Palikyras, S.; Varamogianni-Mamatsi, V.; Zhu, Y.; Ramasamy, S.; Mizi, A.; Liebermann, I.; Stavropoulou, A.; Papadionysiou, I.; Bartsch, D.; Kargapolova, Y.; Sofiadis, K.; Nikolaou, C.; Kurian, L.; Oudelaar, M.; Barbieri, M.; Papantonis, A.

Senescence - the endpoint of replicative lifespan for normal cells - is established via 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 remained unknown. Here, we combine functional assays, super-resolution imaging, and 3D genomics with computational modelling to dissect SICC emergence. We establish that the competition between CTCF-bound and non-bound loci dictates clustering propensity. Upon 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 functionally sustains the senescence splicing program, as SICC disruption fully reverts alternative splicing patterns. We therefore uncover a new paradigm, whereby cells translate changes in nuclear biochemistry into architectural changes directing splicing choices so as to commit to the fate of senescence.