x as in both instances a loss of NPC function has been observed [8][9][10][11] . In particular, dividing cells depend on a constant supply of new NPCs, and indeed NPC assembly is compromised in mitotically aged yeast cells 10 .The mechanisms how FG-Nups are protected from making inappropriate interactions during NPC biogenesis are only beginning to liquid-liquid phase separate 5,6 and aggregate 7 , make NPC biogenesis a multi-step and complex event. Appearance of misassembled NPC intermediates or damaged NPCs is a risk to the cell as it could possibly lead to loss of compartmentalization. In ageing, as well as in disease, it becomes clear how NPC function is intricately interwoven with cell physiology, b WT DNAJB6 Lamin B1 Merge

ObjectivesTo perform a systematic review and meta-analysis of genetic risk factors for age at onset (AO) in spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD).MethodsTwo authors independently reviewed reports on the mathematical relationship between CAG length at the expanded ATXN3 allele (CAGexp), and other genetic variants if available, and AO. Publications from January 1994 to September 2017 in English, Portuguese or Spanish and indexed in MEDLINE (PubMed), LILACS or EMBASE were considered. Inclusion criteria were reports with >20 SCA3/MJD carriers with molecular diagnosis performed by capillary electrophoresis. Non-overlapping cohorts were determined on contact with corresponding authors. A detailed analysis protocol was registered at the PROSPERO database prior to data extraction (CRD42017073071).ResultsEleven studies were eligible for meta-analysis, comprising 10 individual-participant (n=2099 subjects) and two aggregated data cohorts. On average, CAGexp explained 55.2% (95% CI 50.8 to 59.0; p<0.001) of AO variability. Population-specific factors accounted for 8.3% of AO variance. Cohorts clustered into distinct geographic groups, evidencing significantly earlier AO in non-Portuguese Europeans than in Portuguese/South Brazilians with similar CAGexp lengths. Presence of intermediate ATXN2 alleles (27–33 CAG repeats) significantly correlated with earlier AO. Familial factors accounted for ~10% of AO variability. CAGexp, origin, family effects and CAG length at ATXN2 together explained 73.5% of AO variance.ConclusionsCurrent evidence supports genetic modulation of AO in SCA3/MJD by CAGexp, ATXN2 and family-specific and population-specific factors. Future studies should take these into account in the search for new genetic modifiers of AO, which could be of therapeutic relevance.

A loss of the checkpoint kinase ataxia telangiectasia mutated (ATM) leads to impairments in the DNA damage response, and in humans causes cerebellar neurodegeneration, and an increased risk of cancer. A loss of ATM is also associated with increased protein aggregation. The relevance and characteristics of this aggregation are still incompletely understood. Moreover, it is unclear to what extent other genotoxic conditions can trigger protein aggregation as well. Here, we show that targeting ATM, but also ATR or DNA topoisomerases, results in the widespread aggregation of a metastable, disease-associated subfraction of the proteome. Aggregation-prone model substrates, including Huntingtin exon 1 containing an expanded polyglutamine repeat, aggregate faster under these conditions. This increased aggregation results from an overload of chaperone systems, which lowers the cell-intrinsic threshold for proteins to aggregate. In line with this, we find that inhibition of the HSP70 chaperone system further exacerbates the increased protein aggregation. Moreover, we identify the molecular chaperone HSPB5 as a cell-specific suppressor of it. Our findings reveal that various genotoxic conditions trigger widespread protein aggregation in a manner that is highly reminiscent of the aggregation occurring in situations of proteotoxic stress and in proteinopathies.

Biogenesis of nuclear pore complexes (NPCs) includes the formation of the permeability barrier composed of phenylalanine-glycine-rich nucleoporins (FG-Nups) that regulate the selective passage/crossing of biomolecules. The FG-Nups are intrinsically disordered and prone to liquid-liquid phase separate1,2 and aggregate when isolated3. It has remained largely unclear how FG-Nups are protected from making inappropriate interactions during NPC biogenesis. We found that DNAJB6, a molecular chaperone of the heat shock protein network, formed foci next to NPCs. The number of these foci decreases upon removal of proteins involved in the early steps of interphase NPC biogenesis. Reversely, when this process is stalled in the last steps, the number of DNAJB6-containing foci increases and they could be identified as herniations at the nuclear envelope (NE). Immunoelectron tomography showed that DNAJB6 localizes inside the lumen of the herniations arising at NPC biogenesis intermediates. Interestingly, loss of DNAJB6 results in annulate lamellae, which are structures containing partly assembled NPCs associated with disturbances in NPC biogenesis. We find that DNAJB6 binds to FG-Nups and can prevent the aggregation of the FG-region of several FG-Nups in cells and in vitro. Together, our data show that DNAJB6 provides quality control during NPC biogenesis and is the first molecular chaperone that is involved in the surveillance of native intrinsically disordered proteins, including FG-Nups.