Senescent cells cluster CTCF on nuclear speckles to instruct an alternative splicing program

Senescence, the endpoint of normal cells’ replicative lifespan, is accompanied by a complex sequence of molecular events. One such event is the dramatic reorganization of CTCF into senescence-induced clusters (SICCs). However, the molecular determinants, genomic consequences and functional purpose of SICCs remain unknown. Here we combine three-dimensional genomics, super-resolution imaging, DNA tracing and functional assays with modeling to dissect SICC emergence. We find that, on senescence entry, cells repurpose SRRM2—a key component of nuclear speckles—and BANF1—a ‘molecular glue’ for chromosomes—to cluster CTCF and rewire genome architecture. This CTCF-centric reorganization in reference to nuclear speckles helps instruct the senescence splicing program, because disruption of SICCs almost fully reverts alternative splicing patterns and delays senescence onset. We therefore uncover a paradigm whereby human cells translate changes in nuclear biochemistry into architectural changes directing splicing choices to commit to the fate of senescence. Palikyras and colleagues investigate chromatin reorganization upon senescence induction, reporting that components of nuclear speckles coordinate chromatin rewiring and a senescence-associated splicing program. Interventions countering this reorganization delay senescence entry.