Jumping genes are DNA sequences called transposable elements that can move to new locations in the genome. Most human copies are inactive remnants, but a small number can still move. An insertion may disrupt a gene or alter its activity; over evolutionary time, transposable elements have also supplied useful genetic variation and regulatory sequences.
What are jumping genes?
“Jumping genes” is an informal name for transposable elements: stretches of DNA that can change location within a genome. Their name can suggest that vast numbers are continually hopping around, but that is misleading. Transposable-element-derived sequences make up roughly half of human DNA, with estimates varying by source and definition; most copies are damaged or otherwise inactive.
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In a 2017 review, geneticists Haig H. Kazazian Jr. and John V. Moran estimated that about 100 LINE-1 elements per human genome retain the capacity to move. That is an estimate of potentially active copies, not a count of elements moving in every person. The authors describe “hot” LINE-1 elements as responsible for most LINE-1-mediated disease.
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Transposable elements fall into two broad groups, distinguished by how they relocate:
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| Type | How it moves | Human examples |
|---|---|---|
| DNA transposon | Generally uses a cut-and-paste mechanism: the DNA sequence is excised and inserted elsewhere. | Many human copies are inactive remnants. |
| Retrotransposon | Uses a copy-and-paste route: the sequence is transcribed into RNA, converted back into DNA, then inserted at another location. | LINE-1 (L1), Alu and SVA. |
LINE-1 is the principal autonomous retrotransposon discussed in the reviewed literature: it encodes proteins needed for its own copying process. Alu and SVA elements do not encode all the machinery themselves, but can use proteins made by LINE-1.
Cells also restrain this activity. DNA methylation and other forms of transcriptional silencing suppress retrotransposon expression in germline and somatic cells. This helps explain why a large share of the genome can derive from these elements without being mobile today.
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What can an insertion do to DNA?
The effect depends on where an element inserts and what it changes. An insertion can interrupt a gene’s coding sequence, alter how its RNA is spliced, or affect the expression of a nearby gene by landing in a regulatory region. Repeated copies can also misalign and recombine, contributing to deletions, duplications or other rearrangements.
These outcomes are possible, not inevitable: many insertions have no known harmful effect. A specific example of harm is LINE-1-mediated disruption of the F8 gene, which can cause hemophilia A. Kazazian and Moran’s 2017 review reports that, in a historical group of 240 boys with hemophilia A, two had LINE-1 insertions disrupting F8. The review also estimates that about one in every 250 pathogenic human mutations is attributable to LINE-1-mediated retrotransposition—a rare contribution among disease-causing mutations overall.
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What is known about disease links?
Evidence varies by condition. A documented insertion that disrupts a gene can establish a direct genetic cause. By contrast, finding transposable-element expression in diseased tissue, or identifying an element associated with a disease in a study, does not by itself show that the element caused the condition.
- Established insertional mutations: Specific retrotransposon insertions have been documented as causes of genetic disease, including F8 disruption in hemophilia A.
- Associations under study: Retrotransposon activity is investigated in cancer and neurological and psychiatric conditions. The 2017 review notes elevated human endogenous retrovirus expression in affected tissues in several conditions, while stating that its pathogenic role is unknown.
- Psychiatric-disorder candidates: The U.S. National Institute of Child Health and Human Development describes a study that evaluated more than 17,000 transposable elements, identified 76 candidates from genome-wide association findings, and conducted further analyses on 10 candidate insertions. Regulatory effects were observed in human neural stem cells, but these findings do not prove that the elements cause psychiatric disorders.
For that reason, it is accurate to say jumping genes can cause disease through particular insertional mutations, and that other possible links are being studied. It would overstate the evidence to say they generally cause cancer, psychiatric illness or neurodegeneration.
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Can jumping genes also be useful?
Transposable elements have contributed genetic variation during evolution, and some of their sequences have been incorporated into gene-regulatory networks. The 2017 review notes that proteins derived from endogenous retroviruses play important roles in placental development. These examples show that host organisms can co-opt material from transposable elements; they do not mean that every insertion is beneficial.
Kazazian and Moran summarize the balance this way: “Live mobile elements are a rare cause of genetic disease.” They also caution against treating these sequences as simply harmful: “Although we have focused on the harmful effects of retrotransposons in this review, it is clear that transposable elements are not just weeds in the garden.”
Quick Recap
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Sources
- Kazazian HH Jr, Moran JV. “Mobile DNA in Health and Disease”, New England Journal of Medicine, published July 27, 2017.
- “Role of Transposable Elements in Genome Stability: Implications for Health and Disease”, International Journal of Molecular Sciences, 2022.
- National Institute of Child Health and Human Development. “Understanding the Role of ‘Jumping Genes’ in Psychiatric Disorders.”
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