CELF2 Promotes Tau Exon 10 Inclusion via Hinge Domain-Mediated Nuclear Condensation, Driving Cognitive Dysfunction in Tauopathy Models

Alternative splicing is a fundamental mechanism underlying protein diversity. The microtubule-associated protein tau (MAPT) undergoes age-associated alternative splicing of exon 10 to generate 3R and 4R isoforms, and disruption of the 4R:3R ratio is a central feature of tauopathies. However, the molecular mechanisms regulating tau exon 10 splicing remain incompletely understood. Here, we identify the RNA-binding protein CELF2 as a key promoter of tau exon 10 inclusion. Loss of CELF2 in the mouse brain reduces exon 10 inclusion, resulting in a decreased 4R:3R ratio. We show that an intrinsically disordered region (IDR) within the CELF2 hinge domain drives protein condensation and is essential for its splicing activity. This IDR can be functionally substituted by those of FUS or TAF15. CRISPR-based imaging reveals colocalization of CELF2 condensates with tau RNA. Proteomic analyses identify NOVA2 and SFPQ as CELF2 interactors, which co-condense with CELF2 to cooperatively regulate tau exon 10 splicing. A conserved negatively charged residue (D388) within the IDR is critical for condensate formation, protein interactions, and splicing function. Finally, CELF2 condensation capacity correlates with 4R tau expression in vivo and influences locomotor and cognitive performance. These findings uncover a condensate-based mechanism for tau splicing regulation with implications for tau-related neurodegeneration.