Nucleoporins (Nups) are major components of the nuclear pore complex (NPC). Nup153 is a constituent of its nuclear basket, but also has functions outside of nuclear transport in both interphase and mitotic NPC assembly. Nup153 has been shown to interact with the spindle assembly checkpoint factor Mad1, but the relevance of this association is not understood. In this work, Birthe Fahrenkrog and colleagues (Mossaid et al., 2020) now use in situ proximity ligation assays, time-lapse imaging and electron microscopy to dissect the functional significance of the Nup153–Mad1 interaction. They first show that Nup153 and Mad1 only interact in the presence of a nuclear envelope (NE); they form complexes in telophase when NEs form that remain during interphase, before dissociating at the start of mitosis when NEs begin to disassemble. Interestingly, depletion of Mad1 leads to a delayed recruitment of Nup153 to chromatin in anaphase and a prolonged anaphase, whereas ablation of Nup153, but not Mad1, gives rise to defects in NPC assembly and a reduced NPC density. Furthermore, deletion of Nup153 and Mad1 results in an altered NE structure, with a change in membrane curvature at NPCs and increased spacing between the inner and outer nuclear membranes. Taken together, these findings thus suggest that Nup153 has separable roles, one in postmitotic NE formation in concert with Mad1, and another one independent of Mad1 in interphase NPC assembly.
