Non-Coding RNA: Types, Functions, and Mechanisms

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-11

Introduction to Non-Coding RNA

Non-coding RNA (ncRNA) is a class of RNA molecules that are transcribed from DNA but are not translated into protein. For decades, the central dogma of molecular biology—DNA makes RNA makes protein—dominated thinking about gene expression. However, it is now clear that the vast majority of the human genome is transcribed into RNA that never encodes a protein. These non-coding transcripts perform diverse and essential functions, including regulating gene expression at multiple levels, catalyzing biochemical reactions, guiding RNA modifications, and maintaining genome stability.

The term "non-coding" is purely descriptive: it refers to the absence of an open reading frame (ORF) that would allow translation into a functional polypeptide. This does not imply a lack of function. In fact, many ncRNAs are as conserved across species as protein-coding genes, and their dysregulation is linked to numerous human diseases.

The Central Dogma and the RNA World

The central dogma, as originally articulated by Francis Crick, described the flow of genetic information from DNA to RNA to protein. This framework treated RNA primarily as a messenger—a passive carrier of genetic information. However, the discovery of ribozymes (catalytic RNAs) and the ribosome's peptidyl transferase activity revealed that RNA can also perform enzymatic functions. This insight gave rise to the "RNA world" hypothesis, which proposes that early life relied on RNA for both information storage and catalysis before proteins and DNA evolved.

Modern cells retain this ancient reliance on RNA. Ribosomal RNA (rRNA) catalyzes peptide bond formation. Transfer RNA (tRNA) decodes mRNA into amino acid sequences. Small nuclear RNAs (snRNAs) participate in pre-mRNA splicing. These are all non-coding RNAs, and they are indispensable for fundamental cellular processes. The RNA world did not disappear; it evolved into a sophisticated regulatory network layered on top of the protein-centric view of gene expression.

Why Non-Coding RNAs Matter

The scale of non-coding transcription is staggering. Although only about 1.5% of the human genome encodes proteins, more than 70% of the genome is transcribed into RNA. Much of this transcription produces ncRNAs, including thousands of long non-coding RNAs (lncRNAs) and hundreds of microRNAs (miRNAs). These molecules fine-tune gene expression with remarkable precision, often in a cell-type-specific or developmental-stage-specific manner.

Understanding ncRNAs is essential for several reasons. First, they are central to gene regulation: miRNAs alone are predicted to target more than 60% of human protein-coding genes. Second, ncRNA dysregulation is a hallmark of many diseases, including cancer, where specific miRNAs and lncRNAs act as oncogenes or tumor suppressors. Third, ncRNAs have practical applications: they serve as diagnostic biomarkers, therapeutic targets, and tools for gene silencing. For a broader comparison of how coding and non-coding transcripts differ in structure, function, and regulation, see Coding vs Noncoding RNA.

Types of Non-Coding RNA

Non-coding RNAs are broadly classified into two categories: housekeeping ncRNAs and regulatory ncRNAs. Housekeeping ncRNAs are constitutively expressed and perform essential, universal functions in all cells. Regulatory ncRNAs are often expressed in a tissue-specific or condition-specific manner and modulate gene expression.

Housekeeping ncRNAs

Housekeeping ncRNAs are required for basic cellular function and are typically abundant. They include:

• Ribosomal RNA (rRNA): The catalytic and structural component of ribosomes. In eukaryotes, the 80S ribosome consists of a 60S large subunit (containing 28S, 5.8S, and 5S rRNAs) and a 40S small subunit (containing 18S rRNA). rRNA accounts for approximately 80% of total cellular RNA.
• Transfer RNA (tRNA): Adaptor molecules that carry specific amino acids to the ribosome during translation. Each tRNA has an anticodon that base-pairs with a codon on mRNA. tRNAs undergo extensive post-transcriptional modification, including base methylation and pseudouridylation, which are critical for accurate decoding. These modifications are introduced by enzymes that recognize specific tRNA features, a process detailed in tRNA Modification.
• Small nuclear RNA (snRNA): RNA components of the spliceosome, the complex that removes introns from pre-mRNA. The major spliceosome contains U1, U2, U4, U5, and U6 snRNAs. These RNAs recognize splice sites and catalyze the splicing reaction. For more detail on their structure and function, see Small Nuclear RNA.
• Small nucleolar RNA (snoRNA): Guide RNAs that direct chemical modifications of other RNAs, primarily rRNA. C/D box snoRNAs direct 2'-O-methylation, while H/ACA box snoRNAs direct pseudouridylation. They function by base-pairing with target RNAs and recruiting modification enzymes.

Regulatory ncRNAs

Regulatory ncRNAs are more heterogeneous and are classified primarily by size and mechanism:

Regulatory ncRNAs are the focus of intense research because of their roles in development, differentiation, and disease. Their expression is often tightly controlled, and their dysregulation contributes to pathology.

MicroRNAs (miRNAs): Small but Mighty

MicroRNAs are approximately 22-nucleotide RNA molecules that post-transcriptionally regulate gene expression. They are among the most abundant and best-characterized regulatory ncRNAs. The human genome encodes over 2,000 miRNAs, each capable of targeting hundreds of mRNAs.

Biogenesis of miRNAs

miRNA biogenesis is a multi-step process that begins in the nucleus and ends in the cytoplasm:

1. Transcription: miRNA genes are transcribed by RNA polymerase II into primary miRNAs (pri-miRNAs), which are typically several kilobases long and contain a hairpin structure. Some miRNA genes are located in introns of protein-coding genes and are transcribed as part of the host gene's pre-mRNA.

1. Nuclear processing: The pri-miRNA is cleaved by the microprocessor complex, consisting of the RNase III enzyme Drosha and its cofactor DGCR8. This cleavage releases a ~70-nucleotide precursor miRNA (pre-miRNA) with a characteristic stem-loop structure and a 2-nucleotide 3' overhang.

1. Nuclear export: The pre-miRNA is exported to the cytoplasm by Exportin-5 in a Ran-GTP-dependent manner.

1. Cytoplasmic processing: In the cytoplasm, the RNase III enzyme Dicer cleaves the pre-miRNA near the loop, producing a ~22-nucleotide duplex. The duplex is loaded into the RNA-induced silencing complex (RISC), which contains an Argonaute (AGO) protein.

1. Strand selection: One strand of the duplex (the guide strand) is retained in AGO, while the passenger strand is degraded. Strand selection is determined by the thermodynamic stability of the duplex ends; the strand with the less stable 5' end is usually selected as the guide.

1. Target recognition: The mature miRNA guides AGO to target mRNAs through partial base-pairing, primarily within the 3' untranslated region (UTR). Nucleotides 2–8 of the miRNA, called the "seed region," are critical for target recognition.

Mechanism of Gene Silencing

miRNAs silence gene expression through two main mechanisms, both mediated by AGO proteins:

• Translational repression: The miRNA-RISC complex can inhibit translation initiation by competing with the cap-binding complex eIF4F, or inhibit translation elongation by causing ribosome stalling. This mechanism reduces protein production without changing mRNA levels.

• mRNA degradation: If the miRNA has perfect or near-perfect complementarity to the target, AGO can cleave the mRNA directly. More commonly, partial complementarity recruits additional proteins, including GW182 and the CCR4-NOT deadenylase complex, which promote mRNA deadenylation, decapping, and degradation. This pathway is the predominant mechanism in mammals and is linked to general RNA Degradation pathways.

The choice between translational repression and mRNA degradation depends on the degree of complementarity and the cellular context. In animals, most miRNA-target interactions involve partial complementarity, leading primarily to mRNA destabilization. In plants, near-perfect complementarity is more common, resulting in direct mRNA cleavage.

Long Non-Coding RNAs (lncRNAs): Diverse Regulators

Long non-coding RNAs are defined as RNA transcripts longer than 200 nucleotides that lack protein-coding potential. The human genome contains approximately 20,000 lncRNA genes, comparable to the number of protein-coding genes. Unlike miRNAs, lncRNAs are poorly conserved at the sequence level but often show conserved secondary structures and genomic positions.

lncRNAs are transcribed by RNA polymerase II and are often spliced, polyadenylated, and 5'-capped, resembling mRNAs. However, they lack a functional open reading frame. Many lncRNAs are expressed at low levels and in a highly cell-type-specific manner, which has led to debate about their functional significance. Nevertheless, a substantial number of lncRNAs have well-characterized functions.

Mechanisms of lncRNA Action

lncRNAs regulate gene expression through four primary mechanisms:

• Scaffold: lncRNAs can bind multiple proteins simultaneously, bringing them into proximity to form ribonucleoprotein complexes. For example, the lncRNA NEAT1 scaffolds proteins to form paraspeckles, nuclear bodies involved in gene regulation.

• Decoy: lncRNAs can sequester RNA-binding proteins or miRNAs away from their targets. For instance, the lncRNA MALAT1 binds and sequesters splicing factors, modulating alternative splicing. lncRNAs that sequester miRNAs are often called "sponges" or "competing endogenous RNAs" (ceRNAs).

• Guide: lncRNAs can direct chromatin-modifying complexes to specific genomic loci. The lncRNA HOTAIR guides the Polycomb repressive complex 2 (PRC2) to the HOXD locus, where it promotes H3K27 trimethylation and gene silencing.

• Enhancer function: Some lncRNAs are transcribed from enhancer regions and promote the expression of nearby genes. These enhancer RNAs (eRNAs) can stabilize enhancer-promoter looping or recruit co-activators.

The mechanisms of lncRNA action are not mutually exclusive; a single lncRNA can use different mechanisms in different contexts. Many lncRNAs function through their interaction with RNA Binding Protein partners, and their localization—nuclear versus cytoplasmic—often determines their mechanism.

lncRNAs in Development and Disease

Two well-studied lncRNAs illustrate the diversity of lncRNA function:

• XIST (X-inactive specific transcript): XIST is a 17 kb lncRNA that mediates X chromosome inactivation in female mammals. It is expressed from the future inactive X chromosome and coats it in cis, recruiting PRC2 and other chromatin modifiers to establish and maintain heterochromatin. XIST is essential for dosage compensation, ensuring that females do not express twice the X-linked gene dosage of males.

• HOTAIR (HOX transcript antisense RNA): HOTAIR is a 2.2 kb lncRNA expressed from the HOXC locus. It acts in trans, binding PRC2 and the LSD1/CoREST complex to target the HOXD locus, where it promotes H3K27 methylation and H3K4 demethylation, leading to gene silencing. HOTAIR is overexpressed in many cancers, where it promotes metastasis by reprogramming chromatin state.

lncRNAs are also implicated in genomic imprinting (e.g., KCNQ1OT1), dosage compensation (XIST), and pluripotency maintenance (e.g., lincRNA-RoR). Their dysregulation is associated with cancer, neurological disorders, and cardiovascular disease, making them attractive therapeutic targets.

Other Regulatory ncRNAs: siRNAs, piRNAs, and circRNAs

Beyond miRNAs and lncRNAs, several other classes of regulatory ncRNAs play critical roles in genome defense and gene regulation.

siRNAs and RNA Interference

Small interfering RNAs (siRNAs) are ~21-nucleotide double-stranded RNAs that mediate RNA interference (RNAi). Unlike miRNAs, which are encoded in the genome, siRNAs are typically derived from exogenous sources (e.g., viral RNA, transgenes) or from long double-stranded RNA precursors. They can also be delivered synthetically.

The biogenesis of siRNAs differs from miRNAs in that they do not require Drosha processing. Instead, long double-stranded RNA is cleaved directly by Dicer into siRNA duplexes. One strand is loaded into RISC, where it guides AGO to perfectly complementary mRNA targets, leading to their cleavage and degradation.

RNAi is a powerful experimental tool. Synthetic siRNAs are widely used to knock down gene expression in cultured cells and animal models. The specificity and potency of siRNAs have also led to their development as therapeutics, with several siRNA drugs approved for clinical use. The mechanism of siRNA-mediated silencing is distinct from that of antisense oligonucleotides, which act through RNase H-dependent degradation or steric blockade; for a comparison, see Antisense Oligonucleotide.

piRNAs and Transposon Silencing

PIWI-interacting RNAs (piRNAs) are 24–31 nucleotide RNAs that bind to PIWI proteins, a subfamily of Argonaute proteins. piRNAs are primarily expressed in germline cells, where they silence transposable elements to maintain genome integrity.

piRNA biogenesis is distinct from miRNA and siRNA biogenesis. piRNAs are derived from single-stranded precursors transcribed from piRNA clusters, often in a Dicer-independent manner. They are processed through a "ping-pong" amplification loop involving two PIWI proteins, Aubergine and Argonaute 3, which generates secondary piRNAs and amplifies the silencing signal.

piRNAs guide PIWI proteins to complementary transposon transcripts, where they cleave them or recruit chromatin-modifying enzymes to establish repressive epigenetic marks. This silencing is essential for fertility; mutations in piRNA pathway components cause sterility in mice and flies. For more detail on piRNA biology, see Piwi RNA.

circRNAs as Sponges

Circular RNAs (circRNAs) are covalently closed RNA molecules produced by back-splicing, where the 3' end of an exon is joined to the 5' end of an upstream exon. This produces a circular transcript that lacks free ends, making it resistant to exonuclease degradation and more stable than linear RNAs.

circRNAs have multiple functions:

• miRNA sponges: Some circRNAs contain multiple binding sites for specific miRNAs, sequestering them and preventing them from targeting their mRNA substrates. The best-characterized example is CDR1as (ciRS-7), which contains more than 70 conserved binding sites for miR-7 and functions as a miR-7 sponge.

• Protein binding: circRNAs can bind RNA-binding proteins, acting as scaffolds or decoys. Some circRNAs are translated into proteins, despite being circular, through cap-independent translation mechanisms.

• Gene regulation: circRNAs can regulate the transcription of their parent genes by interacting with RNA polymerase II or chromatin modifiers.

circRNAs are abundant in the brain and are differentially expressed in various diseases, making them promising biomarkers.

Methods to Study Non-Coding RNAs

Studying ncRNAs requires specialized methods that differ from those used for protein-coding genes. The choice of method depends on the research question: detection, quantification, functional characterization, or target identification.

High-Throughput Sequencing

• RNA sequencing (RNA-seq): RNA-seq is the gold standard for transcriptome analysis. Total RNA is converted to cDNA, sequenced, and mapped to the genome. For ncRNA analysis, libraries are often prepared with ribosomal RNA depletion (rather than poly-A selection) to capture non-polyadenylated transcripts like lncRNAs and circRNAs. Small RNA-seq uses size selection (18–30 nt) to enrich for miRNAs and piRNAs.

• Microarrays: Microarrays use fluorescently labeled cDNA hybridized to probes on a chip. They are cheaper than RNA-seq but limited to known sequences and have a narrower dynamic range. They are still used for targeted ncRNA profiling.

• Northern blot: Northern blotting detects specific RNA species by size. RNA is separated by denaturing gel electrophoresis, transferred to a membrane, and probed with a labeled complementary oligonucleotide. This method confirms transcript size and abundance but requires relatively large amounts of RNA.

• Quantitative reverse transcription PCR (qRT-PCR): qRT-PCR is the most sensitive method for quantifying specific ncRNAs. RNA is reverse-transcribed to cDNA, and PCR is performed with fluorescent probes (e.g., TaqMan) or SYBR Green. For small RNAs like miRNAs, stem-loop primers are used for reverse transcription to improve specificity. Typical cycling conditions are 95°C for 10 minutes, followed by 40 cycles of 95°C for 15 seconds and 60°C for 1 minute.

Functional Assays

• CRISPR-Cas9 knockout: CRISPR-Cas9 can delete or disrupt ncRNA genes. For lncRNAs, this is challenging because their genomic loci often overlap with enhancers or other genes. CRISPR interference (CRISPRi) and CRISPR activation (CRISPRa) use catalytically dead Cas9 fused to transcriptional repressors or activators to modulate ncRNA expression without altering the genome.

• Antisense oligonucleotides (ASOs): ASOs are short single-stranded DNA or RNA molecules that bind complementary ncRNA transcripts, promoting their degradation by RNase H or blocking their interaction with proteins. ASOs are particularly useful for knocking down nuclear lncRNAs, which are poorly accessible to siRNA.

• Overexpression studies: Transfecting cells with plasmid or viral vectors expressing a ncRNA can reveal gain-of-function phenotypes. For miRNAs, synthetic mimics (double-stranded RNAs resembling the mature miRNA) are commonly used.

• RNA pulldown and crosslinking: To identify RNA-protein interactions, biotinylated RNA is incubated with cell lysates, and bound proteins are identified by mass spectrometry. Crosslinking immunoprecipitation (CLIP) uses UV light to covalently crosslink RNA-protein complexes, followed by immunoprecipitation and sequencing to identify RNA-binding sites.

Bioinformatics Resources

Several databases are essential for ncRNA research:

• miRBase: The primary repository for miRNA sequences and annotations.
• LNCipedia and NONCODE: Databases of lncRNA sequences and annotations.
• TargetScan and miRDB: Prediction tools for miRNA target genes.
• circBase: A database of circRNA sequences.
• RNAcentral: A comprehensive database of ncRNA sequences from multiple sources.

These resources allow researchers to predict targets, examine expression across tissues, and design experiments.

Non-Coding RNAs in Disease and Therapeutics

The dysregulation of ncRNAs is a common feature of human diseases. Their tissue-specific expression and stability in body fluids make them attractive biomarkers, and their ability to modulate gene expression makes them promising therapeutic targets.

ncRNAs as Biomarkers

miRNAs are remarkably stable in blood, plasma, serum, urine, and other body fluids, where they are protected from RNases by encapsulation in exosomes or binding to proteins like Argonaute 2. This stability, combined with their disease-specific expression patterns, makes them excellent non-invasive biomarkers.

• Cancer: miR-21 is upregulated in many solid tumors and is associated with poor prognosis. miR-141 is elevated in the serum of prostate cancer patients. The let-7 family is downregulated in lung cancer and correlates with poor survival.

• Cardiovascular disease: miR-208 is released from damaged cardiomyocytes and can be detected in the blood after myocardial infarction. miR-499 is also elevated in acute myocardial infarction and may help distinguish it from other causes of chest pain.

• Neurological disorders: miR-132 and miR-134 are altered in Alzheimer's disease. In Parkinson's disease, miR-153 and miR-133b show differential expression in blood and brain tissue.

lncRNAs are also emerging as biomarkers. PCA3 is a lncRNA that is highly expressed in prostate cancer and is used in a urine-based diagnostic test. HOTAIR expression in tumor tissue predicts metastasis and poor survival in breast and colorectal cancers.

Therapeutic Applications

Several strategies are being developed to target ncRNAs therapeutically:

• miRNA mimics: Synthetic double-stranded RNAs that restore the function of tumor-suppressor miRNAs. For example, MRX34, a miR-34 mimic, entered clinical trials for liver cancer, though it was halted due to immune-related adverse events.

• Anti-miRs (antagomirs): Chemically modified antisense oligonucleotides that bind and sequester oncogenic miRNAs. Miravirsen, an anti-miR-122, successfully reduced hepatitis C virus (HCV) RNA levels in clinical trials by sequestering miR-122, which HCV requires for replication.

• ASOs targeting lncRNAs: ASOs that degrade oncogenic lncRNAs are in preclinical development. For example, ASOs targeting MALAT1 reduce metastasis in mouse models of lung cancer.

• siRNA therapeutics: Synthetic siRNAs targeting disease-causing genes have been approved. Patisiran, an siRNA targeting transthyretin, is approved for hereditary transthyretin amyloidosis. Inclisiran, an siRNA targeting PCSK9, is approved for hypercholesterolemia.

• CircRNA-based therapies: Engineered circRNAs that act as miRNA sponges or express therapeutic proteins are being explored. Their stability and resistance to exonucleases make them attractive delivery vehicles.

The clinical translation of ncRNA therapeutics faces challenges, including delivery to specific tissues, off-target effects, and immune stimulation. However, the success of siRNA drugs demonstrates the feasibility of RNA-based therapies.

Common Pitfalls and Misconceptions

Students frequently encounter several conceptual difficulties when learning about ncRNAs. Understanding these pitfalls will help you avoid common errors in exams and research.

miRNA vs. siRNA

miRNAs and siRNAs are often confused because they are both ~21–22 nucleotide RNAs that associate with Argonaute proteins. The key differences are:

A common exam question asks which enzyme processes pri-miRNA (Drosha) versus pre-miRNA (Dicer). Remember: Drosha in the nucleus, Dicer in the cytoplasm.

Not All ncRNAs Are Regulatory

Students often assume that all ncRNAs regulate gene expression. This is incorrect. Housekeeping ncRNAs—rRNA, tRNA, snRNA, snoRNA—perform structural and catalytic functions that are essential for protein synthesis and RNA processing. These are not "regulatory" in the sense of modulating gene expression; they are the machinery of gene expression itself. The distinction matters because the regulatory ncRNAs (miRNA, lncRNA, piRNA, circRNA) are the ones typically discussed in the context of gene regulation and disease.

The Myth of Junk DNA

The term "junk DNA" was coined in the 1970s to describe the large fraction of the genome that does not encode proteins. This term is misleading and should be avoided. While some non-coding DNA is likely non-functional, much of it is transcribed into ncRNAs with regulatory roles. The ENCODE project estimated that more than 80% of the human genome has biochemical function, though this figure is debated. The key point is that non-coding does not mean non-functional. Many ncRNAs have clear, experimentally validated functions, and their conservation across species argues for their biological importance.

Confusing lncRNA and mRNA

lncRNAs resemble mRNAs in many ways: they are transcribed by RNA polymerase II, spliced, and often polyadenylated. The critical difference is that lncRNAs lack a functional open reading frame. However, some lncRNAs contain short ORFs that can produce small peptides. This complicates the definition. In practice, lncRNAs are defined by their lack of protein-coding potential, assessed by computational tools that examine ORF length, codon conservation, and ribosome profiling data.

Overlooking RNA Localization

The function of a ncRNA often depends on its subcellular localization. Nuclear lncRNAs like XIST and NEAT1 regulate chromatin and nuclear architecture, while cytoplasmic lncRNAs and miRNAs regulate mRNA stability and translation. When studying a ncRNA, it is essential to determine its localization by RNA fluorescence in situ hybridization (FISH) or subcellular fractionation. For a deeper discussion of how RNA localization affects function, see RNA Localization.

Summary and Key Takeaways

Non-coding RNAs are a diverse class of transcripts that are not translated into protein but perform essential regulatory, catalytic, and structural functions. They are broadly classified into housekeeping ncRNAs (rRNA, tRNA, snRNA, snoRNA) and regulatory ncRNAs (miRNA, siRNA, lncRNA, piRNA, circRNA). miRNAs silence genes post-transcriptionally through mRNA degradation or translational repression. lncRNAs regulate gene expression through scaffold, decoy, guide, and enhancer mechanisms. siRNAs mediate RNA interference, piRNAs silence transposons in the germline, and circRNAs act as miRNA sponges. These molecules are studied using RNA-seq, qRT-PCR, Northern blotting, CRISPR, and bioinformatics tools. Their dysregulation is implicated in cancer, neurological disorders, and cardiovascular disease, and they are being developed as biomarkers and therapeutic targets.

Frequently Asked Questions

What is non-coding RNA?

Non-coding RNA (ncRNA) is RNA that is transcribed from DNA but is not translated into protein. It functions at the RNA level to regulate gene expression, catalyze reactions, or provide structural support. Examples include rRNA, tRNA, miRNA, and lncRNA.

What are examples of non-coding RNAs?

Examples include ribosomal RNA (rRNA), transfer RNA (tRNA), small nuclear RNA (snRNA), small nucleolar RNA (snoRNA), microRNA (miRNA), small interfering RNA (siRNA), PIWI-interacting RNA (piRNA), long non-coding RNA (lncRNA), and circular RNA (circRNA).

What are the types of non-coding RNA?

Non-coding RNAs are classified into housekeeping ncRNAs (rRNA, tRNA, snRNA, snoRNA) that perform essential cellular functions, and regulatory ncRNAs (miRNA, siRNA, lncRNA, piRNA, circRNA) that modulate gene expression.

What is the difference between coding and non-coding RNA?

Coding RNA (mRNA) is translated into protein and contains an open reading frame. Non-coding RNA is not translated into protein. Both are transcribed from DNA, but ncRNAs function directly as RNA molecules.

How do non-coding RNAs regulate gene expression?

Non-coding RNAs regulate gene expression through multiple mechanisms: miRNAs and siRNAs silence mRNAs post-transcriptionally; lncRNAs recruit chromatin modifiers, sequester proteins or miRNAs, and enhance transcription; piRNAs silence transposons; circRNAs sponge miRNAs.

Are non-coding RNAs involved in diseases?

Yes. Dysregulation of ncRNAs is associated with cancer, neurological disorders, cardiovascular disease, and many other conditions. Specific miRNAs and lncRNAs act as oncogenes or tumor suppressors, and their expression patterns are used as diagnostic and prognostic biomarkers.

What methods are used to study non-coding RNAs?

Common methods include RNA sequencing (RNA-seq), quantitative reverse transcription PCR (qRT-PCR), Northern blotting, microarrays, CRISPR-based knockout and activation, antisense oligonucleotide knockdown, RNA pulldown, and bioinformatics databases like miRBase and LNCipedia.

Key Takeaways

• Non-coding RNAs are functional RNA molecules that are not translated into protein; they include housekeeping types (rRNA, tRNA, snRNA, snoRNA) and regulatory types (miRNA, siRNA, lncRNA, piRNA, circRNA).
• miRNAs are ~22-nucleotide RNAs that silence genes by promoting mRNA degradation or translational repression, guided by seed-region complementarity.
• lncRNAs are >200-nucleotide transcripts that regulate gene expression through scaffold, decoy, guide, and enhancer mechanisms, exemplified by XIST and HOTAIR.
• siRNAs mediate RNA interference and are used as experimental tools and therapeutics; piRNAs silence transposons in germ cells; circRNAs act as miRNA sponges.
• ncRNAs are studied using RNA-seq, qRT-PCR, Northern blotting, CRISPR, and bioinformatics databases; each method has specific strengths and limitations.
• ncRNA dysregulation is linked to cancer, neurological, and cardiovascular diseases, and ncRNAs serve as biomarkers and therapeutic targets.
• The term "junk DNA" is outdated; much non-coding DNA is transcribed into functional ncRNAs, and non-coding does not mean non-functional.

Further Reading

• Yan H, Bu P. Non-coding RNA in cancer. Essays in biochemistry. 2021. PubMed 33860799
• Yang K et al. A systematic review of the research progress of non-coding RNA in neuroinflammation and immune regulation in cerebral infarction/ischemia-reperfusion injury. Frontiers in immunology. 2022. PubMed 36275741
• Ning S, Li X. Non-coding RNA Resources. Advances in experimental medicine and biology. 2018. PubMed 30191482
• Staněk D. Long non-coding RNAs and splicing. Essays in biochemistry. 2021. PubMed 33835135
• Glasgow AMA, De Santi C, Greene CM. Non-coding RNA in cystic fibrosis. Biochemical Society transactions. 2018. PubMed 29743276
• Miano V et al. The non-coding epitranscriptome in cancer. Briefings in functional genomics. 2021. PubMed 33564819

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