Regulation of LINE-1 Elements by miR-128 Is Not Conserved in Mouse Embryonic Stem Cells
Open access
Date
2018-12Type
- Journal Article
ETH Bibliography
yes
Altmetrics
Abstract
With respectively 560,000 and 660,000 copies, Long INterspersed Element-1 (LINE-1 or L1) are the main component of the human and mouse genomes (Lander et al., 2001; Waterston et al., 2002). L1s are transposable elements encoding the proteins required for their own mobility and using an RNA intermediate for their retrotransposition (Ostertag and Kazazian, 2001). The vast majority of L1 sequences are inactive, however, some copies—around 100 in human and 3,000 in mouse—retained their ability to retrotranspose (Goodier et al., 2001; Beck et al., 2010). Due to their abundance, and their capacity to mobilize their own RNAs or other cellular RNAs (i.e., Alu elements), L1s have been shown to actively participate to the evolution of the structure and organization of the genome in which they can expand (Feschotte and Pritham, 2007; Cordaux and Batzer, 2009; Pereira et al., 2009). This L1-mediated reshape of the genomic landscape can have beneficial or detrimental outcomes, such as a positive impact on genome variability or resulting in gene disruption leading to diseases (Beck et al., 2011; Kazazian and Moran, 2017). To protect their integrities, genomes have acquired a multitude of mechanisms to regulate L1s through evolution (Bodak et al., 2014; Goodier, 2016). Concisely, mammalian L1 expression and mobility are repressed via DNA methylation in somatic cells, and via the PIWI-piRNA pathway in germ cells. However, both mechanisms are absent at the blastocyst stage, indicating potential new regulation pathways during mammalian early development (Ohnishi et al., 2010; Suh and Blelloch, 2011; Lee et al., 2014).
Since the last decade, several lines of evidence support a role for RNA interference (RNAi) pathway effector proteins in L1 regulation (Soifer et al., 2005; Yang and Kazazian, 2006; Heras et al., 2013). Using mouse Embryonic Stem Cells (mESCs), we recently showed the involvement of the RNAse III DICER in the control of L1 expression and retrotransposition (Bodak et al., 2017a). In mammals, the protein DICER is the central player of RNAi pathways and is necessary for the production of canonical and non-canonical microRNAs (miRNAs), and small interfering RNAs (siRNAs) (Kim et al., 2009; Bodak et al., 2017b). The deletion of Dicer in mESCs led to a strong upregulation of L1s at the RNA and protein levels, as well as a weak but significant increase of L1 mobilization rate (Bodak et al., 2017a). Our results revealed DICER and RNAi pathways as new regulators of L1 expression during early development. In line with our work, the Pedersen laboratory identified the canonical miRNA miR-128 as both, direct and indirect, L1 repressor in human cells (Hamdorf et al., 2015; Idica et al., 2017). In a first study, they identified and characterized miR-128 as a direct L1 repressor via a non-canonical binding site in the L1_ORF2 RNA, leading to the repression of full-length L1 RNAs and a decrease in retrotransposition events (Hamdorf et al., 2015). More recently, the same laboratory identified another binding site of miR-128 in the 3′UTR of Tnpo1 mRNA, a nuclear import factor involved in the L1 mobilization process (Idica et al., 2017). They demonstrated that Tnpo1 repression via miR-128 inhibits L1 retrotransposition by restricting L1 ribonucleoproteins nuclear import (Idica et al., 2017). Therefore, these two studies implicate the canonical microRNA pathway in the regulation of L1 elements via direct and indirect molecular mechanisms.
Both studies were conducted in human cellular systems. The structural differences between human and murine L1s (Bodak et al., 2014), and the great variability of L1 loci transcriptional activity observed between human somatic cell types (Philippe et al., 2016) limit the extension of a regulatory mechanism from one cell type to another, or between species. Consequently, it cannot be simply assumed that miR-128 is repressing L1s during mouse early development. Thus, we investigated if miR-128 also regulate murine L1s in mESCs. First, we assessed miR-128 expression in mESCs using transcriptomics and molecular approaches. Due to the low expression of miR-128 in this system, we subsequently overexpressed miR-128 using mimic microRNA and monitored L1 expression in the corresponding transfected mESCs. The upregulation of miR-128 in mESCs had no effect on L1 expression at RNA and protein levels and did not impact mouse Tnpo1 mRNA levels. Therefore, we concluded that miR-128 is not involved in L1 repression in mESCs and that its regulatory function is not conserved between all mammalian cellular contexts. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000313449Publication status
publishedExternal links
Journal / series
Frontiers in GeneticsVolume
Pages / Article No.
Publisher
Frontiers MediaSubject
LINE-1; miR-128; mouse embryonic stem cell; RNA interference; DicerOrganisational unit
03983 - Ciaudo, C. (ehemalig) / Ciaudo, C. (former)
03983 - Ciaudo, C. (ehemalig) / Ciaudo, C. (former)
03983 - Ciaudo, C. (ehemalig) / Ciaudo, C. (former)
Funding
173120 - Canonical and non-canonical functions of RNA interference proteins during mouse early development (SNF)
More
Show all metadata
ETH Bibliography
yes
Altmetrics