The Kutay lab and collaborators investigated the disassembly of Nuclear Pore Complexes (NPCs) during mitosis, specifically what happens to the nuclear and cytoplasmic rings of the NPCs, which are built of Y-complexes. While most of the Y-complexes become soluble upon NPC disassembly, a fraction of them is bound to the mitotic ER network, where they form foci instead of ring like structures as super-resolution microscopy revealed. Their findings have been published in the article "Super-resolution microscopy reveals focal organization of ER-associated Y-complexes in mitosis" in EMBO Reports.
The outer NPC scaffold is built by rings of Y-complexes. Whereas the bulk of Y-complexes is solubilized during mitosis, a fraction of Y-complexes is found in association with the mitotic ER network where they are organized in form of small focal assemblies that lack features of NPC rings.
- Y-complex Nups display distinct dissociation kinetics during NPC disassembly in vitro.
- 10–20% of Y-complexes associate with the mitotic ER network.
- dSTORM microscopy reveals that ER-associated Y-complexes form small foci instead of ring-shaped structures suited for templated NPC reassembly.
During mitotic entry of vertebrate cells, nuclear pore complexes (NPCs) are rapidly disintegrated. NPC disassembly is initiated by hyperphosphorylation of linker nucleoporins (Nups), which leads to the dissociation of FG repeat Nups and relaxation of the nuclear permeability barrier. However, less is known about disintegration of the huge nuclear and cytoplasmic rings, which are formed by annular assemblies of Y-complexes that are dissociated from NPCs as intact units. Surprisingly, we observe that Y-complex Nups display slower dissociation kinetics compared with other Nups during in vitro NPC disassembly, indicating a mechanistic difference in the disintegration of Y-based rings. Intriguingly, biochemical experiments reveal that a fraction of Y-complexes remains associated with mitotic ER membranes, supporting recent microscopic observations. Visualization of mitotic Y-complexes by super-resolution microscopy demonstrates that they form two classes of higher order assemblies: large clusters at kinetochores and small, focal ER-associated assemblies. These, however, lack features qualifying them as persisting ring-shaped subassemblies previously proposed to serve as structural templates for NPC reassembly during mitotic exit, which helps to refine current models of nuclear reassembly.