Overproduction of a nuclear export signal in fission yeast promotes nuclear expansion through microtubules

In eukaryotes, nuclear size scales with cell size, maintaining a constant nucleocytoplasmic volume ratio, known as the N/C ratio. Although nucleocytoplasmic transport plays a crucial role in nuclear size control, the underlying mechanisms remain elusive. Here, we investigated the impact of overexpression of a nuclear export signal (NES) fused with GFP (NES-GFP) in fission yeast on nuclear size. The overexpression of NES-GFP disrupts nuclear export, leading to the nuclear accumulation of cargo proteins and the formation of intranuclear microtubule bundles, thereby increasing the nuclear volume to cell volume (N/C) ratio dependent on nuclear import and microtubule nucleation. Enhanced formation of intranuclear microtubule bundles in cells overexpressing NES-GFP further accelerates nuclear expansion. We propose that membrane tension in the nucleus plays an important role in nuclear size control.