1. Nucleolar asymmetry and the importance of septin integrity upon cell cycle arrest
- Author
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Alan M. Tartakoff, Fadi J. Najm, and Urvashi Rai
- Subjects
0301 basic medicine ,Nucleolus ,Gene Expression ,lcsh:Medicine ,Septin ,Biochemistry ,Spindle pole body ,Animal Cells ,Medicine and Health Sciences ,Cell Cycle and Cell Division ,lcsh:Science ,Anaphase ,Centromeres ,Multidisciplinary ,Chromosome Biology ,Cell cycle ,Chromatin ,Cell biology ,medicine.anatomical_structure ,Cell Processes ,Epigenetics ,Cellular Structures and Organelles ,Cellular Types ,Cell Nucleolus ,Research Article ,Chromosome Structure and Function ,Saccharomyces cerevisiae Proteins ,Immune Cells ,Immunology ,Antigen-Presenting Cells ,CDC20 ,Saccharomyces cerevisiae ,Biology ,Chromosomes ,Anaphase-Promoting Complex-Cyclosome ,03 medical and health sciences ,medicine ,Genetics ,Cell Nucleus ,030102 biochemistry & molecular biology ,lcsh:R ,Biology and Life Sciences ,Proteins ,Cell Biology ,Cell Cycle Checkpoints ,Cell nucleus ,030104 developmental biology ,Genetic Loci ,lcsh:Q ,Anaphase-promoting complex ,Septins - Abstract
Cell cycle arrest can be imposed by inactivating the anaphase promoting complex (APC). In S. cerevisiae this arrest has been reported to stabilize a metaphase-like intermediate in which the nuclear envelope spans the bud neck, while chromatin repeatedly translocates between the mother and bud domains. The present investigation was undertaken to learn how other features of nuclear organization are affected upon depletion of the APC activator, Cdc20. We observe that the spindle pole bodies and the spindle repeatedly translocate across the narrow orifice at the level of the neck. Nevertheless, we find that the nucleolus (organized around rDNA repeats on the long right arm of chromosome XII) remains in the mother domain, marking the polarity of the nucleus. Accordingly, chromosome XII is polarized: TelXIIR remains in the mother domain and its centromere is predominantly located in the bud domain. In order to learn why the nucleolus remains in the mother domain, we studied the impact of inhibiting rRNA synthesis in arrested cells. We observed that this fragments the nucleolus and that these fragments entered the bud domain. Taken together with earlier observations, the restriction of the nucleolus to the mother domain therefore can be attributed to its massive structure. We also observed that inactivation of septins allowed arrested cells to complete the cell cycle, that the alternative APC activator, Cdh1, was required for completion of the cell cycle and that induction of Cdh1 itself caused arrested cells to progress to the end of the cell cycle.
- Published
- 2017