C9orf72-associated arginine-rich dipeptide repeats induce RNA-dependent nuclear accumulation of Staufen in neurons

Abstract

RNA-binding proteins (RBPs) play essential roles in diverse cellular processes through post-transcriptional regulation of RNAs. The subcellular localization of RBPs is thus under tight control, the breakdown of which is associated with aberrant cytoplasmic accumulation of nuclear RBPs such as TDP-43 and FUS, well-known pathological markers for amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). Here, we report in Drosophila model for ALS/FTD that nuclear accumulation of a cytoplasmic RBP, Staufen, may be a new pathological feature. We found that in Drosophila C4da neurons expressing PR36, one of the arginine-rich dipeptide repeat proteins (DPRs), Staufen accumulated in the nucleus in Importin- and RNA-dependent manner. Notably, expressing Staufen with exogenous NLS—but not with mutated endogenous NLS—potentiated PR-induced dendritic defect, suggesting that nuclear-accumulated Staufen can enhance PR toxicity. PR36 expression increased Fibrillarin staining in the nucleolus, which was enhanced by heterozygous mutation of stau (stau+/−), a gene that codes Staufen. Furthermore, knockdown of fib, which codes Fibrillarin, exacerbated retinal degeneration mediated by PR toxicity, suggesting that increased amount of Fibrillarin by stau+/− is protective. Stau+/− also reduced the amount of PR-induced nuclear-accumulated Staufen and mitigated retinal degeneration and rescued viability of flies expressing PR36. Taken together, our data show that nuclear accumulation of Staufen in neurons may be an important pathological feature contributing to the pathogenesis of ALS/FTD.

A comparison study of pathological features and drug efficacy between Drosophila models of C9orf72 ALS/FTD

“…Due to previous reports indicating that repeat-associated RNA toxicity may be involved in cellular or behavioral defects ( Cunningham et al, 2020 , Goodman et al, 2019 , Kim et al, 2021 , McEachin et al, 2020 ), we quantified the transgene-specific RNA levels in various transgene expressions through quantitative real-time PCR (qRT-PCR) analysis ( Supplementary Fig. S5a-d ).…”

Proximity proteomics of C9orf72 dipeptide repeat proteins identifies molecular chaperones as modifiers of poly-GA aggregation

“…Several of these proteins identified in our proximity proteomics study exhibited a potential functional connection to C9orf72 pathological features. The Drosophila ortholog of double-stranded RNA-binding protein Staufen homolog 2 (STAU2) shows nuclear accumulation when C9orf72-associated arginine-rich dipeptide repeats are expressed, as an important pathological feature in neurons [ 44 ]. Nucleophosmin (NPM1) has been shown to disperse from nucleoli and disrupt its role in organizing ribosomal proteins and RNAs within the nucleolus upon poly-PR expression, suggesting a direct mechanistic link to protein synthesis defects in c9FTD/ALS models [ 94 ].…”

CBP-Mediated Acetylation of Importin α Mediates Calcium-Dependent Nucleocytoplasmic Transport of Selective Proteins in Drosophila Neurons

“…Immunohistochemistry was performed as previously described ( Chung et al, 2017 ; Kim et al, 2021 ; Kwon et al, 2018 ; Park et al, 2020b ). larvae (120 h after egg laying [120 h AEL]), pupae (18 h after puparium formation [18 h APF]), and adult flies were dissected in Schneider’s Insect Medium (Cat.…”