ABSTRACT
When starved of nitrogen, cells of the fission yeast Schizosaccharomyces pombe enter a quiescent ‘G0’ state with smaller nuclei and transcriptional repression. The genomics of S. pombe G0 cells has been well studied, but much of its nuclear cell biology remains unknown. Here, we use confocal microscopy, immunoblots and electron cryotomography to investigate the cytological, biochemical and ultrastructural differences between S. pombe proliferating, G1-arrested and G0 cell nuclei, with an emphasis on the histone acetylation, RNA polymerase II fates and macromolecular complex packing. Compared to proliferating cells, G0 cells have lower levels of histone acetylation, nuclear RNA polymerase II and active transcription. The G0 nucleus has similar macromolecular crowding yet fewer chromatin-associated multi-megadalton globular complexes. Induced histone hyperacetylation during nitrogen starvation results in cells that have larger nuclei and therefore chromatin that is less compact. However, these histone-hyperacetylated cells remain transcriptionally repressed with similar nuclear crowding. Canonical nucleosomes – those that resemble the crystal structure – are rare in proliferating, G1-arrested and G0 cells. Our study therefore shows that extreme changes in nucleus physiology are possible without extreme reorganization at the macromolecular level.
Footnotes
Author contributions
Conceptualization: L.G.; Methodology: L.G., Z.Y.T., S.C., S.A.P., T.L., X.N.; Software: L.G.; Validation: L.G., Z.Y.T., S.C., S.A.P., T.L., X.N.; Formal analysis: L.G., Z.Y.T., S.C.; Investigation: Z.Y.T., S.C., S.A.P., T.L., X.N.; Resources: L.G., J.S.; Data Curation: L.G.; Writing – original draft: L.G., S.C.; Writing – review & editing: L.G., Z.Y.T.; Visualization: L.G., Z.Y.T., S.C.; Supervision: L.G.; Project administration: L.G.; Funding acquisition: L.G.
Funding
This work was supported by a Singapore Ministry of Education T2 MOE2019-T2-2-045 and a T1 R-154-000-B42-114 grant.
Data availability
Tilt series and cryotomograms have been deposited in the Electron Microscopy Public Image Archive (EMPIAR) repository (Iudin et al., 2023) as EMPIAR entry EMPIAR-10339. Surplus tilt-series and many corresponding cryotomograms are deposited under EMPIAR entry EMPIAR-10227.
