Activating translation by phase separation: a novel mechanism for driving spermiogenesis

Phase separation of EEF1E1 promotes tumor stemness via PTEN/AKT-mediated DNA repair in hepatocellular carcinoma

This study aimed to investigate the associations of liquid-liquid phase separation (LLPS) and tumor stemness in hepatocellular carcinomas (HCC). LLPS-related genes were extracted from DrLLPS, LLPSDB and PhaSepDB databases. Stemness index (mRNAsi) was calculated based on the data from TCGA and Progenitor Cell Biology Consortium. Through some series of bioinformatics methods, we first found that stemness index mRNAsi was associated with worse survival outcomes, immune infiltration and therapy sensitivity in HCC. G2M checkpoint and DNA repair pathways were significantly activated with high mRNAsi. Totally, 71 differentially expressed LLPS genes in HCC were correlated with mRNAsi, and a mRNAsi-associated LLPS gene signature (KPNA2, EEF1E1 and ATIC) was identified to predict prognosis for HCC patients. mRNAsi-associated LLPS genes contributed to cluster HCC patients into four molecular clusters that markedly differed on survival, immune infiltration and therapy sensitivity. Further in vivo and in vitro experiments showed that EEF1E1 was highly expressed in HepG2 and HCCLM3 cells, and EEF1E1 silencing observably inhibited tumor cell growth, liver cancer stem cells (CSCs) markers (CD133, EpCAM and SOX2) expression, enhanced DNA damage marker γH2AX expression by activating PTEN/AKT pathway. EEF1E1 could undergo LLPS condensates, and roles of EEF1E1 on tumor cells were partly reversed after inhibiting LLPS using 1, 6-hexanediol. In conclusion, EEF1E1 was identified as a phase separation protein and involves in tumor stemness and DNA damage repair in HCC. EEF1E1 and its LLPS condensate may be novel targets to elaborate the underlying mechanisms of CSCs propagation in HCC.

Frameshift variants in the C-terminal of CTNNB1 cause familial exudative vitreoretinopathy by AXIN1-mediated ubiquitin-proteasome degradation condensation

The β-catenin has two intrinsically disordered regions in both C- and N-terminal domains that trigger the formation of phase-separated condensates. Variants in its C-terminus are associated with familial exudative vitreoretinopathy (FEVR), yet the pathogenesis and the role of these variants in inducing abnormal condensates, are unclear. In this study, we identified a novel heterozygous frameshift variant, c.2104-2105insCC (p.Gln703ProfsTer33), in CTNNB1 from a FEVR-affected family. This variant encodes an unstable truncated protein that was unable to activate Wnt signal transduction, which could be rescued by the inhibition of proteasome or phosphorylation. Further functional experiments revealed the propensity of the Gln703ProfsTer33 variant to form cytoplasmic condensates, exhibiting a lower turnover rate after fluorescent bleaching due to enhanced interaction with AXIN1. LiCl, which specifically blocks GSK3β-mediated phosphorylation, restored signal transduction, cell proliferation, and junctional integrity in primary human retinal microvascular endothelial cells over-expressed with Gln703ProfsTer33. Finally, experiments on two reported FEVR-associated mutations in the C-terminal domain of β-catenin exhibited several functional defects similar to the Gln703ProfsTer33. Together, our findings unravel that the C-terminal region of β-catenin is pivotal for the regulation of AXIN1/β-catenin interaction, acting as a switch to mediate nucleic and cytosolic condensates formation that is implicated in the pathogenesis of FEVR.

A paternal protein facilitates sperm RNA delivery to regulate zygotic development

Sperm contributes essential paternal factors, including the paternal genome, centrosome, and oocyte-activation signals, to sexual reproduction. However, it remains unresolved how sperm contributes its RNA molecules to regulate early embryonic development. Here, we show that the Caenorhabditis elegans paternal protein SPE-11 assembles into granules during meiotic divisions of spermatogenesis and later matures into a perinuclear structure where sperm RNAs localize. We reconstitute an SPE-11 liquid-phase scaffold in vitro and find that SPE-11 condensates incorporate the nematode RNA, which, in turn, promotes SPE-11 phase separation. Loss of SPE-11 does not affect sperm motility or fertilization but causes pleiotropic development defects in early embryos, and spe-11 mutant males reduce mRNA levels of genes crucial for an oocyte-to-embryo transition or embryonic development. These results reveal that SPE-11 undergoes phase separation and associates with sperm RNAs that are delivered to oocytes during fertilization, providing insights into how a paternal protein regulates early embryonic development.