Model of RSC-dependent distribution of Nbp1 and Ndc1 to the new SPB. Kap123 targets Nbp1 to the NPC for import from the cytoplasm (C) into the nucleus (N). (a) In wild-type cells, RSC facilitates appropriate distribution of Nbp1 to the duplicating SPB. Nbp1 stabilizes Ndc1 at the new SPB, which promotes SPB maturation. The new SPB is then able to nucleate both cytoplasmic and nuclear microtubules to facilitate accurate chromosome segregation and ploidy maintenance. (b) In rscΔ mutants, Nbp1 distribution is compromised, resulting in the loss of Ndc1 at SPBs and an accumulation of Ndc1 at NPCs, resulting in nuclear envelope (NE) stress. The resulting dead SPB is able to nucleate microtubules from the cytoplasmic side but not from the nuclear side, resulting in a nondisjunction event and spontaneous diploidization.