A Novel Active L1 Retrotransposon Subfamily in the Mouse

Goodier, John; Ostertag, Eric; Du, Kevin; Kazazian, Haig H.

doi:10.1101/gr.198301

Cited by 215 publications

(266 citation statements)

References 42 publications

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“…The first parameter was the copy number in the genome. The transgene was present at a single copy, whereas there are ∼3,000 copies of potentially active full-length endogenous L1 elements in the mouse genome (54). The second parameter was the ratio of insertion frequencies between the transgene and endogenous L1s.…”

Section: Inhibition Of Retrotransposition Does Not Rescue the Meioticmentioning

confidence: 99%

Intact piRNA pathway prevents L1 mobilization in male meiosis

Newkirk

Lee

Grandi

et al. 2017

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

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The PIWI-interacting RNA (piRNA) pathway is essential for retrotransposon silencing. In piRNA-deficient mice, L1-overexpressing male germ cells exhibit excessive DNA damage and meiotic defects. It remains unknown whether L1 expression simply highlights piRNA deficiency or actually drives the germ-cell demise. Specifically, the sheer abundance of genomic L1 copies prevents reliable quantification of new insertions. Here, we developed a codon-optimized L1 transgene that is controlled by an endogenous mouse L1 promoter. Importantly, DNA methylation dynamics of a single-copy transgene were indistinguishable from those of endogenous L1s. Analysis of Mov10l1 −/− testes established that de novo methylation of the L1 transgene required the intact piRNA pathway. Consistent with loss of DNA methylation and programmed reduction of H3K9me2 at meiotic onset, the transgene showed 1,400-fold increase in RNA expression and consequently 70-fold increase in retrotransposition in postnatal day 14 Mov10l1 −/− germ cells compared with the wildtype. Analysis of adult Mov10l1 −/− germ-cell fractions indicated a stage-specific increase of retrotransposition in the early meiotic prophase. However, extrapolation of the transgene data to endogenous L1s suggests that it is unlikely insertional mutagenesis alone accounts for the Mov10l1 −/− phenotype. Indeed, pharmacological inhibition of reverse transcription did not rescue the meiotic defect. Cumulatively, these results establish the occurrence of productive L1 mobilization in the absence of an intact piRNA pathway but leave open the possibility of processes preceding L1 integration in triggering meiotic checkpoints and germ-cell death. Additionally, our data suggest that many heritable L1 insertions originate from individuals with partially compromised piRNA defense.LINE-1 reporter transgene | meiotic arrest | PIWI-interacting RNA | retrotransposition | spermatogenesis T he bulk of mammalian genomes are made up of transposable elements, the majority of which are retrotransposons (1). Retrotransposons are classified into long-interspersed elements (LINEs), short-interspersed elements (SINEs), and LTR retrotransposons, which collectively account for 43% and 37% of the human and mouse genomes, respectively (2). Retrotransposons amplify in the genome through an RNA intermediate, a process termed retrotransposition. LINEs are autonomous elements. An intact, full-length LINE-1 (L1) encodes two ORFs (i.e., ORF1 and ORF2); both are required for L1 mobilization (3). SINEs are nonautonomous elements and rely on L1's proteins for propagation in the genome (4). LTR retrotransposons are autonomous but appear to be inactivated in the human genome (5). Retrotransposition endangers the integrity of both somatic and germline genomes through insertional mutagenesis. In somatic tissues, both elevated L1 expression and retrotransposition have been strongly associated with many types of human cancers (6, 7). In a few cases, specific retrotransposition events (i.e., insertions) have been determined to drive t...

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Section: Inhibition Of Retrotransposition Does Not Rescue the Meioticmentioning

confidence: 99%

Intact piRNA pathway prevents L1 mobilization in male meiosis

Newkirk

Lee

Grandi

et al. 2017

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

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“…LINE-1 (L1) is the youngest of the four families and the major LINE family in eutherian and marsupial mammals. There are thought to be approximately 3000 active L1s in the mouse genome (Goodier et al 2001) and around 100 in the human (Brouha et al 2003). In the mouse there are three families of active L1s: L1md_A, L1Md_Gf, and L1Md_Tf (DeBerardinis et al 1998;Goodier et al 2001).…”

Section: [Supplemental Materials Is Available For This Article]mentioning

confidence: 99%

“…There are thought to be approximately 3000 active L1s in the mouse genome (Goodier et al 2001) and around 100 in the human (Brouha et al 2003). In the mouse there are three families of active L1s: L1md_A, L1Md_Gf, and L1Md_Tf (DeBerardinis et al 1998;Goodier et al 2001). Members of two of the active families, Gf and Tf, are known to be transcribed from the inactive X Chromosome in female mice, where they have been suggested to facilitate X Chromosome inactivation (XCI) in regions which would otherwise escape inactivation (Chow et al 2010).…”

Section: [Supplemental Materials Is Available For This Article]mentioning

confidence: 99%

Targeted deletion of a 170-kb cluster of LINE-1 repeats and implications for regional control

et al. 2018

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Approximately half the mammalian genome is composed of repetitive sequences, and accumulating evidence suggests that some may have an impact on genome function. Here, we characterized a large array class of repeats of long-interspersed elements (LINE-1). Although widely distributed in mammals, locations of such arrays are species specific. Using targeted deletion, we asked whether a 170-kb LINE-1 array located at a mouse imprinted domain might function as a modulator of local transcriptional control. The LINE-1 array is lamina associated in differentiated ES cells consistent with its AT-richness, and although imprinting occurs both proximally and distally to the array, active LINE-1 transcripts within the tract are biallelically expressed. Upon deletion of the array, no perturbation of imprinting was observed, and abnormal phenotypes were not detected in maternal or paternal heterozygous or homozygous mutant mice. The array does not shield nonimprinted genes in the vicinity from local imprinting control. Reduced neural expression of protein-coding genes observed upon paternal transmission of the deletion is likely due to the removal of a brain-specific enhancer embedded within the LINE array. Our findings suggest that presence of a 170-kb LINE-1 array reflects the tolerance of the site for repeat insertion rather than an important genomic function in normal development.

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“…pBudORF2 spa and pBudORF1 spa contain the coding sequences of the L1 spa (Naas et al, 1998); pBudORF1 A102 and ORF2 A102 contain the coding sequences of the L1 A102 (Goodier et al, 2001); pBudORF1 LRE3 and pBudORF2 LRE3 contain the coding sequences of the L1 LRE3 (Brouha et al, 2002). Plasmids containing the L1 A102 and L1 LRE3 sequences were kind gifts from Dr. John Goodier.…”

Section: Plasmidsmentioning

confidence: 99%

LINE-1 ORF1 protein enhances Alu SINE retrotransposition

Wallace

Wagstaff

Deininger

et al. 2008

Gene

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Retroelements have contributed over one third of the human genome mass. The currently active LINE-1 (L1) codes for two proteins (ORF1p and ORF2p), both strictly required for retrotransposition. In contrast, the non-coding parasitic SINE (Alu) only appears to need the L1 ORF2p for its own amplification. This requirement was previously determined using a tissue culture assay system in human cells (HeLa). Because HeLa are likely to express functional L1 proteins, it is possible that low levels of endogenous ORF1p are necessary for the observed tagged Alu mobilization. By individually expressing ORF1 and ORF2 proteins from both human (L1 RP and LRE3) and rodent (L1 A102 and L1 spa ) L1 sources, we demonstrate that increasing amounts of ORF1 expressing vector enhances tagged Alu mobilization in HeLa cells. In addition, using chicken fibroblast cells as an alternate cell culture source, we confirmed that ORF1p is not strictly required for Alu mobilization in our assay. Supporting our observations in HeLa cells, we find that tagged Alu retrotransposition is improved by supplementation of ORF1p in the cultured chicken cells. We postulate that L1 ORF1p plays either a direct or indirect role in enhancing the interaction between the Alu RNA and the required factors needed for its retrotransposition.

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A Novel Active L1 Retrotransposon Subfamily in the Mouse

Cited by 215 publications

References 42 publications

Intact piRNA pathway prevents L1 mobilization in male meiosis

Intact piRNA pathway prevents L1 mobilization in male meiosis

Targeted deletion of a 170-kb cluster of LINE-1 repeats and implications for regional control

LINE-1 ORF1 protein enhances Alu SINE retrotransposition

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