<p id="P1">Transposable elements represent nearly half of mammalian genomes and are
generally
described as parasites or ‘junk DNA’. The LINE1 retrotransposon is the most abundant
class and is thought to be deleterious for cells, yet is paradoxically highly expressed
during early development. Here we report that LINE1 plays essential roles in mouse
embryonic stem (ES) cells and pre-implantation embryos. In ES cells, LINE1 acts as
a nuclear RNA scaffold that recruits Nucleolin and Kap1/Trim28 to repress
<i>Dux</i>, the master activator of a transcriptional program specific to the 2-cell
embryo.
In parallel, LINE1 RNA mediates binding of Nucleolin and Kap1 to rDNA, promoting rRNA
synthesis and ES cell self-renewal. In embryos, LINE1 RNA is required for
<i>Dux</i> silencing, synthesis of rRNA and exit from the 2-cell stage. The results
reveal an
essential partnership between LINE1 RNA, Nucleolin, Kap1 and peri-nucleolar chromatin
in the regulation of transcription, developmental potency and ES cell self-renewal.
</p><p id="P2">Highly expressed during early embryonic development, LINE1 element-derived
RNA acts
as a nuclear scaffold to facilitate essential gene expression programs
</p><p id="P3">
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