Nuclear pore complexes (NPCs) are established players in cell division and differentiation. However studies on the contribution of individual NPC subunits to these processes are still scarce. Here we have used mouse embryonic stem cells (mESCs) to characterize the role of structural components of the NPCs, focusing on the short arm of the Y-complex that comprises Nup85, Seh1 and Nup43. We show that Seh1 and Nup43, although dispensable at the pluripotent stage, are required for normal cell growth rates at that stage and for mESC viability upon differentiation. Lack of Seh1 or Nup43 in mESCs is associated with a mild reduction of NPC density that is also observed when Seh1 interaction with Nup85 is impaired. Nevertheless, mESC proliferation and differentiation are not altered in these ∆E2-GFP-Nup85 mutants, indicating that it is the integrity of the Y-complex, rather than the number of NPCs, that is critical to ensure these processes.