Somatic mosaicism in neuronal precursor cells mediated by L1 retrotransposition

Muotri, Alysson R.; Chu, Vi; Marchetto, Maria C.; Deng, Wei; Moran, John V.; Gage, Fred H.

doi:10.1038/nature03663

Cited by 884 publications

(1,007 citation statements)

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“…The LINE1 promoter is active in neural precursor cells differentiating into neurons (9,42). Thus, the hippocampus, one of the two regions of the adult brain where new neurons are generated, may not be the only area with a detectable piRNA expression.…”

Section: Discussionmentioning

confidence: 99%

“…Earlier studies found that LINE1 can actively retrotranspose in Drosophila, mouse, and human brain (9,11,41). The LINE1 promoter is active in neural precursor cells differentiating into neurons (9,42).…”

Section: Discussionmentioning

confidence: 99%

“…Somatic retrotransposition and its associated insertional mutagenesis have particularly important implications for brain disorders and are often associated with schizophrenia, Rett syndrome, and neurodegenerative disorders (5-7). The LINE1 (long interspersed nuclear element1) family of retrotransposons in particular is active in human and mouse hippocampus (8,9).…”

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confidence: 99%

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Roles for small noncoding RNAs in silencing of retrotransposons in the mammalian brain

Nandi

Chandramohan

Fioriti

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Piwi-interacting RNAs (piRNAs), long thought to be restricted to germline, have recently been discovered in neurons of Aplysia, with a role in the epigenetic regulation of gene expression underlying long-term memory. We here ask whether piwi/piRNAs are also expressed and have functional roles in the mammalian brain. Large-scale RNA sequencing and subsequent analysis of protein expression revealed the presence in brain of several piRNA biogenesis factors including a mouse piwi (Mili), as well as small RNAs, albeit at low levels, resembling conserved piRNAs in mouse testes [primarily LINE1 (long interspersed nuclear element1) retrotransposon-derived]. Despite the seeming low expression of these putative piRNAs, single-base pair CpG methylation analyses across the genome of Mili/piRNA-deficient (Mili −/− ) mice demonstrate that brain genomic DNA is preferentially hypomethylated within intergenic areas and LINE1 promoter areas of the genome. Furthermore, Mili mutant mice exhibit behavioral deficits such as hyperactivity and reduced anxiety. These results suggest that putative piRNAs exist in mammalian brain, and similar to the role of piRNAs in testes, they may be involved in the silencing of retrotransposons, which in brain have critical roles in contributing to genomic heterogeneity underlying adaptation, stress response, and brain pathology. We also describe the presence of another class of small RNAs in the brain, with features of endogenous siRNAs, which may have taken over the role of invertebrate piRNAs in their capacity to target both transposons, as well as protein-coding genes. Thus, RNA interference through gene and retrotransposon silencing previously encountered in Aplysia may also have potential roles in the mammalian brain.piwi-interacting RNA | transposon | DNA methylation | behavior | endogenous siRNA P iwi-interacting RNAs (piRNAs) are 26-to 32-nt small noncoding RNAs that associate with the piwi clade of the Argonaute family of proteins and whose primary functions in mammals are associated with the silencing of transposons in the germline through de novo DNA methylation (1-4). Transposons constitute 44% of the human genome and could when active contribute to genetic heterogeneity, to alteration of behavior during adaptation, and to responses to stress. Somatic retrotransposition and its associated insertional mutagenesis have particularly important implications for brain disorders and are often associated with schizophrenia, Rett syndrome, and neurodegenerative disorders (5-7). The LINE1 (long interspersed nuclear element1) family of retrotransposons in particular is active in human and mouse hippocampus (8, 9).Although it has long been thought that piRNA expression and function are restricted to the germline, our laboratory and others have previously found that the piRNA pathway is functional in invertebrate neurons as well (10, 11). Aplysia neurons, in particular, have a strikingly abundant expression of piRNAs (contributing to at least 5% of the total noncoding RNA population); they in turn hav...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Roles for small noncoding RNAs in silencing of retrotransposons in the mammalian brain

Nandi

Chandramohan

Fioriti

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Although some degree of insertion preference exists for the direct orientation of immediately adjacent Alu insertions [72], it is likely that the inherent instability of the inverted insertions is the primary reason for their almost complete exclusion from the human genome [71]. Despite the infrequent nature of these inverted loci in humans, the fact that Alu insertions are still occurring in the human population at an appreciable rate [73] indicates that the potential for the de novo generation of inverted loci remains present in each new generation and possibly even in somatic cell lineages; the latter being increasingly likely given recent in vivo evidence demonstrating that L1 can mobilize in the soma [74] as well as ex vivo (cell culture) evidence for the possibility of somatic Alu mobilization [75].…”

Section: Inverted Repeats Andmentioning

confidence: 99%

Inviting instability: Transposable elements, double-strand breaks, and the maintenance of genome integrity

Hedges

Deininger

2007

Mutation Research/Fundamental and Molecular Mechanisms of Mutag

285

248

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The ubiquity of mobile elements in mammalian genomes poses considerable challenges for the maintenance of genome integrity. The predisposition of mobile elements towards participation in genomic rearrangements is largely a consequence of their interspersed homologous nature. As tracts of nonallelic sequence homology, they have the potential to interact in a disruptive manner during both meiotic recombination and DNA repair processes, resulting in genomic alterations ranging from deletions and duplications to large-scale chromosomal rearrangements. Although the deleterious effects of transposable element (TE) insertion events have been extensively documented, it is arguably through post-insertion genomic instability that they pose the greatest hazard to their host genomes. Despite the periodic generation of important evolutionary innovations, genomic alterations involving TE sequences are far more frequently neutral or deleterious in nature. The potentially negative consequences of this instability are perhaps best illustrated by the 25 human genetic diseases that are attributable to TE-mediated rearrangements. Some of these rearrangements, such as those involving the MLL locus in leukemia and the LDL receptor in familial hypercholesterolemia, represent recurrent mutations that have independently arisen multiple times in human populations. While TE-instability has been a potent force in shaping eukaryotic genomes and a significant source of genetic disease, much concerning the mechanisms governing the frequency and variety of these events remains to be clarified. Here we survey the current state of knowledge regarding the mechanisms underlying mobile element-based genetic instability in mammals. Compared to simpler eukaryotic systems, mammalian cells appear to have several modifications to their DNA-repair ensemble that allow them to better cope with the large amount of interspersed homology that has been generated by TEs. In addition to the disruptive potential of nonallelic sequence homology, we also consider recent evidence suggesting that the endonuclease products of TEs may also play a key role in instigating mammalian genomic instability.

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“…Somatic L1 retrotransposition events occur often during embryogenesis (Kano et al., 2009) and in cancerous tissues (Tubio et al., 2014). Numerous studies have shown that L1s can mobilize in both mouse and human brains (Baillie et al., 2011; Evrony et al., 2015; Hazen et al., 2016; Muotri et al., 2005). Greater L1 retrotransposon burdens were reported in DNA from postmortem brains of patients with ataxia telangiectasia (Coufal et al., 2011) and schizophrenia (Bundo et al., 2014).…”

Section: Introductionmentioning

confidence: 99%

Reading LINEs within the cocaine addicted brain

Doyle

Doucet-O’Hare²,

Hammond

et al. 2017

Brain and Behavior

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IntroductionLong interspersed element (LINE)‐1 (L1) is a type of retrotransposon capable of mobilizing into new genomic locations. Often studied in Mendelian diseases or cancer, L1s may also cause somatic mutation in the developing central nervous system. Recent reports showed L1 transcription was activated in brains of cocaine‐treated mice, and L1 retrotransposition was increased in cocaine‐treated neuronal cell cultures. We hypothesized that the predisposition to cocaine addiction may result from inherited L1s or somatic L1 mobilization in the brain.MethodsPostmortem medial prefrontal cortex (mPFC) tissue from 30 CA and 30 control individuals was studied. An Alexafluor488‐labeled NeuN antibody and fluorescence activated nuclei sorting were used to separate neuronal from non‐neuronal cell nuclei. L1s and their 3' flanking sequences were amplified from neuronal and non‐neuronal genomic DNA (gDNA) using L1‐seq. L1 DNA libraries from the neuronal gDNA were sequenced on an Illumina HiSeq2000. Sequences aligned to the hg19 human genome build were analyzed for L1 insertions using custom “L1‐seq” bioinformatics programs.ResultsPreviously uncataloged L1 insertions, some validated by PCR, were detected in neurons from both CA and control brain samples. Steady‐state L1 mRNA levels in CA and control mPFC were also assessed. Gene ontology and pathway analyses were used to assess relationships between genes putatively disrupted by novel L1s in CA and control individuals. L1 insertions in CA samples were enriched in gene ontologies and pathways previously associated with CA.ConclusionsWe conclude that neurons in the mPFC harbor L1 insertions that have the potential to influence predisposition to CA.

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Somatic mosaicism in neuronal precursor cells mediated by L1 retrotransposition

Cited by 884 publications

References 43 publications

Roles for small noncoding RNAs in silencing of retrotransposons in the mammalian brain

Roles for small noncoding RNAs in silencing of retrotransposons in the mammalian brain

Inviting instability: Transposable elements, double-strand breaks, and the maintenance of genome integrity

Reading LINEs within the cocaine addicted brain

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