Dissolution of RNA condensates by the embryonic stem cell protein L1TD1 [CLIP-seq]

L1TD1 is a cytoplasmic RNA-binding protein that is specifically expressed in pluripotent stem cells and, unlike its mouse paralogue, is essential for the maintenance of stemness in human cells. Although L1TD1 is the only known domesticated gene from a LINE-1 (L1) retroelement, the functional legacy from its ancestral protein, ORF1p of L1, and the novelty are so far unknown. Here, we determined RNAs associated with L1TD1 and found that, like ORF1p, L1TD1 binds L1 RNAs, localizes to high-density ribonucleoprotein (RNP) condensates, and increases L1 retrotransposition. Unexpectedly, L1TD1 enhanced the translation of a subset of mRNAs enriched in the condensates. In HeLa cells, ectopically expressed L1TD1 facilitated the dissolution of stress granules and granules formed by pathological mutations of TDP-43 and FUS. The glutamate-rich domain and the ORF1-homology domain facilitated dispersal of the RNPs and induced autophagy, respectively. These results provide insights into how L1TD1 regulates gene expression in pluripotent stem cells. We propose that the ability of L1TD1 to dissolve stress granules may provide novel opportunities for treatments of neurodegenerative diseases caused by disturbed stress granule dynamics. CLIP-seq of endogenous L1TD1 and G3BP2 by using anti-L1TD1 antibody (Sigma-Aldrich, HPA030064), anti-G3BP2 antibody (Bethyl, A302-040A) and IgG controls.