Steinberg et al. report that fungi use motor proteins to distribute their nuclear pores around the nuclear envelope.
In animal cells, the nuclear lamina holds the nuclear pores in place, ensuring that they are evenly spaced. The lamina prevents nuclear pores from clustering, promoting import of cargoes through the pores and helping to organize the chromosomes, which are tethered to the pores. But fungi have no lamin genes, suggesting that they rely on a different mechanism to position their pores.
Steinberg et al. found that fungal cells are constantly adjusting the locations of their nuclear pores. In the pathogenic fungus Ustilago maydis, the motor proteins kinesin-1 and dynein slide the pores around on microtubules. In budding yeast, by contrast, pore movements required the actin cytoskeleton, suggesting that myosin motors are providing the muscle power.
The team also determined what happened if cells couldn't rearrange their pores. The structures clumped in U. maydis cells lacking kinesin-1 and dynein. Transport of cargoes into and out of the nucleus slowed in cells missing either or both of the motor proteins. When a cell moves its nuclear pores, it also moves its chromosomes. Blocking these movements caused chromosomes to gather at the edge of the nucleus, usually near the pore clusters. This could explain why impeding pore movement inhibits nuclear transport. Misplaced chromosomes might obstruct cargoes traveling into and out of the nucleus.