellite, comprises up to 10% of the genome. Alpha satellite is enriched at all human centromere regions and is competent for de novo centromere assembly. Because of thehighly repetitive nature ofalpha satellite, ithas been difficult to achieve genome assemblies at centromeres using traditional next-generation sequencing approaches, and thus, centromeres represent gaps in the current human genome assembly. Moreover, alpha satellite DNA is transcribed into repetitive noncoding RNA and contributes to a large portion of the transcriptome. Recent efforts to characterize these transcripts and their function have uncovered pivotal roles for satellite RNA in genome stability, including silencing "selfish" DNA elements and recruiting centromere and kinetochore proteins. This review will describe the genomic and epigenetic features of alpha satellite DNA, discuss recent findings of noncoding transcripts produced from distinct alpha satellite arrays, and address current progress in the functional understanding of this oft-neglected repetitive sequence. We will discuss unique challenges of studying human satellite DNAs and RNAs and point toward new technologies that will continue to advance our understanding of this largely untapped portion of the genome.

Genetic landscape of long noncoding RNA (lncRNAs) in glioblastoma: identification of complex lncRNA regulatory networks and clinically relevant lncRNAs in glioblastoma.

The major part of the genome that was previously called junk DNA has been shown to be dynamically transcribed to produce non-coding RNAs. Among them, the long non-coding RNAs (lncRNA) play diverse roles in the cellular context and are therefore involved in various diseases like cancer. LncRNA transcript profiling of glioblastoma (n = 19) and control brain samples (n = 9) identified 2,774 and 5,016 lncRNAs to be upregulated and downregulated in GBMs respectively. Correlation analysis of differentially regulated lncRNAs with mRNA and lncRNA identified several lncRNAs that may potentially regulate many tumor relevant mRNAs and lncRNAs both at nearby locations (cis) and far locations (trans). Integration of our data set with TCGA GBM RNA-Seq data (n = 172) revealed many lncRNAs as a host as well as decoy for many tumor regulated miRNAs. The expression pattern of seven lncRNAs- HOXD-AS2, RP4-792G4.2, CRNDE, ANRIL, RP11-389G6.3, RP11-325122.2 and AC123886.2 was validated by TCGA RNA-Seq data and RT-qPCR. Silencing ANRIL, a GBM upregulated lncRNA, inhibited glioma cell proliferation and colony growth. Cox regression analysis identified several prognostic lncRNAs. An lncRNA risk score derived from five lnRNAs-RP6-99M1.2, SOX21-AS1, CTD-2127H9.1, RP11-375B1.3 and RP3-449M8.9 predicted survival independent of all other markers. Multivariate cox regression analysis involving G-CIMP, IDH1 mutation, MGMT promoter methylation identified lncRNA risk score to be an independent poor predictor of GBM survival. The lncRNA risk score also stratified GBM patients into low and high risk with significant survival difference. Thus our study demonstrates the importance of lncRNA in GBM pathology and underscores the potential possibility of targeting lncRNA for GBM therapy.

Recent advances in our understanding of the pathobiology of non-coding RNA

The central dogma of molecular biology recognised RNA as a mere intermediate between DNA sequence and proteins, the main protagonists of cellular functions. The shadow of a wrinkle in this concept appeared when the Human Genome Project revealed that protein-coding genes only account for 2% of our genome and the remaining 98% was originally dismissed as elusive “junk DNA.” Recent advances in next-generation sequencing provided tantalising evidence that 70-90% of human genome is actively transcribed(1). Numerous studies started discerning the functional importance of long and short (>200 and <200 nucleotides, respectively) non-coding transcripts far beyond the initial textbook-engraved infrastructural and information-transmitting role of rRNA, tRNA and mRNA. By “rediscovering the junk,” this essay reviews a selection of recent disease-associated advances in the field of small non-coding RNAs before extending the discussion to long non-coding RNAs and finally to the overarching concepts of competing endogenous RNAs (ceRNAs) and ‘social’ RNA.

A LINE1-Nucleolin Partnership Regulates Early Development and ESC Identity

Transposable elements represent nearly half of mammalian genomes and are generally described as parasites, or "junk DNA." The LINE1 retrotransposon is the most abundant class and is thought to be deleterious for cells, yet it is paradoxically highly expressed during early development. Here, we report that LINE1 plays essential roles in mouse embryonic stem cells (ESCs) and pre-implantation embryos. In ESCs, LINE1 acts as a nuclear RNA scaffold that recruits Nucleolin and Kap1/Trim28 to repress Dux, the master activator of a transcriptional program specific to the 2-cell embryo. In parallel, LINE1 RNA mediates binding of Nucleolin and Kap1 to rDNA, promoting rRNA synthesis and ESC self-renewal. In embryos, LINE1 RNA is required for Dux silencing, synthesis of rRNA, and exit from the 2-cell stage. The results reveal an essential partnership between LINE1 RNA, Nucleolin, Kap1, and peri-nucleolar chromatin in the regulation of transcription, developmental potency, and ESC self-renewal.

Genome-wide prediction of cis-regulatory regions using supervised deep learning methods

BackgroundIn the human genome, 98% of DNA sequences are non-protein-coding regions that were previously disregarded as junk DNA. In fact, non-coding regions host a variety of cis-regulatory regions which precisely control the expression of genes. Thus, Identifying active cis-regulatory regions in the human genome is critical for understanding gene regulation and assessing the impact of genetic variation on phenotype. The developments of high-throughput sequencing and machine learning technologies make it possible to predict cis-regulatory regions genome wide.ResultsBased on rich data resources such as the Encyclopedia of DNA Elements (ENCODE) and the Functional Annotation of the Mammalian Genome (FANTOM) projects, we introduce DECRES based on supervised deep learning approaches for the identification of enhancer and promoter regions in the human genome. Due to their ability to discover patterns in large and complex data, the introduction of deep learning methods enables a significant advance in our knowledge of the genomic locations of cis-regulatory regions. Using models for well-characterized cell lines, we identify key experimental features that contribute to the predictive performance. Applying DECRES, we delineate locations of 300,000 candidate enhancers genome wide (6.8% of the genome, of which 40,000 are supported by bidirectional transcription data), and 26,000 candidate promoters (0.6% of the genome).ConclusionThe predicted annotations of cis-regulatory regions will provide broad utility for genome interpretation from functional genomics to clinical applications. The DECRES model demonstrates potentials of deep learning technologies when combined with high-throughput sequencing data, and inspires the development of other advanced neural network models for further improvement of genome annotations.

Same-Sex Twin Pair Phenotypic Correlations are Consistent with Human Y Chromosome Promoting Phenotypic Heterogeneity

Junk DNA has been long appreciated as an evolutionary facilitator because it can participate in the causation of genetic variation such as chromosome rearrangements and can be exapted into coding or regulatory elements. Recently, it has been proposed that junk DNA variation within natural populations indirectly causes a phenotypic heterogeneity that subsequently promotes genetic capacitance, i.e., the random fluctuation of genetic variation. Junk DNA role as capacitor might drive population traits such as sexual dimorphism, spatiotemporal dynamics, or genetic diversification leading into speciation. Whether the human species also showed junk DNA-based capacitance manifested as a junk DNA-dependent phenotypic heterogeneity that contributed to the etiology and expression of diseases or the evolutionary history of human populations is intriguing. Because the human Y chromosome is highly enriched in junk DNA, humans are sexually dimorphic for the genomic content in junk DNA. Thus, it would be expected that junk DNA-based capacitance in humans were manifested as a sexual dimorphism for phenotypic heterogeneity. Here, I gather supporting evidence for the existence of a sexual dimorphism for putative junk DNA-based phenotypic heterogeneity by analyzing same-sex twin pairs phenotypic concordance.

Locus specific engineering of tandem DNA repeats in the genome of Saccharomyces cerevisiae using CRISPR/Cas9 and overlapping oligonucleotides

DNA repeats constitute a large part of genomes of multicellular eucaryotes. For a longtime considered as junk DNA, their role in genome organization and tuning of gene expression is being increasingly documented. Synthetic biology has so far largely ignored DNA repeats as regulatory elements to manipulate functions in engineered genomes. The yeast Saccharomyces cerevisiae has been a workhorse of synthetic biology, owing to its genetic tractability. Here we demonstrate the ability to synthetize, in a simple manner, tandem DNA repeats of various size by Cas9-assisted oligonucleotide in vivo assembly in this organism. We show that long tandem DNA repeats of several kilobases can be assembled in one step for different monomer size and G/C content. The combinatorial nature of the approach allows exploring a wide variety of design for building synthetic tandem repeated DNA directly at a given locus in the Saccharomyces cerevisiae genome. This approach provides a simple way to incorporate tandem DNA repeat in synthetic genome designs to implement regulatory functions.

Hiding in Plain Sight: Rediscovering the Importance of Noncoding RNA in Human Malignancy.

At the time of its construction in the 1950s, the central dogma of molecular biology was a useful model that represented the current state of knowledge for the flow of genetic information after a period of prolific scientific discovery. Unknowingly, it also biased many of our assumptions going forward. Whether intentional or not, genomic elements not fitting into this paradigm were deemed unimportant and emphasis on the study of protein-coding genes prevailed for decades. The phrase "Junk DNA," first popularized in the 1960s, is still used with alarming frequency to describe the entirety of noncoding DNA. It has since become apparent that RNA molecules not coding for protein are vitally important in both normal development and human malignancy. Cancer researchers have been pioneers in determining noncoding RNA function and developing new technologies to study these molecules. In this review, we will discuss well known and newly emerging species of noncoding RNAs, their functions in cancer, and new technologies being utilized to understand their mechanisms of action in cancer. Cancer Res; 78(9); 2149-58. ©2018 AACR.

CADS: CRISPR/Cas12a-Assisted DNA Steganography for Securing the Storage and Transfer of DNA-Encoded Information.

Because DNA has the merit of high capacity and complexity, DNA steganography, which conceals DNA-encoded messages, is very promising in information storage. The classical DNA steganography method hides DNA with a "secret message" in a mount of junk DNA, and the message can be extracted by polymerase chain reaction (PCR) using specific primers (key), followed by DNA sequencing and sequence decoding. As leakage of the primer information may result in message insecurity, new methods are needed to better secure the DNA information. Here, we develop a pre-key by either mixing specific primers (real key) with nonspecific primers (fake key) or linking a real key with 3'-end redundant sequences. Then, the single-stranded DNA (ssDNA) trans cleavage activity of CRISPR/Cas12a is employed to cut a fake key or remove the 3'-end redundant sequences, generating a real key for further information extraction. Therefore, with the Cas12a-assisted DNA steganography method, both storage and transfer of DNA-encoding data can be better protected.

The role of transposable elements in functional evolution of amphioxus genome: the case of opsin gene family

Transposable elements (TEs) are able to jump to new locations (transposition) in the genome, usually after replication. They constitute the so-called selfish or junk DNA and take over large proportions of some genomes. Due to their ability to move around they can change the DNA landscape of genomes and are therefore a rich source of innovation in genes and gene regulation. Surge of sequence data in the past years has significantly facilitated large scale comparative studies. Cephalochordates have been regarded as a useful proxy to ancestral chordate condition partially due to the comparatively slow evolutionary rate at morphological and genomic level. In this study, we used opsin gene family from three Branchiostoma species as a window into cephalochordate genome evolution. We compared opsin complements in terms of family size, gene structure and sequence allowing us to identify gene duplication and gene loss events. Furthermore, analysis of the opsin containing genomic loci showed that they are populated by TEs. In summary, we provide evidence of the way transposable elements may have contributed to the evolution of opsin gene family and to the shaping of cephalochordate genomes in general.

The pseudogenes of barley.

Pseudogenes have a reputation of being 'evolutionary relics' or 'junk DNA'. While they are well characterized in mammals, studies in more complex plant genomes have so far been hampered by the absence of reference genome sequences. Barley is one of the economically most important cereals and has a genome size of 5.1Gb. With the first high-quality genome reference assembly available for a Triticeae crop, we conducted a whole-genome assessment of pseudogenes on the barley genome. We identified, characterized and classified 89440 gene fragments and pseudogenes scattered along the chromosomes, with occasional hotspots and higher densities at the chromosome ends. Full-length pseudogenes (11015) have preferentially retained their exon-intron structure. Retrotransposition of processed mRNAs only plays a marginal role in their creation. However, the distribution of retroposed pseudogenes reflects the Rabl configuration of barley chromosomes and thus hints at founding mechanisms. While parent genes related to the defense-response were found to be under-represented in cultivated barley, we detected several defense-related pseudogenes in wild barley accessions. The percentage of transcriptionally active pseudogenes is 7.2%, and these may potentially adopt new regulatory roles.The barley genome is rich in pseudogenes and small gene fragments mainly located towards chromosome tips or as tandemly repeated units. Our results indicate non-random duplication and pseudogenization preferences and improve our understanding of the dynamics of gene birth and death in large plant genomes and the mechanisms that lead to evolutionary innovations.

Designing and Reconstruction of pcDNA 3.0 Mammalian Expression Vector with its Multiple Cloning Sites by Directional Cloning Method

Traditional cloning is the cloning in which we use restriction endonucleases to produce DNA fragments with specific complementary end sequences that can be joined together with a DNA ligase enzyme, prior to the transformation. The purpose of this study was to reconstruct the mammalian expression vector by replacing the junk DNA with its natural multiple cloning sites. Plasmid was propagated and digested with Xho1 and Kpn1 enzymes from both sides of junk DNA a 600 bp DNA was cut from the vector and then ligation of 30 bp primer which was designed similar as its multiple sequence sites. Correct insertion was confirmed by plasmid isolation, plasmid colony PCR, PCR of cloned plasmid and comparison on gel electrophoresis with the original one and finally by sequencing. An extra DNA fragment of 600 bp was cut from the vector after restriction digestion. Ligated colonies appeared on the agar plate from which 60 bp colony PCR products was produced. Plasmid isolation after cloning and colony PCR and PCR of cloned plasmid confirmed the cloning. Cloning of multiple cloning sites in pcDNA3.0 mammalian expression vector was performed successfully. Ligation of multiple cloning sites in pcDNA vector provided various restriction enzymes recognition sites for simple and fast cloning.

Long Noncoding RNAs and Their Role in Oncogenesis

The noncoding part of the human genome, which was previously considered nonfunctional or junk DNA, has been the subject of extensive research this decade. Nevertheless, long noncoding RNAs still represent one of the least investigated fields because of their complexity, multiplicity, and diversity. While some long noncoding RNAs have been characterized fairly well, the functions of many others remain poorly understood. Long noncoding RNAs play an essential role in the regulation of gene expression in all tissues and on all developmental stages. They are involved in a number of signaling pathways, and their aberrant functioning can be pathogenic. This review aims to summarize current state-of-the-art structures of these transcripts in this research field, their genomic localization, their functions, and underlying mechanisms. It also focuses on cancer-associated aberrations of long noncoding RNAs, as well as on prospects of their application in tumor diagnostics and therapy. Examples of decreasing the levels of oncogenic long noncoding RNAs via silencing with short interfering RNAs, antisense oligonucleotides, or low molecular-weight inhibitors are also described.

Expressions of Long Non-Coding RNAs in Carcinogenesis of Cervix: A Review

Long non-coding RNAs (lncRNAs) are transcripts longer than 200 nucleotides mostly transcribed by RNA which do not encode proteins. Previously, lncRNAs were considered transcriptional byproducts called “junk DNA” with no biological functions. There are many studies conducted on lncRNAs showing they are actively involved in regulation of epigenetic, transcriptional, and post-transcriptional events. Expressions of lncRNAs are more different in many malignant tumors than in benign tumors and normal tissue. Aberration of lncRNAs is responsible to promote or suppress tumorigenesis and cancer progression. Under different circumstances, lncRNAs exhibit their roles in carcinogenesis such as MALAT1 is responsible for intervening mRNA instability, HOTAIR, MALAT1, ANRIL, PVT1 links with miRNA and histonemodifying complexes, MEG3 associates with miRNA, CCAT2, MEG3, GAS5, UCA1 allies with c-Myc or P53 causing suppression of tumor or oncogenesis. Abnormal expressions of lncRNAs are noticed in gynecological cancers, such as cervical cancer, ovarian cancer, and endometrial cancer. Identification of cervical cancer associated lncRNAs is necessary to understand the molecular biogenesis of cancers. In this review, we summarized the foundation and function of the lncRNAs in terms of tumor progression, invasion, prognosis, apoptosis, metastasis, and chemo-resistance. This review will provide references to determine the clinical applications of lncRNAs as ideal diagnostic biomarkers or therapeutic targets in cervical cancers.

Index to Titles and Authors/Editors of Books Reviewed Volume 92 (2017)

Index to Titles and Authors/Editors of Books Reviewed Volume 92 (2017)

Competing chromosomes explain junk DNA.

Asymmetric modification of microtubules explains preferential inheritance of chromosomes

Studies of lncRNAs in DNA double strand break repair: what is new?

The ‘junk DNA’ that has haunted human genetics for a long time now turns out to hold enormous hidden treasures. As species had their genomes and transcriptomes sequenced, there are an overwhelming number of lncRNA transcripts being reported, however, less than 100 of them have been functionally characterized. DNA damage is recognized and quickly repaired by the cell, with increased expression of numerous genes involved in DNA repair. Most of the time the studies have focused only on proteins involved in these signaling pathways. However, recent studies have implied that lncRNAs can be broadly induced by DNA damage and regulate DNA repair processes by various mechanisms. In this paper, we focus on recent advances in the identification and functional characterization of novel lncRNAs participating in DNA double strand break repair.

Junk DNA: A Journey through the Dark Matter of the Genome by Nessa Carey Columbia University Press, New York, 2015

The term "junk DNA" came into widespread use in 2001, when the near completion of the Human Genome Project revealed that only a small fraction of the DNA sequences in the human genome encodes amino acid sequences in proteins. Was the rest merely junk? A great deal has been learned since then about functions of the noncoding sequences, and in this entertaining volume, Nessa Carey describes what we know about these sequences, with information complete through approximately 2014. This book follows her earlier and well-received book, The Epigenetics Revolution.

Short and Long Noncoding RNAs Regulate the Epigenetic Status of Cells.

The concepts of junk DNA and transcriptional noise are long gone as the existence of noncoding RNAs (ncRNAs) has been tested extensively in recent years. Given that the epigenetic status of cells affects many biological processes, how ncRNAs mechanistically contribute to these processes is of great interest. Recent Advances: Recent studies show that various ncRNAs interact with epigenetic and/or transcription factors to modulate the epigenetic status of cells directly and/or indirectly. There exists growing interest in the field of cardiovascular research to understand the roles of ncRNAs. Due to the large number of ncRNAs in the mammalian genome, only a handful of ncRNAs have been functionally elucidated, which makes it difficult to understand how ncRNAs interact with protein-coding genes and their encoded proteins. Although the canonical function of microRNAs (miRNAs) to inhibit the translation of protein-coding genes is well established, the number of functionally annotated long noncoding RNAs (lncRNAs) is still small, which is especially true in the heart. Future studies must connect the epigenetic controls of various cellular phenomena by incorporating both miRNAs and lncRNAs. Antioxid. Redox Signal. 29, 832-845.