Nuclear Mitochondrial DNA Dynamics in Eukaryotic Genomes

The nuclear genomes of eukaryotes harbour fragments of mitochondrial DNA that have migrated from the organelle and become integrated over evolutionary time. These nuclear mitochondrial DNA segments (NUMTs) arise through spontaneous transfer events that typically involve the repair of chromosomal double-strand breaks. Once inserted, NUMTs may undergo mutation, rearrangement or deletion, and their persistence reflects a balance between genomic drift and selective forces. Although most NUMTs become non-functional pseudogenes, they contribute to genomic diversity, influence gene regulation when inserted near coding regions, and can serve as neutral markers for phylogenetic inference. Rates of numtogenesis vary across taxa: somatic insertions accumulate in post-mitotic tissues of long-lived organisms, while germline insertions fix through population processes. The landscape of NUMTs is shaped by local nuclear architecture—insertions preferentially occur in transposon-rich or intergenic regions—and by repair pathways such as non-homologous end joining. Comparative genomics has revealed hotspots in mitochondrial genomes that repeatedly colonise nuclear DNA, and conserved syntenic analyses illuminate the retention or loss of NUMTs across lineages. Understanding the dynamics of mitochondrial DNA transfer informs studies of genome structure, evolutionary history and mitochondrial disease diagnostics.

Research from Nature Portfolio

One foundational study mapped the distribution of NUMTs across 23 eukaryotic genomes, revealing that some mitochondrial loci repeatedly seed nuclear DNA and that NUMT content correlates with genome size. A synteny-based approach distinguished ancestral insertions predating major divergences in mammals, indicating early waves of colonisation before the split of monotremes and therian mammals. Phylogenetic analyses showed that primate lineages have undergone distinct patterns of NUMT evolution compared with non-primate mammals, and that integration often occurs at naturally occurring chromosomal breaks via non-homologous end joining without extensive deletion of native sequences. These insights established NUMTs both as evolutionary markers and as indicators of the mechanisms underlying DNA repair and genome diversification.

Nuclear Mitochondrial DNA Dynamics in Eukaryotic Genomes publication trend

The graph below shows the total number of articles in nuclear mitochondrial dna dynamics in eukaryotic genomes across all publications each year (not limited to Nature Index journals).

Technical terms

NUMT: A segment of mitochondrial DNA that has become integrated into the nuclear genome and is usually non-functional.

Numtogenesis: The process by which mitochondrial DNA fragments are transferred and inserted into the nuclear genome, often during DNA repair.

Non-homologous end joining: A DNA repair pathway that ligates broken chromosome ends without requiring extensive sequence homology, facilitating NUMT insertion.

Microsynteny: The conservation of small blocks of gene order between different genomes, used to identify orthologous NUMTs across species.

Double-strand break: A type of DNA damage in which both strands of the helix are severed, creating a site for potential mitochondrial DNA integration.

References

1. Somatic nuclear mitochondrial DNA insertions are prevalent in the human brain and accumulate over time in fibroblasts. PLOS Biology (2024).
2. Comparative Genome Microsynteny Illuminates the Fast Evolution of Nuclear Mitochondrial Segments (NUMTs) in Mammals. Molecular Biology and Evolution (2023).
3. Assembly‐free quantification of vagrant DNA inserts. Molecular Ecology Resources (2023).
4. Molecular Poltergeists: Mitochondrial DNA Copies (numts) in Sequenced Nuclear Genomes. PLOS Genetics (2010).
5. Numt-Mediated Double-Strand Break Repair Mitigates Deletions during Primate Genome Evolution. PLOS Genetics (2008).