BACKGROUND:
Tau aggregation is a defining feature of tauopathies, yet its early impact on nuclear and nucleolar organisation remains unclear. The nucleolus, a key site of ribosomal biogenesis, is sensitive to cellular stress and can undergo structural alterations during neurodegenerative processes. This study examined how mutant tau expression influences the nuclear and nucleolar distribution of non-phosphorylated tau (nP-Tau) and associated changes in nucleolar morphology.
METHODS:
A tetracycline-inducible SH-SY5Y cell line expressing 4R-P301S tau was used to model early events in tau-induced stress. Tau expression was induced with 1 µg/mL tetracycline for 1 hour and 48 hours. High-content immunofluorescence imaging (Operetta CLS) combined with in-house 3D analysis pipelines enabled quantitative compartmental assessment (cytoplasm, nucleus, nucleolus) of fluorescence intensity and localisation for 4R Tau and nP-Tau (Tau 1 antibody). Nucleolar size and number were also quantified. Statistical tests included Shapiro-Wilk, Levene’s, one-way ANOVA with Tukey’s post-hoc, and Mann-Whitney U, as appropriate.
RESULTS:
Induction with tetracycline led to a significant increase in 4R Tau expression as early as 1 hour, confirming rapid activation of the model (p < 0.001). At both 1 hour and 48 hours, nP-Tau intensity was markedly elevated within the nucleus and nucleolus (p < 0.01), indicating early tau redistribution. While nucleolar size remained unchanged, there was a non-significant trend towards reduced nucleolar number at both time points compared with uninduced controls. CONCLUSION: Mutant tau expression rapidly induces nuclear and nucleolar accumulation of nP-Tau in SH-SY5Y cells, preceding overt morphological nucleolar stress. These findings suggest that nuclear and nucleolar redistribution of nP-Tau may represent an early molecular event in tau-associated cellular stress, potentially preceding measurable changes in nucleolar structure.