Definition and research guide
This page combines a MeSH definition, publication statistics and selected research abstracts. It is a starting point for reading the literature, not a medical textbook or a systematic evidence review.
Content available: 4 complete abstracts (639 words), 10 references. Full article text is not stored or reproduced here; follow the PMID, DOI or PMC links to read the original sources and their access terms.
Definition
Sequences of DNA in the genes that are located between the exons. They are transcribed along with the exons but are removed from the primary gene transcript by rna splicing to leave mature RNA. Some introns code for separate genes.
Definition: NLM Medical Subject Headings (MeSH) scope note (Public domain (U.S. National Library of Medicine); attribution requested). View the MeSH record.
Also known as: Intron; Intervening Sequences; Sequences, Intervening; Intervening Sequence; Sequence, Intervening.
Where it fits in the MeSH classification
- Broader topics
- DNA, Intergenic; Gene Components
Related concepts
Research landscape
PubMed indexes 30,523 records tagged with the MeSH heading “Introns” (counts retrieved 2026-10-29). 2,626 of them (8.6%) were published from 2020 onward, and the busiest period so far is 2000-2009 with 10,627 records.
Reviews account for 1,168 records (3.8%) and meta-analyses for 82. Randomized controlled trials number 23 (0.1%) as a share of all records on the topic. Randomized trials make up only a small share of this literature, so much of what is known comes from laboratory, observational or descriptive work.
Show the data
| Period | Records |
|---|---|
| through 1999 | 10,059 |
| 2000-2009 | 10,627 |
| 2010-2019 | 7,211 |
| 2020 onward | 2,626 |
Publication-type chart data
| Type | Records | Share |
|---|---|---|
| Reviews | 1,168 | 3.8% |
| Meta-analyses | 82 | 0.3% |
| Randomized controlled trials | 23 | 0.1% |
Method: PubMed query "Introns"[MeSH Terms] with publication-type and date filters, retrieved 2026-10-29.
Reading the evidence in genetics and genomics
Genetic findings vary widely in strength. A variant linked to a condition in one study may not replicate in other ancestries, and most common variants have small effects that are meaningful only in aggregate. Studies of rare, high-impact variants can support strong causal claims about a gene, while association studies describe statistical links that need functional and independent replication. Check the sample size, the ancestry of participants, whether results were replicated, and whether a laboratory or clinical outcome was actually measured.
Evidence from open-access studies
These open-access studies come from PubMed’s best-match results for this heading (papers whose main topic it is), ranked here by citation count, with one recent addition. Each abstract is reproduced in full under its recorded open licence so that you can read the authors’ own words. They illustrate the literature; they are not a systematic summary of it. Citation counts measure attention, not reliability or clinical benefit.
| Study / authors | Year | Source label / design | Europe PMC citations | Licence / source |
|---|---|---|---|---|
| Histone H3K9 Lactylation Confers Temozolomide Resistance in Glioblastoma via LUC7L2-Mediated MLH1 Intron Retention | 2024 | Research article Design not recorded in structured metadata | 119 | cc by PMID 38477507 · DOI · PMC11109612 |
| Intronic ATTTC repeat expansions in STARD7 in familial adult myoclonic epilepsy linked to chromosome 2 | 2019 | Research article Design not recorded in structured metadata | 117 | cc by PMID 31664034 · DOI · PMC6820779 |
| Nanopore sequencing of brain-derived full-length circRNAs reveals circRNA-specific exon usage, intron retention and microexons | 2021 | Research article Design not recorded in structured metadata | 106 | cc by PMID 34376658 · DOI · PMC8355340 |
| Widespread and intron-rich mirusviruses are predicted to reproduce in nuclei of unicellular eukaryotes | 2026 | Research article Design not recorded in structured metadata | 14 | cc by PMID 41315738 · DOI · PMC12768974 |
Histone H3K9 Lactylation Confers Temozolomide Resistance in Glioblastoma via LUC7L2-Mediated MLH1 Intron Retention [1]
Abstract reading summary — source excerpts
- Opening excerpt
- Temozolomide (TMZ) resistance remains the major obstacle in the treatment of glioblastoma (GBM).
- Closing excerpt
- These findings not only shed light on the mechanism of lactylation in GBM TMZ resistance but also provide a potential combined therapeutic strategy for clinical GBM treatment.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (195 words)
Temozolomide (TMZ) resistance remains the major obstacle in the treatment of glioblastoma (GBM). Lactylation is a novel post-translational modification that is involved in various tumors. However, whether lactylation plays a role in GBM TMZ resistance remains unclear. Here it is found that histone H3K9 lactylation (H3K9la) confers TMZ resistance in GBM via LUC7L2-mediated intron 7 retention of MLH1. Mechanistically, lactylation is upregulated in recurrent GBM tissues and TMZ-resistant cells, and is mainly concentrated in histone H3K9. Combined multi-omics analysis, including CUT&Tag, SLAM-seq, and RNA-seq, reveals that H3K9 lactylation is significantly enriched in the LUC7L2 promoter and activates LUC7L2 transcription to promote its expression. LUC7L2 mediates intron 7 retention of MLH1 to reduce MLH1 expression, and thereby inhibit mismatch repair (MMR), ultimately leading to GBM TMZ resistance. Of note, it is identified that a clinical anti-epileptic drug, stiripentol, which can cross the blood-brain barrier and inhibit lactate dehydrogenase A/B (LDHA/B) activity, acts as a lactylation inhibitor and renders GBM cells more sensitive to TMZ in vitro and in vivo. These findings not only shed light on the mechanism of lactylation in GBM TMZ resistance but also provide a potential combined therapeutic strategy for clinical GBM treatment.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 38477507 · DOI · PMC11109612
Intronic ATTTC repeat expansions in STARD7 in familial adult myoclonic epilepsy linked to chromosome 2 [2]
Abstract reading summary — source excerpts
- Opening excerpt
- Familial Adult Myoclonic Epilepsy (FAME) is characterised by cortical myoclonic tremor usually from the second decade of life and overt myoclonic or generalised tonic-clonic seizures.
- Closing excerpt
- These data, in combination with other genes bearing similar mutations that have been implicated in FAME, suggest ATTTC expansions may cause this disorder, irrespective of the genomic locus involved.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (144 words)
Familial Adult Myoclonic Epilepsy (FAME) is characterised by cortical myoclonic tremor usually from the second decade of life and overt myoclonic or generalised tonic-clonic seizures. Four independent loci have been implicated in FAME on chromosomes (chr) 2, 3, 5 and 8. Using whole genome sequencing and repeat primed PCR, we provide evidence that chr2-linked FAME (FAME2) is caused by an expansion of an ATTTC pentamer within the first intron of STARD7. The ATTTC expansions segregate in 158/158 individuals typically affected by FAME from 22 pedigrees including 16 previously reported families recruited worldwide. RNA sequencing from patient derived fibroblasts shows no accumulation of the AUUUU or AUUUC repeat sequences and STARD7 gene expression is not affected. These data, in combination with other genes bearing similar mutations that have been implicated in FAME, suggest ATTTC expansions may cause this disorder, irrespective of the genomic locus involved.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 31664034 · DOI · PMC6820779
Nanopore sequencing of brain-derived full-length circRNAs reveals circRNA-specific exon usage, intron retention and microexons [3]
Abstract reading summary — source excerpts
- Opening excerpt
- Circular RNA (circRNA) is a class of covalently joined non-coding RNAs with functional roles in a wide variety of cellular processes.
- Closing excerpt
- We propose that altered exon usage in circRNAs may reflect resistance to nonsense-mediated decay in the absence of translation.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (150 words)
Circular RNA (circRNA) is a class of covalently joined non-coding RNAs with functional roles in a wide variety of cellular processes. Their composition shows extensive overlap with exons found in linear mRNAs making it difficult to delineate their composition using short-read RNA sequencing, particularly for long and multi-exonic circRNAs. Here, we use long-read nanopore sequencing of nicked circRNAs (circNick-LRS) and characterize a total of 18,266 and 39,623 circRNAs in human and mouse brain, respectively. We further develop an approach for targeted long-read sequencing of a panel of circRNAs (circPanel-LRS), eliminating the need for prior circRNA enrichment and find >30 circRNA isoforms on average per targeted locus. Our data show that circRNAs exhibit a large number of splicing events such as novel exons, intron retention and microexons that preferentially occur in circRNAs. We propose that altered exon usage in circRNAs may reflect resistance to nonsense-mediated decay in the absence of translation.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 34376658 · DOI · PMC8355340
Widespread and intron-rich mirusviruses are predicted to reproduce in nuclei of unicellular eukaryotes [4]
Abstract reading summary — source excerpts
- Opening excerpt
- Mirusviruses infect unicellular eukaryotes and are related to tailed bacteriophages and herpesviruses.
- Closing excerpt
- Collectively, our data strongly suggest that nuclei of unicellular eukaryotes across marine and freshwater ecosystems worldwide are a major niche for replication of intron-rich mirusviruses.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (150 words)
Mirusviruses infect unicellular eukaryotes and are related to tailed bacteriophages and herpesviruses. Here we expand the known diversity of mirusviruses by screening diverse metagenomic assemblies and characterizing 1,202 non-redundant environmental genomes. Mirusviricota comprises a highly diversified phylum of large and giant eukaryotic viruses that rivals the evolutionary scope and functional complexity of nucleocytoviruses. Critically, major Mirusviricota lineages lack essential genes encoding components of the replication and transcription machineries and, concomitantly, encompass numerous spliceosomal introns that are enriched in virion morphogenesis genes. These features point to multiple transitions from cytoplasmic to nuclear reproduction during mirusvirus evolution. Many mirusvirus introns encode diverse homing endonucleases, suggestive of a previously undescribed mechanism promoting the horizontal mobility of spliceosomal introns. Available metatranscriptomes reveal long-range trans-splicing in a virion morphogenesis gene. Collectively, our data strongly suggest that nuclei of unicellular eukaryotes across marine and freshwater ecosystems worldwide are a major niche for replication of intron-rich mirusviruses.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 41315738 · DOI · PMC12768974
Key reviews and meta-analyses
The most cited review-type papers among PubMed’s best-match results for this heading, listed with bibliographic details only. Follow the links for the full text and access terms.
- Research article A rule for termination-codon position within intron-containing genes: when nonsense affects RNA abundance [5]
- Research article Self-splicing of group I introns [6]
- Research article Comparative and functional anatomy of group II catalytic introns--a review [7]
- Research article How introns influence and enhance eukaryotic gene expression [8]
- Research article Introns as mobile genetic elements [9]
- Research article A beginner's guide to eukaryotic genome annotation [10]
References
- Yue Q, Wang Z, Shen Y, Lan Y, Zhong X, Luo X, et al.. Histone H3K9 Lactylation Confers Temozolomide Resistance in Glioblastoma via LUC7L2-Mediated MLH1 Intron Retention. . 2024. PMID 38477507 · DOI · PMC11109612
- Corbett MA, Kroes T, Veneziano L, Bennett MF, Florian R, Schneider AL, et al.. Intronic ATTTC repeat expansions in STARD7 in familial adult myoclonic epilepsy linked to chromosome 2. . 2019. PMID 31664034 · DOI · PMC6820779
- Rahimi K, Venø MT, Dupont DM, Kjems J. Nanopore sequencing of brain-derived full-length circRNAs reveals circRNA-specific exon usage, intron retention and microexons. . 2021. PMID 34376658 · DOI · PMC8355340
- Medvedeva S, Guyet U, Pelletier E, Ruscheweyh HJ, Sunagawa S, Ogata H, et al.. Widespread and intron-rich mirusviruses are predicted to reproduce in nuclei of unicellular eukaryotes. . 2026. PMID 41315738 · DOI · PMC12768974
- Nagy E, Maquat LE. A rule for termination-codon position within intron-containing genes: when nonsense affects RNA abundance. Trends Biochem Sci. 1998. PMID 9644970 · DOI
- Cech TR. Self-splicing of group I introns. Annu Rev Biochem. 1990. PMID 2197983 · DOI
- Michel F, Umesono K, Ozeki H. Comparative and functional anatomy of group II catalytic introns--a review. Gene. 1989. PMID 2684776 · DOI
- Le Hir H, Nott A, Moore MJ. How introns influence and enhance eukaryotic gene expression. Trends Biochem Sci. 2003. PMID 12713906 · DOI
- Lambowitz AM, Belfort M. Introns as mobile genetic elements. Annu Rev Biochem. 1993. PMID 8352597 · DOI
- Yandell M, Ence D. A beginner's guide to eukaryotic genome annotation. Nat Rev Genet. 2012. PMID 22510764 · DOI
About this article
- Sources
- NLM Medical Subject Headings (definition, synonyms); NCBI PubMed (counts, identifiers); Europe PMC (open-access abstracts and citation counts).
- Verification
- Every reference was resolved against PubMed on 2026-10-31; title, year and DOI matched.
- Review state
- automated source verified; no human expert review has been recorded yet.
- Version
- 1, last updated 2026-10-29.
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Evidence strength
EvidenceHelix's computed view of the study designs behind this topic: how common meta-analyses, randomized trials and reviews are, how recent the literature is, and a plain-language reading. It describes the design mix of the literature. It is not a quality appraisal of any study, and it is not medical advice.